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150 Million Years of Fish Evolution in One Handy Figure
Have you ever wished you could have the entire 150 million years of spiny-rayed fish evolution in convenient poster form? Well, wait no longer. Your happy day is here! Trust me … this is one poster featuring mullets you will not be embarrassed to display.
Plus, you can use it as a way to explore diversity and procrastinate. Not feeling like work? Simply glance over and … morwongs?! How did I never know such things existed? Maybe I’ll just have a quick … [2 hours pass]
In this figure, you can see how all the spiny-finned fish (acanthomorphs) — more than 18,000 species of them, which represent nearly one-third of living vertebrates — are related to one another. To accomplish this, the scientists inferred the relationships from the sequences of 10 genes from 520 spiny-rayed fin fish representing most of their families. They combined this data with that of 37 fossil “age constraints” used as reality checks on the actual timing of evolutionary shifts.
So that you can savor appropriately, it’s worth noting that this section of the vertebrate family tree has evidently given scientists significant difficulty, for the team who created it write in July in the Proceedings of the National Academy of Sciencesthat this group of fish has long “remained the last frontier” in drawing the family tree of living vertebrates and that it has presented “one of the most unyielding problems in vertebrate phylogenetics”. Blood… sweat… probably tears went into the creation of this image. Which makes its arrival all the more a moment to appreciate.
These prickly-finned fish include most of the fishes you think of as fish, with several major exceptions including sharks, sturgeon, trout, and salmon. They include fish that live in high mountain lakes and at the bottom of ocean trenches, fish flat as a pancake and puffy (though not fluffy) as a pillow. As advertised, they all have characteristic sharp, bony spines in their fins that any angler can tell you that you must mind when removing a squirming, slippery, and likely panicked fish from the hook.
The scientists found that the group likely evolved in the Early Cretaceous, about 150 million years ago. It’s a bit weird to think about what that means — that the tropical reefs of the Age of Dinosaurs — and all fish-containing ages prior — contained none of the tropical reef fish we recognize today (but what wonders did they contain?).
In the past, scientists wondered what circumstances or events led this group to evolve so much. Some suggested coral reefs were the cradle of the group’s diversity. But in the PNAS study, the five lineages within the group that diversified the most are found in four very different habitats: freshwater (cichlids), open ocean (tuna and friends), cold temperate seafloor (snailfishes), and coral reefs (blennies and gobies). This seemingly confounds any simple explanation for the massive success of the group.
The scientists also found that this group of fish didn’t seem to diversify much in response to the End-Cretaceous Mass Extinction. You can see this in the figure above. The dashed circle is when the Really Big Rock Hit Planet Earth. There doesn’t seem to be a big burst of evolution in its aftermath — that is, a whole lot of new lineages created all at once, perhaps to fill niches vacated by the Really Big Rock. Although it’s well established that many groups of snakes, lizards, birds, and mammals diversified significantly in response to the asteroid strike (although some major groups of these animals did not), it appears that this giant piscine group of vertebrates remained relatively unaffected by what was for many terrestrial vertebrates an Earth-shattering opportunity.
Near T.J., Dornburg A., Eytan R.I., Keck B.P., Smith W.L., Kuhn K.L., Moore J.A., Price S.A., Burbrink F.T. & Friedman M. & (2013). Phylogeny and tempo of diversification in the superradiation of spiny-rayed fishes, Proceedings of the National Academy of Sciences, 110 (31) 12738-12743. DOI:10.1073/pnas.1304661110

February on this blog is going to be Daily Paleo Art Month! Because doing dinosaurs all last July was so much fun I want to do this thing again. Every weekday for the rest of the month I’ll be posting a new image of something strange, obscure, or just plain interesting from the fossil record — only this time we’re staying firmly outside of the Avemetatarsalia (pterosaurs and dinosaurs/birds) to give some less famous critters the spotlight.
#1: Helicoprion
A cartilaginous fish from off the southwest coast of the ancient supercontinent Gondwana (and later Pangaea), Helicoprion first appeared in the late Carboniferous (310 million years ago) and survived up until just past the massive Permian-Triassic extinction (250mya). Despite looking rather shark-like and possibly reaching sizes of around 6m (20ft) long, it was actually closer related to the chimaeras.
For a long time, the only parts of this animal known were bizarre buzzsaw-like spiral whorls of teeth, since cartilage skeletons very rarely fossilize. The ideas for just where in the body this structure was positioned were ridiculously varied.
The most recent reconstruction is based on CT scans of a well-preserved fossil with jaw and skull elements, which showed the whorl taking up the whole lower jaw. It also turns out Helicoprion had no upper teeth at all. It’s thought to have used this arrangement to shred and crush up squid and other soft-bodied marine prey, but there’s still very little known about how such a unique type of teeth evolved in the first place.

Dunkleosteus and Cladoselache by John Sibbick

Dunkleosteus and a Devonian Coelacanth
A Dunkleosteus skull, photographed at the Royal Tyrrell Museum in Drumheller Alberta.  Dunkleosteus was a placoderm fish that lived in the late Devonian, 380 to 360 million years ago.  It was a hypercarnivorous apex predator, feeding on armored prey such as ammonites, arthropods, and other placoderms.  Fully grown individuals had more than 700 kilograms of bite force, enough to easily shear through bone and protective tissues.  Members of the largest species could grow up to 10 meters in length and weigh almost four tonnes.

Parayunnanolepis and Psarolepis by *Gogosardina
Sometime, in the Devonian, on the floors of shallow, green seas, the fish looked like stones. They lives their lives encased in tight-fitting armor. Bodies locked in cuirass, plackart, and pauldron. Arms: gauntlets. Just a keyhole in the helmet for peeking eyes. Life was lived hidden in an envelope of bone; and the world was only touched through chinks in the walls built against one’s own flesh.

Daily Paleo Art Month #2: Vetulicola
Known from the 525-520 million-year-old Lower Cambrian Chengjiang Lagerstätte, Vetulicola is a member of a strange group of creatures known as vetulicolians. About 9cm (3.5in) long, it’s thought to have been an active swimmer that fed on either plankton or seafloor debris.
And nobody’s sure just what these animals are. They were originally thought to be early limbless arthropods, but more recently opinions have swung in the opposite direct and they’re now considered to be early deuterostomes instead.

The ancient inhabitant, Vetulicola (1987)
Phylum : VetulicoliaFamily : VetulicolidaeGenus : VetulicolaSpecies : V. cuneata, V. rectangulata, V. gantoucunensis, V. monile
Middle Cambrian
9 cm long (size)
China (map)
The type species, Vetulicola cuneata (Hou, 1987) has a body composed of two distinct parts of approximately equal length. The front part is rectangular with a carapace-like structure of four rigid cuticular plates, with a large mouth at the front end. The posterior section is slender, strongly cuticularised and placed dorsally. Paired openings connecting the pharynx to the outside run down the sides. These features are interpreted as possible primitive gill slits. Vetulicola cuneata could be up to 9 cm long. The Vetulicola are thought to have been swimmers that were either filter feeders or detritivores.
Vetulicola’s taxonomic position is controversial. Vetulicola cuneata was originally assigned to the crustaceans on the assumption that it was a bivalved arthropod like Canadaspis and Waptia, but the lack of legs, the presence of gill slits, and the four plates in the “carapace” were unlike any known arthropod. Shu et al. placed Vetulicola in the new family Vetulicolidae, order Vetulicolida and phylum Vetulicolia, among the deuterostomes. Shu (2003) later argued that the vetulicolians were an early, specialized side-branch of deuterostomes. Dominguez and Jefferies classify Vetulicola as an urochordate, and probably a stem-group appendicularian. In contrast, Butterfield places Vetulicola among the arthropods.
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