Mesomyzon

Mesomyzon
Temporal range: Early Cretaceous
Fossil specimen
Speculative life restoration
Scientific classification Edit this classification
Kingdom: Animalia
Phylum: Chordata
Infraphylum: Agnatha
Class: Petromyzontida
Order: Petromyzontiformes
Genus: †Mesomyzon
Chang, Zhang & Miao 2006
Species:
†M. mengae
Binomial name
†Mesomyzon mengae
Chang, Zhang & Miao 2006

Mesomyzon is an extinct lamprey genus from freshwater strata of the Early Cretaceous (Barremian–Aptian age) Yixian Formation of China. It contains a single species, M. mengae.

Mesomyzon's exquisitely preserved fossils show a creature very similar to modern-day lampreys, having a well-developed sucking oral disk, a branchial basket, at least seven pairs of gill pouches and corresponding gill arches, impressions of gill filaments, and at least 80 myomeres of its musculature. Its anterior (first) dorsal fin was very long, running down 44%-48% of its body, and it had a ribbon-like preanal skin fold not known in any other lamprey. It had the same three-phase life cycle found in modern lampreys.

A phylogenetic analysis conducted in 2018 shows that Mesomyzon is the fossil lamprey most closely related to modern taxa, though it is not closely related to any modern group. On the other hand, Brownstein & Near (2022) found it to be a member of the lamprey crown group, most closely related to Petromyzontidae. However, a 2023 study found it again to be a derived stem lamprey, with the earlier Yanliaomyzon from the same region found to be more closely related to modern lampreys. This study also suggested Mesomyzon to be a blood feeder.

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