Would you guess that the tiny Ruby-throated Hummingbird (Archilocus colubris) and the giant tyrannosaur Albertosaurus libratus are related? Sometimes organisms that look radically different turn out to be closely related. Such extreme divergence can evolve quite naturally, especially when lineages move into new environments.
Did you know that crocodilians are the nearest living relatives of birds? Although they don’t look very much alike, there is abundant evidence for their close common ancestry, at least among living reptiles. Crocodilians and birds both “sing” to defend their territories and attract mates, build nests for their eggs, and care for their young. And, when we add our knowledge of extinct reptiles, the differences between crocodilians and birds are much less striking.
Albertosaurus was a fierce carnivore; a hummingbird may be no less fierce, but its diminutive size and taste for nectar are unusual for a dinosaur. Albertosaurus probably sported feathers, just like living birds. Birds, it turns out, are just a highly divergent branch in the dinosaur tree, the rest having disappeared long ago. Birds are the dinosaurs that took to the air, dodged the great extinction 65 million years ago and, with some 10,000 species alive today, have been so successful ever since.
A Case of Extreme Divergence in Plants
The water lotus (Nelumbo) was long thought to be closely related to the water lilies (Nymphaeaceae). Surprisingly, the water lotus turns out to be closely related to the sycamore tree (Platanus). This idea was first suggested on the basis of pollen structure, but has now been strongly supported by DNA sequences.
The case of the water lotus illustrates both extreme divergence (water lotus relative to the sycamore) and convergent evolution (water lotus relative to the water lily). The water lotus lineage has undergone extreme evolution of its form in adapting to life in calm, freshwater habitats, and has converged to look like a water lily.