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