Spinosuchus
Encyclopedia
Spinosuchus is a genus
of extinct reptile
of uncertain affinities, from the late Triassic
of Texas
. It has been assigned to a variety of groups over its history, from coelophysid dinosaur
to pseudosuchian
to uncertain theropod dinosaur to proterosuchid
to possible trilophosaur
. This uncertainty is not unusual, given that it is only known from a poorly-preserved, wall-mounted, partial vertebral column of an animal that lived in a time of diverse, poorly-known reptile groups.
In 1922, Ermin C. Case described a partial vertebral column (UMMP 7507) he'd discovered in 1921 from the Tecovas Member of the Carnian
-age Upper Triassic Dockum Formation of Crosby County, Texas
, as Coelophysis
sp. (Coelophysis at that time also being poorly known). He considered it to be about 2.5 meters (8.5 ft) long. Additional material was referred to it, including a femur
(UMMP 3396), an ilium
(UMMP 8870), and a basicranium (UMMP 7473). These additional remains have since been recognized as belonging to a variety of other Triassic animals, all of which were poorly known or unknown at the time: the femur to an aetosaur
, possibly Desmatosuchus
, the ilium to a herrerasaurid
, either Chindesaurus
or Caseosaurus
, depending on the taxonomic
authority, and the basicranium to the rauisuchia
n Postosuchus
.
Friedrich von Huene
recognized it as a new genus in 1932, and named it in honor of Case. He considered it to be a "podokesaurid
". Since the 1970s, though, it has been considered a nondinosaurian. However, a review by Hunt et al. in 1998 suggested that it was a theropod, possibly a herrerasaurid, citing its hollow centra as evidence for dinosaurian affinities. In an abstract for the 1999 Society of Vertebrate Paleontology
meeting and his unpublished thesis, Richards recognized that it had a variety of characters that are apomorphic for various dinosaur subgroups, but that these are also found in different basal archosaur
groups, and that the poorly-preserved, distorted, and reconstructed vertebrae offer no evidence for assignment to any major archosaur group; it does, though, show some resemblances to the trilophosaur
s. Further review, as part of a larger series of papers on the evolution of dinosaurs in the Late Triassic by Sterling Nesbitt, Randall Irmis, and William Parker, found Spinosuchus to be a valid genus. However, the authors could not classify it beyond Archosauriformes
, and disagreed with Richards' trilophosaur hypothesis
. Justin Spielmann and colleagues published a redescription in 2009 that concluded Spinosuchus was a trilophosaurid closely related to Trilophosaurus
.
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 extinct reptile
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...
of uncertain affinities, from the late Triassic
Late Triassic
The Late Triassic is in the geologic timescale the third and final of three epochs of the Triassic period. The corresponding series is known as the Upper Triassic. In the past it was sometimes called the Keuper, after a German lithostratigraphic group that has a roughly corresponding age...
of Texas
Texas
Texas is the second largest U.S. state by both area and population, and the largest state by area in the contiguous United States.The name, based on the Caddo word "Tejas" meaning "friends" or "allies", was applied by the Spanish to the Caddo themselves and to the region of their settlement in...
. It has been assigned to a variety of groups over its history, from coelophysid 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...
to pseudosuchian
Crurotarsi
The Crurotarsi are a group of archosauriformes, represented today by the crocodiles,...
to uncertain theropod dinosaur to proterosuchid
Proterosuchidae
Proterosuchidae is an early, possibly paraphyletic, assemblage of basal archosauriformes whose fossils are known from the Latest Permian of Russia and the Early Triassic of southern Africa, Russia, China, Australia, and Antarctica...
to possible trilophosaur
Trilophosaur
Trilophosaurs were lizard-like Triassic diapsid reptiles related to the archosaurs. The best known genus is Trilophosaurus, a herbivore up to 2.5 meters long. It had a short, unusually heavily-built skull, equipped with massive, broad flattened cheek teeth with sharp shearing surfaces for cutting...
. This uncertainty is not unusual, given that it is only known from a poorly-preserved, wall-mounted, partial vertebral column of an animal that lived in a time of diverse, poorly-known reptile groups.
History
(See Glut, 2002, p. 46-48, for a longer summary)In 1922, Ermin C. Case described a partial vertebral column (UMMP 7507) he'd discovered in 1921 from the Tecovas Member of the Carnian
Carnian
The Carnian is the lowermost stage of the Upper Triassic series . It lasted from about 228.7 till 216.5 million years ago . The Carnian is preceded by the Ladinian and is followed by the Norian...
-age Upper Triassic Dockum Formation of Crosby County, Texas
Texas
Texas is the second largest U.S. state by both area and population, and the largest state by area in the contiguous United States.The name, based on the Caddo word "Tejas" meaning "friends" or "allies", was applied by the Spanish to the Caddo themselves and to the region of their settlement in...
, as Coelophysis
Coelophysis
Coelophysis , meaning "hollow form" in reference to its hollow bones , is one of the earliest known genera of dinosaur...
sp. (Coelophysis at that time also being poorly known). He considered it to be about 2.5 meters (8.5 ft) long. Additional material was referred to it, including a femur
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...
(UMMP 3396), an ilium
Ilium (bone)
The ilium is the uppermost and largest bone of the pelvis, and appears in most vertebrates including mammals and birds, but not bony fish. All reptiles have an ilium except snakes, although some snake species have a tiny bone which is considered to be an ilium.The name comes from the Latin ,...
(UMMP 8870), and a basicranium (UMMP 7473). These additional remains have since been recognized as belonging to a variety of other Triassic animals, all of which were poorly known or unknown at the time: the femur to an aetosaur
Aetosaur
Aetosaurs are an extinct order of heavily armoured, medium- to large-sized Late Triassic herbivorous archosaurs. They have small heads, upturned snouts, erect limbs, and a body covered by plate-like scutes. All aetosaurs belong to the family Stagonolepididae...
, possibly Desmatosuchus
Desmatosuchus
Desmatosuchus is an extinct genus of archosaur belonging to the Order Aetosauria. It was one of the largest aetosaurs, being long and about 1.50 m high. It lived during the Late Triassic in Texas....
, the ilium to a herrerasaurid
Herrerasauridae
Herrerasaurids are among the oldest known dinosaurs, appearing in the fossil record 231.4 million years ago . They became extinct by the end of the Triassic period. Herrerasaurids were small-sized carnivorous theropods or basal saurischians...
, either Chindesaurus
Chindesaurus
Chindesaurus is a genus of saurischian dinosaur named after Chinde Point , near where the genoholotype specimen was discovered in the Chinle Formation of Petrified Forest National Park, Arizona, by Bryan Small in 1985...
or Caseosaurus
Caseosaurus
Caseosaurus is a genus of dinosaur from the Late Triassic of North America. The type species, Caseosaurus crosbyensis, was formally described by Hunt, Lucas, Heckert, Sullivan and Lockley in 1998. It was found in the Dockum Formation of Texas, in strata dating to the Late Triassic...
, depending on the taxonomic
Taxonomy
Taxonomy is the science of identifying and naming species, and arranging them into a classification. The field of taxonomy, sometimes referred to as "biological taxonomy", revolves around the description and use of taxonomic units, known as taxa...
authority, and the basicranium to the rauisuchia
Rauisuchia
Rauisuchia is a group of predatory and mostly large Triassic archosaurs. As a clade, Rauisuchia includes these Triassic forms and all crocodylomorphs, which are descendants of Triassic rauisuchians. The group in its traditional sense is paraphyletic, because it does not include crocodylomorph...
n Postosuchus
Postosuchus
Postosuchus, meaning "crocodile from Post ", was a basal archosaur that lived in what is now North America during the middle through to the late Triassic period...
.
Friedrich von Huene
Friedrich von Huene
Friedrich von Huene was a German paleontologist who named more dinosaurs in the early 20th century than anyone else in Europe.-Biography:...
recognized it as a new genus in 1932, and named it in honor of Case. He considered it to be a "podokesaurid
Coelophysoidea
Coelophysoids were common dinosaurs of the Late Triassic and Early Jurassic periods. They were widespread geographically, probably living on all continents. Coelophysoids were all slender, carnivorous forms with a superficial similarity to the coelurosaurs, with which they were formerly...
". Since the 1970s, though, it has been considered a nondinosaurian. However, a review by Hunt et al. in 1998 suggested that it was a theropod, possibly a herrerasaurid, citing its hollow centra as evidence for dinosaurian affinities. In an abstract for the 1999 Society of Vertebrate Paleontology
Society of Vertebrate Paleontology
The Society of Vertebrate Paleontology was founded in 1940 for individuals with an interest in vertebrate paleontology. SVP now has almost 2,000 members. The society's website states that SVP "is organized exclusively for educational and scientific purposes...
meeting and his unpublished thesis, Richards recognized that it had a variety of characters that are apomorphic for various dinosaur subgroups, but that these are also found in different basal archosaur
Archosaur
Archosaurs are a group of diapsid amniotes whose living representatives consist of modern birds and crocodilians. This group also includes all extinct non-avian dinosaurs, many extinct crocodilian relatives, and pterosaurs. Archosauria, the archosaur clade, is a crown group that includes the most...
groups, and that the poorly-preserved, distorted, and reconstructed vertebrae offer no evidence for assignment to any major archosaur group; it does, though, show some resemblances to the trilophosaur
Trilophosaur
Trilophosaurs were lizard-like Triassic diapsid reptiles related to the archosaurs. The best known genus is Trilophosaurus, a herbivore up to 2.5 meters long. It had a short, unusually heavily-built skull, equipped with massive, broad flattened cheek teeth with sharp shearing surfaces for cutting...
s. Further review, as part of a larger series of papers on the evolution of dinosaurs in the Late Triassic by Sterling Nesbitt, Randall Irmis, and William Parker, found Spinosuchus to be a valid genus. However, the authors could not classify it beyond Archosauriformes
Archosauriformes
Archosauriformes is a clade of diapsid reptiles that developed from archosauromorph ancestors some time in the Late Permian...
, and disagreed with Richards' trilophosaur hypothesis
Hypothesis
A hypothesis is a proposed explanation for a phenomenon. The term derives from the Greek, ὑποτιθέναι – hypotithenai meaning "to put under" or "to suppose". For a hypothesis to be put forward as a scientific hypothesis, the scientific method requires that one can test it...
. Justin Spielmann and colleagues published a redescription in 2009 that concluded Spinosuchus was a trilophosaurid closely related to Trilophosaurus
Trilophosaurus
Trilophosaurus was a lizard-like Triassic diapsid reptile related to the archosaurs. It was a herbivore up to 2.5 meters long. It had a short, unusually heavily-built skull, equipped with massive, broad flattened cheek teeth with sharp shearing surfaces for cutting up tough plant material...
.