The new teeth just kept pushing the old ones out:
The paleontologists found that the Jurassic carnivores Allosaurus and Ceratosaurus had tooth replacement rates of about 100 days, while the Cretaceous Majungasaurus had a much faster replacement rate of about 56 days. “I would have predicted from the incredible abundance of shed Majungasaurus teeth that it replaced its teeth quickly, but I couldn’t have imagined how fast,” D’Emic says. This dinosaur replaced its teeth at rates similar to herbivorous species that kept up quick turnover, and, the researchers estimate, about 14 times faster than the bone-crushing Tyrannosaurus.
But why was Majungasaurus so different from other carnivores? Previous work on theropod dinosaurs focused on the famous tyrannosaurs which replaced their teeth slowly. But tyrannosaurs’ slow rate of tooth replacement might be specialized to the species.
“With this new dataset, it looks like most dinosaurs had high replacement rates regardless of diet,” says University of British Columbia paleontologist Kirstin Brink.Riley Black, “Flesh-Ripping Dinosaurs Replaced Their Teeth Multiple Times a Year” at Smithsonian.com
Curiously, mammal predators don’t replace teeth that way, even though sharks, reptiles, and amphibians can. One theory is:
Abigail Tucker, a professor of development and evolution at King’s College London says that there is a trade-off between the complexity of the teeth and the amount of sets the species gets. Since mammals have the ability to chew, meaning they can grind their teeth sideways (think of the movement a cow or horse makes) we have developed complex sets of teeth with multiple cusps, the bumps and mounds that define the shape of our teeth. While our pointy canine teeth (cuspids) each have only one cusp, our premolars (bicuspids) each have two cusps and our molars each have four or five cusps.Tiffany Wen, “Will dentists help you to grow new teeth?” at BBC
What’s interesting here is that even though just regrowing teeth through life would seem like an advantage, for mammals, more complex teeth turned out to be a bigger advantage.
Note: Manatees can grow new teeth and, of course, rodent and rabbit teeth continue growing through life (but it’s the same tooth really).