What is Megachirella?

Updated November 21, 2014 with a new skull for Megachirella.

It’s a pleasure to report a proper nesting once in a while. Such is the case with Megachirella, named for its large hand. Megachirella (Fig. 1) was originally nested with Marmoretta (Fig. 2) and the large study confirms it.

Figure 1. Megachirella, a flat-headed rhynchocephalian close to Marmoretta and basal to pleurosaurs.

Figure 1. Megachirella, a flat-headed rhynchocephalian close to Marmoretta and basal to pleurosaurs.

Megachirella wachtleri (Renesto and Posenato 2003) KUH-1501, 2 cm skull length, Middle Triassic, ~240 mya, was a smallish lepidosauriform with a moderately elongated neck and a large flattened skull. The teeth were short and stout. The quadrate was highly curved and the eyes were large. The forelimbs were robust and the carpus was well-ossified. The unguals were sharp.

Taxonomic position
The authors reported, Despite being incomplete, the specimen shows enough characters to allow placement within Lepidosauriformes, close to the Middle Jurassic genus Marmoretta.” Yes, they nailed it! That was a great assessment. Distinct from Marmoretta, Megachirella had a bowed quadrate, a larger qj process on the jugal and a narrower nasal.

Behavior and Niche
The authors considered Megachirella not specialized for either arboreal or aquatic life, thus it would have been a generalized predator of insects and other invertebrates both on the ground and on branches.

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

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

Marmoretta
Marmoretta oxoniensis
 (Evans 1991) Middle/Late Jurassic, ~2.5 cm skull length, was orginally considered a a late-surviving sister of kuehneosaursdrepanosaurs  and lepidosaurs, which is true, but a little too generalized. Here (Fig. 3) Marmoretta and Megachirella were derived from a sister to Gephyrosaurus.  See the complete tree.

Megachirella and her sisters.Megachirella and her sisters.

Figure 3. Megachirella and her sisters.

Distinct from Gephyrosaurus, the skull of Marmoretta was flatter overall with a larger orbit. The parietals were longer. The naris was larger and more dorsal. The prefrontal was narrower. The lacrimal was still visible. The jugal was reduced. The postorbitals approached the parietals posterior to the postfrontals.

A flat-headed rhynchocephalian, Marmoretta and Megachirella nest near the base, prior to the fusion of teeth together and to the jaws in many derived taxa.

Late breaking news (11/21/14): These two taxa were basal to the aquatic pleurosaurs.

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.
Renesto S and Posenato R 2003. A new lepidosauromorph reptile from the Middle Triassic of the Dolomites (northern Italy). Rivista Italiana di Paleontologia e Stratigrafia 109(3) 463-474. online pdf

wiki/Megachirella_wachtleri 

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