An amazing time capsule
Ashfall fossil beds in Nebraska record a traumatic moment for Miocene mammals living some 10-12 million years ago in what is now the western USA, when a large volcanic eruption some 1600km away venting from the Yellowstone hotspot buried them in a dense fall of debris dropping out of the air. While difficult for the animals involved, this moment in deep time has proved a boon for palaeontologists, as the fine grained ash preserved a wide diversity of creatures to give us a snapshot of a past ecology entombed in stone. The site is known as a Lagerstatte, a German word given to sites of exceptional fossil preservation or importance in the geological record.
The place is famed for its mammals, and its fossils filled many gaps in our comprehension of their evolution since the asteroid impact that ended the Cretaceous cleared the ecological niches for them to diversify into. They were buried by a waterhole in a deep drift of wind borne ash, where they may have been huddling for relief. Species include Teleoceras, a hippo like cousin of rhinos, various horses at the point where their toe number was diverging, camelids and birds. They died a slow and painful death over up to a month, from asphyxiation as their lungs got lacerated with the millions of shards of glass that formed the volcanic ash, a rare way to drown from within, smaller creatures first. Before the catastrophe the area was an open grassy savannah with interspersed trees enjoying a warmer climate than today’s. The soft ash layer was later protected from erosion by a tougher capping sandstone.
It was spotted in 1971, when a couple of passing geologists noticed a baby rhino skull that had been weathered out by a recent storm. They returned with a team late in the decade, and the rest is now paleontological history…over 200 skeletons have been unearthed from 17 species, some containing unborn foetuses, and others with the remnants of last meals discernible. Like the Jehol beds in China (see http://on.fb.me/1cViPit), the site has been described as a prehistoric Pompeii. The place is now a state historical park, with a museum, ongoing excavation site and fossil preparation laboratory (for more on this process see http://on.fb.me/1PPOiTc), all in all it sounds like the basis for a great day out for us geoscience lovers, with the entry fee supporting research.
One of the joys of writing here is the endless discovery of new places and things of interest, and this one came from a reader comment on a post I did covering another laagerstatte,and I’d never heard of this geowonder otherwise, so please feel free to keep em coming.
Loz
Image credit: 1: Roger Hubbard 2&3: Mawhamba
http://bit.ly/1OYkWmqhttp://bit.ly/1PQxzQChttp://bit.ly/1FiNmnKhttp://ashfall.unl.edu/http://bit.ly/1LYFG7x
(Source: facebook.com)