The oldest sperm thus far has been discovered in a piece of amber that solidified over millions of years.
Scientists believe that the amber solidified when behemoths like Spinosaurus dominated the Earth.
The sperm was found inside a disc of amber located in a mine in northern Myanmar. Scientists found 39 ostracods – 31 of which belong to a never-before-seen species now called Myanmarcypris hui – in the amber.
It is discovered that the giant sperm comes from a more miniscule creature than the toothy Spinosaurus, also known as an ostracod.
An ostracod is known as a class of crustacean or, colloquially, as "seed shrimp”. They typically grow just a few tenths of an inch long, and have a bivalve shell protecting its body. There are thousands of ostracod species alive today, including many who boast giant sperm cells which can reach a jaw-dropping 11.8 millimeters.
Scientists have now found this enormous sperm in an ostracod, which is from the Cretaceous period a 100-million years ago.
This recently discovered sperm is the oldest unambiguous example of any animal sperm by 50-million years.
Researchers discovered that the female's soft tissues were preserved. This included four tiny eggs (each just 50 micrometers in diameter) and a mass of something within the female’s seminal receptacles.
Only a few of the ostracods in the amber piece could be studied using light microscopy, including an individual of the new species, Myanmarcypris hui.
The oldest confirmed animal sperm found before the recent discovery dated to about 50-million years ago, and was found in a worm cocoon from Antarctica.
The giant sperm required lots of energy to make, and lots of space within the animal devoted to the reproductive tract.
He Wang, a paleontologist and postdoctoral researcher at the Chinese Academy of Science, reconstructed a three-dimensional image of this mass, which was sent to Renate Matzke-Karasz, an ostracod expert and paleontologist at Ludwig Maximilian University of Munich, only by using computed tomography.
Matzke-Karasz said; "I immediately congratulated him on having reconstructed the oldest animal sperm."
There are only 20 ostracod soft tissues preserved by fossilization. "It was surprising to find these aquatic animals in fossilized plant resin, so the next step is to seek out other amber specimens from other time periods that might contain ostracods. You might think that this doesn't make sense from an evolutionary standpoint," she said. "But in ostracods, it seemed to work for more than 100-million years."