الأسماء في صفحات التنقل
Rhomaleosaurus cramptoni was an open-water, macropredator of Jurassic seas. It possessed the sharp, conical teeth of a generalist predator that were perfect for capturing a wide range of prey, such as cephalopods, fish, and other marine reptiles. They were known to inhabit the seas surrounding what is now Western Europe, as all fossil remains have been located in the United Kingdom (Massare, 1987; Massare, 1988).
The holotype fossil material of Rhomaleosaurus cramptoni is housed at the National Museum of Eire ⁄ Ireland, Dublin(NMING). It is specimen NMING F8785, and is a complete skeleton prepared in an articulated dorsal view. The skull of that specimen is completely prepared and viewable in three dimensions.
It was excavated from Kettleness, near Whitby, Yorkshire County, England, Southern United Kingdom.
It was pulled from the upper part of the ammonite (Hildoceras bifrons) zone of the region and is aged from the Upper Lias Epoch, Late Early Jurassic.
Interestingly, the holotype for Rhomaleosaurus cramptoni is also the type specimen for the genus.
Rhomaleosaurus cramptoni is a species of extinct marine reptiles called plesiosaurs. While plesiosaurs had an expansive range of existence (~135 million years, from early Jurassic to the late Cretaceous), R. cramptoni had a comparatively short reign of existence during the Toarcian age of the Early Jurassic (183 to 175.6 million years ago) (Ketchum & Benson, 2010).
R. cramptoni is a large, diapsid vertebrate (tetrapods with two holes on each size of their skulls) within the Sauropterygia group, that had a total body length of ~ 7 m (Smith & Dyke, 2008; Smith, 2013). They are highly adapted to life in the water and possess a long neck, sturdy torso and four large flippers that are used to propel themselves through their aquatic environment (Robinson, 1975). Interestingly, the plesiosaur lineage developed an appendicular (limb-based) locomotory style, rather than the axial (trunk-based) propulsion through the aquatic environment that many aquatic tetrapods (four-limbed vertebrates) utilized (Robinson, 1975; Massare, 1988; Lindgren et al., 2013). This means that they most likely propelled themselves through the water with what is called a modified-flying method (O'Keefe and Carrano, 2009).
R. cramptoni was a top predator of Jurassic seas and played an important ecological role in the oceanic ecosystems (Massare, 1987).
Rhomaleosaurusand the others within the rhomaleosaurid family, are fairly morphologically aberrant members of the plesiosaur group. They display a combination of two distinct plesiosaur morphotypes, possessing both long necks and large heads (these two features are otherwise mutually exclusive within the plesiosaurs) (O'Keefe, 2002; O'Keefe & Carrano, 2005). Most plesiosaurs have long necks and small heads (the classic plesiosaur morphotype) or large heads and shorter necks (a group of plesiosaurs, called pliosaurs). The morphological oddness of the rhomaleosaurids led researchers to question the phylogeny (patterns of relationships among species) of the family (Smith & Dyke, 2008). Researchers performed a phylogentic analysis and placed them within the pliosaurs, as a sister group to, both, the Leptocleidoidea and the Pliosauridae (Smith & Dyke, 2008).
R. cramptoni have four large flippers that act as hydrofoils (much like wings of an airplane, except in water) that are "anchored" by a sturdy base composed of gastralia (ribs located along the animals underside, or belly) and a sturdy, closely articulated spinal column (Smith, 2011). R. cramptoni most likely propelled themselves with what is called a modified-flying method (O'Keefe and Carrano, 2009). This method of swimming is where the thrust and lift is provided by the down stroke and the recovery stroke is angled to decrease drag (O'Keefe and Carrano, 2009; Smith, 2011). The front and hind flippers were thought to move almost simultaneously, but with a slight delay in the hind flippers that maximized swimming efficiency (O'Keefe and Carrano, 2009).
Some have discussed the evidence for the presence of small, diamond-shaped caudal (tail) fins in the rhomaleosaurs (Smith, 2013). While there does seem to be indication of the presence of a tail fin (e.g., compressed caudal vertebrae), more fossil material needs to be found to clarify our understanding of the soft tissiue anatomy of the tail region (Smith, 2013).
The total length of the type skull of Rhomaleosaurus cramptoni (NMING F8785) is 88 cm (~35 inches) and the total skeletal length is 7 m (~23 feet) (Smith & Dyke, 2008).
Large plesiosaurs, like Rhomaleosaurus cramptoni, are thought to not have been able to move on land. Weak limb girdle attachment to the spine was, historically, the primary evidence for the argument that the plesiosaurs were completely aquatic. In 2011, researchers described a fossil of an adult plesiosaur bearing a fetus. Based upon this fossil, we can infer that plesiosaurs both gave live-birth and were, therefore, fully aquatic (much like the Icthyosaurus) (O'Keefe & Chiappe, 2011).
The first fossil evidence of Rhomaleosaurus cramptoni was uncovered in 1848 by quarry workers at the Alum quarry, which is along the Yorkshire coast. That specimen, which would eventually become the type specimen, was housed for several years at the castle-home of the Marquis of Normanby, the owner of the quarry. In 1853, the fossil was presented by the Marquis to his friend, Sir Phillip Crampton, who was an anatomist. Crampton took the specimen to Dublin, so that it could be displayed at the 1853 British Association annual meeting. Following this meeting, the specimen was temporarily housed by the Zoological Society of Ireland in a building built to hold the large specimen. It wasn't until 1863 that the specimen was loaned to the Royal Dublin Society and was scientifically analyzed, named and described. It remained at the Royal Dublin Society's museum through the years and several name changes, until it transferred in 1992 to its current home in the National Museum of Ireland's (natural history) museum.
