Calsoyasuchus
Encyclopedia
Calsoyasuchus is a genus
of goniopholidid
mesoeucrocodylia
n that lived in the Early Jurassic
. Its fossilzed remains
were found in the Sinemurian
-Pliensbachian
-age Kayenta Formation
on Navajo Nation
land in Coconino County
, Arizona
, United States
. Formally described as C. valliceps, it is known from a single incomplete skull which is unusually derived
for such an early crocodile relative. This genus was described in 2002 by Ronald Tykowski and colleagues; the species name means "valley head" and refers to a deep groove along the midline of the nasal bone
s and frontal bone
s.
skull (TMM
43631-1) that would be named Calsoyasuchus was discovered in 1997 by members of an expedition composed of crews from Texas Memorial Museum
of the University of Texas at Austin
, the Museum of Comparative Zoology
at Harvard University
, and the Seba Dalkai Navajo Nation School. It was found in the middle third of the silt
y facies
of the Kayenta Formation, near the Adeii Eechii Cliffs. The skull is missing the lower jaws, part of the palate
, most of the suspensorium (the bones that make up the region where the upper and lower jaws articulate), and the occiput
and braincase. Sutures between the skull bones are mostly fused. As preserved, it is about 38.0 centimeters (15.0 in) long, making its owner a moderately sized animal.
The skull was long, low, and curved so that both extremities were higher than the middle. The premaxilla
bones that formed the end of the snout were enlarged to form a wide tip; there were at least four teeth in the right premaxilla and five in the left. The left maxilla
(main tooth-bearing bone of the upper jaw) is more complete than the right, and had at least 29 teeth. There was a deep groove along the midline of the nasals and the frontals; the frontals were fused into a single bone, as is seen in other adult mesoeucrocodylians. Unlike derived neosuchians, it had external antorbital fenestra
e. Tykowski and colleagues subjected the skull to CT scanning
, which revealed internal cavities and air passages, and showed that it had a double-walled secondary palate similar to that of true crocodylians, and similar pneumatic cavities as well.
Tykowski and colleagues performed a cladistic phylogenetic analysis
with their new taxon
, and found that it grouped with Goniopholis
, Sunosuchus
, and, most closely, with Eutretauranosuchus
in a weakly supported clade
, Goniopholididae. They noted that the skull of Calsoyasuchus is very similar to some goniopholid skulls from the younger, Upper Jurassic Morrison Formation
. Calsoyasuchus pushes back the earliest occurrence of goniopholids from the Late Jurassic into the Early Jurassic, and not only helps to bridge a temporal gap between groups of crocodyliforms, but also a morphological
gap. It also implies that some groups of crocodyliforms have long undiscovered histories.
and Pliensbachian
ages of the Early Jurassic, the Kayenta Formation had a diverse fauna
, with the remains of caecilian
s, frog
s, turtle
s, at least five other taxa of crocodylomorphs
, pterosaur
s, theropod, sauropodomorph, and ornithischia
n dinosaur
s, and early relatives of mammals (tritylodontids
and morganucodon
tids).
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 goniopholidid
Goniopholididae
Goniopholididae is an extinct family of moderate-sized semi-aquatic crocodyliforms similar to living crocodiles. They lived between the Early Jurassic and the Late Cretaceous.-Geographical distribution:...
mesoeucrocodylia
Mesoeucrocodylia
Mesoeucrocodylia is the name of the clade that includes Eusuchia and the paraphyletic group Mesosuchia. The group appeared during the Early Jurassic, and continues to the present day....
n that lived in the Early Jurassic
Early Jurassic
The Early Jurassic epoch is the earliest of three epochs of the Jurassic period...
. Its fossilzed remains
Fossil
Fossils are the preserved remains or traces of animals , plants, and other organisms from the remote past...
were found in the Sinemurian
Sinemurian
In the geologic timescale, the Sinemurian is an age or stage in the Early or Lower Jurassic epoch or series. It spans the time between 196.5 ± 2 Ma and 189.6 ± 1.5 Ma...
-Pliensbachian
Pliensbachian
The Pliensbachian is an age of the geologic timescale or stage in the stratigraphic column. It is part of the Early or Lower Jurassic epoch or series and spans the time between 189.6 ± 1.5 Ma and 183 ± 1.5 Ma . The Pliensbachian is preceded by the Sinemurian and followed by the Toarcian.The...
-age Kayenta Formation
Kayenta Formation
The Kayenta Formation is a geologic layer in the Glen Canyon Group that is spread across the Colorado Plateau province of the United States, including northern Arizona, northwest Colorado, Nevada, and Utah. This rock formation is particularly prominent in southeastern Utah, where it is seen in the...
on Navajo Nation
Navajo Nation
The Navajo Nation is a semi-autonomous Native American-governed territory covering , occupying all of northeastern Arizona, the southeastern portion of Utah, and northwestern New Mexico...
land in Coconino County
Coconino County, Arizona
-2010:Whereas according to the 2010 U.S. Census Bureau:*61.7% White*1.2% Black*27.3% Native American*1.4% Asian*0.1% Native Hawaiian or Pacific Islander*3.1% Two or more races*5.2% Other races*13.5% Hispanic or Latino -2000:...
, Arizona
Arizona
Arizona ; is a state located in the southwestern region of the United States. It is also part of the western United States and the mountain west. The capital and largest city is Phoenix...
, United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
. Formally described as C. valliceps, it is known from a single incomplete skull which is unusually 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...
for such an early crocodile relative. This genus was described in 2002 by Ronald Tykowski and colleagues; the species name means "valley head" and refers to a deep groove along the midline of the nasal bone
Nasal bone
The nasal bones are two small oblong bones, varying in size and form in different individuals; they are placed side by side at the middle and upper part of the face, and form, by their junction, "the bridge" of the nose.Each has two surfaces and four borders....
s and frontal bone
Frontal bone
The frontal bone is a bone in the human skull that resembles a cockleshell in form, and consists of two portions:* a vertical portion, the squama frontalis, corresponding with the region of the forehead....
s.
Description
The holotypeHolotype
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...
skull (TMM
Texas Memorial Museum
The Texas Memorial Museum is the main exhibit hall of the Texas Natural Science Center at the University of Texas at Austin in Austin, Texas, USA....
43631-1) that would be named Calsoyasuchus was discovered in 1997 by members of an expedition composed of crews from Texas Memorial Museum
Texas Memorial Museum
The Texas Memorial Museum is the main exhibit hall of the Texas Natural Science Center at the University of Texas at Austin in Austin, Texas, USA....
of the University of Texas at Austin
University of Texas at Austin
The University of Texas at Austin is a state research university located in Austin, Texas, USA, and is the flagship institution of the The University of Texas System. Founded in 1883, its campus is located approximately from the Texas State Capitol in Austin...
, the Museum of Comparative Zoology
Museum of Comparative Zoology
The Museum of Comparative Zoology, full name "The Louis Agassiz Museum of Comparative Zoology", often abbreviated simply to "MCZ", is a zoology museum located on the grounds of Harvard University in Cambridge, Massachusetts. It is one of three museums which collectively comprise the Harvard Museum...
at Harvard University
Harvard University
Harvard University is a private Ivy League university located in Cambridge, Massachusetts, United States, established in 1636 by the Massachusetts legislature. Harvard is the oldest institution of higher learning in the United States and the first corporation chartered in the country...
, and the Seba Dalkai Navajo Nation School. It was found in the middle third of the silt
Silt
Silt is granular material of a size somewhere between sand and clay whose mineral origin is quartz and feldspar. Silt may occur as a soil or as suspended sediment in a surface water body...
y facies
Facies
In geology, facies are a body of rock with specified characteristics. Ideally, a facies is a distinctive rock unit that forms under certain conditions of sedimentation, reflecting a particular process or environment....
of the Kayenta Formation, near the Adeii Eechii Cliffs. The skull is missing the lower jaws, part of the palate
Palate
The palate is the roof of the mouth in humans and other mammals. It separates the oral cavity from the nasal cavity. A similar structure is found in crocodilians, but, in most other tetrapods, the oral and nasal cavities are not truly separate. The palate is divided into two parts, the anterior...
, most of the suspensorium (the bones that make up the region where the upper and lower jaws articulate), and the occiput
Occiput
The occiput is the anatomical term for the posterior portion of the head, in insects the posterior part of those head capsule.-Clinical significance:Trauma to the occiput can cause a basilar skull fracture....
and braincase. Sutures between the skull bones are mostly fused. As preserved, it is about 38.0 centimeters (15.0 in) long, making its owner a moderately sized animal.
The skull was long, low, and curved so that both extremities were higher than the middle. 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....
bones that formed the end of the snout were enlarged to form a wide tip; there were at least four teeth in the right premaxilla and five in the left. The left 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...
(main tooth-bearing bone of the upper jaw) is more complete than the right, and had at least 29 teeth. There was a deep groove along the midline of the nasals and the frontals; the frontals were fused into a single bone, as is seen in other adult mesoeucrocodylians. Unlike derived neosuchians, it had external antorbital fenestra
Antorbital fenestra
An antorbital fenestra is an opening in the skull, in front of the eye sockets. This skull formation first appeared in archosaurs during the Triassic Period. Living birds today possess antorbital fenestrae, but the feature has been lost in modern crocodilians...
e. Tykowski and colleagues subjected the skull to CT scanning
Computed tomography
X-ray computed tomography or Computer tomography , is a medical imaging method employing tomography created by computer processing...
, which revealed internal cavities and air passages, and showed that it had a double-walled secondary palate similar to that of true crocodylians, and similar pneumatic cavities as well.
Tykowski and colleagues performed a cladistic phylogenetic analysis
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...
with their new taxon
Taxon
|thumb|270px|[[African elephants]] form a widely-accepted taxon, the [[genus]] LoxodontaA taxon is a group of organisms, which a taxonomist adjudges to be a unit. Usually a taxon is given a name and a rank, although neither is a requirement...
, and found that it grouped with Goniopholis
Goniopholis
Goniopholis is an extinct genus of crocodyliform that lived in North America, Europe and Asia during the Late Jurassic and Early Cretaceous. Being semi-aquatic it is very similar to modern crocodiles...
, Sunosuchus
Sunosuchus
Sunosuchus is an extinct genus of goniopholidid mesoeucrocodylian. Fossils are known from China, Kyrgyzstan and Thailand and are Jurassic in age, although some may be Early Cretaceous. Five species are currently assigned to the genus: the type species S. miaoi and the species S. junggarensis, S....
, and, most closely, with Eutretauranosuchus
Eutretauranosuchus
Eutretauranosuchus is a genus of goniopholidid mesoeucrocodylian. It is known from several specimens collected from the Late Jurassic-age Morrison Formation, including fossils from Garden Park and Dry Mesa Quarry in Colorado and Como Bluff in Wyoming. The type species is E. delfsi...
in a weakly supported 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...
, Goniopholididae. They noted that the skull of Calsoyasuchus is very similar to some goniopholid skulls from the younger, Upper Jurassic Morrison Formation
Morrison Formation
The Morrison Formation is a distinctive sequence of Late Jurassic sedimentary rock that is found in the western United States, which has been the most fertile source of dinosaur fossils in North America. It is composed of mudstone, sandstone, siltstone and limestone and is light grey, greenish...
. Calsoyasuchus pushes back the earliest occurrence of goniopholids from the Late Jurassic into the Early Jurassic, and not only helps to bridge a temporal gap between groups of crocodyliforms, but also a morphological
Morphology (biology)
In biology, morphology is a branch of bioscience dealing with the study of the form and structure of organisms and their specific structural features....
gap. It also implies that some groups of crocodyliforms have long undiscovered histories.
Paleoecology
During the SinemurianSinemurian
In the geologic timescale, the Sinemurian is an age or stage in the Early or Lower Jurassic epoch or series. It spans the time between 196.5 ± 2 Ma and 189.6 ± 1.5 Ma...
and Pliensbachian
Pliensbachian
The Pliensbachian is an age of the geologic timescale or stage in the stratigraphic column. It is part of the Early or Lower Jurassic epoch or series and spans the time between 189.6 ± 1.5 Ma and 183 ± 1.5 Ma . The Pliensbachian is preceded by the Sinemurian and followed by the Toarcian.The...
ages of the Early Jurassic, the Kayenta Formation had a diverse 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"...
, with the remains of caecilian
Caecilian
The caecilians are an order of amphibians that superficially resemble earthworms or snakes. They mostly live hidden in the ground, making them the least familiar order of amphibians. All extant caecilians and their closest fossil relatives are grouped as the clade Apoda. They are mostly...
s, frog
Frog
Frogs are amphibians in the order Anura , formerly referred to as Salientia . Most frogs are characterized by a short body, webbed digits , protruding eyes and the absence of a tail...
s, turtle
Turtle
Turtles are reptiles of the order Testudines , characterised by a special bony or cartilaginous shell developed from their ribs that acts as a shield...
s, at least five other taxa of crocodylomorphs
Crocodylomorpha
The Crocodylomorpha are an important group of archosaurs that include the crocodilians and their extinct relatives.During Mesozoic and early Tertiary times the Crocodylomorpha were far more diverse than they are now. Triassic forms were small, lightly built, active terrestrial animals. These were...
, pterosaur
Pterosaur
Pterosaurs were flying reptiles of the clade or order Pterosauria. They existed from the late Triassic to the end of the Cretaceous Period . Pterosaurs are the earliest vertebrates known to have evolved powered flight...
s, theropod, sauropodomorph, and ornithischia
Ornithischia
Ornithischia or Predentata is an extinct order of beaked, herbivorous dinosaurs. The name ornithischia is derived from the Greek ornitheos meaning 'of a bird' and ischion meaning 'hip joint'...
n 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...
s, and early relatives of mammals (tritylodontids
Tritylodontidae
Tritylodontids were small to medium-sized, highly specialized and extremely mammal-like cynodonts. They were the last family of the non-mammalian synapsids. One of the last cynodont lines to appear, the Tritylodontidae descended from a Cynognathus-like cynodont...
and morganucodon
Morganucodon
Morganucodon is an early mammalian genus which lived during the Late Triassic. It first appeared about 205 million years ago. This has also been identified with Eozostrodon. Unlike many other early mammals, Morganucodon is well represented by abundant and well preserved, though in the vast...
tids).
External links
- Digimorph page featuring various views and movies of the CT scans of the skull