The largest and heaviest animal to ever live on the Earth, as far as we know, is the blue whale, which is extant today. The blue whale is larger than any dinosaur, even the giant sauropods. The average weight of a blue whale is 160 tons, with the largest specimen being 190 tons, and 110′ 17″ (33.58m) long. The largest sauropod, Argentinosaurus, weighed up to 110 tons. The reason the largest whales are bigger than the largest dinosaurs is simple – whales swim in the ocean, so they have buoyancy to help carry their incredible heft. The ancestors of whales were land mammal of modest size. It was only when they adapted to the water that they grew very large, and the age of gigantism among whales started about 4.5 million years ago.

At least that is what we thought from existing evidence. That is one of the interesting things about paleontology – a single specimen can upend our phylogenetic charts, the history of what evolved into what and when. Essentially we have scattered puzzle pieces that we try to fit together into a branching tree of evolutionary relationships. One specimen that fits outside of the branches of this tree forces scientists to redraw some of the lines, or add new ones.

That is what has happened with a new extinct whale species, discovered in Peru in 2010 but only recently described in detail. The species is appropriately named Perucetus colossus, and it is a whopper. Scientists estimate the weight at 85 to 320 tonnes, depending on assumptions about soft tissue like organs and blubber. If we take the middle of that range, 180 tonnes, that puts it at the upper range for blue whales. If we assume this is an average specimen (statistically likely but not a guarantee) then its size range may exceed that of the blue whale. Perucetus is not, however, longer than the blue whale, it’s a little shorter. But it’s bones are a lot heavier, they are denser and overgrown, which is an adaption found in other shallow water mammals. It’s the heavy bones that makes it potentially heavier than the blue whale, and regardless, this species has the heaviest skeleton known.

But still this specimen is interesting because it is 30 million years old. The earliest whales that were fully aquatic (never left the water) were 40 million years old. So this was fairly soon, evolutionarily speaking, after whales evolved. This is also about 25 million years before our previous oldest specimens of giant whale species, those as large as extant species today. So at least one branch of whale experienced early gigantism. This raises the question – was this branch a dead end, or are their modern descendants. Even if ultimate this line died out, how long did it persist and how many other early giant whale species are out there to find? Now that we know at least one place to look, specimens should be easy to find. They are huge, and the bones are dense.

The specimen itself includes 18 bones, including 13 vertebrae, four ribs and part of the right hip. That is pretty sparse, but paleontologists are good at inferring anatomy from a few clues, comparing specimens to other known species, both extinct and extant. But still, a more complete specimen is always better, and hopefully future discoveries will fill in the missing pieces.

That is another fascinating aspect of following paleontology – scientists essentially make predictions from existing specimens, their reconstructions, and what we know about evolution, and those predictions are then tested by finding new specimens. We are always getting more information – new pieces to the puzzle. A lot of the details of whale evolution are being worked out, specimen by specimen.

But I need to point out that if we go back to prior to the 1980s, there were very few specimens of whale ancestors at all. This lead creationists who deny the mere fact of an evolutionary origin for life on Earth to that “gap” as evidence against evolution. This is one of their go-to moves. They did the same with bird evolution, and they are stilling doing it with bat evolution. Evolutionary theory makes a necessary prediction – whales, because they are mammals, must have evolved from terrestrial mammalian ancestors. Therefore, if evolution is true, there must be specimens out there that fill in the gap between land-based mammals and whales, and showing a plausible transition from one to the other. There are many potential specific details and evolutionary pathways, but we should find something.

Creationism, on the other hand, predicts nothing. If life were just created, there does not have to be transitional species from land mammals to modern whales. There could be, because the “intelligent designer” is apparently funny that way, but there doesn’t have to be. This puts them in a heads I win, tales you lose, situation. They can point to any gaps in the fossil record as evidence against evolution, but when those gaps are filled in they are not evidence against creationism. It’s all good. This is why creationism is not science (one reason) – it is not falsifiable by evidence.

Starting in the 1980s mostly in Pakistan scientists started to find a treasure-trove of ancestral whale specimens. Later finds were located in North Africa and South America. We now have a fairly robust evolutionary tree of whale ancestors, showing, for example, the slow loss of the legs (while retaining remnant hip bones), the transition of the forelimbs to flippers, the movement of the blowhole from the front to the top of the head, and the evolution of baleen (in baleen whales). And of course the massive increase in size, made possible by a fully aquatic life. We keep finding more specimens, like Perucetus, filling in the ever shrinking gaps – just like evolutionary theory predicts we should.