❌

Normal view

There are new articles available, click to refresh the page.
Before yesterdayMain stream

520-million-year-old larva fossil reveals the origins of arthropods

11 August 2024 at 11:30
Image of a small grey object, curved around its abdomen, with a series of small appendages on the bottom.

Enlarge / The fossil in question, oriented with its head to the left. (credit: Yang Jie / Zhang Xiguang)

Around half a billion years ago, in what is now the Yunnan Province of China, a tiny larva was trapped in mud. Hundreds of millions of years later, after the mud had long since become the black shales of the Yuan’shan formation, the larva surfaced again, a meticulously preserved time capsule that would unearth more about the evolution of arthropods.

Youti yuanshi is barely visible to the naked eye. Roughly the size of a poppy seed, it is preserved so well that its exoskeleton is almost completely intact, and even the outlines of what were once its internal organs can be seen through the lens of a microscope. Durham University researchers who examined it were able to see features of both ancient and modern arthropods. Some of these features told them how the simpler, more wormlike ancestors of living arthropods evolved into more complex organisms.

The research team also found that Y. yuanshi, which existed during the Cambrian Explosion (when most of the main animal groups started to appear on the fossil record), has certain features in common with extant arthropods, such as crabs, velvet worms, and tardigrades. β€œThe deep evolutionary position of Youti yuanshi… illuminat[es] the internal anatomical changes that propelled the rise and diversification of [arthropods],” they said in a study recently published in Nature.

Read 10 remaining paragraphs | Comments

500 million-year-old fossil is the earliest branch of the spider’s lineage

Image of a brown fossil with a large head and many body segments, embedded in a grey-green rock.

Enlarge (credit: UNIVERSITY OF LAUSANNE)

In the early 2000s, local fossil collector Mohamed β€˜Ou Said’ Ben Moula discovered numerous fossils at Fezouata Shale, a site in Morocco known for its well-preserved fossils from the Early Ordovician period, roughly 480 million years ago. Recently, a team of researchers at the University of Lausanne (UNIL) studied 100 of these fossils and identified one of them as the earliest ancestor of modern-day chelicerates, a group that includes spiders, scorpions, and horseshoe crabs.

The fossil preserves the species Setapedites abundantis, a tiny animal that crawled and swam near the bottom of a 100–200-meter-deep ocean near the South Pole 478 million years ago. It was 5 to 10 millimeters long and fed on organic matter in the seafloor sediments. β€œFossils of what is now known as S. abundantis have been found early onβ€”one specimen mentioned in the 2010 paper that recognized the importance of this biota. However, this creature wasn’t studied in detail before simply because scientists focused on other taxa first,” Pierre Gueriau, one of the researchers and a junior lecturer at UNIL, told Ars Technica.

The study from Gueriau and his team is the first to describe S. abundantis and its connection to modern-day chelicerates (also called euchelicerates). It holds great significance, because β€œthe origin of chelicerates has been one of the most tangled knots in the arthropod tree of life, as there has been a lack of fossils between 503 to 430 million years ago,” Gueriau added.

Read 10 remaining paragraphs | Comments

❌
❌