Aphrosaurus was an extinct genus of plesiosaur from the Maastrichtian. The type species is Aphrosaurus furlongi (LACM 2748), named by Welles in 1943.[1] The holotype specimen was discovered in the Moreno Formation in Fresno County, California in 1939 by rancher Frank C. Piava.[2] A second specimen - LACM 2832 - was also found in the same formation and initially diagnosed as a juvenile of the same species, but has since been removed from the genus.[3]
In 1943, Samuel Welles described Aphrosaurus furlongi along with several other plesiosaurs from the same fossil assemblage in Fresno County, California.[1]Aphrosaurus was found below a different juvenile species, Morenosaurus stocki,[3] within the Tierra Loma Member of the Panoche Hills. The Moreno Formation dates back to the early Maastrichtian, and is composed of depositional layers of turbidite, sandstone, and shale. It is part of the larger Chico Formation, which contacts the Panoche Formation and, during the Cretaceous, composed a sea shelf along the coast of California and the Pacific Ocean.[4]
The diagnosis of Aphrosaurus as a unique species was initially determined by the presence of a deepened ventral notch on the centra of the cervical vertebrae, which was determined to be an autapomorphy of the species. LACM 2832, found in the same formation, was also initially determined to be Aphrosaurus with ontogenic features, but that classification was rejected in a reappraisal on the basis of systemic differences between the two specimens that likely could not be explained by ontogeny.[3]
Welles took the name Aphrosaurus from the Greek for "sea foam" + "lizard", and furlongi in honor of University of California Berkeley field assistant and specimen preparator Eustace Furlong.[3]
The axial skeleton of the holotype fossil is composed of 18 cervical, three pectoral, and 15 dorsal vertebrae, though Welles initially described "10 posterior cervical preceded by 11 indeterminate cervical and followed by 17 crushed dorsals." The diagnostic ventral groove is visible on the 14th to 6th prepectorals, and the prezygapophyses project anteriorly and meet. Only a few of the vertebrae retain the diapophyses, which slant ventrally in the more posterior half, though that may be an artifact of being crushed. Only three dorsal ribs are preserved, each different from each other, suggesting that they are each from a different section of the skeleton.
In addition to the axial skeleton, a good portion of the appendicular skeleton was also preserved. Both the pectoral and pelvic girdles are mostly complete, with a smooth clavicle-interclavicle complex lacking the keel and suture lines. The scapulae shape is indeterminate due to damage, but likely met in the midline. Two elements were initially labeled by Welles as the ilium, which was rectified when O’Gorman articulated both with the ischium and was able to classify one as a sacral rib instead.
Both fore and hind limbs were preserved, though both humeri and the left femur are very badly damaged. The left humerus has a large muscle scar on the ventral surface. The radius and ulna in both limbs are wider than long, a typical feature seen in plesiosaurus, and an epipodial foramen is present on the right forelimb despite Welles’ initial analysis indicating none present. Welles noted that the right forelimb is severely distorted, and suggested that it was the result of a pathology sustained to the animal when it was alive. The hind limb description is based entirely on the right hind limb due to the damage to the left, and has no separation between the trochanter and capitulum. There is a raised muscle scar on the ventral surface.[3]
Aphrosaurus was a large, highly derived plesiosaur. A 2005 study by O’Keefe et al. comparing the body size and proportions of plesiosaurs across time show that Aphrosaurus, like other late-Cretaceous plesiosaurs, was comparatively large,[5] and a 2001 study also by O’Keefe comparing flipper aspect ratio with equivalent wing proportions on birds and planes indicate a gliding, long-distance type of travel with low agility.[6] Welles described it as "likely less active than Morenosaurus."[1]
Like most plesiosauromorphs, Aphrosaurus probably ate a diet of relatively small prey that were then ground up by gastroliths.[7] A 2008 study by Zammit et al. using a model of the complete vertebral column and neck indicated that while Aphrosaurus and similar plesiosaurs would not have been able to create a "swan curve" of the neck to strike, other feeding methods, including benthic grazing, shallow horizontal curving for ambush, and horizontal or vertical shearing during active pursuit would have been possible.[8]
Based on the fossil assemblage of the Moreno Formation, Aphrosaurus shared the waters of the Late-Cretaceous Pacific with a diverse spread of mosasaurs, turtles, and a variety of other plesiosaurs: Morenosaurus, Fresnosaurus, and Hydrotherosaurus,[9] the latter two of which were larger than Aphrosaurus.[10][11] Notably, five different genera of mosasaurs, mostly mosasaurines, have been discovered in the Moreno Formation. The lack of plioplatocarpines was hypothesized by Lindgren and Schulp in 2010 to indicate an environment as an open ocean with high piscivore competition for resources. Similar genera of mosasaurs in both the Moreno Formation and Western Interior Seaway indicates free exchange of species between both environments.[12]
Within the mostly morphologically similar elasmosaurids, Aphrosaurus can be differentiated by the presence of a deepened ventral notch along the centra of the cervical vertebrae, and a wide, dorsal-ventrally compressed interclavicle-clavicle complex that lacks a ridge along the sternum.[3]
Classification
The Elasmosaurid clade is highly unstable. However, current phylogenetic studies have recovered Aphrosaurus in a highly nested position within the Weddellonectia clade, but outside of the Aristonectinae with the filter-feeding Aristonectes.[3]
Plesiosauroidea is an extinct clade of carnivorous marine reptiles. They have the snake-like longest neck to body ratio of any reptile. Plesiosauroids are known from the Jurassic and Cretaceous periods. After their discovery, some plesiosauroids were said to have resembled "a snake threaded through the shell of a turtle", although they had no shell.
Elasmosaurus is a genus of plesiosaur that lived in North America during the Campanian stage of the Late Cretaceous period, about 80.5million years ago. The first specimen was discovered in 1867 near Fort Wallace, Kansas, US, and was sent to the American paleontologist Edward Drinker Cope, who named it E.platyurus in 1868. The generic name means "thin-plate reptile", and the specific name means "flat-tailed". Cope originally reconstructed the skeleton of Elasmosaurus with the skull at the end of the tail, an error which was made light of by the paleontologist Othniel Charles Marsh, and became part of their "Bone Wars" rivalry. Only one incomplete Elasmosaurus skeleton is definitely known, consisting of a fragmentary skull, the spine, and the pectoral and pelvic girdles, and a single species is recognized today; other species are now considered invalid or have been moved to other genera.
Elasmosauridae is an extinct family of plesiosaurs, often called elasmosaurs. They had the longest necks of the plesiosaurs and existed from the Hauterivian to the Maastrichtian stages of the Cretaceous, and represented one of the two groups of plesiosaurs present at the end of the Cretaceous alongside Polycotylidae.
Muraenosaurus is an extinct genus of cryptoclidid plesiosaur reptile from the Oxford Clay of Southern England. The genus was given its name due to the eel-like appearance of the long neck and small head. Muraenosaurus grew up to 5.2 metres (17 ft) in length and lived roughly between 160 Ma and 164 Ma in the Callovian of the middle Jurassic. Charles E. Leeds collected the first Muraenosaurus which was then described by H. G. Seeley. The specimen may have suffered some damage due to the casual style of Charles Leeds’ collection. The first muraenosaur was recovered with pieces missing from the skull and many of the caudal vertebrae absent. Because the animal was described from Charles Leeds’ collection it was given the name Muraenosaurus Leedsi. M. leedsi is the most complete specimen belonging to the genus Muraenosaurus and also the only species that is undoubtedly a member of the genus. Two other species have been tentatively referred to as members of the genus Muraenosaurus: M. reedii and Muraenosaurus beloclis Seeley 1892, which in 1910 became the separate genus Picrocleidus.
Plotosaurus is an extinct genus of mosasaurs who lived during the Upper Cretaceous (Maastrichtian) in what is now North America. Only one species is recognized, P. bennisoni, described by Berkeley paleontologist Charles Lewis Camp in 1942 from fossils discovered in California. Originally named Kolposaurus, it was changed to Plotosaurus in 1951 when Camp discovered that the name had already been assigned to a type of nothosaur. Unlike other mosasaurids, Plotosaurus possesses a morphology converging with those of ichthyosaurs, suggesting a much more advanced swimming adaptation than some of its close relatives.
Hydrotherosaurus is an extinct genus of elasmosaurid plesiosaur from the Upper Cretaceous Moreno Formation of Fresno County, California, USA. The only known species, H. alexandrae, was named for Annie Montague Alexander in 1943 by Samuel Paul Welles.
Mauisaurus is a dubious genus of plesiosaur that lived during the Late Cretaceous period in what is now New Zealand. Numerous specimens have been attributed to this genus in the past, but a 2017 paper restricts Mauisaurus to the lectotype and declares it a nomen dubium.
Tuarangisaurus is an extinct genus of elasmosaurid known from New Zealand. The type and only known species is Tuarangisaurus keyesi, named by "Pont" Wiffen, Joan Wiffen and Bill Moisley in 1986. The specific name honours Ian W. Keyes of the New Zealand Geological Survey.
Styxosaurus is a genus of plesiosaur of the family Elasmosauridae. Styxosaurus lived during the Campanian age of the Cretaceous period. Three species are known: S. snowii, S. browni, and S. rezaci.
Taniwhasaurus is an extinct genus of mosasaurs that lived during the Campanian stage of the Late Cretaceous. It is a member of the subfamily Tylosaurinae, a lineage of mosasaurs characterized by a long toothless conical rostrum. Two valid species are attached to the genus, T. oweni and T. antarcticus, known respectively from the fossil record of present-day New Zealand and Antarctica. Two other species have been nominally classified within the genus, T. 'capensis' and T. 'mikasaensis', recorded in present-day South Africa and Japan, but their attribution remains problematic due to the fragmentary state of their fossils. The generic name literally means "taniwha lizard", referring to a supernatural aquatic creature from Māori mythology.
Aristonectes is an extinct genus of large elasmosaurid plesiosaurs that lived during the Maastrichtian stage of the Late Cretaceous. Two species are known, A. parvidens and A. quiriquinensis, whose fossil remains were discovered in what are now Patagonia and Antarctica. Throughout the 20th century, Aristonectes was a difficult animal for scientists to analyze due to poor fossil preparation, its relationships to other genera were uncertain. After subsequent revisions and discoveries carried out from the beginning of the 21st century, Aristonectes is now recognised as the type genus of the subfamily Aristonectinae, a lineage of elasmosaurids characterized by an enlarged skull and a reduced length of the neck.
Tatenectes is a genus of cryptoclidid plesiosaur known from the Upper Jurassic of Wyoming. Its remains were recovered from the Redwater Shale Member of the Sundance Formation, and initially described as a new species of Cimoliosaurus by Wilbur Clinton Knight in 1900. It was reassigned to Tricleidus by Maurice G. Mehl in 1912 before being given its own genus by O'Keefe and Wahl in 2003. Tatenectes laramiensis is the type and only species of Tatenectes. While the original specimen was lost, subsequent discoveries have revealed that Tatenectes was a very unusual plesiosaur. Its torso had a flattened, boxy cross-section and its gastralia exhibit pachyostosis (thickening). The total length of Tatenectes has been estimated at 2–3 meters (6.6–9.8 ft).
Albertonectes is an extinct genus of elasmosaurid plesiosaur known from the Late Cretaceous Bearpaw Formation of Alberta, Canada. It contains a single species, Albertonectes vanderveldei. Albertonectes is the longest elasmosaur, and more generally plesiosaur, known to date both in neck and total body length, estimated around 12 metres (39 ft) long and weighing up to 4.8 metric tons.
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.
Augustynolophus is an extinct genus of herbivorous saurolophine hadrosaur dinosaur which was discovered in the Moreno Formation in California, dating to the late Maastrichtian age, making it one of the last dinosaurs known from the fossil record before the Cretaceous–Paleogene extinction event.
Vegasaurus is an extinct genus of elasmosaurid plesiosaur known from the Late Cretaceous Snow Hill Island Formation of Vega Island, Antarctic Peninsula. It contains a single species, Vegasaurus molyi.
Kawanectes is a genus of elasmosaurid plesiosaur, a type of long-necked marine reptile, that lived in the marginal marine environment of Late Cretaceous Patagonia. It contains one species, K. lafquenianum, described in 2016 by O'Gorman.
Chubutinectes is an extinct genus of elasmosaurid plesiosaur from the Late Cretaceous La Colonia Formation of Argentina. The genus contains a single species, C. carmeloi, known from a partial skeleton and associated gastroliths.
Marambionectes is an extinct genus of weddellonectian elasmosaurid plesiosaur from the Late Cretaceous López de Bertodano Formation of Antarctica. The genus contains a single species, M. molinai, known from a partial skeleton.
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