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| Bloomsbury Sigma 2021 ISBN 978-1-4729-8397-8 |
Elsa Panciroli is a young Scottish palaeontologist with a story to tell. She challenges the narrative that mammals were insignificant creatures living in the shadow of the dinosaurs until after the end-Cretaceous extinction.
The first age of mammals, she tells us, was in the Permian 300-250 million years ago. This is when the ancestors of therians were dominant and included large herbivores and carnivores quite as impressive as the later dinosaurs. Then there was another extinction event triggered by massive lava flows lasting 800 thousand years - The Great Dying. Those that survived were mostly small and included the first mammaliaforms.
Yes, the definition of a mammal, especially in the fossil record, is based on us having only two sets of teeth with the deciduous teeth being lost at weaning. So for purists Elsa Panciroli is describing the history of the Synapsids, one of the two great lineages of amniotes, from which mammals arose. The other lineage was Sauropsids that comprises dinosaurs (including birds) and reptiles.
In Pursuit of Early Mammals
The history of synapsids has been told before but in a more academic style by one of Panciroli's heroines Zofia Kielan-Jaworowska (review here).
Some mammalian features undoubtedly evolved earlier than lactation. They include fur and differentiation of the teeth into incisors, canines and molars. The immediate ancestors of therians adopted a nocturnal life style. There is evidence for this in the structure of our eyes (two of the four types of cone in other vertebrates were lost) and most mammals have poorer colour vision than primates where it has been partially regained through evolution of opsins.
Elsa Panciroli started this book while finishing her PhD studying Jurassic fossils from the Isle of Skye. A truly astonishing achievement. The account of synapsid evolution alternates with trips to the field, scanning of fossils embedded in rock using the synchotron near Grenoble and (carefully supervised) viewing of rare Chinese fossils.
Zofia Kielan-Jaworowska in the field
Panciroli is also very much of her time. She laments that many key fossils were taken without consultation of indigenous people. It concerns her that most palaeontologists have been male (despite Kielan Jaworowska see here) and of course she worries intensely about climate change. In a final short chapter she speculates on what type of mammal will surive the current mass extinction.
