Breathing trilobites

How did ancient marine creatures breathe? A major milestone in evolutionary history occurred about 370 million years ago – the water-to-land transition – when a certain fish species converted its fins

A major milestone in evolutionary history occurred about 370 million years ago – the water-to-land transition – when a certain fish species converted its fins to limbs and modified its respiratory organ for air-breathing. So how did the creatures breathe when in water? A new study (Science Advances) has found evidence of advanced breathing organs in 450-million-year-old sea creatures called Trilobites. Fossil studies showed that trilobites used gill-like structures hanging off their thighs to breathe. This went unnoticed for decades as scientists thought the upper branch of the leg was non-respiratory just like the upper branch seen in present-day crustaceans. Advanced Computer tomography or CT scanner helped read the fossil and surrounding rock and 3D models of the gill structures were created. Paleontologist Melanie Hopkins, a research team member at the American Museum of Natural History explained in a release that the new technique helped get a view that would even be hard to see under a microscope. The gill structures were just 10 to 30 microns wide. For comparison, a human hair is about 100 microns thick.