Rare dinosaur egg embryo hints at 6-month incubation times

The popular image of dinosaurs is that of giant lizards. After all, that's where their name came from. Science, however, paints us a different and more complicated story. They were warm-blooded, unlike reptiles and some were actually closer to birds than lizards, having feathers and wings. There were, however, nonavian dinosaurs that were indeed closer to crocodiles than chicken. And these, according to scientists, laid eggs that took 6 months or more to hatch, which, in a sad way, helped bring about their extinction.

You might think it wouldn't be so hard to estimate the incubation period of dinosaur eggs, but we are, after all, talking about creatures that ceased to exist more than 60 million years ago. There are fossilized dinosaur eggs, of course, but extremely rare are the ones that contain a fossilized embryo inside. Fortunately, Gregory M. Erickson of Florida State University was granted access to such embryos, which yielded data that flew in the face of commonly held theories about dinosaur eggs.

The particular method used was quite new. It analyzed the growth lines found in the embryonic teeth of the dinosaur, at first a sheep-sized Protoceratops, to estimate how long the embryo had been incubating. They came up with an 83-day figure, at minimum. That's almost three months. Later they applied the same method to a duck-billed Hypacrosaurus that laid eggs the size of soccer balls and the days lengthened to 171, almost 6 months. The larger the egg, the longer it took to hatch, with some getting to close to a year.

These findings significantly change the narrative on how dinosaurs lived and died. Because of their distant relationship to birds, it was presumed that their incubation periods were similarly short. Longer hatching times, however, put into question parental care for the unhatched offspring. Imagine having to babysit and defend eggs for 6 to even 12 months, without being able to migrate or move far freely.

If correct, then the cards were really stacked against the dinosaurs' survival, meteor or no meteor. Long incubation periods translated to slow repopulation, which meant that these dinosaurs would have eventually died out sooner or later anyway.

SOURCE: New York Times