Shuvosaurus

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Shuvosaurus
Temporal range: Late Triassic,
early to middle Norian
Shuvosaurus head BW.jpg
Shuvosaurus head restoration, after the skull reconstruction of Lehane (2005, 2023)
Scientific classification OOjs UI icon edit-ltr.svg
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Reptilia
Clade: Archosauria
Clade: Pseudosuchia
Clade: Paracrocodylomorpha
Clade:† Poposauroidea
Family:† Shuvosauridae
Genus:† Shuvosaurus
Chatterjee, 1993
Species:
†S. inexpectatus
Binomial name
†Shuvosaurus inexpectatus
Chatterjee, 1993
Synonyms
  • ChatterjeeaLong & Murry, 1995
  • Chatterjeea elegansLong & Murry, 1995

Shuvosaurus (meaning "Shuvo [Chatterjee]'s lizard") [1] is a genus of beaked, bipedal poposauroid pseudosuchian from the Late Triassic (early to middle Norian) of western Texas. Despite superficially resembling a theropod dinosaur, especially the ostrich-like ornithomimids, it is instead more closely related to living crocodilians than to dinosaurs. Shuvosaurus is known by the type and only species S. inexpectatus, and is closely related to the very similar Effigia within the clade Shuvosauridae. Shuvosaurus was originally described from a restored skull and very few fragmentary postcranial bones as a probable ornithomimosaur, or at least a very ornithomimosaur-like early theropod. The true pseudosuchian affinities of Shuvosaurus were only recognised after the discovery of Effigia linked the skull of Shuvosaurus with similar poposauroid skeletal remains found in the same quarry.

Contents

History of discovery

Inaccurate life restoration of Shuvosaurus as a coelophysoid theropod Shuvosaurus BW.jpg
Inaccurate life restoration of Shuvosaurus as a coelophysoid theropod

Fossils of Shuvosaurus were first discovered and collected in 1984 but were not described until 1993 by palaeontologist Sankar Chatterjee, after they were recognised in the late 1980s during preparation by his younger son Shuvo Chatterjee, for whom he named it after (combining "Shuvo" with the Ancient Greek σαῦρος (sauros), meaning "lizard"). [1] [2] These fossils consisted of the partially disarticulated remains of three skulls and a partial lower jaw (the holotype TTU (Texas Tech University)-P9280 and paratypes TTU-P9281 and TTU-P9282), as well as a partial atlas and fragmentary vertebra, scapula and an informally referred tibia. Of these postcranial bones only the atlas belongs to Shuvosaurus, the others have since been reidentified as belonging to an azendohsaurid, an ornithodiran and a neotheropod dinosaur, respectively. [3] [4]

The fossils were collected from the Post Quarry (a.k.a. the Miller Quarry) of the lower Cooper Canyon Formation [a] (Dockum Group) near Post, Garza County, Texas, US, and was one of many new discoveries made at this quarry in the 1980s by Chatterjee and his team from the Texas Tech University (such as Technosaurus and Postosuchus ). [5] Although precise dating is lacking for much of the Dockum Group, including the Post Quarry, it has been correlated to the Adamanian teilzone, a local biostratigraphic unit in the southwestern United States—that has elsewhere been dated to the early to middle Norian stage of the Late Triassic, between 224–215 million years old. [3] [6] The fossils of Shuvosaurus were preserved in a bonebed containing the remains of at least nine partially articulated and associated skeletons alongside the skeleton of a Postosuchus, with a minimum total of 14 individuals indicated by the number of right partial femurs collected. [3]

Upon its description, Chatterjee tentatively interpreted Shuvosaurus as a Triassic member of Ornithomimosauria, a group of theropod dinosaurs otherwise known only from the Cretaceous, due to similar construction of the skull, including toothless jaws and large eye sockets. [1] [5] This is reflected in the species name, inexpectatus, for the unexpected nature of finding a toothless, ornithomimid-like skull in Late Triassic deposits. [2] As with the contemporary purported avian Protoavis and Postosuchus, [b] Chatterjee's proposed affinities of a Late Triassic Post Quarry taxon to Cretaceous coelurosaurs invoked a long ghost lineage and was consequently greeted with scepticism by other researchers (such as Halszka Osmólska in 1997). [7]

The Shuvosaurus skulls were found mixed in with postcranial remains of small pseudosuchians from the Post Quarry—all lacking heads—which Chatterjee had previously described as juveniles of the large predatory rauisuchid Postosuchus (of which the fossils were also associated with) in 1985. However, in a 1995 monograph on Late Triassic tetrapods from the American Southwest, Robert Long and Philip Murry regarded this material as so "radically different" from Postosuchus that they identified it as a new taxon of gracile "rauisuchian" allied to poposaurids (i.e. Poposaurus ) which they named Chatterjeea elegans—named after Sankar Chatterjee and from Latin elegans for "very fine" or "beautiful". In the same publication, however, they raised the possibility that Shuvosaurus and Chatterjeea were in fact the same animal, noting the close association of their remains, lack of any apparent ornithomimosaurian postcrania otherwise referrable to Shuvosaurus in the quarry, and that the available material for Shuvosaurus and the Chatterjeea did not overlap (one known by heads, the other skeletons). [8] Following Long and Murry (1995), opinions were divided on the identity of Shuvosaurus and its proposed synonymy with Chatterjeea. Notable among them, Oliver Rauhut (1997, 2000, 2003) argued that Shuvosaurus was indeed a theropod and distinct from Chatterjeea, but that it was instead a specialised basal taxon convergent with ornithomimosaurs. [4] [9] [10]

In the early 2000s, Sterling Nesbitt and Mark Norell prepared previously unopened plaster-jackets of an unknown archosaur collected from the Whitaker Quarry at Ghost Ranch which combined a Shuvosaurus-like skull with Chatterjeea-like postcrania that they named Effigia in 2006. This discovery showed that Shuvosaurus is more closely related to crocodilians and other pseudosuchians than dinosaurs, and that similarities between it and ornithomimids are indeed the result of convergent evolution, while simultaneously demonstrating that the bodies of Chatterjeea almost certainly belong to Shuvosaurus and therefore that the two are synonymous. [11] [12] Indeed, Shuvosaurus and Effigia are so anatomically similar that in 2007 Spencer Lucas and colleagues proposed that the two genera were synonymous, tentatively subsuming Effigia into Shuvosaurus as the species Shuvosaurus okeeffeae, a proposal that has not been followed in subsequent research. [13]

Shuvosaurus itself would not be thoroughly re-examined for many years until late 2023 and early 2024 when two separate redescriptions were published independently. First, the skull was redescribed by Lehane (2023), based upon the work of his previously unpublished 2005 master's thesis, and was followed shortly after by a complete skeletal osteology from Nesbitt and Chatterjee (2024). [14] Although both were published closely together, the work in each was conducted independently and published in parallel. Notably, Nesbitt and Chatterjee (2024) provide novel interpretations of some of the cranial material, differing from those of previous authors, including Lehane (2023). [3]

Many isolated shuvosaurid remains found in rocks of the southwestern US from throughout the Late Triassic have been referred to Shuvosaurus (including to Chatterjeea), namely from elsewhere in the Dockum Group and the Chinle Formation to the west. However, these referrals have been questioned after the discovery of Effigia, as it shows that many of the traits used to assign material to Shuvosaurus are only diagnostic of Shuvosauridae as a whole. Following their osteological description, Nesbitt and Chatterjee revised the taxonomic diagnosis of Shuvosaurus in 2024 and in doing so restricted Shuvosaurus to the type and associated material of the Post Quarry bonebed alone, as isolated bones cannot be reliably differentiated between the two genera. [3]

Classification

Upon its description Shuvosaurus was tentatively classified as a member of the coelurosaurian theropod clade Ornithomimosauria based on superficial similarity of its reconstructed skull. In an early report of its discovery at the annual Society of Vertebrate Paleontology meeting in 1991 Chatterjee even explicitly referred Shuvosaurus to the derived ornithomimosaur family Ornithomimidae. [15] However, in its formal printed description in 1993 he instead more cautiously referred it to the broader group Ornithomimosauria and therein erected the monotypic family Shuvosauridae. This was in part based on the presence of at least two inferred primitively ancestral (i.e. plesiomorphic) traits (no parasphenoid capsule and a smaller brain cavity) compared to Cretaceous ornithomimosaurs, as well as its general distinctiveness relative to them. [5]

Theropod phylogeny of Chatterjee (1993)
Theropoda
Representation of the cladogram and classification of Shuvosaurus of Chatterjee (1993)

Notably, despite these traits and its much older age, Chatterjee regarded Shuvosaurus as a very derived ornithomimosaur and compared it favourably with ornithomimids, noting a particular resemblance to Dromiceiomimus and a similar braincase construction to that of Struthiomimus . Furthermore, he noted that two other Cretaceous ornithomimosaur families, Garudimimidae and Harpymimidae (each themselves monotypic), paradoxically possessed different plesiomorphic features of their own that were already derived and ornithomimid-like in the Triassic Shuvosaurus. This further complicated the relationship of Shuvosaurus to other ornithomimosaurs. [5]

Although Chatterjee argued in favour of Shuvosaurus being an ornithomimosaur, he nonetheless recognised the alternative possibility that the similarities could have independently evolved in a Triassic theropod. However, he himself considered convergent evolution unlikely in this case based on his interpretation of the morphological evidence that otherwise appeared distinctly ornithomimosaurian. [1] [5]

Chatterjee supported his argument with an early cladistic analysis of theropods (modelled on the phylogeny of Gauthier, 1986) [16] in which Shuvosaurus possessed almost the entire suite of derived cranial characteristics in ornithomimosaurs in the dataset and as such was recovered in that clade. However, this analysis notably only included theropods and was focused entirely on a set of 43 skull traits that characterised the already recognised theropod taxa. [5] The affinity of Shuvosaurus to Ornithomimosauria was subsequently questioned by later researchers, such as Osmólska (1998). [7] Hunt et al. (1998) and Heckert & Lucas (1998) went even further and argued that although Chatterjee (1993) compared specific features of Shuvosaurus strongly to ornithomimosaurs, he had not demonstrated that the skull was definitively even that of a dinosaur in the first place. [17] [18]

Theropod dinosaur affinities for Shuvosaurus were nonetheless still supported by some researchers in the late 1990s and early 2000s, most notably by Oliver Rauhut. In 1997, Rauhut rejected Long and Murry's proposal Shuvosaurus was synonymous with Chatterjeea (and therefore a pseudosuchian) on the basis of theropod-like features of its skull that were unknown in any pseudosuchian at the time (later shown to indeed be convergent by Effigia), but did not identify it as an ornithomimosaur. Instead, he believed Shuvosaurus to be an early-diverging theropod, but could not confidently determine its relationships further due to its numerous derived traits. [4] Rauhut later included Shuvosaurus in a phylogenetic analysis of theropods in 2003, in which it was recovered as a coelophysoid. However, its inclusion led to a polytomy amongst coelophysoids, while their relationships were fully resolved when Shuvosaurus was excluded. [10] A similar relationship was argued for in 2005 in the master's thesis of James Lehane, who specifically identified it as a close relative of "Syntarsus" (now known as Megapnosaurus ). [2] Lehane later revised this classification when formally publishing his description of the skull in 2023, subsequent to the discovery of Effigia. [14]

In 2005 Thomas Lehman and Chatterjee briefly alluded to purported additional material that they claimed suggested Shuvosaurus was a theropod more derived than ceratosaurs. [19] However, this report was never followed up on in literature, and when Shuvosaurus was redescribed in 2024 Chatterjee recognised Shuvosaurus as a poposauroid pseudosuchian closely related to Effigia. [3]

An affinity to pseudosuchians (or at least poposaurs) was made correctly based on its postcrania from the start, first as juvenile Postosuchus by Chatterjee, and then as Chatterjeea by Long and Murry (1995). Long and Murry regarded the Chatterjeea postcrania as belonging to a highly derived "rauisuchian" derived from poposaurids that they classified under the new family Chatterjeeidae. [8] With the discovery of Effigia in 2006 the association between the Shuvosaurus skull and "Chatterjeea" postcrania was made clear and Shuvosaurus was conclusively reidentified as a "rauisuchian" pseudosuchian related to Poposaurus. [12] This grouping of Poposaurus-like taxa was later defined as the clade Poposauroidea. [20] Phylogenetic analyses since then consistently find Shuvosaurus and Effigia as sister taxa, and together with Sillosuchus make up the re-defined family and clade of Shuvosauridae deeply nested within Poposauroidea. [3]

Below is a simplified cladogram modified from Nesbitt (2011), highlighting the relationship of Shuvosaurus to other poposauroids. [20] Such a cladogram reflects the interrelationships of Shuvosaurus and other included poposauroids in subsequent analyses of pseudosuchian relationships, for example, Smith et al. (2024). [21]

Poposauroidea

Notes

  1. ↑ In regional Dockum Group stratigraphic nomenclature, the lower, middle, and upper units of the Texas Cooper Canyon Formation are alternatively split up and equated to their lithostratigraphic equivalents in the Texas panhandle and New Mexico; the Tecovas, Trujillo, and Bull Canyon formations, respectively. The Post Quarry is then sometimes assigned to the Tecovas Formation.
  2. ↑ Postosuchus was originally proposed by Chatterjee to be ancestral to the Cretaceous tyrannosaurs and argued that they evolved from Triassic "rauisuchians", invoking a polyphyletic origin of "carnosaurs" (at the time all large meat-eating theropods).

Related Research Articles

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

Protoavis is a problematic taxon known from fragmentary remains from Late Triassic Norian stage deposits near Post, Texas. The animal's true classification has been the subject of much controversy, and there are many different interpretations of what the taxon actually is. When it was first described, the fossils were described as being from a primitive bird which, if the identification is valid, would push back avian origins some 60–75 million years.

<span class="mw-page-title-main">Rauisuchia</span> Informal group of Triassic archosaurs with pillar-erect posture

"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>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>Gojirasaurus</i> Extinct genus of dinosaurs

Gojirasaurus is a genus of "coelophysoid" theropod dinosaur from the Late Triassic of New Mexico. It is named after the giant monster movie character Godzilla, and contains a single species, Gojirasaurus quayi.

<i>Effigia</i> Extinct genus of Archosaurs

Effigia was an extinct genus of shuvosaurid known from the Late Triassic of New Mexico, south-western USA. With a bipedal stance, long neck, and a toothless beaked skull, Effigia and other shuvosaurids bore a resemblance to the ornithomimid dinosaurs of the Cretaceous Period. However, shuvosaurids were not dinosaurs, but were instead a specialized family of poposauroid pseudosuchians, meaning that their closest living relatives are crocodilians.

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

Arizonasaurus was a ctenosauriscid archosaur from the Middle Triassic. Arizonasaurus is found in the Middle Triassic Moenkopi Formation of northern Arizona. A fairly complete skeleton was found in 2002 by Sterling Nesbitt. The taxon has a large sailback formed by elongated neural spines of the vertebrae. The type species, Arizonasaurus babbitti, was named by Samuel Paul Welles in 1947.

Spinosuchus is an extinct genus of trilophosaurid allokotosaur from the Late Triassic of Texas, southern United States. It has been assigned to a variety of groups over its history, from coelophysid dinosaur to pseudosuchian to uncertain theropod dinosaur and to Proterosuchidae. This uncertainty is not unusual, given that it was 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. However, newly collected material and recent phylogenetic studies of early archosauromorphs suggest that it represents an advanced trilophosaurid very closely related to Trilophosaurus.

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

Poposauridae is a family of large carnivorous archosaurs which lived alongside dinosaurs during the Late Triassic. They were around 2.5 to 5 metres long. Poposaurids are known from fossil remains from North and South America. While originally believed to be theropod dinosaurs, cladistic analysis has shown them to be more closely related to crocodiles.

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

Pseudosuchia is one of two major divisions of Archosauria, including living crocodilians and all archosaurs more closely related to crocodilians than to birds. Pseudosuchians are also informally known as "crocodilian-line archosaurs", in contrast to the "bird-like archosaurs" or Avemetatarsalia. Despite Pseudosuchia meaning "false crocodiles", the name is a misnomer as true crocodilians are now defined as a subset of the group.

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

Rauisuchidae is a group of large predatory Triassic archosaurs. Some disagreement exists over which genera should be included in the Rauisuchidae and which should be in the related Prestosuchidae and Poposauridae, and indeed whether these should even be thought of as separate valid families. Rauisuchidae in the modern sense was defined by Sterling Nesbitt in 2011 as the most inclusive clade containing Rauisuchus tiradentes, but not Prestosuchus chiniquensis, Poposaurus gracilis, or Crocodylus niloticus. In this modern sense, rauisuchids are recovered as members of the clade Loricata, being the sister taxon of Crocodylomorpha, and being more derived than taxa such as Prestosuchus and Batrachotomus. Rauisuchids occurred throughout much of the Triassic, and may have first occurred in the Early Triassic if some archosaurian taxa such as Scythosuchus and Tsylmosuchus are considered to be within the family.

Poposaurus is an extinct genus of pseudosuchian archosaur from the Late Triassic of the southwestern and eastern United States. It belongs to the clade Poposauroidea, an unusual group of Triassic pseudosuchians that includes sail-backed, beaked, and aquatic forms. Fossils have been found in Wyoming, Utah, Arizona, Texas, and Virginia. Except for the skull, most parts of the skeleton are known. The type species, P. gracilis, was described and named by Maurice Goldsmith Mehl in 1915. A second species, P. langstoni, was originally the type species of the genus Lythrosuchus. Since it was first described, Poposaurus has been variously classified as a dinosaur, a phytosaur, and a "rauisuchian".

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

Sillosuchus is a genus of shuvosaurid poposauroid archosaur that lived in South America during the Late Triassic period. Shuvosaurids were an unusual family of reptiles belonging to the group Poposauroidea; although their closest modern relatives are crocodilians, they were bipedal and lightly armored, with dinosaur-like hip and skull structures. Based on skull remains from members of the family such as Effigia, they were also toothless and likely beaked herbivores.

Yarasuchus is an extinct genus of avemetatarsalian archosaur that lived during the Anisian stage of the Middle Triassic of India. The genus was named and described in 2005 from a collection of disarticulated but fairly complete fossil material found from the Middle Triassic Yerrapalli Formation. The material is thought to be from two individuals, possibly three, with one being much more complete and articulated than the other. The type and only species is Y. deccanensis. Yarasuchus was a quadruped roughly 2–2.5 metres (6.6–8.2 ft) long, with an elongated neck and tall spines on its vertebrae. Unlike other quadrupedal Triassic reptiles, the limbs and shoulders of Yarasuchus were slender, and more like those of ornithodirans.

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

Heptasuchus is an extinct genus of loricatan pseudosuchian known from the Middle or Late Triassic upper Chugwater Group of Wyoming, United States. It contains a single species, Heptasuchus clarki, the first formally recognized "rauisuchian" or loricatan pseudosuchian from North America.

<span class="mw-page-title-main">Loricata</span> Extinct clade of reptiles

Loricata is a clade of archosaur reptiles that includes crocodilians and some of their Triassic relatives, such as Postosuchus and Prestosuchus. More specifically, Loricata includes Crocodylomorpha and most "rauisuchians", a paraphyletic grade of large terrestrial pseudosuchians which were alive in the Triassic period and ancestral to crocodylomorphs.

<span class="mw-page-title-main">Poposauroidea</span> Extinct clade of reptiles

Poposauroidea is a clade of advanced pseudosuchians. It includes poposaurids, shuvosaurids, ctenosauriscids, and other unusual pseudosuchians such as Qianosuchus and Lotosaurus. It excludes most large predatory quadrupedal "rauisuchians" such as rauisuchids and "prestosuchids". Those reptiles are now allied with crocodylomorphs in a clade known as Loricata, which is the sister taxon to the poposauroids in the clade Paracrocodylomorpha. Although it was first formally defined in 2007, the name "Poposauroidea" has been used for many years. The group has been referred to as Poposauridae by some authors, although this name is often used more narrowly to refer to the family that includes Poposaurus and its close relatives. It was phylogenetically defined in 2011 by Sterling Nesbitt as Poposaurus gracilis and all taxa more closely related to it than to Postosuchus kirkpatricki, Crocodylus niloticus, Ornithosuchus woodwardi, or Aetosaurus ferratus.

<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.

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

Shuvosauridae is an extinct family of theropod-like pseudosuchians within the clade Poposauroidea. Shuvosaurids existed in North America and South America (Argentina) during the Late Triassic period. Shuvosauridae was named by Sankar Chatterjee in 1993 to include the genus Shuvosaurus.

<span class="mw-page-title-main">Timeline of ornithomimosaur research</span>

This timeline of ornithomimosaur research is a chronological listing of events in the history of paleontology focused on the ornithomimosaurs, a group of bird-like theropods popularly known as the ostrich dinosaurs. Although fragmentary, probable, ornithomimosaur fossils had been described as far back as the 1860s, the first ornithomimosaur to be recognized as belonging to a new family distinct from other theropods was Ornithomimus velox, described by Othniel Charles Marsh in 1890. Thus the ornithomimid ornithomimosaurs were one of the first major Mesozoic theropod groups to be recognized in the fossil record. The description of a second ornithomimosaur genus did not happen until nearly 30 years later, when Henry Fairfield Osborn described Struthiomimus in 1917. Later in the 20th century, significant ornithomimosaur discoveries began occurring in Asia. The first was a bonebed of "Ornithomimus" asiaticus found at Iren Debasu. More Asian discoveries took place even later in the 20th century, including the disembodied arms of Deinocheirus mirificus and the new genus Gallimimus bullatus. The formal naming of the Ornithomimosauria itself was performed by Rinchen Barsbold in 1976.

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  16. ↑ Gauthier, J. A. (1986). "Saurischian monophyly and the origin of birds". In Padian, K. (ed.). The Origin of Birds and the Evolution of Flight. Memoirs of the California Academy of Sciences. Vol. 8. Memoirs of the California Academy of Sciences. pp. 1–55. ISBN   0-940228-14-9.
  17. ↑ Hunt, A. P.; Lucas, S. G.; Heckert, A. B.; Sullivan, R. M.; Lockley, M. G. (1998). "Late Triassic dinosaurs from the western United States". Geobios. 31 (4): 511–531. doi:10.1016/S0016-6995(98)80123-X.
  18. ↑ Heckert, A. B.; Lucas, S. G. (1998). "Global correlation of the Triassic theropod record" (PDF). GAIA: Revista de Geociências: 63–74.
  19. ↑ Lehman, T.; Chatterjee, S. (2005). "Depositional setting and vertebrate biostratigraphy of the Triassic Dockum Group of Texas". Journal of Earth System Science. 114 (3): 325–351. Bibcode:2005JESS..114..325L. doi: 10.1007/BF02702953 . S2CID   128760266.
  20. 1 2 Nesbitt, S.J. (2011). "The early evolution of archosaurs: relationships and the origin of major clades". Bulletin of the American Museum of Natural History. 352: 1–292. doi: 10.1206/352.1 . hdl: 2246/6112 . S2CID   83493714.
  21. ↑ Smith, N.D.; Klein, N.; Sander, M.P.; Schmitz, L. (2024). "A new pseudosuchian from the Favret Formation of Nevada reveals that archosauriforms occupied coastal regions globally during the Middle Triassic". Biol. Lett. 20 (7). doi: 10.1098/rsbl.2024.0136 . PMC   11286145 .
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