the division of the back that contains the neck vertebrae is cervical vertebrae.
division of the back contains the neck vertebrae?
cervical vertebrae
while plesiosaurs varied little in the build of the trunk, and can be called "conservative" in this respect, there were major differences between the subgroups as regards the form of the neck and the skull. plesiosaurs can be divided into two major morphological types that differ in head and neck size. "plesiosauromorphs", such as cryptoclididae, elasmosauridae, and plesiosauridae, had long necks and small heads. "pliosauromorphs", such as the pliosauridae and the rhomaleosauridae, had shorter necks with a large, elongated head. the neck length variations were not caused by an elongation of the individual neck vertebrae, but by increasing the number of these cervical vertebrae. "elasmosaurus" has seventy-two neck vertebrae; the known record is held by the elasmosaurid "albertonectes", with seventy-six cervicals. the large number of joints implied suggested to early researchers that the neck must have been very flexible; indeed, a swan-like curvature of the neck was assumed to be possible - in icelandic plesiosaurs are even called "svaneðlur", "swan lizards". however, modern research has confirmed an earlier conjecture of williston that the long plate-like spines on top of the vertebrae, the "processus spinosi", strongly limited a vertical movement. although horizontal curving was less restricted, in general the neck must have been rather stiff and certainly was incapable of being bent into serpentine coils. this is even more true of the short-necked "pliosauromophs", which had as few as eleven cervicals. with early forms, the amphicoelous or amphiplat neck vertebrae bore double-headed neck ribs; later forms had single-headed ribs. in the remainder of the vertebral column, the number of dorsal vertebrae varied between about nineteen and thirty-two, of the sacral vertebrae between two and six, and of the tail vertebrae between about twenty-one and thirty-two. these vertebrae still possessed the original processes inherited from the land-dwelling ancestors of the sauropterygia and had not been reduced to fish-like simple discs, as happened with the vertebrae of ichthyosaurs. the tail vertebrae possessed chevron bones. the dorsal vertebrae of plesiosaurs are easily recognisable by two large "foramina subcentralia", paired vascular openings at the underside.
plesiosauria
the neural arches of the neck vertebrae were well fused to the centra, leaving no visible sutures, and the neural canal was narrow in the front vertebrae, becoming more prominently developed in the hind vertebrae, where it was as broad as high, and almost circular. the pre-and post-zygapophyses of the neck vertebrae, processes that articulated adjacent vertebrae so they fit together, were of equal length; the former reached entirely over the level of the centrum whereas the latter reached only with their back half. the neural spines of the neck vertebrae appear to have been low, and almost semi-circular by the 20th vertebra. the facets where the neck ribs articulated with the neck vertebrae were placed on the lower sides of the centra, but were only placed higher in the last three vertebrae, reaching around the middle of the sides. the neck ribs were semicircular to quadratic in side view, and were directed rather straight down. the bottom of each neck vertebrae had pairs of nutritive foramina (openings) at the middle, separated by a ridge, which became progressively more prominent and thickened towards the back of the neck.
elasmosaurus