Photo over a gorge with snowclad mountains in the background

Salaany Gol in western Mongolia. The light-coloured rocks visible on either side of the gorge are remnants of a 520 miilion year old Cambrian reef. Photo: Tim Topper

Engineering the Cambrian explosion: The role of reefs in early animal evolution

Often called the rainforests of the oceans, coral reefs are one of the most diverse ecosystems on Earth. Reefs, in various shapes and forms, have been present in Earth’s ocean for over 500 million years, appearing together with the first animal communities. But what was their role in the emergence and diversification of the first animals on our planet?

Project overview

Project period: 2021 - 2026

Participating departments from the museum: Palaeobiology

One of the defining events in the evolutionary history of life on Earth was the radiation of animals during the late Ediacaran and early Cambrian (~555 to 520 Ma before the present). One of the most significant innovations was the evolution and development of the first animal dominated reefs. Despite their importance as biodiversity hot spots in modern oceans, very little is known about the relationships of early reef environments and the diversification of the first animals in the Cambrian. The aim of the project is to explore the role of the first animal-built reefs as drivers of animal evolution during the Cambrian radiation.

Salaany Gol in western Mongolia. The light-coloured rocks visible on either side of the gorge are remnants of a 520 miilion year old Cambrian reef. Photo: Tim Topper

Project description

The global radiation of animals during the late Ediacaran and early Cambrian is perhaps the most important event in the evolutionary history of life on Earth. Many hypotheses have been proposed to explain the triggers behind this explosion; however, the impact of reefs on early animal evolution has not been quantified.

Reefs in time and space

Modern coral reefs, with their complex mosaic of environments and substrates, are some of the most diverse ecosystems on Earth. Despite the repeated collapse of reefs, reef ecosystems have been an almost ubiquitous part of the marine realm throughout the Phanerozoic. In the Cambrian, reefs were built by archaeocyathid-sponges together with a range of microbial organisms. Comparable to modern reefs, Cambrian reef ecosystems were settings of high diversity, especially in Small Shelly Fossils (SSFs).

Small Shelly Fossils and the Cambrian explosion

One of our best windows into the Cambrian explosion are SSFs. Small Shelly Fossils are a diverse assemblage of small (usually 0.5- 2 mm) skeletal fossils that are etched from carbonate rocks by weak acids. The group contains the remains of a range of animals, such as brachiopods and molluscs, but many are problematic and may represent basal members or intermediary stages between living phyla.

Questions to investigate

SSFs are common in reef ecosystems, but did they have habitat preferences and to what extent could they exploit these environments?
How did reef architecture change over time and what effects did this have on animal diversity and evolution?

Financial support

Research support by Vetenskapsrådet (VR, 2017 – 2021) and (VR, 2021-2026).

Selected publications

Topper, T., Betts, M.J., Dorjnamjaa, D., Li, G., Li, L., Altanshagai, G., Enkhbaatar, B. and Skovsted, C.B., 2022. Locating the BACE of the Cambrian: Bayan Gol in southwestern Mongolia and global correlation of the Ediacaran–Cambrian boundary. Earth-Science Reviews, 229, 104017. doi.org/10.1016/j.earscirev.2022.104017 External link.
Li, L., Skovsted, C.B. and Topper, T.P., 2022. Deep origin of the crossed‐lamellar microstructure in early Cambrian molluscs. Palaeontology, 65(4), e12620. doi.org/10.1111/pala.12620 External link.
Li, L., Topper, T.P., Betts, M.J., Dorjnamjaa, D., Altanshagai, G., Enkhbaatar, B., Li, G. and Skovsted, C.B., 2023. Calcitic shells in the aragonite sea of the earliest Cambrian. Geology, 51(1), 8-12. doi.org/10.1130/G50533.1 External link.
Li, L., Betts, M.J., Yun, H., Pan, B., Topper, T.P., Li, G., Zhang, X. and Skovsted, C.B., 2023. Fibrous or Prismatic? A Comparison of the Lamello-Fibrillar Nacre in Early Cambrian and Modern Lophotrochozoans. Biology, 12(1), 113. doi.org/10.3390/biology12010113 External link.
Goñi, I., Skovsted, C.B., Li, L., Li, G., Betts, M.J., Dorjnamjaa, D., Altanshagai, G., Enkhbaatar, B. and Topper, T.P., 2023. New palaeoscolecid plates from the Cambrian Stage 3 of northern Mongolia. Acta Palaeontologica Polonica, 68. doi.org/10.4202/app.01030.2022