Dating an early Mammal Tooth to the very end of the Cretaceous

On Friday 9th November we published an article about the discovery of an ancient tooth, believed to come from an early ancestor of ungulates (hoofed mammals) from 65 million years ago.  The discovery had been made in India, and this find was important as very little is known about late Cretaceous mammals.

To read article: Very ancient udders! Mesozoic cow discovered in India

At first we queried whether the tooth had indeed been recovered from late Maastrichtian strata, thus placing this tooth at the very end of the age of Dinosaurs 65 million years ago.  The diversification and geographical distribution of mammals is still very poorly understood at this particular time in Earth’s history.  Material from the southern continents (Gondwanaland) is particularly rare, with most mammal fossils from this particular faunal stage having been recovered from the northern hemisphere – Laurasia.

However, one of the research scholars who worked on this particular discovery, Omkar Verma of the department of Geology (University of Jammu), was able to furnish us with a little more information.  From the articles and research papers that we were sent, it seems that the tooth was dated using other micro-fossil remains that had been recovered from the same matrix and the same site.  In particular remains of an ancient fish (a ray) Igdabatis indicus; and evidence from the many types of ostracod (crustaceans) and their carapaces indicates that the tooth came from the Maastrichtian faunal stage, placing this ancient mammal at the time of the last of the dinosaurs.

Dating of fossils using “key” or “indicator” species which have a more precise date assigned to them in the palaeontological record is called biostratigraphy.  The remains of I. indicus are associated with the very late Cretaceous and so it seems that the mammalian tooth can be dated to that time period as well.

Ostracods, are still abundant today (the date back to the Cambrian period) and live in both marine and freshwater environments, there are thousands of different genera.  As the carapace or shell can enclose the entire body including the legs they are often referred to as “seed shrimps”, but their importance to micro-palaeontolgists cannot be underestimated.  The huge numbers of micro-fossil remains and their prevalence all over the world enables scientists to accurately date geological deposits and thus assist in the dating of rarer finds such as in this case, the ancient mammalian molar from an ancestor of cows.

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