30 Scientific American, October 2019
the “if it were easy, everyone would do it” hypothesis. In short,
having a big set of jaws to eat with and a big face with which to
signal to mates and rivals might be a great option for a lot of ani-
mals if the costs associated with these traits were not normally
so prohibitive. For example, mammals have big braincases, so
mammal heads become very heavy as they grow larger in overall
dimensions. Pterosaurs might have stumbled into a develop-
mental zone where the proportions of the face were less coupled
to those of the back of the skull. This would have allowed them
to evolve a giant set of jaws without having a huge braincase.
Pterosaurs also had extra openings in their skulls, the largest
of which was an opening in front of the eyes known as an antor-
bital fenestra. Dinosaurs had this opening, too, but pterosaurs
took it further, in some cases evolving an opening so large that
the torso skeleton could have fit inside it. This opening would
have been covered with skin and other tissues in life and proba-
bly would not have been visually obvious, but it made the skull
quite light relative to its volume. The bones of the skull might SOURCE:FLYING MONSTERS,DESIGN STUDIO PRESSIllustration by Terryl WhitlatchGoing Big—and Weird
All pterosaurs had strange proportions. Their hands were highly modified
to support wings, and their heads were large relative to their bodies. Later
pterosaurs evolved even more extreme body plans with proportionately gigantic
heads. In some forms from the Cretaceous period, such as Quetzalcoatlus, the
head and neck could make up more than 75 percent of the animal’s total length.
Ultimately the pterosaurs’ tendency to grow large may have contributed to their
demise at the end of the Cretaceous.250 million years ago 190 160 130 100 70MESOZOIC
TRIASSIC JURASSIC CRETACEOUSRhamphorhynchus
JurassicPterodactylus
JurassicJeholopterus
JurassicDimorphodon
JurassicEudimorphodon
TriassicTropeognathus
Cretaceous1 meter1 foot