Dromicosuchus

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Dromicosuchus
Temporal range: Late Triassic
Dromicosuchus skull.jpg
Holotype at the North Carolina Museum of Natural Sciences
Scientific classification OOjs UI icon edit-ltr.svg
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Reptilia
Clade: Pseudosuchia
Clade: Crocodylomorpha
Genus: Dromicosuchus
Sues et al., 2003
Species:
D. grallator
Binomial name
Dromicosuchus grallator
Sues et al., 2003

Dromicosuchus (Ancient Greek, meaning "fleet or quickly walking crocodile") is an extinct genus of sphenosuchian, a type of basal crocodylomorph, the clade that comprises the crocodilians and their closest kin. It was found in Upper Triassic rocks of North Carolina, United States, and is known from a nearly complete skull and partial skeleton. This specimen is unusual in that it was found beneath the skeleton of a larger rauisuchian ( Postosuchus alisonae ) and has apparent bite damage, suggesting that it was attacked by the larger carnivore before both died and were buried together.

Contents

Discovery

The holotype of Dromicosuchus is a partial skeleton [1] including a nearly complete skull and lower jaws, articulated vertebrae from the atlas to the second tail vertebra, bony armor from the back, ribs and the dermal bones called gastralia, partial shoulder girdles, most of the left arm and leg, and the right upper arm, thigh bone, and shin bone. It was found with the fossils of several other animals in a brick-clay quarry in Durham County, North Carolina, in blocks excavated by University of North Carolina at Chapel Hill students in fall 1994. The fossils came from a mudstone next to a river channel deposit, in Lithofacies Association II of the Deep River basin, part of the extensive Newark Supergroup, dated as pertaining to either the late Carnian or early Norian faunal stages of the Late Triassic. The type species is D. grallator, meaning "one who walks on stilts" in Latin, in reference to its long slender limbs. It was named and described by Hans-Dieter Sues and colleagues in 2003. [2]

When the students excavated the blocks, the fossils were initially identified as the remains as a large, unnamed new genus of poposaurid suchian, which were later described as a new species of Postosuchus (P. alisonae) in 2008. [3] Upon preparation, however, it was discovered that there was the skeleton of a smaller archosaur under its pelvis, and the bones of several different animals as gut contents that remained in place in the rauisuchian fossil: these included bones and scutes of the aetosaur Stegomus , some with tooth marks; bones from the snout, arm, and shoulder of the traversodont cynodont Plinthogomphodon ; phalanx bones of a dicynodont; and a bone fragment from a possible temnospondyl. Additionally, the small archosaur, later named Dromicosuchus, had damage to its neck armor and lower jaw that appears to have been caused by rauisuchian teeth, perhaps those of the animal that was found above it. [2]

Description of the specimen, UNC 15574

The skeleton of the type and only known individual of Dromicosuchus is similarly proportioned to that of Hesperosuchus agilis , and the animal is estimated as 1.2 to 1.3 meters (3.9 to 4.3 ft) long. The age of the animal is not completely clear, because some bones that are ordinarily expected to be fused in adults are fused, but others may not be. The fusion of two shoulder bones suggests that it was mature. The skull was lightly built and triangular, and about 150 millimeters (5.9 inches) long. The eye sockets were circular and about 30 millimeters (1.2 inches) in diameter. There were five teeth per premaxilla (the paired bones that made up the snout), twenty per maxilla (the paired bones that made up the cheeks), and an unknown number in the lower jaw. The teeth differed slightly from the tip of the snout to the cheeks, having more flattened cross-sections and stronger curves in the cheek. The third or fourth tooth of the lower jaw was notably enlarged, fitting into a notch in the upper jaw between the premaxilla and maxilla. [2]

There were at least 23 vertebrae from the skull to the hips. [4] Nine or ten may have been neck vertebrae, the rest forming the back. The hip had two vertebrae anchoring it. Two rows of scutes ran along the middle of the back, as in other basal crocodylomorphs. The limbs are more complete on the left side; the left upper arm was 89 millimeters (3.5 inches) long, and left ulna was 102 millimeters (4.0 inches) long, so the forearm was noticeably longer than the upper arm. The hand was small. For the left hindlimb, the thigh bone was 144 millimeters (5.7 inches) long and the shin was 130 millimeters (5.1 inches) long. [2]

Classification

Sues and his colleagues performed a phylogenetic analysis and found that their new genus (identified as Dromaeosuchus in the diagrams) grouped as a sphenosuchian, possibly closest to Hesperosuchus and Kayentasuchus . Sphenosuchia is a poorly understood and controversial clade of early crocodile relatives, known from the Late Triassic and Jurassic, and it may be paraphyletic, not a natural group. Sues and colleagues found a clade of sphenosuchians in their analysis, but it was weakly supported. [2]

Related Research Articles

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"Rauisuchia" is a paraphyletic group of mostly large and carnivorous Triassic archosaurs. Rauisuchians are a category of archosaurs within a larger group called Pseudosuchia, which encompasses all archosaurs more closely related to crocodilians than to birds and other dinosaurs. First named in the 1940s, Rauisuchia was a name exclusive to Triassic archosaurs which were generally large, carnivorous, and quadrupedal with a pillar-erect hip posture, though exceptions exist for all of these traits. Rauisuchians, as a traditional taxonomic group, were considered distinct from other Triassic archosaur groups such as early dinosaurs, phytosaurs, aetosaurs, and crocodylomorphs.

<i>Saltoposuchus</i> Extinct genus of reptiles

Saltoposuchus is an extinct genus of small, long-tailed crocodylomorph reptile (Sphenosuchia), from the Norian of Europe. The name translated means "leaping foot crocodile". It has been proposed that Terrestrisuchus gracilis and Saltoposuchus connectens represent different ontogenetic stages of the same genus. Saltoposuchus was commonly referred to in popular literature as the ancestor to dinosaurs, however, recent scientific research show that this is not the case.

<i>Postosuchus</i> Genus of reptiles

Postosuchus, meaning "Crocodile from Post", is an extinct genus of rauisuchid reptiles comprising two species, P. kirkpatricki and P. alisonae, that lived in what is now North America during the Late Triassic. Postosuchus is a member of the clade Pseudosuchia, the lineage of archosaurs that includes modern crocodilians. Its name refers to Post Quarry, a place in Texas where many fossils of the type species, P. kirkpatricki, were found. It was one of the apex predators of its area during the Triassic, larger than the small dinosaur predators of its time. It was a hunter which probably preyed on large bulky herbivores like dicynodonts and many other creatures smaller than itself.

<i>Gracilisuchus</i> Genus of fossil reptiles

Gracilisuchus is an extinct genus of tiny pseudosuchian from the Late Triassic of Argentina. It contains a single species, G. stipanicicorum, which is placed in the clade Suchia, close to the ancestry of crocodylomorphs. Both the genus and the species were first described by Alfred Romer in 1972.

<span class="mw-page-title-main">Prestosuchidae</span> Extinct family of reptiles

Prestosuchidae is a polyphyletic grouping of carnivorous archosaurs that lived during the Triassic. They were large active terrestrial apex predators, ranging from around 2.5 to 7 metres in length. They succeeded the Erythrosuchidae as the largest archosaurs of their time. While resembling erythrosuchids in size and some features of the skull and skeleton, they were more advanced in their erect posture and crocodile-like ankle, indicating more efficient gait. "Prestosuchids" flourished throughout the whole of the middle, and the early part of the late Triassic, and fossils are so far known from Europe, India, Africa (Tanzania), Argentina, and Paleorrota in Brazil. However, for a long time experts disagree regarding the phylogenetic relationships of the group, what genera should be included, and whether indeed the "Prestosuchidae" constitute a distinct family.

<span class="mw-page-title-main">Sphenosuchia</span> Suborder of reptiles

Sphenosuchia is a suborder of basal crocodylomorphs that first appeared in the Triassic and occurred into the Middle Jurassic. Most were small, gracile animals with an erect limb posture. They are now thought to be ancestral to crocodyliforms, a group which includes all living crocodilians.

<i>Terrestrisuchus</i> Genus of terrestrial crocodylomorph

Terrestrisuchus is an extinct genus of very small early crocodylomorph that was about 76 centimetres (30 in) long. Fossils have been found in Wales and Southern England and date from near the very end of the Late Triassic during the Rhaetian, and it is known by type and only known species T. gracilis. Terrestrisuchus was a long-legged, active predator that lived entirely on land, unlike modern crocodilians. It inhabited a chain of tropical, low-lying islands that made up southern Britain, along with similarly small-sized dinosaurs and abundant rhynchocephalians. Numerous fossils of Terrestrisuchus are known from fissures in limestone karst which made up the islands it lived on, which formed caverns and sinkholes that preserved the remains of Terrestrisuchus and other island-living reptiles.

<i>Doswellia</i> Extinct genus of reptiles

Doswellia is an extinct genus of archosauriform from the Late Triassic of North America. It is the most notable member of the family Doswelliidae, related to the proterochampsids. Doswellia was a low and heavily built carnivore which lived during the Carnian stage of the Late Triassic. It possesses many unusual features including a wide, flattened head with narrow jaws and a box-like rib cage surrounded by many rows of bony plates. The type species Doswellia kaltenbachi was named in 1980 from fossils found within the Vinita member of the Doswell Formation in Virginia. The formation, which is found in the Taylorsville Basin, is part of the larger Newark Supergroup. Doswellia is named after Doswell, the town from which much of the taxon's remains have been found. A second species, D. sixmilensis, was described in 2012 from the Bluewater Creek Formation of the Chinle Group in New Mexico; however, this species was subsequently transferred to a separate doswelliid genus, Rugarhynchos. Bonafide Doswellia kaltenbachi fossils are also known from the Chinle Formation of Arizona.

<i>Batrachotomus</i> Genus of reptiles

Batrachotomus is a genus of prehistoric archosaur. Fossils of this animal have been found in southern Germany and dated from the Ladinian stage of the Middle Triassic period, around 242 to 237 million years ago. Batrachotomus was described by palaeontologist David J. Gower 22 years after its discovery.

Pachycheilosuchus is an extinct genus of neosuchian from the Early Cretaceous of Texas, United States. Previously known, in part, as the "Glen Rose form", this crocodylomorph is notable for its procoelous vertebrae, otherwise found only in derived eusuchian crocodilians, a thick margin on the maxillae, and a shield of armor on the neck formed by the fusion of six individual scutes.

<i>Junggarsuchus</i> Extinct genus of reptiles

Junggarsuchus is an extinct genus of sphenosuchian crocodylomorph from the Middle or Late Jurassic period of China. The type and only species is J. sloani. The generic name of Junggarsuchus comes from the Junggar Basin, where the fossil was found, and the Greek word "souchos" meaning crocodile. The specific name, "sloani" is in honor of C. Sloan, who is credited with finding the holotype.

<i>Turfanosuchus</i> Extinct genus of reptiles

Turfanosuchus is a genus of archosauriform reptile, likely a gracilisuchid archosaur, which lived during the Middle Triassic (Anisian) of northwestern China. The type species, T. dabanensis, was described by C.C. Young in 1973, based on a partially complete but disarticulated fossil skeleton found in the Kelamayi Formation of the Turfan Basin.

Arganasuchus is an extinct genus of "rauisuchian" (loricatan) archosaur. It is known from a single species, Arganasuchus dutuiti. Fossils of this genus have been found in Upper Triassic rocks of the Argana Basin, Morocco. Though its remains were initially referred to Ticinosuchus when discovered during the 1970s, in 2007 it was identified as a distinct genus with unique features of the pubis and maxilla. Arganasuchus also had several anatomical details in common with Batrachotomus, Fasolasuchus, and Postosuchus, though its relations with other loricatans remains unresolved. Arganasuchus is considered a carnivore due to its large, knife-shaped teeth.

Euscolosuchus is an extinct genus of suchian archosaurs from the Late Triassic of Virginia. It is probably an aetosauriform, as the sister taxon to Acaenasuchus and a relative of aetosaurs.

<i>Pseudhesperosuchus</i> Extinct genus of reptiles

Pseudhesperosuchus is a genus of sphenosuchian, a type of basal crocodylomorph, the clade that comprises the crocodilians and their closest kin. It is known from a partial skeleton and skull found in rocks of the Late Triassic (Norian-age) Los Colorados Formation of the Ischigualasto-Villa Unión Basin in northwestern Argentina.

Parrishia is an extinct genus of sphenosuchian crocodylomorph known from the Late Triassic Chinle, Dockum, and Santa Rosa Formations in Arizona and New Mexico.

<i>Yonghesuchus</i> Extinct genus of reptiles

Yonghesuchus is an extinct genus of Late Triassic archosaur reptile. Remains have been found from the early Late Triassic Tongchuan Formation in Shanxi, China. It is named after Yonghe County, the county where fossils were found. Currently only one species, Y. sangbiensis, is known. The specific name refers to Sangbi Creek, as fossils were found in one of its banks.

<span class="mw-page-title-main">Paracrocodylomorpha</span> Clade of reptiles

Paracrocodylomorpha is a clade of pseudosuchian archosaurs. The clade includes the diverse and unusual group Poposauroidea as well as the generally carnivorous and quadrupedal members of Loricata, including modern crocodylians. Paracrocodylomorpha was named by paleontologist J. Michael Parrish in 1993, although the group is now considered to encompass more reptiles than his original definition intended. The most recent definition of Paracrocodylomorpha, as defined by Sterling Nesbitt in 2011, is "the least inclusive clade containing Poposaurus and Crocodylus niloticus. Most groups of paracrocodylomorphs became extinct at the end of the Triassic period, with the exception of the crocodylomorphs, from which crocodylians such as crocodiles and alligators evolved in the latter part of the Mesozoic.

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<i>Carnufex</i> Extinct genus of reptiles

Carnufex is an extinct genus of crocodylomorph suchian from the Late Triassic of North America. The genus was first described in 2015 by Zanno et al., who named the binomial Carnufex carolinensis, meaning "Carolina butcher". Two specimens are known, the holotype skull and skeleton NCSM 21558, and the referred humerus NCSM 21623. The specimens are from the Carnian-age Pekin Formation, which dates to 231 million years ago. Based on the holotype, Carnufex would have been about 3 m (9.8 ft) long and 1.5 m (4.9 ft) tall, although it may have gotten larger due to the holotype not being fully grown.

References

  1. UNC 15574.
  2. 1 2 3 4 5 Sues, Hans-Dieter; Olsen, Paul E.; Carter, Joseph G.; Scott, Diane M. (2003). "A new crocodylomorph archosaur from the Upper Triassic of North Carolina" (PDF). Journal of Vertebrate Paleontology. 23 (2): 329–343. doi:10.1671/0272-4634(2003)023[0329:ANCAFT]2.0.CO;2. S2CID   17319720.
  3. Peyer, Karin; Carter, Joseph G.; Sues, Hans-Dieter; Novak, Stephanie E.; Olsen, Paul E. (2008-06-12). "A new suchian archosaur from the Upper Triassic of North Carolina". Journal of Vertebrate Paleontology. 28 (2): 363–381. doi:10.1671/0272-4634(2008)28[363:ansaft]2.0.co;2. ISSN   0272-4634.
  4. One or two may have been lost, as there are slight gaps between the blocks of rock holding the skeleton, and Dibothrosuchus , another sphenosuchian, had 24 vertebrae from skull to hips.