Some dinosaurs coped with the cold of winter by venturing beneath the Earth’s surface, according to a study to be published in the journal Cretaceous Research. Three fossilized burrows found in southeastern Australia are the second group of such tunnels found on Earth and, dating back 110 million years, are the oldest.
When dinosaurs roamed the Earth, these burrows were within the Antarctic Circle and temperatures dipped below freezing during the winter. Also, periods of little sunlight likely led to cyclical shortages in vegetation. The burrows support the hypothesis that instead of migrating to escape the cold winters of the Cretaceous period, dinosaurs ventured underground, like modern animals such as alligators and coyotes. The only other known dinosaur burrow was discovered in 2005 in Montana, US. Described two years later, this burrow dated from 95 million years ago and contained the bones of an adult and two juveniles of a small new species of dinosaur called Oryctodromeus cubicularis [BBC News]. Burrows that snaked below the ground may have provided a haven offering protection from predators, along with stable temperatures, constant humidity levels and a place to tend to offspring.
Scientists aren‘t sure which dinosaur species made the newly discovered burrows, but they suspect that the Australian tunnel also was once home to Oryctodromeus cubicularis. Previously, researchers theorised that the small dinosaurs in the region survived harsh weather by sheltering beneath large tree roots or in hollows. [This] find, however, indicates that they may have dug into the soft banks of rivers flowing out of the rift valley [Cosmos]. The burrows have not yet been excavated, but analysis of a 2.1-meter, or seven-foot, long burrow indicates that an animal weighing between 4.5 and nine pounds dug the tunnel.
The finding also suggests that dinosaurs in different parts of the globe, millions of years apart during the Cretaceous period, found similar ways to cope with harsh climatic conditions. The burrows were dug in soil deposited in a valley by massive spring floods of meltwater similar to those seen today on the north slopes of Alaska. The dinosaurs could have lived in the burrows in autumn and winter, but would have had to move out before the following year’s spring floods filled them with fresh sediment [New Scientist].
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