Megachirella: Not at the origin of squamates. Lacertulus is older.

We looked at Lacertulus and the origin of the Squamata in the Late Permian
here in October 2011.

We looked at the splitting of the Tritosauria from the Protosquamata
here in December 2014.

Siimòes et al. 2018
proposed to nest Megachirella watchtleri (Fig. 1) at the origin of squamates in the Middle Triassic, 75 million years earlier than the previously known oldest squamate fossils. They reported, “For the first time, to our knowledge, morphological and molecular data are in agreement regarding early squamate evolution, with geckoes—and not iguanians—as the earliest crown clade squamates. Divergence time estimates using relaxed combined morphological and molecular clocks show that lepidosaurs and most other diapsids originated before the Permian/Triassic extinction event, indicating that the Triassic was a period of radiation, not origin, for several diapsid lineages.”

Figure 1. New µCT scans of Megachirella from Simoes et al. 2018.

Figure 1. New µCT scans of Megachirella from Simoes et al. 2018.

Unfortunately
|they did not include relevant taxa. According to the large reptile tree (LRT, 1224 taxa, www.reptileevolution.com/reptile-tree.htm) Megachirella nests at the base of the Rhynchocephalia (= Sphenodontia) along with Pleurosaurus (excluded from the Simoes team study) when many more relevant taxa are included.

Figure 2. Megachirella nests in the middle of this cladogram, that also nests turtles between rib gliders and choristoderes.

Figure 2. Megachirella nests in the middle of this cladogram, that also nests turtles between rib gliders and choristoderes.

 

Lacertulus is older (Late Permian) and more directly related to squamates.

FIgure 2. Megachirella (Renesto and Posenato 2003) is a sister to the BSRUG diapsid.

FIgure 3. Megachirella (Renesto and Posenato 2003) is a sister to the BSRUG diapsid and reconstructed here.

Nesting turtles with rib gliders
(Coelurosauravus) only hints at major flaws in the Simoes et al. cladogram topology. Nesting Sophineta and Palaegama close to and basal to Megachirella confirms findings made years earlier by the LRT. Marmoretta is also close, but nests within the Rhynchocephalia in the LRT.

Figure 2. Pleurosaurus and Palaeopleurosaurus skulls compared to those of sister taxa.

Figure 2. Pleurosaurus and Palaeopleurosaurus skulls compared to those of sister taxa.

Tijubina (which Simoes redescribed in 2012) is also missing from the Simoes et al. 2018 study.

Figure 1. Palaegama is basal to Coelurosauravus ('rib' gliders), Megachirella (rhynchocephalians), Lacertulus (protosquamates) and Tijubina (tritosaurs)

Figure 5. Palaegama is basal to Coelurosauravus (‘rib’ gliders), Megachirella (rhynchocephalians), Lacertulus (protosquamates) and Tijubina (tritosaurs)

 

 

References
Simòes T, and 8 co-authors 2018. The origin of squamates revealed by a Middle Triassic lizard from the Italian Alps. Nature 557: 706â709 (2018)

Publicity
https://www.livescience.com/62693-mother-of-lizards-fossil.html

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

This site uses Akismet to reduce spam. Learn how your comment data is processed.