Vega Island Stratigraphy, Biostratigraphy, and Chronostratigraphy

Additionally, the Naze dromaeosaur weathered from the lower portion of the Cape Lamb Member again within the Diplomoceras subzone on the Naze of James Ross Island. This places these two dinosaur localities, near the middle of the Gunnarites assemblage zone, just above the level where Crame et al. (2004) recorded a 87Sr/86Sr datum of 71.0 Ma. The charadriiform (shorebirds) bird localities where two different bird specimens were recovered (Case & Tambussi, 1999; Cordes, 2001; Cordes, 2002), are placed into the upper half of the Gunnarites assemblage zone, at level between 37-40 meters above the level where Crame et al. (2004) recorded a 87Sr/86Sr datum of 70.3 Ma.

Based on the rate of sedimentation (Pirrie et al., 1991) it would place the two Cape Lamb localities of the supposed charadriiform specimens, into a very Early Maastrichtian time frame of approximately 70 million years ago. The two specimens of presbyornithids (Noriega and Tambussi, 1995) are now known to be one, an anseriform (ducks, geese and relatives) Vegavis (Clarke et al., 2005) and the second is a proposed gaviiform (loon) assigned to the genus Polarornis (Chatterjee, 2006; Fig. 1).

Both specimens were recovered from concretions coming from the lower part of the Sandwich Bluff Member of Pirrie et al. (1991). In the amphitheater where the fossils were collected, the horizon that produces the fossil is a concretionary layer, some 20 meters above the unconformity, which represents the base of the Sandwich Bluff Member of the Snow Hill Island Formation. This concretionary horizon is associated with the Maorites Assemblage Zone (Pirrie et al., 1991) and the Manumiella (dinoflagellate) Zone of Riding et al. (1992) which are both indicators of a Late Maastrichtian age.

Higher up in the Sandwich Bluff section, dental and pedal material of a hadrosaurine hadrosaur, was recovered from the Late Maastrichtian Sandwich Bluff Member on Vega Island (Case et al., 2000). Additional and abundant avian material has been collected from the same horizon as the hadrosaur. More recently, between the hadrosaur horizon and the lower bird concretionary horizon has come material of a cursorial bird that adds another Antarctic bird to the growing list of avian taxa from Vega Island and the James Ross Basin in general.