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 Unfortunately, Liu and Bever used outdated cladograms.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.

 

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4 thoughts on “Alveusdectes: a small, late-surviving diadectomorph – with procolophonid cheeks

  1. How do you get all basal lepidosaurs to be herbivores from your large reptile tree? If we assume your large reptile tree to be correct, it shows small insectivores to be the basalmost members of your lepidosaur clade.

  2. Neil, I presume you mean “lepidosauromorphs” beginning with captorohinids and kin. And the answer is, this is what the computer spits out. It is odd. It was noted earlier as an apparent character of the clade. If you do indeed mean “lepidosaurs” I don’t see herbivores there.

    • Yeh that’s what I was referring to Captorhinds are mostly insectivores. All the chaps like reiszorhinus and romeria and Concordia: small insectivores. Captorhinus and labidosaurus: carnivores or possibly omnivores. It’s not until the likes of captorhinikos and the moradisaurine captorhinids in the Kungurian and Middle Permian that we get high fibre herbivorous captorhinids. In fact, none of the Captorhinds you included on the lrt are herbivores. Check out Modesto et al 2014 on captorhinikos and reisz & Frobish 2014 on eocasea to see which were herbivores and which were carnivores

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