The early fossil record is littered with bizarre creatures that do not resemble anything living today. And few of those evolutionary enigmas are as perplexing as Typhloesus, an ancient sea animal so strange that paleontologists have referred to it as an alien goldfish.
The bloblike animal has defied taxonomic placement for nearly 50 years. Scientists weren’t sure whether the animal, which had a substantial tail fin and a gut often packed 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 Typhloesus fossils may bring these seemingly extraterrestrial animals down to earth. “It helps us find the branch of the tree of life that Typhloesus belongs to,” said Jean-Bernard Caron, a paleontologist at the Royal Ontario Museum in Toronto.
Caron and Simon Conway Morris, a paleontologist at the University of Cambridge, made the discovery while examining several Typhloesus specimens that had recently been added to the Royal Ontario Museum collection. Those fossils, which are only a couple of centimetres long, were dug up from the Bear Gulch Limestone in Montana, a 330-million-year-old fossil deposit.
When those fossilised creatures were living, this area was blanketed by a balmy bay. Local monsoons washed nutrients into the bay, sparking algal blooms that sapped oxygen from the water and kept scavengers at bay. Those conditions allowed myriad soft-bodied invertebrates to be preserved in incredible detail.
Because many of these ancient sea creatures are delicately imprinted onto the limestone, most of their identities are easy to deduce. However, Typhloesus has perplexed scientists since it was described in 1973. The vaguely fishlike critter was once believed to be a conodont, a jawless, eel-like vertebrate. But a closer inspection revealed that the conodont remains were inside an animal’s digestive tract. That led scientists to conclude that Typhloesus had snacked on conodonts.
When Caron stuck several of the newly gained specimens under a high-powered scanning microscope, he spotted a ribbonlike structure studded with recurved teeth on both sides. Because the toothy apparatus is lodged within the animal’s gut, past analyses had mistaken these rows of tiny teeth for muscle tissue.
In a study published earlier in the month in the journal Biology Letters, the researchers describe the new structure as a radula, a tonguelike structure covered in teeth that snails and other mollusks use to scrape food into their mouths.
The existence of Typhloesus’ toothy radula led the scientists to deduce that the alien goldfish was in fact a mollusk. — NYT
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