The Burgess Shale in British Columbia, Canada, is renowned for its extraordinary conservation of soft tissues in fossils, consisting of limbs and guts.

While trilobites are plentiful in the fossil record thanks to their tough exoskeleton, their soft limbs are seldom maintained and inadequately comprehended.

The trilobite types Olenoides serratus provides a distinct chance to study these appendages.

Harvard University paleontologist Sarah Losso and her associates examined 156 limbs from 28 fossil specimens of Olenoides serratus to rebuild the accurate motion and function of these ancient arthropod appendages, clarifying among the world’s earliest and most effective animals.

“Understanding habits and motion of fossils is difficult, due to the fact that you can not observe this activity like in living animals,” Dr. Losso stated.

“Instead, we needed to depend on thoroughly analyzing the morphology in as numerous specimens as possible, along with utilizing modern-day analogues to comprehend how these ancient animals lived.”

The scientists likewise determined the variety of movement of the legs in the living horseshoe crab types Limulus polyphemus

“Arthropods have actually jointed legs made up of numerous sections that can reach upwards (extend) or downwards (flex),” they stated.

“The series of movement depends upon the distinction in between how far each joint can reach in either instructions.”

“This variety, in addition to the leg and shape of each section, identifies how the animal utilizes the limb for strolling, getting, and burrowing.”

“Horseshoe crabs, typical arthropods discovered along the eastern coast of North America, are often compared to trilobites despite the fact that they are not carefully associated.”

“Horseshoe crabs come from a various branch of the arthropod tree, more carefully associated to spiders and scorpions, whereas trilobites’ household ties stay unpredictable.”

“The contrast is because of the resemblance because both animals patrol the ocean flooring on jointed legs.”

“The outcomes, nevertheless, revealed less resemblance in between the 2 animals.”

Unlike horseshoe crabs, whose limb joints alternate in their expertise for bending and extending– a pattern that helps with both feeding and defense– Olenoides serratus showed an easier, however extremely practical limb style.

“We discovered that the limbs of Olenoides serratus had a smaller sized series of extension and just in the part of the limb further from the body,” Dr. Losso stated.

“Although their limbs were not utilized in precisely the exact same method as horseshoe crabs, Olenoides serratus might stroll, burrow, bring food towards its mouth, and even raise its body above the seafloor.”

To bring their findings to life, the researchers developed advanced 3D digital designs based upon numerous fossil images maintained at various angles.

Since fossilized trilobite limbs are typically compressed flat, rebuilding them in three-dimensions presented a difficulty.

“We depend on remarkably unspoiled specimens, comparing limb conservation throughout numerous angles and completing missing out on information utilizing associated fossils,” stated Harvard University’s Professor Javier Ortega-Hernández.

The group compared the shape of trace fossils with the motion of the limbs.

Olenoides serratus might produce trace fossils of various depths utilizing various motions,” Dr. Losso discussed.

“They might raise their body above the sediment in order to stroll over challenges or to move more effectively in fast-flowing water.”

“Surprisingly, we found that the male types likewise had actually specialized appendages utilized for breeding, which each leg likewise had actually a gill utilized for breathing.”

The outcomes were released on August 4, 2025 in the journal BMC Biology

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S.R. Losso et al2025. Metrology of leg movement in the Burgess Shale Olenoides serratus suggests practical distinctions in between trilobite and xiphosuran appendages. BMC Biol 23, 238; doi: 10.1186/ s12915-025-02335-3