Scientists stumbled upon the oldest brain of any vertebrate

Sci­en­tists stum­bled upon the old­est brain of any vertebrate

Pale­on­tol­o­gist Matt Fried­man was sur­prised to dis­cov­er a high­ly detailed 319-mil­lion-year-old fish brain fos­sil while test­ing micro-CT scans for a larg­er project.

Fried­man of the Uni­ver­si­ty of Michi­gan says. “It’s got all these fea­tures and it’s like, ‘Is this real­ly the brain I’m look­ing at?

“So we zoomed in on that part of the skull and did a sec­ond high-res­o­lu­tion scan, and it became clear that it was exact­ly what we need­ed. , we decid­ed to aim higher.”

Usu­al­ly, traces of such ancient crea­tures remain only from hard parts such as ani­mal bones. Soft tis­sue dete­ri­o­rates quick­ly, so it’s eas­i­er to store.

In this case, how­ev­er, a dense min­er­al, pre­sum­ably pyrite, was leached out and replaced the tex­ture that would have been pre­served longer in the hypox­ic envi­ron­ment. This allowed us to cap­ture details of the cra­nial nerves and soft tis­sue of the small fish Coc­co­cephalus wildi.

Although the spec­i­men has been in the hands of researchers since it was first described in 1925, this fea­ture has remained hid­den to avoid the risk of sci­en­tists using inva­sive research meth­ods. It was.

“The fos­sils, which have been exam­ined many times over the past cen­tu­ry by mul­ti­ple peo­ple, show a remark­able state of preser­va­tion,” Fried­man explains.

“But new tools for look­ing inside fos­sils have revealed anoth­er lay­er of information.

This pre­his­toric estu­ary fish prob­a­bly hunt­ed insects, small crus­taceans and cephalopods by chas­ing them with fins sup­port­ed by bony sticks called rays.

Actinoptery­gii (sub­class Actinoptery­gii) account for more than half of all liv­ing ver­te­brates, such as tuna and sea­hors­es, and 96% of all fish.

This group diverged about 450 mil­lion years ago from the lobe-finned fish that even­tu­al­ly became our ances­tors. C. wil­di then evolved inde­pen­dent­ly from a school of fish that still lives tens of mil­lions of years ago.

“Analy­sis places this tax­on out­side the group that includes all extant ray fish,” write Uni­ver­si­ty of Michi­gan pale­on­tol­o­gist Rodri­go Figueroa and col­leagues in a paper.

“Thus, the details of the brain struc­ture in Coc­co­cephalus have impli­ca­tions for the inter­pre­ta­tion of neu­ro­mor­phol­o­gy at ear­ly stages in the evo­lu­tion of impor­tant ver­te­brate lineages.

Cer­tain mor­pho­log­i­cal details could still be dis­cerned, although some brain fea­tures are lost dur­ing decay and preser­va­tion. They found that this pre­his­toric fore­brain evolved more like our fore­brain than any oth­er liv­ing rayfin fish.

“The brain of Kokkoke­falu is fold­ed inwards, unlike all extant stingray fish,” Fried­man says. “So this fos­sil pre­dates the evo­lu­tion of this fea­ture that is char­ac­ter­is­tic of the ray brain, which was not very clear until the new data on Coc­co­cephalus. It puts some kind of con­straint on when the has evolved.”

Like us, the two cere­bral hemi­spheres come to embrace a cav­i­ty that is a com­bi­na­tion of the ‘V’ and its mir­ror image. In con­trast, the fore­brain of still-liv­ing ray fins con­sists of two lobes with only a thin notch between them.

Researchers are eager to exam­ine oth­er fish fos­sils in the muse­um’s col­lec­tion to see if there are oth­er soft-tis­sue imprints hid­den inside.

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