Fairy shrimp taxa: use as a chronological tool

What is it about?

Fairy shrimp is a group of small, primitive crustaceans that retain ancient morphology and ecology. In particular, the family Chirocephalidae distributed in the Northern Hemisphere is a freshwater taxon with a long evolutionary history. According to the authors' recent research, this taxon emerged more than 100 million years ago and has survived the Mesozoic. Therefore, the authors utilised this taxon as a chronological indicator to investigate changes in the ancient freshwater's geographical distribution.

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Photo by Jean-Baptiste Lefevre on Unsplash

Photo by Jean-Baptiste Lefevre on Unsplash

Why is it important?

Small water bodies often have short lifespans and eventually disappear due to the overgrowth of aquatic plants and sediments on the bottom. However, refugia (a place where species survived locally in an environment in which a wide range of species became extinct, such as during the Ice Age) formed along the shores of large lakes can be crucial for the survival of fairy shrimp in such environments. While lake shorelines move as the lake grows and declines, lakeshore fairy shrimp habitats remain there, which reflects the changes in the geographical distribution of freshwater on a global scale. For example, we identified two fairy shrimp populations in small water bodies formed within Olkhon Island on Lake Baikal. The first population is located on the northwestern coast and is morphologically and genetically closely related to the Gobi Steppe population of Mongolia. The second population is endemic to Olkhon and found in its inland waters. Based on the fossil record and genetic distances, the world's fairy shrimp differentiated time approximately 140 million years ago. However, Lake Baikal formed at most 25 to 30 million years ago.

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