Palatodonta

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Palatodonta
Temporal range: Middle Triassic, 246  Ma
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Palatodonta skull diagram.png
Skull diagram
Scientific classification OOjs UI icon edit-ltr.svg
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Reptilia
Superorder: Sauropterygia
Clade: Placodontiformes
Genus: Palatodonta
Neenan et al., 2013
Type species
Palatodonta bleekeri
Neenan et al., 2013

Palatodonta is an extinct genus of neodiapsid reptile known from the early Middle Triassic (early Anisian stage) of the Netherlands. It was initially described in 2013 as a basal placodontiform closely related to a group of marine reptiles called placodonts, characterized by their crushing teeth and shell-like body armor. Under this interpretation, Palatodonta is transitional between placodonts and less specialized reptiles. Like placodonts, it has a row of large teeth on its palate, but while these teeth are thick and blunt in placodonts, Palatodonta has palatal teeth that are thin and pointed (like the teeth that line the jaws of most other reptiles). [1] A 2023 study instead classified it as a sauropterygomorph and the sister taxon to Eusaurosphargis . In other words, it is close to, but not within, Sauropterygia (the group containing placodonts and other marine reptiles such as nothosaurs and plesiosaurs). [2]

Contents

Discovery

Palatodonta was first named by James M. Neenan, Nicole Klein and Torsten M. Scheyer in 2013 and the type species is Palatodonta bleekeri. The generic name refers to the row of teeth on the palatine bone of the palate. The specific name honours Remco Bleeker, an amateur paleontologist, who discovered the fossil in the summer of 2010 at the Silbeco quarry near Winterswijk. Palatodonta is known from the holotype TW480000470, a well-preserved skull of a juvenile individual. [1]

Description

The skull is tall and has a short, blunt snout. The premaxillae have a long and narrow upper branch extending between the nares (nostril holes), which are large and elliptical. Each premaxilla has four large and chisel-shaped teeth which are slightly procumbent (leaning forwards), similar to many placodonts. The teeth are strongly attached via long roots. [1] The small size of the premaxilla and the rather anterior position of the nares are more similar to Eusarosphargis and terrestrial reptiles rather than most sauropterygians. [2] The maxillae are only partially preserved, forming much of the rear edge of the nares. Maxillary teeth are sharp, narrow, and slightly curved, unlike the plate-like teeth of placodonts. Six teeth were present in the right maxilla as originally preserved, though more were likely present in life. The nasal bones are incomplete, but they appear to have bordered the rear and inner portion of the nares. The orbit (eye socket) was very large and circular. Its front edge was formed by a large prefrontal, and Palatodonta appears to lack a lacrimal bone. The frontals form the front half of the orbit’s upper edge. The lower edge of the orbit was bordered by a slender two-pronged jugal. This “boomerang-shaped” jugal is similar in shape to that of Paraplacodus ; unlike Paraplacodus, it is large enough to exclude the maxilla from the rim of the orbit. [1]

The temporal region (behind the orbit) has two large openings: an upper temporal fenestra which is encircled by bone, and a lower temporal excavation which is open from below. This form of modified diapsid skull is common in early sauropterygians (including Paraplacodus) as well as modern lizards. The upper rear part of the skull roof is composed of the parietals, which enclose a large parietal foramen and each possess a convex bulge in their outer rear portion. Two large curved bones separate the orbit from the upper temporal fenestra: the postfrontal and postorbital. The postorbital sends back a rounded plate; this plate makes up part of the postorbital bridge, a bony bar which separates the two temporal openings. The postorbital bridge is set relatively low on the skull, so that both temporal openings are well-exposed from the side. The jugal also contributes to the postorbital bridge, as well as the front edge of the lower temporal opening. It extends back far enough to contact the large and complex squamosal, thus excluding the postorbital bone from the lower temporal opening. The tendency of the jugal to contact both the prefrontal and squamosal is a trait only shared with Placodus among placodonts. The rear edge of the lower temporal opening is formed by a tall and narrow bone. This bone was originally identified as a quadrate, which would have articulated with the lower jaw. [1] An alternative interpretation considers it to be a reduced quadratojugal, which was previously reported as absent in Palatodonta and basal placodonts. [3]

Micro-CT scanning of the specimen reveals more details of the jaw and internal structures of the skull. The mandible was much more slender than in placodonts, though the rear part is not fully preserved. The dentary has at least 14 pointed teeth which are sharp and narrow, though they become larger and more robust further back in the jaw. The rear of the jaw includes a low coronoid, a thin surangular, and an elongated angular which likely contains the jaw joint. The palatine bone, which lies along the palate (roof of the mouth) parallel to the maxilla, hosted a single row of large teeth similar to those of the maxilla. This is a specialization relative to most other reptiles, which lack palatine teeth or have multiple rows of tiny denticles. Placodonts are another exception with a single row of large teeth on their palatine, though their teeth are broad and plate-like. Other fragments of palate bones, such as the vomer and pterygoid, lack teeth or denticles. The only preserved portion of the braincase is a basisphenoid, the bone which connects the base of the braincase to the palate. The basisphenoid has two holes for each internal carotid artery as well as stout vertical prongs. Various disarticulated phalanges (finger bones) are mixed up with the skull. [1]

Related Research Articles

<span class="mw-page-title-main">Palatine bone</span> Bone of the facial skeleton

In anatomy, the palatine bones are two irregular bones of the facial skeleton in many animal species, located above the uvula in the throat. Together with the maxillae, they comprise the hard palate.

<span class="mw-page-title-main">Placodontia</span> Extinct order of Triassic marine reptiles

Placodonts are an extinct order of marine reptiles that lived during the Triassic period, becoming extinct at the end of the period. They were part of Sauropterygia, the group that includes plesiosaurs. Placodonts were generally between 1 and 2 m in length, with some of the largest measuring 3 m (9.8 ft) long.

<i>Macroplata</i> Extinct genus of reptiles

Macroplata is an extinct genus of Early Jurassic rhomaleosaurid plesiosaur which grew up to 4.65 metres (15.3 ft) in length. Like other plesiosaurs, Macroplata probably lived on a diet of fish, using its sharp needle-like teeth to catch prey. Its shoulder bones were fairly large, indicating a powerful forward stroke for fast swimming. Macroplata also had a relatively long neck, twice the length of the skull, in contrast to pliosaurs.

<i>Elginia</i> Extinct genus of reptiles

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<i>Askeptosaurus</i> Extinct genus of reptiles

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<i>Anatosuchus</i> Extinct genus of reptiles

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<i>Turfanosuchus</i> Extinct genus of reptiles

Turfanosuchus is a genus of archosauriform reptile, likely a gracilisuchid archosaur, which lived during the Middle Triassic (Anisian) of northwestern China. The type species, T. dabanensis, was described by C.C. Young in 1973, based on a partially complete but disarticulated fossil skeleton found in the Kelamayi Formation of the Turfan Basin.

<i>Neopteroplax</i> Extinct genus of amphibians

Neopteroplax is an extinct genus of eogyrinid embolomere closely related to European genera such as Eogyrinus and Pteroplax. Members of this genus were among the largest embolomeres in North America. Neopteroplax is primarily known from a large skull found in Ohio, although fragmentary embolomere fossils from Texas and New Mexico have also been tentatively referred to the genus. Despite its similarities to specific European embolomeres, it can be distinguished from them due to a small number of skull and jaw features, most notably a lower surangular at the upper rear portion of the lower jaw.

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

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Wimanius is a genus of ichthyosaur from the Middle Triassic of Switzerland, containing a single species, Wimanius odontopalatus. It was described by Michael Maisch and Andreas Matzke in 1998 based on an incomplete skull from Monte San Giorgio, a mountain on the Swiss-Italian border. Wimanius possesses teeth on its palate, though whether they were located on the palatine or pterygoid is disputed. Other features of Wimanius include a large orbit and jugals with two rami of similar lengths. Different phylogenetic placements of Wimanius have been recovered by different studies, including it being a mixosaurid relative or a merriamosaur, and a monotypic family, Wimaniidae has been named for it. However, its validity has also been questioned, and synonymy with various other genera has been proposed.

<i>Microleter</i> Extinct genus of reptiles

Microleter is an extinct genus of basal procolophonomorph parareptiles which lived in Oklahoma during the Early Permian period. The type and only known species is Microleter mckinzieorum. Microleter is one of several parareptile taxa described from the Richards Spur fissure fills, and can be characterized from its high tooth count, lacrimal/narial contact, short postfrontal, and slit-like temporal emargination edged by the postorbital, jugal, squamosal, and quadratojugal. Contrary to Australothyris, which had a similar phylogenetic position as a basal procolophonomorph, Microleter suggests that early parareptile evolution occurred in Laurasia and that multiple lineages developed openings or emarginations in the temporal region.

Australothyris is an extinct genus of basal procolophonomorph parareptile known from the Middle Permian of Tapinocephalus Assemblage Zone, South Africa. The type and only known species is Australothyris smithi. As the most basal member of Procolophonomorpha, Australothyris helped to contextualize the origin of this major parareptile subgroup. It has been used to support the hypotheses that procolophonomorphs originated in Gondwana and ancestrally possess temporal fenestrae, due to its large and fully enclosed temporal fenestra and South African heritage. It also possessed several unique features, including a high tooth number, long postfrontal, small interpterygoid vacuity, and a specialized interaction between the stapes and quadrate.

<i>Daemonosaurus</i> Genus of reptiles (fossil)

Daemonosaurus is an extinct genus of possible theropod dinosaur from the Late Triassic of New Mexico. The only known fossil is a skull and neck fragments from deposits of the latest Triassic Chinle Formation at Ghost Ranch. Daemonosaurus was an unusual dinosaur with a short skull and large, fang-like teeth. It lived alongside early neotheropods such as Coelophysis, which would have been among the most common dinosaurs by the end of the Triassic. However, Daemonosaurus retains several plesiomorphic ("primitive") traits of the snout, and it likely lies outside the clade Neotheropoda. It may be considered a late-surviving basal theropod or non-theropod basal saurischian, possibly allied to other early predatory dinosaurs such as herrerasaurids or Tawa.

<i>Jesairosaurus</i> Extinct genus of reptiles

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<i>Vadasaurus</i> Extinct genus of reptiles

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<i>Kadimakara australiensis</i> Extinct species of reptile

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<i>Rugarhynchos</i> Extinct genus of reptiles

Rugarhynchos is an extinct genus of doswelliid archosauriform from the Late Triassic of New Mexico. The only known species is Rugarhynchos sixmilensis. It was originally described as a species of Doswellia in 2012, before receiving its own genus in 2020. Rugarhynchos was a close relative of Doswellia and shared several features with it, such as the absence of an infratemporal fenestra and heavily textured skull bones. However, it could also be distinguished by many unique characteristics, such as a thick diagonal ridge on the side of the snout, blunt spikes on its osteoderms, and a complex suture between the quadratojugal, squamosal, and jugal. Non-metric multidimensional scaling and tooth morphology suggest that Rugarhynchos had a general skull anatomy convergent with some crocodyliforms, spinosaurids, and phytosaurs. However, its snout was somewhat less elongated than those other reptiles.

<i>Polymorphodon</i> Extinct genus of reptiles

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<i>Taytalura</i> Extinct genus of reptiles

Taytalura is an extinct genus of lepidosauromorph reptile from the Late Triassic of Argentina. It contains a single species, Taytalura alcoberi, which is based on a well-preserved skull from the fossiliferous Ischigualasto Formation. As a lepidosauromorph, Taytalura is a distant relative of modern lepidosaurs such as sphenodontians and squamates. Taytalura did not belong to any group of modern lepidosaurs, since it bears unique features, such as unfused bones in the skull roof and teeth which all sit loosely in a deep groove without sockets. Regardless, Micro-CT scanning reveals features of the skull previously only seen in rhynchocephalians. This suggests that the ancestral condition of the skull in lepidosaurs was more similar to sphenodonts than to squamates.

References

  1. 1 2 3 4 5 6 Neenan, J. M.; Klein, N.; Scheyer, T. M. (2013). "European origin of placodont marine reptiles and the evolution of crushing dentition in Placodontia". Nature Communications. 4: 1621. Bibcode:2013NatCo...4.1621N. doi: 10.1038/ncomms2633 . PMID   23535642.
  2. 1 2 Wolniewicz, Andrzej S; Shen, Yuefeng; Li, Qiang; Sun, Yuanyuan; Qiao, Yu; Chen, Yajie; Hu, Yi-Wei; Liu, Jun (2023-08-08). Ibrahim, Nizar; Perry, George H; Benton, Michael (eds.). "An armoured marine reptile from the Early Triassic of South China and its phylogenetic and evolutionary implications". eLife. 12: e83163. doi: 10.7554/eLife.83163 . ISSN   2050-084X. PMC   10499374 . PMID   37551884.
  3. Maisch, Michael W. (2020). "The evolution of the temporal region of placodonts (Diapsida: Placodontia) – a problematic issue of cranial osteology in fossil marine reptiles". Palaeodiversity. 13 (1): 57–68. doi: 10.18476/pale.v13.a6 . ISSN   1867-6294.