Three-eyed distant relative of insects and crustaceans reveals amazing detail of early animal evolution

A team from the University of Leicester, Yunnan Key Laboratory for Palaeobiology and the Institute of Palaeontology at Yunnan University, Chengjiang Fossil Museum, and the Natural History Museum in London, have redescribed a unique fossil animal from rocks nearly 520 million years old that fills in a gap in our understanding of the evolution of animals known as arthropods.

The animal, which has the scientific name Kylinxia, was imaged using a CT scanner which revealed its soft anatomy buried in the rock. The size of a large shrimp, its surprising features include three eyes on the head and a pair of fearsome limbs presumably used to catch prey.

The study is published this week in the high impact journal Current Biology.

Fossils of many kinds of marine animals first appear in rocks from about half a billion years ago and signal a time when complex ecosystems were developing in the world's oceans. One of the key localities for such fossils is the area around the town of Chengjiang in southern China, where the fossils in this study were collected by the Chinese team. The fossils were recovered from the Cambrian Chengjiang biota of China's Yunnan Province, from which over 250 species of exceptionally preserved fossil organisms have been described.

The new find is important for deciphering the history of arthropods. These are animals whose bodies are divided into segments, most of which bear a paired of jointed limbs, like crabs, lobsters, insects, and spiders.

Although there are plenty of arthropods in the fossil record -- most famously the trilobites -- the vast majority only preserve their hard skeletons. Because the new Chinese material is preserved nearly complete, the team were able to image the head of Kylinxia, identifying six segments: the front one bearing eyes, the second with a pair of large grasping limbs, and the other four each bearing a pair of jointed limbs.

Lead author of the study Robert O'Flynn, a PhD student at the University of Leicester School of Geography, Geology and the Environment, said: "The preservation of the fossil animal is amazing. After CT-scanning we can digitally turn it around and literally stare into the face of something that was alive over 500 million years ago. As we spun the animal around, we could see that its head possesses six segments, just as in many living arthropods."

Professor Mark Williams, Robert's primary supervisor at the University of Leicester, said: "Kylinxia, and the Chengjiang biota whence it came, are instrumental to building our understanding of early euarthropod evolution. I like to think that similar discoveries will continue to be made by Robert."

Professor Yu Liu from the Yunnan Key Laboratory for Palaeobiology said: "Robert and I were examining the micro-CT data as part of his doctoral thesis in the hope of refining and correcting previous interpretation of head structures in this genus, Kylinxia. Amazingly, we found that its head is composed of six segments, as in, e.g., insects."

Dr Greg Edgecombe from the Natural History Museum added: "Most of our theories on how the head of arthropods evolved were based on these early-branching species having fewer segments than living species. Discovering two previously undetected pairs of legs in Kylinxia suggests that living arthropods inherited a six-segmented head from an ancestor at least 518 million years ago."

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Fossil site reveals giant arthropods dominated the seas 470 million years ago

Discoveries at a major new fossil site in Morocco suggest giant arthropods -- relatives of modern creatures including shrimps, insects and spiders -- dominated the seas 470 million years ago.

Early evidence from the site at Taichoute, once undersea but now a desert, records numerous large "free-swimming" arthropods.

More research is needed to analyse these fragments, but based on previously described specimens, the giant arthropods could be up to 2m long.

An international research team say the site and its fossil record are very different from other previously described and studied Fezouata Shale sites from 80km away.

They say Taichoute (considered part of the wider "Fezouata Biota") opens new avenues for paleontological and ecological research.

"Everything is new about this locality -- its sedimentology, paleontology, and even the preservation of fossils -- further highlighting the importance of the Fezouata Biota in completing our understanding of past life on Earth," said lead author Dr Farid Saleh, from the University of Lausanne and and Yunnan University.

Dr Xiaoya Ma, from the University of Exeter and Yunnan University, added: "While the giant arthropods we discovered have not yet been fully identified, some may belong to previously described species of the Fezouata Biota, and some will certainly be new species.

"Nevertheless, their large size and free-swimming lifestyle suggest they played a unique role in these ecosystems."

The Fezouata Shale was recently selected as one of the 100 most important geological sites worldwide because of its importance for understanding the evolution during the Early Ordovician period, about 470 million years ago.

Fossils discovered in these rocks include mineralised elements (eg shells), but some also show exceptional preservation of soft parts such as internal organs, allowing scientists to investigate the anatomy of early animal life on Earth.

Animals of the Fezouata Shale, in Morocco's Zagora region, lived in a shallow sea that experienced repeated storm and wave activities, which buried the animal communities and preserved them in place as exceptional fossils.

However, nektonic (or free-swimming) animals remain a relatively minor component overall in the Fezouata Biota.

The new study reports the discovery of the Taichoute fossils, preserved in sediments that are a few million years younger than those from the Zagora area and are dominated by fragments of giant arthropods.

"Carcasses were transported to a relatively deep marine environment by underwater landslides, which contrasts with previous discoveries of carcass preservation in shallower settings, which were buried in place by storm deposits," said Dr Romain Vaucher, from the University of Lausanne.

Professor Allison Daley, also from the University of Lausanne, added: "Animals such as brachiopods are found attached to some arthropod fragments, indicating that these large carapaces acted as nutrient stores for the seafloor dwelling community once they were dead and lying on the seafloor."

Dr Lukáš Laibl, from the Czech Academy of Sciences, who had the opportunity to participate in the initial fieldwork, said: "Taichoute is not only important due to the dominance of large nektonic arthropods.

"Even when it comes to trilobites, new species so far unknown from the Fezouata Biota are found in Taichoute."

Dr Bertrand Lefebvre, from the University of Lyon, who is the senior author on the paper, and who has been working on the Fezouata Biota for the past two decades, concluded: "The Fezouata Biota keeps surprising us with new unexpected discoveries."

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525-million-year-old fossil defies textbook explanation for brain evolution

Fossils of a tiny sea creature that died more than half a billion years ago may compel a science textbook rewrite of how brains evolved.

A study published in Science -- led by Nicholas Strausfeld,a Regents Professor in the University of Arizona Department of Neuroscience, and Frank Hirth, a reader of evolutionary neuroscience at King's College London -- provides the first detailed description of Cardiodictyon catenulum, a wormlike animal preserved in rocks in China's southern Yunnan province. Measuring barely half an inch (less than 1.5 centimeters) long and initially discovered in 1984, the fossil had hidden a crucial secret until now: a delicately preserved nervous system, including a brain.

"To our knowledge, this is the oldest fossilized brain we know of, so far," Strausfeld said.

Cardiodictyon belonged to an extinct group of animals known as armored lobopodians, which were abundant early during a period known as the Cambrian, when virtually all major animal lineages appeared over an extremely short time between 540 million and 500 million years ago. Lobopodians likely moved about on the sea floor using multiple pairs of soft, stubby legs that lacked the joints of their descendants, the euarthropods -- Greek for "real jointed foot." Today's closest living relatives of lobopodians are velvet worms that live mainly in Australia, New Zealand and South America.

A debate going back to the 1800s

Fossils of Cardiodictyon reveal an animal with a segmented trunk in which there are repeating arrangements of neural structures known as ganglia. This contrasts starkly with its head and brain, both of which lack any evidence of segmentation.

"This anatomy was completely unexpected because the heads and brains of modern arthropods, and some of their fossilized ancestors, have for over a hundred years been considered as segmented," Strausfeld said.

According to the authors, the finding resolves a long and heated debate about the origin and composition of the head in arthropods, the world's most species-rich group in the animal kingdom. Arthropods include insects, crustaceans, spiders and other arachnids, plus some other lineages such as millipedes and centipedes.

"From the 1880s, biologists noted the clearly segmented appearance of the trunk typical for arthropods, and basically extrapolated that to the head," Hirth said. "That is how the field arrived at supposing the head is an anterior extension of a segmented trunk."

"But Cardiodictyon shows that the early head wasn't segmented, nor was its brain, which suggests the brain and the trunk nervous system likely evolved separately," Strausfeld said.

Brains do fossilize

Cardiodictyon was part of the Chengjiang fauna, a famous deposit of fossils in the Yunnan Province discovered by paleontologist Xianguang Hou. The soft, delicate bodies of lobopodians have preserved well in the fossil record, but other than Cardiodictyon none have been scrutinized for their head and brain, possibly because lobopodians are generally small. The most prominent parts of Cardiodictyon were a series of triangular, saddle-shaped structures that defined each segment and served as attachment points for pairs of legs. Those had been found in even older rocks dating back to the advent of the Cambrian.

"That tells us that armored lobopodians might have been the earliest arthropods," Strausfeld said, predating even trilobites, an iconic and diverse group of marine arthropods that went extinct around 250 million years ago.

"Until very recently, the common understanding was 'brains don't fossilize,'" Hirth said. "So you would not expect to find a fossil with a preserved brain in the first place. And, second, this animal is so small you would not even dare to look at it in hopes of finding a brain."

However, work over the last 10 years, much of it done by Strausfeld, has identified several cases of preserved brains in a variety of fossilized arthropods.

A common genetic ground plan for making a brain

In their new study, the authors not only identified the brain of Cardiodictyon but also compared it with those of known fossils and of living arthropods, including spiders and centipedes. Combining detailed anatomical studies of the lobopodian fossils with analyses of gene expression patterns in their living descendants, they conclude that a shared blueprint of brain organization has been maintained from the Cambrian until today.

"By comparing known gene expression patterns in living species," Hirth said, "we identified a common signature of all brains and how they are formed."

In Cardiodictyon, three brain domains are each associated with a characteristic pair of head appendages and with one of the three parts of the anterior digestive system.

"We realized that each brain domain and its corresponding features are specified by the same combination genes, irrespective of the species we looked at," added Hirth. "This suggested a common genetic ground plan for making a brain."

Lessons for vertebrate brain evolution

Hirth and Strausfeld say the principles described in their study probably apply to other creatures outside of arthropods and their immediate relatives. This has important implications when comparing the nervous system of arthropods with those of vertebrates, which show a similar distinct architecture in which the forebrain and midbrain are genetically and developmentally distinct from the spinal cord, they said.

Strausfeld said their findings also offer a message of continuity at a time when the planet is changing dramatically under the influence of climatic shifts.

"At a time when major geological and climatic events were reshaping the planet, simple marine animals such as Cardiodictyon gave rise to the world's most diverse group of organisms -- the euarthropods -- that eventually spread to every emergent habitat on Earth, but which are now being threatened by our own ephemeral species."

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Welsh 'weird wonder' fossils add piece to puzzle of arthropod evolution

The most famous fossils from the Cambrian explosion of animal life over half a billion years ago are very unlike their modern counterparts. These "weird wonders," such as the five-eyed Opabinia with its distinctive frontal proboscis, and the fearsome apex predator Anomalocaris with its radial mouthparts and spiny feeding appendages, have become icons in popular culture. However, they were only quite recently recognised as extinct stages of evolution that are crucial for understanding the origins of one of the largest and most important animal phyla, the arthropods (a group that includes modern crabs, spiders, and millipedes).

In an article published today in Nature Communications, two new specimens with striking similarities to Opabinia are described from a new fossil deposit recording life in the Ordovician Period, 40 million years after the Cambrian explosion. This deposit, located in a sheep field near Llandrindod Wells in mid Wales (UK), was discovered during the COVID-19 lockdowns by independent researchers and Llandrindod residents Dr Joseph Botting and Dr Lucy Muir, Honorary Research Fellows at Amgueddfa Cymru -- National Museum Wales.

The quarry is well known as one of several local sites yielding new species of fossil sponges. "When the lockdown started, I thought I'd make one more trip to collect some last sponges before finally writing them up," said Botting, "of course, that was the day that I found something sticking its tentacles out of a tube instead."

"This is the sort of thing that palaeontologists dream of, truly soft-body preservation," said Muir, "we didn't sleep well, that night." That was the beginning of an extensive and ongoing investigation that grew into an international collaboration, with lead author Dr Stephen Pates (University of Cambridge) and senior author Dr Joanna Wolfe (The Department of Organismic and Evolutionary Biology at Harvard University).

Among the fossils unearthed so far are two very unexpected leftovers from the Cambrian "weird wonders." Pates met with Botting and Muir to study the specimens using microscopes purchased through crowd-funding to examine the tiny specimens. The larger specimen measured 13 mm, while the smaller measured a miniscule 3 mm (for comparison Opabinia specimens can be 20 times as long).

Exhaustive studies during this visit revealed additional details in the new specimens. Some of these features are also found in Opabinia, such as triangular, squishy lobopod 'legs' for interacting with the sediment, and -- in the smaller specimen -- a tail fan with blades similar in shape to Opabinia's recently described sister, Utaurora. However other features recognised in the material, such as sclerites covering the head as well as the presence of spines on the proboscis, were not known from any opabiniid and instead hinted at possible radiodont (including Anomalocaris) affinities. The differences between the two specimens led the researchers to wonder were these due to changes during the growth of one species, or did they instead suggest that two distinct species were present in this new deposit?

The authors describe the new taxon, Mieridduryn bonniae, with the larger specimen designated the holotype. The status of the smaller specimen was left open, reflecting these different possibilities. "The size of the smaller specimen is comparable to some modern arthropod larvae -- we had to take into account this possibility in our analyses," said Wolfe.

The genus name Mieridduryn is derived from the Welsh language, and translates as "bramble-snout," reflecting the spiny proboscis in the new material. It is pronounced like "me-airy-theerin." "Many scientific names are made using Latin or Greek words," Muir said, "but we really wanted to honour Wales, where the specimens were discovered, and so chose to use the Welsh language." The species name bonniae pays tribute to the niece of the landowners, Bonnie. "The landowners have been very supportive of our research, and Bonnie has been avidly following our progress, even attending some of our Zoom updates," said Botting.

The researchers used phylogenetic analyses, comparing the new fossils with 57 other living and fossil arthropods, radiodonts, and panarthropods, to determine their place in the history of arthropod evolution. "The best-supported position for our Welsh specimens, whether considered as one or two species, were more closely related to modern arthropods than to opabiniids. These analyses suggested that Mieridduryn and the smaller specimen were not "true" opabiniids," said Pates.

Crucially, these results suggested that a proboscis -- thought to represent a fused pair of head appendages -- was not unique to opabiniids, but instead was present in the common ancestor of radiodonts and deuteropods (more derived, modern arthropods), and through evolutionary time may have reduced to become the labrum that covers the mouth in modern arthropods. However, the second-best-supported position for these specimens was as true opabiniids, so the authors enquired a bit further to test the robustness of this first result.

"These Welsh animals are 40 million years younger than Opabinia and Utaurora" said Wolfe, "so it was important to assess the implications of some features, such as spines on the appendages or a carapace, evolving convergently with radiodonts in our analyses." If some, or all, the features shared between the Welsh animals and radiodonts were instead considered to have evolved convergently, the analyses strongly favoured these specimens being considered true opabiniids, the first from outside North America and the youngest by 40 million years. Whatever the eventual conclusion, the fossils are an important new piece in the arthropod evolutionary jigsaw.

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Trilobites' growth may have resembled that of modern marine crustaceans

Trilobites -- extinct marine arthropods that roamed the world's oceans from about 520 million years ago until they went extinct 250 million years ago, at the end of the Permian period -- may have grown in a similar fashion and reached ages that match those of extant crustaceans, a new study has found.

In a paper published in the journal Paleobiology, researchers from the University of British Columbia and Uppsala University show that the Ordovician trilobite Triarthrus eatoni, some 450 million years ago, reached a length of just above 4 cm in about 10 years, with a growth curve very similar to that of small, slow-growing crustaceans.

"T. eatoni lived in low-oxygen environments and, similarly to extant crustaceans exposed to hypoxic conditions, exhibited low growth rates compared with growth under more oxygenated conditions," said Daniel Pauly, principal investigator of UBC's Sea Around Us initiative and lead author of the study. "Low-oxygen environments make is more difficult for water-breathers to grow, and add to the difficulties of breathing through gills, which, as 2D surfaces, cannot keep up with the growth of their 3D bodies. Thus, under hypoxic conditions, they must remain small if they are to maintain the rest of their body functions."

In the case of trilobites, their exopods -- external branches on the upper part of their limbs -- functioned as gills. Thus, these ancient animals had similar growth constraints to those of their modern counterparts.

To reach these conclusions, Pauly and his colleague from Uppsala University, paleontologist James Holmes, resorted to the analysis of length-frequency data, a method developed within fisheries science and marine biology for studying the growth of fish and invertebrates lacking the physical markings that indicate their age.

The information to perform their analysis was obtained from an earlier publication with information of the length frequency distribution of 295 exceptionally-preserved trilobite fossils collected at 'Beecher's Trilobite Bed' in New York State.

After estimating the parameters of a growth model widely used in fisheries science, the von Bertalanffy growth function, the researchers compared their results with published data on the growth of extant crustaceans. They found that the growth parameters they estimated for Triarthrus eatoni were well within the range of recent, slow-growing crustaceans.

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Arthropods formed orderly lines 480 million years ago

Researchers studied fossilized Moroccan Ampyx trilobites, which lived 480 million years ago and showed that the trilobites had probably been buried in their positions -- all oriented in the same direction. Scientists deduced that these Ampyx processions may illustrate a kind of collective behavior adopted in response to cyclic environmental disturbances.

Though our understanding of the anatomy of the earliest animals is growing ever more precise, we know next to nothing about their behaviour. Did group behaviour arise recently or is it primeval? To answer this question, researchers from the CNRS, the University of Poitiers, UBO, Claude Bernard Lyon 1 University*, Cadi Ayyad University (Marrakech, Morocco), and the University of Lausanne (Switzerland) studied fossilized Moroccan Ampyx trilobites, which lived 480 million years ago. They showed that the trilobites had probably been buried in their positions -- all oriented in the same direction, in orderly lines, maintaining close contact with each other through their long spines -- during storms.

By comparing this observation with the behaviour of living animals such as North American spiny lobsters, the scientists deduced that these Ampyx processions may illustrate a similar kind of collective behaviour -- adopted in response to cyclic environmental disturbances like storms or to chemical signals associated with reproduction.

This example would seem to suggest that group behaviour is of ancient origin and, from an early date, likely conferred an evolutionary advantage on the first animals, allowing them to survive environmental stress and improve their reproductive chances.

*From the Laboratoire de Géologie de Lyon: Terre, Planètes, Environnement (CNRS / ENS de Lyon / Université Claude Bernard Lyon 1), the Laboratoire Géosciences Océan (CNRS / Université Bretagne Occidentale / Université Bretagne Sud), and the Institute of Chemistry of Materials and Media of Poitiers (IC2MP (CNRS / Université de Poitiers).

From Science Daily