May 15, 2014
Researchers Discover World’s Oldest Petrified Sperm In Australian Cave
redOrbit Staff & Wire Reports – Your Universe Online
An international team of researchers working at a fossil site in northwest Queensland, Australia have come across a remarkable, unusual and perhaps even somewhat icky find – the world’s oldest petrified sperm sample.According to reports published by NBC News, the sperm came from a tiny crustacean known as an ostracod and dates back somewhere between 16 million and 23 million years to the early Miocene epoch. An ostracod, also known as a seed shrimp, is a mussel-like bivalve that has tiny appendages and is typically only a few millimeters long.
Despite the shrimp’s small size, ostracod sperm can be as much as one centimeter (0.4 inches) in length. It is believed to have survived so long in its cave environment thanks to bat guano falling into the water to help preserve the cells, explained Stephanie Pappas of Live Science. Seed shrimp have once lived within waters of that cave, she added.
“We can distinguish the typical helical organization of the organelles in the sperm cell, which makes its surface look like a hawser or cable,” explained lead author Renate Matzke-Karasz, a geobiologist at Ludwig-Maximilian University (LMU) in Munich, Germany. “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.”
Matzke-Karasz and her colleagues, who have published their findings in the journal Proceedings of the Royal Society B, analyzed 66 ostracod specimens at the Riversleigh site in Queensland using X-ray tomography, which allowed them to examine the inside of the fossils in three dimensions. They were able to locate the fossilized sperm cells in five of those specimens, according to Pappas.
Matzke-Karasz told Jennifer Viegas of Discovery that ostracods have inhabited the Earth for at least 500 million years, partially due to the fact that they have exceptionally strong sperm that resembles angel hair pasta. While the sperm is technically less than half an inch long, it is “giant” when compared to the size of the creature producing it, she added.
The study authors also found preserved ducts of the female seed shrimp anatomy through which these sperm cells would enter their bodies, Pappas reported. The ducts are spiral in shape and even longer than the ostracod sperm, occasionally reaching lengths of four-times that of a female ostracod’s body.
Analysis of the sperm and the reproductive ducts provides evidence that there has been little change in these body parts over the past several million years, and that they evolved together. Matzke-Karasz told LiveScience that the discovery “suggests that their mode of reproduction represents a functionally successful model.”
Previously, the oldest-known seed shrimp sperm was just a few thousand years old, and while the new ostracod seed is the oldest petrified sperm cells ever discovered, one other specimen is actually older: one belonging to an insect-like springtail that was trapped in amber roughly 40 million years ago. However, Pappas notes that because amber often preserves soft tissue while rock usually does not, the two fossilization methods are viewed differently.