Based on a 480-million-year-old fossil (Calvapilosa kroegeri), scientists learned what a common ancestor of animals such as slugs, snails and squid looked like.
A reproduction of Calvapilosa shows what a primitive mollusk might have looked like
It was bulky and hairy, like patches of fingernails, which sounded like the toes of a hobbit. In fact, this is what scientists have outlined as the common ancestor of animals such as slugs, snails and squid.
The speculation is based on a fossilized mollusk that the researchers believe lived 480 million years ago. It is covered with short spines and has a fingernail-like shell on its head, and inside it is a tooth tongue, which is an organ that grows on the heads of most mollusks to help feed, and it also has 125 rows of teeth.
The researchers believe it was an early ancestor of many marine molluscs, and the finding suggests that the ancestors of all mollusks may have had the same appearance.
The study was published in Nature (click on the bottom left corner to read the original article). Jakob Vinther, a molecular paleontologist at Bristol University in the UK, said: "I think this discovered mollusk looks exactly like the ancestors of all mollusks 530 million years ago. ”
Although the larvae collected by Yale University were only 2 centimeters long, the researchers believe that the newly discovered mollusk once grew to 12 centimeters long. The name Calvapilosa kroegeri is derived from the hairy shell that covers its head, and the second half is a tribute to Björn Kröger, a paleontologist.
Calvapilosa kroegeri fossil, which preserves the feeding site (tooth tongue) and burrs that cover the whole body.
The new discovery has led to a better understanding of some of the fossils found in the past, suggesting that many of the ancient creatures (whose species are often debated due to the lack of detail) are also mollusks because their structure is very similar to that of this newly discovered creature. Vinther said: "We can think about the evolution of mollusks in combination with all the other fossils. ”
The study shows that halkieria, which has two hull-like plates, are also mollusks. Hastelloys are much older, and researchers believe the number of plates has increased over the course of evolution, with modern stone turtles (chitons) having 8 plates on their backs. Vinther said: "The animal we found is at the bottom of the branch where the stone turtle evolved. ”
A non-mollusk called Wiwaxia has scales and spikes, and the researchers further propose an evolutionary route in which the common ancestor of all molluscs had body spines, a single plate, and a tooth tongue before forming numerous branches that eventually formed a diversity of species such as snails, clams, and slugs.
Martin Smith, an invertebrate paleontologist at Durham University who was not involved in the study, found it very interesting. "This is a very important fossil," he said. There is a lot of controversy about the common ancestor of molluscs, and now the diversity of molluscs is so rich that it is difficult to describe what their common ancestor looked like. ”
The common ancestor of molluscs was thought to be shellless in the past, but the new study suggests that the ancestors of molluscs had a shell and a toothed tongue, and that shell disappeared, changed, or became multiple in the course of subsequent evolution. "This completely changed the way we understand the early history of molluscs and read the fossil record," Smith said. ”
Julia Sigwart of Queen's University Belfast said that although the discovered mollusk existed 480 million years ago, it was still too "young" to conclude about the common ancestor appearance of mollusks.
"In the evolution of mollusks, it wasn't particularly ancient fossils," she said. "But, she adds, this fossil does show that mollusks have evolved in many forms over the past 500 million years." Whenever we find these particular fossils, they are very important for us to understand the plan of the organism, because these fossils are so rare! ”
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