New aristonectine elasmosaurid plesiosaur specimens from the Early Maastrichtian of Angola and comments on paedomorphism in plesiosaurs

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Abstract

New elasmosaurid plesiosaur specimens are described from the Early Maastrichtian of Angola. Phylogenetic analyses reconstruct the Angolan taxon as an aristonectine elasmosaurid and the sister taxon of an unnamed form of similar age from New Zealand. Comparisons also indicate a close relationship with an unnamed form previously described from Patagonia. All of these specimens exhibit an ostensibly osteologically immature external morphology, but histological analysis of the Angolan material suggests an adult with paedomorphic traits. By extension, the similarity of the Angolan, New Zealand and Patagonian material indicates that these specimens represent a widespread paedomorphic yet unnamed taxon.

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Methods for Quick Consensus Estimation

Pablo Goloboff, James S. Farris (2001)

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"Pachyostosis" in aquatic amniotes: a review.

Alexandra Houssaye (2009)

During the course of amniote evolution, numerous taxa secondarily adapted to an aquatic life. It appears that many of these taxa primitively display "pachyostosis," an osseous specialization characterized by an increase in bone compactness and/or volume. The term "pachyostosis" is used in morphological and histological descriptions to describe what in fact corresponds to different patterns. The aim of this paper is to present the current state of knowledge relative to this adaptation among aquatic amniotes. All the taxa that have returned to an aquatic environment are listed. Moreover, their degree of adaptation to the marine environment, their life environment, and the nature of their "pachyostotic" pattern, when present, are described. This inventory enables the evaluation of the current quality of the data relative to this specialization and provides an indication of the work that remains to be done. The functional consequences of "pachyostosis," and notably its importance for buoyancy control in the context of hydrostatic regulation of the body trim, are discussed and opposed to the requirement of improved swimming abilities in the case of a hydrodynamic mode of trim regulation. Questions are posed about the signification of the polymorphism displayed by this specialization between different taxa, different specimens of the same taxon and different bones of the same specimen, and the problem of quantification of pachyostosis is discussed. © 2009 ISZS, Blackwell Publishing and IOZ/CAS.