Cold-Seep Mollusks Are Older Than the General Marine Mollusk Fauna

Abstract

The origin and possible antiquity of faunas at deep-sea hydrothermal vents and seeps have been debated since their discovery. We used the fossil record of seep mollusks to show that the living seep genera have significantly longer geologic ranges than the marine mollusks in general, but have ranges similar to those of deep-sea taxa, suggesting that seep faunas may be shaped by the factors that drive the evolution of life in the deep sea in general. Our data indicate that deep-sea anoxic/dysoxic events did not affect seep faunas, casting doubt on the suggested anoxic nature and/or global extent of these events.

Did shifting seawater sulfate concentrations drive the evolution of deep-sea methane-seep ecosystems?

“…The analysis covers the last 150 Myr because the estimate of the sulfate concentrations covered the last 130 Myr [12] and because fossiliferous seep deposits older than Late Jurassic are scarce [6]. Molluscs serve as model group because they have by far the richest fossil record among seep taxa and they have been extensively treated taxonomically in the past years by a small number of specialists, resulting in a relatively homogeneous dataset (electronic supplementary material, table S1).…”

“…Oceanographic events such as widespread anoxia or biological triggers such as the appearance of whales, whose decaying carcasses are often colonized by a similar suite of animals and may therefore act as dispersal stepping stones, have been suggested as potential reasons for the geologically young origin of the vent and seep fauna [5,7,8]. Furthermore, because their diet is based on locally available reduced chemicals, mainly hydrogen sulfide and to a lesser extent methane and hydrogen [9], it was hypothesized that the evolutionary history of these faunas may be independent from that of photosynthesis-based ecosystems on the surface of our planet [6,10]. The ultimate source of sulfide at methane seeps is sulfate dissolved in seawater: it is produced by microbial, sulfate-dependent anaerobic oxidation of methane (AOM) [11].…”

“…Typically, only a few species account for the vast majority of the biomass in these habitats, and these dominant species live in symbiosis with chemoautotrophic bacteria, a strategy called chemosymbiosis [2]. Owing to their high degree of endemism, these vent and seep faunas were regarded geologically ancient 'relic faunas' [3,4], but molecular age estimates and the fossil record indicate a Cretaceous to early Cenozoic origin of the major clades [5,6]. Oceanographic events such as widespread anoxia or biological triggers such as the appearance of whales, whose decaying carcasses are often colonized by a similar suite of animals and may therefore act as dispersal stepping stones, have been suggested as potential reasons for the geologically young origin of the vent and seep fauna [5,7,8].…”

The mitochondrial genome of Ifremeria nautilei and the phylogenetic position of the enigmatic deep-sea Abyssochrysoidea (Mollusca: Gastropoda)

“…Although it is true that living deep-sea fauna have significantly longer geologic ranges than other marine fauna (Kiel and Little, 2006), the rich fossil record of e.g. vent and seep mollusks goes back to the Late Jurassic-Early Cretaceous, suggesting relatively modern (Late Mesozoic or even Cenozoic) origins from non-vent ancestors (Jacobs and Lindberg, 1998;Warén and Bouchet, 2001;Little and Vrijenhoek, 2003;Kiel and Little, 2006).…”

“…Although it is true that living deep-sea fauna have significantly longer geologic ranges than other marine fauna (Kiel and Little, 2006), the rich fossil record of e.g. vent and seep mollusks goes back to the Late Jurassic-Early Cretaceous, suggesting relatively modern (Late Mesozoic or even Cenozoic) origins from non-vent ancestors (Jacobs and Lindberg, 1998;Warén and Bouchet, 2001;Little and Vrijenhoek, 2003;Kiel and Little, 2006). Moreover, early molecular studies also supported relatively younger origin, although based on relatively short sequences and poorly resolved phylogenies that used calibrated strict molecular clocks (Peek et al, 1997;McArthur and Koop, 1999;Shank et al, 1999;Little and Vrijenhoek, 2003).…”