Biotic composition changed dramatically across the Cretaceous-Paleogene (K-Pg) ca. 65 Ma and marks a real phenomenon, a response reflecting myriad complex factors associated with extinction and survivorship processes. In the southern high latitudes, the patterns of macroinvertebrates are proving distinct from the north, indicating that although the mechanisms driving the observed composition and biodiversity may be comparable, they have, in part, a unique suite of historical attributes. The early Danian interval was characterized by opportunistic and migrant taxa that infilled the ecological vacuum left by the mass extinction in this 'brave new world'. But, what is the origin of many new groups recorded in the Danian?
About 40% of Antarctic Danian bivalves have representative congeners/ancestors in the Antarctic Cretaceous, 47% are of probably Austral origin and some 13% are of Cretaceous northern origin. Antarctic early Danian gastropods are predominantly of northern Cretaceous origin at around 50%, followed by those taxa of Austral Cretaceous origin at some 37.5% and fewer from the Antarctic Cretaceous at around 12.5%. The early Danian assemblages were derived from a blend of descendants of both known and uncertain origin, with bivalves and gastropods revealing distinct histories.
New Zealand (NZ) late Danian macroinvertebrate assemblages record the post K-Pg boundary faunal rebound ca. 2 m.y. after the mass extinction, and exhibit the stabilization of shallow marine communities with relatively high species- and genus-level diversity. The NZ faunas are dominated by new species in new genera reflecting both isolation of the region and accelerated evolutionary rates from infilling of niches until communities stabilized. NZ bivalves constitute 34% with a NZ Cretaceous origin, 48% with an Austral Cretaceous origin and 17% with a possible northern origin. Comparable with the Antarctic record, NZ gastropods constitute 12% with a NZ Cretaceous ancestry, 58% with an Austral origin and 29% with Northern Hemisphere progenitors.
New vertebrate material of Chrondrichthyan and non-chondrichthyan groups, chelonioideans, and Aves recently recovered from both mainland NZ and the Chatham Islands adds greatly to the Austral Danian record. Chelonioid carapace, plastron and rib fragments augment the record augment the known fossil turtle occurrences in NZ. The most significant recent discovery is that of several new groups of sea birds (up to 4 taxa) in a single horizon dated at ca. 66-64 Ma on Chatham Island, represented by associated and articulated remains of individual birds-the NZ region's oldest recorded aviary. Rare theropod dinosaur bones are recorded below and above the main bird horizon. These new finds provide important new data on the origins of modern birds during the Cretaceous-early Paleogene Greenhouse phase.