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Ichthyostega moved like a mudskipper

From: Ben Creisler

A couple of recent papers that may be of interest:

Stephanie E. Pierce, John R. Hutchinson and Jennifer A. Clack (2013)
Historical Perspectives on the Evolution of Tetrapodomorph Movement.
Integrative and Comparative Biology (advance online publication)
doi: 10.1093/icb/ict022

Over the past century, various modern analogs have been used to infer
the evolution of locomotor performance in stem tetrapods and their
fish ancestors, with varying success. Here, we conduct a phylogenetic
review of these modern analogs, from chondrichthyans to mammals,
highlighting the broad spectrum of vertebrate clades and locomotor
behaviors. The pros and cons behind utilizing modern analogs for the
early stages of the transition from water to land also are discussed.
In particular, it is noted that any hypothesis about locomotion not
only must be supported by evidence from living animals but must also
be consistent with character transformations in the fossil record. A
“total-evidence” approach that emphasizes what extinct taxa could not
do, rather than focusing on the specifics of how they functioned, is
thus recommended. An example of this approach, which investigates
mobility of the limb joints in modern semi-aquatic animals and in the
Devonian stem tetrapod Ichthyostega, is detailed. We propose that
various locomotion behaviors of modern quadrupeds can be ruled out for
Ichthyostega, but that forelimb “crutching” motions, as seen in living
mudskippers, may have been possible. The potential for movement in
other known Devonian stem tetrapods is assessed through an anatomical
comparison of limb joint morphology—and associated mobility—with
Ichthyostega, and deemed to have been quite similar.

Corey J. Jew, Nicholas C. Wegner, Yuzo Yanagitsuru, Martin Tresguerres
and Jeffrey B. Graham (2013)
Atmospheric Oxygen Levels Affect Mudskipper Terrestrial Performance:
Implications for Early Tetrapods.
Integrative and Comparative Biology (advance online publication)
doi: 10.1093/icb/ict034

The Japanese mudskipper (Periophthalmus modestus), an amphibious fish
that possesses many respiratory and locomotive specializations for
sojourns onto land, was used as a model to study how changing
atmospheric oxygen concentrations during the middle and late Paleozoic
Era (400–250 million years ago) may have influenced the emergence and
subsequent radiation of the first tetrapods. The effects of different
atmospheric oxygen concentrations (hyperoxia = 35%, normoxia = 21%,
and hypoxia = 7% O2) on terrestrial performance were tested during
exercise on a terrestrial treadmill and during recovery from
exhaustive exercise. Endurance and elevated post-exercise oxygen
consumption (EPOC; the immediate O2 debt repaid post-exercise)
correlated with atmospheric oxygen concentration indicating that when
additional oxygen is available P. modestus can increase oxygen
utilization both during and following exercise. The time required
post-exercise for mudskippers to return to a resting metabolic rate
did not differ between treatments. However, in normoxia, oxygen
consumption increased above hyperoxic values 13–20 h post-exercise
suggesting a delayed repayment of the incurred oxygen debt. Finally,
following exercise, ventilatory movements associated with
buccopharyngeal aerial respiration returned to their rest-like pattern
more quickly at higher concentrations of oxygen. Taken together, the
results of this study show that P. modestus can exercise longer and
recover quicker under higher oxygen concentrations. Similarities
between P. modestus and early tetrapods suggest that increasing
atmospheric oxygen levels during the middle and late Paleozoic allowed
for elevated aerobic capacity and improved terrestrial performance,
and likely led to an accelerated diversification and expansion of
vertebrate life into the terrestrial biosphere.


Another paper about tetrapod jaw evolution in Integrative and
Comparative Biology is not posted on the site yet. It's discussed in a
news release.