How Synapsids took the land

The largest extinction event in the Earth's history is largely known because of the fossils of marine invertebrates. A scientist from the Museum für Naturkunde Berlin investigated what happened to vertebrates on land.
In 2010, the Alexander von Humboldt Foundation awarded the Sofja Kovalevskaja Prize to the evolutionary biologist Jörg Fröbisch, enabling him to establish a junior research group and to investigate the initial evolution and diversification of the evolutionary line of mammals, the so-called synapsids, in a five-year research project.

Tracking with CT

The early synapsids are among the first vertebrates to be fully adapted to life on land. Synapsids include not only mammals but also their ancestors. In the project, Fröbisch focused on this extinct line, the so-called non-mammalian synapsids. At 320 million years, this group is as old as reptiles. Mammals only appeared around 200 million years ago. "Here we have the first 120 million years of evolutionary history of the mammalian clade that we wanted to investigate in detail," says Fröbisch.
In this time interval, complex terrestrial ecosystems with diverse species and lifestyles developed on the supercontinent Pangaea: Synapsids from mole to elephant size had a herbivorous or carnivorous, burrowing, climbing or semiaquatic lifestyle.
Fröbisch's team carried out research excavations in Brazil and Russia and applied modern statistical analysis to compile a family tree of synapsids and to investigate the biodiversity of past ecosystems. Using computer tomography, the researchers also recorded the internal and hence previously hidden structures of the fossils in order to record the morphological diversity among synapsids.

Extinction events and survivors

"We wanted to know how the diversity of synapsids and terrestrial ecosystems evolved across the Permian-Triassic mass extinction event," says Fröbisch. In this extinction about 250 million years ago, 80 to 90 percent of all species on Earth disappeared. The team focused on the main surviving groups and how they were affected in species numbers and morphological diversity.
The investigations showed that the Permian-Triassic mass extinction was not the only one: The well-known transition from the pelycosaurs (early from their appearance more reptile-like synapsids) to the more mammal-like therapsids, about 270 million years ago, was also associated with an extinction event.
The Sofja Kovalevskaja Award of the Alexander von Humboldt Foundation enables outstanding young scientists from abroad to set up a research group and carry out innovative projects at a chosen research institution in Germany over a period of five years. The awad was endowed with around 1.5 million euros. "The project has been completed, but the research goes on," says Fröbisch. The evolutionary biologist is continuing his research into the evolutionary history of synapsids and the excavations in Brazil.