Abdalodon

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Abdalodon
Temporal range: Wuchiapingian
~259–254  Ma
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Abdalodon diastematicus life restoration.jpg
A reconstruction of Abdalodon
Scientific classification OOjs UI icon edit-ltr.svg
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Clade: Synapsida
Clade: Therapsida
Clade: Cynodontia
Family:† Charassognathidae
Subfamily:† Abdalodontinae
Genus:† Abdalodon
Kammerer, 2016
Type species
A. diastematicus
Kammerer, 2016

Abdalodon is an extinct genus of late Permian cynodonts, known by its only species A. diastematicus.Abdalodon together with the genus Charassognathus , form the clade Charassognathidae. [1] This clade represents the earliest known cynodonts, and is the first known radiation of Permian cynodonts. [1]

Contents

Abdalodon diastematicus is known from one crushed fossil skull from the Karoo Basin of South Africa. [2] Of all Permian Therapsids, cynodonts are among the most rare (Biarmosuchians being the only therapsids being of comparable rarity). [1] The fossil record of Permian cynodonts is characterized by a long ghost lineage. [1] Abdalodon has been important for discerning the early evolution of cynodonts. Abdalodon, and its sister taxa Charassognathus are both small bodied animals, Abdalodon having a skull around six centimeters in length [1] and the Charassognathus skull being slightly smaller. [3] This suggests that early cynodont evolution occurred at small body size, which could explain the rarity of Permian cynodont fossils, [1] because there is an inherent taphonomic bias against the fossilization of small bodied animals. [4]

Etymology

The genus name Abdalodon means Abdala's Tooth. The genus was named for paleontologist Fernando Abdala who has made significant contributions to understanding the evolution of the earliest cynodonts. The species epithet diastematicus refers to the characteristic tooth free gap between the canines and postcanines on both the upper and lower jaw. [1]

Geology and paleoenvironment

Abdalodon was discovered in rocks from the Beaufort group of the Karoo Basin of South Africa. [2] During the Permian, South Africa made up the southern edge of the supercontinent of Gondwana. Today, the climate of the Karoo Basin is hot and dry, but during the Carboniferous it was cool and semi-arid. The Karoo Basin was situated between the ECCA[ clarification needed ] shallow sea to the north, and the enormous Cape Fold Mountain belt to the south. Flowing from the mountains into the shallow sea was a series of Mississippi size rivers, carrying with them huge amounts of sediments. By the late Permian these sediments filled the shallow sea, leaving behind the ECCA group. The resulting landscape was an extensive series of floodplains. These flood plains progressed farther northward during the late Permian and Triassic. The sediments deposited in these floodplains would become the Beaufort Group. [5] Since the Late Carboniferous, the climate had warmed dramatically, and grew wetter. The environment now supported a diverse array of flora and fauna. [6] These floodplains were inhabited by the earliest reptiles and synapsids. [7] By the Late Permian, they had become home to the earliest cynodonts, including Abdalodon.

Discovery

The only known existing Abdalodon specimen (a single skull), was originally described as a juvenile specimen of Procynosuchus delaharpeae in 2008. Any variation between this skull and other existing Procynosuchus delaharpeae specimens was explained as ontogenetic variation. Classifying the skull as P. delaharpeae extended the stratigraphic range of Procynosuchus a few million years earlier into the Permian. [2] However, this result was questioned on the premise that the intermediate strata between, containing known Procynosuchus delaharpe specimens, and the formation in which this skull had been discovered, were well sampled and have not yielded any Procynosuchus delaharpeae specimens. [1] The skull was re-examined, and it was concluded that the organism whence it came from was fully grown. This meant features previously explained as ontogenetic variation, were in fact unique characters, and that the skull actually belonged to a new genus of early cynodonts which was subsequently named Abdalodon. [1]

Description

Skull

Skull of Abdalodon In left lateral view. Photo courtesy of Christian Kammerer. Cynodont skull.png
Skull of Abdalodon In left lateral view. Photo courtesy of Christian Kammerer.

The only existing specimen for Abdalodon is an incomplete, dorsoventrally crushed skull, In which the lower jaws are tightly occluded to the palate. [1]

Abdalodon diastematicus is characterized by the presence of diastema between the canines and postcanines of the dentary, and on the maxilla, an even longer diastema between the canines and postcanines. The maxilla has an indentation behind the canine root, and in the same area possess several large foramina. These suggest that Abdalodon may have had whiskers. The posterior end of the maxilla bends medially, insetting the postcanines from the labial border of the snout. The dentary of Abdalodon diastematicus has a well defined masseteric fossa (a synapomorphy of cynodonts). It sits high on the coronoid process, and is where the masseter muscle would have attached to the dentary. The postdentary bones, which are of particular importance since they form the ear bones in mammals, are absent or severely damaged. The nasal bone is relatively flat, and is separated from the maxilla at the anterior end of the snout by the septomaxilla (a therapsid synapomorphy). The lacrimal bone is smaller and narrower than is typical for early cynodonts. Additionally the skull has a significantly broader interorbital region, a shorter temporal region, and a broader snout than either of its closest known relatives: Charassognathus gracilis and Procynosuchus delaharpe. This gives the skull stout appearance comparatively. The dorsal side of the orbital margin is formed entirely by the prefrontal and postorbital bones. The zygomatic arch is nearly entirely formed from the jugal bone, which also makes up part of the postorbital bar. [1]

The anterior region palatal surface of the skull is obscured by the lower jaw, which tightly fixed to the palate. The transverse processes of the pterygoid sweep laterally and posteriorly. When first described the skull was considered to have a triangular interpterygoid vacuity, however upon later examination, the status of a pterygoid vacuity was left ambiguous. The dentary symphysis is covered with foramina, suggesting there may have been whiskers there. The dentary symphysis is tall and sharply angled forming a distinct chin. [1]

Dentition

The 8 upper postcanines on Abdalodon diastematicus are tricuspid, with a large minimally curved main cusp, and two smaller accessory cusps. The accessory cusps are nearly symmetrical and sit anterior and posterior to the main cusp. The roots of the postcanines are thecodont, meaning that the teeth sit in sockets in the middle of the jaw. Four upper incisors are present on both sides of the skull, with the most posterior incisor being separated from the canine by short diastema. There is a tip of a new incisor emerging at the base of incisor number 4, on the left side of the jaw. It has been suggested that this was a fifth incisor, however, due to its position immediately under incisor 4, it is most likely a replacement tooth. The incisors are conical smooth teeth with no serrations. The canines, like the incisors, are smooth and conical, and are proportionally to the size of the skull, larger than those seen in Procynosuchus delaharpae or Charassognathus gracilis. [1]

Skull of Abdalodon in several different views. Photo courtesy of Christian Kammerer. Cynodont Skull.png
Skull of Abdalodon in several different views. Photo courtesy of Christian Kammerer.

The dentition of Abdalodon has played a critical role in distinguishing it from Procynosuchus. There are 3 incisors on the lower jaw of Abdalodon, and the lower incisor count is not known to vary ontogenically in any early cynodont, helping to distinguish the genus from Procynosuchus which has 4. The 8 postcanines of Abdalodon are also outside of the range of ontengenic variation for Procynosuchus, which typically has 9 to 11 postcanines. The long diastema between the canine and the postcanines, in both the upper and lower jaw, is unique to Abdalodon. The main cusp of Abdalodon's postcanines is straighter than those of other early cynodonts. Abdalodon's accessory cusps are proportionally larger when compared to the main cusp than in other early cynodonts. The dentition of Abdalodon helps distinguish it from Procynosuchus, the genus to which it was originally attributed. Charassognathus however bears a similar dental formula to Abdalodon, which has been the basis behind grouping them into the clade Charassognathidae. [1] Charrasognathus however lacks the substantial maxillary and dentary diastema found on Abdalodon, as well as the masseteric fossa, which distinguishes the two. [3]

Classification

Early cynodont relations Early cynodont relations.jpg
Early cynodont relations

Abdalodon belongs to clade Charassognathidae, a subclade nested within Cynodonta. Cynodonta are most notable for having given rise to the clade Mammalia. Cynodonta belongs to clade Therapsida, which in turn is a clade within Synapsida. Synapsida represents one of two major branches of the crown group Amniota, (the other being Sauropsida, a clade which includes Lepidosauria, Dinosauria, Aves and Crocodilia). Cynodonta embody the transition from mammal like reptiles into modern mammals.

Paleobiology

Posture

Since there is no postcranial skeleton for Abdalodon, the exact posture is unknown. However, assumptions about Abdalodon’s posture were made, based on data collected from other cynodonts. For most cynodonts the articular surface of the femoral head is oriented 55° from the axis of the femoral shaft, compared with 80° in pelycosaurs and 25° in typical mammals. Additionally, the distal femoral condyles of cynodonts incline 45° from the long axis, but on the pelycosaur femur they run approximately parallel to the long axis. In mammals, the distal femoral condyles are perpendicular to the long axis. Cynodonts also possess a deeper acetabulum than pelycosaurs, and have an expanded ilium, and reduced ischium which is similar to the pelvic structure of modern mammals. [8] When taken into account this evidence, it has been suggested that cynodonts like Abdalodon had a semi-sprawling posture, somewhere between the upright posture of modern mammals, and the sprawling posture of pelycosaurs. It has also been suggested that therapsids including early cynodonts, could have a hind limb posture which could alternate between sprawling and upright posture, in a condition similar to modern crocodilians. This hypothesis is based on the shape of the femoral head, in addition to an ankle joint that seems suited for articulation in both upright and sprawled posture. [8]

Burrowing behavior

Though there is no direct evidence that Abdalodon burrowed, it is plausible that it did. There is clear evidence that the closely related Triassic cynodonts Thrinaxodon and Trirachodon , also from the Karoo Basin of South Africa, were burrowers. This suggests a long history of burrowing behavior in cynodonts. [9]

Diet

Abdalodon's teeth do not appear well suited for chewing or grinding large quantities of plant matter. Therefore, Abdalodon, like most early cynodonts, was most likely an insectivore or carnivore which preyed upon most anything smaller than itself. It was not until the early to middle Triassic that cynodonts began to diversify their diets; some becoming omnivorous or herbivorous, while others remained carnivorous. [10]

See also

Related Research Articles

<span class="mw-page-title-main">Therapsid</span> Clade of tetrapods including mammals

A therapsid is a member of the clade Therapsida, which is a major group of eupelycosaurian synapsids that includes mammals and 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 underneath the body, as opposed to the sprawling posture of many reptiles and salamanders.

<span class="mw-page-title-main">Dinocephalia</span> Extinct clade of stem-mammals

Dinocephalians 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. Dinocephalians included herbivorous, carnivorous, and omnivorous forms. Many species had thickened skulls with many knobs and bony projections. Dinocephalians were the first non-mammalian therapsids to be scientifically described and their fossils are known from Russia, China, Brazil, South Africa, Zimbabwe, and Tanzania.

<i>Thrinaxodon</i> Extinct genus of cynodonts of Early Triassic South Africa

Thrinaxodon is an extinct genus of cynodonts, including the species T. liorhinus which lived in what are now South Africa and Antarctica during the Early Triassic. Thrinaxodon lived just after the Permian–Triassic mass extinction event, its survival during the extinction may have been due to its burrowing habits.

<i>Galesaurus</i> Extinct genus of cynodonts from the Triassic of South Africa

Galesaurus is an extinct genus of carnivorous cynodont therapsid that lived between the Induan and the Olenekian stages of the Early Triassic in what is now South Africa. It was incorrectly classified as a dinosaur by Sir Richard Owen in 1859.

<span class="mw-page-title-main">Gorgonopsia</span> Extinct group of saber-toothed therapsids from the Permian

Gorgonopsia 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, as well as elongated upper and sometimes lower canine teeth and incisors which were likely used as slashing and stabbing weapons. Postcanine teeth are generally reduced or absent. For hunting large prey, they possibly used a bite-and-retreat tactic, ambushing and taking a debilitating bite out of the target, and following it at a safe distance before its injuries exhausted it, whereupon the gorgonopsian would grapple the animal and deliver a killing bite. They would have had an exorbitant gape, possibly in excess of 90°, without having to unhinge the jaw.

<i>Prozostrodon</i> Extinct genus of cynodonts

Prozostrodon is an extinct genus of probainognathian cynodonts that was closely related to mammals. The remains were found in Brazil and are dated to the Carnian age of the Late Triassic. The holotype has an estimated skull length of 6.7 centimetres (2.6 in), indicating that the whole animal may have been the size of a cat. The teeth were typical of advanced cynodonts, and the animal was probably a carnivore hunting reptiles and other small prey.

<i>Moschorhinus</i> Genus of synapsid from late Permian and early Triassic South Africa

Moschorhinus is an extinct genus of therocephalian synapsid in the family Akidnognathidae with only one species: M. kitchingi, which has been found in the Late Permian to Early Triassic of the South African Karoo Supergroup. It was a large carnivorous therapsid, reaching 1.5 m (4.9 ft) in total body length with the largest skull comparable to that of a lion in size, and had a broad, blunt snout which bore long, straight canines.

<i>Theriognathus</i> Extinct genus of therapsids from late Permian South Africa and Tanzania

Theriognathus is an extinct genus of therocephalian therapsid belonging to the family Whaitsiidae, known from fossils from South Africa, Zambia, and Tanzania. Theriognathus has been dated as existing during the Late Permian. Although Theriognathus means mammal jaw, the lower jaw is actually made up of several bones as seen in modern reptiles, in contrast to mammals. Theriognathus displayed many different reptilian and mammalian characteristics. For example, Theriognathus had canine teeth like mammals, and a secondary palate, multiple bones in the mandible, and a typical reptilian jaw joint, all characteristics of reptiles. It is speculated that Theriognathus was either carnivorous or omnivorous based on its teeth, and was suited to hunting small prey in undergrowth. This synapsid adopted a sleek profile of a mammalian predator, with a narrow snout and around 1 meter long. Theriognathus is represented by 56 specimens in the fossil record.

<i>Styracocephalus</i>

Styracocephalus platyrhynchus is an extinct genus of dinocephalian therapsid that existed during the mid-Permian throughout South Africa, but mainly in the Karoo Basin. It is often referred to by its single known species Styracocephalus platyrhynchus. The Dinocephalia clade consisted of the largest land vertebrates and herbivores during the early to mid-Permian. This period is often also referred to as the Guadalupian epoch, approximately 270 to 260 million years ago.

<i>Paraburnetia</i> Extinct genus of therapsids

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–Triassic mass extinction event.

<i>Brasilodon</i> Extinct genus of mammaliamorphs

Brasilodon is an extinct genus of small, mammal-like cynodonts that lived in what is now Brazil during the Norian age of the Late Triassic epoch, about 225.42 million years ago. While no complete skeletons have been found, the length of Brasilodon has been estimated at 12 centimetres (4.7 in). Its dentition shows that it was most likely an insectivore. The genus is monotypic, containing only the species B. quadrangularis. Brasilodon belongs to the family Brasilodontidae, whose members were some of the closest relatives of mammals, the only cynodonts alive today. Two other brasilodontid genera, Brasilitherium and Minicynodon, are now considered to be junior synonyms of Brasilodon.

Cynosaurus is an extinct genus of cynodonts. Remains have been found from the Dicynodon Assemblage Zone in South Africa. Cynosaurus was first described by Richard Owen in 1876 as Cynosuchus suppostus. Cynosaurus has been found in the late Permian period. Cyno- is derived from the Greek word kyon for dog and –sauros in Greek meaning lizard.

<i>Microgomphodon</i> Genus of therapsid from the Middle Triassic of southern Africa

Microgomphodon is an extinct genus of therocephalian therapsid from the Middle Triassic of South Africa and Namibia. Currently only one species of Microgomphodon, M. oligocynus, is recognized. With fossils present in the Cynognathus Assemblage Zone (CAZ) of the Burgersdorp Formation in South Africa and Omingonde Formation of Namibia and ranging in age from late Olenekian to Anisian, it is one of the most geographically and temporally widespread therocephalian species. Moreover, its occurrence in the upper Omigonde Formation of Namibia makes Microgomphodon the latest-surviving therocephalian. Microgomphodon is a member of the family Bauriidae and a close relative of Bauria, another South African bauriid from the CAZ. Like other bauriids, it possesses several mammal-like features such as a secondary palate and broad, molar-like postcanine teeth, all of which evolved independently from mammals.

<i>Progalesaurus</i> Extinct genus of cynodonts

Progalesaurus is an extinct genus of galesaurid cynodont from the early Triassic. Progalesaurus is known from a single fossil of the species Progalesaurus lootsbergensis, found in the Lystrosaurus Assemblage Zone of the Balfour Formation. Close relatives of Progalesaurus, other galesaurids, include Galesaurus and Cynosaurus. Galesaurids appeared just before the Permian-Triassic extinction event, and disappeared from the fossil record in the Middle-Triassic.

Platycraniellus is an extinct genus of carnivorous cynodonts from the Early Triassic. It is known from the Lystrosaurus Assemblage Zone of the Normandien Formation in South Africa. P. elegans is the only species in this genus based on the holotype specimen from the Ditsong National Museum of Natural History in Pretoria, South Africa. Due to limited fossil records for study, Platycraniellus has only been briefly described a handful of times.

<span class="mw-page-title-main">Bauriidae</span> Extinct family of therapsids

Bauriidae is an extinct family of therocephalian therapsids. Bauriids were the latest-surviving group of therocephalians after the Permian–Triassic extinction event, going extinct in the Middle Triassic. They are among the most advanced eutherocephalians and possess several mammal-like features such as a secondary palate and wide postcanine teeth at the back of the jaws. Unlike other therocephalians, bauriids were herbivorous. They were also smaller than earlier members of the group. Two subfamilies are classified within Bauriidae: Nothogomphodontinae and Bauriinae.

<i>Blattoidealestes</i> Extinct genus of therapsid from Middle-Permian South Africa

Blattoidealestes is an extinct genus of therocephalian therapsid from the Middle Permian of South Africa. The type species Blattoidealestes gracilis was named by South African paleontologist Lieuwe Dirk Boonstra from the Tapinocephalus Assemblage Zone in 1954. Dating back to the Middle Permian, Blattoidealestes is one of the oldest therocephalians. It is similar in appearance to the small therocephalian Perplexisaurus from Russia, and may be closely related.

<span class="mw-page-title-main">Charassognathidae</span> Extinct family of cynodonts

Charassognathidae is an extinct family of basal cynodonts known from the Late Permian of South Africa and Zambia. It was named in 2016 by the palaeontologist Christian F. Kammerer, who defined it as all taxa more closely related to Charassognathus gracilis than to Dvinia prima, Galesaurus planiceps or Procynosuchus delaharpeae. The family contains the genera Charassognathus, Abdalodon and Nshimbodon, with the latter two making up the subfamily Abdalodontinae.

<i>Bonacynodon</i> Extinct genus of cynodonts

Bonacynodon is an extinct genus of cynodonts that lived in what is now southern Brazil during the Triassic period. The genus is monotypic, containing only the type species Bonacynodon schultzi. B. schultzi is known from two specimens, consisting of two partial skulls and some badly preserved parts of the postcranium. Both specimens were recovered from the Pinheiros-Chiniquá Sequence, part of the Santa Maria Supersequence of the Paraná Basin. This sequence preserves a faunal association known as the Dinodontosaurus Assemblage Zone, which contains numerous other species of cynodonts, dicynodonts and reptiles. Bonacynodon was a small, likely insectivorous cynodont, whose length has been estimated at around 30 centimetres (12 in). It can be distinguished from other cynodonts by its large, serrated (saw-like) canine teeth. Together with the genus Probainognathus of Argentina, it made up the family Probainognathidae, one of the earliest-diverging lineages of the clade Probainognathia. It was a fairly close relative of mammals, the only group of cynodonts alive today.

Vetusodon is an extinct genus of cynodonts belonging to the clade Epicynodontia. It contains one species, Vetusodon elikhulu, which is known from four specimens found in the Late Permian Daptocephalus Assemblage Zone of South Africa. With a skull length of about 18 centimetres (7.1 in), Vetusodon is the largest known cynodont from the Permian. Through convergent evolution, it possessed several unusual features reminiscent of the contemporary therocephalian Moschorhinus, including broad, robust jaws, large incisors and canines, and small, single-cusped postcanine teeth.

References

  1. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 Kammerer, Christian F. (2016-04-29). "A new taxon of cynodont from the Tropidostoma Assemblage Zone (upper Permian) of South Africa, and the early evolution of Cynodontia". Papers in Palaeontology. 2 (3): 387–397. doi:10.1002/spp2.1046. ISSN   2056-2802.
  2. 1 2 3 J., Botha-Brink; F., Abdala (April 2008). "A new cynodont record from the Tropidostoma Assemblage Zone of the Beaufort Group: implications for the early evolution of cynodonts in South Africa". Palaeontologia Africana. 43: 1–6.
  3. 1 2 Botha, J.; Abdala, F.; Smith, R. (March 2007). "The oldest cynodont: new clues on the origin and early diversification of the Cynodontia". Zoological Journal of the Linnean Society. 149 (3): 477–492. doi: 10.1111/j.1096-3642.2007.00268.x . ISSN   0024-4082.
  4. ↑ Cowen, Richard (9 January 2003). "Biases in the Fossil Record". UCDavis.edu. Archived from the original on 15 January 2019. Retrieved 27 May 2018.
  5. ↑ Rubidge, Bruce; Hancox, John (February 2002). "The Karoo Supergroup". Rocks & Minerals. 77 (1): 54–59. doi:10.1080/00357529.2002.9926658. ISSN   0035-7529. S2CID   127048478.
  6. ↑ Catuneanu, O.; Wopfner, H.; Eriksson, P.G.; Cairncross, B.; Rubidge, B.S.; Smith, R.M.H.; Hancox, P.J. (October 2005). "The Karoo basins of south-central Africa". Journal of African Earth Sciences. 43 (1–3): 211–253. Bibcode:2005JAfES..43..211C. doi:10.1016/j.jafrearsci.2005.07.007. ISSN   1464-343X.
  7. ↑ Rubidge, B. "Biostratigraphy of the Beaufort Group (Karoo Supergroup)", 1995, Biostratigraphic Series - South African Committee for Stratigraphy. Pretoria, South Africa: Council for Geoscience. Report 1.
  8. 1 2 Blob, Richard W. (March 2001). "Evolution of hindlimb posture in nonmammalian therapsids: biomechanical tests of paleontological hypotheses". Paleobiology. 27 (1): 14–38. doi:10.1666/0094-8373(2001)027<0014:eohpin>2.0.co;2. ISSN   0094-8373.
  9. ↑ Damiani, R.; Modesto, S.; Yates, A.; Neveling, J. (2003-08-22). "Earliest evidence of cynodont burrowing". Proceedings of the Royal Society B: Biological Sciences. 270 (1525): 1747–1751. doi:10.1098/rspb.2003.2427. ISSN   0962-8452. PMC   1691433 . PMID   12965004.
  10. ↑ Ruta, Marcello; Botha-Brink, Jennifer; Mitchell, Stephen A.; Benton, Michael J. (2013-10-22). "The radiation of cynodonts and the ground plan of mammalian morphological diversity". Proceedings of the Royal Society B: Biological Sciences. 280 (1769): 20131865. doi:10.1098/rspb.2013.1865. ISSN   0962-8452. PMC   3768321 . PMID   23986112.
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