NEW INTERPRETATION OF THE POSTCRANIAL SKELETON AND OVERALL BODY SHAPE OF THE PLACODONT CYAMODUS HILDEGARDIS PEYER, 1931 (REPTILIA, SAUROPTERYGIA)

Torsten M. Scheyer

ABSTRACT

The enigmatic cyamodontoid placodont Cyamodus hildegardis from the Besano Formation (Middle Triassic) of the Alpine area of Switzerland and northern Italy has previously been reconstructed with a broad, laterally expanded main armour (carapace) and a separate smaller pelvic shield, lending this species a fairly sprawling appearance. A re-examination and a literature review of the postcranial dermal armour and endoskeletal elements of the three best preserved articulated specimens of the species leads to new interpretations of the dermal armour and associated underlying postcranial bones, as well as a new life reconstruction. The carapace of C. hildegardis, carrying a series of similar-sized, enlarged lateral armour plates, is rounder and less laterally expanded than previously hypothesised. The separate pelvic shield, also carrying a smaller set of lateral armour plates that decrease in size with an anteroposterior gradient, covers mainly the pelvic girdle and the base of the tail. The rather short tail is armoured by four series of armour plates that show a simple anteroposterior gradient of size reduction in keeping with an equivalent size reduction in the caudal vertebrae. Until further fossils are recovered, the internal organisation of dermal plates within the two armour shields of C. hildegardis remains little known.

Torsten M. Scheyer. Paläontologisches Institut und Museum, Universität Zürich, Karl Schmid-Strasse 4, CH-8006 Zürich, Switzerland.
 

Keywords: Placodontia; cyamodontoid; Monte San Giorgio; Triassic; dermal armour; Psephoderma alpinum

PE Article Number: 13.2.15A
Copyright: Society of Vertebrate Paleontology July 2010
Submission: 4 February 2010. Acceptance: 10 June 2010