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Encyclopedia | Megachirella wachtleri

Megachirella wachtleri

Megachirella wachtleri,
the ancestor of snakes and lizards

Megachirella wachtleri is a small diapsid reptile with a rather large skull, moderately elongate neck and stout anterior limbs.

Megachirella does not show any significant synapomorphy of the Archosauromorpha, while it shares some of the derived characters diagnosing the Lepidosauromorpha, namely: a postfrontal which enters the upper temporal fenestra with loss of postorbital-parietal contact, the presence of paired sternal plates, and an interclavicle with an elongate posterior stem. Within Lepidosauromorpha, Megachirella wachtleri may be nested within a more restricted assemblage, the Lepidosauriformes (sensu Gauthier et al. 1988) which comprises (Paliguana, Kueheneosauridae + Marmoretta+ Lepidosauria, Evans 1991) on the basis of the presence of the following derived characters: prominent conch formed largely from quadrate, quadrate bowed in lateral view, long paroccipital process which reaches the quadrate, large retroarticular process, quadrate condyle extending below occipital condyle, ectepicondylar foramen complete, first and fifth metacarpals shorter than second and fourth.
Megachirella wachtleri can be considered with some confidence as belonging to Lepidosauriformes, but any attempt to clarify better its taxonomic position is tentative due to the incompleteness of the skull and poor preservation of postcranial elements.
Megachirella does not show any skeletal correlate which can be considered unequivocally as an adaptation to aquatic life. Many characters speak instead for terrestrial habits, like the robustness of the fore-limbs, the height of the scapular blade, the high level of ossification of the carpus and the size and shape of the claws. In addition, the presence of hollow ribs also speaks against aquatic habits since aquatic reptiles usually show pachyostotic, or at least robust, ribs and massive gastralia which act as a ballast, helping sinking into water. It is thus our opinion that the collected specimen represents an allochthonous terrestrial element transported, together with plants, within a marine marginal basin environment.

For more information:
Renesto S., Posenato R.
Megachirella wachtleri - A new lepidosauromorph reptile from the middle Triassic of the Dolomites (2003)

Foto:
Megachirella wachtleri holotype and only known specimen (Renesto and Posenato 2003). To have a scale reference, the humerus is 12.8 mm long


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