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Mosasaur growth rates from long-bone histology

From: Ben Creisler

New in PLoS ONE:

Alexandra Houssaye, Johan Lindgren, Rodrigo Pellegrini, Andrew H. Lee,
Damien Germain & Michael J. Polcyn (2013)
Microanatomical and Histological Features in the Long Bones of
Mosasaurine Mosasaurs (Reptilia, Squamata) – Implications for Aquatic
Adaptation and Growth Rates.
PLoS ONE 8(10): e76741.


During their evolution in the Late Cretaceous, mosasauroids attained a
worldwide distribution, accompanied by a marked increase in body size
and open ocean adaptations. This transition from land-dwellers to
highly marine-adapted forms is readily apparent not only at the gross
anatomic level but also in their inner bone architecture, which
underwent profound modifications.

Methodology/Principal Findings

The present contribution describes, both qualitatively and
quantitatively, the internal organization (microanatomy) and tissue
types and characteristics (histology) of propodial and epipodial bones
in one lineage of mosasauroids; i.e., the subfamily Mosasaurinae. By
using microanatomical and histological data from limb bones in
combination with recently acquired knowledge on the inner structure of
ribs and vertebrae, and through comparisons with extant squamates and
semi-aquatic to fully marine amniotes, we infer possible implications
on mosasaurine evolution, aquatic adaptation, growth rates, and basal
metabolic rates. Notably, we observe the occurrence of an unusual type
of parallel-fibered bone, with large and randomly shaped osteocyte
lacunae (otherwise typical of fibrous bone) and particular
microanatomical features in Dallasaurus, which displays, rather than a
spongious inner organization, bone mass increase in its humeri and a
tubular organization in its femora and ribs.


The dominance of an unusual type of parallel-fibered bone suggests
growth rates and, by extension, basal metabolic rates intermediate
between that of the extant leatherback turtle, Dermochelys, and those
suggested for plesiosaur and ichthyosaur reptiles. Moreover, the
microanatomical features of the relatively primitive genus Dallasaurus
differ from those of more derived mosasaurines, indicating an
intermediate stage of adaptation for a marine existence. The more
complete image of the various microanatomical trends observed in
mosasaurine skeletal elements supports the evolutionary convergence
between this lineage of secondarily aquatically adapted squamates and
cetaceans in the ecological transition from a coastal to a pelagic