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About Traditional Art / Professional Member Brian ChooMale/Australia Group :iconprehistory-alive: Prehistory-Alive
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Microbrachius dicki = Sex in the Devonian by Gogosardina
Microbrachius dicki = Sex in the Devonian
2014, acrylics on paper, digital and photography

Image for = John A. Long, Elga Mark-Kurik, Zerina Johanson, Michael S. Y. Lee, Gavin C. Young, Zhu Min,  Per E. Ahlberg, Michael Newman, Roger Jones, Jan den Blaauwen, Brian Choo & Kate Trinajstic (2014) Copulation in antiarch placoderms and the origin of gnathostome internal fertilization. Nature DOI:doi:10.1038/nature13825

www.nature.com/nature/journal/…


ca.385 million years ago, Middle Devonian (Givetian), Eday Flags, Orkney Islands, Scotland

     In a freshwater stream feeding into Lake Orcadie in equatorial Euramerica. With amorous rivals in pursuit, a male Microbrachius dicki* sweeps a receptive female away from the pack. Swimming side by side, their pectoral fins firmly interlocked with one another, the male inserts one of his enormous claspers into the female’s cloaca where paired genital plates lined with sharp hooks lock the bony phallus in place as sperm is transferred. 

     Reproduction in jawed vertebrates (gnathostomes) involves either external or internal fertilization. It has commonly been argued that internal fertilization can evolve from external, but not the reverse. However the fossil record has thrown multiple spanners into the works.
   
     Placoderms are an extinct group of armoured fishes that are widely resolved as a paraphyletic grade of basal gnathostomes (ie. All modern jawed vertebrates evolved from placoderms). Paired claspers have been found in advanced placoderms (arthrodires and ptyctodonts), suggesting that copulation might actually be the primitive state for Gnathostomata. However, without data on the reproduction of more primitive forms, it could be argued that these were specialized features of certain placoderm subgroups. 

   Now we have discovered that antiarchs, the most primitive jawed vertebrates in the fossil record, engaged in penetrative copulation. Key to this discovery is little Microbrachius, a small Middle Devonian antiarch (about the size and shape of a modern Corydoras catfish) originally described back in 1886 and known material from Scotland, Estonia and China. Numerous newly discovered specimens from the Orkney Islands have revealed that mature males bore proportionally enormous bony claspers.

   These were serious and brutal-looking man-tools, the ventral surface consisting of a slender trunk extending from the rear of the body armour, bearing transverse ribs covered in small knobs, followed by a section bearing whopping great spikes and finally a huge blade like lateral prong for cloacal insertion. The dorsal surface was smooth, bearing a prominent sperm-channel that was probably covered in soft tissue in life. The female had some impressive genital gear as well – a pair of flat bony plates flanking her cloaca with rows of tiny hooks on the dorsal surface. Female genital plates have also been identified in the antiarchs Pterichthyodes and Bothriolepis (male claspers are so far only known from Microbrachius).

   This strongly infers that copulation first appeared very deep in the history of jawed vertebrates. We have compelling evidence that internal fertilization is the default setting for the Gnathostomata and thus spawning (shedding large quantities of eggs and sperm into the surrounding water, as practiced by most living fish and frogs), despite long being considered a "primitive" feature, is in fact a derived state in jawed vertebrates. 

*Yes, Traquair really did name it dicki roughly 1.3 centuries before we discovered it had giant bony male intromittant organs. Robert Dick was a 19th century Scottish fossil hunter who provided the first specimens of this fish.




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Penetrative copulation is the default setting for the Gnathostomata!

Paper = www.nature.com/nature/journal/…
Summary = www.nature.com/news/fossils-re… 
(Note that on the simplified cladogram, the Chondrichthyes branch is mislabelled as Placodermi - and they've credited me as "David Choo")
About to head off for 2 weeks in the northern Simpson Desert in search of Early-Middle Devonian fish fossils. Will be out of contact until the 1st week of August.

We'll take what we can get, but my #1 goal is to find some pituriaspids.

  
Penetrative copulation is the default setting for the Gnathostomata!

Paper = www.nature.com/nature/journal/…
Summary = www.nature.com/news/fossils-re… 
(Note that on the simplified cladogram, the Chondrichthyes branch is mislabelled as Placodermi - and they've credited me as "David Choo")

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Brian Choo
Artist | Professional | Traditional Art
Australia
An Australian vertebrate palaeontologist. I mainly work on Silurian-Devonian fishes, especially basal actinopterygians.
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:iconforuknau:
Foruknau Featured By Owner Aug 14, 2014  Hobbyist Traditional Artist
I must say - I really do enjoy your work, making you my favorite artist if I had to pick one!
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:icongogosardina:
Gogosardina Featured By Owner Aug 16, 2014  Professional Traditional Artist
Thanks very much for your kind comment!
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:iconforuknau:
Foruknau Featured By Owner Aug 16, 2014  Hobbyist Traditional Artist
You're very welcome and deserving of such!
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:iconvorseth:
Vorseth Featured By Owner Jul 2, 2014  Hobbyist Digital Artist
Hey mate :) I'm an aussie amateur fossil collector :) and artist, im about to start doing dinosaur art shortly :D your latest microraptor eating the bird is awesome! keep up the good work, Where in Aus are you based?
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:icongogosardina:
Gogosardina Featured By Owner Jul 2, 2014  Professional Traditional Artist
Hey thanks. Currently I'm in Adelaide.
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