Blood vessels (arteries, veins and capillaries) are not something you would normally associate with fossils, but newly puublished research from Poland shows them preserved in a 247 million year old reptile remains. Rapid iron oxide fossilisation might have created this excellent preservation
Fossil biomolecules from an endogenous source were previously identified in Cretaceous to Pleistocene fossilized bones, the evidence coming from molecular analyses. These findings, however, were called into question and an alternative hypothesis of the invasion of the bone by bacterial biofilm was proposed. Herewith we report a new finding of morphologically preserved blood-vessel-like structures enclosing organic molecules preserved in iron-oxide-mineralized vessel walls from the cortical region of nothosaurid and tanystropheid (aquatic and terrestrial diapsid reptiles) bones.
http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0151143
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