Stretching a quarter of an inch to eight inches long, and flanked by rows of stubby legs along their smooth bodies, these invertebrates aren’t worms at all. “Velvet worm” is something of a misnomer. Modern crocs do look ancient, but they are just the remainders of an even older and stranger lineage. Some-like the 112-million-year-old, approximately 40-foot-long giant Sarcosuchus-looked quite similar to their modern cousins, but there were also formidable ocean-going predators such as Dakosaurus small forms with mammal-like teeth such as Pakasuchus crocs with tusks and extra armor such as Armadillosuchus and lithe, land-dwelling carnivores such as Sebecus. They shared the world with the dinosaurs and came in a startling array of forms. While crocodylians as we know them today-the alligators, gharials and crocodiles that live at the water’s edge-have been around for about 85 million years, they belong to a much more diverse and disparate group of creatures that goes back to the Triassic.Ĭrocodylians are the last living representatives of the crocodylomorpha, an even bigger group that originated over 205 million years ago. Watch any documentary about crocodiles and you’re almost certain to hear the line “They have gone unchanged since the time of the dinosaurs.” That isn’t exactly true. The great Victorian naturalist Thomas Henry Huxley called these creatures “persistent types,” but there is an even simpler name for them-survivors. By chance, these lineages occupied an evolutionary sweet spot. Charles Darwin explained why in his famous book On the Origin of Species: Natural selection may have vastly modified other branches in the tree of life over time, but, among organisms like the lungfish, the quirks and contingencies of their habitats and lifestyles remained so stable that there was little evolutionary pressure to change. Still, many of these organisms look as if they belong to another era. Many species of these living fossils differ significantly from their prehistoric counterparts, and often the apparently archaic creatures are the remaining representatives of lineages that were once more varied and diverse. Creatures such as sharks and crocodiles are often viewed as evolutionary sluggards or “living fossils.” While the rest of nature was caught up in life’s race, the coelacanth and duck-billed platypus sat things out. But, among all that evolutionary change, some organisms have little modified from their distant ancestors. When we think about the history of life on earth and the vast changes that have transpired over millions and millions of years-as single-celled organisms evolved into species as disparate as redwood trees, dragonflies and humans-are wonderfully apparent.
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