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New insights on plesiosaur Aristonectes holotype

Ben Creisler

A recent paper:

José P. O'Gorman (2015)
New insights on the Aristonectes parvidens (Plesiosauria,
Elasmosauridae) holotype: news on an old specimen.
Ameghiniana (advance online publication)

Additional preparation of the holotype of the Maastrichtian
aristonectine elasmosaurid Aristonectes parvidens Cabrera from Chubut
Province, Argentina, permits new observations and reveals features
that were not previously described and allows new interpretations of
those that were previously described. Quantitative comparison with non
aristonectine elasmosaurids shows that the increase in the number of
alveoli in the premaxilla, maxilla and mandible is not a consequence
of increase in skull size increase. Instead, decrease in alveolar size
and interalveolar space, compared with that seen in non-aristonectine
elasmosaurids, is at least as important. Increase in skull length
compared with non-aristonectine elasmosaurids is not as marked as
classically considered: skull length is equivalent to the length of
the first 8–10 cervical vertebrae in non-aristonectines and the first
10–12 in aristonectines. The ratio of atlas-axis complex length to
skull length shows no significant difference between aristonectine and
non-aristonectine elasmosaurids. An aristonectine autapomorphy not
mentioned previously is the decrease in premaxilla anteroposterior
length. This may be correlated with the shortening of the mandibular
symphysis. The cervical region is characterised by a rapid increase in
the BI index of the vertebral centra, indicating a reduction in
lateral mobility of the neck. Increase in alveoli number is achieved
as a result of a number of changes that seem to indicate the
importance of the biological role of the length of the alveolar row
and mouth aperture. These are probably related to change in prey size
and capture strategy compared with that of non-aristonectine
elasmosaurids, such as a change to smaller fishes or invertebrates
and/or a change from ambushing one prey individual to ambushing
multiple simultaneous prey individuals.