‘Exotic goldfish’ finds home
The early fossil record is littered with strange creatures that do not resemble anything alive today. And few of those evolutionary mysteries are as perplexing as the typhlosus, an ancient marine animal so strange that paleontologists refer to it as an exotic goldfish.
The blob-like animal has defied taxonomic placement for nearly 50 years. Scientists weren’t sure whether the animal, whose tail fins and abdomen were often littered with the remains of early fish species, was more closely related to a worm, a jawless fish, or something else entirely.
However, the discovery of a tooth-covered tongue in several typhlosus fossils may have brought these seemingly extraterrestrial animals to Earth. “It helps us find the branch of the tree of life that belongs to the typhlosus,” said Jean-Bernard Caron, a paleontologist at the Royal Ontario Museum in Toronto. “It’s no longer a problematic orphan.”
Caron and Simon Conway Morris, a paleontologist at the University of Cambridge, made the discovery while examining several typhlosus specimens that had recently been added to the Royal Ontario Museum collection. Those fossils, which are only a few centimeters long, were excavated from Bear Gulch Limestone in Montana, a 330-million-year-old fossil deposit.
When those fossil creatures were living, the area was covered by a balmy creek and was home to sharks, the oldest known ancestors of sword-like vertebrates, coelacanths, and vampire squid. The local monsoon flushed nutrients into the bay, causing algal blooms that stripped oxygen from the water and kept scavengers away. Those conditions allowed myriad soft-bodied invertebrates to be preserved in incredible detail.
Since many of these ancient sea creatures are delicately inscribed on the limestone, much of their identification is easy to spot. However, typhlosus has puzzled scientists since it was described in 1973. The obscure fish-like critter was once thought to be a conifer, a jawless, eel-like vertebrate. But closer inspection revealed that the conodont remains were inside an animal’s digestive tract. This led the scientists to conclude that typhlosus had snacked on conodonts.
When Caron glued several newly obtained specimens under a high-powered scanning microscope, he saw a ribbon-like structure studded with bent teeth on either side, like the business end of a chain saw. . Since the dentate apparatus is lodged within the animal’s intestine, previous analyzes mistaken these rows of small teeth for muscle tissue.
In a study to be published Wednesday in the journal Biology Letters, researchers describe the new structure as a radula, a tongue-like structure covered in teeth that snails and other mollusks use to scrape food into their mouths. The researchers hypothesize that the tooth-studded structure was most likely attached to a retractable trunk in Typhloaceus. When typhloesus approached a wavy conodont, its tooth-covered tongue protruded to cover its food.
The existence of the toothed radula of Typhloesus led scientists to conclude that the exotic goldfish was actually a mollusk.
“Having a radula is a very exciting discovery, as it is certain,” said Christopher Whelan, a paleontologist at the American Museum of Natural History who studies cephalopods from Bear Gulch and was not involved in the new study. “Just as all vertebrates have a backbone, so all mollusks have a radula.”
However, it is difficult to tell what type of mollusk the typhlosus was. Caron proposes that the creature was similar to modern sea elephants. These gelatinous slugs swim through the water column and stick their radula by means of a trunk-like proboscis to intercept prey, a hunting style proposed in the new study for typhlosus. Although typhloesus lacked eyes, its flexible body and large tail fin suggest that it was an active swimmer propelling itself through the water column as opposed to inching along the ocean.
But typhloesus fossils predate the fossil record of the remaining swimming snails by more than 100 million years. According to Whelan, this may be because these sea slugs lacked easily fossilized features such as shells, which made them more efficient in the water. As a result, they are rare in most fossil deposits.
typhlosus could help paleontologists learn more about the evolution of mollusks, the second largest group of invertebrates on the planet today. According to Caron, the strangest creatures often have the most important tales to tell.
“The turning point that life can give us is presented by these strange fossils,” he said. “They are enigmatic, but they reveal a lot of important evolutionary information.”
(Written by Jack Tamisia)