How and when did mammals transition from laying eggs to live birth? The fossil record doesn't typically preserve soft tissues like embryos and placentas making this a tough problem. This week we take a look at two new fossil discoveries that begin to answer the question of mammal evolution, and challenge orthodoxy. A cute baby dicynodont fossil from the Triassic of South Africa is the first mammal to be captured 'in ovo' i.e. inside its egg. Secondly, we discuss a new fossil cynodont from the Triassic of Argentina that might have recorded its growth and birth in its bone histology. Using this we begin to piece together our own evolutionary history and estimate when placental mammals 'got cracking'. Along we way we ask if viviparity evolved twice and whether teenagers can be trusted to go to the shops to get eggs.

The papers discussed this week are "The first non-mammalian synapsid embryo from the Triassic of South Africa" by Julien Benoit and colleagues published in PLoS One in April 2026 https://doi.org/10.1371/journal.pone.0345016 and "Early origin of viviparity in the mammalian lineage" by Leandro Carlos Gaetano and colleagues published in Frontiers in Mammal Science https://doi.org/10.3389/fmamm.2026.1845319

Palaeoart by Sophie Vrard.

New finds in palaeontology are dependent on people getting out in the field and digging up fossils, but are the next generation of palaeontologists getting to do that? Opportunities for fieldwork and fieldwork training have become more expensive, which means students might not be getting the training they need. What happens next? In this week's bonus episode, Susie and Rob discuss the importance of fieldwork and whether the next generation of palaeontologists are facing 'an extinction of experience'. We focus on the views of students and early career researchers and ponder what happens to palaeontology if we focus on large scale studies of existing data to the exclusion of digging up new stuff. This is a preview of the full episode available to our Patreon members https://www.patreon.com/cw/FossilFiles

The main paper discuss in this episode is "#Yourpalaeolife: Interrogating the Status of Fieldwork Among Early Career Palaeontology Researchers" by Harriett Nuttall published in Ecology and Evolution in July 2026 https://doi.org/10.1002/ece3.74032

We need your support to be able to continue creating The Fossil Files. To get access to exclusive bonus episodes, you can find us on Patreon https://www.patreon.com/cw/FossilFiles

Sounds play such an important ecological role, but palaeontologists have always had to use their imagination when reconstructing the sound of extinct landscapes: Until now! For the first time a team of scientists have reconstructed the sound of a whole palaeo-community. Using fossil insect wings and some technological approaches to modern animals, the team were able to use physics and AI models to reconstruct the acoustic landscape of a Jurassic forest peppered with the calls of insects. Were the animals avoiding predators or just talking to each other? Listen in and find out.

This week's paper is "Reconstruction of an extinct soundscape reveals ultrasonic communication in the Jurassic" by Jun-Jie Gu, Fernando Montealegre-Zapata and colleagues published in Proceedings of the National Academy of Sciences in August 2026 https://doi.org/10.1073/pnas.2615107123

We also provide some updates from previous episodes:
#5 "Were Neanderthals the first fossil collectors" updated with Roman findings https://doi.org/10.1017/S0068113X26100749
#30 "How can we reconstruct the smell of extinct organisms" smells different using new data from fishes https://doi.org/10.1098/rspb.2025.3277
#25 "A dinosaur covered in porcupine spines & the earliest fossil cloaca" gets a new friend with the discovery of an early mammal cloaca https://doi.org/10.1016/j.isci.2026.116752
And the most controversial of all #4 "Is de-extinction a scam?", well it looks more likely given what got left out when the paper finally came out https://doi.org/10.1016/j.xgen.2026.101306

Widescreen art by Zuo Xiaoran