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Home / Science / A tiny, 400-million-year-old Fishy has changed our view of vertebrate development

A tiny, 400-million-year-old Fishy has changed our view of vertebrate development



This week, our new work published a spectacular 400 million-year-old 3D-preserved fossil fish, Ligulalepis .

The 3D anatomy of the fossil Ligulalepis skull reveals previously unknown details of the pattern of skin skull bones, the shape of the cerebral cavity and other soft tissue features (such as nerves and blood vessels) in this species

Why are we so excited? from the discovery of the structure of one? old fish skull? For Ligulalepis is in a very important position in the vertebrate development tree.

Boneyfish – and us

Pisces are the most diverse group of vertebrates on the planet, with approximately 30,000 known species.

The vast majority of these (about 98 percent!) Are bony fish or osteeichthyanans.

These include most of the fish we like to eat, such as salmon, tuna and trout, as well as fish that we keep as pets, such as goldfish and guppies.

These are called Actinopterygians, as their fins are supported by bony rods, so-called fin rays.

The other large group of bony fish has a robust lobe (sarcopterygii), a group that contains live lungfish and coelacanths as well as several extinct groups.

The Sarcopterygians are an important group because they have developed the first four-legged land animals, the tetrapods.

Today we can consider all living tetrap ods (amphibians, reptiles, birds and mammals) as a subgroup within bony fish.

A thrilling new find

The First Discovery of the Fish Ligulalepis was a small fossil fish skull found in limestone near Wee Jasper in New South Wales about 20 ago

He has since fueled the debate on early East-Eel evolution, with no clear determination as to where this enigmatic fish sits in the pedigree. 1

9659002] Then, about two years ago, a second skull of this fish was discovered by a Flinders University student, Benedict King. The specimen was found in the same limestone outcrop near Wee Jasper.

It was also preserved in 3D, but was more complete than the original one.

Earlier work by us identified electroreceptive sensory pits in this skull of Ligulalepis .

Secrets of the Skull

Both the old and the new skulls were at the center of our new work. Our team first prepared the tiny newer specimen (less than 2 cm long) of weak acetic acid from the rock to expose the bone as the carbonate rock dissolved.

Then we used microcomputed tomography (CT) to visualize the skeletal anatomy of the two known ligulalepis . Mighty X-rays go through the bones to discover many hidden features in the skulls.

The scans revealed an amazing mix of characters in the skulls of these fish. Some features, such as the shape of the inner ear canal, seemed to belong to the cartilaginous fish like the sharks. Other features, such as the overall shape of the brain case, were clearly osteeichtyan (bone fish) characters.

The pattern of bones forming the skullcap was an unexpectedly primitive trait that is also seen in an extinct group of pine fish called placoderms.

Using CT technology, we were able to reconstruct what the brain cavity of this 400-million-year-old fish looks like and enable us to digitally restore the brain shape for the first time (see video below).

A complicated family tree

Before our detailed analysis of this skull, some scientists considered ligulalepis as closely related to the ray fins. Others set it up next to flapfish.

A third school of thought envisioned it even deeper on the fish family tree – and that's near where we put it now, on the "trunk" of the tree that leads to it

The unique location on the tree of life means Ligulalepis gives a good insight into the appearance of the predecessor of the two great radiations of teleost fish.

Furthermore, the detailed analysis of his newly discovered characters helps to explain the early evolutionary radiation of all animals with a bony skeleton – including us humans.

The position of Ligulalepis in the evolutionary pedigree at the base of the East-African radiation. (Brian Choo)

Fossils are missing

Most modern fish are ray-finned (Actinopterygian) with about 29,000 living species. Its origins are confidently traced back to the Middle Devonian, about 390 million years ago with fish such as Cheirolepis from Scotland

However, the existence of the related group "lobe fins" (Sarcopterygier) is much older, with early representatives This group like Guiyu from China, dated about 430 million years ago. This suggests that there are some parts of the early fish fossil stock that are poorly understood.

Our fossil and the new analyzes we have done help to answer the big question of what the ancestor of all modern bony fish looked like. It also illustrates the sequence of changes that these early fish performed to maintain their modern "body plan".

Our analyzes also show that Ligulalepis is the closest known species to a peculiar group of early rags- "19659002] It supports the hypothesis that the first early bone fish originated and radiated in China and then over East Gondwana (Australia and Antarctica), the southernmost part of the southern supercontinent, has emigrated the ancient Chinese terrain

 The Conversation Our results show that the evolutionary pedigree of the first bony fish is much more complicated than we are thought what the importance of paleontology shows to help us with our distant origins.

Alice Clement, Research Associate at the School of Biological Sciences, Flinders University, and John Long, Strategic Professor of Paleontology, Fl Inders University

This article was originally published by The Conversation Read the original article.


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