CM 73372 reconstructed

So far as I know,
Carnegie Museum specimen CM 73372 (Fig. 1) does not yet have a name, nor has it been reconstructed. Weinbaum 2013 included this skull-less image in a Postosuchus study, which makes sense at first sight, given the size, proportions and age (Late Triassic) of both specimens. The large reptile tree (LRT, 1394 taxa) nests CM73372 close to Postosuchus, but closer to Teratosaurus and Smok. Since Teratosaurus is known from skull-only data at present, there is loss of resolution at that node.

Figure 1. CM73372 in situ and reconstructed using DGS methodology. At first glance it seems to be a biped with short fingers, like Postosuchus. In situ image from Weinbaum 2013.

Figure 1. CM73372 in situ and reconstructed using DGS methodology. At first glance it seems to be a biped with short fingers, like Postosuchus. In situ image from Weinbaum 2013.

This is an interesting taxon because
Lucuona et al. 2017 and others nest it basal to Crocodylomorpha. Weinbaum considered it a member of the Archosauria and the Paracrocodylomorpha, a clade the large reptile tree (LRT, 1394 taxa) does not recover.

According to Wikipedia
Loricata was an early name for an order that includes crocodilesalligators, and gharials, although the order is now referred to as Crocodylia. Nesbitt 2011 defined it as the most inclusive clade containing Crocodylus niloticus (the Nile crocodile), but not the extinct Poposaurus gracilisOrnithosuchus longidens, or Aetosaurus ferox. In the LRT, that clade is a junior synonym for Crocodylomorpha, since Poposaurus is a member of the proximal outgroup, the Poposauria. In traditional paleontology Loricata includes Rauisuchia and Crocodylomorpha. If so, then it also includes Poposauria and Dinosauria, but that was not the original intention of this definition.

Paracrocodylomorpha is another clade invalidated by the LRT because it includes Poposauria and Loricata. In the LRT Rauisuchia is the basal clade, followed roughly by Poposauria and Archosauria (crocs + dinos only).

You might recall,
the Nesbitt 2011 cladogram finds phytosaurs arising from a sister to the distinctly different Euparkeria. Taxon exclusion is the problem here. Nesbitt 2011 also finds Ornithosuchia (Ornithosuchus and kin) and Pterosauria forming the first dichotomy arising from a basal sister to Phytosauria. Again taxon exclusion is the problem here, yet widely accepted in the paleo community for reasons unknown (except, possibly ease of use and fear of change). We talked about other odd and topsy-turvy sister taxa recovered by Nesbitt 2011 earlier here, here and here, three blog posts in a nine-part series.

This addition of CM73372 to the LRT sets us up
for tomorrow’s discussion on basal archosaurs.

References
Lecuona A, Desojo JB and Pol D 2017. New information on the postcranial skeleton of Gracilisuchus stipanicicorum (Archosauria: Suchia) and reappraisal of its phylogenetic position. Zoological Journal of the Linnean Society, 2017, XX, 1–40.
Weinbaum J 2013. Postcranial skeleton of Postosuchus kirkpatricki (Archosauria:
Paracrocodylomorpha), from the Upper Triassic of the United States. Geological Society London Special Publications · August 2013.

wiki/Paracrocodylomorpha
wiki/Loricata

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

Reconstructing the hand of Ticinosuchus

Sometimes fossils are wonderfully preserved
and fully articulated. Sometimes they are wonderfully preserved but woefully disarticulated. At such times, most of the bones can be fit together with ease, but the bones of the fingers and toes can be vexing.

Figure 1. Ticinosuchus forelimbs. Note the scattered manual elements here reconstructed to create PILs and match sister taxa patterns.

Figure 1. Ticinosuchus forelimbs. Note the scattered manual elements here reconstructed to create PILs and match sister taxa patterns. Yellow is the radius. Pink is the ulna. Metatarsal 3 is the most robust based on sister taxa. The phalangeal pattern is 2-3-4-5-4.

Case in point: Ticinosuchus
An important taxon in the evolution of crocs and dinosaurs and other Triassic oddities is the basal rauisuchian, Ticinosuchus. It had departed from the rauisuchian ancestors so much that it is basal to the armored herbivorous aetosaurs of the Late Triassic. Most of the elements of both manus of the Ticinosuchus are present, but scattered. That doesn’t mean they’re impossible to put back together again.

Trace the parts.
Move the parts into a logical pattern (thick with thick, thin with thin, gradually tapering digits, phylogenetic bracketing patterns) then test your results to see if PILs (parallel interphalangeal lines) are produced. When all that happens, you can have high confidence in a correct solution.

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

Figure 2. Ticinosuchus overall, hand, foot and skull. The hand is presented as originally interpreted by Krebs and by a new reconstruction based on the tracing in figure 1 and phylogenetic bracketing.

This is a long-armed quadrupedal taxon with long (longer than each metacarpal). Metacarpal 3 was the most robust. Metacarpal 5 was extremely short. Digits 3 and 4 were subequal. Digit 1 was the shortest digit, but digit 5 had smaller phalanges. Where known, sister taxa share most of these traits.

Earlier here, here and here we put the manus of an early archosauriform together.

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

wiki/Ticinosuchus

Just for Fun: A Paleontologist’s Dream…

Paleontologists-Dream

On several levels this is a great moment and great image. Still it inspires a smile as it brings to mind a similar layout in a Gary Larson cartoon from years ago (see below).  :  )

Probably THE classic Gary Larson cartoon draws parallels with the North Carolina professors above, with all due respect.

Probably THE classic Gary Larson cartoon draws certain parallels with the North Carolina professors and their treasured find (above), with all due respect and a tip of the hat to one and all.   :  )

Yes, paleontologists do dream in color.

 

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.