Becky Ferreira

But how far back in the history of living things on Earth does this behavior go? At least 480 million years, according to a study published Thursday in Scientific Reports. It points to evidence of fossilized marine animals called trilobites lining up one-by-one during a time when complex life was still coming of age on Earth.

“Probably, collective behavior developed very early among various groups of arthropods,” said Jean Vannier, a paleontologist at the Université Claude Bernard Lyon 1 in France, and the study’s lead author.

Vannier and his colleagues examined specimens of Ampyx priscus found in Moroccan fossil beds, which preserve single-file lines containing as many as 22 of the small spiny arthropods. The fossils represent some of the oldest evidence of collective synchronized behavior in animals.

These trilobites lived during the Great Ordovician Biodiversification Event, a period defined by a dramatic increase in the variety and complexity of marine life. It was the evolutionary sequel to the first major diversification event, the so-called Cambrian explosion, which established most animal groups in the fossil record some 541 million years ago.

Before the Cambrian, there is “no evidence for group behavior” in animals, Vannier said, because Precambrian life-forms lacked sophisticated nervous systems.

Ampyx trilobites, in contrast, had an anatomy that could have enabled chemical communication and sensory stimulation. Although they were visually blind, the trilobites had long spikes protruding from their rear ends. These appendages clearly overlap and link individuals in the fossilized chains, and perhaps allowed tactile or pheromone signals to be exchanged.

The arrangement is reminiscent of single-file formations assumed by modern spiny lobsters during mass migrations.

Scientists have previously studied these linear clusters in early arthropod fossils and offered a variety of explanations for the interesting patterns. Some have suggested that Ampyx trilobites ended up in lines when they sought shelter in seafloor burrows made by other animals. Researchers have also demonstrated that certain fossil clusters of trilobites were likely deposited by forces such as ocean currents.

Vannier’s team analyzed the sediment that preserves the Moroccan fossils. “We thought it was important to re-explore this topic with new eyes,” he said.

The exceptional preservation of the fossils implies that the trilobites died suddenly when they were buried by sediment, perhaps during a storm, rather than being gradually transported to their resting place by currents. The researchers also didn’t find any evidence of burrows in the sediment that might account for the linear pattern of these particular trilobites.

Almost all of the lined-up trilobites were sexually mature, which could be evidence that the animals were traveling en masse to spawning grounds. The nature of their death and fossilization also suggests it’s possible that they marched together to retreat from dangerous conditions during storms.

“These options are not mutually exclusive,” they wrote in the study. “Ampyx may have alternatively responded to environmental stress and reproduction signals by adopting the same behavior.”

Whatever the precise explanation of this behavior, the trilobite fossils offer a tantalizing glimpse into the early days of coordinated teamwork in animals.

This article originally appeared in

Trilobite Fossils Show Conga Line Frozen for 480 Million Years

You probably don’t think twice when you queue up at the grocery store or join a conga line at a wedding. But this type of single-file organization is a sophisticated form of collective social behavior. And as suggested by the children’s song “The Ants Go Marching One-By-One,” humans are not the only animals that appreciate the value of orderly lines.

<h1>(Trilobites): Some 99 million years ago, a small animal with a weird elongated toe died and became partially entombed in amber. Its lower leg and foot remained undisturbed in the hardened tree resin until amber miners eventually discovered the fossil in Myanmar’s Hukawng Valley in 2014.</h1>

The preserved toe measures less than half an inch from knuckle to claw-tip, making it 41% longer than the next longest digit on the animal’s foot. When traders showed the curious specimen to Chen Guang, a curator at China’s Hupoge Amber Museum, they suggested that it probably belonged to an extinct lizard.

Chen thought that the remains looked more like an avian species, so he looped in Lida Xing, a paleontologist at China University of Geosciences who specializes in Cretaceous birds.

“I was very surprised at the time,” Xing said, recalling that the fossil was “undoubtedly the claw of a bird.”

A handful of Cretaceous bird fossils have been found in Burmese amber, but this is the first to be identified as a new species. Named Elektorornis (“amber bird”) chenguangi, the specimen is described in a study, led by Xing, published Thursday in Current Biology.

E. chenguangi was smaller than a modern sparrow and belonged to a family of birds called Enantiornithes, which was abundant during the Cretaceous period.

Its elongated toe structure has never been observed in other birds, living or extinct. Its foot also sported an unusual layer of bristled feathers, “unlike any adult bird known today,” according to Jingmai O’Connor, a co-author and paleontologist at the Institute of Vertebrate Paleontology and Paleoanthropology in Beijing.

Long toes are associated with arboreal animals that need a firm grip on tree branches. The bristles suggest that the bird’s foot also had a sophisticated sensory system. Xing’s team speculated that E. chenguangi may have used the long, sensitive digit to probe cracks in trees for insects and grubs, just as the aye-aye lemur uses a slim finger to extract food in modern Madagascar.

These sorts of special adaptations may have helped propel Enantiornithes to evolutionary success during the age of dinosaurs. At that time, Enantiornithes overshadowed Neornithes, the group that contains all modern avian species. But that abruptly changed when a huge asteroid hit Earth 66 million years ago.

Enantiornithes were wiped out along with the non-avian dinosaurs, while Neornithes went on to become the diverse group of birds — from ostriches to penguins, eagles to hummingbirds — that currently inhabits our planet.

“Enantiornithines were good enough to survive and dominate in the Cretaceous but maybe not good enough to make it through the mass extinction,” O’Connor said. She noted that the faster maturation cycles and more efficient digestive systems of Neornithes may have given them an edge.

Enantiornithines may no longer be with us, but this amber fossil has provided a sepia-toned snapshot of their lives and their world.

While many fossils trapped in amber like this one are reshaping our understanding of the distant past, they may also be amplifying intractable social tensions in Myanmar in the present.

“Some of these specimens have big price tags, and that money might in some cases help fund armed conflict in Myanmar between the government and militias,” said Steve Brusatte, a paleontologist at the University of Edinburgh, who was not involved in the study.

“These fossils are hugely important, and the scientists studying them have done an excellent job, but I want to be sure that these fossils were not incidentally complicit in human suffering.”

O’Connor agreed that she and her colleagues had growing awareness about ethical problems with the amber trade, but said, “It’s the conflict that has dragged the amber into it, not the other way around.”

This article originally appeared in <a href="https://www.nytimes.com/2019/07/11/science/bird-amber-toe.html" link="null" target="_blank">The New York Times</a>.

Why did this extinct bird have such a weird, long toe?

Chen thought that the remains looked more like an avian species, so he looped in Lida Xing, a paleontologist at China University of Geosciences who specializes in Cretaceous birds.

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Becky Ferreira

Articles written by the author

Trilobite Fossils Show Conga Line Frozen for 480 Million Years

Why did this extinct bird have such a weird, long toe?