July 4th, 2013 
Riffin We present a redescription of Megalocoelacanthus dobiei, a giant fossil coelacanth from Upper Cretaceous strata of North America. Megalocoelacanthus has been previously described on the basis of composite material that consisted of isolated elements. Consequently, many aspects of its anatomy have remained unknown as well as its phylogenetic relationships with other coelacanths. Previous studies have suggested that Megalocoelacanthus is closer to Latimeria and Macropoma than to Mawsonia. However, this assumption was based only on the overall similarity of few anatomical features, rather than on a phylogenetic character analysis. A new, and outstandingly preserved specimen from the Niobrara Formation in Kansas allows the detailed description of the skull of Megalocoelacanthus and elucidation of its phylogenetic relationships with other coelacanths. Although strongly flattened, the skull and jaws are well preserved and show many derived features that are shared with Latimeriidae such as Latimeria, Macropoma and Libys. Notably, the parietonasal shield is narrow and flanked by very large, continuous vacuities forming the supraorbital sensory line canal. Such an unusual morphology is also known in Libys. Some other features of Megalocoelacanthus, such as its large size and the absence of teeth are shared with the mawsoniid genera Mawsonia and Axelrodichthys. Our cladistic analysis supports the sister-group relationship of Megalocoelacanthus and Libys within Latimeriidae. This topology suggests that toothless, large-sized coelacanths evolved independently in both Latimeriidae and Mawsoniidae during the Mesozoic. Based on previous topologies and on ours, we then review the high-level taxonomy of Latimerioidei and propose new systematic phylogenetic definitions.
Megalocoelacanthus dobiei Schwimmer, Stewart & Williams, 1994, AMNH FF 20267 from lower Campanian of the Niobrara Formation.
Ethmosphenoid portion of the skull in right lateral view. Abbreviations: ant.com.so.s.c, anterior commissure of supraorbital sensory line canal; ant.pr, antotic process; a.w.Par, ascending wing of parasphenoid; Bsph, basisphenoid; bucc.can, buccal canal; gr.j.v, groove for jugular vein; L.e, lateral ethmoid; L.r, lateral rostral; Na, nasal; Pa.a, anterior parietal; Pa.p, posterior parietal; Par, parasphenoid; pi, pillar; pr.con, processus connectens; sph.c, sphenoid condyle; So, supraorbital series; so.s.c, supraorbital sensory line canal; v.l.fo, ventrolateral fossa; ?v.pr.Pa, ventral (descending) process of the parietal. Scale bar = 10 cm.
doi:10.1371/journal.pone.0049911.g002
Megalocoelacanthus dobiei Schwimmer, Stewart & Williams, 1994, AMNH FF 20267 from lower Campanian of the Niobrara Formation.
Ethmosphenoid portion of the skull in left lateral view. Abbreviations: ant.pr, antotic process; a.w.Par, ascending wing of parasphenoid; Bsph, basisphenoid; bucc.can, buccal canal; f.v.nas-b.can, foramen for ventral branch of naso-basal canal; gr.j.v, groove for jugular vein; io.s.c, infraorbital sensory line canal; L.e, lateral ethmoid; L.r, lateral rostral; Na, nasal; nos.a, anterior nostril; nos.p, posterior nostril; Pa.p, posterior parietal; Par, parasphenoid; pi, pillar; pr.con, processus connectens; sph.c, sphenoid condyle; So, supraorbital series; so.s.c, supraorbital sensory line canal; v.l.fo, ventrolateral fossa; v.pr.L.r, ventral (descending) process of the lateral rostral; ?v.pr.Pa, ventral (descending) process of the parietal. Scale bar = 10 cm.
doi:10.1371/journal.pone.0049911.g003
Megalocoelacanthus dobiei Schwimmer, Stewart & Williams, 1994, AMNH FF 20267 from lower Campanian of the Niobrara Formation. Isolated snout.
A, right anterolateral view; B, posterior view. Abbreviations: ant.ros, anterior opening for the rostral organ; c.nos.a, canal for the anterior nostril; d.l.Pmx, dorsal lamina of the premaxilla; f.a.n.c, anterior foramen of the nasal capsule; L.r, lateral rostral; m.p.s.c, median pore for the sensory line canal; n.c, nasal capsule; nos.a, anterior nostril; Pmx, premaxilla. Scale bar = 1 cm.
doi:10.1371/journal.pone.0049911.g004
Citation: Dutel H, Maisey JG, Schwimmer DR, Janvier P, Herbin M, et al. (2012) The Giant Cretaceous Coelacanth (Actinistia, Sarcopterygii) Megalocoelacanthus dobiei Schwimmer, Stewart & Williams, 1994, and Its Bearing on Latimerioidei Interrelationships. PLoS ONE 7(11): e49911. doi:10.1371/journal.pone.0049911
Editor: Daphne Soares, University of Maryland, United States of America
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