SVP abstracts 15: Gigantic recumbirostran and reptile herbivory

At first this abstract sounded like
Asaphestera, which the lead author, Mann et al. 2020 mistakenly reassessed their ‘microsaur’, Asaphestera platyris (Fig. 1), as ‘the earliest synapsid’.

Earlier in May, the LRT nested Asaphestera as a microsaur after demonstrating interpretation and reconstruction errors. However, the term ‘gigantic recumbirostran’ should probably not be applied to Asaphestera with a 4cm skull length. Oddly, given the headline, the actual size of the ‘gigantic’ skull was is not mentioned in this abstract.

From the Mann, Calthorpe and Maddin 2020 abstract:
“Currently, it is thought that the establishment of a modern trophic structure with widespread herbivory occurred in the Permian. Herbivorous adaptations in tetrapods that allow for expanded niche exploitation include modifications to craniodental morphology and expansion of the postcranial skeleton (ribs, girdles) to accommodate large guts stocked with microbial endosymbionts to aid in digestion of cellulose. The earliest tetrapod clades to experiment with herbivory (e.g., diadectids, edaphosaurids, and captorhinids), have their origins in the terminal Carboniferous but did not diversify until the Permian.”

Need to add the Cephalerpeton clade (Middle Pennsylvanian), the Stephanospondylus clade (Early Permian) and Caseasauria (Early Permian) to that list.

“Here we present a new large pantylid recumbirostran ‘microsaur’ known from a single skull found in a lycopsid tree stump from the Pennsylvannian-aged Sydney Mines Formation on Cape Breton Island, Nova Scotia. Phylogenetic analysis recovers the new taxon as sister-taxon to Pantylus.”

Pantylus (Fig. 1) and its sister Stegotretus (Berman, Eberth and Brinkman 1988; Fig. 2) are from the Early Permian and Earliest Permian respectively.

Continuing from the Mann, Calthorpe and Maddin 2020 abstract:
“MicroCT analysis reveals complex craniodental specializations that are interpreted as adaptations related to an herbivorous lifestyle. The morphology of the marginal and palatal teeth is similar to the bulbous, durophagous dentition of fossil tetrapods including Pantylus, Euryodus, Opisthodontosaurus, but are also similar to that of modern omnivorous squamates (e.g., Tiliqua tiliqua). However, the palatal teeth are further organized into dense dental fields that together with dentition on the coronoids of the lower jaw form occluding dental batteries, similar to those seen in Permian-aged animals interpreted as herbivores, such as other pantylids, moradisaurines and edaphosaurids.”

“This suggests that the dental apparatus seen in the new taxon functioned similarly in facilitating both grinding and shearing of plant material, consistent with the interpretations made for the other taxa. Our new taxon, however, substantially predates these later occurrences, thus providing the earliest evidence for tetrapod herbivory, and possibly represents the first example of an herbivore for amniotes, if recent phylogenetic hypotheses that recumbirostrans are reptiles are accurate.”

Those hypotheses are not supported by the large reptile tree (LRT, 1751 taxa) where members of the clade Recumbirostra, continue to nest within Microsauria, which includes the extant clade Caeciliidae. Recumbirostra appears to be a junior synonym for Microsauria. Adding taxa resolves this issue.

“The early occurrence and extent of development of a complex dental apparatus in this unexpected data point indicates a far earlier diversification of diet and niche exploitation by early tetrapods than previously recognized.”

Actually not ‘a far earlier diversification… than previously recognized’. We had this nailed far earlier, in 2012.

References
Berman DS, Eberth DA and Brinkman DB 1988. Stegotretus agyrus, a new genus and species of microsaur (amphibian) from the Permo-Pennsylvanian of New Mexico. Annals of Carnegie Museum. 57: 293–323.
Cope ED 1882. Third contribution to the history of the Vertebrata of the Permian formation of Texas. Proceedings of the American Philosophical Society 20:447-461.
Mann A, Calthorpe AS and Maddin HC 2020. A gigantic recumbirostran from the Carboniferous of Nova Scotia reveals adaptations to herbivorous feeding. SVP abstracts 2020.
Mann A et al. (7 co-authors) 2020. Reassessment of historic ‘microsaurs’ from Joggins, Nova Scotia, reveals hidden diversity in the earliest amniote ecosystem. Papers in Palaeontology 2020:1–17.

https://pterosaurheresies.wordpress.com/2020/05/11/asaphestera-the-earliest-amniote-no/

https://pterosaurheresies.wordpress.com/2020/06/21/origin-of-tetrapod-herbivory-effects-on-local-plant-diversity/

wiki/Pantylus
wiki/Stegotretus