In another fascinating snapshot from deep time, an international team of paleontologists has reported the discovery of specimens of a minuscule crustacean that dates back to the Cretaceous (about 100 million years ago), conserved in samples of amber from Myanmar.

The most spectacular find is a single female, which turns out on closer examination to contain giant sperm cells in its reproductive tractM

Ostracods have been around for 500 million years, and thousands of modern species have been described.

Over the past 5 years, hundreds of previously unknown species have been described based on these inclusions.

The images revealed astonishing details of the anatomy of these animals, ranging from their tiny limbs to their reproductive organs.

“The complexity of the reproductive system in these specimens raises the question of whether the investment in giant sperm cells might represent an evolutionarily stable strategy, says Matzke-Karasz.

“In order to prove that the use of giant sperm is not an extravagant whim on the part of evolution, but a viable strategy that can confer an enduring advantage that enables species to survive for long periods of time, we must establish when this mode of reproduction first appeared,” says Matzke-Karasz.

The oldest known ostracod sperm (prior to the new discovery) are 17 million years old, and the previous record age, 50 Myr, was held by a species of worm.

The fact that animals had already developed giant sperm 100 million years ago implies that this reproductive strategy can indeed be successful in the (very) long term, Matzke-Karasz points out.

Reference: “Exceptional preservation of reproductive organs and giant sperm in Cretaceous ostracods” by He Wang, Renate Matzke-Karasz, David J.

Horne, Xiangdong Zhao, Meizhen Cao, Haichun Zhang and Bo Wang, 16 September 2020, Proceedings of the Royal Society B.

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September 12, 2020