Saichangurvel: not an iguanid, but very close…

This appears to be yet another case of a priori taxon exclusion.
Saichangurvel davidsoni (Conrad and Norell 2007; (IGM 3/858; Late Cretaceous) was originally considered a member of the Iguania, but here nests with Acanthodactylus, a lacertid taxon not mentioned in the original text, but nesting as a sister to the Iguania and is a basalmost scleroglossan.

Conrad and Norell report
“Iguania, like Squamata as a whole, has a rich, but patchy fossil record. Although many Cretaceous species have been identified, Saichangurvel davidsoni is the first known from a complete skeleton. Indeed, the recent revelation that none of the Euposaurus remains may be diagnosed as iguanians (Evans, 1993) renders Saichangurvel davidsoni the earliest iguanian known from complete remains.”

Contra Evans 1993
The LRT nests tiny Euposaurus with the much larger Iguana (Fig. 2) as yet one more example of phylogenetic miniaturization at the genesis of major clades. In this case the major clades are Iguania and Squamata. BTW the ResearchGate.net link for Euposaurus takes you to another SE Evans paper.

Distinct from Acanthodactylus,
the teeth of Saichangurvel have three cusps, convergent with Iguana and that may be why the specimen was originally nested with iguanids. The upper temporal fenestrae are not reduced by a posterior extension of the postfrontal. Acanthodactylus has simple cone-shaped teeth.

Figure 1. Saichangurvel in situ, a complete squamate originally considered a member of Iguania but here nesting with Acanthodactylus.

Figure 1. Saichangurvel in situ, a complete squamate originally considered a member of Iguania but here nesting with Acanthodactylus.

The large reptile tree
(LRT) nests Saichangurvel very close to the Iguania (Fig. 2 in pink), but not in that clade. Unfortunately two of the top lizard experts in the world, Conrad and Norell, excluded taxa pertinent to the analysis, like Acanthodactylus and other basal scleroglossans (Fig 2 in green), That’s my only trump card here.

Figure 2. Subset of the LRT focusing on the Iguania and basal Scleroglossa, including Acanthodactylus and Saichangurvel

Figure 2. Subset of the LRT focusing on the Iguania and basal Scleroglossa, including Acanthodactylus and Saichangurvel

References
Conrad JL and Norell MA 2007. A complete late Cretaceous Iguanian (Squamata, Reptilia) from the Gobi and Identification of a new iguanian clade. American Novitates 3584:1-47.
Daza JD, Abdala V, Arias JS, Garcia-Lopez D and Ortiz P 2012. Cladistic Analysis of Iguania and a Fossil Lizard from the Late Pliocene of Northwestern Argentina”. Journal of Herpetology. 46(1):104-119.
Evans SE 1993. A re-evaluation of the Late Jurassic (Kimmeridgian) reptile Euposaurus (Reptilia: Lepidosauria) from Cerin, France. Geobios 27: 621–631.

Advertisements

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 )

Twitter picture

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

Facebook photo

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

Google+ photo

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

Connecting to %s