Myledaphus

Myledaphus is an extinct genus of guitarfish. It currently contains four valid species found in North America (M. bipartitus, M. pustulosus), South America (M. araucanus), and Central Asia (M. tritus).^[4] It is confirmed to have lived during the Late Cretaceous, with possible occurrences in the Paleocene and early Eocene.^[3][5] While the genus is mostly known from teeth, two partial skeletons of M. bipartitus have been found in the Dinosaur Park Formation of Alberta.^[6]

Myledaphus Temporal range: Turonian-Maastrichtian (possible Paleogene occurrences) PreꞒ Ꞓ O S D C P T J K Pg N
Myledaphus bipartitus
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Class:	Chondrichthyes
Subclass:	Elasmobranchii
Order:	Rhinopristiformes
Family:	Rhinobatidae
Genus:	†Myledaphus Cope, 1876[1]
Type species
†Myledaphus bipartitus Cope, 1876
Other species
†Myledaphus tritus Nessov in Nessov & Udovitschenko, 1986[2] †Myledaphus pustulosus Cook, Newbrey, Brinkman, & Kirkland, 2014[3] †Myledaphus araucanus Otero, 2019[4]

Biology

Tooth of Myledaphus bipartitus

Close up of Myledaphus bipartitus jaws.

Myledaphus remains have been found both in marine and fluvial (freshwater) deposits, suggesting it could tolerate a range of salinity.^[7] This genus was able to move into the North American continent due to an intercontinental seaway flood that happened later on in the cretaceous period.^[8] In the Hell Creek Formation, composed predominantly of floodplain and riverine deposits, Myledaphus teeth are very common, accounting for a significant fraction of vertebrate remains found in microsites.^[7]

Skeleton of M. bipartitus

Myledaphus has a durophagus dentition with blunt, polygonal-shaped (hexagonal to rhombic) teeth tessellated into a pavement suited for crushing and grinding hard-bodied prey. Their tooth shape are commonnly described as ray teeth.^[9] Many of their teeth show wear consistent with feeding on mollusks, which were common in the rivers of North America during the Late Cretaceous.^[7]

Myledaphus also have other traits aside from their teeth that can help identify them. Many of their fossils exhibit very similar shapes such as having "large pectoral fins that do not expand anterior to the eyes" but actually they serve to " form an angular disk that expands caudually".^[10]