| Ufudocyclops | |
|---|---|
 | |
| Life restoration ofUfudocyclops | |
Scientific classification | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Clade: | Synapsida |
| Clade: | Therapsida |
| Suborder: | †Anomodontia |
| Clade: | †Dicynodontia |
| Family: | †Stahleckeriidae |
| Subfamily: | †Stahleckeriinae |
| Genus: | †Ufudocyclops Kammereret al.,2019 |
| Species: | †U. mukanelai |
| Binomial name | |
| †Ufudocyclops mukanelai Kammereret al., 2019 | |
Ufudocyclops is anextinctgenus ofstahleckeriiddicynodont from theMiddle Triassic ofSouth Africa. It was found in theBurgersdorp Formation, part of the uppermostCynognathus Assemblage Zone of theBeaufort Group in theKaroo Basin. Thetype and only known species isU. mukanelai. It was a large, beaked herbivore like other Triassic dicynodonts, lacking tusks, and is mostly characterised by unique features of the skull. It is known from three specimens, two of which were previously referred to theTanzanian dicynodontAngonisaurus. The separation ofUfudocyclops fromAngonisaurus indicates that the Middle Triassic fauna of the Beaufort Group in South Africa was not part of a larger shared fauna with those of theManda Beds in Tanzania, as was previously supposed, and suggests that they were separated as more localised faunas, possibly by geographic barriers or in time.Ufudocyclops then would have been a unique part of the uppermostCynognathus Assemblage Zone in South Africa. It is also the oldest known member of thefamily Stahleckeriidae, and implies that the family was already diversifying in the Middle Triassic alongside otherkannemeyeriiforms, not just in theLate Triassic after other families died out.
Ufudocyclops is a large dicynodont, with the largest specimen reconstructed to have an estimated skull length of 35 centimetres (14 in) and the smaller completeholotype skull at approximately 29 centimetres (11 in) long, and an estimated overall body size similar to that ofKannemeyeria. Only skulls and one partial lower jaw are definitively known, and no postcrania from the body has been identified, but it likely resembled other stahleckeriid dicynodonts with a heavily built body, short tail, and stocky limbs, possibly including upright hind-limbs paired with sprawling forelimbs like other large dicynodonts. Like some other stahleckeriids,Ufudocyclops appears to have lacked the tusks characteristic of many other dicynodonts, and was completely toothless.[1][2]
The skull ofUfudocyclops superficially resemblesAngonisaurus, being relatively tall and notably broad behind the snout, with large, sideways facing eyes and prominent tuskless caniniform processes on themaxilla that project away down and forwards from the snout, flaring out slightly to sides, with blunted tips. The lower surfaces of the maxilla are heavily pitted and rugose, as is thepremaxilla and the palate on the roof of the mouth. These textures correspond to the eponymous tortoise-like keratinous beak typical of dicynodonts likeUfudocyclops. The isolated tip of the premaxilla demonstrates that these pits are superficial and do not continue deeper into the bone, as the inner texture of the bone is smooth and tabulate, and so are notforamina.[1]
Like various other dicynodonts, the face is ornamented with bony bosses on the snout around the eyes. The bulbousnasal bones on the top of the snout each sport a single ovoid-shaped boss that overhangs the nostrils and stops just short of theorbits (eye sockets) in front of the eyes. The paired bosses are separated by a 3–7 cm (1–3 in) wide gap of flat, featureless bone between them on top of the snout where the premaxilla and the nasals meet. This is an unusual condition for kannemeyeriiforms, which typically only have a single large boss across the whole surface of the snout. In fact, the bosses are superficially more like those ofcryptodonts—a group ofPermian dicynodonts unrelated to kannemeyeriiforms—that also had a pair of divided nasal bosses. Similar, but smaller, bosses are found on theprefrontal andpostorbital bones, situated around the upper front and back corners of the eyes, respectively. Like the nasal bosses, these two bosses are clearly separated as individual growths, and do not form a continuous rim around the top of the eyes.[1]
The skull ofUfudocyclops is otherwise fairly standard for dicynodonts, however it has some other unique characteristics, such as the form of thejugal bone. In most other dicynodonts the jugal is small and restricted under the eyes, but inUfudocyclops it extends along much of the lateral (outside) face of thezygomatic arch beneath the eyes and cuts off the maxilla, which usually joins to thesquamosal on the zygomatic arch. This unusual setup of the jugal also causes the zygomatic arch to noticeably jut out from the skull under the eyes, compared to other kannemeyeriiforms where it gradually curves out away from the skull. In addition, while most kannemeyeriiforms have the front of the orbits formed only by the jugal and thelacrimal bone,Ufudocyclops also has a very small portion of the maxilla between them too.[1]
Ufudocyclops is also characterised by the unique X-shaped intertemporal bar on the roof of the skull between eachtemporal fenestra, where the large jaw muscles attached. The bar is broad at the front just behind the eyes and at the back of the skull, while the middle is pinched inwards between the two temporal fenestra, creating the characteristic 'X'-shape. The eponymouspineal foramen on the roof of the skull is also proportionately "enormous" (6 cm (2.4 in) long), implyingUfudocyclops had a very well-developedparietal "third eye". The pineal foramen also has a characteristic depression behind it on the intertemporal bar that is deep and triangular in shape.[1]
The lower jaw ofUfudocyclops is only partially known, and is only known from one of the referred specimens. Most of what is preserved consists of the front half of themandibles, namely the twodentaries, as well as asplenial and portions of theangulars. The jaws are also missing the tip of themandibular symphysis at the very front where the two jaw bones are fused, but enough is preserved to suggest the lower beak was somewhat squared off. The dentaries are toothless and covered in pits and grooves like those of the upper jaws, typical of the beaked lower jaws of derived dicynodonts. Additionally, parts of both thearticular bones were found attached to thequadrates of the skull. These show the typical dicynodont arrangement with two rounded condyles divided by a ridge between them that allows for the lower jaw to slide backwards and forwards during feeding.[1]
The first specimens ofUfudocyclops (BP/1/5530 and BP/1/5531) were discovered by palaeontologist P. John Hancox while fossil collecting in the southernKaroo Basin nearSterkstroom in theEastern Cape Province,South Africa in an expedition to assess thestratigraphic range of the dicynodontKannemeyeria. Together with his colleague Bruce S. Rubidge, the skulls were reported in a research letter toSouth African Journal of Science in February 1994, where the fossils were recognised as a third distinct genus of dicynodont from theCynognathus Assemblage Zone (AZ), followingKannemeyeria andKombuisia. At the time Hancox and Rubidge did not attempt to identify the specimens and simply referred to them as a "tuskless dicynodont". They speculated that large dicynodont postcranial remains from the upperCynognathus AZ, previously attributed toKannemeyeria, may have also belonged to their new dicynodont, and that their new dicynodont could be used to further subdivide theCynognathus AZ above the range ofKannemeyeria.[3]
Hancox and Rubidge later briefly described the specimens in August 1996, and then again in more detail in May 2013, referring them both times to the Tanzanian dicynodontAngonisaurus after favourably comparing their skulls. However, the South African specimens were not identical to the TanzanianA. cruickshanki, interpreted as either a difference between species,sexual dimorphism, orintraspecific variation between different populations, so Hancox and Rubidge provisionally diagnosed them asAngonisaurus sp. Nonetheless, they were regarded as the first record ofAngonisaurus outside of theManda Beds in Tanzania. This was suggested to support a shared Middle Triassic fauna between the uppermostCynognathus AZ (now known as theUfudocyclops–Cricodon Subzone) and the Manda Beds, based on the shared presence ofAngonisaurus.[4][5]
The third and best preserved specimen ofUfudocyclops—BP/1/8208, which would become thetype specimen—was not discovered until 2014 and then collected in 2017 as part of a series of joint excavations by theEvolutionary Studies Institute of theUniversity of the Witwatersrand (Johannesburg) and theUniversity of Birmingham (United Kingdom). The skull was found upside down and isolated in a metre thick block of greenish grey fine grainedsandstone, alongside the skull of the large cynodontImpidens. The earlier specimens BP/1/5530 and BP/1/5531 were shown to be identical in form to the type specimen ofUfudocyclops, prompting a reinterpretation of the two fossils as specimens ofUfudocyclops, and notAngonisaurus as originally believed.[1]
The genusUfudocyclops was named from theXhosa wordufudo, meaning "tortoise", in reference to its toothless, tortoise-like beak, and theAncient Greekcyclops, referring to the very large size of the pineal foramen ("third eye"). The species is named in honour of Mr. Pepson "Pepsi" Mukanela as recognition for his skills in fossil preparation at the Evolutionary Studies Institute, including his work on the holotype, who had recently retired before its publication.[1][6] The holotype skull is nearly complete, missing only its left temporal arch and the tips of the caniniform processes. The tip of the snout was also accidentally sawed through during excavation, separating the very front face of the premaxilla from the rest of the skull, but nothing was lost during collection. The condition of the skull is good, preserving much of the surface features including sutures on the skull roof and palate, as well as much of the ornamentation with only some wear on the top of the snout and to the back of the skull. The two referred skulls are much more incomplete and disarticulated, with BP/1/5530 consisting of only a partial skull roof and a single caniniform process, while BP/1/5531 also includes pieces of the palate,braincase and lower jaw.
Initial examinations of the referred specimens BP/1/5530 and BP/1/5531 identified them as belonging to the genusAngonisaurus. This was argued on the basis of a combination of shared features between these specimens andAngonisaurus thought to be unique to them (although they are now known to be more widespread in Kannemeyeriiformes)[1] rather than shared unique traits.[4][5] The poor preservation of these specimens made identification difficult, and it wasn't until the discovery of the nearly complete holotype skull that the distinctiveness ofUfudocyclops could be properly appreciated. Interestingly, while not yet recognised as their own genus, the referred specimens ofUfudocyclops were correctly determined to belong to thefamily Stahleckeriidae, contrasting with associations ofAngonisaurus withShansiodontidae at the time.[4]
Ufudocyclops is distinguished from other kannemeyeriiform dicynodonts, as well asAngonisaurus, by its X-shaped intertemporal bar and deep triangular depression behind the pineal foramen, as well as by the extension of the jugal beneath the eyes and the two distinctly separated nasal bosses.[1]
The relationship ofUfudocyclops with other dicynodonts was testedphylogenetically by Kammerer and colleagues by combining the data from three other recently updated analyses (Angielcyzk & Kammerer 2017,[7] Angielcyzket al. 2018,[8] and Kammerer 2018[9]) and the new information from the holotype ofUfudocyclops. A simplifiedcladogram, an excerpt from the full analysis, focused on the relationships ofUfudocyclops within Kannemeyeriiformes is shown below:[1]
Their results were generally similar to previous studies, although notably within Kannemeyeriiformes the familyShansiodontidae was found to beparaphyletic.
Ufudocyclops andStahleckeria were found to be each other's closest relatives, sharing at least two characteristics between each other. However, Kammerer and colleagues also identified one feature more like those of earlier kannemeyeriiforms, and found that it was almost as equally plausible thatUfudocyclops could be the mostbasal species of Stahleckeriinae. This would also be consistent withUfudocyclops being older than all other stahleckeriines, however, the ancestral appearance of stahleckeriids is poorly understood and so it is unclear whetherUfudocyclops is indeed less derived thanStahleckeria and other stahleckeriines.[1]
Ufudocyclops is known only from the uppermost Burgersdorp Formation, and was a part of the youngest subzone of theCynognathus Assemblage Zone (AZ) fauna. TheCynognathus AZ was previously divided into three informal subzones, simply known as subzones A, B, and C, and were recognised by a characteristic set of fauna in each, as well as shared components throughout them. These subzones were formally defined in 2020 by Hancox and colleagues, who named Subzone C theUfudocyclops–Cricodon Subzone in recognition of the unique co-occurrence ofUfudocyclops, endemic to the subzone, and the cynodontCricodon metabolus.[10] TheCynognathus AZ as a whole has been roughly dated to the Middle Triassic in age, possibly lateAnisian. The Burgersdorp Formation is largely made up of maroonclay-mudstones, believed to have been deposited in an environment with ameandering river flowing through it.[5] The unit of rock that preserved the holotype skull ofUfudocyclops grades fromcross-bedding and laminatedripples to finesiltstone, and some units also preserve traces of roots. These indicate that the area was part a vegetated floodplain close to flowing water, possibly in a river channel itself or formed as acrevasse splay when the river burst its banks.[1]
The fauna of theUfudocyclops–Cricodon Subzone is characterised byUfudocyclops itself, as well as by the presence of the largemastodonsauridtemnospondyl amphibianParacyclotosaurus morganorum.Ufudocycylops also coexisted with another large dicynodont that is referred only toShansiodon sp., as well as various cynodonts including the predatoryCynognathus and the herbivorousDiademodon—both of which are ubiquitous to the entireCynognathus AZ. It also coexisted with twotrirachodontid cynodonts, the large and potentially predatory omnivoreImpidens, and a smaller species tentatively referred toCricodon metabolus.[11] TheUfudocyclops–Cricodon Subzone directly overlays the olderTrirarchodon–Kannemeyeria Subzone that was characterised by the presence of the eponymous dicynodontKannemeyeria, whichUfudocyclops had seemingly replaced ecologically as a large browsing herbivore.[1][10]
Because specimens ofUfudocyclops were once thought to belong toAngonisaurus, it was believed that theUfudocyclops–Cricodon Subzone and the Manda Beds in Tanzania were part of a larger shared fauna distributed throughout Africa during the Middle Triassic, even extending into Antarctica.[5][12] However, the distinction ofUfudocyclops fromAngonisaurus suggests that dicynodonts in Middle Triassic Africa were more divided than had been assumed, separated into different localised faunas and habitats. It is unclear whetherUfudocyclops was geographically restricted to the Karoo Basin from the Manda Beds, or if the two localities were separated in time, but in either caseUfudocyclops was an endemic part of the Karoo dicynodont fauna.[1]
The discovery ofUfudocyclops in the uppermost Karoo Basin also adds to a growing number of stahleckeriids from the Middle Triassic, along with the African generaZambiasaurus andSangusaurus. Stahleckeriid dicynodonts were mostly known from theLate Triassic, and had been suggested to have been a 'slow fuse' lineage that radiated only after the older families of kannemeyeriiforms, such asKannemeyeriidae andShansiodontidae, had already gone extinct. As the oldest and possibly most basal member of the family,Ufudocyclops demonstrates that the group had already diversified alongside other kannemeyeriiforms. Nonetheless,Ufudocyclops suggests that stahleckeriids were able to replace other kannemeyeriiforms following local ecological turnovers, at least locally in the Karoo Basin, where it replacedKannemeyeria after the latter had dominated the precedingTrirarchodon–Kannemeyeria Subzone of theCynognathus AZ.[1]
