Wednesday, June 21, 2006

Mesomyzon, a Cretaceous lamprey

Fossil lampreys are exceedingly rare. The oldest are known from Early Carboniferous and that's about it. These fossils are recorded in limestones, suggesting that they were marine, while modern forms are known to inhabit marine and freshwater environments where they make their living parasitizing fish.

Today in Nature, Mee-mann Chang and colleagues report on a fossil lamprey from the same beds that have yielded feathered dinosaurs. Mesomyzon, figured below, is very similar to modern lampreys in many respects and helps bridge the, albeit rather small, morphological gap between the Carboniferous forms and modern forms. It also tells us that by the Early Cretaceous, lampreys had invaded freshwater habitats.

a, A complete fish (IVPP V14718A) in left view. b, Holotype (IVPP V14719) in right view. c, Drawing of the holotype, with the dorsal fin and caudal region reconstructed on the basis of IVPP V14718A. d, Photograph of head and anterior part of body of the holotype. e, Drawing of the same part as in d. Scale bars, 10 mm (a–c) and 5 mm (d, e). Abbreviations: a., anus; br.b., branchial basket; c.f., caudal fin; d.f., dorsal fin; d.t.?, possible digestive tract; g., gonads; g.a., gill arches; g.f., gill filaments; l., liver; l.e., left eye; l.ot., left otic capsule; ms., myosepta; nc., notochord; or.d., oral disk; p.c.?, possible piston cartilage; pc.c., pericardial cartilage; r.e., right eye; r.ot., right otic capsule. From Chang et al. 2006.

More about lampreys to come.

Chang, M.-m. et al. 2006. A lamprey from the Cretaceous Jehol biota of China. Nature 441: 972-974. <link>

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