Scientists reported that fossilized sperm discovered inside a crustacean such as a pestle trapped in amber 100 million years ago may be the oldest.
The female ostracod was detected by an international team of paleontologists. They believe it was found shortly before it was trapped in resin.
Their findings, published in Proceedings of the Royal Society B, Providing “an extremely rare opportunity”, he added, to learn more about the development of the reproductive process.
By far the oldest known fossil sperm from Antarctica lived inside a worm cocoon 50 million years old.
Crustaceans, a new species called Myanmarcyparis Hui, are now believed to live in coastal and inland waters in Myanmar, surrounded by trees producing large amounts of resin.
A geologist from Ludwig-Maximilions-Universiteet (LMU) in Munich, Drs. A team led by Renate Matteke-Karz analyzed 39 ostracodes trapped in a small piece of amber for 3D X-ray reconstruction.
Researchers found that the ripe giant sperm is stored in a pair of receptors inside the female ostracode, waiting for the egg to mature, adding that it may also be the earliest direct evidence of a complete insemination.
Most animals produce large amounts of very small sperm to increase the likelihood of fertilization. But some, such as fruit flies and modern-day ostrodods, produce small numbers of oversized sperm, which are many times longer than the animal.
In these cases, researchers say, the possibility of fertilization of an egg may increase with the size of the sperm cell. Upon understanding the evolution of such giant sperm, the team can shed light on what it describes as “ancient and advanced examples of evolutionary expertise”.
Dr. Matzke-Karz said: “The most important part of our story is that we can now show that using giant sperm for reproduction is something that can last a long time in Earth’s history.
“At first, we weren’t sure that if animals ‘switched’ to using these giant sperm at a certain point in their evolutionary history, they would go extinct very quickly.
“Ultimately, these are huge costs for animals. Large sperm must be produced, reproductive organs are much larger than other species, they take up a lot of space in the animal, and mating lasts a long time.
“This is a lot of biological energy that must be allocated for reproduction – so you might think that it makes no sense from an evolutionary point of view.
“But in Ostracodes, it went on to work for over 100 million years.”
He said: “From an evolutionary point of view, sexual reproduction with the aid of giant sperm should, therefore, be a well-conceived strategy.”