''Palatodonta'' 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 basal

placodontiform Placodontiformes is an extinct clade of sauropterygian marine reptiles that includes placodonts and the non-placodont ''Palatodonta''. It was erected in 2013 with the description of ''Palatodonta''. Placodontiformes is the most basal clade of Sa ...

marine reptile Marine reptiles are reptiles which have become secondarily adapted for an aquatic or semiaquatic life in a marine environment. The earliest marine reptile mesosaurus (not to be confused with mosasaurus), arose in the Permian period during the ...

known from the early

Middle Triassic In the geologic timescale, the Middle Triassic is the second of three epochs of the Triassic period or the middle of three series in which the Triassic system is divided in chronostratigraphy. The Middle Triassic spans the time between Ma and ...

(early

Anisian In the geologic timescale, the Anisian is the lower stage or earliest age of the Middle Triassic series or epoch and lasted from million years ago until million years ago. The Anisian Age succeeds the Olenekian Age (part of the Lower Triassic Ep ...

stage) of the

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. It is closely related to a group of marine reptiles called

placodont Placodonts (" Tablet teeth") 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 genera ...

s, characterized by their crushing teeth and shell-like

body armor Body armor, also known as body armour, personal armor or armour, or a suit or coat of armor, is protective clothing designed to absorb or deflect physical attacks. Historically used to protect military personnel, today it is also used by variou ...

. ''Palatodonta'' is transitional between placodonts and earlier reptiles; like placodonts, it has teeth on its

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 ...

, 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).

Discovery

''Palatodonta'' was first named by James M. Neenan, Nicole Klein and Torsten M. Scheyer in

2013 File:2013 Events Collage V2.png, From left, clockwise: Edward Snowden becomes internationally famous for leaking classified NSA wiretapping information; Typhoon Haiyan kills over 6,000 in the Philippines and Southeast Asia; The Dhaka garment fact ...

and 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 ...

is ''Palatodonta bleekeri''. The generic name refers to the row of teeth on the

palatine bone 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. (''Palate'' is derived from the Latin ''pa ...

of the palate. The

specific name Specific name may refer to: * in Database management systems, a system-assigned name that is unique within a particular database In taxonomy, either of these two meanings, each with its own set of rules: * Specific name (botany), the two-part (bino ...

honours Remco Bleeker, an amateur paleontologist, who discovered the fossil in the summer of 2010 at the Silbeco quarry near

Winterswijk Winterswijk (; also known as ''Winterswiek'' or ''Wenters'') is a municipality and a town in the eastern Netherlands. It has a population of and is situated in the Achterhoek, which lies in the easternmost part of the province of Gelderland in th ...

. ''Palatodonta'' is known from the

holotype A holotype is a single physical example (or illustration) of an organism, known to have been used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of several ...

TW480000470, a well-preserved

skull The skull is a bone protective cavity for the brain. The skull is composed of four types of bone i.e., cranial bones, facial bones, ear ossicles and hyoid bone. However two parts are more prominent: the cranium and the mandible. In humans, the ...

of a juvenile individual.

Description

The skull is tall and has a short, blunt snout. The

premaxillae 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 ...

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. The

maxillae 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 ...

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 The nasal bones are two small oblong bones, varying in size and form in different individuals; they are placed side by side at the middle and upper part of the face and by their junction, form the bridge of the upper one third of the nose. Eac ...

are incomplete, but they appear to have bordered the rear and inner portion of the nares. 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 ...

(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 lacrimal bone is a small and fragile bone of the facial skeleton; it is roughly the size of the little fingernail. It is situated at the front part of the medial wall of the orbit. It has two surfaces and four borders. Several bony landmarks of ...

. 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 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 ...

. This “boomerang-shaped” jugal is similar in shape to that of ''

Paraplacodus ''Paraplacodus broilli'' is an extinct placodont sauropterygian from the middle Triassic period, from the Anisian until Ladinian stages. The fossils were uncovered in Northern Italy and the species was named in 1931 by Bernhard Peyer. ''Paraplac ...

''; unlike ''Paraplacodus'', it is large enough to exclude the maxilla from the rim of the orbit. 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 Diapsids ("two arches") are a clade of sauropsids, distinguished from more primitive eureptiles by the presence of two holes, known as temporal fenestrae, in each side of their skulls. The group first appeared about three hundred million years ago ...

skull is common in early

sauropterygians Sauropterygia ("lizard flippers") is an extinct taxon of diverse, aquatic reptiles that developed from terrestrial ancestors soon after the end-Permian extinction and flourished during the Triassic before all except for the Plesiosauria became ...

(including ''Paraplacodus'') as well as modern

lizards Lizards are a widespread group of squamate reptiles, with over 7,000 species, ranging across all continents except Antarctica, as well as most oceanic island chains. The group is paraphyletic since it excludes the snakes and Amphisbaenia althou ...

. 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 The skull is a bone protective cavity for the brain. The skull is composed of four types of bone i.e., cranial bones, facial bones, ear ossicles and hyoid bone. However two parts are more prominent: the cranium and the mandible. In humans, the ...

and

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 ...

. 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 The squamosal is a skull bone found in most reptiles, amphibians, and birds. In fishes, it is also called the pterotic bone. In most tetrapods, the squamosal and quadratojugal The quadratojugal is a skull bone present in many vertebrates, including ...

, 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 ''Placodus'' (meaning 'flat tooth') was a genus of marine reptiles belonging to the order Placodontia, which swam in the shallow seas of the middle Triassic period (c. 240 million years ago). Fossils of ''Placodus'' have been found in Central Eur ...

'' 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 Quadrate may refer to: * Quadrate bone * Quadrate (heraldry) * Quadrate lobe of liver * Quadrate tubercle The quadrate tubercle is a small tubercle found upon the upper part of the femur. It serves as a point of insertion of the quadratus femori ...

, which would have articulated with the lower jaw. An alternative interpretation considers it to be a reduced

quadratojugal The quadratojugal is a skull bone present in many vertebrates, including some living reptiles and amphibians. Anatomy and function In animals with a quadratojugal bone, it is typically found connected to the jugal (cheek) bone from the front and ...

, which was previously reported as absent in ''Palatodonta'' and basal placodonts. Micro-CT scanning of the specimen reveals more details of the jaw and internal structures of the skull. The

mandible In anatomy, the mandible, lower jaw or jawbone is the largest, strongest and lowest bone in the human facial skeleton. It forms the lower jaw and holds the lower tooth, teeth in place. The mandible sits beneath the maxilla. It is the only movabl ...

was much more slender than in placodonts, though the rear part is not fully preserved. The

dentary In anatomy, the mandible, lower jaw or jawbone is the largest, strongest and lowest bone in the human facial skeleton. It forms the lower jaw and holds the lower tooth, teeth in place. The mandible sits beneath the maxilla. It is the only movabl ...

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 The suprangular or surangular is a jaw bone found in most land vertebrates, except mammals. Usually in the back of the jaw, on the upper edge, it is connected to all other jaw bones: dentary, angular, splenial and articular The articular bone i ...

, and an elongated angular which likely contains the jaw joint. The

, which lies along the

(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 The vomer (; lat, vomer, lit=ploughshare) is one of the unpaired facial bones of the skull. It is located in the midsagittal line, and articulates with the sphenoid, the ethmoid, the left and right palatine bones, and the left and right maxill ...

and

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 ...

, lack teeth or denticles. The only preserved portion 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 ...

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 The internal carotid artery (Latin: arteria carotis interna) is an artery in the neck which supplies the anterior circulation of the brain. In human anatomy, the internal and external carotids arise from the common carotid arteries, where these b ...

as well as stout vertical prongs. Various disarticulated

phalanges The phalanges (singular: ''phalanx'' ) are digital bones in the hands and feet of most vertebrates. In primates, the thumbs and big toes have two phalanges while the other digits have three phalanges. The phalanges are classed as long bones. ...

(finger bones) are mixed up with the skull.

References

Placodonts Anisian life Middle Triassic reptiles of Europe Fossils of the Netherlands Fossil taxa described in 2013 Sauropterygian genera {{triassic-reptile-stub