Scientists have found what appears to be a fossilized sperm cell from an ancient marine species. This is the oldest and biggest fossil of a sperm ever found, at least of its kind.
European specialists recently discovered a humongous sperm cell in a fossilized female ostracod, or mussel/seed shrimp, winding up to a possibility that the specimen could have had its final mating spree before approaching its death and turning into stone.
The ancient sperm has been dated to be from around the early Miocene epoch 23 million and 16 million years ago.
These ostracods are tiny crustaceans around one mm in size with flat bodies encased in a bivalve-like shell with tiny appendages sticking out, resembling a translucent bean. In some cases though, the sperm is even longer than the male ostracod, about six times the length of the shrimp itself. Therefore, how can one gargantuan gamete fit in a male ostracod's miniscule body? The sperm, which resemble an intricate spin of thin rope, coils itself tightly to fit into the male's testis.
The ostracod is just one of the few organisms that produce "giant sperms," along with the fruit flies of the Drosophila bifurca species, which hold the record of having the longest sperm (two inches in length) and some moth species, to name a few.
The fossil containing the sperm was actually excavated in 1988 by a team of scientists led by professor Mike Archer of the University of New South Wales (UNSW) School of Biological, Earth and Environmental Sciences, but it was only until recently that scientists such as John Neil, a specialist ostracod researcher at La Trobe University, found out that it contained soft tissues, an indication that there is more to unearth in the almost three-decade-old discovery.
The huge petrified sperm was recovered from the Riversleigh World Heritage Fossil Site in Australia, a renowned hotbed of extraordinary primitive animals in the continent such as ancient giant platypuses and flesh-eating kangaroos.
Having been discovered in a cave where bats thrived a million years ago, the fossil shrimp was buried in heaps of guano, hence preserving even the finest details of the tiny shrimp's structure, particularly its reproductive organs.
It was then that Renate Matzke-Karasz of Ludwig Maximilian University of Munich, Germany and Paul Tafforeau of the European Synchrotron Radiation Facility in Grenoble, France that took interest on the specimen and came up with a study, which was published in the Proceedings of the Royal Society B: Biological Sciences journal.
"[T]he discovery of fossil sperm, complete with sperm nuclei, was totally unexpected. It now makes us wonder what other types of extraordinary preservation await discovery in these deposits," said Archer.
Ostracods' sexual patterns are so odd, even the scientists are baffled on how they actually reproduce. Some males have two penes to match a female's two genital openings, while some females do not mate with another male.
"We can distinguish the typical helical organization of the organelles in the sperm cell, which makes its surface look like a hawser or cable," said Matzke-Karasz in a statement. "But the most astounding aspect of our findings is that it strongly suggests that the mode of reproduction in these tiny crustaceans has remained virtually unchanged to this day."
