The earliest evidence of deep-sea vertebrates

Abstract

Vertebrate macroevolution has been punctuated by fundamental habitat transitions from shallow marine origins to terrestrial, freshwater, and aerial environments. Invasion of the deep sea is a less well-known ecological shift because of low fossilization potential and continual loss of abyssal fossil record by ocean floor subduction. Therefore, there has been a lack of convincing evidence of bottom-living vertebrates from pre-Paleogene deep seas. Here, we describe trace fossils from abyssal plain turbidites of the Tethys Ocean, which, combined with nannofossil dating, indicate that fishes have occupied the deep seafloor since at least the Early Cretaceous (Hauterivian–Barremian). These structures are identical to those produced by modern demersal fishes that feed by either scratching the substrate or expose their prey by water flow generated by suction or jetting. The trace fossils suggest activity of at least three fish species exploiting a productive abyssal invertebrate sediment fauna. These observations are consistent with Early Cretaceous vertebrate transition to the deep sea triggered by the availability of new food sources. Our results anticipate the appearance of deep-seafloor fishes in the fossil record by over 80 My while reassessing the mode of vertebrate colonization of the deep sea.

Colonization of the ocean floor by jawless vertebrates across three mass extinctions

“…Vertebrates, which comprise tens of thousands of species distributed across all major ecosystems, underwent their initial diversification in marine habitats during the Ordovician to Devonian Periods, around 480–360 million years ago [ 19 – 21 ]. Despite this ancient history in the ocean, evidence from the fossil record [ 22 ] and molecular phylogenetics [ 23 – 34 ] suggests that most living deep marine vertebrate diversity originates from radiations that took place over the last 100 million years. This observation raises the question of whether any living vertebrate diversity in the ocean benthos can truly be considered geologically ancient.…”

Genome sequencing of Coryphaenoides yaquinae reveals convergent and lineage‐specific molecular evolution in deep‐sea adaptation

“…Depth serves as a driving force in evolution within the deep sea (Gaither et al, 2016). However, the invasion of the deep sea is a less well-known ecological shift (Baucon et al, 2023). Certain deepsea fish species are classified as endangered due to anthropogenic activities (Ramirez-Llodra et al, 2011) and low fecundity and slow growth (Devine et al, 2006).…”

The Paleozoic assembly of the holocephalian body plan far preceded post-Cretaceous radiations into the ocean depths

“…Given their ancient common ancestry with other vertebrates, deepwater chimaeras and ghost sharks lend credence to the hypothesis that mesopelagic and bathypelagic environments have served as a refuge for ancient biodiversity that has become rare or extinct in other ecosystems [22,23]. Evidence from the fossil record [24] and phylogenomic analyses of diverse living deep sea vertebrate clades [25][26][27][28][29][30][31][32][33] suggest younger origins for these deepwater radiations. Thus, chimaeras and ghost sharks stand as one of the remaining potential relict vertebrates in the bathypelagic and mesopelagic zones.…”