Acaenasuchus

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Acaenasuchus
Temporal range: Late Triassic, 228–216.5  Ma
Acaenasuchus.png
Life reconstruction by Andrey Atuchin [1]
Acaenasuchus holotype.png
Holotype scute as seen from five different angles
Scientific classification OOjs UI icon edit-ltr.svg
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Reptilia
Clade: Archosauria
Clade: Pseudosuchia
Clade:† Aetosauriformes
Genus:† Acaenasuchus
Long & Murry, 1995
Species:
†A. geoffreyi
Binomial name
†Acaenasuchus geoffreyi
Long & Murry, 1995
Synonyms
  • Desmatosuchus haplocercusHeckert & Lucas, 2002
  • Machaeroprosopus zuniCamp, 1930 (in part)

Acaenasuchus (from the Greek akaina, meaning "thorn" and suchus, meaning "crocodile") [2] is an extinct genus of pseudosuchian, endemic to what would be presently be known as Arizona during the Late Triassic, specifically during the Carnian and Norian stages of the Triassic. [3] Acaenasuchus had a stratigraphic range of approximately 11.5 million years. [4] Acaenasuchus is further categorized as one of the type fauna that belong to the Adamanian LVF, based on the fauna of the Blue Mesa Member of the Chinle Petrified Forest Formation of Arizona, where Acaenasuchus was initially discovered. [3]

Contents

Discovery and naming

The holotype, UCMP 139576 (a left dorsal paramedian scute), was first discovered by Charles Lewis Camp in 1930. [5] Camp initially named the species " Machaeroprosopus zuni". [3] By 1985, "Machaeroprosopus zuni" was considered a synonym of Desmatosuchus, and was reclassified as a juvenile Desmatosuchus by Robert A. Long and Karen Ballew in 1985. [6] UCMP 139576 was eventually moved into its own taxon and classified under the name Acaenasuchus, upon reclassification by Robert A. Long and Philip A. Murry in 1995. [2] Fun Fact! The species epithet Acaenasuchus geoffreyi was named after Geoffrey Long, Robert A. Long's son, for his "considerable patience while his father was away in the field". [2] Long and Murry are credited for providing the most stable evidence that Acaenasuchus was an independent taxon. Long and Murry identified small dorsal plates along the carapace of Acaenasuchus, and identified what they described to be"ornithischian-like" teeth, in addition to a multitude of other proposed synapomorphies. [2] Some of which are the subjects of active studies regarding Acaenasuchus characterization. [3]

The holotype UCMP 139576 was discovered in the Petrified Forest Member of the Chinle Formation and belongs to a fully grown individual, [2] as opposed to a juvenile as initially believed. The Upper Triassic Chinle Formation of Arizona is abundant with fossils belonging to over 18 different taxa groups. [7] Collections from the 1890s onwards document various holotypes of these ranging taxa, including that of Acaenasuchus. [3]

In addition to the holotype UCMP 139576, 95 other scutes under 90 catalogue numbers likely also belong to Acaenasuchus. [2] [6] Another specimen, known as SMU 75403, was described by Marsh et al. (2020), and consists of representative cranial, vertebral, and appendicular elements as well as previously unknown variations in the dorsal carapace and ventral shield. [8]

Validity of the taxon

The classification of Acaenasuchus as an independent taxon has been the topic of controversy due to its similarities to Desmatosuchus. Upon review by Andrew B. Heckert and Spencer G. Lucas, the characters that Long and Murry claim to distinguish between the two species may not represent novel scute features but rather ontogenetic variation. [6] These characters include pitting over the dorsal scutes of Acaenasuchus and division between the raised boss into two flanges of Acaenasuchus, neither of which are present in Desmatosuchus. [3] Heckert and Lucas argue that the visible pits and grooves over the dorsal scutes of Acaenasuchus indicate a juvenile stage of Desmatosuchus development. They elaborate that this pitting is a developmental ontogenetic feature that has been observed in the maturation process of other Aetosaurs, specifically in the taxa Aetosaurus . [3]

In addition to the ontogenetic variation hypothesis, Heckert and Lucas have determined that of the four locations within the Adamanian LVF where Acaenasuchus holotypes have been excavated, two localities are a site of great abundance of adult Desmatosuchus fossils. [6]

While studies are ongoing, the majority of working paleontologists agree that Acaenasuchus should retain its status as a valid taxon, independent of Desmatosuchus. The "pitting" as an example of ontogenetic developments is not supported strongly... due to the fact that the concept of ontogenetic maturation is a poorly understood phenomena within Aetosauria. [3] To address the geographical proximity of Acaenasuchus fossils to those of adult Desmatosuchus, evidence has not been studied to an extent sufficient to claim synonymy at this time. There are too many variables to consider, such as the possibility that both species lived in close proximity to each other during the Late Triassic period. It is also notable that the Chinle Formation is a region rich in Aetosaur specimens, not solely Desmatosuchus.

Map portrays Chinle Formation exposures in Arizona with localities labeled Chinle Formation exposures in Arizona.jpg
Map portrays Chinle Formation exposures in Arizona with localities labeled

Description

Acaenasuchus was very small and narrow-bodied. [8] It is hypothesized to be less than 0.6m in length. Long and Murry provided the characterization of multiple Acaenasuchus features upon its discovery in 1995. [2] Acaenasuchus possess paramedian scutes with anterior laminae, similar to Desmatosuchus. However, Acaenasuchus is characterized specifically by scutes highly developed through the pre-sacral series. [2] These scutes further include the presence of thorn-like processes parallel along the side of the posterior region of the paramedian scutes. [2] Additionally the scutes are described as highly ornamented with ridges and hollows not present in Desmatosuchus. [8] It was known only by its dermal armor until 2016. The 2016 excavations revealed cranial, mandibular, vertebral, pelvic, etc... bones. [9] [2]

Reconstruction of the skeleton and carapace of Acaenasuchus geoffreyi Acaenasuchus Anatomy.png
Reconstruction of the skeleton and carapace of Acaenasuchus geoffreyi

Paramedian scutes

Acaenasuchus paramedian scutes are relatively small in size, similar to the putative size of the taxa itself. [4] They have decreased transverse angulation and include a transverse furrow on the dorsal face. Acaenasuchus paramedian scutes do not include the "tongue in groove" articulation with adjacent plates as seen on Desmatosuchus. [2] Medial and lateral "wing" structures emanate from the ridges of the pre-sacral scutes. [2] Deeply incised pitting is visualized posterior to the pre-sacral scutes. [2] A division of the raised boss is also noted. [3] The raised boss is absent on cervical paramedian scutes only. [6]

Lateral scutes

In addition to paramedian scute identification, lateral scutes have been similarly described on Acaenasuchus. Lateral scutes are features unique to Aetosaurids. [10] The lateral scutes are longer than they are wide in Acaenasuchus. They have increased angulation when compared to the paramedian scutes, suggesting heavy armor on the dorsal surface when compared to the lateral surface. [2] There are two types of "horn" structures observed on the lateral scutes. Conical horns curved dorsally, laterally, and posteriorly… and were wider than the scutes themselves. [2] Conical horns typically displayed ornamentation such as furrows. Blunt horns showed less curvature and did not include ornamentation. Acaenasucus lateral scutes' lack anterior bars but possess anterior laminae. [6]

Cranium/mandible

There is ornamentation on the lateral side of the maxilla in the form of grooves below the ant-orbital foramen, and ridges and pits above. [9] There is a short anterior process of the maxilla which projects ventrally. [9] The teeth are described as having a rounded tip similar to R. callenderi, and contain broad denticles. [9]

There is ornamentation on the lateral surface of the jugal bone in the form of ridges and pits. [9] The bone is thin and tapers in the posterior direction. [9] An early suchian feature, there is a sharp longitudinal ridge present on the lateral side of the jugal. [7] In Acaenasuchus, the longitudinal ridge lies above a shallow groove. [9]

The frontal bone of Acaenasuchus is relatively narrower in the anterior direction. There is ornamentation on the dorsal surface of the frontal bone in the form of sharp circular ridges and oblong pits. [9] There is a large boss that forms the dorsal surface of the orbit, perhaps representing a palpebral co-ossification to the frontal. [9] There are two foramina present on the ventral surface of the bone beneath the large boss. [9]

The parietal bone is ornamented with sharp ridges and deep pits on the dorsal surface. [9] The dorsal surface of the parietal bone lacks a midline crest. [9]

The squamosal bone of Acaenasuchus is longer anteriorly than it is wide posteriorly. The dorsal surface of the squamosal is ornamented in the form of small ridges and pits. [9] The articular facet is broad.

The surangular articulates the articular. The lateral side of the surangular is ornamented in the form of long ridges and oblong pits. [9] The medial articular foramen is present. [9] The retro-articular process of Acaenasuchus is short and curved. [9]

Vertebral column

Trunk vertebrae are the only non-sacral vertebrae identified on Acaenasuchus thus far. Each is similar in size and includes centrum, neural arches, zygapophyses, and transverse processes. The centrum is amphicoelous, and includes longitudinal depressions on the lateral surfaces just below the neural arch. [9] The neural arch is flat, similar to E. olseni, and dorsoventrally short. [9] The most distal end of the transverse process includes ornamentation in the form of small pits and grooves. [9] The zygapophyses are situated close to each other along the midline of each trunk vertebrae. [9] Sacral vertebrae identified in Acaenasuchus have been reconstructed from fragments of sacral ribs, sacral centra, and sacral vertebra. [9] The centrum is amphicoelous and short much like the trunk vertebrae. The sacral rib is found on the anterior side of the centrum. The neural arch is short. The zygapophyses are separated by a thin slot. [9]

Pectoral girdle

The scapula of Acaenasuchus has not been fully excavated, only the proximal portion of the scapula has been recovered. The articulation with the coracoid has been observed. There is a small tubercle present above the glenoid towards the posterior end of the scapula. [9]

The coracoid has only been partially excavated as well. The proximal end of the coracoid including articulation with the scapula has been described. [9]

The humerus has been recovered including all regions but the mid-diaphysis. Three bulb like structures can be observed on the humeral head. [9] The median humeral head is the largest of the three. A semicircular foramen is observed underneath the humeral head. A sub-circular "cuboid fossa" is described on the distal portion of the humerus. [9]

Pelvic girdle

The ilium is vertically oriented in Acaenasuchus. The lateral surface of the ilium does not have a second crest above the supra-acetabular crest but does have a tubercle between the supra-acetabular crest and the pre-acetabular process. [9] The pre-acetabular process is short and faces anteriorly. Two rib attachment scars are observed on the medial side of the ilium. These scars indicate articulations with two sacral vertebrae. [9] The iliac and ischiadic pedicles are not perforated in Acaenasuchus as they are in dinosauriformes. [9] The obturator foramen perforates the pubis.

The femur is relatively short and solid. The femoral head is "blocky" and includes a short groove on the proximal surface. [9] On the anterior surface, the distal region of the femur is smooth. [9]

Paramedian (A-H) and Lateral (I-EE) scutes of Acaenasuchus including UMCP 139588 Acaenasuchus scutes.jpg
Paramedian (A-H) and Lateral (I-EE) scutes of Acaenasuchus including UMCP 139588

Paleobiology

The carapace of Acaenasuchus is of normal proportions, with most armor including thin anterior laminae. Multiple plates of the carapace include extensive laminae suggesting that the carapace was highly flexible, allowing Acaenasuchus to move swiftly with agility. [2] Caudal armor and pectoral spikes are lost in Acaenasuchus when compared to Desmatosuchus, further suggesting an evolutionary tradeoff between defense and armor in exchange for speed and agility. [8]

Paleoecology

Most excavations of vertebrate fossils from the Chinle Formation occurred over floodplains, bogs, small ponds, and near other fluvial channels. [7] Sandstone deposits represent channel systems flowing throughout the area, gleyed mudstones represent floodplain paleosols, and organic mudstones represent bogs. [7] Acaenasuchus was known to be a terrestrial organism, there is little information available that would suggest the Acaenasuchus had semiaquatic potential. [11] Chinle climates in the Late Triassic, when Acaenasuchus lived, is hypothesized to have had significant precipitation seasonally. There may have been what we would categorize today as a dry and wet season. The Chinle Formation during the Late Triassic was a time and place of great faunal diversity. Archosaurs were evolving and diversifying rapidly, Acaenasuchus is hypothesized to occupy a similar niche to smaller archosaurs of the time. [7]

Taxonomy

Hypothesized evolutionary relationships of A. geoffreyi among Archosauria, Suchia, Pseudosuchia, and Aetosauriformes Phylogenetic Relationships.jpg
Hypothesized evolutionary relationships of A. geoffreyi among Archosauria, Suchia, Pseudosuchia, and Aetosauriformes

Acaenasuchus has been organized under the clade Pseudosuchia, the crocodilian line archosaurs. Acaenasuchus is further organized within the order Aetosauria [6] which is recognized by the presence of a carapace indicated by paramedian and lateral scutes. The carapace is composed of two columns of each dorsal and lateral scutes which have the capacity to vary extensively between individual Aetosaurids.

Acaenasuchus was assigned to the family Stagonolepididae by Irmis (2005). [12] Stagonolepididae is the subfamily of Aetosauria and is described by the following synapomorphies: the presence of a deep fontanelle at the base of the basisphenoid, and the absence of a raised boss, specifically over the cervical paramedian scutes. [13]

In 2020, a phylogenetic analysis found Acaenasuchus to be closely related to Revueltosaurus and Euscolosuchus . [8] Ongoing research classifies A. geoffreyi with other specimens' E. olseni and R. callendri as sister taxa to the group Aetosaurids, rather than a part of the group. This led to the study concluding that Acaenasuchus should be classified under the more broad clade of Aetosauroformes, due to the lateral osteoderms found on their carapace. [14]

Related Research Articles

<span class="mw-page-title-main">Aetosaur</span> Extinct order of heavily armoured reptiles

Aetosaurs are heavily armored reptiles belonging to the extinct order Aetosauria. They were medium- to large-sized omnivorous or herbivorous pseudosuchians, part of the branch of archosaurs more closely related to crocodilians than to birds and other dinosaurs. All known aetosaurs are restricted to the Late Triassic, and in some strata from this time they are among the most abundant fossil vertebrates. They have small heads, upturned snouts, erect limbs, and a body ornamented with four rows of plate-like osteoderms. Aetosaur fossil remains are known from Europe, North and South America, parts of Africa, and India. Since their armoured plates are often preserved and are abundant in certain localities, aetosaurs serve as important Late Triassic tetrapod index fossils. Many aetosaurs had wide geographic ranges, but their stratigraphic ranges were relatively short. Therefore, the presence of particular aetosaurs can accurately date a site in which they are found.

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

Aetosaurus is an extinct genus of pseudosuchian reptile belonging to the order Aetosauria. It is generally considered to be the most primitive aetosaur. Three species are currently recognized: A. ferratus, the type species from Germany and Italy; A. crassicauda from Germany; and A. arcuatus from eastern North America. Additional specimens referred to Aetosaurus have been found in the Chinle Group of the southwestern United States, and the Fleming Fjord Formation of Greenland. Specimens of Aetosaurus occur in Norian-age strata.

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

Desmatosuchus is an extinct genus of archosaur belonging to the Order Aetosauria. It lived during the Late Triassic.

Calyptosuchus is an extinct genus of aetosaur from the Late Triassic of North America. Like other aetosaurs, it was heavily armored and had a pig-like snout used to uproot plants.

<i>Saurosuchus</i> Paracrocodylomorph reptile genus from Late Triassic period

Saurosuchus is an extinct genus of large loricatan pseudosuchian archosaurs that lived in South America during the Late Triassic period. It was a heavy, ground-dwelling, quadrupedal carnivore, likely being the apex predator in the Ischigualasto Formation.

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

Typothorax is an extinct genus of typothoracine aetosaur that lived in the Late Triassic. Its remains have been found in North America. Two species are known: T. coccinarum, the type species, and T. antiquum.

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.

Lucasuchus is an extinct genus of aetosaur. Fossils have been found from the Bull Canyon Formation of the Dockum Group outcropping in the Revuelto Creek locality in Quay County, New Mexico. All specimens date back to the Norian stage of the Late Triassic. The genus was named in 1995 after the American paleontologist Spencer G. Lucas.

<i>Paratypothorax</i> Genus of reptiles

Paratypothorax is an extinct genus of aetosaur, known from a single species, Paratypothorax andressorum. It was a broadly distributed member of the group found in Germany, North America, and possibly parts of Gondwana. The best specimens come from Germany, though for more than a century they were mistakenly considered phytosaur armor. Paratypothorax was a large and wide-bodied typothoracine aetosaur, as well as the namesake of the tribe Paratypothoracisini.

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

Typothoracinae is a clade of aetosaurs within the subfamily Aetosaurinae. It was originally defined as a stem-based taxon including all aetosaurs closer to Typothorax than to Stagonolepis or Desmatosuchus. This definition was later expanded to specifically exclude Aetosaurus; as of 2016, Typothoracinae is defined as the least inclusive clade containing Typothorax and Paratypothorax, but not Aetosaurus,Stagonolepis, or Desmatosuchus. The clade was first named in 2007 under the spelling Typothoracisinae, after its namesake Typothorax. However, this spelling was based on incorrect taxonomic nomenclature, and the clade's name was corrected to Typothoracinae in 2016.

<span class="mw-page-title-main">Aetosaurinae</span> Extinct subfamily of reptiles

Aetosaurinae is one of the two main clades of aetosaurs, the other being Desmatosuchia. It is a stem-based taxon defined as all aetosaurs more closely related to Aetosaurus than Desmatosuchus. Aetosaurinae currently comprises Aetosaurus, similar forms such as Coahomasuchus and Stenomyti, and the widespread and successful aetosaur clade Typothoracinae.

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

Paratypothoracini is a clade of aetosaurs within the group Typothoracinae. It is a node-based taxon that includes Rioarribasuchus (=Heliocanthus), Paratypothorax, Tecovasuchus, and all descendants of their most recent common ancestor. The clade was first named in 2007 under the spelling Paraypothoracisini, after its namesake Paratypothorax. However, this spelling was based on incorrect taxonomic nomenclature, and the clade's name was corrected to Paratypothoracinae in 2016.

<span class="mw-page-title-main">Desmatosuchinae</span> Subfamily of reptiles

Desmatosuchinae is a major subfamily of aetosaurs within the clade Desmatosuchia. It is a stem-based taxon defined as all aetosaurs more closely related to Desmatosuchus than to Stagonolepis,Aetosaurus, or Paratypothorax.

Redondasuchus is an extinct genus of aetosaur. It may be a junior synonym of Typothorax coccinarum, another aetosaur. Redondasuchus is a member of the clade Typothoracisinae within the subfamily Aetosaurinae, and lived during the middle Norian stage of the Late Triassic. Material belonging to the genus has been found from the Redonda Formation in east-central New Mexico. The type species, R. reseri, was named in 1991 after having been referred to as a species of Typothorax since 1985. A second species, R. rineharti, was described in 2006.

Sierritasuchus is an extinct genus of aetosaur in the subfamily Desmatosuchinae. It is known from a small holotype skeleton from the Late Triassic Tecovas Formation of Texas. This skeleton was discovered in 1939 and was originally assigned to the genus Desmatosuchus. It was placed in its own genus in 2008 after having been in the collections of the University of Michigan Museum of Paleontology, with the type species being S. macalpini. The generic name refers to Sierrita de la Cruz Creek where the holotype was found, and the specific name refers to Archie MacAlpin, who discovered the skeleton. Based on the histology of the scutes of the holotype, the individual was a subadult that was not fully grown.

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

Scutarx is an extinct genus of Aetosauriformes, most commonly regarded by its species name Scutarx deltatylus. Scutarx lived around 230 million years ago during the Carnian and Norian stage of the Late Triassic. Scutarx are “medium sized” paramedian osteoderms belonging to the clade Aetosauria, a heavily armored and more herbivorous cousin of crocodiles.

Kryphioparma is an extinct genus of aetosaur from the Late Triassic Blue Mesa Member of the Chinle Formation, Arizona. It is the oldest known member of the subfamily Typothoracinae, and is currently only known from five isolated and incomplete dorsal osteoderms. Regardless, said osteoderms show a clear mix of features that do not match any other known aetosaur and were thus used as the basis for a new genus and species in 2023. The genus is monotypic, only including a single species, Kryphioparma caerula.

<i>Venkatasuchus</i> Genus of reptile

Venkatasuchus is an extinct genus of aetosaur from the Late Triassic Dharmaram Formation of India. It was described in 2023 on the basis of a series of associated osteoderms that formed the paramedian and lateral armour. Based on the osteoderms the carapace of Venkatasuchus was disc-shaped and very wide, with curved, horn-like elements along its sides. Phylogenetic analysis indicates that Venkatasuchus belonged to the subfamily Typothoracinae and more specifically the clade Paratypothoracini, where it is recovered as the sister taxon to Kocurypelta. Venkatasuchus is among the few aetosaurs recovered from the region that would later become Gondwana and lends credence to the idea that late Triassic India represented a connective hub between Laurasian and Gondwanan fauna. The genus is monotypic, meaning it only includes a single species, Venkatasuchus armatum.

Garzapelta is an extinct genus of aetosaur from the Late Triassic Cooper Canyon Formation containing a single species, G. muelleri. Garzapelta is known primarily from an associated collection of osteoderms, although some other bones such as ribs are also known. The anatomy of Garzapelta's armour displays a mix of features otherwise seen in Rioarribasuchus chamaensis, a member of the Paratypothoracini, and taxa of the subfamily Desmatosuchinae. This mix of characters is so distinct that phylogenetic analysis yielded different results based on what parts of the osteoderms were used, suggesting that the current dataset does not account for convergent evolution in osteoderm anatomy. Reyes, Martz and Small suggest that Garzapelta was likely a paratypothoracin that simply evolved lateral osteoderms similar to those of desmatosuchins, reasoning that its armour does not articulate in the way seen in members of the latter group.

References

  1. ↑ New geosciences study shows Triassic fossils that reveal origins of living amphibians. Virginia Tech. Live reconstruction of Funcusvermis gilmorei and A. geoffreyi
  2. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 R. A. Long and P. A. Murry. (1995). Late Triassic (Carnian and Norian) tetrapods from the southwestern United States. New Mexico Museum of Natural History and Science Bulletin 4:1-254
  3. 1 2 3 4 5 6 7 8 9 Parker, W. G.; McCord, R. D. (2005). "Faunal review of the Upper Triassic Chinle Formation of Arizona. Mesa Southwest" (PDF). Mesa Southwest Museum Bulletin. 1 (11): 34–54.
  4. 1 2 Paleobiology Database: Acaenasuchus, basic info
  5. ↑ Camp, C. L., (1930), A study of the phytosaurs with description of new material from western North America: Memoirs of the University of California, v. 19, 174 p.
  6. 1 2 3 4 5 6 7 Heckert, A.B. and Lucas, S. G. (2002). Acaenasuchus geoffreyi (Archosauria: Aetosauria) from the Upper Triassic Chinle Group: Juvenile of Desmatosuchushaplocerus. Upper Triassic Stratigraphy and Paleontology. New Mexico Museum of Natural History and Science Bulletin No. 21.
  7. 1 2 3 4 5 Michael Parrish, J. (1989-01-01). "Vertebrate paleoecology of the Chinle formation (Late Triassic) of the Southwestern United States". Palaeogeography, Palaeoclimatology, Palaeoecology. XIIth INQUA Congress. 72: 227–247. doi:10.1016/0031-0182(89)90144-2. ISSN   0031-0182.
  8. 1 2 3 4 5 Marsh, Adam D.; Smith, Matthew E.; Parker, William G.; Irmis, Randall B.; Kligman, Ben T. (2020-10-12). "Skeletal Anatomy of Acaenasuchus Geoffreyi Long and Murry, 1995 (Archosauria: Pseudosuchia) and its Implications for the Origin of the Aetosaurian Carapace". Journal of Vertebrate Paleontology. 40 (4): e1794885. doi: 10.1080/02724634.2020.1794885 . hdl: 10919/102375 . ISSN   0272-4634.
  9. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 Marsh, Adam D.; Smith, Matthew E.; Parker, William G.; Irmis, Randall B.; Kligman, Ben T. (2020-07-03). "Skeletal Anatomy of Acaenasuchus Geoffreyi Long and Murry, 1995 (Archosauria: Pseudosuchia) and its Implications for the Origin of the Aetosaurian Carapace". Journal of Vertebrate Paleontology. 40 (4): e1794885. doi:10.1080/02724634.2020.1794885. hdl: 10919/102375 . ISSN   0272-4634.
  10. ↑ Roberto De Silva, L.; Desojo, J.B.; Cabreira, S.F.; Aires, A.S; Mueller, R.T.; Pacheco, C.P.; Dias Da Silva, S. (2014). "A new aetosaur from the Upper Triassic of the Santa Maria Formation, southern Brazil". Zootaxa. 3764 (3): 240–278.
  11. ↑ Parker, William G. (2010-03-09). "Reassessment of the Aetosaur 'Desmatosuchus' chamaensis with a reanalysis of the phylogeny of the Aetosauria (Archosauria: Pseudosuchia)". Journal of Systematic Palaeontology. doi:10.1017/S1477201906001994.
  12. ↑ R. B. Irmis. (2005). The vertebrate fauna of the Upper Triassic Chinle Formation in northern Arizona. In S. J. Nesbitt, W. G. Parker, & R. B. Irmis (eds.), Guidebook to the Triassic Formations of the Colorado Plateau in Northern Arizona: Geology, Paleontology, and History. Mesa Southwest Museum Bulletin 9:63-88
  13. ↑ Heckert, A. B.; Lucas, S. G. (2000). "Taxonomy, phylogeny, biostratigraphy" (PDF). Biochronology, Paleobiogeography. 1 (1): 5–10.
  14. ↑ Parker, William G.; Nesbitt, Sterling J.; Irmis, Randall B.; Martz, Jeffrey W.; Marsh, Adam D.; Brown, Matthew A.; Stocker, Michelle R.; Werning, Sarah (October 2022). "Osteology and relationships of Revueltosaurus callenderi (Archosauria: Suchia) from the Upper Triassic (Norian) Chinle Formation of Petrified Forest National Park, Arizona, United States". The Anatomical Record. 305 (10): 2353–2414. doi:10.1002/ar.24757. ISSN   1932-8486. PMC   9544919 . PMID   34585850.
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