This is a typical Cladodont tooth, of a shark_called_''Glikmanius''.html" ;"title="Glikmanius.html" ;"title="shark called ''Glikmanius">shark called ''Glikmanius''">Glikmanius.html" ;"title="shark called ''Glikmanius">shark called ''Glikmanius'' Cladodont (from Latin cladus, meaning branch and Greek Odon, meaning tooth) is the term for a common category of early Devonian shark known primarily for its "multi-cusped" tooth consisting of one long blade surrounded by many short, fork-like

tines Tines (; also spelled tynes), prongs or teeth are parallel or branching spikes forming parts of a tool or natural object. They are used to spear, hook, move or otherwise act on other objects. They may be made of metal, wood, bone or other hard, ...

, designed to catch food that was swallowed whole, instead of being used to saw off chunks of meat like many modern sharks. The skinny teeth would puncture and grasp the prey, keeping it from wriggling free. Because the most common fossil evidence of

cartilaginous Cartilage is a resilient and smooth type of connective tissue. In tetrapods, it covers and protects the ends of long bones at the joints as articular cartilage, and is a structural component of many body parts including the rib cage, the neck and ...

fish is teeth, this term is also used for the

fossil A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved in ...

ised teeth themselves.

History

The fossil tooth of '' Cladodus belifer'', which lived about 260,000,000 years ago in what would someday be Illinois. The roundness of the main tooth, and the small tines around it, show it to be a cladodont. The earliest known

shark Sharks are a group of elasmobranch fish characterized by a cartilaginous skeleton, five to seven gill slits on the sides of the head, and pectoral fins that are not fused to the head. Modern sharks are classified within the clade Selachimor ...

, '' Cladoselache'', was a cladodont existing about 370 million years ago. It had the typical cladodont teeth, which probably also were not regularly replaced like those of modern sharks, but did appear to wear down from use. This shark did indeed appear to swallow its prey whole, fossil examples containing batches of fish arranged tail-first where the shark's stomach should be. Around this time, ''

Stethacanthus ''Stethacanthus'' is an extinct genus of shark-like holocephaliansCoates, M., Gess, R., Finarelli, J., Criswell, K., Tietjen, K. 2016. A symmoriiform chondrichthyan braincase and the origin of chimaeroid fishes. Nature. doi: 10.1038/nature208 ...

'' also begins to appear in the fossil record. Also a cladodont, it survived from the late Devonian to the early

Carboniferous The Carboniferous ( ) is a geologic period and system of the Paleozoic that spans 60 million years from the end of the Devonian Period million years ago ( Mya), to the beginning of the Permian Period, million years ago. The name ''Carboniferous ...

, dying out about 320 million years ago. While the earliest known sharks are cladodont, there is some evidence that they evolved from a common ancestor with "diplodonts", sharks whose teeth have two larger blades poking out, plus a small middle tine that could have become the main blade in cladodont teeth. Some cladodonts appear to have been in existence as recently as the Cretaceous period, based on cladodont teeth found in deep water deposits of Early Cretaceous (

Valanginian In the geologic timescale, the Valanginian is an age or stage of the Early or Lower Cretaceous. It spans between 139.8 ± 3.0 Ma and 132.9 ± 2.0 Ma (million years ago). The Valanginian Stage succeeds the Berriasian Stage of the Lower Cretac ...

) age in Austria and France. At one point,

frilled shark The frilled shark (''Chlamydoselachus anguineus'') and the southern African frilled shark (''Chlamydoselachus africana'') are the two extant species of shark in the family '' Chlamydoselachidae''. The frilled shark is considered a living fossil ...

s were thought to be living descendants of cladodonts, but they are now believed to simply be unrelated, curiously shaped sharks, despite similarly pointy, snagging teeth.

References

{{reflist Devonian sharks Early Devonian fish Teeth