The discovery of one of the oldest known hagfish fossil with its soft tissue preserved shows the eel-shaped fish have remained largely the same since at least the Late Cretaceous period, 66 to 100 million years ago.
Paleontologists have long debated when the hagfish lineage separated from lamprey eels, and whether the latter are more closely related to more advanced animals with backbones.
Hagfish are jawless, boneless vertebrates that live in cold marine environments around the world. They produce slime to protect themselves from predators-in fact, they can produce a litre of slime in less than a second.
"Soft tissues are rarely preserved, but can include 90 per cent of the anatomical information of any animal," explained U of A paleontologist Philip Currie, a co-author on the study who first saw the fossil in 2013 and was impressed by its exquisite preservation.
"The new hagfish fossil had more information on the anatomy of these animals than any other fossil, and thus showed promise for finally solving the debate," said Currie, who added the specimen included chemical traces of slime glands, the first time scientists were able to observe that in such an old specimen.
The researchers, led by then U of A PhD candidate Tetsuto Miyashita, now a post-doctoral fellow at the University of Chicago, conducted a detailed analysis of the soft tissues-including the slime glands, using synchrotron rapid-scanning X-ray fluorescence.
"Results indicated that hagfish have been an independent lineage since at least the late Cretaceous period," said Currie.
The study, "Hagfish From the Cretaceous Tethys Sea and a Reconciliation of the Morphological-Molecular Conflict in Early Vertebrate Phylogeny," is published in PNAS.