Cladoselache
Overview
Cladoselache is a genus
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...

 of extinct
Extinction
In biology and ecology, extinction is the end of an organism or of a group of organisms , normally a species. The moment of extinction is generally considered to be the death of the last individual of the species, although the capacity to breed and recover may have been lost before this point...

 shark
Shark
Sharks are a type of fish with a full cartilaginous skeleton and a highly streamlined body. The earliest known sharks date from more than 420 million years ago....

. It appeared in the Devonian
Devonian
The Devonian is a geologic period and system of the Paleozoic Era spanning from the end of the Silurian Period, about 416.0 ± 2.8 Mya , to the beginning of the Carboniferous Period, about 359.2 ± 2.5 Mya...

 period.

This primitive shark grew to be up to 6 feet (1.8 m) long and roamed the oceans of North America. It is known to have been a fast moving and fairly agile predator due to its streamlined body and deep forked tail. Cladoselache is one of the best known of the early sharks in part due to the well preserved fossil
Fossil
Fossils are the preserved remains or traces of animals , plants, and other organisms from the remote past...

s that were discovered on the 'Cleveland Shale' on the south shore of Lake Erie.
Encyclopedia
Cladoselache is a genus
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...

 of extinct
Extinction
In biology and ecology, extinction is the end of an organism or of a group of organisms , normally a species. The moment of extinction is generally considered to be the death of the last individual of the species, although the capacity to breed and recover may have been lost before this point...

 shark
Shark
Sharks are a type of fish with a full cartilaginous skeleton and a highly streamlined body. The earliest known sharks date from more than 420 million years ago....

. It appeared in the Devonian
Devonian
The Devonian is a geologic period and system of the Paleozoic Era spanning from the end of the Silurian Period, about 416.0 ± 2.8 Mya , to the beginning of the Carboniferous Period, about 359.2 ± 2.5 Mya...

 period.

This primitive shark grew to be up to 6 feet (1.8 m) long and roamed the oceans of North America. It is known to have been a fast moving and fairly agile predator due to its streamlined body and deep forked tail. Cladoselache is one of the best known of the early sharks in part due to the well preserved fossil
Fossil
Fossils are the preserved remains or traces of animals , plants, and other organisms from the remote past...

s that were discovered on the 'Cleveland Shale' on the south shore of Lake Erie. In addition to the skeleton, the fossils were so well preserved that they included traces of skin, muscle fibres, and internal organs, such as the kidney
Kidney
The kidneys, organs with several functions, serve essential regulatory roles in most animals, including vertebrates and some invertebrates. They are essential in the urinary system and also serve homeostatic functions such as the regulation of electrolytes, maintenance of acid–base balance, and...

s.

Appearance

Cladoselache exhibited a combination of derived and ancestral characteristics. It had anatomical features similar to the current mackerel sharks of the family Lamnidae
Lamnidae
Lamnidae is a family of sharks, commonly known as mackerel sharks or white sharks. They are large, fast-swimming sharks, found in oceans worldwide....

.

It had a streamlined body, from five to seven gill slit
Gill slit
Gill slits are individual openings to gills, i.e., multiple gill arches, which lack a single outer cover. Such gills are characteristic of Cartilaginous fish such as sharks, rays, sawfish, and guitarfish. Most of these have five pairs, but a few species have 6 or 7 pairs...

s, and a short, rounded snout that had a terminal mouth opening at the front of the skull. It had a very weak jaw joint compared with modern-day sharks, but it compensated for that with very strong jaw-closing muscles. Its teeth were multi-cusped and smooth-edged, making them suitable for grasping, but not tearing or chewing. Cladoselache therefore probably seized prey by the tail and swallowed it whole.

Its sturdy but light-weight fin spines were composed of dentine and enamel. Cladoselache also had a blade-like structure which was positioned in front of the dorsal fins. These anatomical features made swimming easier and faster.

Unlike most sharks, Cladoselache was almost entirely devoid of scale
Scale (zoology)
In most biological nomenclature, a scale is a small rigid plate that grows out of an animal's skin to provide protection. In lepidopteran species, scales are plates on the surface of the insect wing, and provide coloration...

s with exception of small cusped scales on the edges of the fins, mouth and around the eyes. It also had powerful keels that extended onto the side of the tail stalk and a semi-lunate tail fin, with the superior lobe about the same size as the inferior. This combination helped with its speed and agility which was useful when trying to outswim its probable predator, the heavily armored 10 metres (32.8 ft) long placoderm fish Dunkleosteus
Dunkleosteus
Dunkleosteus is a genus of prehistoric fish, one of the largest arthrodire placoderms ever to have lived, existing during the Late Devonian period, about 380-360 million years ago.This hunter, measuring up to and weighing , was a hypercarnivorous apex predator...

.

Palaeobiology

Members of the Cladoselache genus were predatory sharks, and the well preserved fossils found on the Cleveland Shale revealed a significant amount regarding their eating habits. Within the gut of most Cladoselache fossils were remnants of their stomach contents. These remains included mostly small ray-finned bony fishes, as well as shrimp-like fish and hagfish
Hagfish
Hagfish, the clade Myxini , are eel-shaped slime-producing marine animals . They are the only living animals that have a skull but not a vertebral column. Along with lampreys, hagfish are jawless and are living fossils whose next nearest relatives include all vertebrates...

-like proto-vertebrates. Some of the fish remains were found tail first within the stomach, indicating that Cladoselache was a fast and agile hunter.

A mystery that has yet to be resolved is its method of reproduction. Cladoselache lacked claspers, organs found in modern sharks that are responsible for the transfer of sperm
Sperm
The term sperm is derived from the Greek word sperma and refers to the male reproductive cells. In the types of sexual reproduction known as anisogamy and oogamy, there is a marked difference in the size of the gametes with the smaller one being termed the "male" or sperm cell...

 during reproduction. This is peculiar given that most other early shark fossils show evidence of claspers. While they may have used internal fertilization
Internal fertilization
In mammals, internal fertilization is done through copulation, which involves the insertion of the penis into the vagina. Some other higher vertebrate animals reproduce internally, but their fertilization is cloacal.The union of spermatozoa of the parent organism. At some point, the growing egg or...

, this has yet to be demonstrated.

External links

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