Euchambersia Mirabilis
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''Euchambersia'' 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 ...
genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...
of
therocephalian Therocephalia is an extinct suborder of eutheriodont therapsids (mammals and their close relatives) from the Permian and Triassic. The therocephalians ("beast-heads") are named after their large skulls, which, along with the structure of their te ...
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 ...
s that lived during the
Late Permian Late may refer to: * LATE, an acronym which could stand for: ** Limbic-predominant age-related TDP-43 encephalopathy, a proposed form of dementia ** Local-authority trading enterprise, a New Zealand business law ** Local average treatment effect, ...
in what is now
South Africa South Africa, officially the Republic of South Africa (RSA), is the southernmost country in Africa. It is bounded to the south by of coastline that stretch along the South Atlantic and Indian Oceans; to the north by the neighbouring countri ...
and
China China, officially the People's Republic of China (PRC), is a country in East Asia. It is the world's most populous country, with a population exceeding 1.4 billion, slightly ahead of India. China spans the equivalent of five time zones and ...
. The genus contains two species. 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 ...
''E. mirabilis'' was named by paleontologist
Robert Broom Robert Broom FRS FRSE (30 November 1866 6 April 1951) was a British- South African doctor and palaeontologist. He qualified as a medical practitioner in 1895 and received his DSc in 1905 from the University of Glasgow. From 1903 to 1910, he ...
in 1931 from a skull missing the lower jaw. A second skull, belonging to a probably immature individual, was later described. In 2022, a second species, ''E. liuyudongi'', was named by Jun Liu and Fernando Abdala from a well-preserved skull. It is a member of the family
Akidnognathidae 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 ''Mosch ...
, which historically has also been referred by as the synonymous Euchambersiidae (named after ''Euchambersia''). ''Euchambersia'' was a small and short-snouted therocephalian, possessing large canines as is typical of the group. However, it is notable among therocephalians for possessing ridges on its canines and a large indentation in the side of the skull. It has been proposed that these structures supported a
venom Venom or zootoxin is a type of toxin produced by an animal that is actively delivered through a wound by means of a bite, sting, or similar action. The toxin is delivered through a specially evolved ''venom apparatus'', such as fangs or a sti ...
delivery mechanism. If this statement turns out to be true, then it would be one of the oldest known
tetrapod Tetrapods (; ) are four-limbed vertebrate animals constituting the superclass Tetrapoda (). It includes extant and extinct amphibians, sauropsids ( reptiles, including dinosaurs and therefore birds) and synapsids (pelycosaurs, extinct theraps ...
s to have this characteristic. More recently, the internal structure of the skull of ''Euchambersia'' has been used as stronger evidence in favour of the hypothesis that it was venomous; other possibilities, such as the indentation supporting some sort of sensory organ, still remain plausible.


Discovery and naming

The type specimen of ''Euchambersia mirabilis'' and of ''Euchambersia'' overall was found by
Robert Broom Robert Broom FRS FRSE (30 November 1866 6 April 1951) was a British- South African doctor and palaeontologist. He qualified as a medical practitioner in 1895 and received his DSc in 1905 from the University of Glasgow. From 1903 to 1910, he ...
on the
South Africa South Africa, officially the Republic of South Africa (RSA), is the southernmost country in Africa. It is bounded to the south by of coastline that stretch along the South Atlantic and Indian Oceans; to the north by the neighbouring countri ...
n farm of Vanwyksfontein, owned by a Mr. Greathead, near the town of
Norvalspont Norvalspont is a small town in Pixley ka Seme District Municipality in the Northern Cape province of South Africa. The name is Afrikaans for ''Norval’s ferry'', and named after an enterprising Scot who constructed a ferry here in 1848. The settl ...
. It consists of a single, distorted skull, catalogued as NHMUK R5696, which was described by Broom in 1931. A second, smaller skull, with the specimen number BP/1/4009, was found in 1966 and described by James Kitching in 1977. Both specimens are missing the lower jaw. They originated from the same general layer of rock, in the upper ''Cistecephalus'' Assemblage Zone of the
Beaufort Group The Beaufort Group is the third of the main subdivisions of the Karoo Supergroup in South Africa. It is composed of a lower Adelaide Subgroup and an upper Tarkastad Subgroup. It follows conformably after the Ecca Group and unconformably underlie ...
within the
Karoo Supergroup The Karoo Supergroup is the most widespread stratigraphic unit in Africa south of the Kalahari Desert. The supergroup consists of a sequence of units, mostly of nonmarine origin, deposited between the Late Carboniferous and Early Jurassic, a perio ...
. The ''Cistecephalus'' AZ has been dated to the
Wuchiapingian In the geologic timescale, the Wuchiapingian or Wujiapingian (from in the Liangshan area of Hanzhong, Shaanxi Province) is an age or stage of the Permian. It is also the lower or earlier of two subdivisions of the Lopingian Epoch or Series. The ...
stage of the
Late Permian Late may refer to: * LATE, an acronym which could stand for: ** Limbic-predominant age-related TDP-43 encephalopathy, a proposed form of dementia ** Local-authority trading enterprise, a New Zealand business law ** Local average treatment effect, ...
, between 256.2 and 255.2 million years old. Broom named the genus ''Euchambersia'', which he considered "the most remarkable therocephalian ever discovered", after the eminent
Scottish Scottish usually refers to something of, from, or related to Scotland, including: *Scottish Gaelic, a Celtic Goidelic language of the Indo-European language family native to Scotland *Scottish English *Scottish national identity, the Scottish ide ...
publisher and evolutionary thinker Robert Chambers, whose ''
Vestiges of the Natural History of Creation ''Vestiges of the Natural History of Creation'' is an 1844 work of speculative natural history and philosophy by Robert Chambers. Published anonymously in England, it brought together various ideas of stellar evolution with the progressive tra ...
'' was considered by Broom to be "a very remarkable work" though "sneered at by many". The second species, ''E. liuyudongi'', was named by Jun Liu and Fernando Abdala in 2022 based on a well-preserved skull with an associated lower jaw. It originated from the
Naobaogou Formation The Naobaogou Formation is a geological formation in the Daqing Mountains of China. It is likely of Lopingian age. It consists of three rhythms of sediment, labelled members I-III primarily of purple siltstone Siltstone, also known as aleuroli ...
of
Inner Mongolia Inner Mongolia, officially the Inner Mongolia Autonomous Region, is an autonomous region of the People's Republic of China. Its border includes most of the length of China's border with the country of Mongolia. Inner Mongolia also accounts for a ...
, which is dated more broadly to the
Lopingian The Lopingian is the uppermost series/last epoch of the Permian. It is the last epoch of the Paleozoic. The Lopingian was preceded by the Guadalupian and followed by the Early Triassic. The Lopingian is often synonymous with the informal terms l ...
epoch (which contains the Wuchiapingian). The formation is divided into three
members Member may refer to: * Military jury, referred to as "Members" in military jargon * Element (mathematics), an object that belongs to a mathematical set * In object-oriented programming, a member of a class ** Field (computer science), entries in ...
based on cycles of sedimentation, numbere as members I, II, and III from oldest to youngest; ''E. liuyudongi'' originates from member I. Liu and colleagues had previously described a number of other new species from the middle portion of the Naobaogou Formation, which were among the 80 specimens that had been excavated from at least three field seasons after 2009.


Description

''E. mirabilis'' was small and short-snouted (the snout being about half of the skull length) for a
therocephalia Therocephalia is an extinct suborder of eutheriodont therapsids (mammals and their close relatives) from the Permian and Triassic. The therocephalians ("beast-heads") are named after their large skulls, which, along with the structure of their te ...
n, with the type skull having a reconstructed length of approximately , accounting for crushing and deformation in the fossil. The second known skull belonged to a smaller individual, with a length of ; it was probably immature, judging by the lack of fusion in the skull. The type skull of ''E. liuyudongi'' measures in length and has a shorter snout (less than 40% of the skull length). According to the initial description, the eye socket of ''E. mirabilis'' was rather small. The branches of the
postorbital The ''postorbital'' is one of the bones in vertebrate skulls which forms a portion of the dermal skull roof and, sometimes, a ring about the orbit. Generally, it is located behind the postfrontal and posteriorly to the orbital fenestra. In some ve ...
and
jugal The jugal is a skull bone found in most reptiles, amphibians and birds. In mammals, the jugal is often called the malar or zygomatic. It is connected to the quadratojugal and maxilla, as well as other bones, which may vary by species. Anatomy ...
that usually surround the back and bottom of the eye socket in therocephalians appear to be either very reduced or absent entirely. Meanwhile, the top of the eye socket is formed by the prefrontal, and the
frontal Front may refer to: Arts, entertainment, and media Films * ''The Front'' (1943 film), a 1943 Soviet drama film * ''The Front'', 1976 film Music *The Front (band), an American rock band signed to Columbia Records and active in the 1980s and ea ...
is also small. The skull does not bear a
pineal foramen A parietal eye, also known as a third eye or pineal eye, is a part of the epithalamus present in some vertebrates. The eye is located at the top of the head, is photoreceptive and is associated with the pineal gland, regulating circadian rhythm ...
. Like ''
Whaitsia ''Theriognathus'' (from Greek therion: beast, mammal, Greek, gnathos, “jaw,” +us, pronounced THEH-ree-OG-nah-thuss) is an extinct genus of therocephalian therapsid belonging to the family Whaitsiidae, known from fossils from South Africa, Zam ...
'', the
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 * Medial ...
and
palatine A palatine or palatinus (in Latin; plural ''palatini''; cf. derivative spellings below) is a high-level official attached to imperial or royal courts in Europe since Roman times.
of the
palate The palate () is the roof of the mouth in humans and other mammals. It separates the oral cavity from the nasal cavity. A similar structure is found in crocodilians, but in most other tetrapods, the oral and nasal cavities are not truly sepa ...
are not separated from the transpalatine, further to the side of the jaw, by any sort of opening. ''E. liuyudongi'' differs from ''E. mirabilis'' in several details of these bones: the frontal bone separates the prefrontal from contacting the postorbital, and the postorbital fenestrae at the back of the skull are slit-like instead of rounded. Additionally, the epipterygoid and prootic of the
braincase In human anatomy, the neurocranium, also known as the braincase, brainpan, or brain-pan is the upper and back part of the skull, which forms a protective case around the brain. In the human skull, the neurocranium includes the calvaria or skul ...
are disconnected in ''E. liuyudongi''.


Teeth

Although the skulls of ''E. mirabilis'' are incompletely preserved,
CT scan A computed tomography scan (CT scan; formerly called computed axial tomography scan or CAT scan) is a medical imaging technique used to obtain detailed internal images of the body. The personnel that perform CT scans are called radiographers ...
ning suggests that each
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 b ...
held five
incisor Incisors (from Latin ''incidere'', "to cut") are the front teeth present in most mammals. They are located in the premaxilla above and on the mandible below. Humans have a total of eight (two on each side, top and bottom). Opossums have 18, whe ...
s, with the sockets becoming progressively larger from the first to the fifth incisor. Like other
theriodonts The theriodonts ( clade Theriodontia) are a major group of therapsids which appeared during the Middle Permian and which includes the gorgonopsians and the eutheriodonts, itself including the therocephalians and the cynodonts. Naming In 1876, R ...
, the crowns of the incisors are conical; they also lack serrations, unlike
gorgonopsia 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, a ...
ns and
scylacosauria Scylacosauria is a clade of therocephalian therapsids. It includes the basal family Scylacosauridae and the infraorder Eutherocephalia. Scylacosauridae and Eutherocephalia form this clade to the exclusion of Lycosuchidae, the most basal theroce ...
n therocephalians. The interior edge of the incisors seems to be slightly concave, and the back edge appears to have a ridge. The smaller specimen has a displaced incisor preserved within its nasal cavity; it is more strongly recurved and has wear marks on its top edge, suggesting that it is probably a lower incisor. Its fourth incisor also has a replacement tooth growing behind it, accompanied by
resorption Resorption is the absorption of cells or tissue into the circulatory system, usually by osteoclasts. Types of resorption include: * Bone resorption * Herniated Disc Resorption * Tooth resorption * Fetal resorption * Blood resorption See also ...
of the root. The type specimen of ''E. mirabilis'' preserves the right canine. Like other therocephalians, its canine was very large, resulting in a specialized predatory lifestyle that incorporates a sabertooth bite into prey killing. It is round in cross-section, and bears a prominent ridge on the side of its front surface. Immediately beside this ridge is a shallow depression that becomes wider near the top of the tooth, which is probably the same structure as the groove interpreted by some authors. Unlike ''E. mirabilis'', however, the canines of ''E. liuyudongi'' had neither ridges nor grooves. Theriodonts usually replace their teeth in an alternating (or distichial) pattern, such that the canine tooth is always functional; both skulls of ''E. mirabilis'' show no sign of any replacement canines developing, suggesting that it was reliant on having both canines present and functional simultaneously.


Maxillary fossa and associated canals

Behind the incisors and canines, there were no additional teeth in both the upper and lower jaws (as confirmed by ''E. liuyudongi''). Where teeth would be located in therocephalians that do have teeth behind the canines, there was instead a large depression, or fossa, on the side of 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 t ...
, which was also bounded below by part of the lacrimal and possibly part of the jugal. This fossa is 48% the length of the jaw in the type specimen of ''E. mirabilis'', and 38% in the second skull. In both skulls, this fossa is divided into two parts: a shallower ridge on top, and a larger and deeper depression on the bottom. A wide furrow beginning behind the canine contacts the bottom of the fossa and then passes into the interior of the mouth. The bottom portion of the fossa is strongly pitted and bears a small opening, or foramen, on both the front and back surfaces. In ''E. liuyudongi'', this fossa is deeper still; a bar of the maxilla caps the top of the fossa and contacts the jugal, and the inner wall of the fossa has a large opening to the nasal cavity. Its fossa nearly reaches the mid-height of the snout. CT scanning shows that the openings of ''E. mirabilis'' lead to canals that connect to the
trigeminal nerve In neuroanatomy, the trigeminal nerve ( lit. ''triplet'' nerve), also known as the fifth cranial nerve, cranial nerve V, or simply CN V, is a cranial nerve responsible for sensation in the face and motor functions such as biting and chewin ...
, which controls facial sensitivity. The forward-directed canal also splits into the three main branches of the
infraorbital nerve The infraorbital nerve is a branch of the maxillary nerve, itself a branch of the trigeminal nerve (CN V). It travels through the orbit and enters the infraorbital canal to exit onto the face through the infraorbital foramen. It provides sensory ...
, all of which connect to the socket of the canine; the junction occurs about along the canal, another point of variation between the two skulls. The top branch, the external nasal ramus, splits into four branches in the type skull, but it does not split in the second skull. In other
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 ...
s like ''
Thrinaxodon ''Thrinaxodon'' is an extinct genus of cynodonts, most commonly regarded by its species ''T. liorhinus'' which lived in what are now South Africa and Antarctica during the Early Triassic. ''Thrinaxodon'' lived just after the Permian–Triassic m ...
'', ''
Bauria ''Bauria'' is an extinct genus of the suborder Therocephalia that existed during the Early and MiddleTriassic period, around 246-251 million years ago. It belonged to the family Bauriidae. ''Bauria'' was probably a carnivore or insectivore ...
'', and ''
Olivierosuchus ''Olivierosuchus'' is an extinct genus of therocephalian therapsids. It is a member of the family Akidnognathidae. Fossils of ''Olivierosuchus'' have been found from the Early Triassic ''Lystrosaurus'' Assemblage Zone in South Africa. Unlike ot ...
'', the external nasal ramus generally splits into three or more branches. All of these canals would have brought nerves and nutrient-rich tissue to the root of the canines and the rest of the upper jaw.


Classification

In 1934, ''Euchambersia'' was assigned to the newly named family Euchambersiidae by
Lieuwe Dirk Boonstra Lieuwe Dirk Boonstra (1905 – 1975) was a South African palaeontologist whose work focused on the therapsida, mammal-like reptiles of the Middle ( Tapinocephalus Assemblage Zone, ''Tapinocephalus'' Assemblage Zone) and Late Permian, whose fossil ...
.Boonstra L.D. 1934. "A contribution to the morphology of the mammal-like reptiles of the suborder Therocephalia". ''Annals of the South African Museum'', 31: 215–267 Boonstra initially misspelt the name as Euchambersidae (which is improper Latin), and was subsequently corrected by
Friedrich von Huene Friedrich von Huene, born Friedrich Richard von Hoinigen, (March 22, 1875 – April 4, 1969) was a German paleontologist who renamed more dinosaurs in the early 20th century than anyone else in Europe. He also made key contributions about v ...
in 1940. Euchambersiidae was initially considered to be separate from the families Moschorhinidae and Annatherapsididae; in 1974, Christiane Mendez recognized these groups as closely related subfamilies (renamed Annatherapsidinae, Moschorhininae and Euchambersiinae) within the wider group of her redefined Moschorhinidae (although she also referred to it as Annatherapsididae). The 1986 phylogenetic analysis of
James Hopson James Allen Hopson (born 1935) is an American paleontologist and professor (now retired) at the University of Chicago. His work has focused on the evolution of the synapsids (a group of amniotes that includes the mammals), and has been focused ...
and Herb Barghusen supported Mendez's hypothesis of three subfamilies within Moschorhinidae, but they elected to use the name Euchambersiidae. In 2009, Adam Huttenlocker and colleagues argued that the names Annatherapsididae, Moschorhinidae, and Euchambersiidae are junior synonyms of
Akidnognathidae 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 ''Mosch ...
, since ''
Akidnognathus ''Akidnognathus'' is an extinct genus of therocephalians. See also * List of therapsids This list of therapsids is an attempt to create a comprehensive listing of all genera that have ever been included in the Therapsida excluding mammals and ...
'' (which also belongs in the same family) was named first before any other member of the family. This name has reached wider acceptance among researchers. Huttenlocker and colleagues also later redefined Moschorhininae as all of Akidnognathidae save for '' Annatherapsidus'' and ''Akidnognathus''. In 2008, Ivakhnenko included the Akidnognathidae (as the Euchambersiidae) as the sister group of the family Whaitsiidae in the superfamily Whaitsioidea. However, other researchers do not include the Akidnognathidae in the Whaitsioidea. Phylogenies by Huttenlocker and colleagues found that the Akidnognathidae was instead closest to the
Chthonosauridae ''Chthonosaurus'' is an extinct genus of eutherocephalian therapsids from the Late Permian Kutulukskaya Formation of Russia Russia (, , ), or the Russian Federation, is a transcontinental country spanning Eastern Europe and Northern ...
, with the two forming 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 t ...
to the group containing the Whaitsioidea and the
Baurioidea Baurioidea is a superfamily of therocephalian therapsids. It includes advanced therocephalians such as ''Regisaurus'' and ''Bauria''. The superfamily was named by South African paleontologist Robert Broom in 1911. Bauriamorpha, named by D. M. ...
. Liu and Abdala performed a new phylogenetic analysis in 2022 for the description of ''E. liuyudongi''. They found that the two species form a unified group within the Akidnognathidae, with the rest of the topology being similar to the one found by Huttenlocker and colleagues. The topology recovered by their analysis is shown below, with group labels following Huttenlocker and colleagues.


Paleobiology


Venom

The large maxillary fossae of ''Euchambersia'' have been continual subjects of debate regarding their function. However, most researchers agree that they held some sort of secretory gland. While Broom initially argued that the fossae may have contained the
parotid The parotid gland is a major salivary gland in many animals. In humans, the two parotid glands are present on either side of the mouth and in front of both ears. They are the largest of the salivary glands. Each parotid is wrapped around the ma ...
salivary glands, this proposal was rejected by Boonstra and J.P. Lehman, who noted that the parotid glands tend to be placed behind the eye; they respectively suggested that the fossae held modified
lacrimal gland The lacrimal glands are paired exocrine glands, one for each eye, found in most terrestrial vertebrates and some marine mammals, that secrete the aqueous layer of the tear film. In humans, they are situated in the upper lateral region of each or ...
s and
Harderian gland The Harderian gland is a gland found within the eye's orbit that occurs in tetrapods (reptiles, amphibians, birds and mammals) that possess a nictitating membrane. The gland can be compound tubular or compound tubuloalveolar, and the fluid it s ...
s. However, the latter is also unlikely because Harderian glands are usually placed inside the eye socket.
Franz Nopcsa Franz may refer to: People * Franz (given name) * Franz (surname) Places * Franz (crater), a lunar crater * Franz, Ontario, a railway junction and unorganized town in Canada * Franz Lake, in the state of Washington, United States – see ...
suggested that the maxillary fossae housed venom glands (which may have been derived from lacrimal glands), with the ridged canines and the notches behind the canines allowing the venom to flow passively into the victim's bloodstream. This hypothesis was widely accepted throughout the 20th century and the characteristic morphology of ''Euchambersia'' was used to support possible venom-bearing adaptations among various other prehistoric animals, including the therocephalian ''
Ichibengops ''Ichibengops'' is an extinct genus of therocephalian therapsids known from the type species ''Ichibengops munyamadziensis'', which lived in what is now Zambia during the Late Permian. ''Ichibengops'' was named in 2015 on the basis of fossils fo ...
''. Much of this acceptance has been based on the erroneous assumption that the canines are grooved instead of ridged; grooved canines in ''Euchambersia'' would parallel the fangs of various venomous snakes as well as the venom-delivering incisors of the living
solenodon Solenodons (from el, τέλειος , 'channel' or 'pipe' and el, ὀδούς , 'tooth') are venomous, nocturnal, burrowing, insectivorous mammals belonging to the family Solenodontidae . The two living solenodon species are the Cuban solen ...
s. This interpretation, which has consistently appeared in literature published after 1986, was determined by Julien Benoit to be the result of the propagation of Broom's overly reconstructed diagram of the skull, without the context of the actual specimens. He thus considered it necessary to re-evaluate the hypothesis of a venomous bite in ''Euchambersia''. Additionally, Benoit argued that grooved and ridged canines are not necessarily associated with venomous animals either, as shown by their presence in
hippopotami The hippopotamus ( ; : hippopotamuses or hippopotami; ''Hippopotamus amphibius''), also called the hippo, common hippopotamus, or river hippopotamus, is a large semiaquatic mammal native to sub-Saharan Africa. It is one of only two extan ...
,
muntjacs Muntjacs ( ), also known as the barking deer or rib-faced deer, (URL is Google Books) are small deer of the genus ''Muntiacus'' native to South Asia and Southeast Asia. Muntjacs are thought to have begun appearing 15–35 million years ago, ...
, and
baboon Baboons are primates comprising the genus ''Papio'', one of the 23 genera of Old World monkeys. There are six species of baboon: the hamadryas baboon, the Guinea baboon, the olive baboon, the yellow baboon, the Kinda baboon and the chacma ba ...
s, in which they play a role in grooming or sharpening the teeth; in the latter two, ridged canines are also accompanied by a distinct fossa in front of the eye, which is entirely unconnected with venom. Furthermore, grooved and ridged teeth in non-venomous snakes are used to reduce suctional drag when capturing slippery prey like fish or invertebrates. CT scanning of the known specimens of ''Euchambersia'' by Benoit and colleagues was subsequently used to provide more concrete support in favour of the venom hypothesis. The canals leading into and from the maxillary fossae, as revealed by the scans, would primarily have supported the trigeminal nerve as well as blood vessels. However, the fact that the canals also directly lead to the root of the canines would suggest that they had a secondary role in venom delivery. In all, ''Euchambersia'' seems to have had a venom gland (housed in the maxillary fossae), a delivery mechanism of the venom (the maxillary canals), and an instrument by which a wound for venom delivery can be inflicted (the ridged canines), which satisfy the criteria of a venomous animal as defined by Wolfgang Bücherl. Benoit ''et al.'' noted that this does not conclusively demonstrate that ''Euchambersia'' was actually venomous, especially given the previously stated objections. Additionally, there are no living animals with a delivery system analogous to the proposed system for ''Euchambersia'' (most deliver venom through the lower jaw, while snakes have specialized ducts. An alternate hypothesis suggested by Benoit ''et al.'' involves some kind of sensory organ occupying the maxillary fossa. Uniquely among therapsids, the canal within the maxilla is exposed on the back side of the maxillary fossa, which implies that the canal, carrying the trigeminal nerve, would probably have extended across the fossa, outside of the outline of the skull. Benoit ''et al.'' hypothesized that the fossa may have supported a specialized sensory organ analogous to the pit organ of
pit viper The Crotalinae, commonly known as pit vipers,Mehrtens JM (1987). ''Living Snakes of the World in Color''. New York: Sterling Publishers. 480 pp. . crotaline snakes (from grc, κρόταλον ''krotalon'' castanet), or pit adders, are a subfa ...
s and some other snakes, or alternatively a
ganglion A ganglion is a group of neuron cell bodies in the peripheral nervous system. In the somatic nervous system this includes dorsal root ganglia and trigeminal ganglia among a few others. In the autonomic nervous system there are both sympatheti ...
of nerve cells. It is also possible that this organ functioned as a replacement for the
parietal eye A parietal eye, also known as a third eye or pineal eye, is a part of the epithalamus present in some vertebrates. The eye is located at the top of the head, is photoreceptive and is associated with the pineal gland, regulating circadian rhythm ...
in ''Euchambersia'', like the pit organ does in pit vipers. However, such an expanded sensory organ would be unprecedented among
tetrapod Tetrapods (; ) are four-limbed vertebrate animals constituting the superclass Tetrapoda (). It includes extant and extinct amphibians, sauropsids ( reptiles, including dinosaurs and therefore birds) and synapsids (pelycosaurs, extinct theraps ...
s, and the few other therocephalians that also lack a parietal eye do not have a maxillary fossa either. Thus, Benoit ''et al.'' considered the venom hypothesis as being more plausible. However, in the well-preserved specimen of the second species, ''E. liuyudongi'', neither the
snout A snout is the protruding portion of an animal's face, consisting of its nose, mouth, and jaw. In many animals, the structure is called a muzzle, rostrum, or proboscis. The wet furless surface around the nostrils of the nose of many mammals is c ...
nor the
orbit In celestial mechanics, an orbit is the curved trajectory of an object such as the trajectory of a planet around a star, or of a natural satellite around a planet, or of an artificial satellite around an object or position in space such as a p ...
showed signs of the venomous gland. Only the preorbital (scent) glands are found, supporting the "scent gland hypothesis," although CT scans are required for more knowledge regarding the new species' dentition and skull.


Paleoecology


''E. mirabilis''

The ''Cistecephalus'' Assemblage Zone, from where ''E. mirabilis'' is known, represents a
floodplain A floodplain or flood plain or bottomlands is an area of land adjacent to a river which stretches from the banks of its channel to the base of the enclosing valley walls, and which experiences flooding during periods of high discharge.Goudi ...
that was covered in many small, relatively straight streams. The water level in these streams was probably seasonally dependent. Judging from pollen preserved in the ''Cistecephalus'' AZ, the pollen taxon '' Pityosporites'' (which probably originated from a plant similar to ''
Glossopteris ''Glossopteris'' tymology: from Ancient Greek γλῶσσα (glôssa, " tongue ") + πτερίς (pterís, " fern ")is the largest and best-known genus of the extinct Permian order of seed ferns known as Glossopteridales (also known as Arberia ...
'') was very common, forming some 80% to 90% of the pollen discovered (although the prevalent sediments would not have been ideal for pollen preservation). In the ''Cistecephalus'' AZ, other co-occurring therocephalians included ''
Hofmeyria :''Distinguished from the Late Permian junior synonym of Akidnognathus "Hofmeyria".'' ''Hofmeyria'' is an extinct genus of therocephalians. See also * List of therapsids This list of therapsids is an attempt to create a comprehensive listing ...
'', ''
Homodontosaurus ''Homodontosaurus'' is an extinct genus of therocephalian therapsids from the Late Permian of South Africa. The type species ''Homodontosaurus kitchingi'' was named by South African paleontologist Robert Broom in 1949. Broom based his description ...
'', ''
Ictidostoma ''Ictidostoma'' is an extinct genus of non-mammalian synapsids known from the Tropidostoma Assemblage Zone. See also * List of therapsids This list of therapsids is an attempt to create a comprehensive listing of all genera that have ever been ...
'', ''
Ictidosuchoides ''Ictidosuchoides'' is an extinct genus of ictidosuchid therocephalians. Fossils have been found from the Karoo Basin in South Africa. The genus is known to have been one of the few therocephalians to have survived the Permian-Triassic extinct ...
'', '' Ictidosuchops'', '' Macroscelesaurus'', '' Polycynodon'', and '' Proalopecopsis''. More numerous, however, were the gorgonopsians, which included ''
Aelurognathus ''Aelurognathus'' is an extinct genus of gorgonopsian therapsids from the Permian of South Africa. Discovery The type species is ''Aelurognathus tigriceps'', originally named ''Scymnognathus tigriceps'' by South African paleontologists Rober ...
'', ''
Aelurosaurus ''Aelurosaurus'' ("cat lizard", from Ancient Greek "cat" and "lizard") is a small, carnivorous, extinct genus of gorgonopsian therapsids from the Middle Permian to Late Permian of South Africa. It was discovered in the Karoo Basin of South Afri ...
'', ''
Aloposaurus ''Aloposaurus'' is an extinct genus of gorgonopsian therapsids from the Late Permian of South Africa. It was first named by Robert Broom in 1910, and contains the type species ''A. gracilis'', and possibly a second species ''A. tenuis''. This sma ...
'', ''
Arctognathus ''Arctognathus'' is an extinct genus of gorgonopsids that throve during the Late Permian in the Karoo basin of what is now South Africa. Discovery A carnivore, like all gorgonopsid, ''Arctognathus'' was given its name ("Bear jaw") in referen ...
'', '' Arctops'', ''
Cerdorhinus ''Cerdorhinus'' is an extinct genus of gorgonopsian therapsids from the Permian of South Africa. The type species ''Cerdorhinus parvidens'' was named by South African paleontologist Robert Broom Robert Broom FRS FRSE (30 November 1866 6 Apr ...
'', ''
Clelandina ''Clelandina'' is an extinct genus of rubidgeine gorgonopsian from the Late Permian of ''Cistecephalus'' Assemblage Zone of South Africa. It was first named by Broom in 1948. The type and only species is ''C. rubidgei''. It is relatively rar ...
'', '' Cyonosaurus'', ''
Dinogorgon ''Dinogorgon'' is a genus of gorgonopsid from the Late Permian of South Africa and Tanzania. The generic name ''Dinogorgon'' is derived from Greek, meaning "terrible gorgon", while its species name ''rubidgei'' is taken from the surname of renown ...
'', ''
Gorgonops ''Gorgonops'' (from el, Γοργών 'Gorgon' and 'eye, face', literally 'Gorgon eye' or 'Gorgon face') is an extinct genus of gorgonopsian therapsids, of which it is the type genus, having lived during the Late Permian (Wuchiapingian), about ...
'', ''
Lycaenops ''Lycaenops'' ("wolf-face") is a genus of carnivorous therapsids. It lived during the Middle Permian to the early Late Permian, about 260 mya, in what is now South Africa. Description ''Lycaenops'' measured about and weighed up to . Like the ...
'', ''
Leontocephalus ''Aelurognathus'' is an extinct genus of gorgonopsian therapsids from the Permian of South Africa. Discovery The type species is ''Aelurognathus tigriceps'', originally named ''Scymnognathus tigriceps'' by South African paleontologists Rober ...
'', ''
Pardocephalus ''Aelurognathus'' is an extinct genus of gorgonopsian therapsids from the Permian of South Africa. Discovery The type species is ''Aelurognathus tigriceps'', originally named ''Scymnognathus tigriceps'' by South African paleontologists Rober ...
'', '' Prorubidgea'', ''
Rubidgea ''Rubidgea'' is a genus of Gorgonopsia, gorgonopsid from the upper Permian of South Africa and Tanzania, containing the species ''Rubidgea atrox''. The generic name ''Rubidgea'' is sometimes believed to be derived from the surname of renowned Kar ...
'', ''
Scylacops ''Scylacops'' (meaning "face that tears") is an extinct genus of Gorgonopsia. It was first named by Broom in 1913,Broom, R. "On the Gorgonopsia, a Sub-order of the Mammal-like Reptiles." ''Proceedings of the general meetings for scientific busines ...
'', '' Scymnognathus'', and ''
Sycosaurus ''Sycosaurus'' is an extinct genus of rubidgeine gorgonopsians from the Usili Formation The Usili Formation is a Late Permian geologic formation in Tanzania. It preserves fossils of many terrestrial vertebrates from the Permian, including t ...
''. By far the most abundant herbivore was the
dicynodont Dicynodontia is an extinct clade of anomodonts, an extinct type of non-mammalian therapsid. Dicynodonts were herbivorous animals with a pair of tusks, hence their name, which means 'two dog tooth'. Members of the group possessed a horny, typicall ...
''
Diictodon ''Diictodon'' is an extinct genus of pylaecephalid dicynodont. These mammal-like synapsids lived during the Late Permian period, approximately 255 million years ago. Fossils have been found in the ''Cistecephalus'' Assemblage Zone of the Mad ...
'', with over 1900 known specimens from the ''Cistecephalus'' AZ. Other dicynodonts included ''
Aulacephalodon ''Aulacephalodon'' is an extinct genus of medium-sized dicynodonts, or non-mammalian synapsids, that lived during Permian period, about 299-252 million years ago. Individuals of ''Aulacephalodon'' are commonly found in the Lower Beaufort Group o ...
'', ''
Cistecephalus ''Cistecephalus'' is an extinct genus of dicynodont therapsid from the Late Permian of southern Africa (South Africa and Zambia). It was a small, specialised, burrowing dicynodont, possibly with habits similar to a modern mole. The head was flatt ...
'', ''
Dicynodon ''Dicynodon'' ("two dog-teeth") is a genus of dicynodont therapsid that flourished during the Upper Permian period. Like all dicynodonts, it was herbivorous animal. This reptile was toothless, except for prominent tusks, hence the name. It probab ...
'', ''
Dicynodontoides ''Dicynodontoides'' is a genus of small to medium-bodied, herbivorous, emydopoid dicynodonts from the Late Permian. The name ''Dicynodontoides'' references its “dicynodont-like” appearance (dicynodont = two-dog-tooth) due to the caniniform t ...
'', ''
Digalodon ''Digalodon'' is an extinct genus of kistecephalian dicynodont. For a time it was considered synonymous with other dicynodonts as a small juvenile of a larger genus, such as ''Aulacephalodon'' or ''Dicynodontoides'', however it has since been re ...
'', ''
Dinanomodon ''Dinanomodon'' is a genus of dicynodont from Late Permian (Changhsingian) of the ''Lystrosaurus'' Assemblage Zone, Katberg Formation, and ''Cistecephalus'' Assemblage Zone, Balfour Formation Beaufort Group, Karoo Basin of South Africa ...
'', ''
Emydops ''Emydops'' is an extinct genus of dicynodont therapsid from the Permian of South Africa. ''Emydops'' was first named by South African paleontologist Robert Broom in 1912 when he described ''Emydops minor''. In the following years, the genus gre ...
'', ''
Endothiodon ''Endothiodon'' (/ɛndoʊθiːoʊdɔːn/ "inner tooth" from Greek endothi (ἔνδοθῐ), "within", and odon (ὀδών), "tooth", most likely named for the characteristic of the teeth being placed internally to the maxillaBoos A. S., Schultz C ...
'', '' Kingoria'', ''
Kitchinganomodon ''Kitchinganomodon'' is a genus of dicynodont from Late Permian (Wuchiapingian) of South Africa South Africa, officially the Republic of South Africa (RSA), is the Southern Africa, southernmost country in Africa. It is bounded to the sout ...
'', ''
Oudenodon ''Oudenodon'' is an extinct genus of dicynodont. It was common throughout southern Africa during the Late Permian. Several species of ''Oudenodon'' are known. Both ''O. bainii'', the type species, and ''O. grandis'' are known from South Africa ...
'', ''
Palemydops ''Palemydops'' is an extinct genus of non-mammalian 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, ...
'', ''
Pelanomodon ''Pelanomodon'' is an extinct genus of dicynodont therapsids that lived in the Late Permian period. Fossil evidence of this genus is principally found in the Karoo Basin of South Africa, in the ''Dicynodon'' Assemblage Zone.Kammerer, C. F., K. D ...
'', ''
Pristerodon ''Pristerodon'' is an extinct genus of dicynodont therapsid from the Late Permian of South Africa, Zambia and India. Paleobiology Brain and senses ''Pristerodon'' were among the earliest land animals able to hear airborne sound as opposed to ...
'', and ''
Rhachiocephalus ''Rhachiocephalus'' is an extinct genus of dicynodont 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 orig ...
''. The
biarmosuchia Biarmosuchians are an extinct clade of non-mammalian synapsids from the Permian. They are the most basal group of the therapsids. All of them were moderately-sized, lightly-built carnivores, intermediate in form between basal sphenacodont "pelyc ...
ns ''
Lemurosaurus ''Lemurosaurus'' is a genus of extinct biarmosuchian therapsids from the Late Permian of South Africa. The generic epithet ''Lemursaurus'' is a mix of Latin, lemures “ghosts, spirits”, and Greek, sauros, “lizard”. ''Lemurosaurus'' is easi ...
'', ''
Lycaenodon ''Lycaenodon'' is an extinct genus of biarmosuchian therapsids from the Late Permian of South Africa. It is known from a single species, ''Lycaenodon longiceps'', which was named by South African paleontologist Robert Broom in 1925. Both are smal ...
'', ''
Paraburnetia ''Paraburnetia'' is an extinct genus of biarmosuchian therapsids from the Late Permian of South Africa. It is known for its species ''P. sneeubergensis'' and belongs to the family Burnetiidae. ''Paraburnetia'' lived just before the Permian–T ...
'', and ''
Rubidgina ''Rubidgina'' is a genus of Biarmosuchian 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 e ...
'' were also present, along with the
cynodont The cynodonts () (clade Cynodontia) are a clade of eutheriodont therapsids that first appeared in the Late Permian (approximately 260 mya), and extensively diversified after the Permian–Triassic extinction event. Cynodonts had a wide variety ...
s ''
Cynosaurus ''Cynosaurus'' is an extinct genus of cynodonts. Remains have been found from the ''Dicynodon'' Assemblage Zone in South Africa.T. S. Kemp: ''The Origin and Evolution of Mammals'' Oxford University Press, 2005. ''Cynosaurus'' was first describe ...
'' and ''
Procynosuchus ''Procynosuchus'' (Greek: "Before dog crocodile") is an extinct genus of cynodonts from the Late Permian. It is considered to be one of the earliest and most basal cynodonts. It was 60 cm (2 ft) long. Remains of ''Procynosuchus'' have ...
''. Non-synapsids included the
archosauromorph Archosauromorpha (Greek for "ruling lizard forms") is a clade of diapsid reptiles containing all reptiles more closely related to archosaurs (such as crocodilians and dinosaurs, including birds) rather than lepidosaurs (such as tuataras, liza ...
''
Younginia ''Youngina'' is an extinct genus of diapsid reptile from the Late Permian Beaufort Group ('' Tropidostoma''-'' Dicynodon'' zones) of the Karoo Red Beds of South Africa. This, and a few related forms, make up the family Younginidae, within the ...
''; the
parareptilia Parareptilia ("at the side of reptiles") is a subclass or clade of basal sauropsids (reptiles), typically considered the sister taxon to Eureptilia (the group that likely contains all living reptiles and birds). Parareptiles first arose near the ...
ns '' Anthodon'', ''
Milleretta ''Milleretta'' is an extinct genus of millerettid parareptile from the Late Permian of South Africa. Fossils have been found in the Balfour Formation.Ruta, M., Cisneros, JC., Liebrecht, T., Tsuji, L. A. and Müller, J. 2011Amniotes through major b ...
'', ''
Nanoparia ''Nanoparia'' is an extinct genus of pareiasaur that lived in the Permian. Description It was about 60 cm in length, and weighed around 8 to 10 kilograms. Classification This is an unusual small, spiny specialised form. The skull is ve ...
'', ''
Owenetta ''Owenetta'' is an extinct genus of owenettid procolophonian parareptile. Fossils have been found from the Beaufort Group in the Karoo Basin of South Africa. Although most procolophonians lived during the Triassic, ''Owenetta'' existed during the ...
'', and ''
Pareiasaurus ''Pareiasaurus'' is an extinct genus of pareiasauromorph reptile from the Permian period. It was a typical member of its family, the pareiasaurids, which take their name from this genus. Fossils have been found in the Beaufort Group. Descript ...
''; and the
temnospondyl Temnospondyli (from Greek language, Greek τέμνειν, ''temnein'' 'to cut' and σπόνδυλος, ''spondylos'' 'vertebra') is a diverse order (biology), order of small to giant tetrapods—often considered Labyrinthodontia, primitive amphi ...
''
Rhinesuchus ''Rhinesuchus'' (meaning "rasp crocodile" for the ridged surface texture on its skull bones) is a large temnospondyl amphibian. Remains of the genus are known from the Permian of the South African Karoo Basin's ''Tapinocephalus'' and ''Cistec ...
''.


''E. liuyudongi''

The Naobaogou Formation, from which ''E. liuyudongi'' is known, is part of a series of Late Permian river and lake deposits in Inner Mongolia, which were deposited by
braided river A braided river, or braided channel, consists of a network of river channels separated by small, often temporary, islands called braid bars or, in English usage, ''aits'' or ''eyots''. Braided streams tend to occur in rivers with high sediment l ...
s, floodplains, and floodplain lakes. Therocephalians had been reported from the Naobaogou Formation as early as 1989, but these fossils were later lost. Subsequently, Liu and Abdala confirmed their presence in the formation by describing two other akidnognathids besides ''E. liuyudongi'', '' Shiguaignathus'' and '' Jiufengia'', as well as ''
Caodeyao ''Caodeyao'' (in reference to the village of Caodeyao) is a genus of therocephalian that lived in what is now China during the late Permian. It was found in the Naobaogou Formation The Naobaogou Formation is a geological formation in the Daqin ...
'', a non-akidnognathid therocephalian closely related to the Russian '' Purlovia''. Unlike the more specialized ''E. liuyudongi'', Liu and Abdala's 2022 phylogenetic analysis found ''Shiguaignathus'' and ''Jiufengia'' to be less specialized ( basal) members of Akidnognathinae, while simultaneously originating from the younger member III of the formation. Thus, ''E. liuyudongi'' provides evidence of both a therocephalian genus existing in both southern and north
Pangaea Pangaea or Pangea () was a supercontinent that existed during the late Paleozoic and early Mesozoic eras. It assembled from the earlier continental units of Gondwana, Euramerica and Siberia during the Carboniferous approximately 335 million y ...
and of a specialized akidnognathid genus in northern Pangaea. Like the ''Cistecephalus'' AZ and other Permian palaeoenvironments, dicynodonts were the most commonly preserved animal of the Naobaogou Formation. ''
Daqingshanodon ''Daqingshanodon'' is an extinct genus of dicynodont therapsid from the Late Permian of Inner Mongolia, China. The type species ''D. limbus'' was described in 1989 from a single skull found in the Naobaogou Formation. ''Daqingshanodon'' belongs ...
'' was described in 1989. Subsequently-discovered specimens consist of at least seven different types that may belong to separate species, with one described as '' Turfanodon jiufengensis'', two related to ''Daqingshanodon'', and three or four related to ''
Jimusaria ''Jimusaria'' is an extinct genus of dicynodont therapsid from the Late Permian (Changhsingian) Guodikeng Formation ( Jilicao Group) of China. The type species ''J. sinkianensis'' was originally named as a species of ''Dicynodon'', the first f ...
''. Non-synapsids included the
captorhinid Captorhinidae (also known as cotylosaurs) is an extinct family of tetrapods, traditionally considered primitive reptiles, known from the late Carboniferous to the Late Permian. They had a cosmopolitan distribution across Pangea. Description Cap ...
''
Gansurhinus ''Gansurhinus'' is an extinct genus of moradisaurine captorhinid known from the Middle Permian Qingtoushan Formation of the Qilian Mountains and the Late Permian Naobaogou Formation in the Daqing Mountains of China. It was first named by R ...
''; the parareptilian '' Elginia wuyongae''; and the
chroniosuchia Chroniosuchia is a group of tetrapods that lived from the Middle Permian to Late Triassic in what is now Eastern Europe, Kyrgyzstan, China and Germany. Chroniosuchians are often thought to be reptiliomorphs, but some recent phylogenetic analyses ...
n '' Laosuchus hun''.


See also

*
List of therapsids This list of therapsids is an attempt to create a comprehensive listing of all genera that have ever been included in the Therapsida excluding mammals and purely vernacular terms. The list includes all commonly accepted genera, but also genera tha ...


References

{{Taxonbar, from=Q2386727 Akidnognathids Lopingian synapsids of Africa Fossil taxa described in 1931 Taxa named by Robert Broom