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The oldest animal sperm: scientists discover a 100-million-year-old giant sperm in a fossil

Yet once again nature, science, and chance align together to create a magnificent discovery. Almost 100 million years ago and during what researchers label as “the Cretaceous period”, two ostracods living in Myanmar’s coastal lagoon got trapped inside the resin of a tree. Thus, the cocoon preserved them and the sperm as some sort of time capsule for the next millennia.

A Spectacular Find

Though some might consider this discovery, it is a big deal in the science world. Since the soft tissue decomposes quickly and easily, the discovery of any kind of ancient sperm is rare. However, the recent years were kind to science in this department. In 2014 and 2015, scientists discovered 17-million-year-old ostracod sperm and 50-million-year-old worm sperm respectively. On the other hand, this spectacular finding is considered the oldest ever dating back to the time of the dinosaurs. Furthermore, preserving any species in such a delicate and perfect manner is very rare. Therefore, researchers are considering it as “the oldest unequivocal fossil animal sperm.”

Shattering expectations

When Dave Horne, a micropaleontologist at the Queen Mary University of London, and his colleagues examined inside some of the tiny shelled animals, they were surprised. “We knew from looking at the piece of amber with an ordinary light microscope that there were antennae and legs sticking out of the shell, so we were hopeful of finding internal organs,” Horne says. If delicate parts like legs and antennae are preserved, it’s likely that other soft parts are too, he says. “But what we saw … exceeded expectations.”

They discoveerd that the layout of internal sex organs mirror that of their modern-day counterparts. Furthermore, they found a preserved giant sperm packing her seminal receptacles. In ostracods, a giant sperm is often the result of “competition between sperms of two or more males trying to fertilize the eggs of the same female,” Horne says. “This must be a highly successful reproductive strategy to have lasted for a hundred million years.”

The study also shed light on the male clasper, sperm pumps, hemipenes, eggs along with the female seminal receptacles with giant sperm. Thus, this discovery provides scientists with “unprecedented insights into an unexpectedly ancient and advanced instance of evolutionary specialization.”

A successful strategy

The mere fact that a sperm remained intact after millions of years is proof of successful long term reproductive strategy. Furthermore, Renate Matzke-Karasz, a geobiologist at Ludwig-Maximilians-Universitaet who was involved in the morphological analysis of the specimens stated that “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”.

The discovery will open a window to the ancient lives that lived 100 million years ago. Though small, it will serve as a platform for new questions and answers. Thus, it will serve science and scientists in their journey to discover the world’s secrets.


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