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Mesozoic mammal locomotion

Ben Creisler

A recent paper not yet mentioned:

Meng Chen and Gregory P. Wilson (2015)
A multivariate approach to infer locomotor modes in Mesozoic mammals.
Paleobiology (advance online publication)
DOI: http://dx.doi.org/10.1017/pab.2014.14

Ecomorphological diversity of Mesozoic mammals was presumably
constrained by selective pressures imposed by contemporary
vertebrates. In accordance, Mesozoic mammals for a long time had been
viewed as generalized, terrestrial, small-bodied forms with limited
locomotor specializations. Recent discoveries of Mesozoic mammal
skeletons with distinctive postcranial morphologies have challenged
this hypothesis. However, ecomorphological analyses of these new
postcrania have focused on a single taxon, a limited region of the
skeleton, or have been largely qualitative.

For more comprehensive locomotor inference in Mesozoic mammals, we
applied multivariate analyses to a morphometric data set of extant
small-bodied mammals. We used 30 osteological indices derived from
linear measurements of appendicular skeletons of 107 extant taxa that
sample 15 orders and eight locomotor modes. Canonical variate analyses
show that extant small-bodied mammals of different locomotor modes
have detectable and predictable morphologies. The resulting
morphospace occupation reveals a morphofunctional continuum that
extends from terrestrial to scansorial, arboreal, and gliding modes,
reflecting an increasingly slender postcranial skeleton with longer
limb output levers adapted for speed and agility, and extends from
terrestrial to semiaquatic/semifossorial and fossorial modes,
reflecting an increasingly robust postcranial skeleton with shorter
limb output levers adapted for powerful, propulsive strokes. We used
this morphometric data set to predict locomotor mode in ten Mesozoic
mammals within the Docodonta, Multituberculata, Eutriconodonta,
“Symmetrodonta,” and Eutheria. Our results indicate that these fossil
taxa represent five of eight locomotor modes used to classify extant
taxa in this study, in some cases confirming and in other cases
differing from prior ecomorphological assessments. Together with
previous locomotor inferences of 19 additional taxa, these results
show that by the Late Jurassic mammals had diversified into all but
the saltatorial and active flight locomotor modes, and that this
diversification was greatest in the Eutriconodonta and
Multituberculata, although sampling of postcranial skeletons remains
uneven across taxa and through time.