Colobops: back to Rhynchocephalia

Scheyer et al. 2020 revisit
Colobops noviportensis (unnamed in Sues and Baird 1993; Pritchard et al. 2018; Late Triassic; YPM VPPU 18835; Fig. 1) a tiny 2.5cm long skull originally considered a ‘pan-archosaur’. Using µCT scans, Pritchard et al. scored Colobops and nested it at the base of the Rhynchosauria. Pritchard et al. wrote: “Colobops noviportensis reveals extraordinary disparity of the feeding apparatus in small-bodied early Mesozoic diapsids, and a suite of morphologies, functionally related to a powerful bite, unknown in any small-bodied diapsid.”

Figure 1. Colobops as originally presented and slightly restored.

Figure 1. Colobops as originally presented and slightly restored.

That same week in 2018,
Colobops was added to the large reptile tree (LRT, now 1659+ taxa, then 1085 taxa) where it nested as a sister to the morphologically similar and size similar basal rhynchocephalian, Marmoretta (Fig. 2; Evans 1991). You can read about that nesting here.

Figure 2. Marmoretta, a basal rhynchocephalian in the lineage of pleurosaurs

Figure 2. Marmoretta, a basal rhynchocephalian in the lineage of pleurosaurs

This week,
Scheyer et al. nested Colobops with Sphenodon (Fig. 3), a basal extant rhynchocephalian. Sadly, the authors again omitted Marmoretta (Fig. 2).

Sues and Baird 1993 first described this specimen
without naming it and without a phylogenetic analysis, as a member of the Sphenodontia (Williston 1925), a junior synonym for Rhynchocephalia (Gunther 1867).

Marmoretta oxoniensis (Evans 1991, Waldman and Evans 1994; Middle/Late Jurassic, ~2.5 cm skull length; Fig. 2), orginally considered a sister of kuehneosaursdrepanosaurs and lepidosaurs. Here in the LRT, Marmoretta nests between Megachirella and Gephyrosaurus + the rest of the Rhynchochephalia. Two specimens are known with distinct proportions in the skull roof.

Figure 1. Sphenodon, the extant tuatara, is close to Colobops, but Marmoretta is closer.

Figure 3. Sphenodon, the extant tuatara, is close to Colobops, but Marmoretta is closer.

The LRT minimizes taxon exclusion
because it includes such a wide gamut of taxa, from Cambrian chordates to humans. The Colobops information has been online for the past two years. Colleagues, please use it. Don’t ‘choose’ taxa you think might be pertinent. Let the LRT provide you a long list of validated taxa competing to be the sister to your new discovery.

Final note: 
In the LRT (since 2011) even rhynchosaurs are lepidosaurs. Just add pertinent taxa and your tree will recover the same topology. Traditional paleontologists are taking their time getting around to testing this well-supported hypothesis of interrelationships.


References
Evans SE 1991. A new lizard−like reptile (Diapsida: Lepidosauromorpha) from the Middle Jurassic of Oxfordshire. Zoological Journal of the Linnean Society 103:391-412.
Pritchard AC, Gauthier JA, Hanson M, Bever GS and Bhullar B-AS 2018. A tiny Triassic saurian from Connecticut and the early evolution of the diapsid feeding apparatus. Nature Communications open access DOI: 10.1038/s41467-018-03508-1
Scheyer TM, Spiekman SNF, Sues H-D, Ezcurra MD, Butler RJ and Jones MEH 2020. Colobops: a juvenile rhynchocephalian reptile (Lepidosauromorpha), not a diminutive archosauromorph with an unusually strong bite. Royal Society Open Science 7:192179.
http://dx.doi.org/10.1098/rsos.192179
Sues H-D and Baird D 1993. A Skull of a Sphenodontian Lepidosaur from the New Haven Arkose (Upper Triassic: Norian) of Connecticut. Journal of Vertebrate Paleontology13 (3): 370–372.
Waldman M and Evans SE 1994. Lepidosauromorph reptiles from the Middle Jurassic of Skye. Zoological Journal of the Linnean Society 112:135-150.

wiki/Marmoretta
wiki/Colobops

https://pterosaurheresies.wordpress.com/2018/03/25/colobops-and-taxon-exclusion-issues/

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