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''Barbclabornia'' is an extinct
genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...
of xenacanth from the Early
Permian The Permian ( ) is a geologic period and System (stratigraphy), stratigraphic system which spans 47 million years, from the end of the Carboniferous Period million years ago (Mya), to the beginning of the Triassic Period 251.902 Mya. It is the s ...
and possibly upper Pennsylvanian of
North America North America is a continent in the Northern Hemisphere, Northern and Western Hemisphere, Western hemispheres. North America is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South Ameri ...
. The genus contains a single described species: ''B. luedersensis''. It has been found in several places within Asselian and Atinskian formations, including the Clear Fork, Albany, Wichita, and Dunkard Groups. There are possible examples from the Gzhelian-aged Admire, Monongahela, and Conemaugh groups.


Discovery

''Barbclabornia'' was initially only known from isolated
teeth A tooth (: teeth) is a hard, calcified structure found in the jaws (or mouths) of many vertebrates and used to break down food. Some animals, particularly carnivores and omnivores, also use teeth to help with capturing or wounding prey, tear ...
, which were assigned to the genus ''
Xenacanthus ''Xenacanthus'' (from Ancient Greek wikt:ξένος, ξένος, xénos, 'foreign, alien' + wikt:ἄκανθος, ἄκανθος, akanthos, 'spine') is an extinct genus of Xenacanthida, xenacanth cartilaginous fish. It lived in freshwater environ ...
'' in 1970 based on the belief that all Upper
Paleozoic The Paleozoic ( , , ; or Palaeozoic) Era is the first of three Era (geology), geological eras of the Phanerozoic Eon. Beginning 538.8 million years ago (Ma), it succeeds the Neoproterozoic (the last era of the Proterozoic Eon) and ends 251.9 Ma a ...
xenacanthids belonged to said genus. In 2003, ''X. luedersensis'' would be reassigned to a new genus after differences in tooth structure were described, and with the discovery of a large palatoquadrate bearing ''luedersensis'' teeth at Lake Frederick. The genus ''Barbclabornia'' honors Barbara and Alvie Claborn, who discovered and helped prepare the palatoquadrate respectively.


Description

The teeth of ''Barbclabornia'' are similar to those of '' Bransonella'', and as such are believed to be related. They are very small, being between 1–3 mm tall. They are bicuspid, functionally homodont, and characterized by cristated, cylindrical, cone-like cusps. In contrast to other xenacanth species, these teeth have no central cusp. The anterior teeth possess triangular bases, while the lateral and posterolateral teeth have quadrangular bases. These bases are thick, amounting to 30% of the tooth height. Monocuspid denticles, the largest of which being barely over 2 mm tall, are mostly remarkably claw-like in appearance. These denticles are assumed to be from the mucous membrane fold. ''Barbclabornia'' is also known from a right palatoquadrate, which contains hundreds of these tiny teeth. The palatoquadrate is 37.5 cm (14.7 in) long and incomplete, but is assumed to have a total length of 45 cm (17.7 in). The palatoquadrate is thinner than that of other large xenacanthids, like '' Orthacanthus'', and has a lighter build. Based on other xenacanths, if ''Barbclabornia'''s total length is 10 to 11 times as long as its jaws, it is estimated to have a total length of 4.5 to 5 m (14 to 15 ft) long. This would make it the largest xenacanthid ever found.


Paleoecology

Based on the locations where a majority of specimens have been found, being freshwater dominant and
tetrapod A tetrapod (; from Ancient Greek :wiktionary:τετρα-#Ancient Greek, τετρα- ''(tetra-)'' 'four' and :wiktionary:πούς#Ancient Greek, πούς ''(poús)'' 'foot') is any four-Limb (anatomy), limbed vertebrate animal of the clade Tetr ...
-bearing, ''Barbclabornia'' is most likely a freshwater species, inhabiting
coastal plain A coastal plain (also coastal plains, coastal lowland, coastal lowlands) is an area of flat, low-lying land adjacent to a sea coast. A fall line commonly marks the border between a coastal plain and an upland area. Formation Coastal plains can f ...
s of North America. Combined δ18OP and 87Sr/86Sr measurements confirm that ''Barbclabornia'' was a freshwater inhabitant. The diet of ''Barbclabornia'' can be inferred from its teeth, jaws, and size. Paleontologist Gary D. Johnson initially proposed that the shark could only bite down on its prey and swallow it whole. This would give it a diet of less active prey, primarily small
fish A fish (: fish or fishes) is an aquatic animal, aquatic, Anamniotes, anamniotic, gill-bearing vertebrate animal with swimming fish fin, fins and craniate, a hard skull, but lacking limb (anatomy), limbs with digit (anatomy), digits. Fish can ...
,
amphibian Amphibians are ectothermic, anamniote, anamniotic, tetrapod, four-limbed vertebrate animals that constitute the class (biology), class Amphibia. In its broadest sense, it is a paraphyletic group encompassing all Tetrapod, tetrapods, but excl ...
s, and
arthropod Arthropods ( ) are invertebrates in the phylum Arthropoda. They possess an arthropod exoskeleton, exoskeleton with a cuticle made of chitin, often Mineralization (biology), mineralised with calcium carbonate, a body with differentiated (Metam ...
s. However, Johnson alongside Jiri Zidek, William May, and Alvie Claborn would instead compare the large xenacanth with numerous tiny teeth to be
analogous Analogy is a comparison or correspondence between two things (or two groups of things) because of a third element that they are considered to share. In logic, it is an inference or an argument from one particular to another particular, as oppose ...
to modern
filter feeding Filter feeders are aquatic animals that acquire nutrients by feeding on organic matters, food particles or smaller organisms (bacteria, microalgae and zooplanktons) suspended in water, typically by having the water pass over or through a spe ...
sharks, the
Basking Shark The basking shark (''Cetorhinus maximus'') is the second-largest living shark and fish, after the whale shark. It is one of three Planktivore, plankton-eating shark species, along with the whale shark and megamouth shark. Typically, basking sh ...
and
Whale Shark The whale shark (''Rhincodon typus'') is a slow-moving, filter feeder, filter-feeding carpet shark and the largest known Extant taxon, extant fish species. The largest confirmed individual had a length of . The whale shark holds many records for ...
. This would indicate that ''Barbclabornia'' was a filter feeder which would primarily consume
zooplankton Zooplankton are the heterotrophic component of the planktonic community (the " zoo-" prefix comes from ), having to consume other organisms to thrive. Plankton are aquatic organisms that are unable to swim effectively against currents. Consequent ...
.


References


Further reading

* {{Taxonbar, from=Q25399731, from2=Q25363914 Xenacanths Prehistoric cartilaginous fish Monotypic prehistoric cartilaginous fish genera Paleozoic animals of North America Fossil taxa described in 1970 Permian cartilaginous fish Carboniferous cartilaginous fish