Ophthalmosaurus
Fossil coracoid (top) and shoulder blade (bottom ) from the holotype of Ophthalmosaurus icenius
- Oxford Clay (UK and France)
- Spilsby Sandstone Formation ( United Kingdom)
- Sundance Formation ( United States)
Ophthalmosaurus is a genus of ichthyosaur ( Ichthyopterygia ), which brings together the fossils of medium-sized Thunnosaurier ( Thunnosauria ). Their representatives lived from the Middle Jurassic to the Cretaceous dawn ( approximately 166-145 million years ago ) at the northern edge of the Tethysozeans and the west coast of Laurasias. Opthalmosaurus was given its body shape and its large, reinforced by bone rings eyes observe a fast hunter who made at great depths hunting for fish, ammonites and belemnites and gave birth to its young alive. The genus represents a typical representative of Jurassic ichthyosaurs, all of which were characterized by a tuna- like blueprint and probably occupied a wide range of ecological niches. In their current taxonomic boundaries, the genus is controversial, the European style Ophthalmosaurus icenius and the North American Ophthalmosaurus natans probably do not form a monophyletic group.
The first description of Ophthalmosaurus by Harry Govier Seeley dates from 1874 and is based on material from the English Oxford Clay, from where the most famous finds are. Other material comes from France and the USA. Ophthalmosaurus is considered common type in his discovery layers, but is found especially in Europe often only fragmentary. While the genus was made geographically and taxonomically far in the past few decades, stands out in recent times, separation of the species O. natans in the genus Baptanodon declining, with O. icenius would remain in a monotypic genus as the only way.
Features
Ophthalmosaurus was long up to 4 m, reaching an estimated weight of 930 kg, and is recorded as any other Jurassic ichthyosaur by a tuna- like shape with a long, beak -like snout: The back arched from the head relatively steeply upwards on, reached almost behind the front fins its apex and then fell slightly towards the tail off. The belly line showed a similar trend, while the dorsal and the caudal fin, compared with other genera of ichthyosaurs, very long, high and narrow were. While many ichthyosaurs had a laterally flattened body shape, interpret Ophthalmosaurus fossils indicate a rounder body. This was by its external shape not only extremely streamlined, he was strongly reinforced and stabilized by its bones: the dorsal vertebrae showed typical of later ichthyosaurs hockey puck shape ( very flat and wide), sat close to each other and spread, creating a very thick and rigid spine. The animals were thus no snaking - neither sideways nor up and down - more possible. Conversely, they could achieve by the thrust of fins very high speeds so but because the body was compact and well stabilized against turbulence and deformation. His drive won Ophthalmosaurus probably mainly by the lateral flapping of its crescent -shaped caudal fin, the lower part was probably reinforced by the tail spine and the rest of cartilage tissue. The dorsal fin is also made up of cartilage may have helped to stabilize the situation.
Ophthalmosaurus possessed with relatively long and 50 cm towards the front Tapered jaw. The teeth were in narrow grooves in the upper and lower jaw, were thus not fully thekodont and overall weakly anchored. A diagnostic feature of the genus, the shape of the maxilla, which forms a part of the nostrils. The eyes were like all ichthyosaurs stabilized by an increased scleral ring from 15 bone plates and very large in relation to body size. The scleral protect the eye from high water pressure and thus before deformation, which was especially important when the pressure difference which arose at high speeds between the front and rear parts of the eyes. The shoulder blades were widened towards the body, the front fins had a single additional fingers and were like the smaller rear fins composed of rounded bone limbs; all three features are diagnostic for the genus. The hip consisted of two separate parts, and was, as usual for late Jurassic ichthyosaur, only connected to the hind limbs.
Ecology
The large, light eyes, with a streamlined body of Ophthalmosaurus draw the picture of a fast swimmer, who pushed forward to great depths to make there hunting for its prey. Ophthalmosaurus was probably capable of even at a depth of about 500 m track and catch prey. This Ophthalmosaurus reflects a general development of ichthyosaurs in the Jura, in the tuna -like himself, were able to achieve fast and forms found around the world spreading. However, this way of life refers mainly to the type species O. icenius. For other species, whose membership Ophthalmosaurus mainly based on the general body shape and usually is controversial, there is hardly any specific findings on the habitat. In other cases, the skeletal structure suggests compared with O. icenius a significantly different way of life, such as O. ( Baptanodon ) natans, which might be rather been a shallow-water dwellers less quickly, but agile.
The food consisted of Ophthalmosaurus among other things, belemnites and ammonites, as you can find evidence in fossil skeletons on the basis of fishing hooks and shells of these animals. In addition, fish are likely to have come. The prey was probably used with high speed from fish and Kopffüßerschwärmen out with the pines and then swallowed. As is typical of ichthyosaurs was Ophthalmosaurus viviparous, his boys were so born alive and were already fully buoyant at birth.
Fossil material and stratigraphy
The first Ophthalmosaurus specimens were found in the English Oxford Clay. This rock formation dates from the middle or late Jurassic, ranging from the Callovian to the Kimmeridgian ( 166.1 to 152.1 Mya (unit) | mya ). The fossils recovered there be assigned to all the species O. icenius, for the outside of England find evidence in northwestern France. Overall, the Western European finds of Ophthalmosaurus are numerous, but often receive only fragmentary. The more complete North American fossils, which are summarized as O. baptanodon come from the Sundance Formation of the northwestern United States, which is ( approximately 160 mya ) dated to the Oxfordian. There are also various finds from the Upper Jurassic of the Volga basin in Russia, but their genus affiliation is disputed. Also unclear is the status of English ichthyosaur material derived from the early Cretaceous ( Berriasian, 145 to 139.3 mya ) Spilsby Sandstone Formation of Nettleton. It can not be assigned to O. icenius, but probably belongs to the genus Ophthalmosaurus, so this had existed over the Jura - Cretaceous boundary.
Taxonomy and systematics
Arthropterygius
Mollesaurus
Ophthalmosaurus icenicus
Ophthalmosaurus ( Baptanodon ) natans
Platypterygiinae
The type specimen of the species Ophthalmosaurus icenius and thus the genus Ophthalmosaurus comes from the Peterborough Member of the British Oxford Clay. It covers various parts of a disarticulated skeleton, including pieces of the mandible and the skull, parts of the front flippers, multiple vertebral bodies and arches as well as some ribs. It was exposed and dissected in the 19th century by Charles Leeds. This skeleton is now kept under the inventory number NHMUK R2133 at London's Natural History Museum. Harry Govier Seeley described Ophthalmosaurus 1874 as a second Ichthyosauriergattung ever after Ichthyosaurus. The genus name is derived from the ancient Greek " ophthalmos " for " eye" (in reference to the large eye sockets of the animals ) and " sauros " for "lizard " her. The specific epithet commemorates the Icenier, a Celtic tribe which inhabited the area around the Erstfundort.
Over the decades Ophthalmosaurus were in addition to the type species O. icenius attributed to a number of other fossils or fossil of traditional species whose localities spread across North America and Eurasia: The 1880 by Othniel March erected for fossils from the Oxfordian of Wyoming Art Baptanodon ( " Sauranodon " ) natans was founded in 1910 by Charles William Andrews to Ophthalmosaurus provided, as well as all other North American fossils described in this genus. The Argentine ichthyosaurs of Bajociums ( Ophthalmosaurus periallus ) as well as those presented by Maxim Arkhangelsky and Vladimir Efimov species ( yasikovi O., O. gorodischensis, O. saveljeviensis ) from the Jurassic of Russia were in the Ichthyopterygia monographs by Michael Maisch and Andreas Matzke or slammed by Christopher McGowan and Ryosuke Motani Ophthalmosaurus. The basis for this initially formed mainly head and body shapes of fossils and skeletal reconstructions. Three-dimensional reconstructions of the skull of Robert Appleby, who led this as an argument for the separation of Baptanodon and Ophthalmosaurus were rejected by later authors due to methodological doubt. The differences between the two forms were considered too small to separate the genera. Phylogenetic analyzes based on osteological characters grouped the elements summarized in Ophthalmosaurus forms until the beginning of the 21st century, always together, which spoke against a splitting of the genus. Ophthalmosaurus was accordingly a cosmopolitan genus, O. icenius was for their paleoecology as an example.
Introduction of a range ophthalmosaurider fossil finds from various Jurassic fossil sites in Europe and comparative analysis of skeletal morphology, there was a tendency for splitting Ophthalmosaurus in different genres: Meanwhile, the Argentine finds the genus Mollesaurus be added, while a number of studies consistent differences between O. - icenius were able to work out material and North American Fossils ( Baptanodon ). With the discovery of fossils in Great Britain and Germany, which significantly differed from Ophthalmosaurus, on rails in phylogenetic analyzes, but as a sister taxon of O. natans, in 2012 there were doubts about the final summary in a common genus. While the discoveries as Acamptonectes were given their own genus, O. natans was initially left in the now paraphyletic genus Ophthalmosaurus. The taxonomic status of the Russian and American fossils is unclear since then, which is mainly due to the lack of detailed osteological comparisons.
Development History Ophthalmosaurus is a typical representative of a Middle Jurassic radiation of Thunnosaurier ( Thunnosauria ). This group appeared at the beginning of the Jurassic and was characterized above all by its tuna -like body shape. In the Middle Jurassic several forms that this recipe will be further optimized and summarized as Ophthalmosauridae emerged. Within the Ophthalmosauridae Ophthalmosaurus owned jointly with Mollesaurus and Acamptonectes (and probably Baptanodon ) for the subgroup of Ophthalmosaurinae opposite her sister Platypterygiinae group was characterized by a larger average body and less specialized jaw and skull shapes. While long it ran out because of the fossil record that the Ophthalmosaurinae became extinct at the end of the Jurassic, documented the species described in 2012 Acamptonectes which is currently still within Ophthalmosaurus, the continued existence ophthalmosauriner ichthyosaurs to the Lower Cretaceous.