Lampreys show little evolutionary variation over 360 million yearsBy Catherine Gianaro
Medical Center Public Affairs
Scientists from the University of Witwatersrand in Johannesburg, South Africa, and here at Chicago have uncovered a remarkably well-preserved fossil lamprey from the Devonian period. The discovery reveals that today’s lampreys are “living fossils” because they have remained largely unaltered for 360 million years.
Michael Coates, Associate Professor in Organismal Biology & Anatomy, joined the University of Witwatersrand’s Bruce Rubidge and Rob Gess, graduate student and lead author, in describing the new find in an article published in the Thursday, Oct. 26 issue of Nature.
“Apart from being the oldest fossil lamprey yet discovered, this fossil shows that lampreys have been parasitic for at least 360 million years,” said Rubidge, director of the Bernard Price Institute for Paleontological Research.
Lampreys are long, eel-like parasites that attach themselves to and feed on other fish. Of the 46,000 known species of vertebrates, lampreys and hagfish are the only surviving jawless vertebrates. Lampreys are the most “primitive” of the vertebrates, meaning that they are the least changed from the first vertebrates. Besides lacking jaws, lampreys have no paired pectoral and pelvic fins, and they have no scales.
“This fossil changes how we look at lampreys today,” said Coates. “They’re very ancient, very primitive animals, yet with highly specialized feeding habits.”
It reveals that the anatomical evolution of lampreys is more conservative than scientists have thought, Coates added. Although they have become slightly longer, they specialized early and successfully, and thus appear to have stayed much the same for the past 360 million years.
“This discovery is a monument to the dedication and passion of [Gess], who has spent many months patiently excavating and unearthing the elusive secrets from the prehistoric past,” Rubidge said.
Gess found the new specimen, Priscomyzon riniensis, 18 months ago in an ancient estuary in Grahamstown, South Africa. Preserved with its underside showing, the fossil measures less than 2 inches long and reveals a set of 14 teeth surrounding a mouth that is proportionately larger than mouths of its descendents today.
“The most striking feature of Priscomyzon is its large oral disc, edged with a soft outer lip, supported by an annular cartilage and surrounding a circular mouth,” the authors wrote. “This is the first clear evidence of a Palaeozoic lamprey with an oral disc.”
According to the scientists, this find greatly adds to what was a severely limited lamprey fossil record and, for the first time, places the origin of modern lamprey morphology deep within the Palaeozoic period. It adds new, essential information to the emerging and changing picture of early vertebrate evolution.
Until now, the lamprey fossil record included only those that show a side view and reveal little of the gill basket and feeding apparatus. However, earlier this year, Nature reported on a freshwater lamprey fossil found in the Jehol biota of China (Inner Mongolia) from the Early Cretaceous period (about 125 million years ago).
The newly discovered South African fossil shows that these anatomically specialized fish are “holdovers” from ancient marine ecosystems, Coates said. Obviously exceptional survivors, these animals predate the advent of modern fish and have survived at least four major extinction events.
“There are few representatives of these early branches in vertebrate evolution that are still around today,” Coates said, which is why so much scientific attention has been paid to lampreys. Although highly specialized in their own right, these primitive animals are used as surrogate ancestors for comparative research on living jawed vertebrates.
“It gives us a calibration point,” Coates said. “We study lampreys because, in many respects, they’re so primitive. They never had jaws, they never had [true] teeth, they never had fins, and they never had limbs. Lampreys provide a glimpse of conditions early in vertebrate evolutionary history.”
Because lampreys do not have bones or any substantial cartilage, fossils of these creatures are extremely rare. This fossil not only reveals a nearly complete soft tissue impression, but it also pushes back the lamprey fossil record another 35 million years.
“These are pretty insubstantial animals,” Coates said. “Lacking a boney skeleton, they rot down, leaving no hard parts, like a skull or ribs. So if a fossil site is discovered that yields impressions of the delicate remains of these animals, then this site needs to be explored thoroughly for other examples of exceptional preservation.”
The scientists will continue to sort through much of the indeterminate material that is emerging from an ongoing dig at the discovery site.
Nearly 50 species of lampreys are found today in temperate rivers and coastal seas. Some species live in fresh water for their entire lives, but most are anadromous, migrating from the ocean to fresh water to spawn and reproduce, and then returning to the ocean to grow and mature. When adult lampreys return to fresh water to breed, they stop feeding during winter and spawn the following spring. After approximately three weeks, eggs hatch and become blind larvae called ammocoetes. After four to seven years, the ammocoetes metamorphose into juvenile lampreys, or macropthalmia, which then migrate out to the ocean and become parasitic adult lampreys. Abundant in the Northeast United States, adult lampreys live just a year or two and can grow to as long as two feet.