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Early Carboniferous fauna from Nova Scotia helps fill "Romer's Gap"

Ben Creisler

New in PLoS ONE:

Jason S. Anderson , Tim Smithson, Chris F. Mansky, Taran Meyer &
Jennifer Clack (2015)
A Diverse Tetrapod Fauna at the Base of 'Romer's Gap'.
PLoS ONE 10(4): e0125446.

The lack of fossil tetrapod bearing deposits in the earliest
Carboniferous (‘Romer’s Gap’) has provoked some recent discussions
regarding the proximal cause, with three explanations being offered:
environmental, taphonomic, and collection failure. One of the few, and
earliest, windows into this time is the locality of Blue Beach exposed
in the Tournaisian deposits at Horton Bluff lying along the Avon River
near Hantsport, Nova Scotia, Canada. This locality has long been known
but, because the fossils were deposited in high energy settings they
are almost always disarticulated, so the fauna has not been described
in detail. Recent intensive collection has revealed a diverse
assemblage of material, including for the first time associated
elements, which permits an evaluation of the faunal constituents at
the locality. Although not diagnosable to a fine taxonomic level,
sufficient apomorphies are present to identify representatives from
numerous clades known from more complete specimens elsewhere. The
evidence suggests a diverse fauna was present, including whatcheeriids
and embolomeres. A single humerus previously had been attributed to a
colosteid, but there is some uncertainty with this identification.
Additional elements suggest the presence of taxa otherwise only known
from the late Devonian. Depositional biases at the locality favor
tetrapod fossils from larger individuals, but indirect evidence from
trackways and tantalizing isolated bones evidences the presence of
small taxa that remain to be discovered. The fossils from Blue Beach
demonstrate that when windows into the fauna of ‘Romer’s Gap’ are
found a rich diversity of tetrapods will be shown to be present,
contra arguments that suggested this hiatus in the fossil record was
due to extrinsic factors such as atmospheric oxygen levels. They also
show that the early tetrapod fauna is not easily divisible into
Devonian and Carboniferous faunas, suggesting that some tetrapods
passed through the end Devonian extinction event unaffected.