The water ancestors of the Earth centipedes are characterized for the first time

<div data-thumb = "" data-src = " gfx / news / 2020/1-aquaticances.png "data-sub-html =" One of the biggest gaps in the record of arthropod fossils was how the ancestors of millipedes and millipedes looked, but now this gap is filled. Katya Schulz /Wikimedia commons">

<img src = "" alt = "** Aquatic ancestors of the Earth centipedes, first characterized” title=”One of the biggest gaps in the record of arthropod fossils was how the ancestors of millipedes and millipedes looked, but now this gap has been filled. Credit: Katya Schulz /Wikimedia commons“/>

One of the biggest gaps in the record of arthropod fossils was how the ancestors of millipedes and millipedes looked, but now this gap has been filled. Credit: Katya Schulz /Wikimedia commons

Insects, spiders and millipedes make up the majority of all animals on land. Although not many of them live in water today, their ancestors were once aquatic.

A fossil of 411 million years shows us what one of these groups looked like when they were still spending their days in the water.

The ancestors of modern arthropods, an extremely successful group that includes insects, spiders, centipedes and crabs, originated in the Cambrian period about 541 million years ago.

These creatures were small and completely aquatic, inhabiting the oceans and fresh water at the same time that most of the other main animal lines also began to appear. But at what point these early arthropods then began to fall apart into the main groups of land-living groups that we see today, were not well established.

One of the largest holes in fossil arthropods is the origin of millipedes and millipedes, commonly known as myriapods. So far, not a single aquatic form of this line has been discovered.

Looking at the fossils found in rock Researchers known as Rhynie Chert, estimated to be about 410 million years old, have exquisitely detailed details on some of the tiny arthropods that have been preserved inside. They found that some of these creatures were aquatic myriapods.

Dr. Greg Edgecomb, a paleontologist at the Museum who studies arthropods, worked with colleagues to describe these tiny early relatives of centipedes and centipedes.

“This is something I've been struggling with for a couple of decades, and this is one of the biggest holes in arthropods records of fossils, says Greg. “This is the first opportunity to see how animals look in this gap.”

Description was published in Proceedings of the National Academy of Sciences USA ..

An image of the head of a fossil arthropod showing incredibly detailed how the mouth parts look like centipedes and millipedes. Courtesy: Edgecombe et al. 2020

First animals on land

Arthropods are the most successful animal groups on the planet, accounting for approximately 80% of all animals currently living.

They are one of the few groups of animals that successfully made the transition from oceans to land, while others were amniotes, and were the first to do so at least about 420 million years ago.

As a rule, terrestrial arthropods can be divided into three main groups: hexapods (including insects), arachnids (spiders and their genus), and millipedes (millipedes and millipedes).

But rather, that this happens as a single event, each individual group of arthropods made the transition on their own.

** The aquatic ancestors of the earth centipedes are characterized for the first time

Reconstruction of the water millipede. Courtesy: Edgecombe et al. 2020

“Three major independent events related to ground transformation took place at Arthropods,” Greg explains. “They all had to face the same basic problems because the land was a hostile environment.” Each group had to figure out how to prevent drying out, how to maintain their body and walk, how to excrete, and last but not least, how to breathe.

We know that the first arthropods appeared during the Early Cambrian about 541 million years ago, since their fossils were found in deposits such as Burgess schists, and we know that by the early Devonian they settled well on land.

What happened between these events was less definite.

First terrestrial ecosystems

Rhynie Chert is a field found in Aberdeen, Scotland. This preserves one of the earliest terrestrial ecosystems containing some of the first plants and animals that colonized the earth.

When the rocks formed, the region was a system of pools and springs, not much different from what is today observed in Yellowstone National Park, although not so extreme. Freshwater plants and animals flourished in these basins, and along the edges they began to develop the surrounding lands.

It was in these breeds that Greg’s colleague, Dr. Christina Strullu-Derrien, was able to identify tiny arthropod fossils. Using innovative microscopy methods, Christina was able to depict these animals in amazing detail, demonstrating the excellent anatomy of their mouth parts.

“These small details allow us to see that there are a number of organs in the fossil head that correspond to what we see in the mouth area of ​​living millipedes,” Greg says. This confirmed that they were probably the earliest aquatic living ancestors of all living millipedes and millipedes.

What is interesting about this is that this is not the first time these early myriapods have been discovered in the fossil record.

Known as euticarcinoids, the bodies of these creatures are known in the rocks, from the Cambrian to the Triassic, while traces of them were found on ancient tidal plains and coastal sand dunes. It’s just that these fossils were not detailed enough and were previously mistakenly identified as early relatives of crustaceans or arachnids.

Now, Greg and his colleagues were able to show that this interpretation was incorrect, and that they actually belong to completely different groups of arthropods and help fill this long-standing gap in fossils.

The work also helps to show how the use of modern technology can give a new understanding of old designs.

“Honestly, they are just very pretty fossils,” Greg says. “We can tell more about the shape of these animals than I could even imagine, it would be possible.

“This is one sample image – one of the most magnificent fossils that I will ever have the opportunity to work on.”

Fossil – the oldest known scorpion

Additional Information:
Gregory D. Edgecomb et al. The water groups of stem myriapods close the gap between the dates of molecular divergence and data on terrestrial minerals, Proceedings of the National Academy of Sciences (2020). DOI: 10.1073 / pnas.1920733117

Aquatic ancestors of the Earth centipedes, first characterized (2020, April 7)
retrieved April 7, 2020

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