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Vadasaurus herzogi
Topic Started: Dec 7 2017, 08:05 PM (186 Views)
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Vadasaurus herzogi

Posted Image
This is a Vadasaurus herzogi fossil.
Credit: Mick Ellison Used with permission from the American Museum of Natural History

Temporal range: Late Jurassic (Kimmeridgian)

Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Reptilia
Superorder: Lepidosauria
Order: Rhynchocephalia
Genus: †Vadasaurus
Species:Vadasaurus herzogi

Rhynchocephalia is an order of lizard-like reptiles that includes only two living species of tuatara (Sphenodon punctatus and Sphenodon guntheri), which only inhabit parts of New Zealand. Despite its current lack of diversity, the Rhynchocephalia at one time included a wide array of genera in several families and represents a lineage stretching back to the Mesozoic Era. Many of the niches occupied by lizards today were then held by sphenodontians. There were even several successful groups of aquatic sphenodontians such as pleurosaurs and the bizarre Ankylosphenodon.

Posted Image
Figure 1.Holotype of Vadasaurus herzogi (AMNH FARB 32768) collected from the Late Jurassic marine limestones of Solnhofen, Bavaria. The skull, forelimbs, and first 18 presacral vertebrae and ribs are exposed in the dorsal or dorsolateral view. Posteriorly, the skeleton is rotated approximately 180°, making it visible largely in the ventral view. Left hindlimb is exposed in the dorsal view. Anatomical abbreviations: As, astragalus; Ca, calcaneum; Cdv, caudal vertebra; Co, coracoid; Cr, cervical rib; Cv, cervical vertebra; D, dentary; Dv, dorsal vertebra; F, femur; Fb, fibula; Fr, frontal; Ga, gastralia; H, humerus; I, intermedium; Is, ischium; l, left; Mc, metacarpal; Mt, metatarsal; Mx, maxilla; Ph, phalanx; Pu, pubis; R, radius; r, right; S, scapula; Sc, sternal cartilage; Ss, suprascapular cartilage; Sv, sacral vertebra; T, tibia; U, ulna.

Generic name from the Latin vadare ‘to go forth’, which is also the root of ‘to wade’—refers to the taxon's hypothesized phylogenetic position near the proximal end of a terrestrial-to-marine transformation series that produced the aquatic pleurosaurs—and saurus ‘lizard’. The specific epithet honours the celebrated Bavarian film-maker Werner Herzog for his continuing exploration of the relationship between life and time.

AMNH FARB 32768, a nearly complete and largely articulated skeleton. Like most specimens preserved in lithographic limestone, it exhibits compressional effects that include the flattening and shearing of composite structures and the slight displacement of certain elements. Individual bones, however, are preserved largely in three dimensions.

Type locality and age
Late Jurassic, uppermost Kimmeridgian, Hybonotum zone, Ulmense subzone, Rebouletianum horizon.

Posted Image
Figure 2. The skull of Vadasaurus herzogi (AMNH FARB 32768). Photographs in the dorsolateral (a) and lateral (b) views; labelled line drawing in the dorsolateral view (c); reconstructions of lateral and dorsal views (d). Anatomical abbreviations: An, angular; Ar, articular; cp, cultriform process; Cv, cervical vertebra; D, dentary; dd, dentary dentition; Ecp, ectopterygoid; Ept, epipterygoid; exn, external naris; Fr, frontal; Hy, hyobranchial element; if, incisiform fang; Ju, jugal; mf, mandibular foramen; Mx, maxilla; Na, nasal; Pa, parietal; Pal, palatine; paf, parietal foramen; Pf, prefrontal; Pm, premaxilla; Po, postorbital; Pof, postfrontal; Pr, prootic; Pra, prearticular; Pt, pterygoid; Q, quadrate; Qj, quadratojugal; Sa, surangular; sof, suborbital fenestra; Sq, squamosal; Vo, vomer.

AMNH FARB 32768 is diagnosed as a new rhynchocephalian taxon by a derived combination of the following features: elongate process of the premaxilla, which contacts the prefrontal thereby excluding the maxilla from the external nares, a short nasal process of the premaxilla, postfrontal participation in the upper temporal fenestra, expanded lower temporal fenestra constituting more than a quarter of the total skull length, loss of the subtemporal process of the jugal, elongate dorsal process of the jugal, ascending process of the quadratojugal reaching the midpoint of the temporal plate, low and rectangular neural arches, no distal contact between sacral ribs, robust metatarsals I and V, and more than 40 caudal vertebrae.

Diagnosed as a rhynchocephalian based on an elongate, posterior process of the dentary that reaches the glenoid cavity, acrodont marginal teeth bearing prominent flanges, marginal teeth regionalized with juvenile dentition positioned anteriorly, premaxillary teeth reduced to three, anterior contact of contralateral pterygoids, hourglass-shaped dorsal centra (in the ventral view), prominent second sacral vertebra with bifurcated sacral rib, first caudal vertebra lacking a haemal arch and a large posterior process of the ischium. Diagnosed as deeply nested within Rhynchocephalia based on the absence of individuated lacrimal, fusion of the premaxillary teeth into a chisel-like fang, square-shaped marginal teeth with a prominent flange, no more than two successional teeth, edentate anterior end of the lower jaw, at least a moderately high coronary process, single lateral row of palatine teeth, relatively small orbit, anteriorly positioned parietal foramen, and a narrowing of the parietal between the adductor chambers and development of a sagittal crest. Diagnosed in an exclusive clade with Pleurosauridae based on a triangular skull in the dorsal view, posteriorly tapering maxilla, posteriorly tapering palatine, moderately open interpterygoid vacuity, pterygoid participation in the suborbital fenestra, low angle of the mandibular symphysis, gracile lower jaw, jaw joint positioned dorsal to the maxillary tooth row and an unossified radiale. Although not formally analysed, this clade is also diagnosed by a dorsoventrally compressed and elongate skull, and elongate external nares.

Recently discovered fossil shows transition of a reptile from life on land to life in the sea
Modern New Zealand reptile may be a close relative

Date: December 6, 2017
Source: Johns Hopkins Medicine

Using modern research tools on a 155-million-year-old reptile fossil, scientists at Johns Hopkins and the American Museum of Natural History report they have filled in some important clues to the evolution of animals that once roamed land and transitioned to life in the water.

A report on the new discoveries about the reptile, Vadasaurus herzogi, appears online in the Nov. 8 issue of Royal Society Open Science, and suggests that some of the foot-long animal's features, including its elongated, whip-like tail, and triangular-shaped head, are well suited to aquatic life, while its relatively large limbs link it to land-loving species.

Vadasaurus, which is the Latin term for "wading lizard," was discovered in limestone quarries near Solnhofen, Germany, part of a once-shallow sea long explored for its rich trove of fossil finds.

The well-preserved fossil is housed in the American Museum of Natural History in New York, where the job of unlocking its evolutionary secrets fell to museum research associate Gabriel Bever, Ph.D., who is also assistant professor of functional anatomy and evolution at the Johns Hopkins University School of Medicine, and Mark Norell, Ph.D., the museum's paleontology division chair.

"Anatomic and behavioral characteristics of modern groups of living things accumulated over long spans of time," says Bever. "Fossils can teach us a lot about that evolutionary history, including the order in which those features evolved and their adaptive role in a changing environment."

"Anytime we can get a fossil like this that is so well preserved, and so significant in understanding a major environmental transition, it is very important," says Norell. "It's so important," he adds, "that we can consider Vadasaurus to be the Archaeopteryx of rynchocephalians."

According to Bever, their work adds to the list of sea creatures whose ancestors were land-dwelling vertebrates. They include modern-day whales, seals, and sea snakes, and ancient (and now-extinct) species of ichthyosaurs, mosasaur, and plesiosaurs.

Bever says their study offers evidence that Vadasaurus, likely an adult when it died, can be linked by its anatomy to a small group of marine species called pleurosaurs, which have long been thought to have terrestrial roots. Pleurosaurs lived during the Jurassic period, 185 to 150 million years ago. The eel-like creatures had reduced limbs that were probably used for steering rather than propulsion in the water. Until now, fossils of only three ancient species of pleurosaurs have been discovered.

Using two types of statistical algorithms and reconstructions of evolutionary "trees," Bever and Norell say that Vadasaurus and the pleurosaurs are part of a larger lineage of reptiles called Rhynchocephalia. Like the sea-loving pleurosaurs, Vadasaurus' skull was a triangular shape, an adaptation found among many streamlined, water-dwelling animals, such as most fish, eels and whales. An elongated snout, common among sea animals, featured teeth farther away from the body for ensnaring fish.

By examining the shape and structure of the Vadasaurus' skull, Bever and Norell also concluded that Vadasaurus' bite was likely a quick, side-to-side motion, compared with the slower, stronger bite typical of many land-dwelling animals.

Some 155 million years ago, Vadasaurus' tail had begun to lengthen like most modern sea animals, says Bever, but not to the size of the 5-foot pleurosaur. Vadasaurus, they found, had 24 pre-sacral vertebrae, which span from the head to the beginning of the tail, whereas pleurosaurus had more than 50 such back bones.

Despite its aquatic features, Vadasaurus retained some features more often found among land vertebrates. For example, Vadasaurus still had the large limbs, relative to the size of its body, expected of a land-dwelling reptile. Bever speculates that Vadasaurus did not use its limbs for propulsion in the water, but to steer. He says Vadasaurus may have swum like a modern sea snake, moving its spinal column with an undulating kind of motion.

"Our data indicate that Vadasaurus is an early cousin of the pleurosaur," says Bever. "And these two reptiles are closely related to modern tuatara." The modern tuatara is a lizard-like, land-dwelling reptile that lives on New Zealand's coastal islands and is the single remaining species of rhynchocephalian still left on Earth.

Bever notes that a complete evolutionary history of Vadasaurus will require more data and fossil finds.

"We don't know exactly how much time Vadasaurus was spending on land versus in the water. It may be that the animal developed its aquatic adaptations for some other reason, and that these changes just happened to be advantageous for life in the water," says Bever.

Story Source: https://www.sciencedaily.com/releases/2017/12/171206090713.htm

Journal Reference:
Gabriel S. Bever, Mark A. Norell. A new rhynchocephalian (Reptilia: Lepidosauria) from the Late Jurassic of Solnhofen (Germany) and the origin of the marine Pleurosauridae. Royal Society Open Science, 2017; 4 (11): 170570 DOI: 10.1098/rsos.170570

A new rhynchocephalian is described based on a recently discovered and well-preserved specimen from the Late Jurassic (Kimmeridgian) marine limestones of Solnhofen, Bavaria. Phylogenetic analysis recovers the new taxon as the sister group to Pleurosauridae, a small radiation of rhynchocephalians representing the oldest marine invasion of crown-clade Lepidosauria. The relatively strong evidence for this taxonomically exclusive lineage, within a generally volatile rhynchocephalian tree, places the new taxon in a position to inform the early history of the pleurosaur transition to the sea. The early steps in this transition are distributed throughout the skeleton and appear to increase hydrodynamic efficiency for both swimming and aquatic feeding. This early history may also have included a global truncation of plesiomorphic ontogenetic trajectories that left a number of skeletal features with reduced levels of ossification/fusion. The exact degree to which Vadasaurus had adopted an aquatic ecology remains unclear, but the insight it provides into the origin of the enigmatic pleurosaurs exemplifies the potential of Rhynchocephalia for generating and informing broad-based questions regarding the interplay of development, morphology, ecology and macroevolutionary patterns.
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