''Gorgodon'' 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 ...

basal Basal or basilar is a term meaning ''base'', ''bottom'', or ''minimum''. Science * Basal (anatomy), an anatomical term of location for features associated with the base of an organism or structure * Basal (medicine), a minimal level that is nec ...

synapsid Synapsids + (, 'arch') > () "having a fused arch"; synonymous with ''theropsids'' (Greek, "beast-face") are one of the two major groups of animals that evolved from basal amniotes, the other being the sauropsids, the group that includes rep ...

s. The genus is

monotypic In biology, a monotypic taxon is a taxonomic group (taxon) that contains only one immediately subordinate taxon. A monotypic species is one that does not include subspecies or smaller, infraspecific taxa. In the case of genera, the term "unispec ...

, known only from the

type species In zoological nomenclature, a type species (''species typica'') is the species name with which the name of a genus or subgenus is considered to be permanently taxonomically associated, i.e., the species that contains the biological type specimen( ...

''Gorgodon minutus'' from the

Early Permian 01 or '01 may refer to: * The year 2001, or any year ending with 01 * The month of January * 1 (number) Music * 01'' (Richard Müller album), 2001 * ''01'' (Son of Dave album), 2000 * ''01'' (Urban Zakapa album), 2011 * ''O1'' (Hiroyuki Sawano ...

of the southwestern United States. The only known remains of ''Gorgodon'' are two

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 ...

s consisting of fragments of the

skull The skull is a bone protective cavity for the brain. The skull is composed of four types of bone i.e., cranial bones, facial bones, ear ossicles and hyoid bone. However two parts are more prominent: the cranium and the mandible. In humans, t ...

. ''Gorgodon'' was described and named by paleontologist

Everett C. Olson Everett Claire Olson (November 6, 1910 – November 27, 1993) was an American zoologist, paleontologist, and geologist noted for his seminal research of origin and evolution of vertebrate animals. Through his research studying terrestrial verte ...

in 1962 from the

San Angelo Formation The San Angelo Formation is a geologic formation in Texas. It preserves fossils dating back to the Permian period. It is one of the geologically youngest formations to preserve fossils of pelycosaurs. Stratigraphy and age The San Angelo Formati ...

Knox County, Texas Knox County is a county located in the U.S. state of Texas. As of the 2020 census, its population was 3,353. Its county seat is Benjamin. The county was created in 1858 and later organized in 1886. It is named for Henry Knox, an American Revol ...

. Based on what is known of ''Gorgodon''—the

squamosal The squamosal is a skull bone found in most reptiles, amphibians, and birds. In fishes, it is also called the pterotic bone. In most tetrapods, the squamosal and quadratojugal bones form the cheek series of the skull. The bone forms an ancestral co ...

, quadrate, and

pterygoid Pterygoid, from the Greek for 'winglike', may refer to: * Pterygoid bone, a bone of the palate of many vertebrates * Pterygoid processes of the sphenoid bone ** Lateral pterygoid plate ** Medial pterygoid plate * Lateral pterygoid muscle * Med ...

bones of the back of the skull, the

maxilla The maxilla (plural: ''maxillae'' ) in vertebrates is the upper fixed (not fixed in Neopterygii) bone of the jaw formed from the fusion of two maxillary bones. In humans, the upper jaw includes the hard palate in the front of the mouth. The ...

and

premaxilla The premaxilla (or praemaxilla) is one of a pair of small cranial bones at the very tip of the upper jaw of many animals, usually, but not always, bearing teeth. In humans, they are fused with the maxilla. The "premaxilla" of therian mammal has ...

bones that make up the front of the skull, and several teeth—''Gorgodon'' had a relatively large temporal fenestra and a pair large, conical

caniniform In mammalian oral anatomy, the canine teeth, also called cuspids, dog teeth, or (in the context of the upper jaw) fangs, eye teeth, vampire teeth, or vampire fangs, are the relatively long, pointed teeth. They can appear more flattened however ...

teeth at the front of the jaw. Other distinguishing features of ''Gorgodon'' include the fused connection between the quadrate and squamosal bones and a long transverse process of the pterygoid (a projection extending from the pterygoid bone on the underside of the skull). Olson classified ''Gorgodon'' as a very early

therapsid Therapsida is a major group of eupelycosaurian synapsids that includes mammals, their ancestors and relatives. Many of the traits today seen as unique to mammals had their origin within early therapsids, including limbs that were oriented mor ...

because it had a

heterodont dentition In anatomy, a heterodont (from Ancient Greek, Greek, meaning 'different teeth') is an animal which possesses more than a single tooth morphology (biology), morphology. In vertebrates, heterodont pertains to animals where teeth are differentiate ...

and large temporal fenestra not seen in the most basal synapsids but present in therapsids. He placed it in the

family Family (from la, familia) is a group of people related either by consanguinity (by recognized birth) or affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its members and of society. Idea ...

Phthinosuchidae because its teeth seemed similar to those of ''

Phthinosaurus ''Phthinosaurus'' is an extinct genus of therapsids from the Middle Permian of Russia. The type species ''Phthinosaurus borrisiaki'' was named by Soviet paleontologist Ivan Yefremov in 1940 on the basis of an isolated lower jaw. Because this jaw ...

'', an enigmatic therapsid from the

Middle Permian The Guadalupian is the second and middle series/ epoch of the Permian. The Guadalupian was preceded by the Cisuralian and followed by the Lopingian. It is named after the Guadalupe Mountains of New Mexico and Texas, and dates between 272.95 ...

of Russia that is most likely a

dinocephalia Dinocephalians (terrible heads) are a clade of large-bodied early therapsids that flourished in the Early and Middle Permian between 279.5 and 260 million years ago (Ma), but became extinct during the Capitanian mass extinction event. Dinoceph ...

n. However, the only known teeth of ''Phthinosaurus'' are from its lower jaw and the known teeth of ''Gorgodon'' are from its upper jaw. Olson reasoned that the shape of the teeth of ''Gorgodon'' match what would be expected for the upper teeth of ''Phthinosaurus'' even though there are no

homologous Homology may refer to: Sciences Biology *Homology (biology), any characteristic of biological organisms that is derived from a common ancestor *Sequence homology, biological homology between DNA, RNA, or protein sequences * Homologous chrom ...

features between the two taxa that would support such a relationship. Olson thought that ''Gorgodon'' was more primitive than ''Phthinosaurus'', and that both were ancestors of a group of therapsids called

gorgonopsid Gorgonopsia (from the Greek Gorgon, a mythological beast, and 'aspect') is an extinct clade of sabre-toothed therapsids from the Middle to Upper Permian roughly 265 to 252 million years ago. They are characterised by a long and narrow skull, ...

s. Sidor and Hopson (1995) proposed that ''Gorgodon'' and several other early therapsids that Olson described from the San Angelo Formation were instead the crushed remains of

sphenacodontid Sphenacodontidae (Greek: "wedge point tooth family") is an extinct family of small to large, advanced, carnivorous, Late Pennsylvanian to middle Permian pelycosaurs. The most recent one, ''Dimetrodon angelensis'', is from the late Kungurian or ...

s. Sphenacodontids are a group of non-therapsid synapsids that were common in what is now the southwestern United States during the Early Permian. Although ''Gorgodon'' is most likely a non-therapsid synapsid, its relationship to other synapsids has not been assessed due to its lack of distinguishing anatomical features.

References

{{Taxonbar, from=Q14723563 Prehistoric synapsid genera Monotypic prehistoric animal genera Cisuralian synapsids of North America Fossil taxa described in 1962 Taxa named by Everett C. Olson Cisuralian genus first appearances Cisuralian genus extinctions