The tuatara, which lives in New Zealand and resembles lizards although it is actually a distant cousin has only two species. "In the same period of time that produced more than 8,000 species of snakes and lizards, there were only two species of tuatara," Alfaro said.
Why are there not thousands of species of tuataras?
"That is one of the big mysteries about biodiversity," Alfaro said. "Why these evolutionary losers are still around is a very hard thing to explain. They have been drawing inside straights for hundreds of millions of years. It's a real mystery to biologists how there can be any tuataras, given their low rate of speciation. They must have something working for them that has allowed them to persist. In species richness, these are losers, but in another sense, this highlights how unique they are. There are incredibly disparate patterns of species richness."
Tuataras were a bit more diverse in their heyday; there may have been a few dozen species of them, most of which have become extinct, Alfaro said.
In contrast, there are more than 9,000 bird species, more than 5,400 mammal species, approximately 5,500 frog species, some 3,000 snake species and 5,200 lizard species, Alfaro said.
The number of frog species, although it sounds high, is about what Alfaro would expect, given how old they are approximately 250 million years old.
"Our analysis suggests we should not be surprised to see a group with that many species in that amount of time," Alfaro said.
There are almost 60,000 species of jawed vertebrates. Alfaro and his colleagues report evidence for exceptional diversification rates in nine taxonomic groups of jawed vertebrates. Interes
|Contact: Stuart Wolpert|
University of California - Los Angeles