Continuing problems in vertebrate paleontology – part 1

A quick glance through various paleontology topics
on various Wikipedia pages reveals a rather long list of antiquated views that remain as false paradigms. These were falsified by testing in the large reptile tree. We’ll just bring up a few of these at a time while waiting for more interesting paleo-news to break.

  1. The first amniotes, referred to as “basal amniotes”, resembled small lizards and evolved from the amphibian reptiliomorphs about 312 million years ago. Move that back to 340 mya for phylogenetically widespread fossil evidence of basal amniotes and to 360 mya for their hypothetical origins.
  2. The first dichotomy within the Amniotes produced the clades Synapsida and Sauropsida. In the LRT several amniote clades precede the advent of the Synapsida. The last common ancestors of all amniotes are Silvanerpeton and Gephyrostegus bohemicus. The first dichotomy produced the new Lepidosauromorpha and the new Archosauromorpha. Synapsids nest deeply within the new Archosauromorpha.
  3. Diadectomorpha is a clade of large reptile-like amphibians. The LRT nests all diadectomorphs deep within the new Lepidosauromorpha. 
Figure 1. A new reconstruction of Gephyrostegus bohemicus. This species lived 30 million years after the origin of the Amniota in the Visean, 340 mya. Note the lack of posterior dorsal ribs. This trait shared by all basalmost amniotes, may provide additional space for massive eggs in gravid females, but is also shared with males, if there were males back then.

Figure 1. A new reconstruction of Gephyrostegus bohemicus, a late-surviving basalmost amniote. This species lived 30 million years after the other amniotes in the Visean, 340 mya. Note the lack of posterior dorsal ribs. This trait shared by all basalmost amniotes, may provide additional space for massive eggs in gravid females, but is known in all specimens.

And while we’re at it…
This comes courtesy of Ben Creisler at the DML TheSociety of Vertebrate Paleontology 2016 Meeting Program and Abstract Book is available here:

PLEASE NOTE! Content is embargoed until the actual presentation.
“Unless specified otherwise, coverage of abstracts presented orally at the Annual Meeting is strictly prohibited until the start time of the presentation, and coverage of poster presentations is prohibited until the relevant poster session opens for viewing.”
There is one abstract in there
that confirms something I discovered four years ago, which brings some satisfaction that it was discovered again.

Former reptile: Gymnarthrus. Former reptile, former amphibian: Diadectes. Both from Case 1910.

Case 1910
described several skulls from what he presumed were Permian deposits in Archer County, Texas. Yes, they are Early Permian and home to many a Dimetrodon.

Among the several skulls
was Gymnarthrus willoughbyi (Fig. 1), known from a tiny 1.6cm skull. Case reported: “It was thought at first that both the basisphenoid and the parasphenoid process constituted the the parasphenoid bone and that the animal was an amphibian, but this is impossible… the animal approaches the intermediate form between the amphibians and reptiles.” Today we know Gymnarthrus to be one of the lizard mimics, the lepospondyl microsaurs. Case also wrote, “The nearest approach to this form is the small amphibian skull described by Broili as Cardiocephalous sternbergii, but this is described as having the skull complete, no parietal foramen, teeth regularly diminishing in size anteriorly but with cutting edges and lyra present.” I don’t know what lyra are in this context.

Figure 1. Gymarthrus willougbyi, drawn by Case 1910 on the left and von Huene 1913 on the right.

Figure 1. Gymarthrus willougbyi, drawn by Case 1910 on the left and von Huene 1913 on the right. These are apparently freehand sketches and, judging by the perspective implied by the large orbit on the right, sketched from two distances.

Carroll and Gaskill 1978
allied Gymnarthrus with Cardiocephalus, another microsaur.

Figure 2. Diadectes phaseolinus in situ, as originally illustrated and as reillustrated above according to phylogenetic bracketing.

Figure 2. Diadectes phaseolinus in situ, as originally illustrated and as reillustrated above according to phylogenetic bracketing. Case reported the tail was as long as the presacral portion of the column, but did not illustrate it that way for this specimen. No intercentra were present.

Case also identified Diadectes as a reptile
(order Cotylosauria), but later authors (and currently Wikipedia, taken from a PhD thesis by R Kissel 2010) considered it a reptile-like amphibian. The large reptile tree nests Diadectes as derived from Milleretta and all the “Diadectomorpha” listed in Wikipedia are reptiles. Limnoscelis, Orobates and Tseajaia do not nest with Diadectes in the large reptile tree, but bolosaurids and procolophonids do. So we’ve got some housecleaning to do at that node.

The interesting thing about this Diadectes specimen,
according to Case 1910, is the set of expanded dorsal ribs beneath the scapulae. He writes, “The ribs of the third, fourth and fifth vertebrae show a well defined articular end with a distinct neck. The bodies of these ribs are expanded into thin triangular plates, with the front edge straight and the posterior edge drawn out into a point which overlaps the succeeding rib; this forms a strong protection for the anterior thoracic region. The sixth, seventh and eighth [ribs] are overlain by thin, narrow, plates which continue backward the protection of the thoracic region to a point opposite the posterior end of the scapula.” Some, but not all Diadectes specimens have such expanded ribs.

Case presumed
that gastralia (his ‘abdominal ribs’  were present. They are not. Case notes “the animal was distinctly narrow chested, with the bones of the the girdle strongly interlocked. Diadectes had practically no neck.”

Based on the mounted skeleton, Case reiterated
“the suggestions previously made by the author that these animals are the nearest discovered forms to the ancestors of turtles.” That old hypothesis has not been confirmed by the large reptile tree, as noted earlier.

References
Carroll RL and Gaskill P 1978. The Order Microsauria. Memoirs of the American Philosophical Society 126:1-211 [J. Mueller/T. Liebrecht/T. Liebrecht]
Case EC 1910.
 New or little known reptiles and amphibians from the Permian (?) of Texas. Bulletin of the American Museum of Natural History 28 (17):163-181.
Huene FRF von and Gregory WK 1913. The skull elements of the Permian Tetrapoda in the American Museum of Natural History, New York. Bulletin of the AMNH ; v. 32, article 18.: 315-386.

Orobates in 3D

Wikipedia considers Orobates an anamniote (not a reptile = amniote) close to Diadectidae, which are also considered anamniotes. So does a recent paper by Nyakatura et al. 2015 who un-deformed the MNG 10181, the holotype, using CT scans and software (Fig. 1).

Figure 1. A 3D Orobates produced from CT scans by Nyakatura et al. 2015.

Figure 1. A 3D Orobates produced from CT scans by Nyakatura et al. 2015.

From the Nyakaturs et al. 2015 introduction
“Orobates pabsti (Holotype MNG 10181) is one of the most basal diadectids, from the lower Permian of Germany (Bromacker quarry, Tambach Formation, Tambach-Dietharz, Thuringia). Because of its phylogenetic position, this nearly complete, articulated, comparatively well-preserved specimen can be considered a key fossil. Additionally, fossil trackways from the ichnospecies Ichnotherium sphaerodactylum of the same locality were unequivocally produced by Orobates pabsti rendering this combination of body fossil and fossil trackways the oldest known track-trackmaker association and offering direct evidence of its locomotor behavior.”

It appears that Nyakatura et al. did everything right 
to produce a good virtual model of Orobates.

Figure 1. Limnoscelis and two suitable ancestral taxa, Orobates and Milleretta, all shown to scale (below) and to fit (above).

Figure 2. Limnoscelis and two suitable ancestral taxa, Orobates and Milleretta, all shown to scale (below) and to fit (above).

Their only fault
was trusting an old cladogram that gave them a mistaken nesting outside the Reptilia. The large reptile tree nests Orobates inside the Reptilia, inside the Lepidosauromorpha, with the clade Diadectidae derived from the undisputed reptile, Millleretta (Fig. 2). No stem (=pre) amniotes more closely match the morphology.

Once again
an old, traditional sour matrix seems to be at fault.

References
Berman, DS et al. 2004. A new diadectid (Diadectomorpha), Orobates pabsti, from the Early Permian of Central Germany. Bulletin of Carnegie Museum of Natural History 35 :1-36. doi: 10.2992/0145-9058(2004)35[1:ANDDOP]2.0.CO;2
Nyakatura JA, Allen VR, Lauströer J, Andikfar A, Danczak M, Ullrich H-J, et al. 2015. A Three-Dimensional Skeletal Reconstruction of the Stem Amniote Orobates pabsti (Diadectidae): Analyses of Body Mass, Centre of Mass Position, and Joint Mobility. PLoS ONE 10(9): e0137284. doi:10.1371/journal.pone.0137284

wiki/Orobates

Adding taxa to the Diadectes clade

Adding a few
and distinct Diadectes specimens (no two appear to be conspecific) opens the door to new insights into that corner of the cladogram. Some of the data are from 3D skull images with sutures delineated. Others are from firsthand observation. Some data are from drawings. Berman et al. 1992 made an interesting observation that prior authors illustrated the skull roof of Diadectes in a variety of ways (Fig. 1). The caption does not indicate that all were drawn from the same specimen. I suspect they were not.

Figure 1. How Berman et al. copied the illustrations of prior authors who each figured the skull roof of Diadectes. Perhaps these were several distinct specimens, not just one.

Figure 1. How Berman et al. copied the illustrations of prior authors who each figured the skull roof of Diadectes. Perhaps these were several distinct specimens, not just one. Not sure, at this point, which illustrations represent which specimens.

The Berman et al. phylogenetic analysis
included seven taxa, including two suprageneric taxa, Pelycosauria and Captorhinomorpha. They included only nine characters. The anamniote, Seymouria, was the outgroup. The first clade included Pelycosauria + (Limnoscelis +(Tseajaia and Diadectes). The second clade included Captorhinomorpha + Petrolacosaurus. The large reptile tree includes hundreds more taxa and characters. The pertinent subset is shown here (Fig. 2). It is also clear from the Berman et al. taxon set that they thought they were dealing with a small set of basal reptiles and pre-reptiles. In 2015 it is clear that they did not include the pertinent taxa they should have as some of these taxa are not related to any of the others except distantly.

Figure 2. How the large reptile tree lumps and splits the several Diadectes specimens now included here. Note that bolosaurids, including Phonodus, now nest within other Diadectes specimens.

Figure 2. How the large reptile tree lumps and splits the several Diadectes specimens now included here. Note that bolosaurids, including Phonodus, now nest within other Diadectes specimens.

Now, with current data
it is becoming increasingly clear that both bolosaurids and procolophonids nest within  a fully reptilian Diadectes clade. It is also clear that the genus Diadectes needs to be further split, as Kissel (2010) started to do by renaming Silvadectes and Oradectes from former Diadectes species.

Skeleton of Diadectes. Perhaps unnoticed are the broad dorsal ribs of this taxon, basal to Stephanospondylus, Procolophon and pareiasaurs.

Figure 3. Skeleton of Diadectes (UC 706, UC 1078). Perhaps unnoticed are the broad dorsal ribs of this taxon, basal to Stephanospondylus, Procolophon and pareiasaurs.

Also note
the placement of Stephanospondylus as a proximal sister taxon to the diadectids nesting at the base of the pareiasaurs (including turtles). Turtles are sisters to pareiasaurs and they ARE pareiasaurs because they are derived from pareiasaurs, just as birds are derived from theropod dinosaurs.

Figure 4. Click to enlarge. Stephanospondylus based on parts found in Stappenbeck 1905. Several elements are re-identified here. Note the large costal plates on the ribs, as in Odontochelys. The pubis apparently connected to a ventral plastron, not preserved. The interclavicle was likely incorporated into the plastron.

Figure 4. Click to enlarge. Stephanospondylus based on parts found in Stappenbeck 1905. Several elements are re-identified here. Note the large costal plates on the ribs, as in Odontochelys. The pubis apparently connected to a ventral plastron, not preserved. The interclavicle was likely incorporated into the plastron.

Like everyone who studies prehistoric reptiles
there is a day when you don’t know anything about a taxon and later there is a day when you are making contributions to Science. Those days keep on coming.

References
Berman DS, Sumida SS and Lombard E 1992. Reinterpretation of the Temporal and Occipital Regions in Diadectes and the Relationships of Diadectomorphs. Journal of Vertebrate Paleontology 66(3):481-499.
Kissel R 2010. Morphology, Phylogeny, and Evolution of Diadectidae (Cotylosauria: Diadectomorpha). Thesis (Graduate Department of Ecology & Evolutionary Biology University of Toronto).

The Phonodus-Bolosaurus-Bashkyroleter connection

This post might be boring.
These are the unpopular, rarely studied plain-looking reptiles that ultimately gave rise to many of the most interesting clades.

Bolosaurids
are rarely studied, rarely included in phylogenetic analyses and little has been published on them. Bolosaurus and Belebey are the classic specimens. Long-legged Eudibamus has been added to this clade by traditional workers (Berman et al. 2000), but the large reptile tree nests it instead with basal diapsids, like long-legged Petrolacosaurus.

The busiest and most difficult corner
of the large reptile tree always seemed to be between Milleretta and Macroleter (Fig. 1).This subset of the tree also includes many previous enigmas here resolved, including  turtles.

Figure 1. A subset of the large reptile tree focusing on the taxa between Milleretta and Lepidosauriformes, perhaps the most difficult corner of the large reptile tree.

Figure 1. A subset of the large reptile tree focusing on the taxa between Milleretta and Lepidosauriformes, perhaps the most difficult corner of the large reptile tree.

Phonodus was originally considered a procolophonid.
(Modesto et al. 2010). Here (Fig. 2) Phonodus nests close to procolophonids, but closer to bolosaurids. As an Early Triassic taxon, Phonodus represents a late surviving member of a Late Pennsylvanian/Earliest Permian radiation that produced Early Permian diadectids and others. Based on its unusual teeth, Phonodus was highly derived.

Figure 1. Phonodus tracing. This turns out to be a basal bolosaurid.

Figure 2. Phonodus tracing. This turns out to be a basal bolosaurid, close to procolophonids. Note the deeply excavated squamosal. The naris was originally overlooked. 

A related taxon
Bashkyroleter (Fig. 3) was originally considered a nyctoleterid parareptile (not a valid clade). Here (Fig. 1) Bashkyroleter is basal to the bolosaur/diadectid/procolophon clade and pareiasaur/turtle clade AND the remainder of the lepidosauromorpha, including the lanthanosuchids proximally. So, it is a key taxon, largely overlooked except for one paper (Müller and Tsuji 2007) on reptile auditory capabilities.

Yes,
this solidification of the large reptile tree involved some topology changes. Science is self correcting. New data brings new insights. One of these new insights involved Bashykyroleter and a previously overlooked connection of the lateral to the naris. (Fig. 2).

Figure 2. Bashkyroleter appears to have a small naris/lacrimal connection.

Figure 3. Bashkyroleter appears to have a small naris/lacrimal connection as shown above. If anyone has a dorsal, occipital  or palatal view of this taxon, please send it along. Another deeply embayed squamosal. 

References
Berman, DS, Reisz RR, Scott D, Henrici AC, Sumida SS and Martens T 2000. Early Permian bipedal reptile. Science 290: 969-972.
Modesto SP, Scott DM, Botha-Brink J and Reisz RR 2010. A new and unusual procolophonid parareptile from the Lower Triassic Katberg Formation of South Africa. Journal of Vertebrate Paleontology 30 (3): 715–723. doi:10.1080/02724631003758003.
Müller J and Tsuji LA 2007. Impedance-Matching Hearing in Paleozoic Reptiles: Evidence of Advanced Sensory Perception at an Early Stage of Amniote Evolution. PLoS ONE 2 (9): e889. doi:10.1371/journal.pone.0000889. PMC 1964539. PMID 17849018

The origin of Limnoscelis

Limnoscelis, according to Wikipedia, “is a genus of large (1.5 m in total length), very reptile-like diadectomorph (a type of reptile-like amphibian) from the Early Permian of North America. Contrary to other diadectomorphans, Limnoscelis appear to have been a carnivore. Though the post cranial skeleton is very similar to the early large bodied reptiles like pelycosaurs and pareiasaurs, the digits lacked claws, and the bones of the ankle bones were fused like in other reptile-like amphibians. This would not allow them to use their feet actively in traction, but rather as holdfasts, indicating Limnoscelis primarily hunted slow moving prey.”

Figure 1. Limnoscelis and two suitable ancestral taxa, Orobates and Milleretta, all shown to scale (below) and to fit (above).

Figure 1. Limnoscelis and two suitable ancestral taxa, Orobates and Milleretta, all shown to scale (below) and to fit (above).

The large reptile tree nested Limnoscelis well within the Lepidosauromorpha branch of the Reptilia/Amniota along with the smaller Orobates and not far from tiny Milleretta (Fig. 1). The latter two are the most suitable ancestral morphologies yet found on the large reptile tree.

Limnoscelis and Orobates do not nest with Diadectes and other diadectomorphs, but also, not too far away from that clade. The Limnoscelis clade still nests with Tseajiaia and Tetraceratops.

Are those carnivorous teeth in Limnoscelis?
Most sister taxa in surrounding clades are likely herbivores. Some related taxa had canines, but not Limnoscelis.

Figure 4. Tetraceratops and LRT relatives including Saurorictus, Limnoscelis, Orobates and Milleretta.

Figure x. Tetraceratops and LRT relatives including Saurorictus, Limnoscelis, Orobates and Milleretta.

When are we going find consensus
on the nesting of Limnoscelis? We need a competing large gamut phylogenetic analysis to confirm or refute the topology recovered by the large reptile tree. Either that, or let the results of the large reptile tree get published.

Added Janurary 10, 2019
Saurorictus (Fig. 2; Late Permian; Modesto and Smith 2001; SAM PK-8666), nesting at the base of the captorhinids and their sisters, is the proximal outgroup taxon in the LRT now. Except for size, the resemblance is striking.

Figure 1. Limnoscelis and its outgroup sister, Saurorictus.

Figure 2. Limnoscelis and its outgroup sister, Saurorictus.

References
Berman DS, Reisz RR and Scott D 2010. Redescription of the skull of Limnoscelis paludis Williston (Diadectomorpha: Limnoscelidae) from the Pennsylvanian of Canon del Cobre, northern New Mexico: In: Carboniferous-Permian Transition in Canon del Cobre, Northern New Mexico, edited by Lucas, S. G., Schneider, J. W., and Spielmann, New Mexico Museum of Natural History & Science, Bulletin 49, p. 185-210.
Modesto SP and Smith RMH 2001. A new Late Permian captorhinid reptile: a first record from the South African Karoo. Journal of Vertebrate Paleontology 21(3): 405–409.
Romer AS 1946. The primitive reptile Limnoscelis restudied American Journal of Science, Vol. 244:149-188
Williston SW 1911. A new family of reptiles from the Permian of New Mexico: American Journal of Science, Series 4, 31:378-398.

wiki/Saurorictus
wiki/Limnoscelis

 

A shift in the topology of the large reptile tree

As loyal readers know…

  1. I have challenged others to find taxa that are improperly nested.
  2. So far this year no one has stepped up to the challenge. Well, they had their chance…
  3. Yesterday I discovered a mistake in the large reptile tree and made the correction (Fig. 1). The diadectomorph clade (including procolophonids) have moved closer to the bolosaurids and pareiasaurs.
Figure 1. A shift in the tree topology moves diadectids (and procolophonids) closer to pareiasaurs and away from limnoscelids. But Orobates stayed back.

Figure 1. A shift in the tree topology moves diadectids (and procolophonids) closer to pareiasaurs and away from limnoscelids. But Orobates stayed back. At the bottom of the chart, that line leads to macroleterids and nycteroleterids, then on to the lepidosauriformes and lepidosaurs.

The problem was
so much of the data for the taxa around these nodes are represented by drawings, sometimes with errors. The most difficult taxa and perhaps the least interesting of all reptiles (judging by the number of papers written about them) are also at this node: Saurorictus, Milleretta (both specimens) and the bolosaurids (sans Eudibamus, which nests with Petrolacosaurus). While a single tree was found then, and is also found now, the bootstrap scores were not strong, now or then. The present bootstrap scores could use a boost owing to the skull-only and otherwise unfortunately incomplete data in several taxa often represented only by drawings. Many taxa were rescored.

The other problem was
diadectomorphs nest pretty well with Orobates, millerettids, caseasaurs and limnoscelids. Now they nest just a little better with bolosaurs and pareiasaurs. At one point it was either way.

What sparked this change?
When I added Bashkyroleter, added data to Procolophon and Belebey, and created a new skull restoration of Sauropareion. Issues arose and I took another look at several dozen taxa.

On the plus side,
Stephanospondylus (still known from very poor data) has traditionally been considered a diadectomorph. Now it nests as a sister to that clade. Some diadectids had some widely expanded ribs, as did Stephanospondylus. Both were experimenting with a morphology that would be perfected in their now closer relatives, the turtles.

The limnoscelids and their kin, including Orobates, are all long-bodied taxa now. The diadectids plus pareiasaurs plus turtles are all shorter bodied taxa with progressively wider bodies and shorter tails.

The true procolophonids (Procolophon and kin) are now closer to the nycteroleterids and owenettids, which were traditionally associated in a large single clade. They’re still not directly related.

As noted earlier, one of the earmarks of good Science is correcting errors. I encourage the finding of errors in reptileevolutiion.com. Behind the scenes, as you already know, I make corrections and additions all the time. As mentioned earlier:

Carl Sagan (in the Demon Haunted World) wrote:
“Science has built-in error-correcting mechanisms—because science recognizes that scientists, like everybody else, are fallible, that we make mistakes, that we’re driven by the same prejudices as everybody else. There are no forbidden questions. Arguments from authority are worthless. Claims must be demonstrated. Ad hominem arguments—arguments about the personality of somebody who disagrees with you—are irrelevant; they can be sleazeballs and be right, and you can be a pillar of the community and be wrong.”

In other words,
watch out for those who hold dearly to their paradigms, whether religious or scientific. It’s okay to test those paradigms.

Urumqia – a very basal lepidosauromorph

Urumqia liudaowanensis (Zhang et al. 1984) ~20 cm snout-vent length, Lower Permian.

Figure 1. Urumqia liudaowanensis (Zhang et al. 1984) ~20 cm snout-vent length, Late Permian.

Here’s a gephyrostegid/basal amniote/basal lepidosauromorph
you may not have heard of. (Remember lepidosauromorphs in the large reptile tree constitute about half of all amniotes). It is considered China’s oldest known tetrapod.

Urumqia liudaowanensis (Zhang et al. 1984, Fig. 1) ~20 cm snout-vent length, Late Permian Lucaogou Formation), was originally considered a discosaurid seymouriamorph. Here it nests at the base of the lepidosauromorph reptiles. Shifting Urumqia to the discosaurid seymouriamorphs adds 39 steps to the large reptile tree.

Derived from 
Gephyostegus bohemicusUrumqia was basal to Bruketererpeton, Thuringothyris, and all lepdiosaurs, turtles, diadectids, pterosaurs and other various lepidosauromorphs starting with Saurorictus and Cephalerpeton. Phylogenetically Urumqia must have made a first appearance in the Viséan (335 mya, Mississipian, Carboniferous) despite its late appearance in the Late Permian (255 mya).

Figure 1. Basal amniotes to scale. Click to enlarge.

Figure 2. Basal amniotes to scale. Click to enlarge. Urumqia nests on the right hand column with Cephalerpeton and Thuringothyris.

Distinct from G. bohemicus,
Urumqia had shorter limbs, longer (but not long) posterior dorsal ribs and a robust tail with elongate caudals. The palate included a suborbital fenestra. The cheek may have included a small lateral temporal fenestra convergent with others. The carpals and tarsals were poorly ossified.

Figure 4. Extant lizards, A. gravid, B. in the process of laying eggs, C. with egg clutch.

Figure 3. Extant lizards, A. gravid, B. in the process of laying eggs, C. with egg clutch.

Notably
the posterior dorsal ribs were much shorter than the gastralia. So the gastralia create a wide posterior torso, ideal for carrying large amniote eggs (Fig. 3), as we learned earlier.

The new topology of basal reptiles
is based on the inclusion of several more species based taxa not previously considered. This new topology show that synapsids were not the first clade to branch off. Rather all taxa closer to archosaurs (here considered the new Archosauromorpha) split from all taxa closer to lepidosaurs (here considered the new Lepidosauromorpha) at the onset of the Reptilia (=Amniota).

References
Zhang F, Li Y, and Wan X. 1984. A new occurrence of Permian seymouriamorphs in Xinjiang, China. Vertebrate Palasiatica22(4):294-306.

Alveusdectes: a small, late-surviving diadectomorph – with procolophonid cheeks

Earlier we looked at the overlooked similarities of Diadectes and Procolophon (Fig. 1).

In the large reptile tree Procolophon nests with Diadectes, and both share a large otic notch, a trait Wiki says makes Diadectes an amphibian.

Figure 1. In the large reptile tree Procolophon nests with Diadectes, and both share a large otic notch, a trait Wiki says makes Diadectes an amphibian.

In the large reptile tree these two clades (procolophonids and diadectomorphs) nest together. No one has ever seen that before or since.

A new discovery
(Liu and Bever 2015) links these two clades closer together. Unfortunately, Liu and Bever used outdated cladograms. Taxon exclusion was the source of their errors. From their abstract: “Diadectomorpha is a clade of Late Palaeozoic vertebrates widely recognized as the sister group of crown-group Amniota* and the first tetrapod lineage to evolve high-fibre herbivory**. Despite their evolutionary importance, diadectomorphs are restricted stratigraphically and geographically, with all records being from the Upper Carboniferous and Lower Permian of North America and Germany. We describe a new diadectomorph, Alveusdectes fenestralis, based on a partial skull from the Upper Permian of China. The new species exhibits the derived mechanism for herbivory and is recovered phylogenetically as a deeply nested diadectid. Approximately 16 Myr younger than any other diadectomorph, Alveusdectes is the product of at least a 46 Myr ghost lineage. How much of this time was probably spent in Russia and/or central Asia will remain unclear until a specimen is described that subdivides this cryptic history, but the lineage assuredly crossed this region before entering the relatively isolated continent of North China. The discovery of Alveusdectes raises important questions regarding diadectomorph extinction dynamics including what, if any, ecological factors limited the diversity of this group in eastern Pangea. It also suggests that increased sampling in Asia will likely significantly affect our views of clade and faunal insularity leading up to the Permo-Triassic extinction.”

* This is an error.
Diadectomorpha are derived from Milleretta and kin in the large reptile tree.

** Another error.
Basalmost lepidosauromorphs were all herbivores.

In dorsal view
the skull of Alvuedectes has a strongly triangular appearance, similar to that of procolophonids. Most of the skull must be restored because it is missing. And it can be restored in at least two ways (Fig. 2).

Figure 2. Alvuesdectes (from Liu and Bever 2015) restored and compared to Diadectes and Procolophon. Note the triangular shape of the skull in dorsal view.

Figure 2. Alvuesdectes (from Liu and Bever 2015) restored and compared to Diadectes and Procolophon. Note the triangular shape of the skull in dorsal view. Click to enlarge.

Liu and Bever did not compare
their find to any procolophonids, only diadectomorphs. This is why the large reptile tree was created, to provide an umbrella study to provide taxa for more focused studies. It is unfortunate that Liu and Bever did not reference this study, which has been online for over four years. Procolophonids continued to the Late Triassic, which makes procolophonids the “last diadectomorphs.”

References
Liu J and Bever GS 2015. The last diadectomorph sheds light on Late Palaeozoic tetrapod biogeography. Biol. Lett.11: 20150100.

 

The evolution of Limnoscelis from Milleretta and Orobates

Figure 1. Limnoscelis based on Berman et al. 2010.

Figure 1. Limnoscelis based on Berman et al. 2010.

Wikipedia reports that Limnoscelis (Williston 1911) was a large (1.5m) diadectomorph (a type of reptile-like amphibian) from the Early Permian. They report, distinct from other diadectomorphs, Limnoscelis appears to have been a carnivore, but one without claws. Palaeos likewise nests Limnoscelis as an anamniote.

On the other hand…
The large reptile tree nests Limnoscelis and other diadectomorphs deep within the Reptilia.  Here we’ll take a look at Limnoscelis with a few of its closest ancestors, Orobates and MillerettaTseajaia and Tetraceratops are a sister clade to Limnoscelis.

Figure 2. Milleretta (RC14 and RC70 specimens), Orobates and Limnoscelis. 1. long anterior teeth. 2. Orbit loses dorsal exposure.

Figure 2. Milleretta (RC14 and RC70 specimens), Orobates and Limnoscelis. 1. long anterior teeth. 2. Orbit loses dorsal exposure.

Limnoscelis paludis (Williston 1911) Late Pennsylvanian, 1.5m in length. Distinct from Orobates, the skull of Limnoscelis had a deeper premaxilla with more robust premaxillary fangs and a higher naris. The rostrum was longer. The orbit was relatively smaller. As in Milleretta a depression appeared between the ectopterygoid and pterygoid and the palate was otherwise similar. The neural spines were expanded. The elongated posterior process of the ilium is larger. The anterior caudals had smaller transverse processes. More posterior vertebrae had ribs.

Figure 3. Milleretta, Orobates and Limnoscelis. Lower images are to scale. Not the development of the posterior ilium process in Orobates and Limnoscelis.

Figure 3. Milleretta, Orobates and Limnoscelis. Lower images are to scale. Note the development of the posterior ilium process and broader cheek bones in Orobates and Limnoscelis. The expanded ribs of Milleretta are not retained in these taxa.

The literature hasn’t made the connection from Milleretta to Orobates and Limnoscelis, hence the need for a large reptile tree. When you put them together, though, the similarities start to shine through. The evolution of Orobates is one of creating a giant Milleretta. The evolution of Limnoscelis is one of creating a giant Orobates, without the girth of the diadectids.

Funny that in doing so, Limnoscelis started fooling paleontologists into thinking it was an amphibian of sorts, but one that didn’t look like any amphibians anyone has ever seen.

So that’s how you get one carnivore from out of the diadectomorpha. Limnoscelis is a milleretid.

References
Berman DS Reisz RR and Scott D 2010. Redescription of the skull of Limmoscelis paludis Williston (Diadectomorpha: Limnoscelidae) from the Pennsylvanian of Canon del Cobre, northern New Mexico: In: Carboniferous-Permian Transition in Canon del Cobre, Northern New Mexico, edited by Lucas, S. G., Schneider, J. W., and Spielmann, New Mexico Museum of Natural History & Science, Bulletin 49, p. 185-210.
Romer AS 1946. The primitive reptile Limnoscelis restudied American Journal of Science, Vol. 244:149-188
Williston SW 1911. A new family of reptiles from the Permian of New Mexico: American Journal of Science, Series 4, 31:378-398.

wiki/Limnoscelis