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Echidna walking gait as clue to narrow tracks of basal and early synapsids



From: Ben Creisler
bcreisler@gmail.com

A non-dinosaur paper that may be of interest as applied to tetrapod
trackmakers such as "pelycosaurs" that left narrow tracks despite a
"sprawling" limb configuration:

P. P. Gambaryan & A. N. Kuznetsov (2013)
An evolutionary perspective on the walking gait of the long-beaked echidna.
Journal of Zoology (advance online publication)
DOI: 10.1111/jzo.12014
http://onlinelibrary.wiley.com/doi/10.1111/jzo.12014/abstract

The speed, gait and trackway of the long-beaked echidna's walk are
reported for the first time. The gait formula is devised. Despite its
sprawling limb posture, echidna's walking technique shows fundamental
differences from that of the classical sprawlers such as urodelans and
lizards, which are: (1) the presence of the pace-like lateral stages
of support and even their prevalence over the diagonal ones; (2) the
narrow, though sprawling, limb posture and, consequently, the narrow
trackway; (3) rolling, skidding and yawing of the trunk from side to
side; (4) forelimb in-fingerness, which presumably provides the major
thrust for these side-to-side movements. On the whole, the echidna's
sprawling type is more upright than in urodelans and lizards and is
closer to the parasagittal type of therians. Like therians, echidnas
already employ dynamic equilibration instead of the static one. The
question is posed of whether mammalian ancestors have ever walked in
the manner of urodelans and lizards.