''Echinochimaera'' ("prickly chimera") is an extinct

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial n ...

chimaeriform Chimaeras are cartilaginous fish in the order Chimaeriformes , known informally as ghost sharks, rat fish, spookfish, or rabbit fish; the last three names are not to be confused with rattails, Opisthoproctidae, or Siganidae, respectively. A ...

fish Fish are aquatic, craniate, gill-bearing animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish as well as various extinct related groups. Approximately 95% ...

, known from the Lower Carboniferous

Bear Gulch Limestone The Bear Gulch Limestone is a limestone-rich geological lens in central Montana, renowned for the quality of its late Mississippian-aged fossils. It is exposed over a number of outcrops northeast of the Big Snowy Mountains, and is often considere ...

Montana Montana () is a U.S. state, state in the Mountain states, Mountain West List of regions of the United States#Census Bureau-designated regions and divisions, division of the Western United States. It is bordered by Idaho to the west, North ...

United States The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country primarily located in North America. It consists of 50 U.S. state, states, a Washington, D.C., federal district, five ma ...

. It is one of the earliest Chimaeriformes known.

Taxonomy

The genus' name derives from the

Greek Greek may refer to: Greece Anything of, from, or related to Greece, a country in Southern Europe: *Greeks, an ethnic group. *Greek language, a branch of the Indo-European language family. **Proto-Greek language, the assumed last common ancestor ...

''εχινό'' (''echino'') meaning spiny, and

chimaera Chimaeras are cartilaginous fish in the order Chimaeriformes , known informally as ghost sharks, rat fish, spookfish, or rabbit fish; the last three names are not to be confused with rattails, Opisthoproctidae, or Siganidae, respectively. A ...

. It is assigned to the

order Order, ORDER or Orders may refer to: * Categorization, the process in which ideas and objects are recognized, differentiated, and understood * Heterarchy, a system of organization wherein the elements have the potential to be ranked a number of ...

Chimaeriformes.

Species

The two known ''Echinochimaera'' species lived in the

Upper Mississippian The Upper Mississippian cultures were located in the Upper Mississippi River, Mississippi basin and Great Lakes region of the American Midwest. They were in existence from approximately A.D. 1000 until the Protohistory, Protohistoric and early H ...

(

Serpukhovian The Serpukhovian is in the ICS geologic timescale the uppermost stage or youngest age of the Mississippian, the lower subsystem of the Carboniferous. The Serpukhovian age lasted from Ma to Ma. It is preceded by the Visean and is followed b ...

). Fossils of the species were found in the

. Both species have rounded bodies and paddle-like tails as well as large

pectoral Pectoral may refer to: * The chest region and anything relating to it. * Pectoral cross, a cross worn on the chest * a decorative, usually jeweled version of a gorget * Pectoral (Ancient Egypt), a type of jewelry worn in ancient Egypt * Pectoralis ...

fins, two

dorsal fin A dorsal fin is a fin located on the back of most marine and freshwater vertebrates within various taxa of the animal kingdom. Many species of animals possessing dorsal fins are not particularly closely related to each other, though through c ...

s and a

jaw The jaw is any opposable articulated structure at the entrance of the mouth, typically used for grasping and manipulating food. The term ''jaws'' is also broadly applied to the whole of the structures constituting the vault of the mouth and serv ...

fused to the

braincase In human anatomy, the neurocranium, also known as the braincase, brainpan, or brain-pan is the upper and back part of the skull, which forms a protective case around the brain. In the human skull, the neurocranium includes the calvaria or skul ...

. The paddle-like tails indicate that ''E. meltoni'' was likely not a predator nor a fast swimmer.

''Echinochimaera meltoni''

''E. meltoni'' was first described by Richard Lund, an

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palaeontologist Paleontology (), also spelled palaeontology or palæontology, is the scientific study of life that existed prior to, and sometimes including, the start of the Holocene epoch (roughly 11,700 years before present). It includes the study of fossi ...

, in 1977. The fossils found of ''E. meltoni'' have shown a great deal of

sexual dimorphism Sexual dimorphism is the condition where the sexes of the same animal and/or plant species exhibit different morphological characteristics, particularly characteristics not directly involved in reproduction. The condition occurs in most an ...

, males being found to have a maximum 150mm body length while the maximum body length found in females was only 70mm (juveniles were 13-20mm). In general, the females only grew to about half the size of the males. Males also had four pairs of spikes which may have been used to defend against

predator Predation is a biological interaction where one organism, the predator, kills and eats another organism, its prey. It is one of a family of common feeding behaviours that includes parasitism and micropredation (which usually do not kill ...

s and to identify the fish as male. There was a relative abundance of immature male fossils found, and that together with the significant sexual dimorphism indicate there was extreme

sexual selection Sexual selection is a mode of natural selection in which members of one biological sex choose mates of the other sex to mate with (intersexual selection), and compete with members of the same sex for access to members of the opposite sex (in ...

among the species.

''Echinochimaera snyderi''

''E. snyderi'' was described, like ''E. meltoni'', by Richard Lund. It was described in 1988 based on juvenile specimens, all with a body length under 90mm. ''E. snyderi'' differs from ''E. meltoni'' in fin detail as well as jaw shape and teeth near the front edge of the face rather than a tooth plate, in mature specimens later found its mature size was found to be larger than ''E. meltoni''.

References

{{Taxonbar, from=Q3718511 Carboniferous cartilaginous fish Prehistoric cartilaginous fish genera Chimaeriformes Mississippian fish of North America Fossil taxa described in 1977