A Northern Dawn for Dinosaurs
I caught some razzing recently from an Australian friend who thought perhaps I was a little over- enthusiastic about the far north. "It's not really the center of the universe," she said.
Foo. She's just bitter because north-polar projection maps, the best kind, don't show Australia at all. The north usually plays some role in almost any matter. Consider the dinosaurs, for example.
No, it' s not that the north had something to do with the extinction of those giant reptiles. The best evidence is that about 65 million years ago, a huge chunk of celestial debris smashed into our planet, and the ensuing catastrophes put an end to the dinosaur family, among many others. Most, but not all, scientists think that the main body of that deadly asteroid hit the northern edge of the Yucatan Peninsula in what is now Mexico. Northern Yucatan isn't part of what we think of as the real north, so our preferred turf can't take any credit for the departure of the dinosaurs.
Ah, but did you ever think about how the dinosaurs got to be so dominant in the first place? Neither did I, until an article in the journal Science caught my attention. "Late Triassic Extinctions and the Origin of the Dinosaurs" discusses what must have been fairly lively times on old Earth. The late Triassic, the era of interest for author Michael J. Benton, fell between 230 and 202 million years before our time.
The fossil record shows great changes in the kinds of animals occupying the land during that period. Varieties that had long held sway were replaced by others. In paleontologists' lingo, the paleotetrapods gave way to the neotetrapods, the old four-feet gave way to the new four-feet, translating literally. Among the newly successful kinds were some still with us, such as the crocodilians, but the conspicuous newcomers were the dinosaurs.
Dinosaurs were present about 230 million years back, but they weren't impressive in size or numbers. These early dinosaurs made up about six percent of the animals recovered from fossil beds of the time.
Then, about five million years later, in what is called the Carnian-Norian mass extinction event, whole categories of animals abruptly vanished from the fossil record. Not the dinosaurs. They flourished, probably filling niches left empty when earlier successful types of animals suddenly were wiped out. Within a few million years, dinosaur remains accounted for 25 to 60 percent of the fossils. By 202 million years before the present, dinosaurs were diverse, sometimes gigantic, and dominant among land animals.
Thus, whatever caused the extinction event of 225 million years ago was apparently an important contributor to the rise of the dinosaurs. Some evidence for another asteroid impact at about that time does exist. The clues are the sort familiar from studies of the Cretaceous-Tertiary boundary, the 65-million-year-old event that led to the dinosaurs' extinction. Grains of shocked quartz and unusual amounts of iridium have been found in sedimentary layers of the proper age, for example.
Even better, geologists have located a crater of the proper size and age to mark the landfall of such an asteroid. The site of the crater credited with eliminating the early dinosaurs' competition is Manicouagan, in Quebec, Canada. So, possibly thanks to a far-northern asteroid impact long ago, there once was a real Jurassic Park, as well as the pale but profitable imitation now at the movies.
To be fair, I must admit that there's still a great deal of debate about the whole thing (as one might expect for circumstances occurring a couple hundred million years in the past). I hope further research bears out the suggestion, though. It seems very appropriate that an asteroid impact opened the door for the dinosaurs, just as another slammed it shut.
