Sphenacodontidae (Greek: "wedge point tooth family") is an

extinct Extinction is the termination of a kind of organism or of a group of kinds (taxon), usually 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 ...

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 ...

of small to large, advanced,

carnivorous A carnivore , or meat-eater (Latin, ''caro'', genitive ''carnis'', meaning meat or "flesh" and ''vorare'' meaning "to devour"), is an animal or plant whose food and energy requirements derive from animal tissues (mainly muscle, fat and other ...

, Late Pennsylvanian to

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 ± ...

pelycosaur Pelycosaur ( ) is an older term for basal or primitive Late Paleozoic synapsids, excluding the therapsids and their descendants. Previously, the term ''mammal-like reptile'' had been used, and pelycosaur was considered an order, but this is ...

s. The most recent one, ''Dimetrodon angelensis'', is from the late Kungurian or early Roadian

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 ...

. However, given the notorious incompleteness of the fossil record, a recent study concluded that the Sphenacodontidae may have become extinct as recently as the early Capitanian. Primitive forms were generally small (60 cm to 1 meter), but during the later part of 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 Sawan ...

these animals grew progressively larger (up to 3 meters or more), to become the

top predators An apex predator, also known as a top predator, is a predator at the top of a food chain, without natural predators of its own. Apex predators are usually defined in terms of trophic dynamics, meaning that they occupy the highest trophic le ...

of their environments. Sphenacodontid fossils are so far known only from

North America North America is a continent in the Northern Hemisphere and almost entirely within the Western Hemisphere. It is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South America and th ...

and

Europe Europe is a large peninsula conventionally considered a continent in its own right because of its great physical size and the weight of its history and traditions. Europe is also considered a Continent#Subcontinents, subcontinent of Eurasia ...

Characteristics

The skull is long, deep and narrow, an adaptation for strong jaw muscles. The front teeth are large and dagger-like, whereas the teeth in the sides and rear of the jaw are much smaller (hence the name of the well-known genus ''

Dimetrodon ''Dimetrodon'' ( or ,) meaning "two measures of teeth,” is an extinct genus of non-mammalian synapsid that lived during the Cisuralian (Early Permian), around 295–272 million years ago (Mya). It is a member of the family Sphenacodont ...

'' – "two-measure tooth", although all members of the family have this attribute). Several large (~3 meters) and advanced members of this group ('' Ctenospondylus'', '' Sphenacodon'', '' Secodontosaurus'' and ''

'') are distinguished by a tall sail along the back, made up of elongated

vertebra The spinal column, a defining synapomorphy shared by nearly all vertebrates, Hagfish are believed to have secondarily lost their spinal column is a moderately flexible series of vertebrae (singular vertebra), each constituting a characteristi ...

l neural spines, which in life must have been covered with skin and blood vessels, and presumably functioned as a

thermoregulatory Thermoregulation is the ability of an organism to keep its body temperature within certain boundaries, even when the surrounding temperature is very different. A thermoconforming organism, by contrast, simply adopts the surrounding temperatur ...

device. However, possession of a sail does not appear to have been essential for these animals. For example, there is the case in which one genus ('' Sphenacodon'' – fossils known from

New Mexico ) , population_demonym = New Mexican ( es, Neomexicano, Neomejicano, Nuevo Mexicano) , seat = Santa Fe, New Mexico, Santa Fe , LargestCity = Albuquerque, New Mexico, Albuquerque , LargestMetro = Albuquerque metropolitan area, Tiguex , Offi ...

) lacks a sail, while a very similar and closely related genus (''

'' – fossils known from

Texas Texas (, ; Spanish: ''Texas'', ''Tejas'') is a state in the South Central region of the United States. At 268,596 square miles (695,662 km2), and with more than 29.1 million residents in 2020, it is the second-largest U.S. state by ...

) has one. During the

Permian The Permian ( ) is a geologic period and 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 251.9 Mya. It is the last period of the Paleo ...

, these two regions were separated by a narrow sea-way, but it is not clear why one geographically isolated group should evolve a sail, but the other group not.

Classification

The

Sphenacodontidae is actually paraphyletic as originally described, defined by shared primitive synapsid characters; these animals constitute an evolutionary gradation from primitive

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 reptil ...

to 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 more ...

. The

clade A clade (), also known as a monophyletic group or natural group, is a group of organisms that are monophyletic – that is, composed of a common ancestor and all its lineal descendants – on a phylogenetic tree. Rather than the English ter ...

Sphenacodontia Sphenacodontia is a stem-based clade of derived synapsids. It was defined by Amson and Laurin (2011) as "the largest clade that includes '' Haptodus baylei'', '' Haptodus garnettensis'' and '' Sphenacodon ferox'', but not '' Edaphosaurus pogoni ...

is used to designate the

monophyletic In cladistics for a group of organisms, monophyly is the condition of being a clade—that is, a group of taxa composed only of a common ancestor (or more precisely an ancestral population) and all of its lineal descendants. Monophyletic gr ...

group that includes sphenacodontids and all their descendants (including mammals), while Sphenacodontidae in the strict sense includes only specialised pelycosaurs, and not earlier more primitive members of the family like ''Haptodus'', ''Palaeohatteria'', ''Pantelosaurus'', and ''Cutleria'' (in pre-

cladistic Cladistics (; ) is an approach to biological classification in which organisms are categorized in groups ("clades") based on hypotheses of most recent common ancestry. The evidence for hypothesized relationships is typically shared derived char ...

classifications all included under the genus ''Haptodus''). The clade Sphenacodontoidea is used by Laurin and Reisz 1997 to designate the

most recent common ancestor In biology and genetic genealogy, the most recent common ancestor (MRCA), also known as the last common ancestor (LCA) or concestor, of a set of organisms is the most recent individual from which all the organisms of the set are descended. The ...

of Sphenacodontidae and Therapsida and all their descendants, and is defined by certain features of the skull.

References

* Carroll, R. L. (1988), ''Vertebrate Paleontology and Evolution'', WH Freeman & Co. * Colbert, E. H., (1969), ''Evolution of the Vertebrates'', John Wiley & Sons Inc (2nd ed.) * Laurin, M. and Reisz, R. R., 1997
Autapomorphies of the main clades of synapsids
* Reisz, R. R., 1986, ''Handbuch der Paläoherpetologie – Encyclopedia of Paleoherpetology, Part 17A Pelycosauria'' Verlag Dr. Friedrich Pfeil, * Romer, A. S., (1947, revised ed. 1966) Vertebrate Paleontology, University of Chicago Press, Chicago * Romer, A. S. and Price, L. I., (1940), ''Review of the Pelycosauria'', Geological Society of America Special Papers, No 28

External links

Synapsida: Sphenacodontia

Deuterostoma/Chordata/Synapsida/Pelycosauria/Sphenacodontidae
- list of species {{Taxonbar, from=Q131809 Prehistoric synapsid families Pennsylvanian first appearances Guadalupian extinctions Taxa named by Othniel Charles Marsh

Characteristics

Classification

See also

References

External links