Aristonectes Cabrera, 1941

Sauropterygia > Eosauropterygia > Eusauropterygia > Pistosauroidea > Plesiosauria >

Plesiosauroidea > Euplesiosauria > Cryptocleidoidea > Cimoliasauridae (O'Keefe, 2001a)

or Elasmosauridae (Gasparini et al. 2003)

Synonyms: Morturneria (see Chaterjee and Small, 1989)

A. Parvidens Cabrera, 1941(Type and only species)

Material: 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.

Distribution: 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.

The skull of Aristonectes in various aspects (from Gasparini et al. 2003)

The reconstructed skull of 'Morturneria' (=Aristonectes) in left lateral view (from Chaterjee and Small, 1989)

Discussion

Aristonectes ranges across the whole of the southern hemisphere. It has a large number of small pin-like teeth; a feeding guild has been proposed to accommodate such plesiosaur oddities (see also Cryptoclidus, Kimmerosaurus, Kaiwhekea): a 'trap guild' (Chatterjee and Small, 1989). This may be analogous to the extant Crabeater seal, which has sieve-like teeth for capturing krill (Martill et al. 1994).

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 affinities of Aristonectes have long remained in dispute. The taxon was first interpreted as elasmosaurid (Cabrera, 1941) and later also by Bardet et al. (1991) and most recently by 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).

The now redundant 'Morturneria' is a member of the newly defined Cimoliasauridae of O'Keefe (2001a). The synonymy makes this species 11% more complete in terms of characters suitable for use in cladistic analyses (personal observation) and we can thus regard its phylogenetic position with more accuracy. Thus, the recent observation (Gasparini et al. 2003) that the genus Morturneria is a junior synonym of Aristonectes and the description of a new skull from Chile (Suarez and Fritis, 2002) is of great value.

Brown (1981) noted the possibility that the occipital condyle of Aristonectes incorporates the exoccipital, a character shared only by the cryptoclidids (sensu Brown, 1981) and Eurycleidus, (Cruickshank, 1994b). This state can now be confirmed for Aristonectes as considered 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.