Into what? Crocobirds?
The subhead at Smithsonian Magazine reads, “Despite their reputation as “living fossils,” crocodiles have changed dramatically in the last two million years.” Just yesterday, we noted someone else crabbing about the term “living fossils” — referring to life forms that show no significant changes from, say, fifty million to hundreds of millions of years:
Crocodiles look like they belong to another time, an era when reptiles ruled. But appearances can be deceiving. Today’s crocodiles are not holdovers that have gone unchanged since the Jurassic, but are one expression of a great, varied family that’s been around for over 235 million years. More than that, crocodiles are still evolving—and faster than they have at other times in their family’s scaly history.
The seemingly contradictory conclusion about crocodylian evolution comes from a recent study published in Proceedings of the Royal Society B by University College London anatomist Ryan Felice and colleagues. By comparing three-dimensional models to track anatomical landmarks on crocodylian skulls over time, the researchers found that modern crocodile species in Australia, southeast Asia and the Indo-Pacific are evolving quickly despite looking like semi-aquatic antiques. Modern croc species look so similar not because of conserving ancient traits, but because crocodiles are evolving the same skull shapes over and over again through time.
Riley Black, “Modern Crocodiles Are Evolving at a Rapid Rate” at Smithsonian Magazine (October 7, 2021)
Wait. They are “evolving the same skull shapes over and over again through time”? But that’s like walking around in a circle. If no distance is actually travelled, just a pattern repeated, it is not evolution, as the term is commonly used. When people say that cowlike creatures turned into whales, they are talking about evolution (whether it happened that way or not).
Two crocodiles with similar skull shapes, then, might not be close relatives. Instead, distantly-related crocodiles are converging on the same skull shapes because they’re feeding on similar prey and living in similar habitats, with an array of species repeating a small number of skull shapes. The fact that distantly-related branches on the crocodile family tree are converging on similar skull shapes, University of Tennessee paleontologist Stephanie Drumheller-Horton says, suggests that crocodiles are evolving rapidly to repeatedly fill the same set of niches.
Riley Black, “Modern Crocodiles Are Evolving at a Rapid Rate” at Smithsonian Magazine (October 7, 2021)
Okay, convergent evolution is a form of evolution but when we use the term, we usually mean strikingly different life forms converging on the same pattern of development. In this case, they’re all crocodilians anyway and they all end up looking that way.
It would be interesting to know why stasis became such a threatening concept in some quarters.
The paper is open access.
(“All crocodilians share the same characteristic features.”)
You may also wish to read: Three-eyed dinosaur shrimp are NOT living fossils!, docent insists. Despite the fact that they go back 350 million years to the Devonian period.
and
Stasis: Life goes on but evolution does not happen