Dinosaurs: the known unknowns

 kw: book reviews, nonfiction, paleontology, dinosaurs

This is the femur of a Titanosaur (Patagotitan mayorum) found not too long ago in Patagonia, the "largest dinosaur ever found" (so far!). The discoverers note that this animal was not yet full grown…

A picture similar to this (but with poorer lighting) graces the color plates section of How Fast Did T. rex Run: Unsolved Questions from the Frontiers of Dinosaur Science by David Hone.

How big was the whole animal? In elephants, the tibia is about 2/3 the length of the femur, and this femur is about 8 feet long, so the tibia might be about 5 to 5.5 feet long. Put that on top of a foot the size of a love seat, perhaps 1.5 feet high, and we have a hip socket roughly 15 feet up there. David Hone's book notes that the weight of this animal was between 50 and 100 tons, putting it in the same league as blue whales.

Guess what question never gets answered? How fast Tyrannosaurus rex could run, or whether it could run at all. Of course, the length of its legs and the general physics of inverted pendulums indicates that its walking speed was 3 miles per hour when "moseying along", and in the range of 15-25 mph when walking briskly. I tend to favor a maximum of 15 mph, just from proportion. Humans mosey in the 1-1.5 mph range, with a steady pace of 3 mph when going somewhere, and "power walking" in the 4-5 mph range. It is not (yet) known whether T. rex could run at all, and if so, how fast. However, it is pretty certain that they could not jump. Elephants cannot, and probably neither can rhinos (one website I found claims that some rhinos can jump). Moving a 6-8 ton mass upward fast enough to stay aloft long enough to raise one's legs off the ground? No way.

How Fast is not about what we know, but about what we don't, with suggestions for finding out more. We'll never learn it all, but that is what science is for: expanding knowledge into an infinite realm. The 16 chapters discuss numerous kinds of knowledge we know only in part, or hardly at all. For example, what color or colors were dinosaurs? We could look at big lizards and crocodilians (especially caimans like this one).

For decades, illustrations of Mesozoic landscapes have depicted the animals as mostly "elephant colored". But in Chapter 11, "Appearance", we learn of rare finds that include melanosomes (color packets) that can still be characterized. They show that some dinosaurs were spotted or striped, and give us a hint as to colors. Many seem to have been countershaded (darker on top, lighter beneath), which makes an animal harder to spot.

The chapter following, "Reproduction", points out that we know nothing so far, except the fact that it had to have happened, or there would be no eggs, no young, no dinosaurs, period. There are some apparent mega-nests that have been found, where for several yards all around you are walking on dinosaur eggs. It's hard to imagine tyrannosaurs or brontosaurs coupling, but fertilization of eggs has to take place inside the female's reproductive tract (no milt-spraying on already-laid eggs such as we see for many fish).

I was also quite taken with this illustration of representatives of the three major clades of dinosaurs: theropods, sauropodomorphs, and ornithischians. I added the gray bars for clarity. This drawing is on p. 58 in Chapter 4, "Diversity".

A close look will reveal that the ornithischians have the greatest in-clade diversity. While theropods are mostly variations on the tyrannosaur scheme—though they include the birds—and sauropodomorphs are mostly variations on the Brontosaurus/Brachiosaurus body plan, the ornithischians include ceratopsians, ankylosaurs, stegosaurs and hadrosaurs. The ornithischians are united in having hips that resemble bird hips, while the other two clades have hips more like those of lizards. It's a quirk of evolution that certain lizard-hipped theropods evolved into birds, re-developing the bird pelvis. As usual, scientists await fossils that will show how this process came about.

We find that the number of species of Mesozoic dinosaurs is less than 2,000, while about 10,000 modern species of bird (today's dinosaurs) have been described so far. No doubt there are thousands of dinosaur species yet to be discovered. 

Reading How Did was great fun. Dr. Hone's knowledge is comprehensive, and he has been to many of the key exposures at which dinosaur fossils are found, including those in China that have yielded numerous extremely-well-preserved feathered dinosaur fossils. A full size T. rex may not have sported many feathers, but the young ones, and smaller species, certainly did. Thirty years ago we had no unambiguous fossils with clearly-preserved feathers. New finds lead to new science. That is a key message of this book.