Acleistorhinidae
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Acleistorhinidae is an
extinct Extinction is the termination of an organism by the death of its Endling, last member. A taxon may become Functional extinction, functionally extinct before the death of its last member if it loses the capacity to Reproduction, reproduce and ...
family Family (from ) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). It forms the basis for social order. Ideally, families offer predictabili ...
of Late Carboniferous and Early Permian-aged ( Moscovian to Kungurian stage)
parareptile Parareptilia ("near-reptiles") is an extinct group of Basal (phylogenetics), basal Sauropsida, sauropsids ("Reptile, reptiles"), traditionally considered the sister taxon to Eureptilia (the group that likely contains all living reptiles and birds ...
s. It is defined as a node based clade including the last common ancestor of '' Acleistorhinus pteroticus'' and '' Colobomycter pholeter'' and all its descendants. Acleistorhinids are most diverse from the Richards Spur locality of the Early Permian of
Oklahoma Oklahoma ( ; Choctaw language, Choctaw: , ) is a landlocked U.S. state, state in the South Central United States, South Central region of the United States. It borders Texas to the south and west, Kansas to the north, Missouri to the northea ...
. Richards Spur acleistorhinids include '' Acleistorhinus'', '' Colobomycter'', '' Delorhynchus'', '' Feeserpeton'' and '' Klastomycter''. Other taxa include '' Carbonodraco'' from the Late Carboniferous of
Ohio Ohio ( ) is a U.S. state, state in the Midwestern United States, Midwestern region of the United States. It borders Lake Erie to the north, Pennsylvania to the east, West Virginia to the southeast, Kentucky to the southwest, Indiana to the ...
and '' Karutia'' from the Early Permian of
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. Acleistorhinidae is commonly considered a subgroup of lanthanosuchoids, related to taxa such as '' Chalcosaurus'', '' Lanthaniscus'' and '' Lanthanosuchus''. However, a re-examination of parareptile phylogeny conducted by Cisneros ''et al.'' (2021) argued that lanthanosuchids were not closely related to acleistorhinids. The phylogenetic analysis conducted by these authors recovered acleistorhinids as the
sister group In phylogenetics, a sister group or sister taxon, also called an adelphotaxon, comprises the closest relative(s) of another given unit in an evolutionary tree. Definition The expression is most easily illustrated by a cladogram: Taxon A and ...
of the clade Procolophonia, while lanthanosuchids were recovered within the procolophonian subgroup Pareiasauromorpha. Acleistorhinidae is notable for being the oldest-known parareptilian clade. The family is diagnosed by the presence two synapomorphies: (1) the largest
tooth 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, tea ...
is located far anteriorly on the maxilla; and (2) cranial ornamentation consists of sparse and shallow circular dimples.


Diet

Two specimens of acleistorhinids described from the Richards Spur fissure-fill locality in
Oklahoma Oklahoma ( ; Choctaw language, Choctaw: , ) is a landlocked U.S. state, state in the South Central United States, South Central region of the United States. It borders Texas to the south and west, Kansas to the north, Missouri to the northea ...
have provided compelling evidence of the diet of acleistorhinids. One specimen, OMNH 73362, was later referred to '' Delorhynchus cifellii'', a species named in 2014. The other specimen, OMNH 73364, has not been formally described. Fragments of
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 ...
cuticles are present in between the many palatal teeth of both skulls. The fragments in OMNH 73362 are thought to be the segments of an antenna, while the fragments in OMNH 73364 are thought to be part of a cercus. In acleistorhinids, the marginal teeth, which are small and recurved, are suggestive of an insectivorous diet, as they probably were used for gripping and piercing arthropod cuticle. The denticulated palate, with three pairs of tooth fields and smaller teeth in between the fields, is seen as an adaptation for holding food in the oral cavity. The teeth, which possess cutting edges, may also have been suitable for a carnivorous diet in which vertebrate flesh may have been consumed. It is possible that acleistorhinids would have preyed on
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 ...
s that were small enough to swallow whole. It is likely that one acleistorhinid, ''Colobomycter pholeter'', specialized either on invertebrates with hard cuticles or on small tetrapods.


References

Prehistoric reptile families {{permian-reptile-stub