References
Reference
Cruickshank, Arthur R I and Fordyce, R. Ewan ((date unknown)) High latitude Late Cretaceous plesiosaurs in Gondwana; Journal of African Earth Sciences,
High latitude Late Cretaceous plesiosaurs in Gondwana
Principal Author
Arthur R I Cruickshank
Other Authors
R. Ewan Fordyce
Header
Academic paper
Journal
Journal of African Earth Sciences
Abstract
(Abstract only)
Plesiosaurs (Reptilia: Plesiosauria) are an important component of many Mesozoic marine communities. They are divided into two superfamilies, the Pliosauroidea and the Plesiosauroidea which are distinguished conventionally on the basis of skull and neck proportions, among other characters (Brown, 1.981). The Plesiosauroidea ('plesiosaurs') have 'small' heads and long necks, in contrast to the Pliosauroidea ('pliosaurs'). The latter were the dominant macro-predators of the open seas, whereas the former were adapted to feed on small or soft-bodied prey. The pliosaurs comprise a single family, whereas there are three plesiosaur families - the Pliosauridae, Elasmosauridae and Cryptoclididae. These relationships can be demonstrated cladistically (Fig. 1). The Plesiosauridae are restricted to the Early Jurassic, but the long-necked Elasmosauridae represent one of the great success stories of the Mesozoic, and last right to the end of the Maastrichtian as the most commonly-found plesiosaurian taxon. The Cryptoclididae are first seen in the Middle Jurassic (Callovian) of Europe, but seem to undergo a complicated radiation in the Late Cretaceous, becoming very large, especially in the Southern (Gondwana) Realm (Cabrera, 1 941; Casmiquela, 1 969; Chatterjee and Small, 1 989; Cruickshank and Fordyce, in prep.). Cryptoclidids are not known later than the Kimmeridgian in Europe, nor apparently earlier than the Late Cretaceous in the palaeo-Pacific region. They are assumed to have invaded the southern oceans via the western Tethyan Seaway sometime in Late Jurassic or Early Cretaceous times (Gasparini, 1 997). A recently recognised new genus of large cryptoclidid (Cruickshank and Fordyce, in prep.) shows adaptations in its skull morphology for wide gape and fast jaw-closing action, suggesting predation on large soft-bodied species, such as cephalopods, lightly armoured fish or even medusoids. The position and size of the eyes indicates at least partial binocular vision and a life in deep waters or of poor visibility. We speculate that the evolution of these large forms reflects an early phase in the development of Southern Ocean cooling and the concomitant increase in oceanic productivity.
Plesiosaurs (Reptilia: Plesiosauria) are an important component of many Mesozoic marine communities. They are divided into two superfamilies, the Pliosauroidea and the Plesiosauroidea which are distinguished conventionally on the basis of skull and neck proportions, among other characters (Brown, 1.981). The Plesiosauroidea ('plesiosaurs') have 'small' heads and long necks, in contrast to the Pliosauroidea ('pliosaurs'). The latter were the dominant macro-predators of the open seas, whereas the former were adapted to feed on small or soft-bodied prey. The pliosaurs comprise a single family, whereas there are three plesiosaur families - the Pliosauridae, Elasmosauridae and Cryptoclididae. These relationships can be demonstrated cladistically (Fig. 1). The Plesiosauridae are restricted to the Early Jurassic, but the long-necked Elasmosauridae represent one of the great success stories of the Mesozoic, and last right to the end of the Maastrichtian as the most commonly-found plesiosaurian taxon. The Cryptoclididae are first seen in the Middle Jurassic (Callovian) of Europe, but seem to undergo a complicated radiation in the Late Cretaceous, becoming very large, especially in the Southern (Gondwana) Realm (Cabrera, 1 941; Casmiquela, 1 969; Chatterjee and Small, 1 989; Cruickshank and Fordyce, in prep.). Cryptoclidids are not known later than the Kimmeridgian in Europe, nor apparently earlier than the Late Cretaceous in the palaeo-Pacific region. They are assumed to have invaded the southern oceans via the western Tethyan Seaway sometime in Late Jurassic or Early Cretaceous times (Gasparini, 1 997). A recently recognised new genus of large cryptoclidid (Cruickshank and Fordyce, in prep.) shows adaptations in its skull morphology for wide gape and fast jaw-closing action, suggesting predation on large soft-bodied species, such as cephalopods, lightly armoured fish or even medusoids. The position and size of the eyes indicates at least partial binocular vision and a life in deep waters or of poor visibility. We speculate that the evolution of these large forms reflects an early phase in the development of Southern Ocean cooling and the concomitant increase in oceanic productivity.
Language
English