New Clues About an Ancient Mystery
For more than 270 million years trilobites dominated the oceans, leaving behind an astonishing record of fossils. Yet scientists have long debated a fundamental question: how did these early marine arthropods extract oxygen from seawater? Recent research from Harvard University and collaborators provides the most compelling evidence to date that the feathery structures attached to their legs functioned as gill‑like organs.
Turning Legs into Respiratory Surfaces
Trilobite appendages consist of two branches. The inner branch clearly served locomotion, allowing the creature to crawl along the seafloor. The outer branch, however, is covered with delicate, hair‑like plates called lamellae. By constructing high‑resolution 3D models of two species—Olenoides serratus (≈68 mm long) and Triarthrus eatoni (≈36 mm long)—researchers measured the total area provided by these lamellae. The larger specimen possessed roughly 16,600 mm² of surface, while the smaller one offered about 2,160 mm². Because respiratory efficiency scales with exposed area, these numbers indicate a substantial capacity for gas exchange.
Size, Lamellae Length, and Environmental Adaptation
Extending the analysis to nine additional Cambrian trilobites revealed a clear scaling trend: bigger trilobites displayed dramatically larger lamellar areas, not by adding more plates but by elongating existing ones. This pattern mirrors the way modern crustaceans increase gill surface as they grow.
Comparisons with living arthropods such as lobsters and Atlantic spider crabs showed that the ratio of respiratory surface to body mass in trilobites falls within the range of contemporary species. Such parity reinforces the hypothesis that the lamellae were genuinely functional gills.
Ecological Implications
The study also hints at ecological specialization. Triarthrus eatoni likely inhabited low‑oxygen waters; its relatively long lamellae would have compensated for the paucity of dissolved oxygen. Conversely, the gigantic Redlichia rex possessed proportionally smaller lamellae, suggesting either a slower metabolism or reliance on alternative oxygen‑uptake pathways.
Understanding how trilobites breathed sheds light on their energetic budget, locomotor abilities, and ultimately the reasons behind their prolonged success in Paleozoic seas.
These findings, published in Biology Letters, invite a reassessment of ancient arthropod physiology and emphasize that even structures once considered ornamental may have played a vital role in survival.
Source: https://scientias.nl/deze-oeroude-zeedieren-hadden-waarschijnlijk-kieuwen-op-hun-poten/#respond