Order Bulletin 23 | Back to Bulletin Listing
Mosasaurs
were large, marine platynotan lizards which became abundant and
diversified during the latter half of Cretaceous time, but disappeared
at the close of the period. Three subfamilies are recognized within the
Family Mosasauridae: the Mosasaurinae (including the new tribes,
Mosasaurini, Globidensini and Plotosaurini), the Plioplatecarpinae
(including the new tribes, Plioplatecarpini and Prognathodontini), and
the Tylosaurinae. At present thirteen genera and thirty species are
diagnosed from the North American Cretaceous, with one new genus (Ectenosaurus) and one new species (Plioplatecarpus primaevus).
Of the older names available, nineteen generic and twenty-nine specific
names have been placed into synonymy, two generic and eighteen specific
names are based on indeterminate material, and an additional generic
and six specific names are only of dubious validity.
The osteolow of mosasaurs is described in detail and with reference to
the soft anatomy. Mosasaurs possessed a good sense of sight and a poor
sense of smell. A calcified tympanum, present in all three subfamilies,
was probably useful in transmitting waterborne sound to the middle ear
and is not indicative of deep-diving habits. Streptostylic quadrates
permitted anteroposterior movement of the mandibles, which in turn
facilitated the underwater swallowing of prey. Mosasaurs swam by
lateral undulations of the body, the flippers and relatively long neck
serving as ovgans of equilibration. They fed on smaller mosasaurs,
chelonians, fish, ammonites, belemnites, echinoderms and pelecypods,
and or the most part were highly active aquatic carnivores.
Mosasaurs inhabited subtropical epicontinental seas of less than 100
fathoms (about 180 meters) depth and of variable salinity. Individual
forms had a wide geographic distribution that was little affected by
changes in depositional environments. The range of many species of
mosasaurs inhabiting the western edge of the North Atlantic basin
probably extended into western European waters. Those from the eastern
edge of the Pacific basin appear to have belonged to a distinct
zoogeographic province.
Mosasaurs descended from primitive middle Cretaceous varanoids
(aigialosaurs) possessing many cranial characteristics of mosasaurs but
with a postcranial morphology similar to that of the modern Varanus.
Ancestral mosasaurs seem to have been of two basic types; forms with
long bodies and short dilated tails giving rise to the mosasaurines,
and forms with short bodies and long pointed tails giving rise to the
plioplatecarpines and tylosaurines. During their relatively brief
geologic existence mosasaurs exhibited a few clearly progressive
trends, such as a tendency to increase in overall size, to telescope
the frontals over the anterior edge of the parietals (consequently
suppressing kinesis), to increase the number of pygal vertebrae, and to
alter the primitive webbed paddIes into long, hyperphalangic flippers.
