A Snapshot in Time part 2 - The Daohugou Biota In the first post of this pair (see: tmblr.co/

A Snapshot in Time part 2 - The Daohugou BiotaIn the first post of this pair (see: http://tmblr.co/Zyv2Js1lLwcex) we discussed the Jehol formation in China, the best example of an early Cretaceous environment, preserved like Pompeii by a series of volcanic eruptions pushing dead animals into lakes and burying them in the ash that fossilised them.While argument rages over the connections between the organisms from these two lake sediment sequences, separated by a crucial 30 million years in time during which birds separated from dinosaurs (amongst other significant events), they do occupy the same stratigraphic column, and had similar conditions of deposition, fossilisation and preservation. However researchers can’t agree yet on which species characterises which biota, nor on where the line between them lies (see the saga of lumpers and splitters at http://on.fb.me/1PpsZnU)Deposited during an interval spanning roughly 164-158 million years back, it is made up of lake sediments interspersed with volcanic rocks from pyroclastic flows, much like the Jehol formation. Unlike the latter, it has been folded and mixed up by erosion and volcanic activity, testifying to more active tectonics than when the later beds were deposited in similar geographic settings. There has been some controversy over their actual age, though most agree on the window quoted above using arguments from biostratigraphy (where fossils are in the stack) shows the rocks to be earlier. The latest radioactive dates also support the accepted window. Like the Jehol many soft tissues, fur, feathers and others have been perfectly preserved by the fine grained ash.Many early mammals have been found here, including early aquatic creatures and the first gliding squirrel type critter. The trees included conifers and ginkoes. The earliest birds were just recently found here, as researcher hoped, giving a glimpse into their first days on Earth, just after their divergence from dinosaurs (the subject of my third upcoming post).Together these two formations make up the only detailed record of a land ecosystem of this period anywhere, and their unique nature promises many exciting discoveries in the future. More new creatures will turn up, and the comparison between these two excellently preserved and similar ecosystems geologically ‘photographed 30 million years apart in time will reveal many new insights into evolution at one of its critical phases for several major clades.LozImage credit: Graphic: Julia MolnarSalamander Chunerpeton: Sullivan et al, referenced belowSinornithosaurus: Dave_NGMC91Graphic 2, the early mammal Castorocauda: Nobu Tamurahttp://bit.ly/1zMUki0http://bit.ly/1hJIgl7http://bit.ly/1Pp4Yx5 -- source link
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