"Pliosaurus" andrewsi

Last updated

"Pliosaurus" andrewsi
Temporal range: Middle Jurassic, Callovian~(166.1–163.5 Ma) [1]
Ꞓ
O
S
D
C
P
T
J
K
Pg
N
↓
'Pliosaurus' andrewsi tooth.png
Four-sided view of one of the teeth from the holotype of "P." andrewsi (NHMUK PV R3891).
Scientific classification OOjs UI icon edit-ltr.svg
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Reptilia
Superorder:† Sauropterygia
Order:† Plesiosauria
Family:† Pliosauridae
Clade:† Thalassophonea
Genus:
†" Pliosaurus "
Species:
†"P." andrewsi
Binomial name
†"Pliosaurus" andrewsi

"Pliosaurus" andrewsi is an extinct species of pliosaurid plesiosaurs that lived during the Callovian stage of the Middle Jurassic, in what is now England. The only known fossils of this taxon were discovered in the Peterborough Member of the Oxford Clay Formation. Other attributed specimens have been discovered in various corners of Eurasia, but these are currently seen as indeterminate or coming from other taxa. The taxonomic history of this animal is quite complex, because several of its fossils were attributed to different genera of pliosaurids, before being concretely named and described in 1960 by Lambert Beverly Tarlo as a species of Pliosaurus . However, although the taxon was found to be valid, subsequent revisions found that it is not part of this genus, and therefore a taxonomic revision must be carried out on this species.

Contents

"P." andrewsi has a skull that would have had an elongated snout capable of catching agile prey. Its teeth are round in cross section, with some longitudinal ridges on them. Unlike Pliosaurus, "P." andrewsi is among the most basal representatives of the Thalassophonea, a group of pliosaurids characterized by a short neck. "P." andrewsi would have inhabited an epicontinental (inland) sea that was around 30–50 metres (100–160 ft) deep. It shared its habitat with a variety of other animals, including invertebrates, fish, thalattosuchians, ichthyosaurs, and other plesiosaurs. At least five other pliosaurids are known from the Peterborough Member, but they were quite varied in anatomy, indicating that they would have eaten different food sources, thereby avoiding competition.

Research history

Discovery and identification

Mandibles of Peloneustes philarchus (top) and that referred to "Pliosaurus" andrewsi (bottom). Peloneustes and Pliosaurus andrewsi Mandibles.png
Mandibles of Peloneustes philarchus (top) and that referred to "Pliosaurus" andrewsi (bottom).

The first possible mention of "Pliosaurus" andrewsi in scientific literature dates back to 1871, in which John Phillips catalogued pliosaur fossils having been discovered by Charles Leeds in the Oxford Clay Formation, England. [2] : 316–318  This formation, well known because of its significant preservation of plesiosaurians, is dated to the Callovian stage of the Middle Jurassic, [3] [4] a period ranging from 166 to 164 million years. [1] The specimen, consisting of a swimming paddle and a mandible which are rather well preserved, was assigned the scientific name of Pleiosaurus? grandis in Phillips' review. [2] : 317–318  The specimen consists of an elongated mandibular symphysis possessing 11 pairs of teeth, of which the fifth and sixth anterior ones are caniniform. Based on these descriptions, Richard Lydekker referred the specimen to the newly named Peloneustes philarchus in 1889. [5] : 49–50  [6] : 163  The following year, Lydekker assigned the mandible to the proposed species Peloneustes evansi, due to its larger size than specimens attributed to Peloneustes philarchus. When Lambert Beverly Tarlo officially described "Pliosaurus" andrewsi in 1960, the mandible was attributed to this new species name. [6] : 163–164  However, in the official 2022 description of Eardasaurus , another pliosaurid from the Oxford Clay Formation, Phillips's mandible (cataloged as NHMUK R2443) is considered as a specimen of undetermined affinities and cannot be clearly attributed to "P." andrewsi. [4]

In 1913, Charles William Andrews attributed a partial skeleton of another large pliosaur found by Leeds to Peloneustes evansi, noting that while the mandible and vertebrae were similar to other specimens of that species, they remain quite different from those of Peloneustes philarchus. Therefore, Andrews considered it possible that Peloneustes evansi belonged to a distinct genus that would have been morphologically intermediate between Peloneustes and Pliosaurus . [7] : 72  In 1958, Tarlo considered the larger remains attributed to Peloneustes evansi to belong to a new species of Pliosaurus, determining them to be very different from Peloneustes, just as Andrews previously suggested. [8] : 439–441  Two years later, in 1960, he named the taxon Pliosaurus andrewsi and designated the partial skeleton (cataloged as NHMUK R3891) as the holotype of this species. [6] : 163–164  The holotype specimen is a skeleton consisting of a mandible, teeth, a complete vertebral column as well as parts of the fore and hind limbs. [7] : 72  [6] : 164  [9] [3] Tarlo also gave an anatomical description showing the main differences with other pliosaurs of the Oxford Clay Formation. [6] : 163–164  The specific epithet andrewsi is named in honor of Andrews, [10] who was the first to propose that the fossil remains of this taxon belong to a different genus from Peloneustes. [7] : 72 

The taxonomic identity of this species remained undisputed for decades, [11] [12] but in the early 2010s phylogenetic and anatomical revisions showed that it did not belong to the genus Pliosaurus. [13] After this discovery, the taxon was renamed as "Pliosaurus" andrewsi in studies published since, the quotation marks indicating its non-belonging within this genus. [14] [9]

Formerly attributed specimens

Description

The mandible of "P." andrewsi has a mandibular symphysis which contains up to 12 pairs of teeth, [9] [18] of which the seventh pair is broad and caniniform. [6] : 164  The total number of teeth in each ramus would have been approximately 32, [6] : 164  indicating a total number of 64 teeth in the mandible. [9] The mandible in general is quite similar to that of Pliosaurus brachydeirus. [6] : 164  Based on this morphology, "P." andrewsi would have had an elongated snout capable of catching small, agile prey. [11] The main distinguishing feature of "P." andrewsi is the morphology of its teeth. The teeth are round in cross section and the dental crown quite smooth, nevertheless having some longitudinal ridges. Unique case of dental wear among plesiosaurians, the crown has an abrasion which extends considerably further than any other known representatives of the group. [6] : 164  [9] [3] [4] [18] The teeth of "P." andrewsi are suited for cutting, suggesting that it also attacked large prey. [12]

The articular surfaces of the cervical vertebrae have a circular outline with a narrow peripheral groove. Cervical ribs are double-headed, [6] : 164  a common feature among Jurassic pliosaurs. Characteristically, the cervical vertebrae lack ventral ridges and ventral surface ornamentation. [9] The neck length of the holotype specimen would have been approximately 78.3 cm according to David Martill and colleagues in 2023. [19] : 367  [lower-alpha 1] Despite the fact that the vertebral column of "P." andrewsi is fully known, Tarlo did not analyze the caudal and dorsal vertebrae, because they do not have enough notable features to be described in detail. He also mentions that some isolated vertebrae assigned to "P." andrewsi are indistinguishable from those of its contemporary Simolestes vorax . The scapula is similar to that of P. brachydeirus, but is somewhat expanded distally. [lower-alpha 2] The humerus is shorter and wider than the femur. The tibia, fibula and ulna are longer than they are wide, but in the radius, these proportions are reversed, being wider than long. [6] : 164 

Classification

Since the first descriptions made on the fossils now referred to "Pliosaurus" andrewsi, they were classified in different genera of the Pliosauridae, a family to which the taxon has always been assigned since. [20] [4] In 1960, Tarlo classified this species in the genus Pliosaurus due to the morphology of the mandible, which is very similar to that of the type species P. brachydeirus. [6] : 164  Subsequently, "P." andrewsi was historically recognized as a species of Pliosaurus until 2010, in which phylogenetic analyzes placed it outside of this genus. [13] Revisions conducted in 2012 on the genus Pliosaurus also confirm this placement, as the taxon has unique characteristics that distinguish it from other species in the genus. One of the main distinguishing features is the shape of its teeth, being conical, unlike all valid species of Pliosaurus, having trihedral shaped teeth. [14] [9] [18] Therefore, "P." andrewsi does not belong to Pliosaurus and needs a taxonomic revision, which is also confirmed by a similar study published in 2013. [21] The same year, Benson and Patrick S. Druckenmiller named a new clade within Pliosauridae, Thalassophonea. This clade included the "classic", short-necked pliosaurids while excluding the earlier, long-necked, more gracile forms. [22] In all analyses carried out since then, "P." andrewsi is among the most basal representatives of this clade, in a position generally located between Peloneustes and Simolestes, unlike Pliosaurus, which is among the most derived representatives. [21] [4] Although its phylogenetic position allows it to be qualified as valid and distinct, [4] its taxonomy is unclear and needs a redescription. [14] [9] [3]

The following cladogram follows Ketchum and Benson, 2022. [4]

Marmornectes candrewi

Thalassophonea

Peloneustes philarchus Peloneustes Skull Dorsal View - Extracted.png

Eardasaurus powelli Eardasaurus Skull Dorsal View - Extracted.png

"Pliosaurus" andrewsi

Simolestes vorax Simolestes Skull Dorsal View.png

Liopleurodon ferox Liopleurodon Skull Dorsal View - Extracted.png

Pliosaurus spp. Pliosaurus Skull Dorsal View - Extracted.png

Brachaucheninae USNM 2361 - Brachauchenius lucasi skull.png

Palaeoenvironment

A clay pit in the Peterborough Member Bradley Fen clay pit in Lower Oxford Clay - geograph.org.uk - 81094.jpg
A clay pit in the Peterborough Member

"P." andrewsi is known from the Peterborough Member (formerly known as the Lower Oxford Clay) of the Oxford Clay Formation. [20] While "P." andrewsi has been listed as coming from the Oxfordian stage (spanning from about 164 to 157 million years ago) [1] of the Upper Jurassic, [6] the Peterborough Member actually dates to the Callovian stage (spanning from about 166 to 164 million years ago) [1] of the Middle Jurassic. [20] The Peterborough Member spans from the late Lower Callovian to the early Upper Callovian, occupying the entirety of the Middle Callovian. [23] It overlays the Kellaways Formation [23] and is overlain by the Stewartby Member of the Oxford Clay Formation. [24] The Peterborough Member is primarily composed of grey bituminous (asphalt-containing) [23] shale and clay rich in organic matter. [25] [26] These rocks are sometimes fissile (splittable into thin, flat slabs). [24] The member is about 16–25 metres (52–82 ft) thick, stretching from Dorset to Humber. [23]

The Peterborough Member represents an epicontinental sea during a time of rising sea levels. [26] When it was deposited, it would have been located at a latitude of 35°N. [24] This sea, known as the Oxford Clay sea, was largely encircled by islands and continents, which provided the seaway with sediment. [24] Its proximity to land is demonstrated by the preservation of terrestrial fossils such as driftwood in the Oxford Clay, in addition to a clastic dike in the lower levels of the Peterborough Member, with the dike's formation being facilitated by rainwater. [25] The southern region of the Oxford Clay Sea was connected to the Tethys Ocean, while it was connected to more boreal regions on its northern side. This allowed for faunal interchange to occur between the Tethyan and boreal regions. This sea was approximately 30–50 metres (100–160 ft) deep within 150 kilometres (93 mi) of the shoreline. [24] [20]

Map of the world in the Jurassic, the Oxford Clay Formation is located at E1 Paleogeography and paleoclimate of the Late Jurassic - 150 Ma with dinosaur fossil localities.png
Map of the world in the Jurassic, the Oxford Clay Formation is located at E1

The surrounding land would have had a Mediterranean climate, with dry summers and wet winters, though it was becoming increasingly arid. Based on information from δ18O isotopes in bivalves, the water temperature of the seabed of the Peterborough Member varied from 14–17 °C (57–63 °F) due to seasonal variation, with an average temperature of 15 °C (59 °F). Belemnite fossils provide similar results, giving a water temperature range with a minimum 11 °C (52 °F) to a maximum between 14 °C (57 °F) or 16 °C (61 °F), with an average temperature of 13 °C (55 °F). [24] While traces of green sulphur bacteria indicate euxinic water, with low oxygen and high hydrogen sulfide levels, abundant traces of benthic (bottom-dwelling) organisms suggest that the bottom waters were not anoxic. [27] [26] Oxygen levels appear to have varied, with some deposits laid down in more aerated conditions than others. [24]

Contemporaneous biota

There are many kinds of invertebrates preserved in the Peterborough Member. Among these are cephalopods, which include ammonites, belemnites, and nautiloids. Bivalves are another abundant group, while gastropods and annelids are less so but still quite common. Arthropods are also present. Brachiopods and echinoderms are rare. Despite not being known from fossils, polychaetes probably would have been present in this ecosystem, due to their abundance in similar modern environments and burrows similar to ones produced by these worms. Microfossils pertaining to foraminiferans, coccolithophoroids, and dinoflagellates are abundant in the Peterborough Member. [11]

A wide variety of fish are known from the Peterborough Member. These include the chondrichthyans Asteracanthus , Brachymylus , Heterodontus (or Paracestracion ), [11] Hybodus , Ischyodus , Palaeobrachaelurus , Pachymylus , Protospinax , Leptacanthus , Notidanus , Orectoloboides , Spathobathis , and Sphenodus . Actinopterygians were also present, represented by Aspidorhynchus , Asthenocormus , Caturus , Coccolepis , Heterostrophus , Hypsocormus , Leedsichthys , Lepidotes , Leptolepis , Mesturus , Osteorachis , Pachycormus , Pholidophorus , and Sauropsis . [28] These fish include surface-dwelling, midwater, and benthic varieties of various sizes, some of which could get quite large. They filled a variety of niches, including invertebrate eaters, piscivores, and, in the case of Leedsichthys, giant filter feeders. [11]

Mounted skeleton of Cryptoclidus, a plesiosaur from the Peterborough Member, at the American Museum of Natural History Cryptoclidus skeleton.jpg
Mounted skeleton of Cryptoclidus , a plesiosaur from the Peterborough Member, at the American Museum of Natural History

Plesiosaurs are common in the Peterborough Member, and besides pliosaurids, are represented by cryptoclidids, including Cryptoclidus, Muraenosaurus , Tricleidus , and Picrocleidus . [20] They were smaller plesiosaurs with thin teeth and long necks, and, unlike pliosaurids such as Peloneustes, would have mainly eaten small animals. [11] The ichthyosaur Ophthalmosaurus also inhabited the Oxford Clay Formation. Ophthalmosaurus was well adapted for deep diving, thanks to its streamlined, porpoise-like body and gigantic eyes, and probably fed on cephalopods. [11] Many genera of crocodilians are also known from the Peterborough Member. These include the gavial-like teleosauroids Charitomenosuchus , Lemmysuchus , Mycterosuchus , and Neosteneosaurus [29] and the mosasaur-like [11] metriorhynchids Gracilineustes , Suchodus , Thalattosuchus , [30] and Tyrannoneustes . [31] While uncommon, the small piscivorous pterosaur Rhamphorhynchus was also part of this marine ecosystem. [11]

Skeletal mount of Liopleurodon ferox at the University of Tubingen, another pliosaurid from the Peterborough Member Liopleurodon ferox Tubingen 2.JPG
Skeletal mount of Liopleurodon ferox at the University of Tübingen, another pliosaurid from the Peterborough Member

More pliosaurid species are known from the Peterborough Member than any other assemblage. [20] Besides "P." andrewsi, these pliosaurids include Liopleurodon ferox , Simolestes vorax, Peloneustes philarchus, Marmornectes candrewi , [32] Eardasaurus powelli , and, potentially, Pachycostasaurus dawni . [33] [4] However, there is considerable variation in the anatomy of these species, indicating that they fed on different prey, thereby avoiding competition (niche partitioning). [34] : 249–251  [35] The large, powerful pliosaurid Liopleurodon ferox appears to have been adapted to take on large prey, including other marine reptiles and large fish. [34] : 242–243, 249–251  The long-snouted Eardasaurus powelli like Liopleurodon also has teeth with cutting edges and may have also taken large prey. [4] Simolestes vorax, with its wide, deep skull and powerful bite, appears to have been a predator of large cephalopods. [34] : 243–244, 249–251 Peloneustes, like "P." andrewsi, possesses an elongated snout, an adaptation for feeding upon small, agile animals. [11] However, the teeth of Peloneustes are better adapted for piercing, while those of "P." andrewsi are suited to cutting, indicating a preference for larger prey. [12] "Pliosaurus" andrewsi is also larger than Peloneustes. [11] Marmornectes candrewi is also similar to Peloneustes, bearing a long snout, and perhaps also fed on fish. [22] [32] Pachycostasaurus dawni is a small, heavily built pliosaur that probably fed on benthic prey. It has a weaker skull than other pliosaurids and was more stable, so it probably used different feeding methods to avoid competition. [35] Unlike the other pliosaurids of the Oxford Clay, Pachycostasaurus was rather rare, perhaps mainly living outside of the depositional area of the Oxford Clay Formation, possibly inhabiting coastal regions, deep water, or even rivers instead. [35] While several different types of pliosaurids were present in the Middle Jurassic, the long-snouted piscovorous forms such as "P." andrewsi died out at the Middle-Upper Jurassic boundary. This seems to have been the first phase of a gradual decline in plesiosaur diversity. While the cause of this is uncertain, it may have been influenced by changing ocean chemistry, and, in later phases, falling sea levels. [22]

Notes

  1. ↑ In this study, specimen NHMUK R3891 is nominally classified in Peloneustes evansi, [19] : 367  a taxon nevertheless considered as a nomen dubium since 2011. [20]
  2. ↑ The scapula in question comes from an attributed specimen which is cataloged as NHMUK R2437. [6] : 164  [19] : 367 

Related Research Articles

<span class="mw-page-title-main">Pliosauroidea</span> Extinct clade of reptiles

Pliosauroidea is an extinct clade of plesiosaurs, known from the earliest Jurassic to early Late Cretaceous. They are best known for the subclade Thalassophonea, which contained crocodile-like short-necked forms with large heads and massive toothed jaws, commonly known as pliosaurs. More primitive non-thalassophonean pliosauroids resembled plesiosaurs in possessing relatively long necks and smaller heads. They originally included only members of the family Pliosauridae, of the order Plesiosauria, but several other genera and families are now also included, the number and details of which vary according to the classification used.

Liopleurodon is an extinct genus of large, carnivorous marine reptile belonging to the Thalassophonea, a clade of short-necked pliosaurid plesiosaurs. Liopleurodon lived from the Callovian Stage of the Middle Jurassic to the Kimmeridgian stage of the Late Jurassic Period. It was the apex predator of the Middle to Late Jurassic seas that covered Europe. The largest species, L. ferox, is estimated to have grown over 6 metres (20 ft) in length based on a large skull.

Peloneustes is a genus of pliosaurid plesiosaur from the Middle Jurassic of England. Its remains are known from the Peterborough Member of the Oxford Clay Formation, which is Callovian in age. It was originally described as a species of Plesiosaurus by palaeontologist Harry Govier Seeley in 1869, before being given its own genus by naturalist Richard Lydekker in 1889. While many species have been assigned to Peloneustes, P. philarchus is currently the only one still considered valid, with the others moved to different genera, considered nomina dubia, or synonymised with P. philarchus. Some of the material formerly assigned to P. evansi have since been reassigned to "Pliosaurus" andrewsi. Peloneustes is known from many specimens, including some very complete material.

<i>Rhomaleosaurus</i> Genus of rhomaleosaurid plesiosaur from the Early Jurassic period

Rhomaleosaurus is an extinct genus of Early Jurassic rhomaleosaurid pliosauroid known from Northamptonshire and from Yorkshire of the United Kingdom. It was first named by Harry Seeley in 1874 and the type species is Rhomaleosaurus cramptoni. It was one of the earliest large marine reptile predators which hunted in the seas of Mesozoic era, measuring about 7 metres (23 ft) long. Like other pliosaurs, Rhomaleosaurus fed on ichthyosaurs, ammonites and other plesiosaurs.

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

Trinacromerum is an extinct genus of sauropterygian reptile, a member of the polycotylid plesiosaurs. It contains two species, T. bentonianum and T. kirki. Specimens have been discovered in the Late Cretaceous fossil deposits of what is now modern Kansas and Manitoba.

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

Pliosaurus is an extinct genus of thalassophonean pliosaurid known from the Late Jurassic of Europe and South America. Most European species of Pliosaurus measured around 8 metres (26 ft) long and weighed about 5 metric tons, but P. rossicus and P. funkei would have been one of the largest plesiosaurs of all time, exceeding 10 metres (33 ft) in length. This genus has contained many species in the past but recent reviews found only six to be valid, while the validity of two additional species awaits a petition to the International Code of Zoological Nomenclature. Currently, P. brachyspondylus and P. macromerus are considered dubious, while P. portentificus is considered undiagnostic. Species of this genus are differentiated from other pliosaurids based on seven autapomorphies, including teeth that are triangular in cross section. Their diet would have included fish, cephalopods, and marine reptiles.

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

Brachauchenius is an extinct genus of pliosaurid that lived in North America and Morocco during the Late Cretaceous.

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

Leptocleidus is an extinct genus of plesiosaur, belonging to the family Leptocleididae. It was a small plesiosaur, measuring only up to 3 m (9.8 ft).

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

Simolestes is an extinct pliosaurid genus that lived in the Middle to Late Jurassic. The type specimen, BMNH R. 3319 is an almost complete but crushed skeleton diagnostic to Simolestes vorax, dating back to the Callovian of the Oxford Clay formation, England. The genus is also known the Tithonian of India (S.indicus). The referral of this species to Simolestes is dubious, however. S.keileni from France was moved to the new genus Lorrainosaurus in 2023.

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

Colymbosaurus is a genus of cryptoclidid plesiosaur from the Late Jurassic (Callovian-Tithonian) of the UK and Svalbard, Norway. There are two currently recognized species, C. megadeirus and C. svalbardensis.

<span class="mw-page-title-main">Leptocleididae</span> Extinct family of reptiles

Leptocleididae is a family of small-sized plesiosaurs that lived during the Early Cretaceous period. They had small bodies with small heads and short necks. Leptocleidus and Umoonasaurus had round bodies and triangle-shaped heads. Leptocleidids have been found in what were shallow nearshore, freshwater and brackish habitats. Hilary F. Ketchum and Roger B. J. Benson (2010), transferred Brancasaurus, Kaiwhekea, Nichollssaura and Thililua to this family. However, Ketchum and Benson (2011) reassigned Kaiwhekea and Thililua to their original positions, as an elasmosaurid and a polycotylid, respectively.

Eurycleidus is an extinct genus of large-bodied rhomaleosaurid known from the Early Jurassic period of the United Kingdom. It contains a single species, E. arcuatus. Like other plesiosaurs, Eurycleidus 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.

Eromangasaurus is an extinct genus of elasmosaurid known from northern Queensland of Australia.

<i>Pachycostasaurus</i> Extinct species of reptile

Pachycostasaurus is an extinct Pliosauroid from the Oxford Clay formation of Peterborough, England.

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

Gallardosaurus is a genus of pliosaurid plesiosaur from the Caribbean seaway. It contains the single species Gallardosaurus iturraldei. Gallardosaurus was found in middle-late Oxfordian-age rocks of the Jagua Formation of western Cuba. Gallardosaurus is believed to be evolutionarily connected to Peloneustes, a pliosaurid commonly found in the Oxfordian-aged sediment.

Marmornectes is a genus of pliosaurid known from the Middle Jurassic of Bedfordshire, United Kingdom.

<span class="mw-page-title-main">Timeline of plesiosaur research</span>

This timeline of plesiosaur research is a chronologically ordered list of important fossil discoveries, controversies of interpretation, taxonomic revisions, and cultural portrayals of plesiosaurs, an order of marine reptiles that flourished during the Mesozoic Era. The first scientifically documented plesiosaur fossils were discovered during the early 19th century by Mary Anning. Plesiosaurs were actually discovered and described before dinosaurs. They were also among the first animals to be featured in artistic reconstructions of the ancient world, and therefore among the earliest prehistoric creatures to attract the attention of the lay public. Plesiosaurs were originally thought to be a kind of primitive transitional form between marine life and terrestrial reptiles. However, now plesiosaurs are recognized as highly derived marine reptiles descended from terrestrial ancestors.

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

Megacephalosaurus is an extinct genus of short-necked pliosaur that inhabited the Western Interior Seaway of North America about 94 to 93 million years ago during the Turonian stage of the Late Cretaceous, containing the single species M. eulerti. It is named after its large head, which is the largest of any plesiosaur in the continent and measures up to 1.75 meters (5.7 ft) in length. Megacephalosaurus was one of the largest marine reptiles of its time with an estimated length of 6–9 meters (20–30 ft). Its long snout and consistently sized teeth suggest that it preferred a diet of smaller-sized prey.

Luskhan is an extinct genus of brachauchenine pliosaur from the Cretaceous of Russia. The type and only species is Luskhan itilensis, named by Valentin Fischer and colleagues in 2017 from a well-preserved and nearly complete skeleton. As an early-diverging brachauchenine, Luskhan consequently exhibits an intermediate combination of traits seen in more basal and more derived pliosaurs. However, Luskhan departs significantly from other pliosaurs in that it exhibits a lack of adaptations in its skull to feeding on large prey; its slender snout, small teeth, and short tooth rows instead indicate a skull adapted for feeding on small, soft prey. With these features, it is the pliosaur that approaches closest to the distantly-related piscivorous polycotylids, having convergently evolved these traits more than 10 million years apart.

Eardasaurus is a genus of thalassophonean pliosaurid from the middle Jurassic Oxford Clay Formation. The animal would have measured over 4.7 m (15 ft) long and possessed a high amount of teeth relative to other pliosaurs. Its teeth show distinct ridges formed by the tooth enamel, some of which are very pronounced and similar to carinae, giving the teeth a cutting edge.

References

  1. 1 2 3 4 Cohen, K.M.; Finney, S.; Gibbard, P.L. (2015). "International Chronostratigraphic Chart" (PDF). International Commission on Stratigraphy.
  2. 1 2 J. Phillips (1871). Geology of Oxford and the valley of the Thames. Oxford: Clarendon Press.
  3. 1 2 3 4 5 D. Foffa; Mark T. Young; Stephen L. Brusatte (2018). "Filling the Corallian gap: New information on Late Jurassic marine reptile faunas from England". Acta Palaeontologica Polonica . 63 (2): 287–313. doi: 10.4202/app.00455.2018 . hdl: 20.500.11820/729f4cac-6217-4a21-b22c-8683b38c733b . S2CID   52254345.
  4. 1 2 3 4 5 6 7 8 9 H. F. Ketchum; R. B. J. Benson (2022). "A new pliosaurid from the Oxford Clay Formation of Oxfordshire, UK". Acta Palaeontologica Polonica . 67 (2): 297–315. doi: 10.4202/app.00887.2021 . ISSN   0567-7920. S2CID   249034986.
  5. ↑ R. Lydekker (1889). "On the remains and affinities of five genera of Mesozoic reptiles". The Quarterly Journal of the Geological Society of London . 45 (1–4): 41–59. doi:10.1144/GSL.JGS.1889.045.01-04.04. S2CID   128586645.
  6. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 L. B. Tarlo (1960). "A review of the Upper Jurassic pliosaurs". Bulletin of the British Museum (Natural History). 4 (5): 145–189.
  7. 1 2 3 C. W. Andrews (1913). A descriptive catalogue of the marine reptiles of the Oxford clay. Based on the Leeds Collection in the British Museum (Natural History), London. Vol. 2. London: British Museum.
  8. ↑ L. B. Tarlo (1958). "A review of pliosaurs". XVTH Internal. Cong. Zool. London. 9: 438–442.
  9. 1 2 3 4 5 6 7 8 E. M. Knutsen (2012). "A taxonomic revision of the genus Pliosaurus (Owen, 1841a) Owen, 1841b" (PDF). Norwegian Journal of Geology. 92: 259–276.
  10. ↑ B. Creisler (2012). "Ben Creisler's Plesiosaur Pronunciation Guide". Oceans of Kansas. Retrieved 26 June 2021.
  11. 1 2 3 4 5 6 7 8 9 10 11 D. M. Martill; M. A. Taylor; K. L. Duff; J. B. Riding; P. R. Bown (1994). "The trophic structure of the biota of the Peterborough Member, Oxford Clay Formation (Jurassic), UK". Journal of the Geological Society. 151 (1): 173–194. Bibcode:1994JGSoc.151..173M. doi:10.1144/gsjgs.151.1.0173. S2CID   131200898.
  12. 1 2 3 J. A. Massare (1987). "Tooth morphology and prey preference of Mesozoic marine reptiles". Journal of Vertebrate Paleontology. 7 (2): 121–137. Bibcode:1987JVPal...7..121M. doi:10.1080/02724634.1987.10011647.
  13. 1 2 H. F. Ketchum; R. B. J. Benson (2010). "Global interrelationships of Plesiosauria (Reptilia, Sauropterygia) and the pivotal role of taxon sampling in determining the outcome of phylogenetic analyses". Biological Reviews . 85 (2): 361–392. doi:10.1111/j.1469-185X.2009.00107.x. PMID   20002391. S2CID   12193439.
  14. 1 2 3 P. S. Druckenmiller; E. M. Knutsen (2012). "Phylogenetic relationships of Upper Jurassic (Middle Volgian) plesiosaurians (Reptilia: Sauropterygia) from the Agardhfjellet Formation of central Spitsbergen, Norway" (PDF). Norwegian Journal of Geology. 92: 277–284.
  15. ↑ É. Buffetaut; Varavudh Suteethorn; Haiyan Tong; Romain Amiot (2008). "An Early Cretaceous spinosaur theropod from southern China". Geological Magazine . 145 (5): 745–748. Bibcode:2008GeoM..145..745B. doi:10.1017/S0016756808005360. S2CID   129921019.
  16. ↑ T. Maryańska (1976). "Aberrant pliosaurs from the Oxfordian of Poland". Prace Museum Ziemi. 20: 201–206.
  17. ↑ D. Madzia; T. Szczygielski; A. S. Wolniewicz (2021). "The giant pliosaurid that wasn't—revising the marine reptiles from the Kimmeridgian, Upper Jurassic, of Krzyżanowice, Poland". Acta Palaeontologica Polonica . 66 (1): 99–129. doi: 10.4202/app.00795.2020 . S2CID   231801208.
  18. 1 2 3 S. Sachs; D. Madzia; B. Thuy; B. P. Kear (2023). "The rise of macropredatory pliosaurids near the Early-Middle Jurassic transition". Scientific Reports . 13 (1): 17558. Bibcode:2023NatSR..1317558S. doi: 10.1038/s41598-023-43015-y . PMC   10579310 . PMID   37845269.
  19. 1 2 3 D. M. Martill; M. L. Jacobs; R. E. Smith (2023). "A truly gigantic pliosaur (Reptilia, Sauropterygia) from the Kimmeridge Clay Formation (Upper Jurassic, Kimmeridgian) of England". Proceedings of the Geologists' Association . 134 (3): 361–373. Bibcode:2023PrGA..134..361M. doi: 10.1016/j.pgeola.2023.04.005 . S2CID   258630597.
  20. 1 2 3 4 5 6 7 H. F. Ketchum; R. B. J. Benson (2011). "The cranial anatomy and taxonomy of Peloneustes philarchus (Sauropterygia, Pliosauridae) from the Peterborough member (Callovian, Middle Jurassic) of the United Kingdom". Palaeontology. 54 (3): 639–665. Bibcode:2011Palgy..54..639K. doi: 10.1111/j.1475-4983.2011.01050.x . S2CID   85851352.
  21. 1 2 R. B. J. Benson; M. Evans; A. S. Smith; J. Sassoon; S. Moore-Faye; H. F. Ketchum; R. Forrest (2013). "A Giant Pliosaurid Skull from the Late Jurassic of England". PLOS ONE . 8 (5): e65989. Bibcode:2013PLoSO...865989B. doi: 10.1371/journal.pone.0065989 . PMC   3669260 . PMID   23741520.
  22. 1 2 3 R. B. J. Benson; P. S. Druckenmiller (2014). "Faunal turnover of marine tetrapods during the Jurassic–Cretaceous transition". Biological Reviews. 89 (1): 1–23. doi:10.1111/brv.12038. PMID   23581455. S2CID   19710180.
  23. 1 2 3 4 K. L. Duff. "Palaeoecology of a bituminous shale –the Lower Oxford Clay of central England". Palaeontology. 18 (3): 443–482.
  24. 1 2 3 4 5 6 7 C. Mettam; A. L. A. Johnson; E. V. Nunn; B. R. Schöne (2014). "Stable isotope (δ18O and δ13C) sclerochronology of Callovian (Middle Jurassic) bivalves (Gryphaea (Bilobissa) dilobotes) and belemnites (Cylindroteuthis puzosiana) from the Peterborough Member of the Oxford Clay Formation (Cambridgeshire, England): evidence of palaeoclimate, water depth and belemnite behaviour" (PDF). Palaeogeography, Palaeoclimatology, Palaeoecology. 399: 187–201. Bibcode:2014PPP...399..187M. doi:10.1016/j.palaeo.2014.01.010. hdl: 10545/592777 . S2CID   129844404.
  25. 1 2 J. D. Hudson; D. Martill (1994). "The Peterborough Member (Callovian, Middle Jurassic) of the Oxford Clay Formation at Peterborough, UK". Journal of the Geological Society. 151 (1): 113–124. Bibcode:1994JGSoc.151..113H. doi:10.1144/gsjgs.151.1.0113. S2CID   130058981.
  26. 1 2 3 S. Belin; F. Kenig (1994). "Petrographic analyses of organo-mineral relationships: depositional conditions of the Oxford Clay Formation (Jurassic), UK". Journal of the Geological Society. 151 (1): 153–160. Bibcode:1994JGSoc.151..153B. CiteSeerX   10.1.1.1001.7308 . doi:10.1144/gsjgs.151.1.0153. S2CID   131433536.
  27. ↑ F. Kenig; J. D. Hudson; J. S. S. Damsté; B. N. Popp (2004). "Intermittent euxinia: Reconciliation of a Jurassic black shale with its biofacies". Geology. 32 (5): 421–424. Bibcode:2004Geo....32..421K. doi:10.1130/G20356.1.
  28. ↑ D. M. Martill (1991). "Fish". In Martill, D. M.; Hudson, J. D. (eds.). Fossils of the Oxford Clay (PDF). London: The Palaeontological Association. pp. 197–225. ISBN   0901702463.
  29. ↑ M. M. Johnson; M. T. Young; S. L. Brusatte (2020). "The phylogenetics of Teleosauroidea (Crocodylomorpha, Thalattosuchia) and implications for their ecology and evolution". PeerJ. 8: e9808. doi: 10.7717/peerj.9808 . PMC   7548081 . PMID   33083104.
  30. ↑ M. T. Young; A. Brignon; S. Sachs; J. J. Hornung; D. Foffa; J. J. N. Kitson; M. M. Johnson; L. Steel (2021). "Cutting the Gordian knot: A historical and taxonomic revision of the Jurassic crocodylomorph Metriorhynchus". Zoological Journal of the Linnean Society. 192 (2): 510–553. doi:10.1093/zoolinnean/zlaa092.
  31. ↑ S. Sachs; M. T. Young; P. Abel; H. Mallison (2019). "A new species of the metriorhynchid crocodylomorph Cricosaurus from the Upper Jurassic of southern Germany" (PDF). Acta Palaeontologica Polonica . 64 (2): 343–356. doi: 10.4202/app.00541.2018 .
  32. 1 2 H. F. Ketchum; R. B. J. Benson (2011). "A new pliosaurid (Sauropterygia, Plesiosauria) from the Oxford Clay Formation (Middle Jurassic, Callovian) of England: Evidence for a gracile, longirostrine grade of Early-Middle Jurassic pliosaurids". Special Papers in Palaeontology. 86: 109–129. ISSN   0038-6804. OCLC   2450768.
  33. ↑ L. F. Noè; J. Liston; M. Evans (2003). "The first relatively complete exoccipital-opisthotic from the braincase of the Callovian pliosaur, Liopleurodon" (PDF). Geological Magazine. 140 (4): 479–486. Bibcode:2003GeoM..140..479N. doi:10.1017/S0016756803007829. S2CID   22915279. Archived from the original (PDF) on 9 June 2020.
  34. 1 2 3 L. F. Noè (2001). A taxonomic and functional study of the Callovian (Middle Jurassic) Pliosauroidea (Reptilia, Sauropterygia) (PhD). Chicago: University of Derby.
  35. 1 2 3 A. R. I. Cruickshank; D. M. Martill; L. F. Noè (1996). "A pliosaur (Reptilia, Sauropterygia) exhibiting pachyostosis from the Middle Jurassic of England". Journal of the Geological Society. 153 (6): 873–879. Bibcode:1996JGSoc.153..873C. doi:10.1144/gsjgs.153.6.0873. S2CID   129602868.

See also

This page is based on this Wikipedia article
Text is available under the CC BY-SA 4.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.