Thalattosaurus

Thalattosaurus

Name: Thalattosaurus
Pronounced: Tha-La-Toe-Saw-Russ
Classification: Thalattosauria
Sub-family: Thalattosauridae
Temporal Range: Middle to Late Triassic (241-223 Mya)
Length: 2 metres

Information:

– Discovery: 
Thalattosaurus was first named in 1904 by American paleontologist John C. Merriam, alongside the creation of thalattosauria order. The original fossil specimen was recovered from Wapiti Lake in British Columbia, Canada. This fossil contained parts of the animals skull, an incomplete jaw and some ribs. Since then, a number specimens have been recovered from Triassic deposits in both the USA and Canada.

– Description: Similarly to its relatives, Thalattosaurus was an excellent swimmer. It was a very lengthy animal, measuring up to 2 metres long with a body that was effectively streamlined. It had a very long, flattened tail which have been used as the primary method of locomotion through the water. The limbs of Thalattosaurus were fairly short but its feet were webbed and paddle-like, which would have helped the animal turn sharply in the water when hunting prey.

It is believed that Thalattosaurus would have hunted in shallow waters near the shoreline, a theory highlighted by the fact that the fossil specimens recovered from Wapiti Lake were found in sandstone. In addition, the flattened tail and clawed feet would have provided assistance against the force of surf when clambering up the shore. Although all thalattosaurs were believed to spend time both on land and in the water, it is unlikely that Thalattosaurus would have ventured into deep waters. The skull itself was fairly flat but housed a number of sharp teeth that would have effectively crushed any shelled prey items as well as been used to snatch up agile fish.

(Restoration Source: http://datab.us/i/thalattosaur)

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Askeptosaurus

Askeptosaurus

askeptosaurus skeleton

Name: Askeptosaurus
Pronounced: Ah-Skep-Toe-Saw-Russ
Classification: Thalattosauria
Sub-family: Askeptosauridae
Temporal Range: Middle Triassic (235-225 Mya)
Length: 2 metres

Information:

– Discovery: 
Askeptosaurus is the type specimen of the askeptosaurid group, one of the two sub-families of thalattosaurs. The first remains were discovered in 1925 by Hungarian paleontologist Franz Nopcsa von Felső-Szilvás. Since then, a handful of fossils have been recovered in Europe, specifically from Switzerland and Italy. Until 2000, Askeptosaurus was the only animal classed within the askeptosaurid group but it has since been joined by three other species.

– Description: Askeptosaurus was an extremely slender creature that likely swam similarly to a modern-day eel. Its tail was very lengthy and accounted for around half of the animals total length of 2 metres. All the vertebrae were of a fairly similar height, meaning that Askeptosaurus had a very linear, streamlined, spinal column. The limbs of Askeptosaurus were fairly short but its feet were webbed, which would have helped the animal steer itself whilst underwater. It is believed that Askeptosaurus would have held a predominantly aquatic lifestyle whilst coming ashore to rest.

It is likely that Askeptosaurus would have hunted in deep water. It had large eyes that were suited to conditions of low light and, like ichthyosaurs, they had protective bony rings around the eye sockets that would have prevented them from collapsing under the high water pressure of great depths. The skull of Askeptosaurus was very narrow but it had a toothy, elongated jaw that would have been utilised to snatch up fish.

(Restoration Source: https://en.wikipedia.org/wiki/Askeptosaurus#/media/File:Askeptosaurus_BW.jpg)
(Skeletal Source: http://www.reptileevolution.com/askeptosaurus.htm)

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Thalattosaurs

Thalattosaurs

We started off our Triassic series looking at the placodonts, a group of turtle-like marine reptiles and then the nothosaurs. Both of these animal groups existed solely during the Triassic era before becoming extinct at the Triassic-Jurassic boundary. The final group of Triassic-exclusive marine reptiles that we are going to look at are the thalattosaurs.

The thalattosaurs (temporal range: 240-210 Mya) were a group of marine reptiles that first appeared in the seas of the Middle Triassic. These animals bore a significant resemblance to modern day lizards and their exact classification has been the cause of much controversy. Currently they are widely accepted as members of the diapsid clade but they have been considered close relatives of both the ichthyosaurs and the archosaurs. At this point in time they are classified alone within the Thalattosauria order, which was created in 1904 by American paleontologist John C. Merriam.

It is believed that the thalattosaurs would have spent their lives predominantly in water but they displayed a number of terrestrial qualities that suggest they would have come ashore at regular intervals. The thalattosaurs were fairly small marine reptiles, with some of the larger species growing to lengths of around 3 meters. Unlike the nothosaurs, whose primary method of propulsion was from their powerful limbs, the thalattosaurs relied on a specially adapted tail to power themselves through the water. This laterally compressed tail was long and paddle-like. This, coupled with slender main bodies, meant that the thalattosaurs were efficiently streamlined and would have made effective underwater hunters. It is believed that the thalattosaurs would have breathed air, needing to come up to the surface for oxygen when in the water.

The one variant feature of the different thalattosaur species was their snout. One of the main sub-families of the Thalattosauria order, the Askeptosauroidea, had long, narrow, pointed skulls with an extended rostra at the end of the skull which pushed the nostrils backwards so that they were positioned close to the eyes. The other sub-family, the Thalattosauroidea, have shorter, downturned snouts with an upper jaw that was longer than the lower one.

Picture: Miodentosaurus, a member of the thalattosaur family.
(Source: https://en.wikipedia.org/wiki/Thalattosaur#/media/File:Miodentosaurus_BW.jpg)

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Keichousaurus

Keichousaurus_BW

keichousaurus

Name: Keichousaurus
Pronounced: Kay-Choo-Saw-Russ
Classification: Nothosauroidea
Sub-family: Keichousauridae
Temporal Range: Middle to Late Triassic (240-225 Mya)
Length: 0.3 metres

Information:

– Discovery: 
Keichousaurus is unique in that it is one of the only known nothosaurs found exclusively in Asia. The first known fossil was recovered in 1958 from the Chinese town of Guizhou by paleontologist Chung Chien Young. Young was very much a pioneer of vertebrate paleontology in China and he is highly regarded as one of the most respected geologists in Asia. His research into dinosaurs and other prehistoric life helped to elevate China’s importance within the paleontology world.

– Description: Keichousaurus was a tiny nothosaur, with fully grown specimens measuring just 30 centimetres in length. It is one of only two nothosaurs classified within the keichousaurid sub-family and indeed, looked distinctively different from its nothosaur relatives. It had a very small head and a short snout but a lengthy, serpentine-like neck that would have been used to capture small, agile fish. This distinctive neck meant Keichousaurus looked more like a miniature plesiosaur and some believe that Keichousaurus is in fact a direct ancestor, or at least an ancestral form, of the later giant plesiosaurs.

As well as this neck, Keichousaurus had a distinctly broad ulna. This ulna would have increased the surface area of the forelimbs, making Keichousaurus very efficient through the water. These specialised limbs likely mean that Keichousaurus was predominantly an aquatic animal, possibly more so than some of its close relatives. Each limb had five webbed digits at the end. The tail of Keichousaurus was exceptionally muscular and studies of the caudal vertebrae suggest that the tail would have been able to beat from side to side, acting as an extra mode of propulsion. The combination of powerful limbs and tail would have made Keichousaurus a highly efficient, maneuverable, underwater hunter.

A few Keichousaurus fossils have been discovered with juvenile animals within the main specimen itself. The position of these young specimens, within the mobile pelvis of the adult, suggest that they are in fact waiting to be born and this suggests that Keichousaurus was viviparous, giving birth to live young rather than laying eggs. This birthing method again reinforces the idea that Keichousaurus was primarily a marine creature.

(Restoration Source: https://en.wikipedia.org/wiki/Keichousaurus#/media/File:Keichousaurus_BW.jpg)
(Restoration Sketch Source: http://red-dilopho.deviantart.com/art/Keichousaurus-sketches-36970035)

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Lariosaurus

Lariosaurus

Name: Lariosaurus
Pronounced: La-Ree-Oh-Saw-Russ
Classification: Nothosauroidea
Sub-family: Nothosauridae
Temporal Range: Middle Triassic (240-235 Mya)
Length: 0.6 metres

Information:

– Discovery:
The first Lariosaurus specimen was discovered in 1830, recovered from the glacial Lake Como in Italy. It was named by Italian paleontologist G. Curioni in 1847 and was placed within the nothosauroid order. A number of fossils have been discovered throughout western Europe and in China.

– Description: Lariosaurus was one of the smallest of the known nothosaurs, growing to lengths of just 60 centimetres. It was also one of the most primitive looking, with relatively small flippers and possessing a significantly short neck in comparison to its relatives. It is believed that the rear legs were five-toed with claws, and likely to be webbed. The front legs would have been more paddle-like but the lack of length in both sets of limbs would have hindered Lariosaurus‘ swimming ability. With front limbs more suited to swimming and hind limbs more suited to a life on land, it would appear that Lariosaurus was a marine reptile in transition towards a more aquatic life.

In one specimen, the remains of two juvenile Cyamodus were discovered, suggesting that Lariosaurus would have hunted young placodonts. The fangs, at the front of a broad head, would have interlocked upon closing, forming a viscous trap that would have also been effective at catching fish.

It appears that this species of nothosaur was viviparous (able to bear live young) as several specimens have been found with embryos, indicating that they carried their young to maturity within their bodies. This knowledge has made Lariosaurus one of the more important nothosaur discoveries, although it is still unknown whether all nothosaurs would have given birth this way or whether some would have laid eggs.

(Restoration Source: http://masahatto2.p2.bindsite.jp/pg181.html)

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Nothosaurus

Nothosaurus

nothosaurus skeleton

Name: Nothosaurus
Pronounced: No-Foe-Saw-Russ
Classification: Nothosauroidea
Sub-family: Nothosauridae
Temporal Range: Middle to Late Triassic (240-210 Mya)
Length: 4 metres

Information:

– Discovery:
Nothosaurus is the best known member of the nothosaur family and its discovery in 1834 by German paleontologist G. von Munster led to the creation of the nothosauroid order. A number of fossils have been discovered throughout Europe, North Africa and even in China.

A number of Nothosaurus specimens have been named but the initial discovery was recovered from the Germanic Muschelkalk, a sequence of sedimentary rock strata that stretches throughout central and western Europe. A fully complete Nothosaurus skeleton can be found in the Natural History Museum in Berlin Germany (see picture above).

– Description: Nothosaurus was one of the longest surviving of the nothosaurs, roaming the Triassic coastline for around 30 million years. It was also one of the largest, growing to lengths of around four metres. It had a distinctively long skull with lengthy jaws that were equipped with sharp interlocking, needle-like teeth. Even though Nothosaurus could snap its jaws with incredible force, the muscles used for opening its mouth were very weak, meaning it would have hunted small prey items. The majority of its diet would have most likely consisted of fish but it is believed that it would have also tackled small or juvenile marine reptiles.

Nothosaurus did not have flippers, instead it had short legs with webbed feet which would have been used to propel the animal through the water when swimming. These feet combined with a streamlined, powerful body and a lengthy eel-like tail would have made it a fantastic swimmer. It is believed that Nothosaurus would have hunted in the shallow inshore waters but would have returned to land to rest and so as to avoid larger marine predators. Like the other marine reptiles of the time, Nothosaurus lacked gills so would have had to return to the waters surface in order to breath.

(Restoration Source: https://en.wikipedia.org/wiki/Nothosaurus#/media/File:Nothosaurus_BW.jpg)
(Skeletal Source: http://dinosaurs.about.com/od/aquaticdinosaurs/p/nothosaurus.htm)

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Ceresiosaurus

Ceresiosaurus

Name: Ceresiosaurus
Pronounced: Say-Ree-See-Oh-Saw-Russ
Classification: Nothosauroidea
Sub-family: Nothosauridae
Temporal Range: Middle Triassic (245-240 Mya)
Length: 3 metres

Information:

– Discovery:
Ceresiosaurus was first named in 1931 by paleontologist Bernhard Peyer. Fossils have been discovered in both southern Switzerland and northern Italy but the majority of specimens have been recovered from the world famous Monte San Giorgio mountain. This site in Switzerland was named a UNESCO World Heritage Site in 2003 due to it being one of the single best records of Triassic marine life.

– Description: Ceresiosaurus was one of the most elongated of the nothosaurs. It is believed that the animal would have grown to lengths of around three metres and it had some of the longest flippers ever seen within the nothosauroid family. These lengthy paddles were a result of an increased number of bones in each toe.

Ceresiosaurus had a powerful tail, a lengthy neck and body. These features led many to believe that Ceresiosaurus would have moved through the water through the use of body undulations. However the bone structure, especially in the thick tail and strong hips, suggest that it was a pursuit diver and hunted underwater using its strong, elongated paddles, much like a modern-day penguin.

(Restoration Source: http://masahatto2.p2.bindsite.jp/pg181.html)

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