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| Graulia branchiodonta Manuelli, Mondéjar Fernández, Dollman, Jakata & Cavin, 2024 |
Abstract
Although the split of coelacanths from other sarcopterygians is ancient, around 420 million years ago, the taxic diversity and the morphological disparity of the clade have remained relatively low, with a few exceptions. This supposedly slow evolutionary pace has earned the extant coelacanth Latimeria the nickname “living fossil”. This status generated much interest in both extinct and extant coelacanths leading to the production of numerous anatomical studies. However, detailed descriptions of extinct taxa are made difficult due to the quality of the fossil material which generally prevents fine comparisons with the extant Latimeria. Here we describe a new genus and species of coelacanth, Graulia branchiodonta gen. et sp. nov. from the Middle Triassic of Eastern France, based on microtomographical imaging using synchrotron radiation. Through exquisite 3D preservation of the specimens, we reconstructed the skeletal anatomy of this new species at an unprecedented level of detail for an extinct coelacanth, and barely achieved for the extant Latimeria. In particular, we identified a well-developed trilobed ossified lung whose function is still uncertain. The skeletal anatomy of G. branchiodonta displays the general Bauplan of Mesozoic coelacanths and a phylogenetic analysis resolved it as a basal Mawsoniidae, shedding light on the early diversification of one of the two major lineages of Mesozoic coelacanths. However, despite its exquisite preservation, G. branchiodonta carries a weak phylogenetic signal, highlighting that the sudden radiation of coelacanths in the Early and Middle Triassic makes it currently difficult to detect synapomorphies and resolve phylogenetic interrelationships among coelacanths in the aftermath of the great Permo-Triassic biodiversity crisis.
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| Graulia branchiodonta gen. et sp. nov. Photographs of the specimens in laterodorsal view. (A) MHNG GEPI V5787, holotype. (B) MHNG GEPI V5788. |
Systematic paleontology
Class OSTEICHTHYES Huxley, 1880
Subclass SARCOPTERYGII Romer, 1955
Infraclass ACTINISTIA Cope, 1891
Order COELACANTHIFORMES Huxley, 1861
Suborder LATIMERIOIDEI Schultze, 1993
Family MAWSONIIDAE Schultze, 1993
Graulia branchiodonta gen. et sp. nov.
Holotype: MHNG GEPI V5787, complete specimen
Diagnosis: Mawsoniid coelacanth characterized by the following association of characters: anteromedial process of the posterior parietal present; one pair of lateral extrascapulars; few pores at the sutural contact with bones enclosing the supraorbital sensory canal.; the presence of anterior branches of the supratemporal commissure; a preoperculum with an anterior blade-like portion; a simple anterior end of the lachrymojugal; the infraorbital sensory canal running at the anterior margin of the postorbital; long teeth on the ceratobranchial tooth plates; denticles on the rays of the first dorsal fin and on the first rays of the dorsal lobe of the caudal fin; tri-lobed unpaired lung; scales ornamented with pointed small tubercles. Only known species, same diagnosis as for the genus.
Locality: Sarraltroff, 57400 Moselle, Grand Est, France.
Etymology: The genus name Graulia refers to the Graoully, Graouli or Graully, a mythical dragon from the folklore of Lorraine, the region of France where the specimens were found. The species name branchiodonta, from the greek βράγχια “gills” and ὀδούς, ὀδόντος “tooth” refers to the large teeth found on the ceratobranchials.
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| Graulia branchiodonta gen. et sp. nov., interpretative body reconstructions and detailed skull drawings in lateral view. (A) body profile. (B) lateral view of skull and pectoral girdle. (C) lateral view of skull and pectoral girdle with neurocranium highlighted. (D) lateral view of skull and pectoral girdle with palate and hyobranchial skeleton highlighted. |
Luigi Manuelli, Jorge Mondéjar Fernández, Kathleen Dollman, Kudakwashe Jakata and Lionel Cavin. 2024. The most detailed anatomical reconstruction of a Mesozoic coelacanth. PLoS ONE. 19(11): e0312026. DOI: doi.org/10.1371/journal.pone.0312026
