Thescelosaurus
Encyclopedia
Thescelosaurus was a genus
of small ornithopod
dinosaur
that appeared at the very end of the Late Cretaceous
period in North America
. It was a member of the last dinosaurian fauna
before the Cretaceous-Tertiary extinction event
around 65.5 million years ago. The preservation and completeness of many of its specimens indicate that it may have preferred to live near stream
s.
This bipedal ornithopod is known from several partial skeletons and skulls that indicate it grew to between 2.5 and 4.0 meters (8.2 to 13.1 ft) in length on average. It had sturdy hind limbs, small wide hands, and a head with an elongate pointed snout. This genus of dinosaur is regarded as a specialized hypsilophodont
and a herbivore
. Several species have been suggested for this genus. Three are currently recognized as valid
, the type species
T. neglectus, as well as T. garbanii and T. assiniboiensis.
The genus attracted media attention in 2000, when a specimen unearthed in 1993 in South Dakota
was interpreted as including a fossil
ized heart
. There was much discussion over whether the remains were actually of a heart. Many scientists now doubt the identification of the object and the implications of such an identification.
Thescelosaurus was a heavily built bipedal animal, probably herbivorous, but possibly omnivorous
. It would have browsed in the first meter or so from the ground, feeding selectively, with food held in the mouth by cheek
s while chewing
. There was a prominent ridge along the length of both maxilla
e (the tooth-bearing "cheek" bones), and a ridge on both dentaries (tooth-bearing bone of the lower jaw). The ridges and position of the teeth deeply internal to the outside surface of the skull are interpreted as evidence for muscular cheeks. Aside from the long narrow beak, the skull also had teeth in the premaxilla
, or upper beak (a primitive trait among ornithopods), and long rod-like bones called palpebrals
over the eyes, giving it heavy bony eyebrows. Its teeth were of two types
: small pointed premaxillary teeth, and leaf-shaped cheek teeth. Six small teeth were present in both premaxillae, with a toothless section at the tip of the beak.
It had short, broad, five-fingered hands, four-toed feet with hoof
-like toe tips
, and a long tail braced by ossified
tendon
s from the middle back to the tip, which would have reduced the flexibility of the tail. The rib cage was broad, giving it a wide back, and the limbs were robust. This animal may have been able to move on all fours
, given its fairly long arms and wide hands, but this idea has not been followed up in the scientific literature (although it does appear in popular works). Charles M. Sternberg
reconstructed it with the upper arm
oriented almost perpendicular to the body, another idea that has gone by the wayside. As noted by Peter Galton
, the upper arm bone of most ornithischians articulated with the shoulder by an articular surface that consisted of the entire end of the bone, instead of a distinct ball and socket as in mammals. The orientation of the shoulder's articular surface also indicates a vertical and not horizontal upper arm in dinosaurs. Thescelosaurus was probably slower than other hypsilophodonts, because of its heavier build and leg structure. Compared to them, it had unusual hindlimbs, because the upper leg
was longer than the shin
, the opposite of Hypsilophodon
and running animals in general. One specimen is known to have had a bone pathology
, with the long bones
of the right foot fused at their tops, hindering swift movement.
Large thin flat mineralized plates have been found next to the ribs' sides. Their function is unknown; they may have played a role in respiration
. However, muscle scars or other indications of attachment have not been found for the plates, which argues against a respiratory function. Recent histological study of layered plates from a probable subadult indicates that they may have started as cartilage
and became bone as the animal aged. Such plates are known from several other ornithopods and their cerapoda
n relatives.
The nature of this genus' integument, be it scales or something else, is currently unknown, although potential evidence is known; Charles Gilmore
described patches of carbon
ized material near the shoulders as possible epidermis, with a "punctured" texture but no regular pattern, and William J. Morris suggested that armor
was present, in the form of small scute
s present at least along the midline of the neck of one specimen. Scutes have not been found with other articulated specimens of Thescelosaurus, though, and Morris's scutes could be crocodilia
n in origin.
Overall, the skeletal anatomy of this genus is well documented, and restorations have been published in several papers, including skeletal restorations and models. The skeleton is known well enough that a detailed reconstruction of the hip and hindlimb muscles has been made. The animal's size has been estimated in the 2.5–4.0 m range for length (8.2–13.1 ft) for various specimens, and a weight of 200–300 kilogram
s (450–660 pounds
), with the large type specimen of T. garbanii estimated at 4–4.5 meters (13.1–14.8 feet) long. As discussed more fully under "Discovery, history, and species", it may have been sexually dimorphic
, with one sex
larger than the other. Juvenile
remains are known from several locations, mostly based on teeth.
and other small ornithopods as a hypsilophodont
id, although recognized as being distinct among them for its robust build, unusual hindlimbs, and, more recently, its unusually long skull. Peter Galton
in 1974 presented one twist to the classic arrangement, suggesting that because of its hindlimb structure and heavy build (not cursorial
, or built for running, by his definition), it should be included in the Iguanodont
idae. This has not been followed, with Morris arguing strongly against Galton's classification scheme. At any rate, Galton's Iguanodontidae was not a natural group due to polyphyly
, and so would not be recognized under modern cladistic usage.
This cladogram
is from Boyd et al. (2009). The group consisting of Parksosaurus, and Thescelosaurus is roughly what modern informal usage of Thescelosaurinae corresponds to. Additional ornithopods beyond Tenontosaurus are omitted. Dinosaurs described as hypsilophodonts are found from Agilisaurus or Hexinlusaurus to Hypsilophodon or Gasparinisaura.
Thescelosaurus is often informally given its own family or subfamily, Thescelosauridae or Thescelosaurinae. Three recent studies have found it to be a close relative of Parksosaurus
, although neither named a specific clade
, and one of the studies (Norman et al., 2004) is difficult to interpret because it did not include Iguanodont
ia in its diagrams. This area of the dinosaur family tree is complicated by a lack of research. While Hypsilophodontidae was found to be a natural group in the early 1990s, this hypothesis has fallen out of favor and Hypsilophodontidae has typically been found to be a unnatural family leading into Iguanodontia (paraphyly
), with various small clades of closely related taxa. Oddly, Thescelosaurus has been regarded as both very basal
and very derived
among the hypsilophodonts. One issue specifically concerning Thescelosaurus is that not all of the remains assigned to T. neglectus necessarily belong to it. Clint Boyd and colleagues found that while the clade Thescelosaurus included the genus Bugenasaura and the species that had been assigned to it, there were at least two and possibly three species within Thescelosaurus, and several specimens previously assigned to T. neglectus could not yet be assigned to a species within the genus.
of Thescelosaurus (USNM
7757) was discovered in 1891 by paleontologists
John Bell Hatcher
and William H. Utterback, from beds
of the late Maastrichtian
-age Upper Cretaceous Lance Formation
of Niobrara County (at the time part of Converse County), Wyoming
, USA
. The skeleton, however, remained in its shipping crates for years until Charles W. Gilmore
of the Smithsonian Institution
' National Museum of Natural History
had it prepared and described it in a short paper in 1913, naming it T. neglectus (neglectus: "neglected"). At the time, he thought it was related to Camptosaurus
. He provided a detailed monograph
in 1915, describing the well-preserved skeleton. The type specimen was found largely in natural articulation and was missing only the head and neck, which were lost due to erosion
. The name comes from the surprise Gilmore felt at finding such a good specimen that had been unattended to for so long. He considered it to be a light, agile creature, and assigned it to the Hypsilophodontidae, a family of small bipedal dinosaurs.
Other remains of similar animals were found throughout the late 19th century and 20th century, although they did not receive much attention. Another well-preserved skeleton from the slightly older Horseshoe Canyon Formation
, in Alberta
, Canada
, was named T. warreni by William Parks in 1926. This skeleton had notable differences from T. neglectus, and so Charles M. Sternberg
placed it in a new genus, Parksosaurus, in 1937. Sternberg also named an additional species, T. edmontonensis, based on another articulated skeleton, this time including a partial skull (NMC
8537), and drew attention to the genus' heavy build and thick bones; due to these differences from the regular light hypsilophodont build, he suggested that the genus warranted its own subfamily, Thescelosaurinae. T. edmontonensis has, since Peter Galton's 1974 review, generally been considered a more robust individual (possibly the opposite sex
of the type individual) of T. neglectus. However, Boyd and colleagues found that they could not assign it to either of their valid species of Thescelosaurus and regarded the specimen as of uncertain placement
in the genus. The other point of contention regarding T. edmontonensis is its ankle, which Galton claimed was damaged and misinterpreted, but which was regarded by William J. Morris (1976) as truly different from T. neglectus.
In his paper, Morris described a specimen (SDSM
7210) consisting of a partial skull with heavy ridges on the lower jaw and cheek, two partial vertebrae, and two finger bones
as an unidentified species of Thescelosaurus, from the late Maastrichtian-age Hell Creek Formation
of Harding County
, South Dakota
, USA. He drew attention to its premaxillary teeth and deeply inset toothline which he interpreted as supporting the presence of muscular cheeks. Morris also pointed out the outwardly flaring premaxilla (which would have given it a wide beak) and large palpebrals. This skull was recognized as an unnamed hypsilophodont for many years, until Galton made it the type specimen of new genus and species Bugenasaura infernalis (large-cheeked lizard belonging to the lower regions", infernalis being a reference to the Hell Creek Formation). Morris also named a new possible species of Thescelosaurus for specimen (LACM
33542): ?T. garbanii (with a question mark because he was uncertain that it belonged to the genus). LACM 33542 comprised a large partial hindlimb ("a third larger than described specimens of T. neglectus and Parksosaurus
or nearly twice as large as Hypsilophodon
") including a foot, tarsus
, shin bones, and partial thigh bone, along with five cervical (neck) and eleven dorsal (back) vertebrae, from the Hell Creek Formation of Garfield County
, Montana
, USA. The specimen was discovered by amateur paleontologist
Harley Garbani (hence the name). T. garbanii would have been about 4.5 meters (15 feet) long, greater than average specimens of T. neglectus. Aside from the size, Morris drew attention to the way the ankle was constructed, which he considered to be unique except in comparison with Thescelosaurus edmontonensis, which he regarded as a separate species. Because Morris believed that the ankles of T. garbanii compared favorably to those of T. edmontonensis, he tentatively assigned it to Thescelosaurus. However, the scientific literature has favored Galton's view that T. edmontonensis was not different from T. neglectus (see above). In the same paper that he described Bugenasaura, Galton demonstrated that the features Morris had thought connected T. garbanii and T. edmontonensis were the result of damage to the latter's ankle, so T. garbanii could also be considered distinct from Thescelosaurus. To better accommodate this species, Galton suggested that it belonged to his new genus Bugenasaura as B. garbanii, although he also noted that it could be belong to the similarly sized pachycephalosaurid
Stygimoloch
, or be part of a third, unknown dinosaur.
Clint Boyd and colleagues published a reassessment of Thescelosaurus, Bugenasaura, and Parksosaurus in 2009, using new cranial material as a starting point. They found that Parksosaurus was indeed distinct from Thescelosaurus, and that the skull of Bugenasaura infernalis was essentially the same as a skull found with a postcranial skeleton that matched Thescelosaurus. Because B infernalis could not be differentiated from Thescelosaurus, they regarded the genus as a synonym of Thescelosaurus, the species as dubious
, and SDSM 7210 as an example of T. sp. They found that LACM 33542, although fragmentary, was a specimen of Thescelosaurus, and agreed with Morris that the ankle structure was distinct, returning it to T. garbanii. Finally, they noted that another specimen, RSM
P.1225.1, differed from T. neglectus in some anatomical details, and may represent a new species. Thus, Thescelosaurus per Boyd et al. (2009) is represented by at least two, and possibly three valid species: type species T. neglectus, T. garbanii, and a possible unnamed species. In December 2011
, RSM P.1225.1 was finally assigned to its own species, Thescelosaurus assiniboiensis. It was first named by Caleb Marshal Brown, Clint A. Boyd and Anthony P. Russell and it is known only from its holotype
, a small, articulate
d and almost complete skeleton from the Frenchman Formation
(late Maastrichtian
stage) of Saskatchewan.
True Thescelosaurus remains are known definitely only from late Maastrichtian
-age rocks, from Alberta (Scollard Formation
) and Saskatchewan
(Frenchman Formation
), Canada, and Wyoming (Lance Formation
), South Dakota (Hell Creek Formation
), Montana (Hell Creek), and Colorado
(Laramie Formation
), USA. With the exception of birds, it was one of the last extant genera of dinosaurs, its remains being found as close as 3 meters to the boundary clay containing the iridium
layer that closes the Cretaceous. There are reports of teeth from older, Campanian
-age rocks, particularly from the Dinosaur Park Formation
of Alberta, but these specimens are not from Thescelosaurus and are much more likely those of Orodromeus
. More specimens are known than have been officially described for this genus, such as the Triebold specimen, which has been the source of several skeletal casts
for museums.
When Galton revisited Thescelosaurus and Bugenasaura in 1999, he described the dentary tooth UCMP
46911 from the Upper Jurassic of Weymouth, England
as cf. Bugensaura. If it is indeed a tooth from a thescelosaur-like animal, this would significantly extend the stratigraphic
range of the group.
; two papers suggest it preferred channels
to floodplain
s, but another suggests it preferred the opposite. The possible preference for channels is based on the relative abundance of thescelosaur fossils in sandstone
s, representing channel environments, in comparison to mudstone
s, representing floodplain environments. No bonebeds
or accumulations of multiple individuals have yet been reported. Dale Russell
, in a popular work, noted that Thescelosaurus was the most common small herbivore in the Hell Creek Formation of the Fort Peck
area. He described the environment of the time as a flat floodplain, with a relatively dry subtropical
climate that supported a variety of plants ranging from angiosperm
trees, to bald cypress
, to fern
s and ginkgo
s. Although most dinosaur skeletons from this area are incomplete, possibly due to the low preservation potential of forests, Thescelosaurus skeletons are much more complete, suggesting that this genus frequented stream channels. Thus when a Thescelosaurus died, it may have been in or near a river, making it easier to bury and preserve for later fossilization. Russell tentatively compared it to the capybara
s and tapir
s. Other dinosaurs that shared its time and place include the ceratopsids
Triceratops
and Torosaurus
, hadrosaurids Edmontosaurus
and Anatotitan
, ankylosaurid
Ankylosaurus
, pachycephalosauria
ns Pachycephalosaurus
and Stygimoloch
, and the theropods
Ornithomimus
, Troodon
, and Tyrannosaurus
. Thescelosaurus was also abundant in the Lance Formation. Toe bones from this genus are the most common finds after fossils of Triceratops and Edmontosaurus, and it may have been the most common dinosaur there, if the Lance Formation had a preservation bias against small animals.
In 2000, a skeleton of this genus informally known as "Willo", now on display at the North Carolina Museum of Natural Sciences
, was described as including the remnants of a four-chambered heart and an aorta
. It had been originally unearthed in 1993 in northwestern South Dakota. The authors had found the internal detail through computed tomography
(CT) imagery. They suggested that the heart had been saponified
(turned to grave wax
) under airless burial conditions, and then changed to goethite
, an iron mineral
, by replacement of the original material. The authors interpreted the structure of the heart as indicating an elevated metabolic rate
for Thescelosaurus, not reptilian
cold-bloodedness
.
Their conclusions have been disputed; soon after the initial description, other researchers published a paper where they assert that the heart is really a concretion
. As they note, the anatomy given for the object is incorrect (for example, the "aorta" narrows coming into the "heart" and lacks arteries
coming from it), it partially engulfs one of the ribs and has an internal structure of concentric layers in some places, and another concretion is preserved behind the right leg. The original authors defended their position; they agreed that it was a type of concretion, but one that had formed around and partially preserved the more muscular portions of the heart and aorta.
A study published in 2011 applied multiple lines of inquiry to the question of the object's identity, including more advanced CT scanning, histology
, X-ray diffraction
, X-ray photoelectron spectroscopy
, and scanning electron microscopy. From these methods, the authors found that: the object's internal structure does not include chambers but is made up of three unconnected areas of lower density material, and is not comparable to the structure of an ostrich
's heart; the "walls" are composed of sedimentary minerals not known to be produced in biological systems, such as goethite, feldspar
minerals, quartz
, and gypsum
, as well as some plant fragments; carbon
, nitrogen
, and phosphorus
, chemical element
s important to life, were lacking in their samples; and cardiac cellular structures were absent. There was one possible patch with animal cellular structures. The authors found their data supported identification as a concretion of sand from the burial environment, not the heart, with the possibility that isolated areas of tissues were preserved.
The question of how this find reflects metabolic rate and dinosaur internal anatomy is moot, though, regardless of the object's identity. Both modern crocodilia
ns and bird
s, the closest living relatives of dinosaurs, have four-chambered hearts (albeit modified in crocodilians), so dinosaurs probably had them as well; the structure is not necessarily tied to metabolic rate.
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
of small ornithopod
Ornithopod
Ornithopods or members of the clade Ornithopoda are a group of ornithischian dinosaurs that started out as small, bipedal running grazers, and grew in size and numbers until they became one of the most successful groups of herbivores in the Cretaceous world, and dominated the North American...
dinosaur
Dinosaur
Dinosaurs are a diverse group of animals of the clade and superorder Dinosauria. They were the dominant terrestrial vertebrates for over 160 million years, from the late Triassic period until the end of the Cretaceous , when the Cretaceous–Paleogene extinction event led to the extinction of...
that appeared at the very end of the Late Cretaceous
Late Cretaceous
The Late Cretaceous is the younger of two epochs into which the Cretaceous period is divided in the geologic timescale. Rock strata from this epoch form the Upper Cretaceous series...
period in North America
North America
North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...
. It was a member of the last dinosaurian fauna
Fauna
Fauna or faunæ is all of the animal life of any particular region or time. The corresponding term for plants is flora.Zoologists and paleontologists use fauna to refer to a typical collection of animals found in a specific time or place, e.g. the "Sonoran Desert fauna" or the "Burgess shale fauna"...
before the Cretaceous-Tertiary extinction event
Cretaceous-Tertiary extinction event
The Cretaceous–Paleogene extinction event, formerly named and still commonly referred to as the Cretaceous-Tertiary extinction event, occurred approximately 65.5 million years ago at the end of the Maastrichtian age of the Cretaceous period. It was a large-scale mass extinction of animal and plant...
around 65.5 million years ago. The preservation and completeness of many of its specimens indicate that it may have preferred to live near stream
Stream
A stream is a body of water with a current, confined within a bed and stream banks. Depending on its locale or certain characteristics, a stream may be referred to as a branch, brook, beck, burn, creek, "crick", gill , kill, lick, rill, river, syke, bayou, rivulet, streamage, wash, run or...
s.
This bipedal ornithopod is known from several partial skeletons and skulls that indicate it grew to between 2.5 and 4.0 meters (8.2 to 13.1 ft) in length on average. It had sturdy hind limbs, small wide hands, and a head with an elongate pointed snout. This genus of dinosaur is regarded as a specialized hypsilophodont
Hypsilophodont
Hypsilophodonts were small ornithopod dinosaurs, regarded as fast, herbivorous bipeds on the order of 1–2 meters long . They are known from Asia, Australia, Europe, New Zealand, North America, and South America, from rocks of Middle Jurassic to late Cretaceous age...
and a herbivore
Herbivore
Herbivores are organisms that are anatomically and physiologically adapted to eat plant-based foods. Herbivory is a form of consumption in which an organism principally eats autotrophs such as plants, algae and photosynthesizing bacteria. More generally, organisms that feed on autotrophs in...
. Several species have been suggested for this genus. Three are currently recognized as valid
Valid name (zoology)
In zoological nomenclature, the valid name of a taxon is the zoological name that is to be used for that taxon following the rules in the International Code of Zoological Nomenclature . In other words: a valid name is the correct zoological name of a taxon.In contrast, an invalid name is a name...
, the type species
Type species
In biological nomenclature, a type species is both a concept and a practical system which is used in the classification and nomenclature of animals and plants. The value of a "type species" lies in the fact that it makes clear what is meant by a particular genus name. A type species is the species...
T. neglectus, as well as T. garbanii and T. assiniboiensis.
The genus attracted media attention in 2000, when a specimen unearthed in 1993 in South Dakota
South Dakota
South Dakota is a state located in the Midwestern region of the United States. It is named after the Lakota and Dakota Sioux American Indian tribes. Once a part of Dakota Territory, South Dakota became a state on November 2, 1889. The state has an area of and an estimated population of just over...
was interpreted as including a fossil
Fossil
Fossils are the preserved remains or traces of animals , plants, and other organisms from the remote past...
ized heart
Heart
The heart is a myogenic muscular organ found in all animals with a circulatory system , that is responsible for pumping blood throughout the blood vessels by repeated, rhythmic contractions...
. There was much discussion over whether the remains were actually of a heart. Many scientists now doubt the identification of the object and the implications of such an identification.
Description
Omnivore
Omnivores are species that eat both plants and animals as their primary food source...
. It would have browsed in the first meter or so from the ground, feeding selectively, with food held in the mouth by cheek
Cheek
Cheeks constitute the area of the face below the eyes and between the nose and the left or right ear. They may also be referred to as jowls. "Buccal" means relating to the cheek. In humans, the region is innervated by the buccal nerve...
s while chewing
Mastication
Mastication or chewing is the process by which food is crushed and ground by teeth. It is the first step of digestion and it increases the surface area of foods to allow more efficient break down by enzymes. During the mastication process, the food is positioned between the teeth for grinding by...
. There was a prominent ridge along the length of both maxilla
Maxilla
The maxilla is a fusion of two bones along the palatal fissure that form the upper jaw. This is similar to the mandible , which is also a fusion of two halves at the mental symphysis. Sometimes The maxilla (plural: maxillae) is a fusion of two bones along the palatal fissure that form the upper...
e (the tooth-bearing "cheek" bones), and a ridge on both dentaries (tooth-bearing bone of the lower jaw). The ridges and position of the teeth deeply internal to the outside surface of the skull are interpreted as evidence for muscular cheeks. Aside from the long narrow beak, the skull also had teeth in the premaxilla
Premaxilla
The incisive bone is the portion of the maxilla adjacent to the incisors. It is a pair of small cranial bones at the very tip of the jaws of many animals, usually bearing teeth, but not always. They are connected to the maxilla and the nasals....
, or upper beak (a primitive trait among ornithopods), and long rod-like bones called palpebrals
Palpebral (bone)
The palpebral bone is a small dermal bone found in the region of the eye socket in a variety of animals, including crocodilians and ornithischian dinosaurs. In ornithischians, it can form a prong that projects from the front upper corner of the orbit...
over the eyes, giving it heavy bony eyebrows. Its teeth were of two types
Heterodont
The anatomical term heterodont refers to animals which possess more than a single tooth morphology. For example, members of the Synapsida generally possess incisors, canines , premolars, and molars. The presence of heterodont dentition is evidence of some degree of feeding/hunting specialization...
: small pointed premaxillary teeth, and leaf-shaped cheek teeth. Six small teeth were present in both premaxillae, with a toothless section at the tip of the beak.
It had short, broad, five-fingered hands, four-toed feet with hoof
Hoof
A hoof , plural hooves or hoofs , is the tip of a toe of an ungulate mammal, strengthened by a thick horny covering. The hoof consists of a hard or rubbery sole, and a hard wall formed by a thick nail rolled around the tip of the toe. The weight of the animal is normally borne by both the sole...
-like toe tips
Phalanx bones
In anatomy, phalanx bones are those that form the fingers and toes. In primates such as humans and monkeys, the thumb and big toe have two phalanges, while the other fingers and toes consist of three. Phalanges are classified as long bones.The phalanges do not have individual names...
, and a long tail braced by ossified
Ossification
Ossification is the process of laying down new bone material by cells called osteoblasts. It is synonymous with bone tissue formation...
tendon
Tendon
A tendon is a tough band of fibrous connective tissue that usually connects muscle to bone and is capable of withstanding tension. Tendons are similar to ligaments and fasciae as they are all made of collagen except that ligaments join one bone to another bone, and fasciae connect muscles to other...
s from the middle back to the tip, which would have reduced the flexibility of the tail. The rib cage was broad, giving it a wide back, and the limbs were robust. This animal may have been able to move on all fours
Quadruped
Quadrupedalism is a form of land animal locomotion using four limbs or legs. An animal or machine that usually moves in a quadrupedal manner is known as a quadruped, meaning "four feet"...
, given its fairly long arms and wide hands, but this idea has not been followed up in the scientific literature (although it does appear in popular works). Charles M. Sternberg
Charles Mortram Sternberg
Charles M. Sternberg was an American-Canadian fossil collector and paleontologist, son of Charles Hazelius Sternberg.Late in his career, he collected and described Pachyrhinosaurus, Brachylophosaurus, Parksosaurus and Edmontonia...
reconstructed it with the upper arm
Humerus
The humerus is a long bone in the arm or forelimb that runs from the shoulder to the elbow....
oriented almost perpendicular to the body, another idea that has gone by the wayside. As noted by Peter Galton
Peter Galton
Peter M. Galton is a British vertebrate paleontologist working in America, who has to date written or co-written about a hundred papers in scientific journals or chapters in paleontology textbooks, especially on ornithischian and prosauropod dinosaurs.With Robert Bakker in a joint article...
, the upper arm bone of most ornithischians articulated with the shoulder by an articular surface that consisted of the entire end of the bone, instead of a distinct ball and socket as in mammals. The orientation of the shoulder's articular surface also indicates a vertical and not horizontal upper arm in dinosaurs. Thescelosaurus was probably slower than other hypsilophodonts, because of its heavier build and leg structure. Compared to them, it had unusual hindlimbs, because the upper leg
Femur
The femur , or thigh bone, is the most proximal bone of the leg in tetrapod vertebrates capable of walking or jumping, such as most land mammals, birds, many reptiles such as lizards, and amphibians such as frogs. In vertebrates with four legs such as dogs and horses, the femur is found only in...
was longer than the shin
Tibia
The tibia , shinbone, or shankbone is the larger and stronger of the two bones in the leg below the knee in vertebrates , and connects the knee with the ankle bones....
, the opposite of Hypsilophodon
Hypsilophodon
Hypsilophodon is an ornithopod dinosaur genus from the Early Cretaceous period of Europe. It was a small bipedal animal with an herbivorous or possibly omnivorous diet...
and running animals in general. One specimen is known to have had a bone pathology
Pathology
Pathology is the precise study and diagnosis of disease. The word pathology is from Ancient Greek , pathos, "feeling, suffering"; and , -logia, "the study of". Pathologization, to pathologize, refers to the process of defining a condition or behavior as pathological, e.g. pathological gambling....
, with the long bones
Metatarsus
The metatarsus or metatarsal bones are a group of five long bones in the foot located between the tarsal bones of the hind- and mid-foot and the phalanges of the toes. Lacking individual names, the metatarsal bones are numbered from the medial side : the first, second, third, fourth, and fifth...
of the right foot fused at their tops, hindering swift movement.
Respiration (physiology)
'In physiology, respiration is defined as the transport of oxygen from the outside air to the cells within tissues, and the transport of carbon dioxide in the opposite direction...
. However, muscle scars or other indications of attachment have not been found for the plates, which argues against a respiratory function. Recent histological study of layered plates from a probable subadult indicates that they may have started as cartilage
Cartilage
Cartilage is a flexible connective tissue found in many areas in the bodies of humans and other animals, including the joints between bones, the rib cage, the ear, the nose, the elbow, the knee, the ankle, the bronchial tubes and the intervertebral discs...
and became bone as the animal aged. Such plates are known from several other ornithopods and their cerapoda
Cerapoda
Neornithischia is a clade of the dinosaur order Ornithischia. They are the sister group of the Thyreophora within the clade Genasauria. Neornithischians are united by having a thicker layer of asymmetrical enamel on the inside of their lower teeth...
n relatives.
The nature of this genus' integument, be it scales or something else, is currently unknown, although potential evidence is known; Charles Gilmore
Charles W. Gilmore
Charles Whitney Gilmore was an American paleontologist, who named dinosaurs in North America and Mongolia, including the Cretaceous sauropod Alamosaurus, Alectrosaurus, Archaeornithomimus, Bactrosaurus, Brachyceratops, Chirostenotes, Mongolosaurus, Parrosaurus, Pinacosaurus, Styracosaurus and...
described patches of carbon
Carbon
Carbon is the chemical element with symbol C and atomic number 6. As a member of group 14 on the periodic table, it is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds...
ized material near the shoulders as possible epidermis, with a "punctured" texture but no regular pattern, and William J. Morris suggested that armor
Armour (zoology)
Armour in animals is external or superficial protection against attack by predators, formed as part of the body , usually through the hardening of body tissues, outgrowths or secretions. It has therefore mostly developed in 'prey' species...
was present, in the form of small scute
Scute
A scute or scutum is a bony external plate or scale, as on the shell of a turtle, the skin of crocodilians, the feet of some birds or the anterior portion of the mesonotum in insects.-Properties:...
s present at least along the midline of the neck of one specimen. Scutes have not been found with other articulated specimens of Thescelosaurus, though, and Morris's scutes could be crocodilia
Crocodilia
Crocodilia is an order of large reptiles that appeared about 84 million years ago in the late Cretaceous Period . They are the closest living relatives of birds, as the two groups are the only known survivors of the Archosauria...
n in origin.
Kilogram
The kilogram or kilogramme , also known as the kilo, is the base unit of mass in the International System of Units and is defined as being equal to the mass of the International Prototype Kilogram , which is almost exactly equal to the mass of one liter of water...
s (450–660 pounds
Pound (mass)
The pound or pound-mass is a unit of mass used in the Imperial, United States customary and other systems of measurement...
), with the large type specimen of T. garbanii estimated at 4–4.5 meters (13.1–14.8 feet) long. As discussed more fully under "Discovery, history, and species", it may have been sexually dimorphic
Sexual dimorphism
Sexual dimorphism is a phenotypic difference between males and females of the same species. Examples of such differences include differences in morphology, ornamentation, and behavior.-Examples:-Ornamentation / coloration:...
, with one sex
Gender
Gender is a range of characteristics used to distinguish between males and females, particularly in the cases of men and women and the masculine and feminine attributes assigned to them. Depending on the context, the discriminating characteristics vary from sex to social role to gender identity...
larger than the other. Juvenile
Juvenile (organism)
A juvenile is an individual organism that has not yet reached its adult form, sexual maturity or size. Juveniles sometimes look very different from the adult form, particularly in terms of their colour...
remains are known from several locations, mostly based on teeth.
Classification
Thescelosaurus has generally been allied to HypsilophodonHypsilophodon
Hypsilophodon is an ornithopod dinosaur genus from the Early Cretaceous period of Europe. It was a small bipedal animal with an herbivorous or possibly omnivorous diet...
and other small ornithopods as a hypsilophodont
Hypsilophodont
Hypsilophodonts were small ornithopod dinosaurs, regarded as fast, herbivorous bipeds on the order of 1–2 meters long . They are known from Asia, Australia, Europe, New Zealand, North America, and South America, from rocks of Middle Jurassic to late Cretaceous age...
id, although recognized as being distinct among them for its robust build, unusual hindlimbs, and, more recently, its unusually long skull. Peter Galton
Peter Galton
Peter M. Galton is a British vertebrate paleontologist working in America, who has to date written or co-written about a hundred papers in scientific journals or chapters in paleontology textbooks, especially on ornithischian and prosauropod dinosaurs.With Robert Bakker in a joint article...
in 1974 presented one twist to the classic arrangement, suggesting that because of its hindlimb structure and heavy build (not cursorial
Cursorial
Cursorial is a biological term that describes an organism as being adapted specifically to run. It is typically used in conjunction with an animal's feeding habits or another important adaptation. For example, a horse can be considered a "cursorial grazer", while a wolf may be considered a...
, or built for running, by his definition), it should be included in the Iguanodont
Iguanodont
Iguanodonts were herbivorous dinosaurs that lived from the mid-Jurassic to Late Cretaceous. Some members include Camptosaurus, Callovosaurus, Iguanodon, Ouranosaurus, and the hadrosaurids or "duck-billed dinosaurs". Iguanodonts were one of the first groups of dinosaurs to be found...
idae. This has not been followed, with Morris arguing strongly against Galton's classification scheme. At any rate, Galton's Iguanodontidae was not a natural group due to polyphyly
Polyphyly
A polyphyletic group is one whose members' last common ancestor is not a member of the group.For example, the group consisting of warm-blooded animals is polyphyletic, because it contains both mammals and birds, but the most recent common ancestor of mammals and birds was cold-blooded...
, and so would not be recognized under modern cladistic usage.
Cladistics
Cladistics is a method of classifying species of organisms into groups called clades, which consist of an ancestor organism and all its descendants . For example, birds, dinosaurs, crocodiles, and all descendants of their most recent common ancestor form a clade...
is from Boyd et al. (2009). The group consisting of Parksosaurus, and Thescelosaurus is roughly what modern informal usage of Thescelosaurinae corresponds to. Additional ornithopods beyond Tenontosaurus are omitted. Dinosaurs described as hypsilophodonts are found from Agilisaurus or Hexinlusaurus to Hypsilophodon or Gasparinisaura.
Thescelosaurus is often informally given its own family or subfamily, Thescelosauridae or Thescelosaurinae. Three recent studies have found it to be a close relative of Parksosaurus
Parksosaurus
Parksosaurus was a genus of hypsilophodont ornithopod dinosaur from the early Maastrichtian-age Upper Cretaceous Horseshoe Canyon Formation of Alberta, Canada. It is based on most of a partially articulated skeleton and partial skull, showing it to have been a small, bipedal, herbivorous dinosaur...
, although neither named a specific clade
Clade
A clade is a group consisting of a species and all its descendants. In the terms of biological systematics, a clade is a single "branch" on the "tree of life". The idea that such a "natural group" of organisms should be grouped together and given a taxonomic name is central to biological...
, and one of the studies (Norman et al., 2004) is difficult to interpret because it did not include Iguanodont
Iguanodont
Iguanodonts were herbivorous dinosaurs that lived from the mid-Jurassic to Late Cretaceous. Some members include Camptosaurus, Callovosaurus, Iguanodon, Ouranosaurus, and the hadrosaurids or "duck-billed dinosaurs". Iguanodonts were one of the first groups of dinosaurs to be found...
ia in its diagrams. This area of the dinosaur family tree is complicated by a lack of research. While Hypsilophodontidae was found to be a natural group in the early 1990s, this hypothesis has fallen out of favor and Hypsilophodontidae has typically been found to be a unnatural family leading into Iguanodontia (paraphyly
Paraphyly
A group of taxa is said to be paraphyletic if the group consists of all the descendants of a hypothetical closest common ancestor minus one or more monophyletic groups of descendants...
), with various small clades of closely related taxa. Oddly, Thescelosaurus has been regarded as both very basal
Basal (phylogenetics)
In phylogenetics, a basal clade is the earliest clade to branch in a larger clade; it appears at the base of a cladogram.A basal group forms an outgroup to the rest of the clade, such as in the following example:...
and very derived
Derived
In phylogenetics, a derived trait is a trait that is present in an organism, but was absent in the last common ancestor of the group being considered. This may also refer to structures that are not present in an organism, but were present in its ancestors, i.e. traits that have undergone secondary...
among the hypsilophodonts. One issue specifically concerning Thescelosaurus is that not all of the remains assigned to T. neglectus necessarily belong to it. Clint Boyd and colleagues found that while the clade Thescelosaurus included the genus Bugenasaura and the species that had been assigned to it, there were at least two and possibly three species within Thescelosaurus, and several specimens previously assigned to T. neglectus could not yet be assigned to a species within the genus.
Discovery, history, and species
The type specimenHolotype
A holotype is a single physical example of an organism, known to have been used when the species was formally described. It is either the single such physical example or one of several such, but explicitly designated as the holotype...
of Thescelosaurus (USNM
National Museum of Natural History
The National Museum of Natural History is a natural history museum administered by the Smithsonian Institution, located on the National Mall in Washington, D.C., United States. Admission is free and the museum is open 364 days a year....
7757) was discovered in 1891 by paleontologists
Paleontology
Paleontology "old, ancient", ὄν, ὀντ- "being, creature", and λόγος "speech, thought") is the study of prehistoric life. It includes the study of fossils to determine organisms' evolution and interactions with each other and their environments...
John Bell Hatcher
John Bell Hatcher
John Bell Hatcher was an American paleontologist and fossil hunter best known for discovering Torosaurus.-Biography:...
and William H. Utterback, from beds
Stratum
In geology and related fields, a stratum is a layer of sedimentary rock or soil with internally consistent characteristics that distinguish it from other layers...
of the late Maastrichtian
Maastrichtian
The Maastrichtian is, in the ICS' geologic timescale, the latest age or upper stage of the Late Cretaceous epoch or Upper Cretaceous series, the Cretaceous period or system, and of the Mesozoic era or erathem. It spanned from 70.6 ± 0.6 Ma to 65.5 ± 0.3 Ma...
-age Upper Cretaceous Lance Formation
Lance Formation
The Lance Formation is a division of Late Cretaceous rocks in the western United States. Named after Lance Creek, Wyoming, the microvertebrate fossils and dinosaurs represent important components of the latest Mesozoic vertebrate faunas...
of Niobrara County (at the time part of Converse County), Wyoming
Wyoming
Wyoming is a state in the mountain region of the Western United States. The western two thirds of the state is covered mostly with the mountain ranges and rangelands in the foothills of the Eastern Rocky Mountains, while the eastern third of the state is high elevation prairie known as the High...
, USA
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
. The skeleton, however, remained in its shipping crates for years until Charles W. Gilmore
Charles W. Gilmore
Charles Whitney Gilmore was an American paleontologist, who named dinosaurs in North America and Mongolia, including the Cretaceous sauropod Alamosaurus, Alectrosaurus, Archaeornithomimus, Bactrosaurus, Brachyceratops, Chirostenotes, Mongolosaurus, Parrosaurus, Pinacosaurus, Styracosaurus and...
of the Smithsonian Institution
Smithsonian Institution
The Smithsonian Institution is an educational and research institute and associated museum complex, administered and funded by the government of the United States and by funds from its endowment, contributions, and profits from its retail operations, concessions, licensing activities, and magazines...
' National Museum of Natural History
National Museum of Natural History
The National Museum of Natural History is a natural history museum administered by the Smithsonian Institution, located on the National Mall in Washington, D.C., United States. Admission is free and the museum is open 364 days a year....
had it prepared and described it in a short paper in 1913, naming it T. neglectus (neglectus: "neglected"). At the time, he thought it was related to Camptosaurus
Camptosaurus
Camptosaurus is a genus of plant-eating, beaked ornithischian dinosaurs of the Late Jurassic period of western North America. The name means 'flexible lizard', ....
. He provided a detailed monograph
Monograph
A monograph is a work of writing upon a single subject, usually by a single author.It is often a scholarly essay or learned treatise, and may be released in the manner of a book or journal article. It is by definition a single document that forms a complete text in itself...
in 1915, describing the well-preserved skeleton. The type specimen was found largely in natural articulation and was missing only the head and neck, which were lost due to erosion
Erosion
Erosion is when materials are removed from the surface and changed into something else. It only works by hydraulic actions and transport of solids in the natural environment, and leads to the deposition of these materials elsewhere...
. The name comes from the surprise Gilmore felt at finding such a good specimen that had been unattended to for so long. He considered it to be a light, agile creature, and assigned it to the Hypsilophodontidae, a family of small bipedal dinosaurs.
Horseshoe Canyon Formation
The Horseshoe Canyon Formation is part of the Edmonton Group and is up to 230m in thickness. It is Late Campanian to Early Maastrichtian in age and is composed of mudstone, sandstone, and carbonaceous shales...
, in Alberta
Alberta
Alberta is a province of Canada. It had an estimated population of 3.7 million in 2010 making it the most populous of Canada's three prairie provinces...
, Canada
Canada
Canada is a North American country consisting of ten provinces and three territories. Located in the northern part of the continent, it extends from the Atlantic Ocean in the east to the Pacific Ocean in the west, and northward into the Arctic Ocean...
, was named T. warreni by William Parks in 1926. This skeleton had notable differences from T. neglectus, and so Charles M. Sternberg
Charles Mortram Sternberg
Charles M. Sternberg was an American-Canadian fossil collector and paleontologist, son of Charles Hazelius Sternberg.Late in his career, he collected and described Pachyrhinosaurus, Brachylophosaurus, Parksosaurus and Edmontonia...
placed it in a new genus, Parksosaurus, in 1937. Sternberg also named an additional species, T. edmontonensis, based on another articulated skeleton, this time including a partial skull (NMC
Canadian Museum of Nature
The Canadian Museum of Nature is a natural history museum in Ottawa, Ontario, Canada. Its collections, which were started by the Geological Survey of Canada in 1856, include all aspects of the intersection of human society and nature, from gardening to gene-splicing...
8537), and drew attention to the genus' heavy build and thick bones; due to these differences from the regular light hypsilophodont build, he suggested that the genus warranted its own subfamily, Thescelosaurinae. T. edmontonensis has, since Peter Galton's 1974 review, generally been considered a more robust individual (possibly the opposite sex
Sexual dimorphism
Sexual dimorphism is a phenotypic difference between males and females of the same species. Examples of such differences include differences in morphology, ornamentation, and behavior.-Examples:-Ornamentation / coloration:...
of the type individual) of T. neglectus. However, Boyd and colleagues found that they could not assign it to either of their valid species of Thescelosaurus and regarded the specimen as of uncertain placement
Incertae sedis
, is a term used to define a taxonomic group where its broader relationships are unknown or undefined. Uncertainty at specific taxonomic levels is attributed by , , and similar terms.-Examples:*The fossil plant Paradinandra suecica could not be assigned to any...
in the genus. The other point of contention regarding T. edmontonensis is its ankle, which Galton claimed was damaged and misinterpreted, but which was regarded by William J. Morris (1976) as truly different from T. neglectus.
In his paper, Morris described a specimen (SDSM
South Dakota School of Mines and Technology
The South Dakota School of Mines and Technology is a public institution of higher learning in Rapid City, South Dakota governed by the South Dakota Board of Regents. Founded in 1885 as the Dakota School of Mines, Tech offers degree programs in engineering and science fields. 2,354 students were...
7210) consisting of a partial skull with heavy ridges on the lower jaw and cheek, two partial vertebrae, and two finger bones
Phalanx bones
In anatomy, phalanx bones are those that form the fingers and toes. In primates such as humans and monkeys, the thumb and big toe have two phalanges, while the other fingers and toes consist of three. Phalanges are classified as long bones.The phalanges do not have individual names...
as an unidentified species of Thescelosaurus, from the late Maastrichtian-age Hell Creek Formation
Hell Creek Formation
The Hell Creek Formation is an intensely-studied division of Upper Cretaceous to lower Paleocene rocks in North America, named for exposures studied along Hell Creek, near Jordan, Montana...
of Harding County
Harding County, South Dakota
As of the census of 2000, there were 1,353 people, 525 households, and 352 families residing in the county. The population density was 0.5 people per square mile . There were 804 housing units at an average density of 0.3 per square mile...
, South Dakota
South Dakota
South Dakota is a state located in the Midwestern region of the United States. It is named after the Lakota and Dakota Sioux American Indian tribes. Once a part of Dakota Territory, South Dakota became a state on November 2, 1889. The state has an area of and an estimated population of just over...
, USA. He drew attention to its premaxillary teeth and deeply inset toothline which he interpreted as supporting the presence of muscular cheeks. Morris also pointed out the outwardly flaring premaxilla (which would have given it a wide beak) and large palpebrals. This skull was recognized as an unnamed hypsilophodont for many years, until Galton made it the type specimen of new genus and species Bugenasaura infernalis (large-cheeked lizard belonging to the lower regions", infernalis being a reference to the Hell Creek Formation). Morris also named a new possible species of Thescelosaurus for specimen (LACM
Natural History Museum of Los Angeles County
The Natural History Museum of Los Angeles County opened in Exposition Park, Los Angeles, California, USA in 1913 as the Museum of History, Science, and Art. The moving force behind it was a museum association founded in 1910. Its distinctive main building, with fitted marble walls and domed and...
33542): ?T. garbanii (with a question mark because he was uncertain that it belonged to the genus). LACM 33542 comprised a large partial hindlimb ("a third larger than described specimens of T. neglectus and Parksosaurus
Parksosaurus
Parksosaurus was a genus of hypsilophodont ornithopod dinosaur from the early Maastrichtian-age Upper Cretaceous Horseshoe Canyon Formation of Alberta, Canada. It is based on most of a partially articulated skeleton and partial skull, showing it to have been a small, bipedal, herbivorous dinosaur...
or nearly twice as large as Hypsilophodon
Hypsilophodon
Hypsilophodon is an ornithopod dinosaur genus from the Early Cretaceous period of Europe. It was a small bipedal animal with an herbivorous or possibly omnivorous diet...
") including a foot, tarsus
Tarsus (skeleton)
In tetrapods, the tarsus is a cluster of articulating bones in each foot situated between the lower end of tibia and fibula of the lower leg and the metatarsus. In the foot the tarsus articulates with the bones of the metatarsus, which in turn articulate with the bones of the individual toes...
, shin bones, and partial thigh bone, along with five cervical (neck) and eleven dorsal (back) vertebrae, from the Hell Creek Formation of Garfield County
Garfield County, Montana
-Politics:Garfield County is a solidly Republican county. It might be the most Republican county in Montana and one of the most Republican in the nation....
, Montana
Montana
Montana is a state in the Western United States. The western third of Montana contains numerous mountain ranges. Smaller, "island ranges" are found in the central third of the state, for a total of 77 named ranges of the Rocky Mountains. This geographical fact is reflected in the state's name,...
, USA. The specimen was discovered by amateur paleontologist
Paleontology
Paleontology "old, ancient", ὄν, ὀντ- "being, creature", and λόγος "speech, thought") is the study of prehistoric life. It includes the study of fossils to determine organisms' evolution and interactions with each other and their environments...
Harley Garbani (hence the name). T. garbanii would have been about 4.5 meters (15 feet) long, greater than average specimens of T. neglectus. Aside from the size, Morris drew attention to the way the ankle was constructed, which he considered to be unique except in comparison with Thescelosaurus edmontonensis, which he regarded as a separate species. Because Morris believed that the ankles of T. garbanii compared favorably to those of T. edmontonensis, he tentatively assigned it to Thescelosaurus. However, the scientific literature has favored Galton's view that T. edmontonensis was not different from T. neglectus (see above). In the same paper that he described Bugenasaura, Galton demonstrated that the features Morris had thought connected T. garbanii and T. edmontonensis were the result of damage to the latter's ankle, so T. garbanii could also be considered distinct from Thescelosaurus. To better accommodate this species, Galton suggested that it belonged to his new genus Bugenasaura as B. garbanii, although he also noted that it could be belong to the similarly sized pachycephalosaurid
Pachycephalosauria
Pachycephalosauria is a clade of ornithischian dinosaurs. Well-known genera include Pachycephalosaurus, Stegoceras, Stygimoloch, and Dracorex. Most lived during the Late Cretaceous Period, in what is now North America and Asia. They were all bipedal, herbivorous/omnivorous animals with thick skulls...
Stygimoloch
Stygimoloch
Stygimoloch is a putative genus of pachycephalosaurid dinosaur from the end of the Cretaceous period, roughly 65 million years ago...
, or be part of a third, unknown dinosaur.
Clint Boyd and colleagues published a reassessment of Thescelosaurus, Bugenasaura, and Parksosaurus in 2009, using new cranial material as a starting point. They found that Parksosaurus was indeed distinct from Thescelosaurus, and that the skull of Bugenasaura infernalis was essentially the same as a skull found with a postcranial skeleton that matched Thescelosaurus. Because B infernalis could not be differentiated from Thescelosaurus, they regarded the genus as a synonym of Thescelosaurus, the species as dubious
Nomen dubium
In zoological nomenclature, a nomen dubium is a scientific name that is of unknown or doubtful application...
, and SDSM 7210 as an example of T. sp. They found that LACM 33542, although fragmentary, was a specimen of Thescelosaurus, and agreed with Morris that the ankle structure was distinct, returning it to T. garbanii. Finally, they noted that another specimen, RSM
Royal Saskatchewan Museum
The Royal Saskatchewan Museum was established in Regina as the Provincial Museum in 1906 to "secure and preserve natural history specimens and objects of historical and ethnological interest." It was the first museum in Saskatchewan, Canada, and the first provincial museum in the three Prairie...
P.1225.1, differed from T. neglectus in some anatomical details, and may represent a new species. Thus, Thescelosaurus per Boyd et al. (2009) is represented by at least two, and possibly three valid species: type species T. neglectus, T. garbanii, and a possible unnamed species. In December 2011
2011 in paleontology
-Lobopods:-Arachnids:-Insects:-Newly named jawless vertebrates:-Newly named acanthodian:-Newly named cartilaginous fishes:-Newly named bony fishes:-Newly named lepospondyls:-Newly named temnospondyls:-Newly named lissamphibians:...
, RSM P.1225.1 was finally assigned to its own species, Thescelosaurus assiniboiensis. It was first named by Caleb Marshal Brown, Clint A. Boyd and Anthony P. Russell and it is known only from its holotype
Holotype
A holotype is a single physical example of an organism, known to have been used when the species was formally described. It is either the single such physical example or one of several such, but explicitly designated as the holotype...
, a small, articulate
Articulate
Articulate may refer to:*Articulate *Articulate sign*Articulate sound*Joint, also known as articulation*Word modified by an article...
d and almost complete skeleton from the Frenchman Formation
Frenchman Formation
The Frenchman Formation is a division of Upper Cretaceous rocks found in Saskatchewan, Canada. More accurately described as Late Maastrichtian, these rocks contain the youngest of dinosaur genera, much like the Hell Creek Formation in the United States....
(late Maastrichtian
Maastrichtian
The Maastrichtian is, in the ICS' geologic timescale, the latest age or upper stage of the Late Cretaceous epoch or Upper Cretaceous series, the Cretaceous period or system, and of the Mesozoic era or erathem. It spanned from 70.6 ± 0.6 Ma to 65.5 ± 0.3 Ma...
stage) of Saskatchewan.
Temporal and geographic range
Maastrichtian
The Maastrichtian is, in the ICS' geologic timescale, the latest age or upper stage of the Late Cretaceous epoch or Upper Cretaceous series, the Cretaceous period or system, and of the Mesozoic era or erathem. It spanned from 70.6 ± 0.6 Ma to 65.5 ± 0.3 Ma...
-age rocks, from Alberta (Scollard Formation
Scollard Formation
-References:* Ryan, M. J., and Russell, A. P., 2001. Dinosaurs of Alberta : In: Mesozoic Vertebrate Life, edited by Tanke, D. H., and Carpenter, K., Indiana University Press, pp. 279-297....
) and Saskatchewan
Saskatchewan
Saskatchewan is a prairie province in Canada, which has an area of . Saskatchewan is bordered on the west by Alberta, on the north by the Northwest Territories, on the east by Manitoba, and on the south by the U.S. states of Montana and North Dakota....
(Frenchman Formation
Frenchman Formation
The Frenchman Formation is a division of Upper Cretaceous rocks found in Saskatchewan, Canada. More accurately described as Late Maastrichtian, these rocks contain the youngest of dinosaur genera, much like the Hell Creek Formation in the United States....
), Canada, and Wyoming (Lance Formation
Lance Formation
The Lance Formation is a division of Late Cretaceous rocks in the western United States. Named after Lance Creek, Wyoming, the microvertebrate fossils and dinosaurs represent important components of the latest Mesozoic vertebrate faunas...
), South Dakota (Hell Creek Formation
Hell Creek Formation
The Hell Creek Formation is an intensely-studied division of Upper Cretaceous to lower Paleocene rocks in North America, named for exposures studied along Hell Creek, near Jordan, Montana...
), Montana (Hell Creek), and Colorado
Colorado
Colorado is a U.S. state that encompasses much of the Rocky Mountains as well as the northeastern portion of the Colorado Plateau and the western edge of the Great Plains...
(Laramie Formation
Laramie Formation
The Laramie Formation is a geologic formation of Cretaceous age, named by Clarence King in 1876 for exposures in northeastern Colorado, in the United States....
), USA. With the exception of birds, it was one of the last extant genera of dinosaurs, its remains being found as close as 3 meters to the boundary clay containing the iridium
Iridium
Iridium is the chemical element with atomic number 77, and is represented by the symbol Ir. A very hard, brittle, silvery-white transition metal of the platinum family, iridium is the second-densest element and is the most corrosion-resistant metal, even at temperatures as high as 2000 °C...
layer that closes the Cretaceous. There are reports of teeth from older, Campanian
Campanian
The Campanian is, in the ICS' geologic timescale, the fifth of six ages of the Late Cretaceous epoch . The Campanian spans the time from 83.5 ± 0.7 Ma to 70.6 ± 0.6 Ma ...
-age rocks, particularly from the Dinosaur Park Formation
Dinosaur Park Formation
The Dinosaur Park Formation is the uppermost member of the Judith River Group, a major geologic unit in southern Alberta. It was laid down over a period of time between about 76.5 and 75 million years ago. The formation is made up of deposits of a high-sinuosity fluvial system, and is capped...
of Alberta, but these specimens are not from Thescelosaurus and are much more likely those of Orodromeus
Orodromeus
Orodromeus is a genus of herbivorous ornithopod dinosaur from the Late Cretaceous of North America.-Discovery and naming:...
. More specimens are known than have been officially described for this genus, such as the Triebold specimen, which has been the source of several skeletal casts
Casting
In metalworking, casting involves pouring liquid metal into a mold, which contains a hollow cavity of the desired shape, and then allowing it to cool and solidify. The solidified part is also known as a casting, which is ejected or broken out of the mold to complete the process...
for museums.
When Galton revisited Thescelosaurus and Bugenasaura in 1999, he described the dentary tooth UCMP
University of California Museum of Paleontology
The University of California Museum of Paleontology is a paleontology museum located on the campus of the University of California, Berkeley....
46911 from the Upper Jurassic of Weymouth, England
England
England is a country that is part of the United Kingdom. It shares land borders with Scotland to the north and Wales to the west; the Irish Sea is to the north west, the Celtic Sea to the south west, with the North Sea to the east and the English Channel to the south separating it from continental...
as cf. Bugensaura. If it is indeed a tooth from a thescelosaur-like animal, this would significantly extend the stratigraphic
Stratigraphy
Stratigraphy, a branch of geology, studies rock layers and layering . It is primarily used in the study of sedimentary and layered volcanic rocks....
range of the group.
Habitat
Conflicting reports have been made as to its preferred habitatHabitat (ecology)
A habitat is an ecological or environmental area that is inhabited by a particular species of animal, plant or other type of organism...
; two papers suggest it preferred channels
River
A river is a natural watercourse, usually freshwater, flowing towards an ocean, a lake, a sea, or another river. In a few cases, a river simply flows into the ground or dries up completely before reaching another body of water. Small rivers may also be called by several other names, including...
to floodplain
Floodplain
A floodplain, or flood plain, is a flat or nearly flat land adjacent a stream or river that stretches from the banks of its channel to the base of the enclosing valley walls and experiences flooding during periods of high discharge...
s, but another suggests it preferred the opposite. The possible preference for channels is based on the relative abundance of thescelosaur fossils in sandstone
Sandstone
Sandstone is a sedimentary rock composed mainly of sand-sized minerals or rock grains.Most sandstone is composed of quartz and/or feldspar because these are the most common minerals in the Earth's crust. Like sand, sandstone may be any colour, but the most common colours are tan, brown, yellow,...
s, representing channel environments, in comparison to mudstone
Mudstone
Mudstone is a fine grained sedimentary rock whose original constituents were clays or muds. Grain size is up to 0.0625 mm with individual grains too small to be distinguished without a microscope. With increased pressure over time the platey clay minerals may become aligned, with the...
s, representing floodplain environments. No bonebeds
Bone bed
A bone bed is any geological stratum or deposit that contains bones of whatever kind. Inevitably, such deposits are sedimentary in nature. Not a formal term, it tends to be used more to describe especially dense collections...
or accumulations of multiple individuals have yet been reported. Dale Russell
Dale Russell
Dale A. Russell is a Canadian geologist/palaeontologist, currently Research Professor at The Department of Marine Earth and Atmospheric Sciences of North Carolina State University...
, in a popular work, noted that Thescelosaurus was the most common small herbivore in the Hell Creek Formation of the Fort Peck
Fort Peck, Montana
Fort Peck is a town in Valley County, Montana, United States. The population was 240 at the 2000 census.-History:The name Fort Peck is associated with Col. Campbell K. Peck, the partner of Elias H. Durfee in the Leavenworth, Kansas, trading firm of Durfee and Peck...
area. He described the environment of the time as a flat floodplain, with a relatively dry subtropical
Subtropics
The subtropics are the geographical and climatical zone of the Earth immediately north and south of the tropical zone, which is bounded by the Tropic of Cancer and the Tropic of Capricorn, at latitudes 23.5°N and 23.5°S...
climate that supported a variety of plants ranging from angiosperm
Flowering plant
The flowering plants , also known as Angiospermae or Magnoliophyta, are the most diverse group of land plants. Angiosperms are seed-producing plants like the gymnosperms and can be distinguished from the gymnosperms by a series of synapomorphies...
trees, to bald cypress
Taxodium
Taxodium is a genus of one to three species of extremely flood-tolerant conifers in the cypress family, Cupressaceae...
, to fern
Fern
A fern is any one of a group of about 12,000 species of plants belonging to the botanical group known as Pteridophyta. Unlike mosses, they have xylem and phloem . They have stems, leaves, and roots like other vascular plants...
s and ginkgo
Ginkgo
Ginkgo , also spelled gingko and known as the Maidenhair Tree, is a unique species of tree with no close living relatives...
s. Although most dinosaur skeletons from this area are incomplete, possibly due to the low preservation potential of forests, Thescelosaurus skeletons are much more complete, suggesting that this genus frequented stream channels. Thus when a Thescelosaurus died, it may have been in or near a river, making it easier to bury and preserve for later fossilization. Russell tentatively compared it to the capybara
Capybara
The capybara , also known as capivara in Portuguese, and capibara, chigüire in Venezuela, Colombia, and Ecuador ronsoco in Peru, chigüiro, and carpincho in Spanish, is the largest living rodent in the world. Its closest relatives are agouti, chinchillas, coyphillas, and guinea pigs...
s and tapir
Tapir
A Tapir is a large browsing mammal, similar in shape to a pig, with a short, prehensile snout. Tapirs inhabit jungle and forest regions of South America, Central America, and Southeast Asia. There are four species of Tapirs: the Brazilian Tapir, the Malayan Tapir, Baird's Tapir and the Mountain...
s. Other dinosaurs that shared its time and place include the ceratopsids
Ceratopsidae
Ceratopsidae is a speciose group of marginocephalian dinosaurs including Triceratops and Styracosaurus...
Triceratops
Triceratops
Triceratops is a genus of herbivorous ceratopsid dinosaur which lived during the late Maastrichtian stage of the Late Cretaceous Period, around 68 to 65 million years ago in what is now North America. It was one of the last dinosaur genera to appear before the great Cretaceous–Paleogene...
and Torosaurus
Torosaurus
Torosaurus is a genus of ceratopsid dinosaur that lived during the late Cretaceous period , between 70 and 65 million years ago. It possessed one of the largest skulls of any known land animal. The frilled skull reached in length...
, hadrosaurids Edmontosaurus
Edmontosaurus
Edmontosaurus is a genus of crestless hadrosaurid dinosaur. It contains two species: Edmontosaurus regalis and Edmontosaurus annectens. Fossils of E. regalis have been found in rocks of western North America that date from the late Campanian stage of the Cretaceous Period 73 million years ago,...
and Anatotitan
Anatotitan
Anatotitan is a genus of flat-headed or hadrosaurine hadrosaurid ornithopod dinosaur from the very end of the Cretaceous Period, in what is now North America...
, ankylosaurid
Ankylosauridae
An ankylosaurid is a member of the Ankylosauridae family of armored dinosaurs that evolved 125 million years ago and became extinct 65 million years ago during the Cretaceous-Tertiary extinction event...
Ankylosaurus
Ankylosaurus
Ankylosaurus is a genus of ankylosaurid dinosaur, containing one species, A. magniventris...
, pachycephalosauria
Pachycephalosauria
Pachycephalosauria is a clade of ornithischian dinosaurs. Well-known genera include Pachycephalosaurus, Stegoceras, Stygimoloch, and Dracorex. Most lived during the Late Cretaceous Period, in what is now North America and Asia. They were all bipedal, herbivorous/omnivorous animals with thick skulls...
ns Pachycephalosaurus
Pachycephalosaurus
Pachycephalosaurus is a genus of pachycephalosaurid dinosaur. It lived during the Late Cretaceous Period of what is now North America. Remains have been excavated in Montana, South Dakota, and Wyoming. It was an herbivorous or omnivorous creature which is only known from a single skull and a few...
and Stygimoloch
Stygimoloch
Stygimoloch is a putative genus of pachycephalosaurid dinosaur from the end of the Cretaceous period, roughly 65 million years ago...
, and the theropods
Theropoda
Theropoda is both a suborder of bipedal saurischian dinosaurs, and a clade consisting of that suborder and its descendants . Dinosaurs belonging to the suborder theropoda were primarily carnivorous, although a number of theropod groups evolved herbivory, omnivory, and insectivory...
Ornithomimus
Ornithomimus
Ornithomimus is a genus of ornithomimid dinosaur from the Late Cretaceous Period of what is now North America.In 1890 Ornithomimus velox was named by Othniel Charles Marsh on the basis of a foot and partial hand from the Maastrichtian Denver Formation. Another seventeen species have been named since...
, Troodon
Troodon
Troodon is a genus of relatively small, bird-like dinosaur from the Late Cretaceous period . Discovered in 1855, it was among the first dinosaurs found in North America...
, and Tyrannosaurus
Tyrannosaurus
Tyrannosaurus meaning "tyrant," and sauros meaning "lizard") is a genus of coelurosaurian theropod dinosaur. The species Tyrannosaurus rex , commonly abbreviated to T. rex, is a fixture in popular culture. It lived throughout what is now western North America, with a much wider range than other...
. Thescelosaurus was also abundant in the Lance Formation. Toe bones from this genus are the most common finds after fossils of Triceratops and Edmontosaurus, and it may have been the most common dinosaur there, if the Lance Formation had a preservation bias against small animals.
"Heart of stone"
North Carolina Museum of Natural Sciences
The North Carolina Museum of Natural Sciences is located in Raleigh, North Carolina. This museum is the oldest established museum in North Carolina and the largest museum of its kind in the Southeast...
, was described as including the remnants of a four-chambered heart and an aorta
Aorta
The aorta is the largest artery in the body, originating from the left ventricle of the heart and extending down to the abdomen, where it branches off into two smaller arteries...
. It had been originally unearthed in 1993 in northwestern South Dakota. The authors had found the internal detail through computed tomography
Computed tomography
X-ray computed tomography or Computer tomography , is a medical imaging method employing tomography created by computer processing...
(CT) imagery. They suggested that the heart had been saponified
Saponification
Saponification is a process that produces soap, usually from fats and lye. In technical terms, saponification involves base hydrolysis of triglycerides, which are esters of fatty acids, to form the sodium salt of a carboxylate. In addition to soap, such traditional saponification processes...
(turned to grave wax
Adipocere
Adipocere , also known as corpse, grave or mortuary wax, is a wax-like organic substance formed by the anaerobic bacterial hydrolysis of fat in tissue, such as body fat in corpses...
) under airless burial conditions, and then changed to goethite
Goethite
Goethite , named after the German polymath Johann Wolfgang von Goethe, is an iron bearing oxide mineral found in soil and other low-temperature environments. Goethite has been well known since prehistoric times for its use as a pigment. Evidence has been found of its use in paint pigment samples...
, an iron mineral
Iron
Iron is a chemical element with the symbol Fe and atomic number 26. It is a metal in the first transition series. It is the most common element forming the planet Earth as a whole, forming much of Earth's outer and inner core. It is the fourth most common element in the Earth's crust...
, by replacement of the original material. The authors interpreted the structure of the heart as indicating an elevated metabolic rate
Metabolism
Metabolism is the set of chemical reactions that happen in the cells of living organisms to sustain life. These processes allow organisms to grow and reproduce, maintain their structures, and respond to their environments. Metabolism is usually divided into two categories...
for Thescelosaurus, not reptilian
Reptile
Reptiles are members of a class of air-breathing, ectothermic vertebrates which are characterized by laying shelled eggs , and having skin covered in scales and/or scutes. They are tetrapods, either having four limbs or being descended from four-limbed ancestors...
cold-bloodedness
Poikilotherm
A poikilotherm is an organism whose internal temperature varies considerably. It is the opposite of a homeotherm, an organism which maintains thermal homeostasis. Usually the variation is a consequence of variation in the ambient environmental temperature...
.
Their conclusions have been disputed; soon after the initial description, other researchers published a paper where they assert that the heart is really a concretion
Concretion
A concretion is a volume of sedimentary rock in which a mineral cement fills the porosity . Concretions are often ovoid or spherical in shape, although irregular shapes also occur. The word 'concretion' is derived from the Latin con meaning 'together' and crescere meaning 'to grow'...
. As they note, the anatomy given for the object is incorrect (for example, the "aorta" narrows coming into the "heart" and lacks arteries
Artery
Arteries are blood vessels that carry blood away from the heart. This blood is normally oxygenated, exceptions made for the pulmonary and umbilical arteries....
coming from it), it partially engulfs one of the ribs and has an internal structure of concentric layers in some places, and another concretion is preserved behind the right leg. The original authors defended their position; they agreed that it was a type of concretion, but one that had formed around and partially preserved the more muscular portions of the heart and aorta.
A study published in 2011 applied multiple lines of inquiry to the question of the object's identity, including more advanced CT scanning, histology
Histology
Histology is the study of the microscopic anatomy of cells and tissues of plants and animals. It is performed by examining cells and tissues commonly by sectioning and staining; followed by examination under a light microscope or electron microscope...
, X-ray diffraction
X-ray scattering techniques
X-ray scattering techniques are a family of non-destructive analytical techniques which reveal information about the crystallographic structure, chemical composition, and physical properties of materials and thin films...
, X-ray photoelectron spectroscopy
X-ray photoelectron spectroscopy
X-ray photoelectron spectroscopy is a quantitative spectroscopic technique that measures the elemental composition, empirical formula, chemical state and electronic state of the elements that exist within a material...
, and scanning electron microscopy. From these methods, the authors found that: the object's internal structure does not include chambers but is made up of three unconnected areas of lower density material, and is not comparable to the structure of an ostrich
Ostrich
The Ostrich is one or two species of large flightless birds native to Africa, the only living member of the genus Struthio. Some analyses indicate that the Somali Ostrich may be better considered a full species apart from the Common Ostrich, but most taxonomists consider it to be a...
's heart; the "walls" are composed of sedimentary minerals not known to be produced in biological systems, such as goethite, feldspar
Feldspar
Feldspars are a group of rock-forming tectosilicate minerals which make up as much as 60% of the Earth's crust....
minerals, quartz
Quartz
Quartz is the second-most-abundant mineral in the Earth's continental crust, after feldspar. It is made up of a continuous framework of SiO4 silicon–oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall formula SiO2. There are many different varieties of quartz,...
, and gypsum
Gypsum
Gypsum is a very soft sulfate mineral composed of calcium sulfate dihydrate, with the chemical formula CaSO4·2H2O. It is found in alabaster, a decorative stone used in Ancient Egypt. It is the second softest mineral on the Mohs Hardness Scale...
, as well as some plant fragments; carbon
Carbon
Carbon is the chemical element with symbol C and atomic number 6. As a member of group 14 on the periodic table, it is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds...
, nitrogen
Nitrogen
Nitrogen is a chemical element that has the symbol N, atomic number of 7 and atomic mass 14.00674 u. Elemental nitrogen is a colorless, odorless, tasteless, and mostly inert diatomic gas at standard conditions, constituting 78.08% by volume of Earth's atmosphere...
, and phosphorus
Phosphorus
Phosphorus is the chemical element that has the symbol P and atomic number 15. A multivalent nonmetal of the nitrogen group, phosphorus as a mineral is almost always present in its maximally oxidized state, as inorganic phosphate rocks...
, chemical element
Chemical element
A chemical element is a pure chemical substance consisting of one type of atom distinguished by its atomic number, which is the number of protons in its nucleus. Familiar examples of elements include carbon, oxygen, aluminum, iron, copper, gold, mercury, and lead.As of November 2011, 118 elements...
s important to life, were lacking in their samples; and cardiac cellular structures were absent. There was one possible patch with animal cellular structures. The authors found their data supported identification as a concretion of sand from the burial environment, not the heart, with the possibility that isolated areas of tissues were preserved.
The question of how this find reflects metabolic rate and dinosaur internal anatomy is moot, though, regardless of the object's identity. Both modern crocodilia
Crocodilia
Crocodilia is an order of large reptiles that appeared about 84 million years ago in the late Cretaceous Period . They are the closest living relatives of birds, as the two groups are the only known survivors of the Archosauria...
ns and bird
Bird
Birds are feathered, winged, bipedal, endothermic , egg-laying, vertebrate animals. Around 10,000 living species and 188 families makes them the most speciose class of tetrapod vertebrates. They inhabit ecosystems across the globe, from the Arctic to the Antarctic. Extant birds range in size from...
s, the closest living relatives of dinosaurs, have four-chambered hearts (albeit modified in crocodilians), so dinosaurs probably had them as well; the structure is not necessarily tied to metabolic rate.
External links
- Thescelosaurus in the Paleobiology DatabasePaleobiology Database' is an online resource for information on the distribution and classification of fossil animals, plants, and microorganisms.-History:The Paleobiology Database was founded in 2000. It has been funded by the National Science Foundation and the Australian Research Council...
. - Willo, the Dinosaur with a Heart - The official site for "Willo", from the North Carolina Museum of Natural Sciences.
- Ornithopoda at the Thescelosaurus! site.