Beneath the waves, there are strange, almost alien creatures that raise questions about the evolution of life on Earth and where we began. Answers can be hidden tunicates.
Tunicates are filter feeders that include sea squirts and salps. Very common ascidiacean These species are stationary and are attached to rocks or the bottom of the sea, while appendicular colors swimming freely. However, they all reproduce as larvae that resemble tadpoles. Running tunicates begin to grow into something that looks like a large larva. The others eventually grow to the surface and suck their tails while transforming into two siphons.
Although this is surprising, there is strong evidence that tunicates are close relatives of mammals, but mystery surrounds them. How did it change, and where did it come from? 500 million year old fossils are now telling us more about the evolution of these amazing species.
Evolutionary enigma
It was discovered by evolutionist Karma Nanglu of Harvard University, now known as Megasiphon thylakos has begun to answer some of the unknowns about tunicates. Although they have been around since the Early Cambrian, tunicates are rarely found in the fossil record. Well maintained M. thylakos the model provides more insight into their evolution and their relationship with vertebrates such as humans.
“[The fossil] showing the difference between [free swimming] appendicularians and all other tunicates occurred 50 million years earlier than currently expected,” Nanglu and his research team said in a recently published study. Nature. “Finally, M. thylakos shows that the main components of the modern tunicate system were established before the Cambrian explosion.
Because tunicates are not found in prehistoric times, it is unclear whether they originated as ascidiaceans, or as appendicularians. Unfortunately, the vestiges of the tunicate that already exist, Shankouclava aningense, it is unknown. It has some ascidiacean features but lacks some features that define ascidiaceans, such as feeding siphons.
There are two theories about the evolution of tunicates. The first suggests that their ancestral forms were mobile, such as appendicularians, and that sessile species descended from mobile ancestors. A second hypothesis states that the genetic makeup of modern tunicates makes it unclear whether their ancestral form was motile or sessile.
New evidence from ancient rocks
Because of its visual features, especially the shape of the tube and siphons that are very similar to modern ascidiaceans, M. thylakos fossils may indicate that ancient tunicates began as sedentary creatures.
What was also noticeable were the shiny black laces that ran down her body. Nanglu and his team took pictures of the fossils and compared them to samples of the tunicate that existed before. Ciona intestinalis. It turned out that the groups looked very similar to the muscles C. intestines they use it to open and close their siphons when feeding. The M. thylakos the body system that is now thought to have emerged after the Cambrian Explosion, which may have been the greatest explosion of new life the Earth has ever seen.
Where really the basis of M. thylakos’ a body embedded in a rock or under the sea is not visible due to decay. Despite this, they are very similar to existing tunicates C. intestines Nanglu has confirmed that the first tunicates were rare, like their descendants.
Unexpected relatives
So how can tunicates be related to us? Like humans, tunicates belong to a phylum Chordates. Chordates share several features in common, but the most common is the flexible rod, support, or notochord, which runs down the length of the animal. There are only two groups that are not born with vertebrates – tunicates and cephalochordates. Cephalochordates, viz lancelets, were considered to be the most closely related to vertebrates because they looked more complex and similar. This was a thought until 2006 education found that tunicates are closer to mammals than cephalochordates.
“Tunicates are a very important group of marine mammals, phylogenetically as a sister group to Vertebrata, which makes them important to uncover our origins,” Nanglu said in the study.
Although the tunicates are still a mystery, many fossils are probably out there, just waiting to surface in what was once an ancient ocean. They may have a lot to say about where they—and we—came from.
Nature, 2023. DOI: 10.1038/s41467-023-39012-4 (About DOIs).
Elizabeth Rayne is a creature that writes. His work has appeared on SYFY WIRE, Space.com, Live Science, Grunge, Den of Geek, and Forbidden Futures. When he’s not writing, he can move, draw, or play like someone no one has ever heard of. Follow him on Twitter @quothravenrayne.