Cymbospondylus (Triassic ichthyosaur) distribution and life style

[Ben Creisler <bcreisler@gmail.com>]

From: Ben Creisler
bcreisler@gmail.com

A new paper not yet mentioned on the DML. I don't have the page
numbers, unfortunately.



Marco Balini & Silvio C. Renesto (2012)
CYMBOSPONDYLUS VERTEBRAE (ICHTHYOSAURIA, SHASTASAURIDAE) FROM THE
UPPER ANISIAN PREZZO LIMESTONE (MIDDLE TRIASSIC, SOUTHERN ALPS) WITH
AN OVERVIEW OF THE CHRONOSTRATIGRAPHIC DISTRIBUTION OF THE GROUP.
Rivista Italiana di Paleontologia e Stratigrafia 118(1):
http://www.rivistaitalianadipaleontologia.it/118-1_141.html


Four vertebral centra from the well known fossil-bearing Prezzo
Limestone (Upper Anisian, Middle Triassic) at the newly discovered
locality Piazza Brembana (Bergamo) are described. The four bones were
found exposed on the bed surface in an articulated position. Despite
the incompleteness of three centra due to erosion, their otherwise
fairly good preservation facilitated their study and attribution to a
shastasaurid ichthyosaur. Even though the classification of isolated
vertebral centra at the genus level is controversial, the presence of
diapophyses truncated by the cranial margin of the centra is still
considered to be diagnostic for Cymbospondylus. The new discovery
comes from an ammonoid-bearing facies, which is not unusual for
ichthyosaurs, and the bio-chronostratigraphic position of the Piazza
Brembana bones is accurately defined by ammonoids from the lowest part
of the Trinodosus Zone (Illyrian, Middle Triassic). Records of
Cymbospondylus in the Southern Alps, Germanic Basin, western United
States and Spitsbergen are summarized and all previous occurrences of
the genus are bio-chronostratigraphically correlated by utilizing the
abundant ammonoid literature. The single occurrence of Phantomosaurus
neubigii is also considered, since this species is regarded in the
literature as the sister taxon of Cymbospondylus. Material referred to
Cymbospondylus extends from a single occurrence in the Olenekian (late
Early Triassic) to the Longobardian (Late Ladinian), and its
stratigraphic distribution is strictly controlled by the development
of basins. Within these basins the distribution of specimens appears
to include relatively protected and shallow waters. Such a
distribution is consistent with the mode of life of this group of
ichthyosaurs as suggested by morphofunctional analysis.
Cymbospondylus, like most Triassic Ichthyosaurs, probably was an
undulatory swimmer, more maneuverable but slower than their Jurassic
successors.