| Tribodus Temporal range: | |
|---|---|
Scientific classification  | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Chondrichthyes |
| Subclass: | Elasmobranchii |
| Order: | † Hybodontiformes |
| Genus: | † Tribodus Brito & Ferreira, 1989 |
| Type species | |
| †Tribodus limae Brito & Ferreira, 1989 | |
| Other species | |
| |
Tribodus is an extinct genus of hybodont. It lived during the mid Cretaceous (Albian-Cenomanian) with fossils being known from northern South America, North Africa, and southern Europe. [1]
This genus is known from articulated and somewhat complete specimens of Tribodus limae from the Romualdo Formation and Alcântara Formation of northeastern Brazil, making it one of the few hybodonts to be known from full body remains. [2] [3] Like other hybodonts, Tribodus had dorsal fin-spines and cephalic spines in male individuals. [3] The skin of Tribodus had two distinct types of dermal denticles. [4] Tribodus limae reached a total length of about 1 metre (3.3 ft). [5] 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 unlike other hybodonts, with a number of cartilage struts connecting the upper and lower jaws which enhanced jaw strength. [3] The teeth of Tribodus were specialised for durophagy (consuming hard shelled organisms). They were small, less than 5 millimetres (3⁄16 in) 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. [1] [6] [3] It is suggested to have been a benthic feeder, with shrimp being discovered as stomach contents in some specimens. [3]
Species of Tribodus have been found in shallow marine as well as fluvial and deltaic environments. It may have spawned in shallow-water vegetated areas. [5]
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. [3] 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. [7]
Chondrichthyes is a class of jawed fish that contains the cartilaginous fish or chondrichthyans, which all have skeletons primarily composed of cartilage. They can be contrasted with the Osteichthyes or bony fish, which have skeletons primarily composed of bone tissue. Chondrichthyes are aquatic vertebrates with paired fins, paired nares, placoid scales, conus arteriosus in the heart, and a lack of opercula and swim bladders. Within the infraphylum Gnathostomata, cartilaginous fishes are distinct from all other jawed vertebrates.
Elasmobranchii is a subclass of Chondrichthyes or cartilaginous fish, including modern sharks, rays, skates, and sawfish. Members of this subclass are characterised by having five to seven pairs of gill clefts opening individually to the exterior, rigid dorsal fins and small placoid scales on the skin. The teeth are in several series; the upper jaw is not fused to the cranium, and the lower jaw is articulated with the upper. The details of this jaw anatomy vary between species, and help distinguish the different elasmobranch clades. The pelvic fins in males are modified to create claspers for the transfer of sperm. There is no swim bladder; instead, these fish maintain buoyancy with large livers rich in oil.
Cladoselache is an extinct genus of shark-like chondrichthyan from the Late Devonian (Famennian) of North America. It was similar in body shape to modern lamnid sharks, but was not closely related to lamnids or to any other modern (selachian) shark. As an early chondrichthyan, it had yet to evolve traits of modern sharks such as accelerated tooth replacement, a loose jaw suspension, enameloid teeth, and possibly claspers.
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Ptychodus is a genus of extinct large durophagous (shell-crushing) lamniform sharks from the Cretaceous period, spanning from the Albian to the Campanian. Fossils of Ptychodus teeth are found in many Late Cretaceous marine sediments worldwide.
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 (Neoselachii) as part of the clade Euselachii. They are distinguished from other chondrichthyans by their distinctive fin spines and cephalic spines present on the heads of males. An ecologically diverse group, they were abundant in marine and freshwater environments during the late Paleozoic and early Mesozoic, but were rare in open marine environments by the end of the Jurassic, having been largely replaced by modern sharks, though they were still common in freshwater and marginal marine habitats. They survived until the end of the Cretaceous, before going extinct.
Onchopristis is an extinct genus of sclerorhynchoid from the Cretaceous of North Africa, Europe, and North America. Its name is derived from the Ancient Greek ónkos and prístis. It contains two valid species, O. numida and O. dunklei, though some researchers argue that both may be considered a single taxon with variation in morphology caused by a wide geographical range. Specimens of Onchopristis have been discovered in coastal and fluvial deposits dated from the Barremian to the Maastrichtian age, making this genus one of the oldest and longest-lived sclerorhynchoid genera.
Lonchidion is a genus of extinct hybodont in the family Lonchidiidae. The genus first appears in the fossil record during the Middle Triassic (Ladinian) and was among the last surviving hybodont genera, with its youngest known fossils dating to the very end of the Cretaceous (Maastrichtian).
Meristodonoides is an extinct genus of hybodont. The type species is M. rajkovichi, which was originally a species in the genus Hybodus. The species, along with other Hybodus species such as H. butleri and H. montanensis, was reassigned to Meristodonoides by Charlie J. Underwood and Stephen L. Cumbaa in 2010. The species is primarily known from remains from the Cretaceous of North America, spanning from the Aptian/Albian to Maastrichtian, making it one of the last surviving hybodont genera, though records of the genus likely extend as far back as the Late Jurassic, based on an undescribed skeleton from the Tithonian of England, and fragmentary teeth from the Kimmeridgian of Poland, England and Switzerland. Other remains of the genus are known from the Coniacian of England, the Aptian-Albian of France, and the Campanian of European Russia. The morphology of the teeth suggests an adaptation to tearing prey. Fossils from the Western Interior Seaway suggest that it preferred nearshore marine environments, being absent from deeper-water areas, with it likely also being able to tolerate brackish and freshwater conditions.
Roulletia is an extinct genus of sand sharks or Haimirichiid shark. It was described by Romain Vullo, Henri Cappetta, and Didier Néraudeau in 2007, and the type species is R. bureaui, which existed during the upper Cenomanian of what is now France. The genus was named after its type locality, Roullet-Saint-Estèphe, while the species epithet honours Michel Bureau, an amateur paleontologist who gathered the material for the species. Another species, R. canadensis, was described from the Cenomanian of Canada by Charlie J. Underwood and Stephen L. Cumbaa in 2010. The species epithet refers to the country in which it was discovered. It has been suggested tentatively this genus may be related to Haimirichia, which has been placed in its own family (Haimirichiidae) based on soft-tissue preservation.
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