Dinosaurs - Chronology - 106 million years ago

There is considerable evidence for the existence of dinosaurs in polar latitudes. This episode is based on remarkable finds made at two sites in Australia. The evidence for that part of Australia being then within the Antarctic Circle and being seasonally very cold is based on several lines of evidence. We can determine the palaeolatitude from magnetised particles in certain rocks. Evidence for the climate being seasonally cold comes from both plant fossils and sedimentary structures which form when the ground freezes.

A better picture
This fossil assemblage from Australia is remarkable because there are several different animals found at the site giving us a fuller picture of the palaeoenvironment - life in the area at the time

At least some of the animals must have been year round residents - Leaellynasaura were too small to have migrated hundreds of miles in and out every year. Leaellynasaura may have had special a adaptation for life in the polar regions.

Their skulls seem to have had especially large eye sockets; their large eyes may have allowed them to see better in the continuous low light levels of the polar winter.

Hanging in there
Some of the fossil vertebrates at these sites are very important because some very primitive animals seem to have survived here that had become extinct elsewhere.
Labyrinthodont amphibians, like Koolasuchus, were previously thought to have died out over 100 million years earlier, in this environment it occupied a crocodilian niche as the climate was too cold for crocodiles.

The earliest known dinosaur found in polar palaeolatitudes is called Cryolophosaurus (which means frozen crested reptile), found in Antarctica. It is a meat-eating dinosaur but we do not know if it migrated in during the summer months or lived there year round. Dinosaurs from polar latitudes are also known from the Late Cretaceous of Alaska, but they are very similar to those from further south and are probably just a migrant population.

The existence of dinosaurs at polar latitudes is significant because it means they either had to hibernate or go into an inactive state in the polar winter or they had some way of maintaining a high body temperature independent of the outside conditions, i.e. they were warm blooded.

Many people think that some, if not all, dinosaurs were warm blooded, but it is hard to prove. However these polar discoveries are strong evidence for warm-bloodedness in at least some dinosaurs.