Recent discoveries in Brazil have significantly advanced our understanding of the evolutionary history of ray-finned fish brains. Research led by Rodrigo Tinoco Figueroa, a doctoral student at the University of Michigan, has unearthed remarkably well-preserved brains in late Paleozoic ray-finned fishes. These findings, which include other rare soft tissues like fragments of the heart, eyes, meninges, and gill filaments, challenge previous assumptions and provide a richer understanding of ancient fish anatomy.
Figueroa, the lead author of a study published in Current Biology, emphasized the importance of these fossils. “These fossils not only show extensive preservation of soft tissue but also provide a glimpse into the evolution of the brain of fish that lived more than 290 million years ago,” he said. Such fossils offer invaluable direct evidence of past soft tissue elements, often altering our understanding of living species.
Working under paleontologist Matt Friedman in the University of Michigan's Department of Earth and Environmental Sciences, Figueroa's research forms part of his doctoral dissertation. Among the specimens, one labeled CP 065 stood out for its exceptional preservation and scientific significance. “In addition to being the first specimen in which I noticed an everted brain, it is also one of the best-preserved fossils I have ever seen,” Figueroa noted.
This particular fossil, estimated to be over 290 million years old, remarkably preserves not just the brain and cranial nerves, but also delicate structures like the meninges, gill filaments, blood vessel fragments, heart parts, and possibly even skeletal muscles. “It is certainly a unique find. Specimens like this are the best way to bring paleontology closer to biology and vice versa,” Figueroa added.
The research utilized advanced imaging techniques, including CT scans of fossilized ray-finned fish skulls. These specimens were on loan from the Paleontological Center of the University of Contestado in Mafra, Santa Catarina, Brazil. “Using micro-CT of fossils and contrast-enhanced micro-CT of extant species provides us with new three-dimensional data,” Figueroa explained. This method offers insights that go beyond traditional paleontological approaches, potentially transforming future research with the addition of new fossils and comparative material from living species.
Figueroa scanned eight specimens from Mafra, discovering some level of soft tissue fossilization in all of them. Most notably, the brains were preserved with detailed morphology, akin to those found in earlier studies, such as the Coccocephalus. “After a more detailed examination of all these brains and the associated osteology of the specimens, I was able to determine that there were two distinct species,” he said. The bone morphology of one species indicated a close relation to younger fossils, aligning it nearer to the group encompassing all 35,000 extant species of ray-finned fish.
Source: University of Michigan