You heard it here in 2011: diadectids are amniotes

Co-author, David S. Berman,
has been saying diadectids are amniotes since the 1990s, but not with a comprehensive taxon list, and, apparently nobody listened. The consensus apparently prefers their diadectids with tadpoles.

Here’s what Wikipedia reports
“Diadectes (meaning crosswise-biter) is an extinct genus of large, very reptile-like amphibians that lived during the early Permian period (Artinskian–Kungurian stages of the Cisuralian epoch, between 290 and 272 million years ago^[1]). Diadectes was one of the very first herbivorous tetrapods, and also one of the first fully terrestrial animals to attain large size.”

Figure 1 Skeleton of Diadectes. Perhaps unnoticed are the broad dorsal ribs of this taxon, basal to Stephanospondylus, Procolophon and pareiasaurs.

Klembara et al. 2019 report
on the inner ear morphology of diadectids and seymouriamorphs. From the abstract:
“Two pivotal clades of early tetrapods, the diadectomorphs and the seymouriamorphs, have played an unsurpassed role in debates about the ancestry of amniotes for over a century, but their skeletal morphology has provided conflicting evidence for their affinities. Both maximum parsimony and Bayesian inference analyses retrieve seymouriamorphs as derived non‐crown amniotes and diadectomorphs as sister group to synapsids.”

Figure 2. Cladogram from Klembara et al. 2019. Green shows reptile taxa in the LRT.

Dr. David Marjanovic wrote in the DML:
“Amniota is a crown-group; there’s technically no such thing as a “stem-amniote”, because if it’s on the stem, it’s not an amniote.”

Unfortunately, Klembara et al. don’t have enough taxa
to understand that Amniota is a junior synonym for Reptilia. So Repitilomorpha works well for pre-reptiles. More importantly, for the subject at hand, Diadectes (Fig. 1) and kin have been deeply nested within the large reptile tree (LRT, 1583 taxa) since 2011. This is an online resource you can use to double check your taxon list, just to make sure it is up to date. The Klembara et al. taxon list (Fig. 2) is so inadequate it nests several reptiles apart from one another and omits dozens of others pertinent to this issue.

Figure 3. Subset of the LRT focusing on basal lepidosauromorphs and Diadectes.

Bottom line, when you add enough taxa
diadectomorphs are not close to synapsids, but arise from millerettids.

At least the Klembara team
moved diadectomorphs inside the Amniota. That’s a minor victory. Add the above taxa to your cladogram (Fig. 2) and see where Diadectes nests. That’s what the LRT is here for… to help workers avoid taxon exclusion.

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References
Klembara J, Hain M, Ruta M, Berman DS, Pierce SE and Henrici AC 2019. Inner ear morphology of diadectomorphs and seymouriamorphs (Tetrapoda) uncovered by high-resolution x-ray microcomputed tomography, and the origin of the amniote crown group. Palaeontology (advance online publication) Future publication date: August 5, 2020
doi: https://doi.org/10.1111/pala.12448
https://onlinelibrary.wiley.com/doi/full/10.1111/pala.12448

wiki/Diadectes

Walking Orobates video on YouTube and in Nature

This is a wonderful experiment/demonstration/simulation
and a wonderful fossil, matching a digitized 300 million-year-old Orobates skeleton to Orobates tracks.

This time the problem comes from basal tetrapod experts
One writes in the Dinosaur Mailing List, “As so much else in amniote phylogeny, it remains unclear whether the diadectomorphs are just outside Amniota or just inside. The question has never been tested in an analysis with enough taxa and enough characters; some matrices may have had close to enough of one, but definitely not of both, and there haven’t been many in total in the first place.”

Another comes from SmithsonianMag.com
“At first glance, the 300 million-year-old Orobates pabsti might look like a chunky lizard. In actuality, this animal from the Permian period is what experts know as a stem amniote—a vertebrate that’s part of the evolutionary lineage between amphibians, which reproduce in the water, and the last common ancestor of mammals and reptiles, which lay eggs on land.”

A third comes from the title of the Nature paper (Nyakatura et al. 2019)
“Reverse-engineering the locomotion of a stem amniote.” Clearly the authors have never heard of an amphibian-like reptile.

This is an example of wrong thinking.
The large reptile tree (LRT, 1378 taxa) nests Orobates deep inside the Reptilia (the clade Amniota is a junior synonym, see below). There are those who say the LRT needs more characters to… what? The LRT already lumps and splits virtually all of its taxa in complete resolution documenting a gradual accumulation of traits at every node. That is the yardstick by which all cladograms should be judged. How will adding characters suddenly shift taxa on the tree topology? Taxa nest where they do because they most closely resemble their sisters. And that clade most closely resembles their more distant sisters in a series that ultimately includes all tested taxa. All other possible nesting sites for taxa are provided in a wide gamut analysis.

Apparently basal tetrapod experts are hoping the LRT is somehow wrong. If so, which taxa are wrongly nested and where should they nest instead? They simply need to add the pertinent taxa listed in the LRT to their own analyses with their own character lists to find out for themselves and report the results. This is how science works. Anyone can repeat the experiment, but the experiment in this case, requires pertinent taxa, not more characters.

Case in point:
Remember how Hone and Benton 2007, 2009 deleted pertinent taxa in their purported quest to test two competing hypotheses on pterosaur origins? When they found out the fenestrasaurs were attracting pterosaurs, they deleted the fenestrasaurs and never did find out where pterosaurs originated.

Comment to Nature
“This is a wonderful experiment/demonstration/simulation. The problem comes from the systematics of Orobates. Testing a wide gamut of tetrapod taxa nests Orobates between Limnoscelis and Tseajaia + Tetraceratops. This clade nests between Saurorictus + Captorhinidae and Milleretta, all traditional amniotes. Phylogenetic analysis nests the amphibian-like reptiles Gephyrostegus (Late Carboniferous) and Silvanerpeton (Early Carboniferous) as the last common ancestors of all included amniote taxa. Three nodes of amphibian-like reptiles nest between these two and the Saurorictus + Captorhinidae clade. So Orobates nests well within the Amniota, now a junior synonym for the clade Reptilia. The wide gamut cladogram is found online here: http://reptileevolution.com/reptile-tree.htm”

References
Nyakatura JA, et al. (11 co-authors) 2019. Reverse-engineering the locomotion of a stem amniote. Nature.com PDF online.

Articles from the popular press:

https://www.smithsonianmag.com/science-nature/scientists-used-robot-study-how-prehistoric-lizards-evolved-walk-land-180971283/

The humpback Diadectes

Diadectids and Diadectomorpha are basal lepidosauromorph reptiles once thought to be the closest anamniotes (amphibians) to amniotes. Wikipedia still promotes this antiquated hypothesis. Here (Fig. 1) you’ll see that Diadectes and Procolophon both evolved from a sister to Romeria primus as recovered by the large reptile tree.

Figure 1. The evolution of Diadectes and Procolophon from tiny Romeria primus to scale. Cope’s Rule is in effect here as the derived taxa are indeed larger, even on the branch leading to Procolophon.

Today we’ll look at a humpback diadectid, Diadectes (formerly Diasparactus) zenos (UC679). You’ll note the neural spines are much larger than in sister taxa.

Figure 2. Diadectes (Diasparactus) zenos to scale with other Diadectes specimens. Note the long neural spines. These were likely a hump support, not a finback, adding bulk to this already bulky reptile.

The high neural spines of D. zenos were robust, more like those of a bison, than a Dimetrodon. That’s why they may have supported fatty or meaty tissues, rather than a sail.

The skull of D. zenos is poorly known, but the palate is well exposed. The dorsal ribs are short, as is the tail. Note that the axis bone  (cervical #2) grows from D. zenos to D. sammiguelensis (Fig. 2).

Earlier we looked at a putative diadectid, Stephanospondylus, which is actually a diadectid mimic that was ancestral to turtles. It had no neural spines, and neither do turtles, because they don’t need back muscles when they have a shell.

The anterior dorsal ribs of D. zenos were the widest among diadectids. These helped support that large pectoral girdle.

Please contact the writer(s) of the Wikipedia article and encourage them to update their account of Diadectes. You can’t be derived from reptiles and still be a ‘reptile-like amphibian.’

References
Berman DS, Sumida SS and Martens T 1998. Diadectes (Diadectomorpha: Diadectidae) from the Early Permian of central Germany, with description of a new species. Annals of Carnegie Museum 67:53-93.
Case EC 1907. Restoration of Diadectes. The Journal of Geology 15(6):556–559.
Case EC 1910.“New or little known reptiles and amphibians from the Permian (?) of Texas”. Bulletin of the American Museum of Natural History 28:136–181.
Case EC, Williston SW and Mehl MG 1913. Permo-Carboniferous Vertebrates from New Mexico. Carnegie Institution. 81 pp. online pdf
Cope ED 1878a. Descriptions of extinct Batrachia and Reptilia from the Permian formation of Texas. Proceedings of the American Philosophical Society 17:505-530.
Cope ED 1878b. A new Diadectes. The American Naturalist 12:565.
Kissel R 2010. Morphology, Phylogeny, and Evolution of Diadectidae (Cotylosauria: Diadectomorpha). Thesis (Graduate Department of Ecology & Evolutionary Biology University of Toronto).

Wiki/Diadectes

How close are Caseasaurs and Diadectids?

Pretty darn close it appears.

And these two clades have NEVER been closely associated before. This is the sort of wonderful nesting you get when you just let it happen with a large gamut of reptiles.

Of course this goes against the grain of traditional paleontology that puts caseasaurs like Eothyris, Oedaleops, Casea, Cotylorhynchus and Ennatosaurus improbably and awkwardly alongside synapsids, like Varanodon and Ophiacodon.

Tradition also puts diadectids like Orobates and Diadectes outside the Reptilia alongside other amphibians. The large reptile tree solves all such problems. The two clades, Diadectidae and Caseasauria, are close kin as it turns out. And the skull images bear this out, if you just ignore the lateral temporal fenestra, which is a trait that comes and goes with the Millerettidae, of which the caseasaurs are members.

Figure 1. The diadectid, Orobates, alonside the casesaurs, Oedaleops, Ennatosaurus and Casea. Boy they sure do look alike, overall and in several details save the lateral temporal fenestra. That used to be a big deal that falsely segregated taxa. Now it’s just another character trait. Part of the mix.

I hate it when a blind eye is turned to toward such relationships. Tradition trumps testing in most cases. That’s why I’m here… to encourage young free thinkers to test everything in the Reptilia to see if it matches tradition or the large reptile tree.

Both clades find a common ancestor close to Romeria primus and Concordia, two taxa known chiefly from skulls close to the the base of the new Lepidosauromorpha, Cephalerpeton and Captorhinidae.

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.

What is Saurorictus?

Figure 1. Saurorictus australis reconstructed. The parietal, outlined in gray, is largely unknown. Click for more info.

Saurorictus australis
Captorhinids were basal lepidosauromorph reptiles that appeared in the Early Permian and evolved multiple tooth rows by the Late Permian.  Saurorictus (Modesto and Smith 2001) SAM PK-8666 was originally considered a late-surviving single-tooth row captorhinid that had “very slender marginal teeth” and reportedly lacked a supratemporal.

Figure 2. Saurorictus, Macroleter and Lanthanosuchus demonstrating the evolution of one to another and another of these three sister taxa. The derived sister taxon is Nyctiphruretus. An ancestor includes a sister to Orobates. The size increase is important.

A Larger Tree Nests Saurorictus Elsewhere
Here the large reptile tree nested Saurorictus with Lanthanosuchus and Macroleter, far from the captorhinids.  Like another sister, Nyctiphruretus, Saurorictus lacked an indented squamosal and lacked a lateral temporal fenestra. To move Saurorictus to the captorhinids requires an additional 17 steps. Saurorictus also nests between Stephanospondylus (which leads to turtles) and Nyctiphruretus (which leads to owenettids and lepidosauriformes). So this is a key taxon. And a tiny one!

Figure 3. The supratemporal in Saurorictus (ST, in pink) was originally considered a part of the parietal which is reasonable given their paradigm that Saurorictus was a captorhinid.

Missing a Supratemporal? Maybe Not.
The worst preservation in SAM PK-8666 occurs on the skull roof. The parietal is barely present and the pineal opening is nowhere to be found. Just dorsal to the squamosal is a plate-like bone that Modesto and Smith (2001) considered a parietal lacking a supratemporal between it and the squamosal. The skull of Saurorictus does indeed resemble that of captorhinids in general. The supratemporal in captorhinids is a tiny splint of bone and such a bone is indeed missing. I added the Saurorictus data (lacking a supratemporal) to the large reptile tree and was surprised to see it nested with Lanthosuchus and Macroleter, taxa with a large, plate-like supratemporal. Now the lack of a supratemporal seemed to be a very odd autapomorphy. Reexamining the published image (Modesto and Smith 2001) of Saurorictus I realized that the corner of bone originally labeled as a parietal was a large and mislabeled plate-like supratemporal, matching sister taxa.

Figure 4. Saurorictus nests with Macroleter and Lanthanosuchus.

Different and Similar
At first it would appear odd that round-skulled Saurorictus should nest with the cantilevered skulls of Macroleter and Lanthanosuchus, but round-skulled Nyctiphruretus also nests nearby. Diadectes and Procolophon also nest nearby, but Orobates is a more basal sister that shares certain plesiomorphic traits with Saurorictus. Here, apparently, we’re seeing a small, simple, pleisomorphic taxon that gives rise to the various odder, more derived sisters.

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
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.

wiki/Saurorictus

The Heretical Procolophon + Diadectes Sisterhood

Why Didn’t Anybody See This Before?
Procolophon (Owen 1876) and Diadectes (Cope 1878a, b) are sister taxa recovered by the large study. Think of Procolophon (early Triassic) as just a little Diadectes (early Permian) only tens of millions of years later. In the present and growing list of 279 reptiles and their ancestors, no other taxon shares more characters with Procolophon than Diadectes (Figs. 1, 2).

DeBraga (2001, 2002) failed to include Diadectes in his dissertation and phylogenetic analysis focused on Procolophon, but instead attempted to work out turtle and Sclerosaurus relations with Procolophon. Like others before him, DeBraga considered Owenetta and Barasaurus to be sister procolophonids, but in the large study there are many intervening taxa that falsify this hypothesis. DeBraga (2001, 2002) considered Tichvinskia (complete skeleton with oversize orbits) and Contritosaurus (jaw fragment) to be sister taxa to Procolophon. I don’t have data on them. Sauorpareion and Nyctiphruretes are widely considered procolophonids due to their large orbits, but these were actually taxa that were derived from sisters to Diadectes, Stephanospondylus, Lanthanosuchus and Macroleter > all preceding Sauorpareion and Nyctiphruretes in the lineage leading toward owenettids and lepidosauriformes. Hence, if all these are considered procolophonids, then they represent steps in a grade, not a monophyletic clade.

Cisneros and Shultz (2002) considered Procolophon a cotylosaur (stem reptile).

Figure 1. Basal Diadectomorpha to scale and separated with colors by clade.

Lee 1993 defined Procolophoniformes as the most recent common ancestor of Owenettidae and Procolophonidae and all its descendants. Unfortunately, this definition reiterates the Diadectomorpha in this study and includes the Lepidosauriformes here.

Seeley 1888 (amended by Laurin and Reisz 1995) defined Procolophonidae by a series of apomorphic characters.

Owen 1876 diagnosed Procolophon with a single posterolateral directed horn (spike) projecting from the quadratojugal.

Nesting Diadectes 
Several prior and traditional studies considered Diadectes a pre-reptile, a member of the Reptilomorpha, and a sister to Seymouria. Here the large study found Diadectes nested deep within the Reptilia.  It’s interesting that both Procolophon and Diadectes have been discussed in relation to turtles, but, to my knowledge, never together. The large otic notch of Diadectes is also found in Procolophon. This is not a pre-reptile character, but developed by convergence in diadectomorphs that was retained in all subsequent descendants through Macroleter and absent in Nyctiphruretes and more or less continued in Barasaurus and Candelaria. 

Considered one of the earliest herbivores, Diadectes gave rise to Procolophon, also an herbivore. The partial secondary palates (medial arcs of the palatines) of Diadectes are not found in Procolophon or other sisters.

These results reiterate the value of a large umbrella study that includes representatives from all the major reptile and pre-reptile clades. The large study illuminates previously overlooked relationships, like the Procolophon – Diadectes link.

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
Carroll RL and Lindsay W 1985. Cranial anatomy of the primitive reptile Procolophon. Canadian Journal of Earth Sciences 22, 1571-1587.
Cisneros JC and Schultz CL 2002. Procolophon brasiliensis n. sp. a new procolophonid reptile from the lower Triassic of southern Brazil. Neues Jahrbach fur Geologie und Palaontologie 2002:641-648.
Cope ED 1878a. Descriptions of extinct Batrachia and Reptilia from the Permian formation of Texas. Proceedings of the American Philosophical Society 17:505-530.
Cope ED 1878b. A new Diadectes. The American Naturalist 12:565.
DeBraga M 2001. The postcranial anatomy of Procolophon (Parareptilia: Procolophonidae) and its implications for the origin of turtles. PhD thesis, University of Toronto.
DeBragra M 2003. The postcranial skeleton, phylogenetic position and probable lifestyle of the Early Triassic reptile Procolophon trigoniceps. Canadian Journal of Earth Sciences 40: 527-556.
Owen R 1876. Descriptive and Illustrated Catalogue of the Fossil Reptilia of South Africa in the Collection of the British Museum. London, British Museum (Natural History).

wiki/Diadectes
wiki/Procolophon

Moving Diadectomorphs Into the Reptilia

The Traditional View: Reptile-like Amphibians
Diadectomorphs are widely considered to be reptile-like amphibians that lived during the Late Carboniferous and Early Permian. However, no diadectomorph tadpoles are known and these taxa lack a long list of amphibian characters (see below). These often big (2-3 m long), bulky (wider than tall torsos) taxa include herbivores and carnivores, all were slow-moving and cold-blooded.

Traditionally diadectomorphs included these taxa: Diadectes, Orobates, Stephanospondylus, Tseajaia, Limnoscelis.

Figure 1. Basal Diadectomorpha

The Heretical View
The larger study found diadectomorphs to nest within the Reptilia and within the Lepidosauromorpha branch. So tadpoles will never be found. Additions to the diadectomorphs include Solenodonsaurus, Lanthanosuchus,  chroniosuchids, Tetraceratops and Procolophon, which nests as a sister to Diadectes. Pareiasaurs, like Anthodon and turtles are also basal diadectomorphs. All were derived from earlier precursor sisters to Oedaleops, Romeria primus and Concordia. Successors within this monophyletic clade branching off Lanthanosuchus  and Nyctiphruretus include lizards, snakes, pterosaurs and their kin.

Reptile-like Amphibians???
There are no other “amphibians” that even vaguely resemble this group of bulky Early Permian reptiles — especially those close to basal reptiles like Cephalerpeton, Casineria and Westlothiana. Calling diadectomorphs “reptile-like amphibians” was a mismatch from the beginning.

The Procolophon Missed Connection
The resemblance between the recognized reptile Procolophon and Diadectes was completely overlooked. The resemblance between pareiasaurs and diadectids was also overlooked. None of these taxa have labyrinthodont teeth. None have palatal fangs. None have an intermedium (a bone in the temple of pre-reptile amphibians).

The Otic Notch
Diadectomorphs did have a classic amphibian trait: an otic notch, which is a concave embayment at the back of the skull, roofed over by an overhang of skull roof. Presumably it framed a large eardrum or tympanum. Trouble is, these well-established reptiles also had an otic notch: Concordia, Oedaleops, Procolophon, Odontochelys, Proganochelys, Lanthanosuchus and Macroleter and Sauropareion. They’re all sisters to the diadectidomorphs.

The Age of Bulk – The Early Permian in Pangaea
It’s odd to consider that reptiles as fragile and aerial as pterosaurs and kuehneosaurs could have evolved from bulky diadectids and flattened lanthanosuchids, but the family tree indicates exactly such a lineage. Diadectes and Limnoscelis were formerly considered dead-ends. Now they are key taxa. So, what was happening in the Early Permian to encourage such bulking up?

The continents were locked together into a supercontinent known as Pangaea, with the east coast of North America blended into western Europe and north Africa. The Appalachian and Atlas mountains were virtually continuous and equatorial. From Texas to Germany the climate was tropical. This is the zone that produced most of the known basal diadectomorphs in vast coal forests. Large carnivores, like Dimetrodon, were on the rise. Dimetrodon warmed up faster and was able to become more active earlier aided by its large dorsal-sail solar collector. The bulk of a large Diadectes or Anthodon stored heat better due to a smaller surface-to-volume ratio. Retaining a portion of yesterday’s heat within a bulky body is considered inertial homeothermy. Larger plant eaters are better able to defend themselves due to their bulk and the risk the predator takes trying to attack larger prey.

Summary
It’s too bad that traditional paradigms continue to hamper working palaeontologists when a large gamut study is available that more parsimoniously nests several misplaced and enigmatic taxa and clades. Hopefully this blog will jog others to create trees with a similar large gamut of taxa to test and refine the present one.

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
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
Berman DS, Sumida SS, and Lombard RE 1992. Reinterpretation of the temporal and occipital regions in Diadectes and the relationship of diadectomorphs. Journal of Paleontology 66:481-499.
Berman DS, Sumida SS and Martens T 1998. Diadectes  (Diadectomorpha:  Diadectidae) from the Early Permian of central Germany, with description of a new species. Annals of Carnegie Museum 67:53-93.
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.
Cope ED 1878a. Descriptions of extinct Batrachia and Reptilia from the Permian formation of Texas. Proceedings of the American Philosophical Society 17:505-530.
Cope ED 1878b. A new Diadectes. The American Naturalist 12:565.
Kissel R 2010. Morphology, Phylogeny, and Evolution of Diadectidae (Cotylosauria: Diadectomorpha). Thesis (Graduate Department of Ecology & Evolutionary Biology University of Toronto).
Moss JL 1972. The Morphology and phylogenetic relationship of the Lower Permian tetrapodTseajaia campi Vaughn (Amphibia: Seymouriamorpha): University of California Publications in Geological Sciences 98:1-72.
Romer AS 1946. The primitive reptile Limnoscelis restudied American Journal of Science, Vol. 244:149-188
Vaughn PP 1964. Vertebrates from the Organ Rock Shale of the Cutler Group, Permian of Monument Valley and Vicinity, Utah and Arizona: Journal of Paleontology 38:567-583.
Williston SW 1911. A new family of reptiles from the Permian of New Mexico: American Journal of Science, Series 4, 31:378-398.

HMNH link to Diadectes
wiki/Limnoscelis
wiki/Orobates
wiki/Tseajaia
wiki/Diadectes