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Edenopteron, giant Devonian sarcopterygian from Australia



From: Ben Creisler
bcreisler@gmail.com


A new non-dino paper in PLoS ONE:


Ben Young, Robert L. Dunstone, Timothy J. Senden & Gavin C. Young (2013)
A Gigantic Sarcopterygian (Tetrapodomorph Lobe-Finned Fish) from the
Upper Devonian of Gondwana (Eden, New South Wales, Australia).
PLoS ONE 8(3): e53871.
doi:10.1371/journal.pone.0053871
http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0053871

Edenopteron keithcrooki gen. et sp. nov. is described from the
Famennian Worange Point Formation; the holotype is amongst the largest
tristichopterids and sarcopterygians documented by semi-articulated
remains from the Devonian Period. The new taxon has dentary fangs and
premaxillary tusks, features assumed to be derived for large Northern
Hemisphere tristichopterids (Eusthenodon, Hyneria, Langlieria). It
resembles Eusthenodon in ornament, but is distinguished by longer
proportions of the parietal compared to the post-parietal shield, and
numerous differences in shape and proportions of other bones. Several
characters (accessory vomers in the palate, submandibulars overlapping
ventral jaw margin, scales ornamented with widely-spaced deep grooves)
are recorded only in tristichopterids from East Gondwana
(Australia-Antarctica). On this evidence Edenopteron gen. nov. is
placed in an endemic Gondwanan subfamily Mandageriinae within the
Tristichopteridae; it differs from the nominal genotype Mandageria in
its larger size, less pointed skull, shape of the orbits and other
skull characters. The hypothesis that tristichopterids evolved in
Laurussia and later dispersed into Gondwana, and a derived subgroup of
large Late Devonian genera dispersed from Gondwana, is inconsistent
with the evidence of the new taxon. Using oldest fossil and most
primitive clade criteria the most recent phylogeny resolves South
China and Gondwana as areas of origin for all tetrapodomorphs. The
immediate outgroup to tristichopterids remains unresolved – either
Spodichthys from Greenland as recently proposed, or Marsdenichthys
from Gondwana, earlier suggested to be the sister group to all
tristichopterids. Both taxa combine two characters that do not
co-occur in other tetrapodomorphs (extratemporal bone in the skull;
non-cosmoid round scales with an internal boss). Recently both
‘primitive’ and ‘derived’ tristichopterids have been discovered in the
late Middle Devonian of both hemispheres, implying extensive ghost
lineages within the group. Resolving their phylogeny and biogeography
will depend on a comprehensive new phylogenetic analysis.