47-458: Akidnognathidae is an extinct family of therocephalian therapsids from the Late Permian and Early Triassic of South Africa , Russia and China . The family includes many large-bodied therocephalians that were probably carnivorous, including Moschorhinus and Olivierosuchus . One akidnognathid, Euchambersia , may even have been venomous. Akidnognathids have robust skulls with
94-604: A subfamily of the Scaloposauridae, which currently appears to be a wastebasket taxon . In the classification of Haughton and Brink, the akidnognathids includes several therocephalians still recognized as such as well as several other genera, now classified as scylacosaurids . English and American paleontologists D. M. S. Watson and Alfred Romer moved many of these therocephalians into the family Whaitsiidae in 1956, although many were moved back to Akidnognathidae in later years. In 1974, Christiane Mendrez established
141-593: A wastebin taxon , dustbin taxon or catch-all taxon ) is a term used by some taxonomists to refer to a taxon that has the purpose of classifying organisms that do not fit anywhere else. They are typically defined by either their designated members' often superficial similarity to each other, or their lack of one or more distinct character states or by their not belonging to one or more other taxa. Wastebasket taxa are by definition either paraphyletic or polyphyletic , and are therefore not considered valid taxa under strict cladistic rules of taxonomy. The name of
188-612: A few representatives of the subgroup called Eutherocephalia survived into the Early Triassic . Some genera belonging to this group are believed to have possessed venom , which would make them the oldest tetrapods known to have such characteristics. However, the last therocephalians became extinct by the early Middle Triassic , possibly due to climate change , along with competition with cynodonts and various groups of reptiles — mostly archosaurs and their close relatives, including archosauromorphs and archosauriforms . Like
235-445: A pair of large caniniform teeth in their upper jaws. The family is morphologically intermediate between the more basal therocephalian group Scylacosauridae and the more derived group Baurioidea . The first known fossils of akidnognathids consists of two skulls which were discovered during a series of excavations carried out from 1899 until 1914 by Vladimir Amalitsky and his companion Anna P. Amalitsky [ ru ] in
282-547: A secondary palate in most taxa. Therocephalians and cynodonts both survived the Permian-Triassic mass extinction ; but, while therocephalians soon became extinct, cynodonts underwent rapid diversification. Therocephalians experienced a decreased rate of cladogenesis , meaning that few new groups appeared after the extinction. Most Triassic therocephalian lineages originated in the Late Permian, and lasted for only
329-654: A short period of time in the Triassic, going extinct during the late Anisian . Therocephalia was first named and conceived of by Robert Broom in 1903 as an order to include what he regarded as primitive theriodonts, based primarily on Scylacosaurus and Ictidosaurus . However, his original concept of Therocephalia differed strongly from the modern classification by also including various genera of gorgonopsians (including Gorgonops ) and dinocephalians . From 1903 to 1907 Broom added more therocephalian genera, as well as some non-therocephalians, to this group, including
376-490: A sister relationship between cynodonts and Eutherocephalia. The oldest known therocephalians first appear in the fossil record at the same time as other major therapsid groups, including the Gorgonopsia , which they resemble in many primitive features. For example, many early therocephalians possess long canine teeth similar to those of gorgonopsians. The therocephalians, however, outlasted the gorgonopsians, persisting into
423-596: A skull from an undescribed taxon was identified in the Fremouw Formation , Antarctica, and is dated to the Lower Triassic . [REDACTED] Therocephalian Therocephalia is an extinct clade of eutheriodont therapsids (mammals and their close relatives) from the Permian and Triassic periods. The therocephalians ("beast-heads") are named after their large skulls, which, along with
470-426: A wastebasket taxon may in some cases be retained as the designation of an evolutionary grade , however. The term was coined in a 1985 essay by Stephen Jay Gould . There are many examples of paraphyletic groups, but true "wastebasket" taxa are those that are known not to, and perhaps not intended to, represent natural groups, but are nevertheless used as convenient groups of organisms. The acritarchs are perhaps
517-474: Is another feature shared with mammals. The discovery of maxilloturbinal ridges in forms such as the primitive therocephalian Glanosuchus , suggests that at least some therocephalians may have been warm-blooded. The later therocephalians included the advanced Baurioidea , which carried some theriodont characteristics to a high degree of specialization. For instance, small baurioids and the herbivorous Bauria did not have an ossified postorbital bar separating
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#1732780286503564-553: Is likely represented by immature specimens from other disparate therocephalian families. In another example, the name 'Pristerognathidae' was extensively used for a group of basal therocephalians for much of the 20th century, but it has since been recognised that the name Scylacosauridae holds precedent for this group. Furthermore, the scope of 'Pristerognathidae' was unstable and variably was limited to an individual subgroup of early therocephalians (alongside others such as Lycosuchidae, Alopecodontidae, and Ictidosauridae) to encompassing
611-602: Is the only akidnognathid known from Russian territory. The first akidnognathid to be described was the type genus Akidnognathus , named in 1918 by Sidney Henry Haughton from a skull discovered by reverend John H. Whaits in the Beaufort Group , South Africa . The specimen comes more precisely from the upper Cistecephalus Assemblage Zone , within the Karoo Supergroup . It is in the Karoo supergroup where
658-407: Is written in improper Latin , German paleontologist Friedrich von Huene changed the spelling of the name to Euchambersiidae in 1940. The taxon Akidnognathidae was first named in 1954 by South African paleontologists paleontologists Haughton and Adrian Smuts Brink, basing their proposal on Akidnognathinae, which was created in 1928 by Ferenc Nopcsa . Nopcsa originally established Akidnognathinae as
705-521: The Bauriamorpha . Bauriamorphs were classified separately from therocephalians for many decades, though were often inferred to have evolved from therocephalians in parallel with cynodonts, each typically from different therocephalian stock. The inclusion of baurioids under Therocephalia was only firmly established in the 1980s, namely by Kemp (1982) and Hopson and Barghusen (1986). Various therocephalian subgroups and clades have been proposed since
752-480: The Gorgonopsia and many cynodonts, most therocephalians were presumably carnivores . The earlier therocephalians were, in many respects, as primitive as the gorgonopsians, but they did show certain advanced features. There is an enlargement of the temporal opening for broader jaw adductor muscle attachment and a reduction of the phalanges (finger and toe bones) to the mammalian phalangeal formula. The presence of an incipient secondary palate in advanced therocephalians
799-566: The Karoo of South Africa , but have also been found in Russia , China , Tanzania , Zambia , and Antarctica . Early therocephalian fossils discovered in Middle Permian deposits of South Africa support a Gondwanan origin for the group, which seems to have spread quickly across Earth. Although almost every therocephalian lineage ended during the great Permian–Triassic extinction event ,
846-512: The Northern Dvina , in present-day European Russia . In an article published posthumously in 1922, Amalitsky established a new taxon of therocephalians under the name Anna petri , in honor of his companion. In his description he judges it to be similar to Scylacosaurus . In 1963, Oskar Kuhn proposed changing the name of the genus to Annatherapsidus , seeing that Anna was an already preoccupied taxon. Currently, Annatherapsidus
893-457: The anomodont Galechirus . The latter's inclusion highlighted Broom's view of therocephalians as 'primitive' and ancestral to other therapsids, believing anomodonts to be descended from a therocephalian-like ancestor such as Galechirus . However, by 1908 he considered its and some other non-therocephalian's inclusions to the group to be doubtful. In 1913, Broom reinstated Gorgonopsia as distinct from Therocephalia, but for many decades after there
940-401: The monophyly of Therocephalia has been supported by subsequent researchers. Below is a cladogram modified from an analysis published by Christian A. Sidor, Zoe. T Kulik and Adam K. Huttenlocker in 2022, simplified to illustrate the relationships of the major recognised therocephalian subclades. It is based on the data matrix first published by Huttenlocker et al. (2011), and represents
987-708: The orbit from the temporal opening—a condition typical of primitive mammals. These and other advanced features led to the long-held opinion, now rejected, that the ictidosaurs and even some early mammals arose from a baurioid therocephalian stem. Mammalian characteristics such as this seem to have evolved in parallel among a number of different therapsid groups, even within Therocephalia. Several more specialized lifestyles have been suggested for some therocephalians. Many small forms, like ictidosuchids, have been interpreted as aquatic animals. Evidence for aquatic lifestyles includes sclerotic rings that may have stabilized
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#17327802865031034-412: The taxonomic name contains too much unrelated "baggage" to be successfully salvaged. As such, it is usually dumped in favour of a new, more restrictive name (for example, Rhynchocephalia ), or abandoned altogether (for example, Simia ). A related concept is that of form taxon , "wastebasket" groupings that are united by gross morphology. This is often result of a common mode of life, often one that
1081-414: The 21st century, asserting that a family-level group is established on the oldest referable genus and thus Akidnognathidae takes precedent for this group of non-whaitsioid eutherocephalians. On the other hand, some groups previously thought to be artificial have turned out to be valid. The aberrant therocephalian family Lycosuchidae, once identified by the presence of multiple functional caniniform teeth ,
1128-1215: The Akidnognathidae was instead closest to the Chthonosauridae , with the two forming the sister group to the group containing the Whaitsioidea and the Baurioidea . Subsequent classifications published after this study tend to follow this pattern. The cladogram below follows a phylogenetic analysis led by Jun Liu and Fernando Abdala in 2022, largely sharing the topology recovered by Huttenlocker and Sidor: Lycosuchus Gorynychus Scylacosauridae Scylacosuchus Ophidostoma Hofmeyria Ictidostoma Mirotenthes Whaitsiidae Baurioidea Chthonosauridae Annatherapsidus Shiguaignathus Jiufengia USNM PAL 412421 Akidnognathus Olivierosuchus Promoschorhynchus Moschorhinus Cerdosuchoides Euchambersia Akidnognathids are known from various fossils identified in Russia, South Africa and China. However,
1175-544: The Russian paleontologist Leonid Tatarinov proposed that these pits were part of an electroreception system in aquatic therocephalians. However, it is more likely that these pits are enlarged versions of the ones thought to support whiskers, or holes for blood vessels in a fleshy lip. The genera Euchambersia and Ichibengops , dating from the Lopingian , particularly attract the attention of paleontologists, because
1222-1016: The broad topologies found by other iterations of this dataset, such as Sigurdsen et al. (2012), Huttenlocker et al. (2014), and Liu and Abdala (2022). An example of the lability of these relationships is demonstrated by Liu and Abdala (2023), who recovered an alternative topology with Chthonosauridae nested deeply within Akidnognathidae. Biarmosuchus tener Titanophoneus potens Gorgonopsia Anomodontia Charassognathus Dvinia Procynosuchus Lycosuchus Scylacosauridae Scylacosuchus Perplexisaurus Chthonosauridae Akidnognathidae Ophidostoma Hofmeyriidae Whaitsiidae Ictidosuchus Ictidosuchoides Ictidosuchops Regisaurus Urumchia Karenitidae Lycideops Choerosaurus Tetracynodon Scaloposaurus Ericiolacertidae Notictoides Nothogomphodon danilovi Ordosiodon Hazhenia Bauriidae Wastebasket taxon Wastebasket taxon (also called
1269-405: The clade Eutheriodontia . However, some researchers have proposed that therocephalians are themselves ancestral to cynodonts, which would render therocephalians cladistically paraphyletic relative to cynodonts. Historically, cynodonts are often proposed to descend from (or are closest to) the therocephalian family Whaitsiidae under this hypothesis, however a 2024 study instead found support for
1316-569: The clade Scylacosauria , while others have suggested they are each other's sister taxa. Within Eutherocephalia, major clades corresponding to the families Akidnognathidae , Chthonosauridae , Hofmeyriidae , Whaitsiidae are recognised, along with various subclades grouped under Baurioidea. However, while individual groups of therocephalians are broadly recognised as valid, the interrelationships between them are often poorly supported. As such, there are few higher-level named clades uniting
1363-434: The crocodile-like Triassic group Rauisuchia . One of the roles of taxonomists is to identify wastebasket taxa and reclassify the content into more natural units. Sometimes, during taxonomic revisions, a wastebasket taxon can be salvaged after doing thorough research on its members, and then imposing tighter restrictions on what continues to be included. Such techniques "saved" Carnosauria and Megalosaurus . Other times,
1410-418: The early-Middle Triassic period as small weasel-like carnivores and cynodont-like herbivores. While common ancestry with cynodonts (and, thus, mammals) accounts for many similarities between these groups, some scientists believe that other similarities may be better attributed to convergent evolution , such as the loss of the postorbital bar in some forms, a mammalian phalangeal formula , and some form of
1457-406: The entirety of early therocephalians. Similarly, various names have been used for therocephalians corresponding to the family Adkidnognathidae in 20th century literature, including Annatherapsididae, Euchambersiidae (the oldest available name) and Moschorhinidae, and members have often had a confused relationship to whaitsiids. Consensus on the name and contents of Akidnognathidae was only achieved in
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1504-417: The existence of Eutherocephalia, but also found cynodonts to be the sister taxon to the whaitsiid therocephalian Theriognathus and thus rendering Therocephalia paraphyletic. Later phylogenetic analyses of therocephalians, initiated by Huttenlocker (2009), emphasise using a broader selection of therocephalian taxa and characters. Such analyses have reinforced Therocephalia as a sister clade to cynodonts, and
1551-580: The eye under the pressure of water and strongly developed cranial joints, which may have supported the skull when consuming large fish and aquatic invertebrates. One therocephalian, Nothogomphodon , had large sabre-like canine teeth and may have fed on large animals, including other therocephalians. Other therocephalians such as bauriids and nanictidopids have wide teeth with many ridges similar to those of mammals, and may have been herbivores . Many small therocephalians have small pits on their snouts that probably supported vibrissae (whiskers). In 1994,
1598-446: The family Moschorhinidae, while recognizing three subfamilies making it up, namely Annatherapsidinae, Moschorhininae and Euchambersiinae. In 1975, the same author proposed another name to designate the group, Annatherapsididae, although she maintained the validity of the three subfamilies previously cited. In their phylogenetic revision of therapsids published in 1986, James Hopson and Herb Barghusen supported Mendrez's hypothesis that
1645-419: The fossil skulls attributed to them have some structures which suggests that these two animals had organs for distributing venom. The therocephalians evolved as one of several lines of non-mammalian therapsids , and have a close relationship to the cynodonts, which includes mammals and their ancestors. They are broadly regarded as the sister group to cynodonts by most modern researchers, united together as
1692-563: The group have since been declared dubious, and it now only includes Lycosuchus and Simorhinella . Modern therocephalian taxonomy is instead based upon phylogenetic analyses of therocephalian species, which consistently recognises two groups of early therocephalians (the Lycosuchidae and Scylacosauridae) while more derived therocephalians form the clade Eutherocephalia. Some analyses have found scylacosaurids to be closer to eutherocephalians than to lycosuchids, and so have been united as
1739-401: The group included three subfamilies, but both authors preferred to use the name Euchambersiidae instead. While the name Euchambersiidae may have priority over Akidnognathidae because it was named first, Akidnognathidae is currently considered as the valid name because it is based on the first named genus of the group, Akidnognathus , this latter having been named in 1918 while Euchambersia
1786-524: The group was named, although their contents and nomenclature have often been highly unstable and some previously recognized therocephalian clades have turned out to be artificial or based upon dubious taxa. This has led to some prevalent names in therocephalian literature, sometimes in use for decades, being replaced by lesser-known names that hold priority. For example, the Scaloposauridae was based on fossils with mostly juvenile characteristics and
1833-652: The majority of known akidnognathids will be identified, with at least two additional genera, namely Euchambersia and Proalopecopsis , also from the upper Cistecephalus Assemblage Zone. Akidnognathids were historically only reported from Russia and South Africa, but it was from 2017 that paleontologists Jun Liu and Fernando Abdala described several taxa from the Naobaogou Formation , in Inner Mongolia , China , from several fossils collected on this fossil site since 2009. Among these described taxa,
1880-400: The most famous example. Wastebasket taxa are often old (and perhaps not described with the systematic rigour and precision that is possible in the light of accumulated knowledge of diversity) and populous. Fossil groups that are poorly known due to fragmentary remains are sometimes grouped together on gross morphology or stratigraphy , only later to be found to be wastebasket taxa, such as
1927-426: The multiple subclades, with the exceptions of Whaitsiioidea (uniting Hofmeyriidae and Whaitsiidae) and Baurioidea. Early phylogenetic analyses of therocephalians, such as that of Hopson and Barghusen (1986) and van den Heever (1994), recovered and validated many of the therocephalian subtaxa mentioned above in a phylogenetic context. However, the higher-level relationships were difficult to resolve, particularly between
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1974-561: The structure of their teeth, suggest that they were carnivores . Like other non-mammalian synapsids , therocephalians were once described as " mammal-like reptiles ". Therocephalia is the group most closely related to the cynodonts , which gave rise to the mammals , and this relationship takes evidence in a variety of skeletal features. Indeed, it had been proposed that cynodonts may have evolved from therocephalians and so that therocephalians as recognised are paraphyletic in relation to cynodonts. The fossils of therocephalians are numerous in
2021-493: The subclades of Eutherocephalia (i.e. Hofmeyriidae, Akidnognathidae, Whaitsiidae and Baurioidea). For example, Hopson and Barghusen (1986) could only recover Eutherocephalia as an unresolved polytomy . Despite these shortcomings, subsequent discussions of therocephalian relationships relied almost exclusively on these analyses. Later analyses focused on the relationships of early cynodonts, namely Abdala (2007) and Botha et al. (2007), included some therocephalian taxa and supported
2068-470: The two authors identify a second species of Euchambersia , a genus that was previously reported only in South Africa. The first family-level name used to classify an akidnognathid was Euchambersidae, erected by South African paleontologist Lieuwe Dirk Boonstra in 1934, in reference for the genus Euchambersia , which is possibly one of the oldest known venomous tetrapods . Noting that the taxon
2115-698: Was named in 1931. It is on the basis of this affirmation that this name has achieved wider acceptance within the scientific literature . In 1974, Leonid Petrovich Tatarinov proposed uniting the Akidnognathidae (then named Annatherapsididae), the Whaitsiidae and the Moschowhaitsiidae within a superfamily called Whaitsioidea . Multiple authors have disagreed with this proposition, but others like Mikhail Ivakhnenko in 2008 and Adam Huttenlocker in 2009, share Tatarinov's point of view. However, phylogenies led by Huttenlocker and Christian Sidor found that
2162-407: Was proposed to represent an unnatural group based on a study of canine replacement in early therocephalians by van den Heever in 1980. However, subsequent analysis has exposed additional synapomorphies supporting the monophyly of this group (including delayed caniniform replacement), and Lycosuchidae is currently considered a valid basal clade within Therocephalia. However, most genera included in
2209-403: Was still confusion from him and other researchers over which genera belonged to which group. The group's rank also varied from order, suborder and infraorder depending on authors' preferred therapsid systematics. At the same time, the small 'advanced' therocephalians now classified under Baurioidea were often regarded as belonging to their own subgroup of therapsids distinct from therocephalians,
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