August 2025: Early Amphibian Micropholis stowi Huxley

SNSB-BSPG 1934 VIII 43
Early Triassic, c. 245 Ma
Donnybrook, South Africa

Modern amphibians are divided into three groups: the gymnophionans (caudate), the caudates (salamanders), and the anurans (frogs). Frogs are by far the most species-rich of these (more than 7,800 of the almost 9,000 current amphibian species) and one of the most highly specialized groups of amphibians. Due to the significant anatomical differences between modern groups, it was long uncertain whether all modern amphibians are descendants from a common ancestor or whether they descended from different ancient amphibian groups. We now know that modern amphibians have a common ancestor, and this ancestor belongs to the group of temnospondyls, an important evolutionary lineage within the amphibians, which also includes Micropholis (Fig. 1). The ancient representatives of the temnospondyls (excluding modern lineages) occur from the Early Carboniferous (about 350 million years ago) to the Late Early Cretaceous (about 115 million years ago), with the group reaching its peak in the Triassic period. Anatomically, they resemble most modern salamanders, although the skull is much more strongly ossified and still has a parietal foramen on the upper surface (Fig. 2).

Like most temnospondyls, Micropholis was a semiaquatic animal that lived primarily in bodies of water such as ponds, lakes, and rivers, feeding on small fish and invertebrates. It is striking that mass aggregations of such temnospondyls, such as the one on display here, are quite common in South African sites. The explanation for this can be found in the climate of the time: During the Early Triassic period, the supercontinent Pangaea, which united all present-day continents, had reached its greatest integration. This enormous accumulation of continental mass, surrounded by a vast ocean, led to extreme weather conditions that turned large parts of the continent’s interior into deserts, while in many coastal areas, torrential rains alternated with periods of extreme drought. During the dry periods, small ponds and lakes often dried up. The amphibians living in them retreated to ever-shrinking bodies of water until these, too, dried out, leaving the densely packed carcasses of the animals behind—and in ideal cases, they turned into fossils.

Oliver Rauhut