Dear Torben,

I am not a specialist in deep-sea fauna per se, but I do work extensively on amphipod phylogenetics. In our recent global phylogeny of amphipoda we found that all deep-sea clades (>1km) have radiated relatively recently (Late Cretaceous to Cenozoic), coinciding with significant cooling and oxygenation of abyssal waters. Paper is here Article The late blooming amphipods: Global change promoted post-Jur...

A very useful general paper on the topic is this one Article The dynamics of biogeographic ranges in the deep sea

RG doesn't allow uploading, I can send you copies if needed.

This is a very interesting topic. As far as I am aware most extant deep-sea fauna (except isopods) is of relatively recent origin (

Some studies have indicated that some deep-sea fishes, such as the grenadiers (Family Macrouridae), have been present in the deep sea for over 100 million years.

There is also evidence for deep-sea extinctions, although these events are often difficult to detect due to the patchy nature of deep-sea sampling. One example of a deep-sea extinction is the loss of the monoplacophoran mollusks, which were once common in the deep sea but are now only found in shallow waters (correct me if I am wrong).

There are many examples of deep-sea radiations, where certain groups of organisms have diversified and adapted to life in the deep sea. One well-known example is the radiation of deep-sea crabs in the family Bythograeidae, which have evolved unique adaptations for life in the deep sea, such as specialized respiratory structures and elongated limbs for walking on soft sediments. Another example is the radiation of deep-sea octopods in the genus Grimpoteuthis, also known as "Dumbo octopuses", which have evolved a distinctive ear-like structure used for swimming.

Dear Dr. Torben,

Deep-sea clades, or groups of organisms that have diversified in the deep-sea environment, can vary greatly in age. Some clades have radiated relatively recently, while others have a long evolutionary history. The age of a clade depends on various factors, including the availability of suitable habitats, the dispersal ability of the organisms, and the nature of environmental changes over time.

There is evidence for deep-sea extinctions, as there have been multiple periods of global environmental change throughout the Earth's history. For example, during the Cretaceous-Paleogene extinction event approximately 66 million years ago, many deep-sea organisms, including some ammonites and foraminifera, went extinct. More recently, human activities such as deep-sea trawling and pollution have also had negative impacts on deep-sea biodiversity.

Some good examples of deep-sea radiations include the crustacean order Decapoda, which includes crabs, lobsters, and shrimp, as well as various groups of fishes, such as anglerfishes, lanternfishes, and rattails. These groups have diversified to occupy different ecological niches in the deep sea, such as benthic (bottom-dwelling) or pelagic (open-water) habitats. Isopods, as you mentioned, are another example of a group that has diversified in the deep sea.

For further reading, I recommend the following papers:

Thiel, H., & Schriever, G. (1993). Organization of deep-sea pelagic communities. Philosophical Transactions of the Royal Society B: Biological Sciences, 341(1292), 23-28.

Rex, M. A. (1981). Community structure in the deep-sea benthos. Annual Review of Ecology and Systematics, 12(1), 331-353.

Brandt, A., & Poore, G. C. (2003). Higher-level systematics of the isopod family Munnopsidae (Crustacea: Asellota)–morphology, classification, and a revised molecular approach. Zoological Journal of the Linnean Society, 139(4), 461-490.

Ravail Singh thanks for your comment. Do you have recommendations in terms of papers? I am especially keen on papers that mention deep-sea extinctions. But also the taxa you mentioned with regard to radiations are intersteing. Can you recommend papers?

Article The Biological Effects of Ionising Radiation on Crustaceans: A Review

https://deepseanews.com/2014/01/is-the-sea-floor-littered-with-dead-animals-due-to-radiation-no/

https://www.eurekalert.org/news-releases/693644

https://hps.org/publicinformation/ate/q11179.html

These above sources will help you to sum up your answer. I got some sources once I was following the discussion on another plateform

Hi Thorben,

here some suggestions:

Thuy, B., Knox, L., Numberger-Thuy, L.D., Smith, N.S., and Sumrall, C.D. 2023. Ancient deep ocean as a harbor of biotic innovation revealed by Carboniferous ophiuroid microfossils. Geology, Article Ancient deep ocean as a harbor of biotic innovation revealed...

Thuy, B., Kiel, S., Dulai, A., Gale, A.S., Kroh, A., Lord, A.R., Numberger-Thuy, L.D., Stöhr, S., and Wisshak, M. 2014. First glimpse into Lower Jurassic deep-sea biodiversity: in-situ diversification and resilience against extinction. Proceedings of the Royal Society B 281: 20132624.

Lorion, J., Kiel, S., Faure, B.M., Kawato, M., Ho, S.Y.W., Marshall, B.A., Tsuchida, S., Miyazaki, J.-I., and Fujiwara, Y. 2013. Adaptive radiation of chemosymbiotic deep-sea mussels. Proceedings of the Royal Society B 280: 20131243.

Williams, S.T., Smith, L.M., Herbert, D.G., Marshall, B.A., Warén, A., Kiel, S., Dyal, P., Linse, K., Vilvens, C., and Kano, Y. 2013. Cenozoic climate change and diversification on the continental shelf and slope: evolution of gastropod diversity in the family Solariellidae (Trochoidea). Ecology and Evolution 3: 887–917.

Lindner, A., Cairns, S.D., and Cunningham, C.W. 2008. From offshore to onshore: Multiple origins of shallow-water corals from deep-sea ancestors. PLoS ONE 3: e2429.

Viele Grüsse, Steffen