A Gigantic Sarcopterygian (Tetrapodomorph Lobe-Finned Fish) from the Upper Devonian of Gondwana (Eden, New South Wales, Australia)

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.This research was supported by Australian Research Council [www.arc.gov.au] Discovery Grants DP0558499 (‘Australia’s exceptional Palaeozoic fossil fishes, and a Gondwana origin for land vertebrates’) and DP0772138 (‘Old brains, new data–early evolution of structural complexity in the vertebrate head’). Surface scanning and 3D printing equipment was partly financed by an Australian National University [www.anu.edu.au] Major Equipment Grant (10MEC15). No additional external funding received for this study. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript

A gigantic sarcopterygian (tetrapodomorph lobe-finned fish) from the upper Devonian of Gondwana (Eden, New South Wales, Australia).

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

<i>Edenopteron keithcrooki</i> gen. et sp. nov.

<p>Holotype (ANU V3426). Parietal and post-parietal shields in approximate life position (latex casts whitened with ammonium chloride).</p

<i>Edenopteron keithcrooki</i> gen. et sp. nov.

<p>Holotype (ANU V3426). <b>A</b>, <b>B</b>, Interpretive outlines of bone sutures and other structures on the latex casts illustrated in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0053871#pone-0053871-g004" target="_blank">Figure 4A, B</a>.</p

<i>Edenopteron keithcrooki</i> gen. et sp. nov.

<p>Holotype (ANU V3426). <b>A</b>, composite latex of pieces a7 (anterior) and a14 (posterior) showing snout in dorsal view; <b>B</b>, composite latex (a8, b7) showing internal snout surface, and ventral view of dermal bones of part of the palate. <b>C</b>, inner view of anterior end of right maxilla (latex casts whitened with ammonium chloride).</p

<i>Edenopteron keithcrooki</i> gen. et sp. nov.

<p>Holotype (ANU V3426). Four spaced sections through XCT-scanned portion of left vomer from near the tip (<b>A</b>) to the basal attachment of the fang (<b>D</b>).</p

<i>Edenopteron keithcrooki</i> gen. et sp. nov.

<p>ANU V3478. Incomplete flattened skull and left cheek in dorsal view, preserved on pieces f4 (left side) and h1 (right side) (latex cast whitened with ammonium chloride).</p

<i>Edenopteron keithcrooki</i> gen. et sp. nov.

<p>Three-dimensional model at life size (on display at Canberra Museum and Gallery, December 2011) used as a basis for the reconstructions of <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0053871#pone-0053871-g023" target="_blank">Figure 23A–C</a>.</p

<i>Edenopteron keithcrooki</i> gen. et sp. nov.

<p>Right cheek unit of holotype (ANU V3426). <b>A</b>, external view; <b>B</b>, internal view (latex casts whitened with ammonium chloride).</p

<i>Edenopteron keithcrooki</i> gen. et sp. nov.

<p>Holotype (ANU V3426). <b>A</b>, steinkern of left mandibular joint in lateral view (whitened with ammonium chloride). <b>B</b>, preserved bone of jaw symphysis in ventral view. <b>C</b>, Interpretive drawing of specimen in B.</p