Life underground: Burrowing in prehistoric times

A comprehensive review of fossils, some of which were discovered within the framework of the ongoing BROMACKER research project, reveals the origin and early evolution of vertebrate burrowing behaviour and provides new insights into the impact of climate change.

The ability to live underground is widespread among continental vertebrates, so understanding the origin and early evolution of fossorial vertebrates and the architecture and function of the burrows they excavate is an important component of the history of Life on Earth.

Dr. Lorenzo Marchetti and his colleagues, mostly from the Museum für Naturkunde Berlin, analysed not only the fossil bones and trace fossils during a large interval of time – from Devonian to Triassic, but also compared their lifestyle – burrowing behaviours of the animals, their geographic provenance and discussed it in the frame of climate change. The new results show an older appearance of several features related to the burrowing behaviour and their relationship with global warming and mass extinctions. These results are published in the scientific journal Earth-Science Reviews.

After a short overview of convergent morphological and behavioural adaptations seen in modern fossorial taxa and the diversity of extant vertebrate burrows, the team reviews the fossil record of inferred vertebrate burrows and fossorial vertebrates from the Devonian to the Triassic. Results highlight a probable Devonian earliest occurrence of fossoriality in continental vertebrates (Dipnoi) and a Carboniferous earliest occurrence of fossoriality in tetrapods (Recumbirostra).

During the Devonian-Carboniferous, burrows were probably used primarily for aestivation or temporary shelter and evidence of fossoriality is restricted so far to European and North American localities. During the Permian, fossoriality became geographically widespread and developed in new, distantly-related vertebrate lineages, such as diapsids and synapsids. Additionally, there was a size increase and all the main structural features of sub-vertical and sub-horizontal burrows were acquired, as well as the probable use of burrows as permanent shelters or for breeding. It is evidenced how the radiation of fossorial forms and increase in abundance and complexity of burrows are contemporaneous with climatic crises such as the Cisuralian aridification, culminating in the Artinskian Warming Event (AWE), and the end-Guadalupian and end-Permian extinction events.

After the end-Permian mass extinction, vertebrate fossoriality became a common and widespread feature of continental environments and in more distal floodplain areas, probably as a consequence of changing fluvial regimes. During the Triassic, fossoriality is recorded in even more groups, such as Procolophonidae and Temnospondyli. The first definite complex burrows used as permanent shelters appeared as early as the Early Triassic, and evidence of shared burrow use by different clades appears, suggesting an emerging role of burrowers as ecosystem engineers.

Publication: L. Marchetti, M.J. MacDougall, M. Buchwitz, A. Canoville, M. Herde, C.F. Kammerer and J. Fröbisch. Origin and early evolution of vertebrate burrowing behavior. Earth-Science Reviews 250 (2024). https://doi.org/10.1016/j.earscirev.2024.104702