I had this thought that other day.
Whales have been my favorite animals ever since I was a child, and this was partly because every resource out there regards whales as the largest animals to have ever lived. Since getting a stats degree and working as a data scientist the last few years, I occasionally think about how improbable it is that somehow we are coincidental contemporaries with the largest (heaviest) animal to have EVER lived. The main question is: How are we so confident blue whales are the heaviest animals to ever live? It seems to me that we are overconfident.
With so much of the fossil record unknown to us, it seems exceedingly likely that there have been heavier animals that we don’t know about. E.g. Shonisaurs were around for much longer than modern rorquals have been, and it seems very possible that there were prehistoric animals that were heavier (if not shonisaurs, insert another group of aquatic megafauna). I imagine a large proportion of fossils that fit the bill likely are preserved in areas that are currently covered by water and inaccessible for excavation and discovery, so we’re really only finding fossils that’re at the ‘tip of the iceberg’ .
I find the fact that the ‘random’ shonisaur/shastasaur we’re finding seem to be at least in the 60ft range seems to be convincing indication that, as a population, there were individuals that exceeded the max size of a blue whale. It’s extremely unlikely that the specimen we’re uncovering are anywhere near maximum size. As a thought experiment, the median adult rorqual (pre-whaling) was probably something like 50ft long/20tons; the median adult blue whale probably in the 70-75ft range and 60-80t, and the next earth civilization 200million years from now are far more likely to find the median specimens than the maximum. This suggests to me that if the 3 following conditions hold, its very likely that the largest shonisaur was heavier than the largest blue whale: 1) we can find a shonisaur and be confident that its about 70ft long (and assume its close to median size), 2) Shonisaurs are heavier given the same length; if this is not true then increase the length requirement for the shonisaur we need to find 3) distribution of weight across population is comparable between shonisaurs and blue whales; having similar distribution means that x stdev larger than mean will have similar weights.
The other possibility is, of course, there are specific reasons modern environment conditions increases the upper allowable limit for animal weight. The following article does present some interesting arguments that blue whale (and rorqual) gigantism was caused by increase in upwelling, and their choice of prey (krill). Neither of these sound like unique events given 500million years of macro fauna evolution. Also 500million years is a lot of time for convergent evolution to produce similar sized reptiles/fish in previous iterations of similar environmental conditions.
https://www.scientificamerican.com/article/why-are-blue-whales-so-gigantic/#:~:text=A%20blue%20whale%20can%20grow,half%20the%20blue%20whale’s%20weight.
Curious if anyone has had similar thoughts. Would be curious to hear from those who know more than me on if I have missed anything or am drastically wrong about something.