Elasmosauridae
| Elasmosauridae | ||||||||||||
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Reconstructed skeleton of Thalassomedon hanigtoni in the American Museum of Natural History |
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| Temporal occurrence | ||||||||||||
| Toarcian ( Lower Jurassic ) to Maastrichtian ( Upper Cretaceous ) | ||||||||||||
| 183 to 65.5 million years | ||||||||||||
| Locations | ||||||||||||
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| Systematics | ||||||||||||
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| Scientific name | ||||||||||||
| Elasmosauridae | ||||||||||||
| Cope , 1869 |
The Elasmosauridae are a family of very long-necked Plesiosauria from the Jurassic and Cretaceous . In the late Cretaceous period they were the only surviving plesiosaurs , along with the short-necked Polycotylidae .
features
The Elasmosauridae had 32 to 72 cervical vertebrae , the individual vertebrae were even longer than with other plesiosaurs, especially the vertebrae that 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 premaxillary . In advanced forms, the premaxillary teeth and the anterior maxillary teeth were enlarged. The premaxillary teeth and the enlarged maxillary teeth were separated by a few smaller teeth above the suture between the premaxillary and maxillary . The lower jaw originally had 24 pairs of teeth, which were reduced in the Cretaceous Elasmosaurids, with a minimum of 14 pairs. The teeth were structured by numerous longitudinal edges.
In the course of the development of the fins, there was an increase in the number of finger bones (hyperphalangia). The longest finger contained up to 17 individual bones.
Jurassic elasmosaurids differed from those of the Cretaceous period in a number of features, most notably in the anatomy of the shoulder girdle . As with all plesiosaurs, their shoulder blades are much smaller than the coracoid . In contrast, many late Cretaceous forms have a well-developed shoulder blade to which strong muscles could attach, so that the animals were much more agile than their earlier relatives. In the Cretaceous Elasmosaurids, the right and left coracoid meet in the midline of the animal, then diverge and form a heart-shaped opening. Jurassic elasmosaurids and all other plesiosaurs lack this opening in the front shoulder girdle. In late Jurassic and Cretaceous forms, the cervical ribs only have contact with the cervical vertebrae with a joint head.
Way of life
The longevity of the elasmosaurids raises the question of their way of life. Undoubtedly they were not fast hunters like the short-necked plesiosaurs. The long neck had the effect of a forward oar when swimming, and the Elasmosauridae had weaker fins than their relatives. Some scientists speculated that the elasmosaurids were close to the surface of the sea, catching fish with their necks stretched down. Others believed that, lying on the surface of the water, they lifted their necks and heads high above it and then snatched fish swimming by like herons from the water. The neck, however, was relatively immobile close to the trunk and could probably not be lifted far out of the water. It is most likely that they lurked prey on the bottom of the Cretaceous shallow seas. The discovery of ballast stones in the stomach area of some fossil elasmosaurids and the high-lying eyes support this theory.
Systematics
Traditionally, all long-necked plesiosaurs were placed in the family, but recent research has complicated the plesiosaur systematics. In addition to the Elasmosauridae, there are also long-necked Cryptoclids in which the previous Elasmosaurids Colymbosaurus and Tricleidus were placed. Robert Bakker is of the opinion that the Elasmosaurids of the Cretaceous Period evolved independently of the late Jurassic of pliosaurs similar to Leptocleidus , so that the Elasmosauridae are a polyphyletic , unnatural group. Kenneth Carpenter restores the Elasmosaurids including the Jurassic forms and sees them as close relatives of the short-necked Polycotylidae , which are also Plesiosaurs ie S. (Plesiosauroidea).
Genera
- Albertonectes
- " Alzadasaurus "
- Aphrosaurus
- ? Aristonectes
- Brancasaurus
- Callawayasaurus
- Elasmosaurus
- ? Eretmosaurus
- Fresnosaurus
- Futabasaurus
- Hydralmosaurus
- ? Hydrorion
- Hydrotherosaurus
- Lagen anectes
- Leurospondyle
- Libonectes
- Mauisaurus
- Microcleidus
- Morenosaurus
- ? Morturneria
- Muraenosaurus
- Nakonanectes
- Occitanosaurus
- Styxosaurus
- Thalassomedon
- Turangisaurus
- Vegasaurus
- " Woolungasaurus "
- Zarafasaura
The late Cretaceous genera Artistonectes and Morturneria are only very poorly known. Their skulls are similar to those of the Cryptoclididae , but were placed in the Elasmosauridae by Bardet in 1995. In addition to the genera mentioned here, there may be two more that have not yet been described. A very large (10 m) elasmosaurid in the Courtenay Museum , found on the Puntledge River west of Courtenay on east Vancouver Island , may be a new genus. Its lower jaw is very long with a length of half a meter for an elasmosaurid. Another potentially new genus is represented by the fossil described as "Elasmosaurus" amalitskii , which was found from layers of the Turonium near Liski in Russia. It consists only of a few vertebrae and the greatly elongated abdominal ribs .
Individual evidence
- ↑ Plesiosauria.com Elasmosauridae ( Memento of the original from July 16, 2009 in the Internet Archive ) Info: The archive link has been inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice.
- ↑ The Plesiosaur Directory by Adam Stuart Smith Elasmosauridae ( Memento of the original from July 16, 2009 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice.
- ↑ a b Palæos Elasmosauridae
- ↑ a b c Pterosauria Translation and Pronunciation Guide by Ben Creisler ( Memento from November 9, 2007 in the Internet Archive )
- ↑ Richard Ellis : Sea Dragons. Predators of the Prehistoric Oceans. University Press of Kansas, Lawrence KS 2003, ISBN 0-7006-1269-6 , p. 192.
- ^ Sven Sachs, Jahn J. Hornung and Benjamin P. Kear. 2017. A New Basal Elasmosaurid (Sauropterygia: Plesiosauria) from the Lower Cretaceous of Germany. Journal of Vertebrate Paleontology. doi: 10.1080 / 02724634.2017.1301945
- ↑ Serratos, DJ, P. Druckermiller, and RBJ Benson. 2017. A New Elasmosaurid (Sauropterygia, Plesiosauria) from the Bearpaw Shale (Late Cretaceous, Maastrichtian) of Montana Demonstrates Multiple Evolutionary Reductions of Neck Length within Elasmosauridae. Journal of Vertebrate Paleontology. doi: 10.1080 / 02724634.2017.1278608
- ^ José Patricio O'Gorman, Leonardo Salgado, Eduardo B. Olivero and Sergio A. Marenssi. 2015. Vegasaurus molyi, gen. Et sp. nov. (Plesiosauria, Elasmosauridae), from the Cape Lamb Member (Lower Maastrichtian) of the Snow Hill Island Formation, Vega Island, Antarctica, and Remarks on Wedellian Elasmosauridae. Journal of Vertebrate Paleontology. 35 (3); e931285. doi: 10.1080 / 02724634.2014.931285
