SVP abstracts – 6 on Westlothiana

Igielman and Benson 2022 report,
“The Visean tetrapod Westlothiana lizzae, from East Kirkton, Scotland, was initially described as a “reptiliomorph”, close to crown amniotes. However, anatomical data are incomplete because most bones are embedded in matrix, and phylogenetic analyses have yielded inconsistent results.

The large reptile tree (LRT, 2170 taxa) nests Westlothiana (Fig 1) among the basal Archosauromorpha prior to the splitting of the Synapsida and Prodiapsida and after Casineria within the crown group Reptilia (= Amniota).

Be careful here. You don’t want to “Pull a Larry Martin” by noting one or a few traits. Don’t trust any authority, website, textbook or resource. Better to just run your own analysis on all the body parts against a wide gamut of taxa and then report any convergent characters or reversals.

“Westlothiana is also shows to have a distinctly microsaur-like large tabular. Phylogenetic analysis recovers Westlothiana as the sister taxon to the well supported amniote diadectamorph clade.

The authors need to add more taxa. The LRT recovers Diadectes and kin among the Lepidosauromorpha, the basalmost amniote lineage that started out as herbivores. As mentioned above, Westlothiana (Fig 1) nests within the other basal branch of Reptilia.

This suggests the retention of a large tabular and primitive palatal dentition, including palatal fangs, closer to crown amniotes than has been previously hypothesised. The advanced age of Westlothiana also indicates that many of the key divergences along the amniote stem had occurred by the Early Carboniferous.”

Silvanerpeton, the last common ancestor of all reptiles in the LRT, was coeval in the Viséan. So Westlothiana was not of an “advanced age”. The authors are correct in reporting the initial radiation of reptiles occurred by then. The authors need to spell out what the “key divergences” are, because the abstract gives no indication that they know what those are due to taxon exclusion.

Westlothiana lizzaie
(Smithson & Rolfe 1990; Viséan, Early Carboniferous, 338 mya), lived earlier than any other known reptile, except Tulerpeton. Derived from the basalmost archosauromorph, Eldeceeon, Westlothiana was basal to Brouffia. Westlothiana was close to coeval Casineria,

References
Igielman B and Benson R 2022. New anatomical data of the enigmatic Carboniferous tetrapod Westlothiana lizzare from synchotron phase-contrast CT reveals retention of primitive characters close to the amniote crown. SVP abstracts 2022: 191.
Smithson TR & Rolfe WDI 1990. Westlothiana gen. nov. :naming the earliest known reptile. Scottish Journal of Geology no 26, pp 137–138.

reptileevolution.com/westlothiana.htm
wiki/Westlothiana