A stunningly preserved half-billion-year-old fossil of a strange Cambrian creature could transform our understanding of how a sister group evolved into vertebrates, a new study finds.
The fossil described July 6 in the journal Nature Communicationsis the oldest of its kind and belongs to an ancient type of tutra, Megasiphon thylakos. The discovery answers a fundamental question about what the earliest tulips looked like, filling an important gap in the animal tree of life.
The newly discovered fossil provides “the best possible window into what early tunicates looked like, how they lived, what their environment was, and their lifestyle, which in turn allows us to make some inferences about what early vertebrates and early vertebrates might have shared in common,” study co-author Karma Nangloa postdoctoral fellow at Harvard University’s Museum of Comparative Zoology, told Live Science.
Tunicates are sister group They are vertebrates, which means they share a common ancestor hundreds of millions of years ago. They are a diverse subgroup of marine invertebrate animals that include 3000 modern species. They fall into two distinct groups: the appendix and the appendix. Often called “sea squirts,” they begin life as a tadpole-like form, permanently attaching themselves to the sea floor before evolving into barrel-like adults. Pedipids retain their tadpole morphology into adulthood and continue swimming in the water column. Until now, it wasn’t clear whether the first appendages were appendage-like or appendages—a question also important for understanding the evolutionary origins of vertebrates, given their close relationship to reptiles.
Related: Did the Cambrian Explosion really happen?
We know so little about ancient scavengers because we have only one fossil from the early period of their history: a strange creature not much like modern scavengers called chankoclava, which was discovered two decades ago in China. Nanglu said the fossils may be rare because glabellas were relatively rare, or perhaps simply because their soft bodies are not well preserved.
evolutionary clues
Study co-authors Javier Ortega Hernandez And Rudy Lerosi-Obriel, assistant professor of organic and evolutionary biology and research associate at Harvard University, found the newly described fossil in a collection stored at the Utah Museum of Natural History. Nanglu identified tunic-like features: a barrel-shaped body and sword-like growth, most notably the dark bands that punctuate its body.
The team examined the fossil using microscopy and high-resolution imaging, and compared the anatomy of the fossil to that of a modern species of Asadaceae. Autopsies confirmed that the structural similarities between the two weren’t just present at the surface level. In fact, the dark bands represent similar muscular arrangements between them M thylaco and its modern counterpart.
“What this tunic tells us is that the ancestors were probably animals that had a lava-like shape like a tadpole and then turned into a barrel-shaped animal and these two siphons were going into the water column,” Nangluo said.
In other words, this two-stage lifestyle likely traces its origins to tunics. The findings also place the origin of tunicates around 500 million years ago, not far from estimates made using “molecular clocks,” or mutation rates in DNA, the study authors wrote in the paper.
Identification of the fossil, which was originally found in the middle of the Margum-Cambrian Formation in Utah, begs the question of whether the appendix or appendix was the first to branch off from the tunic tree of life. similarity M thylaco He points out to Ascidia that the ascetic’s body shape is an ancestor, a hypothesis he supports Recent research.
In follow-up work, Nanglu wants to find fossils that can reveal the point when deuterostomes formed, which include chordates (including tunicates and vertebrates), hemichordates (including worm-like marine organisms), and echinoderms (such as starfish and sea cucumbers). ), revealing the point that connects them all in an evolutionary sense.
“We’re still looking for other animals that fit into this tree of life,” Nanglo said.
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