Hidden for 70 million years, a tiny fossil fish is rewriting freshwater evolution

The specimen, studied by researchers at Western University, the Royal Tyrrell Museum of Palaeontology and worldwide collaborators, is a skeleton of a fish about 4 cm lengthy from the Late Cretaceous interval (the age of the enduring Tyrannosaurus Rex, about 100.5 million to 66 million years in the past.) A brand new type of fish totally, it’s now named Acronichthys maccognoi.

A research detailing the invention was printed on October 2 within the excessive affect journal, Science.

“The reason Acronichthys is so exciting is that it fills a gap in our record of the otophysans supergroup. It is the oldest North America member of the group and provides incredible data to help document the origin and early evolution of so many freshwater fish living today,” mentioned Neil Banerjee, Earth sciences professor and writer on the research.

Banerjee collaborated with a world crew together with Lisa Van Loon, adjunct Earth sciences professor at Western, Don Brinkman, curator emeritus on the Royal Tyrell Museum, Juan Liu from the University of California, Berkeley and Alison Murray from the University of Alberta.

Otophysans are distinctive in the best way the primary 4 vertebrae are modified to transmit vibrations to the ear from the swim bladder (a gas-filled inner organ that permits fish to take care of their place within the water with out expending vital vitality), mainly functioning as a human ear. This is definitely noticed within the skeleton of the discovered fossil of Acronichthys by the bare eye. Van Loon, utilizing synchrotron beamlines at each the Canadian Light Source in Saskatoon, Saskatchewan, and the Advanced Photon Source in Lemont, Illinois, captured a extra subtle, detailed look with computed tomography (micro-CT) scans.

Micro-CT scans are non-destructive (important when finding out prehistoric fossils), high-resolution X-ray photographs that create 3D digital fashions of objects by taking a collection of 2D X-ray projections as an object, on this case the Acronichthys, rotates.

“Many of the fossil specimens collected by the Royal Tyrrell Museum are incredibly fragile, and some are impossible to extract from the rock itself, so micro-CT scans provide not only the best method for acquiring detailed images of what’s inside, they’re also the safest way to avoid destroying the fossil all together,” mentioned Van Loon.

One fish, two fish, pink fish, blue fish

While the invention of Acronichthys introduces a brand new species to paleontological information, it additionally gives important information to hint the origins of otophysans, because the supergroup is known to have began as a marine (saltwater) species earlier than transitioning to a freshwater species. The discovery suggests the transition from marine to freshwater species occurred no less than twice throughout otophysans’ evolution.

The research estimated a brand new divergence time for otophysans from marine to freshwater species at round 154 million years in the past (the Late Jurassic interval) – after Pangea, the supercontinent, started to interrupt aside about 200 million years in the past. The researchers are left making an attempt to know how the tiny Acronichthys moved from continent to continent (as its freshwater ancestors now reside on each continent besides Antarctica) in the event that they could not swim throughout saltwater oceans.

“Dinosaurs are pretty exciting, so a lot of time and effort has been focused on them so we know a lot about what they were like, but we’ve only scratched the surface when it comes to understanding the diversity of prehistoric freshwater fish,” mentioned Brinkman. “There’s still so much we don’t know, and a fossil site right here in Canada is giving us the key to understanding the origins of groups that now dominate rivers and lakes around the world.”