The oldest human ancestor in 540 million year old rock

The oldest human ancestor that lived 540 million years ago was shaped like a sack and had no anus.

Human ancestors had mouths that took up most of their bodies and no anus. Photo: Jian Han/Northwest University, China.

Our oldest fossil ancestor is a deuterostome discovered in 540-million-year-old limestone in central China, the International Business Times reports. The creature gave rise to a range of life forms that include today's starfish and sea squirts.

According to the study published in the journal Nature, the deuterostomes discovered are the earliest in this phylum. "Deuterostomes gave rise to a wide variety of animals, from humans to starfish to sea urchins. That level of diversity raises the question: What did the common ancestor of animals look like?" said Simon Conway Morris of the University of Cambridge in the UK, lead author of the study.

The 540-million-year-old fossil creature was very small, measuring only about 1.3 mm long, 0.8 mm wide and 0.9 mm high, with a very large mouth compared to the rest of its body, measuring 0.3-0.5 mm across. It also had four conical holes on each side.

"This is a landmark for deuterostomes, and the precursor to fish gills. Water flows through the gills and out the side of the animal," said Conway Morris.

This is a primitive way for animals to get rid of waste. The researchers were unable to identify an anus in any of the deuterostome specimens they found.

Finding primitive deuterostomes is a major step forward in the fossil record from very small, simple organisms that had to gather oxygen by diffusion to larger animals like fish that breathe through gills. “This is part of the answer to how complex things evolve,” Conway Morris said.

Forty-five specimens of deuterostomes were found in ancient limestone in Shaanxi Province, China. Researchers had to remove about three tons of limestone to retrieve the tiny fossils.

Deuterostomes have been discovered before, but none have been dated to 540 million years ago. The creatures were fossilized in a process called phosphate fossilization, in which phosphate molecules rapidly replace the creatures' body parts before they break down. The researchers are still unsure how old the creatures were.

According to VNE