Saturday, March 09, 2013

Dunkleosteus - biggest (non-shark) fish ever?

Where did my favorite predator, Dunkleosteus, rank among the largest fish ever?

Answer: it should make the top 5.

There’s some doubt here, because all we have of Dunkleosteus is the armored skull and forebody. The rest is conjectural. (I talked to a fossil seller once who said he’d seen a fossil slab with a whole baby Dunk on it, but he hadn’t bought it and didn’t know who had it.) If we assume the largest estimates are correct, the Dunk was up to 10m (33 feet) long and weighed about four tons.

The modern day record holder for largest fish is the whale shark, which reaches a confirmed length around 12.65m (41.5 feet). This specimen, from Pakistan in 1947, weighed a reported 21.5 metric tons, although it’s hard to believe it was actually weighed vs. being estimated. A 20m, 34mt shark was reportedly landed in Taiwan in 1987, and an extreme estimate of a 23m (75-foot) shark is given in Michael Bright’s book There are Giants in the Sea. Settling for the proven records, the whale shark reigns as the largest of all time,

The modern second place goes to the basking shark: a generally accepted record from Canada from 1851 12.27m (40.3 ft), and an estimated 19mt. Again, the claims go much larger. Third place goes to the great white shark, with a maximum length of about 7m (22feet). Then there are two prehistoric contenders. The extinct Carcharodon megalodon reached at least 15m: while claims of 30m and up are no longer taken seriously, 17-18m is possible. Then we have Leedsichthys problematicus, a filter feeder from the Jurassic period which was the subject of wild estimates up to 27m (approaching blue whale territory.) Dr. Darren Naish argues these were far too high, based on extrapolations of measurements from incomplete skeletons, and an average size of 9m was more likely. Still, we have to put an asterisk here when we class Dunkleosteus is the bigger fish.

So we have Dunkleosteus claiming to be the biggest non-shark fish (albeit from an extinct class, Placodermi) and Leedsichthys the largest bony fish (though from an extinct order, the Pachycormiformes, in the extant superclass Osteichthyes (yes, the proper rank and composition of this group here is debated, and no, I'm not qualified to pronounce on it)).

(There is an element of doubt among the sharks, because experts are debating a shark named Edestus giganteus from the Carboniferous period. Parahelicoprion mariosuarezi of the Permian times may also have been longer than the Dunk, though most reconstructions of the latter picture it as elongate, thus making it uncertain where it ranks in weight/mass. So we’re setting both of those aside for the moment.)

When we slot every fish that ever lived in a row, Dunkleosteus gets fourth place after the three biggest sharks, and second place among predatory fish. Not bad for an animal that appeared so early (380 MYA) and vanished too soon (for me, anyway).

Richard Ellis, Aquagenesis: The Origin and Evolution of Life in the Sea, 2001.
Gerald Wood, The Guinness Book of Animal Facts and Feats, 1983.
Darren Naish, Tetrapod Zoology,
“Summary of Large Whale Shark Rhincodon typus Smith, 1828.”

Dunkleosteus, as rendered by an expert artist for the Smithsonian and un-rendered by my own inexpert photography.


Laurence Clark Crossen said...

I do not think there is much difference between Carcharodon and the great white other than size. There are Carcharodon teeth of intermediate sizes between their largest size and the size of a great white.

Matt Bille said...

Scientists debate today whether Meg and the GW belong in the same genus. There is a good discussion in Great White Shark, by Ellis and McCosker.