Lampreys underwent radical changes in ecology and morphology during the Jurassic era

Abstract

AbstractLampreys, the oldest living jawless vertebrates, represent an iconic model in evolutionary biology and are always intriguing for their bizarre feeding behavior of sucking blood or gouging out tissues from their victims. They seemingly underwent few changes in morphology and feeding habit since their first appearance in the Late Devonian. However, their evolutionary history is not so simple, as demonstrated by two superbly preserved large lampreys from the Middle-Late Jurassic Yanliao Biota of North China. These fossils present radical changes in the feeding apparatus, body size, and life-history strategy of their group during the Jurassic era and paved the way for the origin of living lampreys. Their extensively toothed feeding structures are radically different from the simply structured dentition of their unusually small-sized and probably non-predatory Palaeozoic relatives but surprisingly resemble the Southern Hemisphere pouched lamprey, which foreshadows an ancestral flesh-eating habit for modern lampreys. In the petromyzontiform timetree recalibrated on the basis of these stem lampreys, the evolutionary increase of lampreys’ body size accompanied the establishment of the modern-type three-phased life cycle, which was likely triggered by the concurrent evolutionary thinning of the body integument of their most significant piscine hosts in the Early Jurassic. Our study also places modern lampreys’ origin in the Southern Hemisphere of the Late Cretaceous, followed by an early Cenozoic anti-tropical disjunction in distribution, hence challenging the conventional wisdom of their biogeographical pattern arising from a recent origin in the Northern Hemisphere or the tectonic fragmentation of Pangean supercontinent as far back as 200 million years ago.