The oldest sperm ever found on Earth has been discovered in a piece of amber along with several ostracods from approximately 100 million years ago. The ostracod is a crustacean that has a bivalve shell protecting its body. It is very tiny as it only grows a few tenths of an inch in length. However, its sperm cells are surprisingly huge with the longest ever recorded measuring 0.46 inches – much longer than the ostracod itself.
The amber in which the sperm and ostracods were found was only around the size of a postage stamp and was discovered in a mine located in the northern part of Myanmar. Inside of the amber were 39 ostracods with 31 of them belonging to a previously unknown species called Myanmarcypris hui that measured just 0.02 inches in length. The Myanmarcypris hui species lived along the coasts of Myanmar and inland waters surrounded by many trees that created large amounts of resin. (Pictures of the Myanmarcypris hui species can be seen here.)
The most interesting find was an adult female whose soft tissues were still well-preserved and they discovered four small eggs as well as sperm inside of her. A reconstructed three-dimensional image was created of the female ostracod by He Wang who is a paleontologist and postdoctoral researcher at the Chinese Academy of Science. He then sent the image to an ostracod expert and paleontologist at Ludwig Maximilian University of Munich named Renate Matzke-Karasz who congratulated Wang on reconstructing the world’s oldest animal sperm. The researchers estimated that the sperm each measured 200 micrometers in length.
Prior to this discovery, the oldest sperm from an ostracod was 17 million years old and the world’s oldest sperm from any type of animal dated back approximately 50 million years and was found in a worm cocoon in Antarctica.
Matzke-Karasz said that an animal having giant sperm actually takes a lot of energy in order to mate with a female, specifically making enough room within the reproductive tract. “You might think that this doesn't make sense from an evolutionary standpoint,” she stated, adding, “But in ostracods, it seemed to work for more than 100 million years.”
Their study was published in the journal Proceedings of the Royal Academy B and can be read in full here.
The fact that they were able to discover soft tissue still well-preserved from ostracods in amber was a pretty rare find so the researchers are hoping to locate more specimens in fossilized amber dating back to that time period. We’ll keep our eyes open for any new giant sperm stories.