2023-07-06 11:39:57
Artist’s reconstruction of Megasiphon thylakos – FRANZ ANTHONY
MADRID, 6 Jul. (EUROPA PRESS) –
Harvard scientists have described a new 500-million-year-old fossil of the wonderfully bizarre group of marine invertebrates, the tunicates.
In a new study in Nature Communicationspostdoctoral researcher Karma Nanglu and his team describe the new animal, named Megasiphon thylakos, which reveals that ancestral tunicates lived as stationary, filter-feeding adults and probably underwent metamorphosis from a tadpole-like larva.
Tunicates are truly bizarre creatures that come in all shapes and sizes with a wide variety of lifestyles. The basic shape of an adult tunicate is typically barrel-like with two siphons projecting from its body. One of the siphons sucks water with food particles through the suction, allowing the animal to feed using an internal basket-like filter device. After the animal feeds, the other siphon expels the water.
There are two main lineages of tunicates, ascidiaceans (often called “sea squirts”) and appendicularia. Most sea squirts begin life tadpole-like and mobile, then transform into a barrel-shaped adult with two siphons. They live their adult life attached to the seabed. On the contrary, the appendicular they retain the appearance of a tadpole as they grow into adults and are free-swimming in the upper waters.
“This idea that they start out as a tadpole-like larva that, when it’s ready to develop, basically butts its head off a rock, sticks to it, and starts metamorphosing by reabsorbing its own tail to become this being with two siphons. it’s just awesome,” says Nanglu it’s a statement.
Interestingly, tunicates are the closest relatives of vertebrates, which include fish, mammals, and even humans. It’s hard to imagine how this strange-looking creature could be related to vertebrates if it weren’t for that tadpole beginning. The Tunicate’s close relationship with vertebrates makes studying them critical to understanding our own evolutionary origins. Unfortunately, it’s not easy to do as tunicates are almost completely absent from the entire fossil record, with only a handful of fossils appearing convincingly as members of the group.
With so few fossils, scientists relied primarily on what could be learned from modern tunicate species. Because no one knew the morphology and ecology of the last common ancestor of tunicates, scientists could only hypothesize that it was a benthic animal with two siphons, like ascidiaceans, or a free-swimming animal like appendicularians. .
M. thylakos had all the basic features of an ascidiacean tunicate, a barrel-shaped body and two prominent siphon-shaped growths. But the feature that most caught the attention of the team were the dark bands that ran up and down the body of the fossil.
The high-powered images of M. thylakos allowed the researchers to perform a side-by-side comparison with a modern sea squirt. The researchers used dissected sections of the modern Ciona tunicate to identify the nature of Megasiphon’s dark bands. The comparisons revealed remarkable similarities between Ciona’s muscles, which allow the tunicate to open and close its siphons, and the dark bands observed in the 500-million-year-old fossil.
“Megasiphon’s morphology suggests to us that the ancestral lifestyle of tunicates involved a motionless adult filter-feeding with its large siphons,” Nanglu said. “It is so rare to find not just a tunicate fossil, but one that provides a unique and unparalleled insight into the early evolutionary origins of this enigmatic group.”
M. thylakos is the only soft tissue-preserving definitive tunicate fossil discovered to date. It is the oldest of its kind originating from the middle Cambrian Marjum Formation in Utah. The fossil was recognized as a tunicate by co-authors’ Research Associate Rudy Lerosey-Aubril and Professor Javier Ortega-Hernández (both in the Department of Organic and Evolutionary Biology) while visiting the Utah Museum of Natural History (UMNH). in 2019.
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