Jesairosaurus and the drepanosaurs leave the Tritosauria :-(

My earlier reconstruction
of the basal lepidosauriform, Jesairosaurus (Fig. 1; contra Jalil 1997, not a protorosaur/prolacertiform) included several errors based on attempting to create a chimaera of several specimens of various sizes based on scale bars. In this case, scale bars should not have been used. Rather fore and hind parts had to be scaled to common elements, like dorsal vertebrae, as shown below (Fig. 2). I think this version more accurately reflects the in vivo specimen, despite its chimeric origins. All of the partial skeletons assigned to this genus were discovered at the same Early to Middle Triassic sandstone site and two were touching one another. A larger skull, ZAR 7, shows the variation in size from the skull to shoulders remains of the ZAR 6 specimen.

Figure 1. New reconstruction of the basal lepidosauriform, Jesairosaurus (Jalil 1993).

Figure 1. New reconstruction of the basal lepidosauriform, Jesairosaurus (Jalil 1997). The wide and flat ribs are interesting traits for a likely arboreal reptile.

Mother of all drepanosaurs
The Drepanosauria is an odd clade of slow-moving arboreal reptiles that includes Hypuronector, Vallesaurus, Megalancosaurus and Drepanosaurus (Figs. 2, 3). Jesairosaurus was not a drepanosaur, but nested basal to this clade before the present revisions. It remains basal to the Drepanosauria now with revisions.

The revised reconstruction of Jesairosaurus 
shifts this clade away from Huehuecuetzpalli, Macrocnemus and the rest of the Tritosauria. Now Jesairosaurus and the drepanosaurs nests between Saurosternon, Palaegama and the so-called “rib” gliders, beginning with Coelurosauravus.

A short history of Jesairosaurus
Shortly after their discovery Lehman 1971 referred the several hematite encrusted specimens to the Procolophonida. Further preparation showed that they were referable to the Diapsida, according to Jalil (1990) and the, more specifically, to the Prolacertiformes (Jalil 1997) as a sister to Malerisaurus with Prolacerta as a common ancestral sister. Jalil did not include the closest sisters of Jesairosaurus as revealed by the present analysis.

With a much larger list of taxa,
the large reptile tree nests Malerisaurus between the Antarctica specimen assigned to Prolacerta (AMNH 9520) and the holotype of Prolacerta. Jesairosaurus, as mentioned above, nests with the basal lepidosauriformes. Any traits shared with protorosaurs are by convergence. Deletion of Jesairosaurus does not affect the nesting of the Drepanosauria as basal lepidosauriformes.

Figure 3. Drepanosaurs and their ancestor sisters, Jesairosaurus and Palaegama to scale.

Figure 3. Drepanosaurs and their ancestor sisters, Jesairosaurus and Palaegama to scale.

Arboreal
This new nesting shifts drepanosaurs closer to kuehneosaurs (Figs. 3, 4), another notably arboreal clade.

Figure 3. The new nesting for Jesairosaurus and the drepanosaurs as sisters to the Kuehneosaurs, several nodes away from Huehuecuetzpalli and the tritosaurs.

Figure 3. The new nesting for Jesairosaurus and the drepanosaurs as sisters to the Kuehneosaurs, several nodes away from Huehuecuetzpalli and the tritosaurs.

Certainly
there will someday be more taxa to fill in the current large morphological gaps in and around Jesairosaurus, but here’s what we have at present (Fig. 3) with regard to the origin of the so-called “rib” gliders (actually dermal rods, not ribs, as shown by Coelurosauravus) and the origin of the drepanosaurs.

Figure 4. Jesarosaurus to scale with sisters Palaegama and Coelurosauravus.

Figure 4. Jesairosaurus to scale with sisters Palaegama and Coelurosauravus.

The shifting of a clade
like Jesairosaurus + Drepanosauria occurred due to inaccurate reconstructions used for data. Science builds on earlier errors and inaccuracies. I let the computer figure out where taxa nest in a cladogram of 606 possible nesting sites, minimizing the negative effects of bias and tradition.

It’s sad
to see the drepanosaurs leaving the Tritosauria as it contains several oddly Dr. Seuss-ian variations on the tritosaur theme.

Also note the nesting
of the basal Rhynchocephalians, Megachirella and Pleurosaurus, between the palaegamids and the tritosaurs (Fig. 4). In the course of this study, both also received updates to their skull reconstructions. The former was difficult to interpret without knowing where it nested. What appeared to be an odd sort of a squamosal in Megachirella now appears to be a pair of displaced pleurosaur-like premaxillae. For Pleurosaurus I should not have trusted a prior line drawing by another worker. Here I used DGS to create what appears to be a more accurate skull without so many apparent autapomorphies.

References
Jalil N 1990. Sur deux cranes de petits Sauria (Amniota, Diapsida) du Trias moyen d’ Algerie. Comptes Rendus de I’ Academic des Sciences, Paris 311 :73 1- 736.
Jalil N-E 1997. A new prolacertiform diapsid from the Triassic of North Africa and the interrelationships of the Prolacertiformes. Journal of Vertebrate Paleontology 17(3), 506-525.
Lehman JP 1971. Nouveaux vertebres du Trias de la Serie de Zarzai’tine. Annales de Paleontologic (Vertebres) 57 :71-93.

 

 

SVP 19 – Something vague about a new clade: “Archelosauria”

Pritchard 2015
provides a teaser abstract that sets up the situation, but provides no solution.

From the abstract
“Since the earliest Triassic, saurian reptiles have been critical components of terrestrial ecosystems. However, molecular and fossil evidence indicates that the divergence between the two constituent lineages (Lepidosauria, Archelosauria [turtles + archosaurs]) took place deep in the Permian Period. A large number of early-diverging stem-archosaur and stemlepidosaur clades have been described from the Permian and Triassic, exhibiting an extraordinary range of bauplans. However, the interrelationships of these stem taxa are poorly resolved, owing to fragmentary records and poor preservation in many groups. As such, the timing of both the initial taxonomic and morphological diversifications of Sauria remain poorly understood. To resolve this phylogenetic uncertainty and the first radiation of crown reptiles, a new phylogenetic data matrix was constructed from a broad sample of Permo-Triassic diapsids. New, three-dimensionally preserved fossils from a number of poorly understood stem groups (e.g., long-necked Tanystropheidae, chameleon-like Drepanosauromorpha) allowed coding of many previously unknown morphologies. Iterations of this data matrix were subjected to both standard parsimony analysis and Bayesian tip-dating methodologies. The results of this analysis suggest that at least ten distinct lineages of Permo-Triassic diapsids survived the PTE, substantially more than went extinct at that time. They do not form a monophyletic Protorosauria clade, a group traditionally considered to include most long-necked, small-headed early archosauromorphs. Instead, these taxa include no fewer than six separate Permo-Triassic diapsid lineages. Indeed, character optimizations strongly suggest that a long-necked, lizard-like bauplan was ancestral for Archosauromorpha. The inclusion of fragmentary fossil material from Early Triassic archosauromorphs indicates that a great deal of morphological diversity existed in saurian groups within the first five million years of the Triassic.**”

*Archelosauria is not recovered in the large reptile tree. Not sure why the molecules do what they do, nesting turtles with archosaurs (hence the clade name).
** This is a teaser abstract. No conclusions are presented. I cannot compare the data here to the cladogram recovered in the large reptile tree.

References
Pritchard A 2015. Resolving the first radiation of crown reptiles. Journal of Vertebrate Paleontology abstracts

SVP 20 – a Euryodus (microsaur) -like captorhinid, Opisthodontosaurus

We looked at this taxon, Opisthodontosaurus, earlier here.
Reisz et al. 2015 describe a captorhinid basal reptile similar to a microsaur.

Figure 1. Opisthodontosaurus (above) with missing bones in color. Black lines represent the referred specimen, OMNH 77470 scaled to fit the holotype, OMNH 77469, here in ghosted lines. Colors represent missing bones.

Figure 1. Opisthodontosaurus (above) with missing bones in color. Black lines represent the referred specimen, OMNH 77470 scaled to fit the holotype, OMNH
77469, here in ghosted lines. Colors represent missing bones.

From the abstract
“The Lower Permian fossiliferous infills of the Dolese Brothers Limestone Quarry, near Richards Spur, Oklahoma, have preserved the most diverse assemblage of terrestrial vertebrates, including small-bodied reptiles, lepospondyl microsaurs, and dissorophoid temnospondyls. One taxon that was previously only known from isolated jaw elements at the locality was the microsaur Euryodus primus. Although it is known from more complete material elsewhere, other remains of E. primus have remained elusive at the Dolese Brothers Quarry.

Figure 1. Euryodus primus, a microsaur nesting between Scincosaurus and Micraroter. Note the odd posterior canine teeth.

Figure 1. Euryodus primus, a microsaur nesting between Scincosaurus and Micraroter. Note the odd posterior canine teeth, much more exaggerated than in Opisthodontosaurus.

The recent discovery of partial articulated skulls and skeletons of a small reptile at Dolese permits the recognition that the dentigerous elements that were previously assigned to Euryodus primus from this locality belong instead to a new captorhinid eureptile. The new captorhinid represents a major departure from other members of this clade in the unique anatomy of its jaws and dentition, which are characterized by their bulbous maxillary and dentary teeth. Three enlarged teeth are present on the maxilla, one in the anterior and two in the posterior region, whereas the premaxillary dentition is homodont and small. In addition, the largest dentary tooth is present along the posterior half of the bone. The dentary is characterized by the presence of a large well-developed coronoid process and deep lateral excavation in the posterior one-quarter of the bone. A phylogenetic analysis of captorhinid eureptiles yields two most parsimonious trees, with one in which the new captorhinid is recovered as the sister taxon to Concordia, this clade in turn being the sister to all other captorhinids, and a second in which the new captorhinid is the sister to all other derived captorhinids, to the exclusion of Concordia and Thuringothyris

The sisters to captorhinids
also include Saurorictus (actually a basal captorhinid), Romeria primusReiszorhinus and Cephalerpeton in the large reptile tree, none of which have enlarged posterior teeth. Cephalerpeton had a complete set of enlarged maxillary teeth with an oddly raised posterior dentary, below the orbit. All of these taxa have a much taller squamosal and a much smaller suptratemporal. The postorbital and postfrontal are triangular. None of these taxa have a dentary with a deep lateral excavation, but otherwise are all quite similar to microsaurs.

Unique among microsaurs
Euryodus
is rather unique among microsaurs with its enlarged posterior teeth. So the headline of Reisz, Leblanc and Scott is a little misleading. The large reptile tree nests Euryodus in a separate clade (Microsauria) from Opisthodontosaurus (with Cephalerpeton).

References
Reisz R, Leblanc A and Scott D 2015. A new early Permian captorhinid reptile (Amniota: Eureptilia) from Richards Spur, Oklahoma, shows remarkable dental and mandibular convergence with microsaurs.

New Origin of Birds YouTube Video

Just in time for Turkey Day!
We’ve seen a lot of data coming in recently with news on Archaeopteryx and reconstructions of basal birds together with their addition to the large reptile tree. In an attempt at simplifying the evolutionary process, here is a YouTube video of < 6 minutes that pulls the origin and evolution of basal birds together based on the cladogram recovered at ReptleEvolution.com.

origin_of_birds_588.jpg

Click to view YouTube video.

Happy Thanksgiving
to my USA readers.

New ichthyosaur family tree by Ji et al. 2015

A recent paper on ichthyosaur systematics
(Ji et al. 2015, Fig. 1) adds newly discovered taxa and the tree is getting nice and big.

Unfortunately,
at the base of their cladogram Ji et al. place a distinctly different proximal outgroup for ichthyosaurs than what was recovered in the large reptile tree (subset shown in Fig. 1, click to enlarge). They appear to be guessing. Apparently they are not sure how ichthyosaurs are related to other reptiles.

Here 
proximal outgroup taxa for ichthyosaurs include Wumengosaurus, Thaisaurus and Xinminosaurus (in ascending order) not Thadeosaurus. These large reptile tree taxa demonstrate a gradual accumulation of basal ichthyosaur traits. The Ji et al taxa, HovasaurusClaudiosaurus and Thadeosaurus do not. In the large reptile tree these three are basal younginiformes, related, yes, but much more distantly related to ichthyosaurs.

Figure 1. Ichthyosaur family trees compared. Left: subset of the large reptile tree. Right: from Ji et al. 2015. Note the lack of correct outgroups in the Ji et al study. They have no idea which taxa are proximal ancestors.

Figure 1. Click to enlarge. Ichthyosaur family trees compared. Left: subset of the large reptile tree. Right: from Ji et al. 2015. Note the lack of correct outgroups in the Ji et al study. They have no idea which taxa are proximal ancestors. Yellow are taxa found in both trees.

So, as an experiment, 
we’ll delete the large reptile tree proximal outgroup taxa in order to match more closely the Ji et al taxon list. What is recovered now?

  1. Hovasaurus, Claudiosaurus and Thadeosaurus now nest together in an outgroup clade.
  2. Xinminosaurus, Grippia and (Shastasaurus alexandrae + Utatsusaurus + (Shastasaurus  pacificus + Hupehsuchus) now form an unresolved clade at the base of the Ichythyosauria.
  3. Then Chaohusaurus nests at the base of the rest of the Ichthyosauria with the same topology as the subset of the large reptile tree.

A few differences between the two topologies without deletions…
Note the morphological mismatches in the Ji et al. topology not found in the large reptile tree.

  1. In the large reptile tree Chaohusaurus nests between two similar taxa, Parvinatator and Besanosaurus. In the Ji et al. tree Chaohusaurus nests between the mismatched and odd Hupehsuchus and a clade of basal ichthyosaurs as the basalmost ichthyosaur, even though it has a derived ichthyosaur shape and traits.
  2. In the large reptile tree the derived, but still Triassic, Cymbospondylus petrinus nests between its contemporary, Mixosaurus and several other giant serpentine ichthyosaurs. All have a depressed cranium with a central ridge. The unrelated flat-headed C. buchseri nests elsewhere with similar deep-bodied, high-crested Shonisaurus popularis. By contrast, in the Ji et al. tree C. piscosus (= petrinus) and C. buchseri nest together with the very primitive, very small, Xinminosaurus, which does not have such a depressed cranium with a central crest.
  3. Ji et al. have a clade of Shastasauridae that includes only shastasaurs. In the large reptile tree, that clade also includes the odd little hupehsuchids and demonstrates how these little toothless enigmas evolved from larger forbearers. Ji et al. provided several skull reconstructions. Perhaps a few more would help to resolve the distinct topologies.

Those are the major issues.
The rest can be swept up later. I’d like to see the authors either expand their own taxon list or work off the large reptile tree to confidently establish a series of outgroup taxa for the Ichthyosauria that actually demonstrate a gradual accumulation of character traits, instead of doing what they did. Then we might have closer correspondence in tree topology. And we’re going to have to figure out Cymbospondylus… is it derived? or primitive?

References
Ji C, Jiang D-Y,  Motani R, Rieppel O, Hao -C & Sun Z-Y 2015. Phylogeny of the Ichthyopterygia incorporating recent discoveries from South China, Journal of Vertebrate Paleontology, DOI: 10.1080/02724634.2015.1025956

SVP 18 – the pelycosaur Dimetrodon via Dr. Robert Bakker

Bakker et al (2015)
show evidence that Dimetrodon (Fig. 1) fed on aquatic prey as there were too few terrestrial reptilian herbivores to sustain their numbers.

Figure 1. Dimetrodon, a sailback pelycosaur synapsid reptile of the Early Permian.

Figure 1. Dimetrodon, a sailback pelycosaur synapsid reptile of the Early Permian.

From the abstract
“In restorations, Dimetrodon often appear feeding upon large land herbivores, e.g., Diadectes and Edaphosaurus. 􀁄􀁑􀀃􀁄􀁏􀁗􀁈􀁕􀁑􀁄􀁗􀁌􀁙􀁈􀀃􀁙􀁌􀁈􀁚􀀏􀀃􀀲􀁏􀁖􀁒􀁑􀂶􀁖􀀃􀀤􀁔􀁘􀁄􀁗􀁌􀁆􀀃􀀩􀁒􀁒􀁇􀀃 Base Theory (AFBT) recognizes non-terrestrial prey as key for dimetrodont food webs. Over 45% of the bones are severely tooth-marked; ubiquitous shed Dimetrodon teeth are mingled with tooth-marked bones in every depositional unit. The CBB lacks any structures that indicate high current energy, so the hydraulic forces probably did not wash in bones from beyond the trough, though bloated whole carcasses could have floated in. There are 39 Dimetrodon, one each of the large herbivores Edaphosaurus and Diadectes, three of the large non-herbivore, non-apex carnivore Secodontosaurus, and three of the semi-terrestrial amphibian Eryops calculated form postcrania. Did benthic amphibians and fish fill the gap in prey? The benthic amphibian Diplocaulus is abundant in every bone-rich unit. Xenacanth sharks are very common in several layers; each shark carried a large, well ossified head spine. AFBT is corroborated: dimetrodonts fed intensively on aquatic prey at the CBB.”

Combine this with what we know of Spinosaurus, and finback reptiles appear to have been largely aquatic in habitat. That’s heresy joining the mainstream.

There is also a good Dimetrodon video (52 min.)
on YouTube featuring Dr. Bakker as he describes how the vast majority of Dimetrodon tails are missing, neatly cut and probably carried away for their meat (because that’s where the most of it is!) by other Dimetrodons.

References
Bakker RT et al. 2015. Dimetrodon and the earliest apex predators: The Craddock bone bed and George Ranch Facies show that aquatic prey, not herbivores, were key food sources. Journal of Vertebrate Paleontology abstracts.

Jim Hopson (U. Chicago) awarded Romer-Simpson Medal

Jim Hopson, Professor Emeritus, University of Chicago, honored with the Romer-Simpson medal at the Dallas 2015 meeting of the Society of Vertebrate Paleontology. Well deserved.

Jim Hopson, Professor Emeritus, University of Chicago, honored with the Romer-Simpson medal at the Dallas 2015 meeting of the Society of Vertebrate Paleontology. Well deserved.

I’m happy to report
that Jim Hopson has been awarded the highest honor the Society of Vertebrate Paleontology can bestow, the Romer-Simpson Medal for a lifetime of achievement.

Hopson focused his research
on the origin of mammals. His work indicated that mammals descended from a single lineage of mammal-like reptiles. His work on tooth replacement in mammal-like reptiles was one of the first to show that growth patterns and dental anatomy can be used to study these extinct species.

On the side
Hopson served as the expert editor for my book, “From the Beginning, the Story of Human Evolution” (Peters 1991). Shortly thereafter, in the late 80s Dr. Hopson was kind enough to host my field trip to Chicago. He showed me the collections there and at the Field Museum. Dr. Hopson also provided reams of photocopies of his work on synapsids. Much of that went into the book, which remains largely accurate today. You can read the book online in PDF form here.

Figure 1. From the Beginning - The Story of Human Evolution was published by Little Brown in 1991 and is now available as a FREE online PDF from DavidPetersStudio.com

From the Beginning – The Story of Human Evolution published by Little Brown in 1991 and is now available as a FREE online PDF from DavidPetersStudio.com by clicking here.

However, the latest
cladograms and basal mammal studies can be found at ReptileEvolution.com.

Read more
about Jim Hopson and his contributions to vert paleo here.

A note about the Liaoning bird embryo from a few days ago…
Dr. Zhou was kind enough to send a high resolution image of the specimen and I have updated the imagery and conclusions posted here on the Liaoning bird embryo. In short, the embryo now nests with the holotype (London specimen) of Archaeopteryx, which nested and still nests as a basal enantiornithine bird. Happily, this analysis confirms both the original identification of the embryo as an enantiornithine, AND a close relationship to Archaeopteryx. 

High resolution will get you there,
but low resolution can still get you close…