Elasmosauridae
Reconstructed skeleton of Thalassomedon hanigtoni in the American Museum of Natural History
- Worldwide
The Elasmosauridae are a family of long-necked very Plesiosauria from the Jurassic and Cretaceous. In the late Cretaceous period they were, together with the short-necked Polycotylidae, the only surviving plesiosaurs.
Features
The Elasmosauridae had 32-72 cervical vertebrae, the vertebrae were to even longer than other plesiosaurs, especially the vertebrae, which were closer to the body. Their body length was three to 14 meters.
The animals had a maximum of five pairs of teeth on the premaxilla. In advanced forms of the Prämaxillarzähne and the front seat Maxillarzähne were enlarged. The Prämaxillarzähne and the enlarged Maxillarzähne were separated by a few smaller teeth on premaxilla and maxilla between the seam. The lower jaw had originally 24 pairs of teeth that have been reduced in the Cretaceous Elasmosauriden, at a minimum of 14 pairs. The teeth were structured by numerous longitudinal edges.
As part of the fin development, there was an increase in the finger bones ( Hyperphalangie ). The longest finger contained up to 17 individual bones.
Jurassic Elasmosauriden differed from those of the Cretaceous period by a number of features, especially in the anatomy of the shoulder girdle. As with all plesiosaurs her shoulder blade is much smaller than the coracoid. Many, however, late Cretaceous forms have a well-developed shoulder blade, could ramp up to the strong muscles, so that the animals were much more mobile than their earlier relatives. In Cretaceous Elasmosauriden meet the right and left coracoid in the midline of the animal, then diverge and form a heart-shaped opening. Jurassic Elasmosauriden and all other plesiosaurs missing this opening in the front shoulder belt. In Late Jurassic and Cretaceous forms the cervical ribs have only one joint head contact with the cervical vertebrae.
Way of life
The Langhalsigkeit the Elasmosauriden raises the question of their life. Undoubtedly, there were no quick hunter, short-necked plesiosaur like. Had the long neck while swimming the effect of a forward rails rudder, also the Elasmosauridae had weaker fins than their relatives. Some scientists have speculated that the Elasmosauriden were close to the sea and with the stretched down neck caught fish. Others assumed that they, lying on the water surface, neck and head much further lifted and then snapped like herons passing fish from the water. The neck, however, was close to the fuselage relatively immobile and was not likely to be lifted out of the water. Most likely, they lurked at the bottom of Cretaceous shallow seas for prey. The discovery of serving as ballast stones in the stomach of some fossil Elasmosauriden and the eyes are far above support this theory.
System
Traditionally, long-necked plesiosaurs were all placed in the family, but recent research has complicated the classification of plesiosaurs. In addition, there is also the Elasmosauridae necked Cryptocliden in the previous Elasmosauriden Colymbosaurus and Tricleidus were asked. Robert Bakker is of the opinion that the Elasmosauriden the Cretaceous period, regardless of the Late Jurassic of Pliosauriern similar Leptocleidus evolved so that the Elasmosauridae are a polyphyletic unnatural group. Kenneth Carpenter, the Elasmosauriden including the Jurassic forms back in and sees them as close relatives of the short-necked Polycotylidae, but they are also Pelsiosaurier ie S. ( Plesiosauroidea ).
Genera
- Albertonectes
- " Alzadasaurus "
- Aphrosaurus
- ? Aristonectes
- Brancasaurus
- Callawayasaurus
- Elasmosaurus
- ? Eretmosaurus
- Fresnosaurus
- Futabasaurus
- Hydralmosaurus
- ? Hydrorion
- Hydrotherosaurus
- Leurospondylus
- Libonectes
- Mauisaurus
- Microcleidus
- Morenosaurus
- ? Morturneria
- Muraenosaurus
- Occitanosaurus
- Styxosaurus
- Thalassomedon
- Turangisaurus
- " Woolungasaurus "
- Zarafasaura
The late Cretaceous genera Artistonectes and Morturneria are known only very inadequately. Their skulls are similar to those of Cryptoclididae, but were provided by Bardet in the Elasmosauridae 1995. In addition to the classes discussed here, there are two additional, previously undescribed policy. A Courtenay Museum of stored, very large (10 m) Elasmosauride, which was west of Courtenay in the east found on Puntledge River from Vancouver Iceland is perhaps a new genus. His jaw is very long with a length of half a meter for a Elasmosauriden. Another potentially new genus is represented by the fossil amalitskii described as " Elasmosaurus ", which was found in layers of the Turonian in Liski in Russia. It consists only of a few vertebrae and the highly elongated belly ribs.