Tag Archives: trilobites

New Research Uncovers the Secrets of Burgess Shale Trilobites

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Appendages of arthropods serve various functions, including feeding, locomotion, and reproduction. Fossils dating back to the Cambrian period (539-487 million years ago) provide remarkable details of extinct arthropod appendages, enhancing our understanding of their anatomy and ecological roles. However, due to the limited number of fossils and often incomplete preservation, studies on appendage functions typically depend on idealized reconstructions. This new research focuses on the paleontological species Olenoides serratus, a prolific trilobite from the Cambrian Burgess Shale, noteworthy for its numerous well-preserved specimens featuring soft tissue that allow for a detailed analysis of appendage functionality.

Olenoides serratus from Burgess Shale. Image credit: Losso et al., doi: 10.1186/s12915-025-02335-3.

Situated in British Columbia, Canada, the Burgess Shale is renowned for its exceptional fossil preservation, including soft tissues such as limbs and internal organs.

While trilobites are common in fossil records, their soft limbs are seldom preserved due to their hard exoskeleton, leading to a limited understanding of these structures.

The trilobite species Olenoides serratus offers a unique chance to investigate these appendages further.

Harvard paleontologist Sarah Ross and her team examined 156 limbs from 28 fossil specimens of Olenoides serratus to reconstruct the precise movements and functions of these ancient arthropod appendages, shedding light on one of the earliest successful aquatic animals.

“Understanding the behavior and movement of fossils poses challenges, as we cannot observe their activities like we do with living organisms,” stated Dr. Ross.

“Instead, we meticulously analyzed the morphology of numerous specimens while also utilizing modern analogues to infer how these ancient creatures lived.”

The researchers also assessed the range of motion of the legs of living horseshoe crab species Limulus polyphemus.

“Arthropods possess articulated legs composed of multiple segments that can flex upwards or downwards,” they noted.

“The range of motion is influenced by the specific directional capabilities of each joint.”

“This range, combined with the limbs’ shape and segment configuration, determines how the animal utilizes its appendages for walking, grasping, and burrowing.”

Horseshoe crabs, commonly found along the eastern coast of North America, are compared with trilobites due to their analogous behaviors.

“Despite their close relation to spiders and scorpions, horseshoe crabs are part of a different branch of the arthropod tree, whereas trilobite relationships remain ambiguous.”

The comparison arises from both animals’ adaptation of articulated limbs for navigating the seafloor.

However, the findings revealed that their similarities were minimal.

In contrast to horseshoe crabs, characterized by specialized limb joints for bending and expanding—facilitating feeding and protection—Olenoides serratus exhibited a simpler yet highly functional limb structure.

“We found that the limbs of Olenoides serratus had minimal extension, primarily far from the body,” Dr. Ross explained.

“Their limbs functioned differently than those of horseshoe crabs. Olenoides serratus could walk, dig, bring food to their mouths, and even elevate their bodies above the seafloor.”

To realize these findings, the scientists constructed advanced 3D digital models based on hundreds of fossil images captured from various angles.

Since trilobite limbs are often crushed and flattened, reconstructing them in three dimensions presents a significant challenge.

“We depend on exceptionally well-preserved specimens, comparing limb structures from multiple angles while leveraging related fossils to fill in any missing details,” said Professor Javier Ortega-Hernandez of Harvard University.

The team correlated the morphology of trace fossils to the movements of the limbs.

“The different movements of Olenoides serratus could create trace fossils with varying depths,” Dr. Ross elaborated.

“They were capable of raising their bodies on deposits, allowing them to traverse obstacles and navigate efficiently through swift currents.”

Remarkably, the researchers found that males possessed specialized appendages for mating, and each leg featured gills for respiration.

The findings were published in the journal BMC Biology on August 4th, 2025.

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Loss et al., 2025. Quantification of leg mobility in Burgess Shale Olenoides serratus reveals the functional differences between trilobite and Xiphosuran appendages. BMC Biol 23, 238; doi:10.1186/s12915-025-02335-3

Source: www.sci.news

Newly discovered fossils show that trilobites possessed five pairs of head appendages

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Based on multiple analytical techniques applied to two well-preserved soft-bodied specimens of trilobites, the Late Ordovician species Triarturus Eatonii and Middle Cambrian species Polygonum gracilis, paleontologists claim that there was an additional pair of cephalopods just behind the antennae, indicating that the trilobite had five pairs of cephalopods and six segments.

Triarturus Eatonii Image credit: Jin-bo Hou and Melanie J. Hopkins, doi: 10.1111/pala.12723.

Trilobites are extinct arthropods that dominated the marine fauna of the Paleozoic Era.

During their lifetime on Earth, which lasted much longer than the dinosaurs, they survived two major extinctions and dominated undersea ecosystems.

They appeared in the ancient oceans of the Early Cambrian period about 540 million years ago, long before life appeared on land, and disappeared during the mass extinction at the end of the Permian period about 252 million years ago.

They are incredibly diverse, with around 20,000 species, and fossils of their exoskeletons have been found all over the world.

Like other arthropods, trilobites have a body made up of many segments and a head made up of several fused segments.

Like the rest of the trilobite’s body (the thorax and tail), these segments are associated with appendages whose functions range from sensing to feeding to locomotion.

“The number of these segments and how it relates to other important features, such as eyes and legs, is important for understanding how arthropods relate to each other and how they evolved,” said Dr. Melanie Hopkins, curator and head of the Department of Palaeontology at the American Museum of Natural History.

The segments on a trilobite’s head can be counted in two different ways: by looking at the grooves (called sulci) on the top of the trilobite fossil’s hard exoskeleton, and by counting the pairs of antennae and legs preserved on the underside of the fossil.

However, trilobites’ soft appendages are rarely preserved, and when looking at trilobite head segments, researchers frequently find a mismatch between these two methods.

In the new study, Dr. Hopkins and Dr. Hou Jinbo of Nanjing University studied Triarturus Eatonii.

These fossils are known for their golden glow from well-preserved pyrite replacements, and show that there are additional, previously undescribed legs beneath the head.

“This incredible preservation method allows us to view the 3D appendages of hundreds of specimens directly from the ventral side of the animals, just like grabbing an appendage from a horseshoe crab on the beach and turning it upside down to view it,” Dr. Hou said.

Exceptionally well preserved compared to other trilobite species, Polygonum gracilis based on the fossil, which was discovered in the Burgess Shale of British Columbia, the authors propose a model for how the appendages may have been attached to the head in relation to grooves in the exoskeleton.

“This model resolves apparent inconsistencies and shows that the trilobite head contained six segments: the anterior segment associated with the origin of eye development, and five additional segments each associated with a pair of antennae and four pairs of walking legs,” the researchers explained.

Their paper published in the journal Paleontology.

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Jin-bo Hou & Melanie J. Hopkins. 2024. New evidence for five cephalopods in trilobites and its implications for trilobite head segmentation. Paleontology 67(5):e12723; doi:10.1111/pala.12723

Source: www.sci.news