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| Toarcocephalus morlok Cooper, López-Arbarello & Maxwell, 2024 DOI: 10.26879/1326 Artwork by S. Cooper. |
ABSTRACT
The non-neopterygian group †Coccolepididae, a moderately diverse predominantly freshwater family, remains an imperfectly known Mesozoic group of actinopterygians, currently classified within Chondrostei based on the presence of several acipenseriform synapomorphies. Coccolepidids first appear during the Early Jurassic in marine sediments, although their fossils are poorly known from this time, and none have yet been described from the Toarcian (Upper Lias). Here, we describe a new genus and species of coccolepidid fish, †Toarcocephalus morlok gen. et sp. nov. from the Lower Jurassic (Toarcian) Posidonienschiefer Formation of Holzmaden in southern Germany. †Toarcocephalus morlok is diagnosed by a unique combination of characters including a shallow lower jaw with a massive angular, opercle and subopercle equal in size, preopercle that only borders the subopercle but does not reach the opercle; dermal skull bones strongly punctate, with externally smooth upper and lower jaw bones. Discovery of a coccolepidid at Holzmaden represents the first occurrence of the group from a Toarcian deposit, as well as the oldest record of the family in mainland Europe. Both described specimens of †T. morlok were victims of successful predation events: one individual was likely decapitated (pabulite) and the other preserved within a regurgitalite (fossilized oral ejecta). The evolution of Coccolepididae is discussed briefly in relation to a marine/freshwater origin.
Keywords: Coccolepididae; Chondrostei; Posidonienschiefer Formation; Early Jurassic; paleobiogeography; regurgitalite
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| Cranial reconstruction of †Toarcocephalus morlok gen. et sp. nov. with missing regions based on reconstruction of ‘Coccolepis’ liassica in Gardiner (1960). Missing or speculative areas are indicated with a dashed line and coloured in grey. Abbreviations: ag = angular; an = antorbital; br = branchiostegal rays; cl = cleithrum; d = dentary; dpt = dermopterotic; dsph = dermosphenotic; esc = extrascapular; g = gular plate; hyo = hyomandibula; io.c = infraorbital sensory canal; j = jugal; msc = mandibular sensory canal; mx = maxilla; na = nasal; nar = external naris; op = opercle; poc = postorbital canal; pop = preopercle; ro = rostral; scl = supracleithrum; scr = sclerotic ring; sop= subopercle. |
SYSTEMATIC PALAEONTOLOGY
Class ACTINOPTERYGII Cope, 1887
Subclass ?CHONDROSTEI Müller, 1845 sensu Grande and Bemis (1996)
Family †COCCOLEPIDIDAE Berg, 1940 sensu López-Arbarello et al. (2013)
†Toarcocephalus gen. nov.
†Toarcocephalus morlok gen. et sp. nov.
Diagnosis. †Toarcocephalus morlok gen. et sp. nov. is diagnosed from all other coccolepidid fishes by the following unique combination of characters: upper and lower jaws smooth and unornamented; mandible well elongated and gracile, longer than maxilla and shallow posteriorly; angular large and lenticular; large postorbital expansion of maxilla strongly convex and twice as long as deep with a strongly recurved ventral margin; short premaxilla holding several recurved teeth that are slightly larger than those on the maxilla; skull roof very weakly tuberculated with pronounced striated ridges that are marginally serrated; subopercle trapezoidal and equal in size to opercle; preopercle slender, forming a posteroventral lobular expansion, only as tall as the subopercle and extending no further than the midpoint of the postorbital plate of the maxilla; operculum and supracleithrum mostly smooth with fine, regularly spaced punctae; supracleithrum massive, accounting for more than 80% of operculum height; large triangular dorsal process on the supracleithrum; nine branchiostegal rays, each thin, lacking distal expansions and confined to the posterior corner of the mandible; gular plate egg-shaped and placed roughly at the midpoint of the lower jaw length; elongated hyomandibula obliquely inclined forward, thin and weakly bow-shaped; ceratohyal well elongated but thin; hypohyals short and robust; sclerotic ring thin and delicate; scales weakly developed; vertebral column aspondylous, composed of simple arcocentral arches with proportionately short spines.
Etymology. Generic name chosen for its discovery in Toarcian-aged strata, with suffix -cephalus for head, denoting the diagnostic cranium. Species epithet morlok named after the savage subterranean antagonists in H.G. Wells’ The Time Machine (1895), due to their similarly grotesque appearance characterised by large eyes, a blunt face and pointed teeth.
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| Palaeoart depiction of †Toarcocephalus morlok gen. et sp. nov. swimming in the twilight of the Posidonia Shale Sea. The post-cranium is based on †‘Coccolepis’ liassica and †Coccolepis bucklandi. Artwork by S. Cooper. |
Samuel L.A. Cooper, Adriana López-Arbarello and Erin E. Maxwell. 2024. First Occurrence of A †coccolepidid fish (?Chondrostei: †Coccolepididae) from the Upper Lias (Toarcian, Early Jurassic) of southern Germany. Palaeontologia Electronica. 27(1):a23. DOI: 10.26879/1326
