Temporal range: Early Cretaceous, 140–125 Ma
With large clavicles and interclavicle and small scapulae, Leptocleidus resembled the Early Jurassic Rhomaleosaurus and members of the Cretaceous family, Polycotylidae. The animal had 21 teeth on either side of its maxilla and approximately 35 teeth on each side of the mandible. The Leptocleidus' triangle-shaped skull had a crest running from a ridge on the end of the nose to the nasal region. Differing from other pliosaurids, Leptocleidus had single-headed cervical ribs and a deep depression in the centra of the neck vertebrae. Leptocleidus was on an average of 3 meters (10 feet) long. Leptocleidus superstes however, was found to be almost 50% smaller (1.5m, 5 ft) making it the smallest known species.
Distribution and habitat
Leptocleidus, unlike many pleisiosaurs, lived in shallow lagoons and likely visited brackish and fresh water systems (such as the mouths of large rivers). This led A. R. I. Cruikshank to infer that this movement to fresh water was an attempt to flee larger plesiosaurs and pliosaurs. Most species are known from The British Isles but L. capensis was discovered in Cape Province, South Africa.
Leptocleidus is known from the following sediments:
- L. capensis is known from the Sundays River Formation (Valanginian age), Cape Province, South Africa.
- L. clemai found near Kalbarri in the Carnarvon Basin (Hauterivian-Barremian age) Western Australia.
- L. superstes is known from the Upper Weald Clay (Barremian age), Sussex, England.
- Leptocleidus sp. from the Vectis Formation (lower Aptian age), Isle of Wight.
Cladogram based on Ketchum and Benson (2011):
- Ketchum, H. F.; Benson, R. B. J. (2010). "Global interrelationships of Plesiosauria (Reptilia, Sauropterygia) and the pivotal role of taxon sampling in determining the outcome of phylogenetic analyses". Biological Reviews. 85 (2): 361–392. doi:10.1111/j.1469-185X.2009.00107.x. PMID 20002391.
- Smith AS, Dyke GJ. 2008. The skull of the giant predatory pliosaur Rhomaleosaurus cramptoni: implications for plesiosaur phylogenetics. Naturwissenschaften e-published 2008.
- Cruikshank A. R. I. (1997). "A lower Cretaceous Pliosauroid from South Africa". Annals of the South African Museum. 105: 206–226.
- Hilary F. Ketchum and Roger B. J. Benson (2011). "A new pliosaurid (Sauropterygia, Plesiosauria) from the Oxford Clay Formation (Middle Jurassic, Callovian) of England: evidence for a gracile, longirostrine grade of Early-Middle Jurassic pliosaurids". Special Papers in Palaeontology. 86: 109–129. doi:10.1111/j.1475-4983.2011.01083.x.
- O'Keefe F. R. (2001). "A cladistic analysis and taxonomic revision of the Plesiosauria (Reptilia: Sauropterygia)". Acta Zoologica Fennica. 213: 1–63.