''Tribodus'' is an extinct genus of

hybodont Hybodontiformes, commonly called hybodonts, are an extinct group of shark-like cartilaginous fish (chondrichthyans) which existed from the late Devonian to the Late Cretaceous. Hybodonts share a close common ancestry with modern sharks and rays ( ...

. It lived during the mid Cretaceous (

Albian The Albian is both an age (geology), age of the geologic timescale and a stage (stratigraphy), stage in the stratigraphic column. It is the youngest or uppermost subdivision of the Early Cretaceous, Early/Lower Cretaceous epoch (geology), Epoch/s ...

Cenomanian The Cenomanian is, in the International Commission on Stratigraphy's (ICS) geological timescale, the oldest or earliest age (geology), age of the Late Cretaceous epoch (geology), Epoch or the lowest stage (stratigraphy), stage of the Upper Cretace ...

) with fossils being known from northern South America, North Africa, and southern Europe.R. Vullo, D. Néraudea
When the “primitive” shark ''Tribodus'' (Hybodontiformes) meets the “modern” ray ''Pseudohypolophus'' (Rajiformes), the unique co-occurrence of these two durophagous Cretaceous selachians in Charentes (SW France)
Acta Geologica Polonica, 58 (2) (2008), pp. 249-255

Description

This genus is known from articulated and somewhat complete specimens of ''Tribodus limae'' from the

Romualdo Formation The Romualdo Formation is a geologic Lagerstätte, Konservat-Lagerstätte in northeastern Brazil's Araripe Basin where the states of Pernambuco, Piauí and Ceará come together. The geological formation, previously designated as the Romualdo Mem ...

Açu Formation The Açu Formation is an Early Cretaceous (Albian) geologic geologic formation, formation of the Potiguar Basin in Ceará, northeastern Brazil. The formation comprises coarse-grained sandstones deposited in a fluvial, fluvio-river delta, deltaic ...

and

Alcântara Formation The Alcântara Formation is a geological Formation (geology), formation in Northeast Region, Brazil, northeastern Brazil whose strata date back to the Cenomanian of the Late Cretaceous. Fossil content Dinosaurs Sauropods Theropods ...

of northeastern Brazil, making it one of the few hybodonts to be known from full body remains. Like other hybodonts, ''Tribodus'' had dorsal fin-spines and cephalic spines in male individuals. The skin of ''Tribodus'' had two distinct types of

dermal denticles A fish scale is a small rigid plate that grows out of the skin of a fish. The skin of most jawed fishes is covered with these protective scales, which can also provide effective camouflage through the use of reflection and colouration, as w ...

. ''Tribodus limae'' reached a total length of about . The lower jaw was relatively short and did not extend to the snout region and articulated with the upper jaw at exclusively at the

hyoid arch The pharyngeal arches, also known as visceral arches'','' are transient structures seen in the embryonic development of humans and other vertebrates, that are recognisable precursors for many structures. In fish, the arches support the gills a ...

unlike other hybodonts, with a number of cartilage struts connecting the upper and lower jaws which enhanced jaw strength. The teeth of ''Tribodus'' were specialised for

durophagy Durophagy is the eating behavior of animals that consume Seashell, hard-shelled or exoskeleton-bearing organisms, such as corals, shelled mollusks, or crabs. It is mostly used to describe fish, but is also used when describing reptiles, including ...

(consuming hard shelled organisms). They were small, less than across and polygonal with a low cusp, and collectively formed a flat pavement that was effective at grinding, similar to those of living myliobatoid rays. It is suggested to have been a

benthic The benthic zone is the ecological region at the lowest level of a body of water such as an ocean, lake, or stream, including the sediment surface and some sub-surface layers. The name comes from the Ancient Greek word (), meaning "the depths". ...

feeder, with shrimp being discovered as stomach contents in some specimens. Species of ''Tribodus'' have been found in shallow marine as well as

fluvial A river is a natural stream of fresh water that flows on land or inside caves towards another body of water at a lower elevation, such as an ocean, lake, or another river. A river may run dry before reaching the end of its course if it ru ...

and

deltaic A river delta is a landform, archetypically triangular, created by the deposition of the sediments that are carried by the waters of a river, where the river merges with a body of slow-moving water or with a body of stagnant water. The creati ...

environments. It may have spawned in shallow-water vegetated areas.

Classification

Its placement within the Hybodontiformes is uncertain. Historically it has been asserted to be a member of the family Acrodontidae with other durophagous hybodonts, based on the presence of columnar osteodentine in its teeth. However, other authors have suggested that it should instead be placed in the family Distobatidae due the morphology of its teeth closely resembling members of that family.

References

Hybodontiformes Cretaceous cartilaginous fish Prehistoric fish of South America Early Cretaceous animals of South America Albian life Aptian life Cenomanian life Cretaceous Brazil Fossils of Brazil Romualdo Formation Fish described in 1989 Taxa named by Alberto Brito {{paleo-cartilaginous-fish-stub