According to new research on well-preserved fossils:
A new study has found the first evidence of sophisticated breathing organs in 450-million-year-old sea creatures. Contrary to previous thought, trilobites were leg breathers, with structures resembling gills hanging off their thighs.
Trilobites were a group of marine animals with half-moon-like heads that resembled horseshoe crabs, and they were wildly successful in terms of evolution. Though they are now extinct, they survived for more than 250 million years — longer than the dinosaurs.
Thanks to new technologies and an extremely rare set of fossils, scientists from UC Riverside can now show that trilobites breathed oxygen and explain how they did so. Published in the journal Science Advances, these findings help piece together the puzzle of early animal evolution.
“Up until now, scientists have compared the upper branch of the trilobite leg to the non-respiratory upper branch in crustaceans, but our paper shows, for the first time, that the upper branch functioned as a gill,” said Jin-Bo Hou, a UCR paleontology doctoral student who led the research.
Among the oldest animals on earth, this work helps situate trilobites on the evolutionary tree more securely in between older arthropods, a large group of animals with exoskeletons, and crustaceans.University of California – Riverside, “450-million-year-old sea creatures had a leg up on breathing” at ScienceDaily
How this finding situates trilobites more securely between older arthropods and crustaceans is unclear. Apparently, crustaceans don’t breathe through their legs. Did the older arthropods breathe through their legs? In any event, this find implies that the crustaceans underwent a dramatic switch in breathing mechanics, of which we apparently don’t have an account. How could we? We only found out about what the trilobites do very recently.
And how long would it take to evolve gills by purely Darwinian methods?
The paper is open access.