Recently, a team of researchers in China made an extraordinary discovery, unearthing two extremely well-preserved lamprey fossils dating back 160 million years. These fossils also include the largest lamprey found to date, providing new insights into the group's enigmatic evolutionary history.
Lampreys are one of two groups of jawless vertebrates living today that first appeared in the fossil record about 360 million years ago during the Devonian Period (419.2 million – 358.9 million years ago). These ancient fish, of which 31 species are still alive today, typically have suction-cup mouths full of teeth, which they use to latch on to prey and extract blood and other body fluids.
The fossils recent described date back to the Jurassic period (201.3 million – 145 million years ago) and fill a gap between early fossil discoveries and lineages existing today. The researchers pulled the specimens from a fossil bed in northeastern China and named them Yanliaomyzon occisor and Y. ingensdentes — their species names meaning "killer" in Latin and "big teeth" in Greek, respectively.
"These fossil lampreys were exceptionally preserved, showing a complete set of feeding structures," the researchers wrote in a study published Tuesday (Oct. 31) in the journal Nature Communications.
By analyzing the early fossils, it was clear to the study authors that lampreys have undergone major changes from the Devonian to the present. However, until now, large gaps in the fossil record meant that scientists did not know when these changes occurred. Y. occisor, the larger of the two recently discovered fossils, measured 64.2 centimeters long and is the largest lamprey fossil ever discovered, according to the study.
Current lamprey species can grow to be much larger than this; sea lampreys (Petromyzon marinus) grow up to 120 cm long, and Pacific lampreys (Entosphenus tridentatus) can reach up to 85 cm. On the other hand, the first lampreys were only a few centimeters long, had small, simple teeth, and likely lacked the glands that produce anticoagulants, which their modern counterparts use to keep their prey's blood moving. The mouthparts of these early lampreys indicate that they were not predators or parasites, but instead fed on algae. "Their feeding opportunities were quite limited because most of their potential hosts back then had thick scales or armor" that they could not have penetrated, the researchers added.
The newly described fossils featured "extensively toothed" mouths, suggesting lampreys were preying on other animals at least 160 million years ago, according to the study. The mouthparts of Y. occisor and Y. ingensdentes were strikingly similar to those of modern sac lampreys (Geotria australis), indicating "an ancestral meat-eating habit for modern lampreys," the authors wrote. This predatory lifestyle likely led to an increase in lamprey body size during the Jurassic period, they added. Lampreys also underwent major changes in their life history between the Devonian and Jurassic, according to the study. The large size of Y. occisor, in particular, is similar to later species that evolved a three-stage life cycle—including a larval, metamorphic, and adult phase—indicating that it may also have a tri- phasic and migrate to rivers to reproduce.
The discovery fills a gap in the evolutionary history of lampreys, shedding light on both changes in their eating habits and the modernization of their life history during the Jurassic period, according to the study.
