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 Unfortunately, Liu and Bever used outdated cladograms.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

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 primes to scale.

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.

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

Ambedus – a basal diadectid(?) with a shallow dentary

Diadectids come in many sizes, all bulky. Wiki considers them to be anamniotes (pre-reptiles), the first herbivores among tetrapods and the first tetrapods to attain large size. These are all debatable.

Ambedus pusillus (Kissel and Reisz 2004) is from the Early Permian of Ohio. It was considered the most primitive diadectid and one of the smallest. Like larger taxa, it had labiolingually broad blunt teeth with a central cusp over many of them. This genus is represented by MCZ 9436 (Fig. 1).

Kissel (2010) wrote: “Diagnosis: A small diadectid distinguishable from other members of the group by: 1) a shallow dentary; 2) relatively high maxillary and mandibular tooth count; 3) lack of a labial parapet of dentary; 4) anterior teeth of maxilla and dentary conical, in contrast to the incisiform anterior teeth of other diadectids; and 5) shallow alveolar shelf, which suggests a relatively shallow tooth implantation.”

Figure 1. Ambedus pusillus compared to candidate sister taxa. The shallow mandible and small size of this adult does not match the deep mandible found in diadectids, but more closely matches millerettids, solenodonsaurs and chroniosuchids. The outgroup of all of these taxa is Romeria primes, which has a medium depth dentary.

Figure 1. Ambedus pusillus compared to candidate sister taxa. The shallow mandible and small size of this adult does not match the deep mandible found in diadectids, but more closely matches millerettids, solenodonsaurs and chroniosuchids. The outgroup of all of these taxa is Romeria primus, which has a medium depth dentary. The labiolingually wide teeth of Ambedus connect it to diadectids, but Kissel and Reisz should have compared it to these taxa, too. You can’t be sure of basal status without including several even more basal taxa in the outgroup. Is Ambedus really a diadectid or a millerettid or a romeriid with convergent teeth? Maybe the teeth appeared first. More data would help.

Not a juvenile
Kissel (2010) wrote, “the remains described herein as A. pusillus possess none of the features that typify known juvenile individuals of previously described diadectid taxa. All elements are therefore thought to represent those of adult individuals.”

Short tooth roots
Kissel (2010) wrote, “The shallow alveolar shelf in Ambedus pusillus suggests that tooth implantation was not as deep as that in other diadectids. The shallow alveolar shelf of MCZ 9436 indicates that root length is less than crown height in Ambedus, as observed in the diadectomorphs Limnoscelis and Tseajaia.”

No dentine infolding
Kissel (2010) wrote, “In no specimen is it possible to determine if the marginal teeth of Ambedus exhibit infolding of the dentine, a feature present in all other diadectomorphs.”

No incisiform teeth
Kissel (2010) wrote, “The maxillary dentition of heretofore known diadectids consists of two incisiform teeth that are succeeded by a series of molariform cheek teeth. The maxillary dentition of Ambedus adheres to this general pattern, but the anteriormost teeth of MCZ 9436 are not incisiform.”

Unique tooth number
Kissel (2010) wrote, “MCZ 9438, a complete left dentary, possesses a complete tooth row, and a total of 22 teeth are present. Such a tooth count represents the greatest yet recorded for a diadectid, with the mandibular tooth counts of other diadectids including 14 to 18 for Diadectes, 15 for Diasparactus, 14 for Desmatodon and  17 for Orobates.”

Humerus not referred
Kissel (2010) also referred to MCZ 8667 an isolated humerus that was collected within the same vicinity as the maxillae and dentaries. Kissel wrote: “Because the humerus exhibits no features indicative of Diadectidae, it is not referred to Ambedus pusillus, and it is therefore not described herein.” 

Summary
What we learn from the above is Ambedus is not very much like other diadectids. One wonders then, is it something else? Related taxa with a shallow dentary and more teeth include Solenodonsaurus and the chroniosuchids, neither of which had diadectid teeth. Milleretta is also similar (Fig. 1). Not sure about the tooth shapes there. Then again there’s a third, perhaps more likely possibility based on tooth shape and number. Ambedus may be the romeriid root taxon for all three of these clades with a nod toward the diadectidae based on tooth shape. If so, that humerus may come back “into play.” Notably the manus of Romeria priimus is very slender and very un-diadectid-like. Not sure what the rest of it looks like. We’ll see if the humerus data helps answer those questions. Currently it’s on loan.

References
Kissel R 2010. Morphology, Phylogeny, and Evolution of Diadectidae (Cotylosauria: Diadectomorpha). Toronto: University of Toronto Press. pp. 185. online pdf
Kissel RA and Reisz RR 2004. Ambedus pusillus, new genus, new species, a small diadectid (Tetrapoda: Diadectomorpha) from the Lower Permian of Ohio, with a consideration of diadectomorph phylogeny. Annals of Carnegie Museum 73:197-212.

 

The deep mandible of Tseajaia

The original reconstruction of Tseajaia (Vaughn 1964, Moss 1972) has a problem (Fig. 1). The mandible is too deep to fit inside the jaws. But, no worries! It’s a quick fix.

Figure 1. The original reconstruction of the Tseajaia skull and closed mandibles did not take into account the great depth of the anterior mandible. That is remedied here.

Figure 1. The original reconstruction of the Tseajaia skull and closed mandibles did not take into account the great depth of the anterior mandible. That is remedied here.

References
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.
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.

wiki/Tseajaia

Revisiting Tetraceratops: a bone misidentified.

Updated January 11, 2020
with better data in Spindler 2020.

Updated June 14, 2021
with a new tracing of Martensius, a new sister for Tetraceratops.

In a nutshell: 
Better data helped to re-identify the jumble of bones in the posterior skull and palate.

Figure 5. Tetraceratops tracing using DGS and freehand illustration by Spindler 2020.

Figure 1. Tetraceratops tracing using DGS and freehand illustration by Spindler 2020.

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

Figure 2. Tetraceratops and LRT relatives including Saurorictus, Limnoscelis, Orobates and Milleretta.

As reported earlier,
Tetraceratops is still a sister to the limnoscelids,  Tetraceratops is not a basal therapsid/synapsid, as reported earlier by referenced authors (see below, none of whom tested with limnoscelids). In the large reptile tree it nest with the above (Fig. 2) taxa. 

An additional note
The Amson and Laurin (2011) reconstruction (with large lateral temporal fenestrae) was also tested as if it were a valid taxon. And it, too, nested with limnoscelids, even with a large lateral temporal fenestra. So the nesting is robust.

We looked at Tetraceratops earlier here and here.

References
Amson E and Laurin M 2011. On the affinities of Tetraceratops insignis, an Early Permian synapsid. Acta Palaeontologica Polonica 56(2):301-312. online pdf
Conrad J and Sidor CA 2001. Re−evaluation of Tetraceratops insignis (Synapsida: Sphenacodontia). Journal of Vertebrate Paleontology 21: 42A.
Laurin M and Reisz RR. 1996. The osteology and relationships of Tetraceratops insignis, the oldest known therapsid. Journal of Vertebrate Paleontology 16:95-102. doi:10.1080/02724634.1996.10011287.
Matthew WD 1908. A four-horned pelycosaurian from the Permian of Texas. Bulletin of the American Museum of Natural History 24:183-185.
Sidor CA and Hopson JA 1998. “Ghost lineages and “mammalness”: Assessing the temporal pattern of character acquisition in the Synapsida”. Paleobiology 24: 254–273.

wiki/Tetraceratops

Diadectes is not an Amphibian. And Procolophon is a diadectid.

Tradition and Wikipedia reports that “Diadectes is an extinct genus of large, very reptile-like amphibians.” This is an outdated hypothesis that has to go. Wiki further reports, “Diadectes combines a reptile-like skeleton with a more primitive,seymouriamorph-like skull.”

Earlier we looked at Diadectes, noting that it nests deep inside the plant-eating side of the Reptilia, the new Lepidosauromorpha.

Let’s take a look at that skull again. 
Wiki reports, “Among its primitive features, Diadectes has a large otic notch (a feature found in all labyrinthodonts, but not in reptiles) with an ossified tympanum.” Other reptiles with a large otic notch include several close relatives of Diadectes, including a sister taxon, Procolophon (Fig. 1). The resemblance is not just superficial, yet Wiki reports, “Procolophon was a genus of lizard-like procolophonid reptiles.” Why was Procolophon considered a reptile and Diadectes an amphibian? It can’t be the notch. It’s the same on both. Procolophon was simply smaller diadectid that lived later in time. Take a look a the various Diadectes skulls  on the Wiki page and you’ll see that the otic notch is bigger on some, smaller on others. It’s not homologous with the similar structure in amphibians. Seymouria retains an intertemporal bone and has palatal fangs. Diadectes does not.

 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.

The Otic Notch
The otic notch simply redeveloped by convergence in diadectids and procolphonids, yet one got labeled a reptile and one an amphibian. I don’t know why. Both Procolophon (Owen 1876) and Diadectes (Cope 1878a, b) were first described long ago. Perhaps this is some sort of tradition from a time when we didn’t know very much about prehistory. If anyone has original literature, I’d like to see it.

Ancestors in the Large Reptile Tree
Orobates
 has a small otic notch and nests primitive to the diadectids and procolophonids. Tseajaia, Solenodonsaurus and the chroniosuchids all have an otic notch and all are considered by Wiki to be amphibians, but here nest in the Reptilia. All these taxa and the diadectids + procolphonids have Concordia in their pedigree. It has virtually no otic notch, but you can see how it could have begun here. Funny thing is, Wiki reports, Concordia is close to the origin of the captorhinid reptiles, and it is too in the large reptile tree. These sorts of problems emphasize the importance of adding lots of taxa to basal reptile studies. The more you add, the more Diadectes nests with Procolophon deep inside the Reptilia.

Herbivorous
Wiki reports, “Diadectes was one of the very first herbivorous tetrapods.” One look at the chronological reptile tree indicates that two other herbivores, Cephalerpeton and Concordia preceded Diadectes chronologically. So do Orobates and Stephanospondylus. Captorhinids are likewise herbivores, but they are found in younger rocks despite their more primitive nesting.

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
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.
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).

Are Diadectomorphs Reptiles (= Amniotes)?

Mickey Mortimer was kind enough to provide some interesting literature refs regarding the non-reptile status of Diadectomorphs (= Diadectes, Limnoscelis and Tseajaia). That means these taxa would have developed from tadpoles and non-amniote eggs laid in water. The large reptile tree found these taxa to be related to one another deep within the Reptilia, and also related to procolophonids, pareiasaurs, chroniosuchids and turtles. That means diadectomorphs would have laid eggs in dry areas without the young developing form tadpoles. M. Mortimer’s comments followed an earlier post linking caseasaurs and diadetids (but not as sisters, only cousins).

From M. Mortimer’s notes:
“Laurin and Reisz (1995) list several characters of Amniota. Diadectomorphs lack: [my comments follow in brackets]:
– Frontal contacting orbit. [also lacking in Eothyris, Orobates, pareiasaurs and turtles! And… among non-amniotes the frontal contacts the orbit in Cacops and Doleserpeton.]
– Occipital condyle almost as high as it is broad. [Procolophon and turtles also lack this trait.]
– Labyrinthodont infolding of enamel absent (Kemp, 2003). [Diadectes infolding of enamel also absent (double negative here), so this may be a convergent trait with Limnoscelis and labyrinthodonts].
– Axial centrum tilted anterodorsally. [I can’t comment on this hard-to-see trait].
– Cleithrum restricted to anterior edge of scapulocoracoid. [I never knew it wrapped around or did anything else.]
– Presence of three scapulocoracoid ossifications.”[often in basal reptiles (Paleothyris, Eocaptorhinus, the scapulocoracoid is completely fused.]

According to M. Mortimer: “More problematic are-
– Occipital flange of squamosal gently convex.  Even if I understood it, they say diadectomorphs’ condition may be an autapomorphy. [such gentle convexity, wherever present, is difficult to determine from drawings and photos].
– Transverse flange bearing a row of large teeth on its posterior edge.  Also in Limnoscelis, so could work with synapsid diadectomorphs. [So, Limnoscelis gets a free pass. Captorhinids, caseids, Belebey, Milleretta, etc. etc.  also lack a row of large teeth on the transverse flange.]
– Presence of astragalus.  They followed Rieppel’s (1993) model, but O’Keefe et al. (2006) showed amniotes have the same astragalar homology as Diadectes. [Okay].

M. Mortimer further reported, “Not to mention diadectomorphs aren’t even sister to caseasaurs in your tree.  You have derived diadectids by procolophonids, basal diadectomorphs strewn with Solenodonsaurus, Tetraceratops and chroniosuchians, and caseasaurs sister to various taxa usually placed in Parareptilia, and these three clades are successively less closely related to lepidosaurs.” 

No, they’re not sisters (lots of branching in the Millerettids + Caseasauria), but shared a recent common ancestor, Romeria primus.

M. Mortimer also noted that “Berman et al. (1992) and Berman (2000) both suggested diadectomorphs were the sister group of synapsids as opposed to the sister group of amniotes. Kemp (2003) analysed their evidence, concluding-
– A posterolateral corner of the skull table formed entirely or nearly entirely by the supratemporal is only found is Tseajaia, which I note would make it ambiguous synapomorphy is [if] diadectomorphs and synapsids were sister taxa.
– A long posterior expansion of postorbital that contacts supratemporal to exclude the parietal lappet from contacting the squamosal is primitively present in cotylosaurs, including basal sauropsids.
– Presence of an otic trough of the opisthotic is shared, but not by varanopids, which I note isn’t a problem if caseasaurs are basal.
– A deep, nonsculptured component of the tabular which contacts the distal end of a ventrally displaced, laterally directed paroccipital process, enclosing laterally a small, ventrally displaced, posttemporal fenestra is absent in Limnoscelis and Desmatodon, so is more likely convergent in synapsids and Diadectes.

Nicely put. All I can say is the several hundred traits used to determine the tree topology of the large reptile nested the casesaurs and diadectids where they did because they and 320+ other taxa provided the opportunity and motive. As an experiment, moving all three caseasaurs to the synapsids adds 24 steps. Caseasaurs become strange bedfellows with the basal synapsids and basal protodiapsids derived from a sister to Protorothyris.

The other thing that could be happening here, is this: the Diadectomorpha are on the primitive side of the Amniota and the Synapsida were the first clade to break off from the rest. That alone could indicate a relationship in a traditional sense. Then again, if Berman et al. 1992 and Berman 2000 included casesaurs within their suprageneric Synapsida, then they recovered what the large reptile tree recovered, sans all the other basal reptiles included in the large reptile tree but not included in their analysis.

Thank you for your thoughts, Mickey.

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.

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.

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.

Orobates and Tetraceratops

Updated January 11, 2020
with better data in Spindler 2020.

Updated June 14, 2021
with a new tracing of Martensius, a new sister for Tetraceratops.

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

Figure 1. Tetraceratops and LRT relatives including Saurorictus, Limnoscelis, Orobates and Milleretta.

The phylogenetic position
of the Early Permian Tetraceratops has been controversial. Originally Matthew (1908)  considered it an eothyridid. Others considered it  a sphenacodontid (Conrad and Sidor 2001), or the basalmost therapsid (Laurin and Reisz 1996, Amson and Laurin (2011). This study found Tetraceratops to nest with Tseajaia within the Limnoscelidae within the Diadectomorpha and within the new Lepidosauromorpha. No one else had ever tested such a relationship. The outgroup was Orobates, a taxon that might provide some clues to the post-crania of Tetraceratops, which is otherwise unknown.

Tetraceratops was half the length of Orobates, if the skull proportions are any clue. Tetraceratops also has a distinct and derived skull structure with a highly curved lower jaw, a reduced naris, and fewer large teeth. The famous bony protuberances of the skull are likely intraspecific traits associated with secondary sexual characters and dominance. These can also be seen in similar patterns in TseajaiaTetraceratops was a likely herbivore, as were its closest kin. We don’t know what the tail of Tseajaia looked like, but it was likely rather gracile, as in Orobates. It would be interesting to see the shape of the dentary in Tseajaia, but every image I’ve seen has the jaws tightly closed, but the ventral margin is highly curved.

It still seems odd that anyone would think such an odd specimen, like Tetraceratops, was a basal form of such a large clade, like the therapsids, since it resembles none of them. This may represent just another case of having a blind eye to all possibilities because a large reptile tree was not employed. Here it is represents a derived herbivore with sprawling limbs leaving no descendants.


References
Amson E and Laurin M 2011. On the affinities of Tetraceratops insignis, an Early Permian synapsid. Acta Palaeontologica Polonica 56(2):301-312. online pdf
Conrad J and Sidor CA 2001. Re−evaluation of Tetraceratops insignis (Synapsida: Sphenacodontia). Journal of Vertebrate Paleontology 21: 42A.
Matthew WD 1908. A four-horned pelycosaurian from the Permian of Texas.
Bulletin of the American Museum of Natural History 24:183-185.
Laurin M and Reisz RR. 1996. The osteology and relationships of Tetraceratops insignis, the oldest known therapsid. Journal of Vertebrate Paleontology 16:95-102. doi:10.1080/02724634.1996.10011287.

wiki/Tetraceratops