Aristonectes Cabrera, 1941
The mysterious plesiosaur Aristonectes has a large number of small pin-like teeth. A special feeding guild, the 'trap guild', has been proposed to accommodate Aristonectes and other plesiosaurs with similar dentitions (Chatterjee and Small, 1989) such as Cryptoclidus, Kimmerosaurus, and Kaiwhekia. These plesiosaurs may have fed in a similar way to the extant Crabeater seal, which has sieve-like teeth for capturing krill (Martill et al. 1994).
The affinities of Aristonectes have long remained in dispute. The taxon was first interpreted as elasmosaurid by Cabrera (1941) and later also by Bardet et al. (1991) and Gasparini et al. (2003). However, it has also been variously interpreted as an 'aberrant pliosaur' (Welles, 1962), a cryptoclidid (Brown, 1981; Chatterjee and Small, 1989) and as 'cimoliasaurid' (Persson, 1963). O'Keefe (2001a) included 'Morturneria' in his cladistic analysis, a taxon recently recognised as a junior synonym of A. parvidens (Gasparini et al. 2003). The now redundant 'Morturneria' was included in Cimoliasauridae by O'Keefe (2001a) but this family is now considered invalid. The new family Aristonectidae was recently erected to accomodate Aristonectes and its close relatives.
As currently understood, Aristonectes has a wide geographical range across the whole of the southern hemisphere. The synonymy of 'Morturneria' with Aristonectes makes this species 11% more complete in terms of characters suitable for use in cladistic analyses (personal observation) and we can therefore regard its phylogenetic position with more accuracy. A partial skull from Chile was also referred to this genus (Suarez and Fritis, 2002). Brown (1981) noted the possibility that the occipital condyle of Aristonectes incorporates the exoccipital, a character shared only with the cryptoclidids (sensu Brown, 1981) and a Jurassic specimen referred to Eurycleidus by Cruickshank (1994b). The presence of this character is confirmed for Aristonectes by Gasparini et al. (2003): the posterior protrusion at the base of the exoccipital (see Chatterjee and Small, 1989 fig. 8) when paired with the "very short [basioccipital], without a separating groove" (Brown 1981) would complete the occipital condyle.
A. parvidens Cabrera, 1941
Type: MLP 40-XI-14-6; part of a skull and mandible, atlas-axis complex and 21 cervical vertebrae, 8 caudal vertebrae and an incomplete limb. Reffered material: TTU P 9219, incomplete skull and mandible plus associated cervical material; SGO-PV-957, posterior cranium and incomplete mandible.
Age and Location
Type: Paso del Sapo Formation, Fefipan Member, Maastrichtian, Canadon del Loro, middle Chubut River (42° 40' S-70° 00' W), northwest Chubut Province, Patagonia, Argentina.