Thursday, March 30, 2023

[PaleoIchthyology • 2023] Maghriboselache mohamezanei • Broad Snouted cladoselachian (Symmoriiformes: Cladoselachidae) with Sensory Specialization at the Base of modern Chondrichthyans

Maghriboselache mohamezanei 
Klug, Coates, Frey, Greif, Jobbins, Pohle, Lagnaoui, Haouz & Ginter, 2023

Throughout the Silurian and Devonian, cartilaginous fish successively evolved their specialized skeletal and dental characteristics, and increasingly refined their sensory systems. The Late Devonian shark taxon Maghriboselache mohamezanei gen. et sp. n. from the eastern Anti-Atlas of Morocco is known from multiple specimens preserving most of its skeletal features, which in some instances are preserved in three dimensions. Key details of the dentition, jaws, and pectoral skeleton are shared with the iconic genus Cladoselache. Phylogenetic analyses place the family Cladoselachidae as the sister group of symmoriiforms and these groups as sister group of the holocephalans. Further phylogenetic results corroborate that the initial evolutionary radiation of crown chondrichthyans occurred within or before the Late Devonian. Remarkably, this new stem holocephalan is equipped with a wide snout and large laterally separated nasal capsules: the earliest known example of this condition in the chondrichthyan and (perhaps) gnathostome record. This suggests sensory specialization approaching that of extant broad-rostrum elasmobranchs and represents a significant addition to increasingly apparent ecomorphological diversity among early chondrichthyans.

Photo and drawing of a nearly complete skeleton of Maghriboselache mohamezanei n. gen. et sp., AA.BER.DS.01. The marked fin spine belongs to the posterior fin

Skeletal reconstruction of possibly a male (A dorsal. B lateral) and possibly a female (C bottom, lateral) of Maghriboselache mohamezanei n. gen. et sp. The according details were collected from the mentioned specimens. Note the presence of anterior dorsal fin spine in the supposed males, possibly serving a role during copulation. Claspers are not present in the supposed males of our sample. The photos show the according regions of specimens displayed in Fig. 1 and the Additional file 1

Systematic palaeontology
Chondrichthyes (Huxley, 1880).
Holocephali (Bonaparte, 1838).

Symmoriiformes (Zangerl, 1981).
Cladoselachidae (Dean, 1909a).

Diagnosis: Symmoriiform chondrichthyans with pectoral fins with distally broad, flat, strap-like radials. Cleaver-shaped palatoquadrate with otic process shorter than palatine process; jaw articulation barely posterior to occipital level. Teeth with tall median cusp flanked by much smaller lateral cusps and tooth base with a deep basolabial depression flanked by adjacent projections.

Remarks: This family now comprises the genera Cladoselache and Maghriboselache, thus far limited to the Famennian of the USA and Morocco.

Maghriboselache gen. n.

Etymology: From the Arabic word al Maghrib for Morocco and the Greek word σέλαχος (selachos) for cartilaginous fish.
Diagnosis: Cladoselachiid distinguished by neurocranium with broad flattened rostrum enclosing large, widely separated, nasal capsules. Rostral span, including the nasal capsules, matches span of the postorbital arcade. Postorbital arcade surrounds small jugular foramen. Ventral extremity of postorbital arcade extends anteriorly, contributing to orbit floor and almost meeting posterolateral extremity of rostral cartilage and postnasal wall. Otic process of palatoquadrate anteroposteriorly short, in lateral view terminating level with, or just caudal to, the posterior extremity of the occipital cartilage. Dentition with enlarged teeth on the mandibular symphysis. Scapulocoracoid with ventrally broad scapula process and sturdy coracoid region with slender, distinct, procoracoid cartilage. Anterior dorsal fin spine (if present): long, laterally flattened and smooth, curved posteriorly throughout length.

Maghriboselache mohamezanei sp. n.
Holotype: AA.MEM.DS.12, which preserves the 3D neurocranium, teeth, shoulder girdle, and most fins, and hence most of the relevant body parts.
Age: Thylacocephalan Layer, late early to early middle Famennian, Late Devonian.

Type locality: Mousgar, southern Maïder, southeastern Anti-Atlas, Morocco.

Etymology: Referring to Moha Mezane (El Khraouia & Merzouga, Morocco), French linguist and amateur geologist, specialized in fossils and minerals from the southern Tafilalt. He found many important specimens including some of the material described here.

Reconstruction of Maghriboselache mohamezanei n. gen. et sp. in its habitat. Thylacocephalans, cephalopods with orthoconic conchs, placoderms such as Dunkleosteus and osteichthyans populated the water column during the middle Famennian in the Anti-Atlas

Christian Klug, Michael Coates, Linda Frey, Merle Greif, Melina Jobbins, Alexander Pohle, Abdelouahed Lagnaoui, Wahiba Bel Haouz and Michal Ginter. 2023. Broad Snouted cladoselachian with Sensory Specialization at the Base of modern Chondrichthyans. Swiss Journal of Palaeontology.  142:2. DOI: 10.1186/s13358-023-00266-6