More data on the Aetosauroides skull

Seven years ago Aetosauroides nested between
Ticinosuchus and Aetosaurus at the base of the Aetosauria in the large reptile tree (LRT, 1269 taxa) based on a line drawing of the skull lacking several parts (Fig. 1). We first talked about this nesting here in 2011.

Today
Brust et al. 2018 bring more complete data on the skull of Aetosauroides (Fig. 1). As far as the nesting goes, the previous line drawing was good enough, despite the missing parts and cartoonish tracing.

Figure 1. Aetosauroides skull UFSM 11505 from Brust et al. 2018 with color applied to bones here. Small inset shows best previous data.

Figure 1. Aetosauroides skull UFSM 11505 from Brust et al. 2018 with color applied to bones here. Small inset shows best previous data.

Unfortunately,
Brust et al. excluded Ticinosuchus (Figs. 2, 3) from the cladogram. Instead they employed the unrelated Revueltosaurus and Postosuchus as outgroup taxa. As readers know by now, taxon exclusion has hampered many studies in the past and, apparently, this continues into the present.

Figure 2. Aetosaur skulls compared to Ticinosuchus, the long-sought outgroup to this clade.

Figure 2. Aetosaur skulls compared to Ticinosuchus, the long-sought outgroup to this clade.

Vjushkovia, Ticinosuchus and the base of the Stagonolepidae (aetosaurs)

Figure 3. Vjushkovia, Ticinosuchus and the base of the Stagonolepidae (aetosaurs)

The new data for Aetosauroides
was added to the LRT and the tree topology did not change. Revueltosaurus continues to nest with Fugusuchus, far from aetosaurs.

Figure 4. Subset of the LRT focusing on the Euarchosauriformes, including the Aetosauria.

Figure 4. Subset of the LRT focusing on the Euarchosauriformes, including the Aetosauria.

References
Brust ACB, Desojo JB, Schultz CL, Paes-Neto VD and Da-Rosa AAS 2018. Osteology of the first skull of Aetosauroides scagliai Casamiquela 1960 (Archosauria: Aetosauria) from the Upper Triassic of southern Brazil (Hyperodapedon Assemblage Zone) and its phylogenetic importance. https://doi.org/10.1371/journal.pone.0201450

Ticinosuchus and the aetosaurs, redux

Except for
the skull of Ticinosuchus ferox (Krebs 1965; Middle Triassic, ~ 230 mya, ~3 m in length), I have been using the traditional Krebs reconstruction for the post-crania. Here (Fig.1 ) I finally present my own tracing and reconstruction of Ticinosuchus.

Figure 1. Aetosaurus, Stagonlepis and Ticinosuchus shown together to scale. Ticinosuchus is the basalmost taxon in this clade, unrecognized by other cladograms. Perhaps this is due to differences in skull reconstructions.

Figure 1. Aetosaurus, Stagonlepis and Ticinosuchus shown together to scale. Ticinosuchus is the basalmost taxon in this clade, unrecognized by other cladograms. Perhaps this is due to differences in skull reconstructions. Note the phylogenetic miniaturization at the origin with Aetosaurus.

The morphological differences
between the Krebs and present reconstructions are few. However the posture here (Fig. 1) is a little more sacrum high, based on the long robust hind limbs, as also seen in Stagonolepis (Fig.1). Earlier we looked at the sharp premaxilla in Ticinosuchus that was previously overlooked by all workers. It’s a key trait shared with aetosaurs (Fig. 2).

Figure 2. Aetosaur skulls compared to Ticinosuchus, the long-sought outgroup to this clade.

Figure 2. Aetosaur skulls compared to Ticinosuchus, the long-sought outgroup to this clade.

Historical Notes from Nesbitt 2011
“Krebs (1963, 1965) argued that Ticinosuchus and Rauisuchus were more closely related to crocodylians than to any other group—a view that was opposed by various workers (e.g., Hughes, 1963; Romer, 1966, 1972b; Bonaparte, 1982) who thought that rauisuchids were proterosuchians.”

“Bonaparte (1981, 1984), placed Rauisuchus, Fasolasuchus, Prestosuchus, Saurosuchus, Ticinosuchus and various other fragmentary forms into Rauisuchidae.”

Nesbit 2011
identified the angular premaxilla as a questionable lacrimal. No reconstruction was offered to support this arrangement. He nested Ticinosuchus in a polygamy with a wide range of taxa including Revuletosaurus + Aetosauria, Turfanosuchus, Gracilisuchus, Qianosuchus and Prestosuchus.

Revueltosaurus?
Nesbitt 2011 nested Revueltosaurus at the base of the aetosaurs. The large reptile tree nests Revueltosaurus with Tasmaniosaurus and Fugusuchus (Fig. 3), altogether a sister clade to the Erythrosuchia and not far from Euparkeria. Revueltosaurus has a round premaxilla.

Figure 1. Revueltosaurus compared to its big sister, Fugusuchus, a basal erythrosuchid.

Figure 3. Revueltosaurus compared to its big sister, Fugusuchus, a basal erythrosuchid.

 

References
Krebs B 1965. Ticinosuchus ferox nov. gen. nov. sp. Ein neuer Pseudosuchier aus der Trias des Monte San Giorgio. Schweizerische Palaontologische Abhandlungen 81:1-140.
Lautenschlager S and Desojo JB 2011. Reassessment of the Middle Triassic rauisuchian archosaurs Ticinosuchus ferox and Stagonosuchus nyassicus. Paläontologische Zeitschrift Online First DOI: 10.1007/s12542-011-0105-1
Nesbitt SJ 2011. The early evolution of archosaurs: relationships and the origin of major clades. Bulletin of the American Museum of Natural History 352: 292 pp.

wiki/Ticinosuchus

 

Revueltosaurus: closer to Aetosaurus? or to Fugusuchus?

This post was updated December 8, 2014 with a new nesting of Revueltosaurus with Fugusuchus as a basal erythrosuchid. 

Yesterday we saw a higher resolution Revueltosaurus skull in lateral view and we noted a disagreement in the phylogenetic nesting of this Late Triassic oddball.

According to Nesbitt (2011)…
Nesbitt (2011) nested the odd herbivorous Triassic archosauriform, Revueltosaurus, at the base of the aetosaurs, including Aetosaurus and Stagonolepis. Outgroups include an unresolved clade including Gracilisuchus, Turfanosuchus and Ticinosuchus. Outgroups to this clade include Riojasuchus and Ornithosuchus (= Ornithosuchidae) at the base of the “Pseudosuchia“. Wiki follows Nesbitt (2011).

According to Parker (2014?)…
William Parker, the discoverer of the twelve-specimen nest of Revueltosaurus skeletons, will soon publish a large monograph on this genus. His analysis will also nest Revueltosaurus with aetosaurs. He’s very sure of that.

Figure 1. Revueltosaurus compared to its big sister, Fugusuchus, a basal erythrosuchid.

Figure 1. Revueltosaurus compared to its big sister, Fugusuchus, a basal erythrosuchid.

According to the large reptile tree…
On the other hand, the large reptile tree does not recover the Nesbitt tree topology, but finds Revueltosaurus nests with Fugusuchus (Fig. 1) at the base of the Erythrosuchidae. To move Revueltosaurus to the Aetosauridae requires an additional 35 steps. t.

Like Aetosaurs:
Revueltosaurus is a heavily armored quadruped and a plant eater (judging by its teeth). I’m told by Parker the following traits are identical in Revueltosaurus and aetosaurs: scapula/coracoid, humerus, squamosal and armor design. You can see (Fig. 1) that despite being twice the size, Revueltosaurus has more gracile girdles and limbs and larger hands and feet than Aetosaurus. And the skull has a distinctly different shape in nearly all regards, including the squamosal. Even so…

An herbivorous rauisuchid, with several aetosaur and turtle-like traits.
On Revueltosaurus, the naris is rather unique. The lateral processes of the premaxilla have become more robust, reducing the size of the naris and moving them to an anterior position.  Revueltosaurus shares these traits with Fugusuchus.

Figure 2. Revueltosaurus pelves compared to Aetosaurus and Postosuchus. Red arrows point to limit of femoral head. Blue arrows point to acetabular shelf that roofs over the femur in rauisuchids.

Figure 2. Revueltosaurus pelves compared to Aetosaurus and Postosuchus. Red arrows point to limit of femoral head. Blue arrows point to acetabular shelf that roofs over the femur in rauisuchids. Revueltosaurus is a small slow quadrupedal plant eater, so it doesn’t have the long booted pelvis of Postosuchus. But note the similarity of the broad ischium to Aetosaurus!  Wm. Parker tells me, “It’s the plesiomorphic archosauriform condition with the very short anterior process. Lacks the deep supracetabular buttress found in rauisuchids. It actually looks like a juvenile aetosaur and it is difficult to tell them apart.” Schoch reports the aetosaur oblique posterior ridge is unlike the supraacetabular ‘boss’ of rauisuchids.

The pelvis should settle the argument
But it doesn’t. The pelvis of Revueltosaurus appears to bear a acetabular boss beneath which the femur articulates and supports. In aetosaurs the pelvis has a simpler shape without the boss. In aetosaurs the pelvis is wider at the top, which provides a broad platform for the armor, and angles inward ventrally. We don’t have a pelvis and hind limb for Fugusuchus, but Euparkeria is not far off. So is Gargainia. Both have similar elements.Here again, the different nesting sites appear to be based on employing macro-traits or micro-traits. This is a problem I have no solution for at present.

Figure 2. Revueltosaurus

Figure 2. Revueltosaurus

 

References
Hunt AP 1989. A new ornithischian dinosaur from the Bull Canyon Formation (Upper Triassic) of east-central New Mexico. In Lucas, S. G. and A. P. Hunt (Eds.), Dawn of the age of dinosaurs in the American Southwest 355–358.
Nesbitt SJ 2011. The early evolution of archosaurs: relationships and the origin of major clades. Bulletin of the American Museum of Natural History 352: 292 pp.
Parker WG., et al. 2005
. The Pseudosuchian Revueltosaurus callenderi and its implications for the diversity of early ornithischian dinosaurs. In Proceedings of the Royal Society London B 272(1566):963–969.

wiki/Revueltosaurus

Revueltosaurus in higher resolution

An online photo of Revueltosaurus (Fig. 1) adds details and clarifies problems. There is also a Vimeo video here featuring paleontologist, William Parker, who authors the Chinleana blogsite. He also discovered 11 skeletons of Revueltosaurus from one site with two that are nearly complete or complete. From that data the complete skeleton (Fig. 1) has been recreated.

Figure 1. Revueltosaurus skull from online source (link above) color coded to bone. Above, the aetosaur, Stagonolepis, to which Nesbitt and Parker nest Revueltosaurus. In contrast, the large reptile tree nests Fugusuchus with Revueltosaurus as a derived herbivorous erythrosuchid.

Figure 1. Revueltosaurus skull from online source (link above) color coded to bone. Above, the aetosaur, Stagonolepis, to which Nesbitt and Parker nest Revueltosaurus. In contrast, the large reptile tree nests Fugusuchus with Revueltosaurus as a derived herbivorous erythrosuchid.

With this data, Nesbitt (2011) nested Revueltosaurus at the base of the Aetosauria with Aetosaurus and Stagonolepis.

In counterpoint,
The large reptile tree, employing a different character list, nested Revueltosaurus with Postosuchus, as a derived, smaller, somewhat turtle-ized rauisuchid.

We’ll look at the pros and cons of both analyses tomorrow.

References
Hunt AP 1989. A new ornithischian dinosaur from the Bull Canyon Formation (Upper Triassic) of east-central New Mexico. In Lucas, S. G. and A. P. Hunt (Eds.), Dawn of the age of dinosaurs in the American Southwest 355–358.
Nesbitt SJ 2011. The early evolution of archosaurs: relationships and the origin of major clades. Bulletin of the American Museum of Natural History 352: 292 pp.
Parker WG., et al. 2005
. The Pseudosuchian Revueltosaurus callenderi and its implications for the diversity of early ornithischian dinosaurs. In Proceedings of the Royal Society London B 272(1566):963–969.

wiki/Revueltosaurus

Brachycheirotherium – probably not produced by Typothorax

A recent paper on complete Typothorax specimens (Heckert et al. 2010, Fig. 1) also raised the possibility that Brachycheirotherium tracks (Fig. 1) could be made by aetosaurs like Typothorax.

Figure 1. Typothorax from Heckert et al. 2010 along with reconstructed pes, and Stagonolepis manus and pes. Brachycheirotherium track is too narrow for this tank-like taxon and digit 4 is too long.

Figure 1. Typothorax from Heckert et al. 2010 along with reconstructed pes, and Stagonolepis manus and pes. Brachycheirotherium track is too narrow for this tank-like taxon and digit 4 is too long in Brachycheirotherium compared to Typothorax. The Brachycheirotherium pedes line up on digit 2. The manus track is wider, but not as wide as reconstructed in Typothorax.

Close but no cigar.
The Typothorax pes is not the best match for Brachycheirotherium tracks. Such a narrow-gauge (pedal 2 is on the midline) would seem unlikely for such a wide tank-like reptile. The Stagonolepis pes is a better match by virtue of a relatively longer pedal digit 4. Ticinosuchus (Fig. 2) is also better by virtue of its more slender body, capable of producing such a narrow-gauge trackway in which pedal digits 2 were aligned along the midline during the step cycle, one of the traits of the Brachycheirotherium track (Fig. 1).

Figure 2. Ticinosuchus overall, hand, foot and skull.

Figure 2. Ticinosuchus overall, hand, foot and skull. Ticinosuchus nests as the ancestor taxon to aetosaurs.

References
Heckert AB, Lucas SG, Rinehart LF, Celesky MD, Spielmann JA and Hunt AP 2010. Articulated skeletons of the aetosaur Typothorax coccinarum Cope (Archosauria: Stagonolepididae) from the Upper Triassic Bull Canyon Formation (Revueltian: early-mid Norian), eastern New Mexico, USA. Journal of Vertebrate Paleontology 30 (3): 619–642.

Strange Bedfellows – Nesbitt (2011) – Part 9 – The Wrap-Up: Rauisuchians, Aetosaurs and Crocs

Sometimes we miss the big picture. 
Here then, for your approval and disapproval are comparisons between closest kin found by the Nesbitt (2011) tree versus those found by the large reptile tree.

The origin of the Aetosauria, Rauisuchia and Crocodylomorpha is today’s topic.
Nesbitt (2011) recovered the clade Loricata to include rauisuchians and their descendants, the crocodylomorpha (Fig. 1). Nesbitt (2011) mentioned Vjushkovia along with other erythrosuchids, but neglected to include it in his family tree. That was unfortunate. The large reptile tree found Vjushkovia a key taxon at the base of the Rauisuchia (Fig. 4), the Ticinosuchus/Aetosaur clade (Fig. 3) and the Crocodylomorpha (Fig. 5). Euparkeria and the Ornithosuchidae were recovered as outgroups for Vjushkovia in the LRT. Nesbitt (2011) nested the two pre-dinosaur plant-eaters together, Revueltosaurus with the Aetosauria, but otherwise there is little the two clades share.

Loricata according to Nesbitt (2011). Here Nesbitt recovers basal crocs arising from derived rauisuchians. The large reptile tree found both crocs and rauisuchians to be derived from a derived erythrosuchid, Vjushkovia, which was not listed by Nesbitt (2011).

Figure 1. Loricata according to Nesbitt (2011). Here Nesbitt recovers basal crocs arising from derived rauisuchians. The large reptile tree found both crocs and rauisuchians to be derived from a derived erythrosuchid, Vjushkovia, which was not listed by Nesbitt (2011). As a rule, major clades typically arise from generalized basal members, not derived taxa. Apparent exceptions, like the origin of pterosaurs from Longisquama, actually follow this pattern as pterosaurs originated from a basal longisquamid without several of the derived traits seen only on Longisquama.

The Nesbitt Tree Illustrated with Taxa
Here (Fig. 2) are many of the taxa recovered by Nesbitt (2011) in phylogenetic order. Much of this matches the large reptile tree. For instance, all of the rauisuchids nested together. However, derived rauisuchids did not give rise to crocs in the LRT. The morphological leap between Postosuchus and Hesperosuchus in the Nesbitt (2011) tree has a completely different pattern in the LRT.

Figure 2. The lineage of crocodylomorphs as recoverd by Nesbitt (2011).

Figure 2. The lineage of crocodylomorphs as recoverd by Nesbitt (2011). That’s a pretty big morphological jump between Postosuchus and Hesperosuchus (still waiting on data for CM73372, hence the place saver oval.) Even so, given the included taxa,  I can see the logic of Nesbitt’s tree, but the shared traits of these two are convergent when more taxa are added. There’s less of jump in the large reptile tree where Postosuchus is among the most derived of rauisuchians and Hesperosuchus and Dromicosuchus have many predecessor taxa in the Crocodylomorpha and basal Archosauria.

The Large Reptile Tree Illustrated with Taxa
In phylogenetic order, taxa within the large reptile tree (Figs. 3-5) appear to form more gradual transitions, have a better chronological order, and the most derived taxa in the various extinct clades actually lead to extinction. Generalized basal taxa give rise to derived forms. For instance, in the LRT a sister to Vjushkovia gave rise to the fish-eaters, Ticinosuchus and Yarasuchus + Qianosuchus and a sister to amored Ticinosuchus gave rise to heavily armored aetosaurs, both taxa with toothless premaxillae. Unfortunately Nesbitt (2011) did not reconstruct the skull of Ticinosuchus. Otherwise the aetosaur connection would have been more obvious.

Vjushkovia, Ticinosuchus and the base of the Stagonolepidae (aetosaurs)

Figure 3. Vjushkovia, Ticinosuchus and the base of the Aetosauria (Stagonolepidae). There’s still a pretty big jump here between Vjushkovia and Ticinosuchus, ameliorated by Qianosuchus (Fig. 4).

The Rauisuchia (Fig. 4) arose from a sister to the small derived erythrosuchid, Euparkeria. Vjushkovia was a descendant taxon that gave rise to several clades as is readily apparent here (details at reptileevolution.com):

Figure 4. The lineage of Rauisuchians, crocs and kin according to their skulls. Here the gradual accumulation of derived traits is easier to demonstrate.

Figure 4. The lineage of Rauisuchians, crocs and kin according to their skulls. Here the gradual accumulation of derived traits is easier to demonstrate.

Vjushkovia: basal to Aetosaurs, Crocs and Rauisuchids
The modifications that evolved in the descendants of Vjushkovia produced a lineage of decreasing size that ultimately produced tiny bipedal crocs (Figs. 4-5). There is no indication of a link between Postosuchus and Hesperosuchus (Nesbitt 2011) when you add these taxa.

Figure 1. Ten basal bipedal crocodylomorphs descending from a sister to Decuriasuchus.

Figure 1. Ten basal bipedal crocodylomorphs descending from a sister to Decuriasuchus.

Larger Studies Brings Greater Resolution
The LRT recovered different branching for the aetosaurs and crocs simply by adding more taxa and, in the case of Ticinosuchus, by more fully describing the formerly enigmatic skull. Images of these taxa demonstrate gradual transitions that are confirmed by 228 character scores leading to complete resolution.

Several notes in the dinosaur blog called these traits convergences, but convergence is defined by the initial phylogenetic distance and only a few traits are shared. Here large suites of traits were shared by sister taxa, the definition of homology.

As always, I encourage readers to see specimens, make observations and come to your own conclusions. Test. Test. And test again.

Evidence and support in the form of nexus, pdf and jpeg files will be sent to all who request additional data.

References
Nesbitt SJ 2011.
 The early evolution of archosaurs: relationships and the origin of major clades. Bulletin of the American Museum of Natural History 352: 292 pp.

From Whence Arrived the Aetosaurs?

Few paleontologists have ventured to guess, or determine through analysis, from whence arrived the aetosaurs. They don’t look much like any other archosauriforms. They seem to appear as sideshows in various analyses. Notably the latest analyses find no consensus. Nesbitt (2011) nested aetosaurs with Revueltosaurus. Outgroup taxa included Turfanosuchus and Gracilisuchus. Brusatte et al. (2010) nested Aetosauria with Gracilisuchus, Erpetosuchus and Crocodylomorpha. The Phytosauria was the outgroup.

“From whence arrived the praying mantis?” — Ogden Nash

Here aetosaurs nested with Ticinosuchus, a basal rauisuchian with a small head, short rostrum,  a reduced lateral temporal fenestra, a large mandibular fenestra, an upturned toothless dentary tip, a toothless premaxilla, a smaller pectoral girdle and scutes both above and below its tail. The hands and feet are also close matches. Ticinosuchus was also a sister to Qianosuchus and Yarasuchus, the long-necked rauisuchians sharing a dorsal naris with the basal rauisuchian, Vjushkovia and aetosaurs. It helped, of course, to actually reconstruct the skull of Ticinosuchus. It’s more aetosaur-like than previously thought. The size reduction between Ticinosuchus and Aetosaurus, the most primitive aetosaur, parallels other size reductions prior to major morphological changes in basal reptiles, mammals and birds. Chronologically the Late Triassic aetosaurs succeeded the Middle Triassic Ticinosuchus.

Figure 1. Vjushkovia, Ticinosuchus and the base of the Stagonolepidae (aetosaurs)

Figure 1. Vjushkovia, Ticinosuchus and the base of the Stagonolepidae (aetosaurs)

Little Aetosaurus
As we’re finding over and over again, whenever a major clade is introduced, its basal member is small. Aetosaurus is less than a third the size of its phylogenetic predecessor, Ticinosuchus, but the skull length is more than half that of Ticinosuchus. The development of more extensive armor and an herbivorous dentition coincides with this size reduction. The only catch is, Aetosaurus is not the earliest known aetosaur. Perhaps it was a late survivor. All other aetosaurs, including earlier specimens, were larger with a more extensive armor coating and an expanded gut for plant digestion.

 Aetosauroides.

Figure 2. Aetosauroides.

Aetosauroides
Aetosauroides scagliai (Casamiquela 1960) Late Triassic (~210 mya) was a transitional taxon between Aetosaurus and Ticinosuchus. It had unconstricted tooth crowns, postnarial contact between the premaxilla and nasal, and a ventral margin of the dentary without a sharp inflexion. The teeth were primitive. I do not know the size of the skull. It was described as “large.”

As always, I encourage readers to see specimens, make observations and come to your own conclusions. Test. Test. And test again.

Evidence and support in the form of nexus, pdf and jpeg files will be sent to all who request additional data.

References
Desojo JB and Ezcurra M.D 2011. A reappraisal of the taxonomic status of Aetosauroides(Archosauria, Aetosauria) specimens from the Late Triassic of South America and their proposed synonymy with Stagonolepis. Journal of Vertebrate Paleontology 31(3):596-609. doi:10.1080/02724634.2011.572936
Fraas O 1877. Aetosaurus ferratus Fr. Die gepanzerte Vogel-Echse aus dem Stubensandstein bei Stuttgar. Festshrift zur Feier des vierhundertjährigen Jubiläums der Eberhard-Karls-Universät zu Tübingen, Wurttembergische naturwissenschaftliche jahreshefte 33 (3): 1–22.
Krebs B 1965. Ticinosuchus ferox nov. gen. nov. sp. Ein neuer Pseudosuchier aus der Trias des Monte San Giorgio. Schweizerische Palaontologische Abhandlungen 81:1-140.
Lautenschlager S and Desojo JB 2011. Reassessment of the Middle Triassic rauisuchian archosaurs Ticinosuchus ferox and Stagonosuchus nyassicus. Paläontologische Zeitschrift Online First DOI: 10.1007/s12542-011-0105-1
Schoch R 2007. Osteology of the small archosaur Aetosaurus from the Upper Triassic of Germany. Neues Jahrbuch für Geologie und Paläontologie – Abhandlung. 246/1:.1–35. DOI: 10.1127/0077-7749/2007/0246-0001
Walker AD 1961. Triassic reptiles from the Elgin area: StagonolepisDasygnathus and their allies. Philosophical Transactions of the Royal Society B 244:103-204.

wiki/Aetosaur
wiki/Stagonolepis