A Elasmosaurid Plesiosaur from the middle Cretaceous Cambridge Greensand of England.

The Plesiosaurians were possibly the most successful clade of Mesozoic Marine Reptiles, first appearing in the Late Triassic, and surviving till the End Cretaceous Extinction. Their basic bauplan was simple, with a rigid body and four paddle-like limbs used for propulsion, although within this framework they produced considerable diversity, with distinctive groups such as the Thalassophonean Pliosaurs and Cryptoclidian Plesiosaurs appearing in the Middle Jurassic and the Leptocleidids and Elasmosaurids appearing around the End of the Jurassic.

The middle Cretaceous was a period of about 14 million years during which there was significant turnover in many groups of organisms. It was during this period that the Ichthyosaurs disappeared and the Mosasaurs first appeared and diversified. Within the Plesiosaurians, the Pliosaurs vanished during this interval, while the Euelasmosaurida underwent a significant evolutionary radiation.

The  Cambridge Greensand forms the lowest member of the West Melbury Marly Chalk Formation. This Albian–early Cenomanian bed comprises micaceous, glauconitic, silt marl with a basal lag of reworked phosphatic nodules usually associated with Vertebrate fossils and exotic clasts, often encrusted in small Oysters and other epibionts. The Cambridge Greensand contains one of England's richest Vertebrate fossil assemblages, and dates to the crucial middle Cretaceous period of high biotic turnover. However, many of the skeletons recovered from this deposit are fragmentary in nature, and some may have been reworked from the underlying Gault Formation. Furthermore, most of the sites from which they were recovered are not exposed on the surface; these sites were uncovered by phosphate miners in the nineteenth century, and have largely been covered over again.

In a paper published in the journal Acta Palaeontologica Polonica on 30 October 2025, Jose O'Gorman of the División Paleontología Vertebrados at the Museo de La Plata, and Roger Benson of the American Museum of Natural History and the Department of Earth Sciences at the University of Oxford, redescribe CAMSM X50356, a partial Elasmosaurid Plesiosaur skeleton in the collection of the Sedgwick Museum in Cambridge.

CAMSM X50356 was excavated near the village of Fen Ditton in Cambridgeshire. It is a disarticulated, partial skeleton, comprising 37 cervical centra, 3 pectoral centra, 20 dorsal centra, 5 sacral centra, 3 caudal centra, isolated neural arches, fragmentary ribs, part of a scapula, one almost complete propodial, and several propodial fragments. A basioccipital bone included with the original collection is rejected by O'Gorman and Benson as clearly belonging to an Platypterygiine Ichthyosaur.

(A) Location of the study area in the UK. (B) Geological map of eastern England showing the distribution of the Cambridge Greensand (red star). (C) Cambridge Greensand phosphate quarrying areas near Cambridge.  (D) Lithologic and stratigraphic scheme of the Albian/Cenomanian boundary interval in Cambridgeshire. (E) Original inked label of CAMSM X50356. O'Gorman & Benson (2025).

The skeleton if thought to have come from an immature Animal, as the neural arches of the vertebrae have detached from the centra, a sign of incomplete ossification. Many of the elements show signs of abrasion, and some of encrustation by Oysters, suggesting that the remains were exposed on the seabed for some time before being buried. 

(A)–(D) Taphonomic features of four cervical centra of CAMSM X50356 (Elasmosauridae indet.) from Fen Ditton, near Cambridge, UK, upper Albian–lower Cenomanian, Oyster encrustations. (A₁) Cervical cetrum in posterior view; (A₂) and (A₃), details of incrusted oysters; (B₁) cervical centrum in ventral view; (B₂) detail of incrusted oyster; (C₁) cervical centrum in left lateral view; (C₂) detail of incrusted oyster. (D) Cervical centrum in dorsal view. (E) Platypterygiinae indet. CAMSM X50356 (Elasmosauridae indet.) from Fen Ditton, near Cambridge, UK, upper Albian–lower Cenomanian, basioccipital in dorsal (E₁) and posterior (E₂) views. Scale bars are 20 mm. O'Gorman & Benson (2025).

CAMSM X50356 has 37 preserved cervical vertebrae, which can be identified as such by the presence of a  ventrolateral parapophysys (bony ridge on the underside). This sequence is incomplete, with the atlas and axis (first two vertebrae, which form a joint with the skull and are slightly modified for this purpose), and potentially other vertebrae missing, giving a minimum count of 39. Furthermore, there are twenty preserved dorsal vertebrae, defined by the absence of parapophysis, which again is the minimum number, suggesting that CAMSM X50356 was long, even for an Elasmosaur.

CAMSM X50356 (Elasmosauridae indet.) from Fen Ditton, near Cambridge, UK, upper Albian–lower Cenomanian. (A) Sacral centra in posterior (A₁), right lateral (A₂), ventral (A₃), and dorsal (A4) views. (B) Caudal centra in posterior (B₁), left lateral (B₂), ventral (B₃), and dorsal (B₄) views. Scale bars are 20 mm. O'Gorman & Benson (2025).

A phylogenetic analysis recovered CAMSM X50356 as the basalmost known Elasmosaurid, not corresponding to any other described member of the group. It is also the only Elasmosaurid with cervical central longer than high but without lateral ridges, suggesting that this was the basal condition in the group, even if absent from all other members. 

CAMSM X50356 (Elasmosauridae indet.) from Fen Ditton, near Cambridge, UK, upper Albian–lower Cenomanian. (A) Sacral centra in posterior (A₁), right lateral (A₂), ventral (A₃), and dorsal (A₄) views. (B) Caudal centra in posterior (B₁), left lateral (B₂), ventral (B₃), and dorsal (B₄) views. Scale bars are 20 mm. O'Gorman & Benson (2025).

The Sedgwick Museum collection also contains several Elasmosaur specimens from the Cambridge Greensand listed under the names Plesiosaurus euryspondilus and Plesiosaurus euryspondilus, species for which no known formal description exists. These specimens were collected by the palaeontologist Hary Seely in the 1860s, who noted that 'These names are only intended for the convenience of students using the Museum, and not necessarily to take rank as names of described species'. O'Gorman and Benson examined several of these specimens, and could not find any features which could be used to distinguish them from CAMSM X50356, however, they do not consider that either that specimen, nor any of Seely's material, show sufficient diagnostic features to be formally described as a species.

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An Early Cretaceous Plesiosaur from Ellesmere Island, Canada.

The Plesiosaurs were a group of Marine Reptiles which appeared in the Triassic and persisted till the End of the Cretaceous. The group obtained a global distribution during the Jurassic, when the supercontinent of Pangea broke up and high global temperatures led to large areas of the world's continents being submerged. However, towards the end of this period the situation had changed, when falling sealevels led to many ocean basins becoming isolated, many groups of large Marine Reptiles becoming extinct, and faunal communities becoming provincialized in different ocean basins. Plesiosaurs are not thought to have been strongly affected by the End Jurassic Extinction Event, but their fossil record is poor during the Early Cretaceous, limiting our understanding of the group during this interval.

In a paper published in the journal Acta Palaeontologica Polonica on 2 December 2024, Lene Delsett of the Natural History Museum at the University of Oslo, adam Smith of Nottingham Natural History Museum, Stephen Ingrams of Llandudno, and Simon Schneider of the Cambridge Arctic Shelf Programme, describe a Plesiosaur from the Early Cretaceous Deer Bay Formation of Ellesmere Island in the Canadian Arctic.

The specimen was excavated in 1952 by the Danish geologist Johannes Christian Troelsen, however, while he mentioned it in a report of his expedition to the area, it was never formally described. It was sent to the University of Copenhagen, where it appears to have undergone some preparation work by a student working under the supervision of curator Eigil Nielsen, and possibly subsequent curator Niels Bonde. The remains were subsequently packed into a series of wooden crates, one of which was opened and examined by Adam Smith in 2005. This box were subsequently misplaced, possibly during the flooding which affected the museum in 2011, but was subsequently relocated by curators Bent Lindow and Arden Bashfortht, and its contents transferred to a draw s in the main fossil Vertebrate collection. Two further crates, labelled '“Reptile Creek, Troelsen’s office' were discovered in 2019, and found to contain several girdle elements of the Plesiosaur specimen. Another box was discovered in the collections of the Zoological Museum in 2020, containing what was labelled as part of a 'Scoresbysund Plesiosaur', but which clearly belong to the Elis Island specimen. Another box, labelled 'NHMD 189689' contained some fragmentary ribs which also appeared to belong to the Elis Island specimen, but in the absence of any documentation were not included in the study.

The surviving specimen comprises 22 non-consecutive vertebrae from the cervical, dorsal, and caudal regions, hundreds of rib fragments, partial girdle elements, all four propodials, and several distal limb elements. All these elements are worn, and the larger elements mostly fragmentary. Delsett et al. were able to assign the specimen to the Cryptoclidid genus Colymbosaurus, but, due to the fragmentary nature of the specimen and a limited amount of overlapping material with other specimens, were not able to determine whether it belonged to either of the two previously described species in the genus, or from a different, as yet undescribed species. 

Selected vertebrae of Plesiosaur Colymbosaurus sp. NHMD 189834 from Ellesmere Island, Nunavut, Canada, upper Berriasian–lower Valanginian. (A) Cervical vertebra (centrum C), in articular (A₁), dorsal (A₂), ventral (A₃), and lateral (A₄) views. (B), (C) Pectoral vertebrae. (B) Centrum E in articular view. (C) Centrum D, in articular (C₁) and lateral (C₂) views. (D) Sacral? rib. (E)–(G) Dorsal vertebrae. (E) Centrum H, in articular (E₁) and lateral (E₂) views. (F) Centrum M (dorsal?) in articular view. (G) Centrum I in articular view. (H), (I) Caudal vertebrae. (H) Centrum O in articular view. (I) Centrum P in articular (I₁) and lateral (I₂) views. The letters used in the element names are written on the individual elements. Delsett et al. (2024).

Previous known specimens of Colymbosaurus spp. have been described from Spitsbergen, southern England and western Russia, so the Elis Island specimen represents a significant range expansion for the genus. The genus was therefore present in two separate ocean basins, the Boreal Arctic and Boreal Atlantic, which were connected by two seaways, one running between Norway and Greenland beneath the modern North Atlantic, and one in present day western Russia.

Map with Cryptoclidid occurrences in the Northern hemisphere. (1) Ellesmere Island; (2) Spitsbergen; (3) Great Britain; (4), (5) Russia. Delsett et al. (2024).

The Boreal Ocean during the Late Jurassic and Early Creraceous has been considered to have been an ecologically depleted environment, with most of the described fossils being Bivalves, Ammonites, and Belemnites. However, Cryptoclidid Pleisiosaurs were large, predatory Animals, reliant on Fish for at least part of their protein intake, which implies that these must also have been present. Delsett et al. suggest that, few deposits from this interval are noted for their fossil content, at least part of the apparent absence of many Animal groups may be because most studies of these deposits have concentrated on their stratigraphy rather than their faunal diversity, and therefore useful index fossils, such as shelled Molluscs tend to have been described, whereas less stratigraphically useful fossils, such as Plesiosaurs or Fish, may have been overlooked.

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A new specimen of the Hupehsuchian Nanchangosaurus throws light on the origin of the earliest Mesozoic Marine Reptiles.

The first groups of Mesozoic Marine Reptiles returned to the seas early in the Triassic, quickly gaining suites of specialist adaptations to pelagic life which have made it hard to determine their closest terrestrial relatives. The most notable of these groups is the Ichthyopterygia (Ichthyosaurs and close relatives), a group which for a long time were considered to be of uncertain affinities, and which today are placed within the Diapsida, but with no widely accepted hypothesis on their relationship to other members of this group. The sister group to the Ichthyopterygia is considered to be the Omphalosauridae, another group of highly modified pelagic Marine Reptiles, with the two groups forming the Ichthyosauriformes.

The Hupehsuchians are a group of small Mesozoic Marine Reptiles known only from the Early Triassic deposits of the Nanzhang-Yuan’an region of Hubei Province, South China. As with other Marine Reptile groups, their affinities were for a long time hard to determine, though in the last decade it has been realised that they are the sister group to the Ichthyosauriforms, with the two groups together being referred to as the Ichthyosauromorphs. Hupehsuchians had elongate bodies with slender heads, dermal plates on their dorsal surfaces, dense ribs and tightly packed gastralia. Importantly, they were fairly small, ranging from 40 cm to about 2.3 m in length, and restricted to shallow-marine environments, suggesting that they may be closer to the terrestrial origins of the Ichthyosauromorphs than other members of the group.

A large number of Hupehsuchian specimens have been found, and the anatomy of the group reasonably well understood. However, almost all of these specimens are preserved in lateral view, with only three specimens known with their skulls preserved in ventral view, which presents challenges when comparing Hupehsuchians to other groups

In a paper published in the journal Historical Biology on 25 May 2024, Jun Liu, Fan Wu, and Yu Qiao of the Division of Geology at Hefei University of Technology describe a new Hupehsuchian specimen from the Early Triassic Jialingjiang Formation in Yuan’an County, in the west of Hubei Province, China, which is preserved in ventral view, and discuss the implications of this for our understanding of the origins of the Hupehsuchians and related groups.

The specimen, HFUT YAV-10-001, is a small, well-preserved Hupehsuchian on a slab and counter-slab in ventral view, and held in the collection of the Geological Museum of Hefei University of Technology. This comprises the skull, a set of 36 articulated vertebrae and associated ribs, and a partial appendicular skeleton, including both pectoral girdle, forelimbs and partial hindlimbs. The majority of the bones are preserved on the main slab, while vertebral and rib fragments and the right pectoral girdle and forelimb elements are preserved on the counter slab. 

The Hupehsuchian HFUT YAV-10-001 from the Early Triassic of Hubei Province, South China. (A) Photograph of the skeleton on the main slab. (B) Photograph of the skeleton on the counter slab. (C) Interpretive drawing of the skeleton on the main slab. (D) Interpretive drawing of the skeleton on the counter slab. Scale bars are 1 cm. Abbreviations: 2 and 4, distal carpals; I, IV and V, metacarpals; ax, axis; axr, axis rib; bo, basioccipital; Cl, clavicle; cna#, cervical neural arch; Co, coracoid; da, dermal armour; dna#, dorsal neural arch; dns#, dorsal neural spine; dnss, dorsal neural spine second (distal) segment; dr#, dorsal rib; F, femur; Fi, fibula; H, humerus; i, intermedium; mand, mandibular ramus; pm, premaxilla; R, radius; r, radiale; Sc, scapula; Ti, tibia; U, ulna; u, ulnare. Jun et al. (2024).

Jun et al. consider HFUT YAV-10-001 to be referable to the genus Nanchangosaurus, having the same number of cervical vertebrae, as well as distinctively low neural spines, as well as lacking a parapophysis, and having subequally-sized scapula and coracoid bones. However, it differs from the previously described Nanchangosaurus suni in a number of features, including having forelimbs which are longer compared to the size of the Animal, and a smaller overall size, with Nanchangosaurus suni reaching about 20 cm in length, while HFUT YAV-10-001, which is clearly an adult, has an estimated size of only 15 cm. This could be a sign that HFUT YAV-10-001 represents a new species of Nanchangosaurus, but it may also indicate that Nanchangosaurus suni was sexually dimorphic, something which has been suggested in early Ichthyosauriforms and Sauropterygians, and which might therefore be predicted in an early Hupehsuchian. For this reason, Jun et al. assign specimen HFUT YAV-10-001 to Nanchangosaurus cf. suni.

The different aspect in which HFUT YAV-10-001 enables significant extra features to be added to a matrix used for the phylogenetic analysis of Diapsidans. Jun et al. recover HFUT YAV-10-001 as a Hupehsuchian, and the Hupehsuchians as the sister group to the Ichthyosauriformes, together  forming the Ichthyosauromorphs, as with previous studies. Their analysis further suggests that the Ichthyosauromorphs form the sister to the Sauropterygomorpha (a diverse group of Mesozoic Marine Reptiles which included groups such as the Nothosaurs and Plesiosaurs), and that this larger grouping forms a sister group to the Thallatosauria, a group of Lizard-like Marine and semi-Marine Reptiles, again restricted to the Triassic.  This grouping of the Ichthyosauromorphs, Sauropterygomorphs, and Thalattosaurs was in turn found to be the sister group to the Archosauromorphs, the group that includes the Archosaurs (Pterosaurs, Crocodilians, and Dinosaurs) plus close outgroups such as the Rhynchosaurs and Tanystrophids.

Simplified phylogeny of Sauria showing the relationships of Ichthyosauromorphs to other Reptiles. Jun et al. (2024).

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Dinocephalosaurus orientalis: New specimens shed new light upon a remarkable marine Archosauromorph from the Middle Triassic of southwestern China.

Archosauromorphs first appeared in the Permian, and became the dominant Vertebrate group in terrestrial ecosystems during the Mesozoic. While Archosauriform groups such as the Pseudosuchians (Crocodile-lineage Archosaurs) and Avemetatarsalians (Pterosaurs and Dinosaurs) became the dominat groups of Archosaurs from the Jurassic onwards, a variety of non-Archosauriform Archosauromorphs, such as the Rhynchosauria, Allokotosauria, and Tanystropheidae played an important role in Triassic ecosystems. The Tanystropheidae are one of a number of groups of highly gracile (slender) Triassic Archosauromorphs, once thought to represent a single clade, but now thought to be a loose group of basal Archosauromorphs, refered to as non-Crocopodans, where the Crocopodans comprise the Rhynchosauria, Allokotosauria, and Archosauriforms.

These gracile non-Crocopodans were a diverse group, inhabiting terrestrial, freshwater, and marine environments, and in one case (Ozimek volans),  possibly taking to the air. However, their delicate skeletons did not favour preservation, and many species are known only from compressed and fragmentary remains. One such species is Dinocephalosaurus orientalis, a non-Crocopodan Archosauromorph from the Middle Triassic Guanling Formation of Guizhou Province, China, which was described in 2003 from a specimen comprising an isolated, well-preserved skull and the first three anterior cervical vertebrae preserved in articulation. Subsequent specimens revealed that Dinocephalosaurus orientalis was of similar size and proportions to the better known Tanystropheus longobardicus, but while both species have extremely elongated necks, exceeding the lengths of their trunks, the  neck of Tanystropheus longobardicus has 13 elongated  cervical vertebrae, whereas Dinocephalosaurus orientalis has at least  32 vertebrae in  its  neck.  Furthermore, a specimen which cannot confidently be assigned to the species, but which must clearly be closely related, was found to be gravid, with an embryo (not an egg) within its abdominal cavity, indicating the birth of live young, almost certainly an adaptation to a fully marine lifestyle.

In a paper published in journal Earth and Environmental Science Transactions of the Royal Society of Edinburgh on 23 February 2024, Stephan Spiekman of the Staatliches Museum für Naturkunde Stuttgart, Wei Wang of the Institute of Vertebrate Palaeontology and Palaeoanthropology of the Chinese Academy of Sciences, Lijun Zhao of the Zhejiang Museum of Natural History, Oliver Rieppel of the Field Museum of Natural History, Nicholas Frazer of National Museums Scotland, and Chun Li, also of the Institute of Vertebrate Palaeontology and Palaeoanthropology of the Chinese Academy of Sciences, describe five new specimens of Dinocephalosaurus orientalis, and discuss their implications for our understanding of the species. 

The holotype of Dinocephalosaurus orientalis. (a) Photograph. (b) Photograph with interpretative drawing. Abbreviations: fr, frontal; j, jugal; la, lacrimal; mx, maxilla; na, nasal; op, opisthotic; pa, parietal; pl, palatine; pm, premaxilla; pof, postfrontal; po, postorbital; pro, prootic; pt, pterygoid; scl, sclerotic plates; soc, supraoccipital; sq, squamosal. Spiekman et al. (2024).

The first additional specimen described by Spiekman et al., IVPP V13898, has previously been described in 2008, and is the specimen upon which most of our current understanding of the species is based. This specimen comprises the skull, most of the vertebral column, elements of all four limbs and some elements of the pectoral and pelvic girdle. This specimen is more complete than the holotype (first specimen described), however, the skull is relatively poorly preserved, strongly dorsoventrally compressed and exposed in ventral view.

Dinocephalosaurus orientalis, IVPP V13898 (referred specimen). (a) Photograph. (b) Interpretative drawing. Spiekman et al. (2024).

The second next specimen, IVPP V17977, is described for the first time, as are all subsequent specimens. This specimen comprises the skull and mandible preserved in ventral view on one block, followed by the first to the 16th cervical vertebrae, together with associated cervical ribs, preserved in articulation on three additional slabs.

Dinocephalosaurus orientalis, IVPP V17977 (referred specimen). (a) The specimen as preserved on four slabs (photograph, scale bar in cm). (b) Interpretative drawing of the skull, lower jaw and cervical vertebrae 2–9. Abbreviations: ang, angular; ax, axis; bs, basisphenoid; cv, cervical vertebra; d, dentary; ncr, neural crest; oph, opisthotic; pl, palatine; poz, postzygapophysis; prz, prezygapophysis; pt, pterygoid; q, quadrate; v, vomer. Spiekman et al. (2024).

The second new specimen, ZMNH M8727, comprises elements of an exploded skull, a total of 28 cervical vertebrae of which the axis and the following 17 cervical vertebrae are preserved in articulation; two scattered vertebrae located next to the 28th cervical vertebra, one of them exposed in anterior view, a string of six vertebrae lying in front of the remains of the pectoral girdle and forelimbs, plus associated cervical, dorsal and gastral ribs.

Dinocephalosaurus orientalis, ZMNH M8727 (referred specimen). (a) Photograph. (b) Interpretative drawing. Abbreviations: ax, axis; co, coracoid; d, dentary; hu, humerus; mx, maxilla; pm, premaxilla; pt, pterygoid; q, quadrate; ra, radius; sc, scapula; ul, ulna. Spiekman et al. (2024).

The third new specimen, ZMNH M8728, comprises a partially preserved skull exposed in right lateral view, plus the cervical and most of the dorsal vertebral column represented by 56 vertebrae preserved in articulation (i.e. 32 cervical vertebrae and 23 dorsal vertebrae), cervical and dorsal ribs; elements of both pectoral girdles and forelimbs; and the gastral rib basket.  

Dinocephalosaurus orientalis, ZMNHM8728 (referred specimen). (a) Photograph. (b) Interpretative drawing. Abbreviations: cl, clavicle; co, coracoid; co-sc, articulated coracoid and scapula; cr, cervical rib; cv, cervical vertebra; hu, humerus; ns, neural spine; ra, radius; ul, ulna. Spiekman et al. (2024).

The next new specimen, ZMNH M8752, comprises the skull and mandible, neck, trunk and complete tail, ribs, gastral ribs, pectoral girdle and forelimbs as well as pelvic girdle and hindlimbs, making it one of the most complete specimens known.

Dinocephalosaurus orientalis, ZMNH M8752 (referred specimen). (a) Photograph. (b) Interpretative drawing. Abbreviations: as, astragalum;  ca, calcaneum; ca.v, caudal vertebra; cl, clavicle; co, coracoid; cv, cervical vertebra; do.v, dorsal vertebra; dt, distal tarsal; fib,  fibula; hu, humerus; in, intermedium; mand, mandible; ra, radius; sc, scapula; tib, tibia. Spiekman et al. (2024).

The final new specimen, IVPP V20295, however, is the most complete and fully articulated specimen recovered to date, comprising a skull is preserved in dorsal view and is in complete articulation with the neck and the rest of the body, which is essentially exposed on its left side. The total vertebral count is 145, comprising 32 cervical vertebrae, 30 dorsal vertebrae, 2 sacral vertebrae and 81 caudal vertebrae.

Dinocephalosaurus orientalis IVPP V20295.Complete articulated skeleton in dorsal to left lateral view. Abbreviations: ax, axis; ca.v, caudal vertebra; cv, cervical vertebra; do.v, dorsal vertebra; ga, gastralia; l.co, left coracoid; l.fe, left femur; l.hu, left humerus; l.il, left ilium; l.is left  ischium; l.man, left manus; l.pes, left pes; l.pu, left pubis; l.ra, left radius; l.sc, left scapula; r.hu, right humerus; r.co, right coracoid; r.fi, right fibula; r,ma, right manus; r.ra, right radius; r.sc, right scapula; r.ti, right tibia; r.ul, right ulna. Spiekman et al. (2024).

Based upon this new material, Spiekman et al. re-interpret Dinocephalosaurus orientalis as a large non-Crocopodan Archosauromorph, reaching as much as 6 m in length, with a neck twice as long as its trunk. It's post-orbital skull is short, and the suborbital fenestra has been obliterated. There is a single fang on each pre-maxillary, as well as further fangs on the front part of the maxilla and dentary. There are 62 pre-sacral vertebrae, of which 32 are cervical, as well as two sacral vertebrae and 81 caudal vertebrae. The limbs are reduced, apparently due to paedomorphosis (the retention of juvenile traits in adults), with a lack of suturing in several places in clearly adult specimens, and a reduction in the number of phalanges.

Dinocephalosaurus orientalis, ZMNHM8728, interpretative drawings of selected elements. (a) Right mandibular ramus in lateral view. (b) Right pterygoid in lateral view. (c) Posterior cervical vertebrae and anteriormost dorsal vertebra (cv26–do.v1) in right lateral view. (d) Mid-dorsal vertebrae in right lateral view. (e) Right forelimb, as preserved. (f) Left forelimb, as preserved. Abbreviations: ang, angular; ar, articular; c, centrum; cv, cervical vertebra; d, dentary; dc, distal carpal; do.v, dorsal vertebra; hu, humerus; int, intermedium; mc, metacarpal; ncr, neural crest; ns, neural spine; pl.p.pt, palatine process of the pterygoid; poz, postzygapophysis; prz, prezygapophysis; q.p.pt, quadrate process of the pterygoid; sang, surangular; sym, symphysis; tr.p, transverse process; tr.p.pt, transverse process of the pterygoid; ra, radius; rad, radiale; ul, ulna; uln, ulnare. Spiekman et al. (2024).

Spiekman et al. also note that a specimen of an aparently gravid Dinocephalosaurus has been described from a different location, Luoping County in Yunnan Province. This specimen is incomplete making confident assignment to the same species difficult, but has no traits which would justify erecting a second species. Notably, although presumably an adult, this specimen is only about half  the size of the largest specimens from the Guanling Formation specimens, suggesting  that if it does belong to the same species, then that species  must have  shown strong sexual dimorphism.

Specimens of Dinocephalosaurus orientalis are quite abundant in the Guanling Formation, a coastal deposit laid down in the eastern Tethys Ocean, but no similar specimens have to date been found in deposits from the western Tethys, which outcrop in Europe and the Middle East, despite many of these sites having been sampled extensively for over three centuries. However, based upon their new material, Spiekman et al. not that two maxillae from the Lower Muschelkalk of Krapkowice and Gogolin in Upper Silesia, Poland, and a dentary from the Lower Muschelkalk of Winterswijk in the Netherlands, currently assigned to 'Lamprosauroides goepperti', show strong similarities to Dinocephalosaurus orientalis, although the extremely fragmentary nature of this European material prevents a proper re-evaluation at this time.

Extremely elongate necks appear to have been achieved at least twice in non-Crocopodan Archosauromorphs, with Dinocephalosaurus orientalis increasing the number of vertebrae in its neck, while Tanystropheus spp. increased the length of the individual cervical vertebrae. While this might seem likely to have given Dinocephalosaurus orientalis a more flexible neck than Tanystropheus spp., both taxa had elongated cervical ribs which would have served to stiffen the neck, something widespread in non-Crocopodan Archosauromorphs. 

It is possible thar the arrangement of cervical ribs and an elongate neck would have facilitated suction feeding, however, both taxa have 'fish-trap' dentition, suggesting that this is unlikely, as the long teeth would tend to prevent prey being drawn into the buccal cavity. Instead Spiekman et al. theorise that both taxa probably caught prey with a lateral snapping motion of the head, something which has also been proposed for piscivorous Triassic Sauropterygians. 

Restoration of Dinocephalosaurus orientalis. The skull in (a) left lateral; (b) dorsal; and (c) ventral views. (d) The skeleton in left lateral view with a silhouette of a diver for scale. Abbreviations; ect, ectopterygoid; fr, frontal; j, jugal; la, lacrimal; mx, maxilla; na, nasal; pa, parietal; pal, palatine; pm, premaxilla; po, postorbital; pof, postfrontal; prf, prefrontal; pt, pterygoid; q, quadrate; sq, squamosal; vo, vomer. Spiekman et al. (2024).

The largest specimens of Dinocephalosaurus orientalis are considered to be adults with some confidence, showing full fusion of the bones of the skull and trunk region. Notably, a specimen from the Triassic of Yunnan, which appears very similar to Dinocephalosaurus orientalis, but is not complete enough to confidently assign to the species, is gravid, suggesting either that Dinocephalosaurus orientalis was sexually dimorphic, or that a second, much smaller species of Dinocephalosaurus was also present. The limbs of Dinocephalosaurus orientalis are underdeveloped, with little development of articular surfaces and poorly ossified carpus and tarsus, even compared to the functionally similar Tanystropheus spp., suggesting that Dinocephalosaurus orientalis had a greater degree of adaption to a marine environment, and was probably not capable of leaving the water and crawling onto land. 

See also...

Eardasaurus powelli: A new Pliosaurid from England's Middle Jurassic Oxford Clay Formation.

The earliest known Pliosaurid Plesiosaurians date from rocks of the Earliest Jurassic. Long-snouted forms showing adaptations to for a specialist piscivoran diet appearing by the end of the Early Jurassic. Classical 'pliosauromorph' forms with large bodies, short necks, and heads which form a high proportion of the total body-length, appearing by the Middle Jurassic, and reaching sizes of 10-12 m by the Late Jurassic. This bodyform then remained essentially unchanged until the group disappeared in the early Late Cretaceous.

One of the most important deposits for the study of this group is the Oxford Clay Formation of England, which has been studied since the nineteenth century, and has produced a large and diverse assemblage of Plesiosaurs, with at least five valid described species: Simolestes vorax, Liopleurodon ferox, Peloneustes philarchus, 'Pliosaurus' andrewsi, and Marmornectes candrewi (a sixth, Pachycostasaurus dawni, is problematic, since it was described from a juvenile specimen that could potentially belong to several of the other species). Many of these are known from multiple specimens, notably Peloneustes philarchus, of which 21 examples have been found.

Many of these specimens, as well as other spectacular fossils from the same formation, were collected from pits which primarily extracted clay for the brick-making industry. The heyday of this industry was in the second half of the nineteenth century, when the brothers Charles and Alfred Leeds collected numerous Plesiosaur (and other) specimens from the clay pits around Peterborough in Cambridgeshire, including the holotypes of Simolestes vorax and 'Pliosaurus' andrewsi. The brick-making industry has declined greatly since this time, with a subsequent decline in the amount of activity at clay pits, and therefore the number of fossils recovered from them, but spectacular new finds are still reported from time to time, with the most recently described Oxford Clay Plisiosaur, Marmornectes candrewi, having been recovered from a clay pit in Bedfordshire in 1998.

In a paper published in the journal Acta Palaeontologica Polonica on 23 May 2022, Hilary Ketchum of the Oxford University Museum of Natural History, and Roger Benson of the Department of Earth Sciences at the University of Oxford, describe a new species of Pliosaurid from the Peterborough Member of the Oxford Formation, collected from the former ARC Cassington gravel pit near Yarnton, Oxfordshire.

The new Pliosaur is named Eardasaurus powelli, where 'Eardasaurus' is a combination of the  Old English 'eard', meaning 'native soil or dwelling', from which the village name Yarnton was derived, and '-saurus' the Greek for Lizard, commonly used as a suffix for large Mesozoic Animals, while 'powelli' honours Philip Powell, former Assistant Curator at the Oxford University Museum of Natural History, who took part in the excavation of the specimen from which the species is described in 1994, and carried out preparation work on its skull and postcranial skeleton.

The species is described from a single specimen, OUMNH PAL-J.2247, which was discovered during the construction of a deep silt pond. This specimen was partially embedded in six concretions, which enclosed the posterior two-thirds of the cranium, parts of the vertebral series, and the hindlimb.

Holotype of the Pliosaurid Plesiosaur Eardasaurus powelli (OUMNH PAL-J.2247) from the Middle Jurassic of Yarnton, Oxfordshire, UK. Photograph of the specimen on display in Oxford University Museum of Natural History. Skeleton laid out as discovered, with the exception of the left hindlimb (highlighted in black), which was originally disarticulated. An artist’s reconstruction of Eardasaurus powelli  is partially visible in the top right-hand side of the image. Ketchum & Benson (2022).

Specimen OUMNH PAL-J.2247  measures approximately 4.7 m long from the tip of the snout to the end of the (incomplete) tail, as preserved, and includes the cranium, lower jaw, four scleral ossicles, two hyoids, more than 40 teeth and tooth fragments (including both disarticulated and in situ teeth), atlas-axis complex, 57 postaxial vertebrae (comprising 18 cervicals, 3 pectorals, 24 dorsals, 4 sacrals, and 8 caudals, along with disarticulated neural arches, neural spines, ribs, and chevrons), and 11 gastralia. The preserved appendicular skeleton includes the distal end of the right humerus plus a partial left forelimb discovered in articulation, which includes the radius, ulna, proximal and distal carpals, and 17 phalanges. There is a partial left hindlimb compri sing the femur, proximal and distal tarsals. In total 40 complete phalanges, plus six partial phalanges were found disarticulated and cannot confidently be assigned to any particular limb. Of the limb girdles, only the interclavicle and a clavicle are preserved.

Eardasaurus powelli is a Longirostrine Pliosaurid with a high number (35-40) of alveoli on its maxilla, a jugal with fluted ornamentation on its orbital margin, a step-like contact between the jugal and the squamosal, a 'lacrimal' bone formed by the neomorphic ossification in the anteroventral orbit margin (and not homologous to the lacrimal of other Tetrapods) which is dorsoventrally slender with a posterior rod-like projection.

Eardasaurus powelli also has a pattern of enamel ridges on its larger (mesial) teeth, something also seen in Peloneustes philarchus, but absent in other Pliosaurids from the Oxford Clay. It also has five to six premaxillary teeth, a  prominent mediolateral constriction of the rostrum at the premaxilla–maxilla suture, a diastema (gap) between premaxillary and maxillary dentitions, a  maxilla excluded from contact with the medial margin of external naris by an anterior extension of the frontal, a proportionally elongate posterior interpterygoid vacuities compared to other Middle Jurassic Pliosaurids, a mediolaterally expanded mandibular symphysis, nine pairs of dentary teeth adjacent to the mandibular symphysis, a  splenial which encloses the posterior margin of the anterior opening of Meckel’s canal, and a coronoid exposed on the lateral surface of the mandible, a strongly convex medial expansion of the surangular in dorsal view.

Holotype of the Pliosaurid Pleasiosaur Eardasaurus powelli (OUMNH PAL-J.2247) from the Middle Jurassic of Yarnton, Oxfordshire, UK. Cranium in dorsal view. Photograph (A₁), interpretive drawing (A₂), light grey, broken bone; mid grey filler; dark grey, matrix. Ketchum & Benson (2022).

A phylogenetic analysis carried out by Ketchum and Benson recovered Eardasaurus powelli as an early-diverging Thalassophonean Pliosaurid, forming the sister taxon to the derived group comprising 'Pliosaurus' andrewsi, Simolestes vorax, Liopleurodon ferox, Pliosaurus spp., and Brachaucheninae.

Phylogenetic topology for Pliosauridae, focussing on Early–Middle Jurassic representatives, based on Bayesian Mkv analysis. Numbers indicate posterior support for nodes demonstrating strong support for many aspects, but weaker support for relationships among Peloneustes philarchus, Anguanax zignoi, and Eardasaurus powelli, which are tentatively recovered as grade leading to more derived Pliosaurids. Ketchum & Benson (2022).

Eardasaurus powelli has a pattern of deep ridges on its teeth which would have formed additional deep cutting surfaces in life. Such ridges are ecologically significant, as they are typically associated with macropradatory behaviour (i.e. attacking large prey). Such ridges are found in a range of taxa, although they are rare (but not unknown) in Pliosaurids, although Ketchum & Benson suggest that this may be due to under-reporting rather than a true absence.

See also...

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