''Macroplata'' (meaning "big plate") is an extinct

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial n ...

of Early

Jurassic The Jurassic ( ) is a Geological period, geologic period and System (stratigraphy), stratigraphic system that spanned from the end of the Triassic Period million years ago (Mya) to the beginning of the Cretaceous Period, approximately Mya. The J ...

rhomaleosaurid plesiosaur which grew up to in length and weighed up to . 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. A different species, ''Macroplata longirostris'' (previously called ''

Plesiosaurus ''Plesiosaurus'' (Greek: ' ('), near to + ' ('), lizard) is a genus of extinct, large marine sauropterygian reptile that lived during the Early Jurassic. It is known by nearly complete skeletons from the Lias of England. It is distinguishable by ...

longirostris''), which lived somewhat later, during the

Toarcian The Toarcian is, in the ICS' geologic timescale, an age and stage in the Early or Lower Jurassic. It spans the time between 182.7 Ma (million years ago) and 174.1 Ma. It follows the Pliensbachian and is followed by the Aalenian. The Toarc ...

stage, was also included in the genus; however, in 2011, Benson ''et al.'' reclassified it as a pliosaurid in the genus '' Hauffiosaurus'', ''H. longirostris''.

Description

''Macroplata'' bore an elongated

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, t ...

, with more than half of its cranial length taken up by a roughly triangular snout. The premaxillae (front upper jaw bones) bear six teeth each, with the first being the smallest and the second, third, and fourth the largest. Together, they form the rounded region at the front of the jaw, and have a rough outer surface bearing

foramina In anatomy and osteology, a foramen (;Entry "foramen"
in

, ridges, and grooves. The snout is constricted where the premaxillae border 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 tw ...

(the larger upper jaw bones). These bones continue to contact each other until they reach the level of the

external nares A nostril (or naris , plural ''nares'' ) is either of the two orifices of the nose. They enable the entry and exit of air and other gasses through the nasal cavities. In birds and mammals, they contain branched bones or cartilages called turbi ...

(openings for the nostrils). While the premaxillae become narrow beyond this point, they extend far back on the skull, forming a ridge rearward of the external nares. The top side of each maxilla is ornamented like that of the premaxillae. The front edges of 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 a ...

s (eye openings) are formed by the maxillae. The maxillae also seem to make up the front and outer rims of the external nares, although poor preservation makes it difficult to verify this. The better-preserved maxilla of the holotype bears 18 alveoli (tooth sockets), with the smallest at the back. The maxillary teeth are separated from the premaxillary teeth by a gap ( diastema). The teeth of ''Macroplata'' have circular cross-sections and possess vertical ridges that all at least come close to the tooth's tip (few actually reach it). The frontals of ''Macroplata'' are long, spanning from external nares to temporal fenestrae (large openings at the back of the skull), and widen towards the back of the skull. They bear foraminae and probably formed the rear edges of the external nares. The frontals are separated from each other by the premaxillae in the front and the parietals (bones at the back of the skull roof) at the rear, with a small area of contact between. The frontals articulate with the prefrontals above the orbits. The prefrontals form part the orbits' upper edge. 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, th ...

s form the border between the orbits and the temporal fenestrae, and each bone bearing a ridge running perpendicularly to the skull's length. Upon the discovery of ''Macroplata'', its pineal foramen was claimed to be both large and small by different sources. As it was later obscured by plaster, its true size is unknown. The

parasphenoid The parasphenoid is a bone which can be found in the cranium of many vertebrates. It is an unpaired dermal bone which lies at the midline of the roof of the mouth. In many reptiles (including birds), it fuses to the endochondral (cartilage-derived) ...

(a midline bone in the rear part 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 s ...

) is smooth and approximately diamond-shaped, with a wide surface at its front that articulates with the pterygoids. The posterior interpterygoid vacuities (openings located on the palate) are roughly elliptical. Unlike in other plesiosaurs, their hind ends are angled inwards, making this trait an

autapomorphy In phylogenetics, an autapomorphy is a distinctive feature, known as a derived trait, that is unique to a given taxon. That is, it is found only in one taxon, but not found in any others or outgroup taxa, not even those most closely related to t ...

of ''Macroplata''. It is unclear where the parasphenoid meets the basioccipital (the lower bone of the rear braincase), although a possible suture between these bones is present roughly at the level of the hind end of the posterior interpterygoid vacuities. This suggests that the rearmost part of the palate was composed of the basioccipital. The occipital condyle (the surface to which the vertebrae articulate) juts out beyond the palate when viewed from below. The occipital condyle is formed solely by the basioccipital, with the exoccipital-opisthoics (side bones of the rear braincase) not participating. The paraoccipital processes (the elongated regions of the exoccipital-opisthoics) of the latter bones bear wide upper surfaces and slope downwards and forwards. The

foramen magnum The foramen magnum ( la, great hole) is a large, oval-shaped opening in the occipital bone of the skull. It is one of the several oval or circular openings (foramina) in the base of the skull. The spinal cord, an extension of the medulla oblonga ...

(the opening above the occipital condyle) is constricted into an 8-shape. The supraoccipital (the top bone of the rear braincase) is wider than tall. The

mandibular symphysis In human anatomy, the facial skeleton of the 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 p ...

(where the two sides of the lower jaw meet and fuse) bears seven or eight tooth pairs and is covered by foraminae on its sides. The suture between 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 teeth in place. The mandible sits beneath the maxilla. It is the only movable bone ...

(tooth-bearing lower jaw bone) and angular (one of the rear mandibular bones) takes the shape of a straight line sloping upwards and backwards. The splenial (an inner mandibular bone) might form part of the mandibular symphysis. It continues to contact the bottom of the dentary until the angular separates them further rearwards. The angular forms the entire lower surface of the rear mandible, widening below the jaw joint before narrowing to form the lower part of the retroarticular process. The

articular The articular bone is part of the lower jaw of most vertebrates, including most jawed fish, amphibians, birds and various kinds of reptiles, as well as ancestral mammals. Anatomy In most vertebrates, the articular bone is connected to two oth ...

forms the top part of the retroarticular process (a spikelike projection of bone behind the jaw joint). The retroarticular process is broad and weakly angled towards the skull's midline. ''Macroplata'' bears 26 cervical (neck) vertebrae. The parts of the

atlas An atlas is a collection of maps; it is typically a bundle of maps of Earth or of a region of Earth. Atlases have traditionally been bound into book form, but today many atlases are in multimedia formats. In addition to presenting geograp ...

and axis, the first two cervical vertebrae, are not entirely fused together. The centrum (vertebral body) of the atlas is surrounded by the crescent-shaped atlantal intercentrum below and the atlantal

neural arches The spinal column, a defining synapomorphy shared by nearly all vertebrates, Hagfish are believed to have secondarily lost their spinal column is a moderately flexible series of vertebrae (singular vertebra), each constituting a characteristi ...

on the sides, and is not visible from below. The lower surface of the intercentrum of the axis tapers to a point facing forwards. Beyond the axis, the undersides the cervical centra bear keels, with a prominent pit on each side in which a small subcentral

foramen In anatomy and osteology, a foramen (;Entry "foramen"
in

(holes on the bottom of the vertebrae) is located. The moderately long cervical centra are amphicoelous (concave on both sides) and slightly wider than tall. The fronts, backs, and sides of the centra are rough. The zygapophyses span about as wide as the centra, and the joints they articulate with are directed upwards and inwards. The lower parts of the

neural spines The spinal column, a defining synapomorphy shared by nearly all vertebrates,Hagfish are believed to have secondarily lost their spinal column is a moderately flexible series of vertebrae (singular vertebra), each constituting a characteristic i ...

are narrow from side to side. The cervical vertebrae increase in size towards the back of the neck, and the articulations between the neural arches and centra become increasingly pointed. The

cervical ribs A cervical rib in humans is an extra rib which arises from the seventh cervical vertebra. Their presence is a congenital abnormality located above the normal first rib. A cervical rib is estimated to occur in 0.2% to 0.5% (1 in 200 to 500) of th ...

are double-headed (the surface connecting to the vertebrae is forked) and their heads are roughly circular.

Classification

Following Benson ''et al.'' (2012):

References

External links

Macroplata
- the Plesiosaur Directory {{Taxonbar, from=Q132773 Early Jurassic plesiosaurs of Europe Fossil taxa described in 1930 Rhomaleosaurids Sauropterygian genera

Description

Classification

See also

References

External links