Although limited in size, Antarctica has ice-free areas that play a crucial role in understanding this region’s ancient history. Fossils found in these regions reveal insights into the climate and diverse life forms that once thrived there. Therefore, these areas provide a window into the continent’s past, helping scientists to piece together how the climate and biodiversity of Antarctic environments have transformed over millions of years. Also, the study of these ice-free areas can provide information on how these environments have evolved and adapted under changing environmental conditions.
During expeditions in the austral summers of 2011, 2012, and 2013, a group of Argentinian and Swedish researchers made an interesting discovery in Seymour Island, Antarctica Peninsula (64°14’S, 56°37’W). The team found the remains of a frog-like creature from sediment samples of the Eocene period, dating around 40 million years ago (Figure 1). The remains consisted of a fossil ilium which can be assigned to a lissamphibian order Anura, and a sculptured skull bone that can be most probably assigned a hyperossified anuran (Figure 2). These samples were then transported, and several pictures were taken with specialized equipment for building a 3D model of the bone fragments and detailed analysis. The remains can be found in the Swedish Museum of Natural History in Stockholm where are stored until today.
Figure 1. Geological time scale scheme (left) and a map of how the Antarctic Continent would look like during the Paleogene and Eocene periods (right). The red circles indicate the location where Seymour Island would have been. Image credit Ray Troll’s creative approach (left) and Reguero et al. (2013) (right).
Based on the characteristics of the fossils, the specimens were assigned to the South American genus Calyptocephalla, of the family Calyptocephalellidae, also known as helmeted frogs. Fossils of calyptocephalellids are widely known from Patagonia since the Late Cretaceous, but became extinct in Argentine Patagonia during the Miocene, probably caused by the rise of the Andes leading to a decrease of humidity. This hypothesis is supported by the occurrence of this family that survived to the present day in a temperate and humid refuge in the central Chilean Andes. Figure 3 provides an illustration of how the environment would look like 40 million years ago in the Antarctic Peninsula. Moreover, this finding supports Gondwana cosmopolitanism, which refers to the widespread distribution of certain organisms across different continents that were once part of the supercontinent Gondwana.
Figure 2. Images of the fossils of an ilium (left) and skull bone (right) of an anuran. Image credit to the article featured in this post.
Figure 3: Reconstruction of the Eocene environment in which the Calyptocephalla helmeted frog inhabited. Image credit to the article featured in this post.
Source: Mörs T., Reguero M., & Vasilyan D. (2020) First fossil frog from Antarctica: implications for Eocene high latitude climate conditions and Gondwanan cosmopolitanism of Australobatrachia. Scientific Reports 10: 5051. DOI: https://doi.org/10.1038/s41598-020-61973-5
Author: Ricardo Matias