Evidence for Low Temperatures and Biologic Diversity in Cretaceous High Latitudes of Australia

Abstract

A diverse terrestial biota inhabited polar latitudes during the Cretacous, 105 to 130 Ma (million years ago), along what is now the southeast coast of Australia This biota, from rocks in the Otway and Strzelecki groups, cnsisted of more than 150 taxa of vertebrates, invertebrates, and plants. Oxygen isotope ratios in diagenetic calcite suggest that mean annual temperatures were most likely less than 5 degrees C, and rings present in the fossil araucarian-podocarp-ginko woods indicate saonality. Southeastern Austalia, thus, seems to have had a cool, seasonal, nontropical climate. Dinosaurs that have been recovered are up to five species and three genera of hypsilophodontids, all of which were endemic, and three species of theropods. The occurrence of Allosaurus sp. and labyrinthodont amphibians, which had become extinct elsewhere in the Jurassic, indicate that isolation may have allowed extended surival of these taxa in Australia. In that dinosaurs coped with high latitude for at least 65 million years [Valaginian to Albian time in Australia and Campanian to Maastrictian time (80 to 65 Ma) in Alaska] suggests that cold and darkness may not have been prime factors bringing about the extinction of dinosaurs and some other groups at the Cretaceous-Tertiary boundary, unless they were prolonged.

Polar dinosaurs on parade: a review of dinosaur migration

“…The distribution of polar dinosaurs is widespread and taxonomically variegated (Rich et al 1988, Nelms 1989, Hammer & Hickerson 1993, Molnar & Wiffen 1994, Slaughter et al 1994, Gangloff 1995, Case et al 2000, Fiorillo & Parrish 2004, Gangloff et al 2005see Rich et al 1997 for a review). Considerable taxonomic overlap is observable, at least at the generic level, between polar and more temperate latitudes.…”

“…Rich et al (1988) described a flora dominated by ginkgoes, podocarps, and araucarian conifers. Isotopic (d 18 O) records indicate that mean annual palaeotemperatures were around 58C (Rich et al 1988, Gregory et al 1989, with seasonal freezing as evidenced by cryoturbation structures (Constantine et al 1998), although Morath & White (2004) have suggested that a marine influence may have had an ameliorating affect on the climate. As such, temperatures were markedly warmer at the poles then than they are today, allowing a flourishing dense polar vegetation that was not conducive to freedom of movement (i.e.…”

“…hadrosaurs) were perhaps more predisposed to travel long distances to escape harsh winters (e.g. Rich et al 1988, Clemens & Nelms 1993, New Zealand's dinosaurs may simply have been precluded from undertaking such journeys. Such a taxonomically diverse fauna implicates the adaptive ability of dinosaurs as a whole, and obviates a universal explanation for dinosaur migration.…”

“…Polar assemblages tend to have unusual faunal compositions. Hysilophodonts are a group of small ornithischians that, while rare in the Northern Hemisphere, tend to dominate Austral polar communities (Rich et al 1988). The enlarged optic lobes and expanded orbits found in the Australian hypsilophodont, Leallynosaura amicagraphica Rich & Vickers-Rich, 1989, suggest this animal had acute vision compared with its northern, low-latitude counterparts (Rich et al 1988).…”

Post-Gondwana Africa and the vertebrate history of the Angolan Atlantic Coast

“…Dinosaur localities of Early Cretaceous Victoria were formed at the most southerly paleolatitudes of any known dinosaur sites (>70°S; Rich et al, 1988), including those in Antarctica now . During the Cretaceous, Australia and Antarctica were conjoined.…”