Not all Dinosaurs are Extinct

Friday, June 1, 2018

Mesozoic maniraptoran dinosaurs that possess all kinds of bird-like and not-so-bird-like combinations of anatomical characters are published all the time. This reconstruction, by Emily Willoughby, depicts Serikornis from the Upper Jurassic of China. According to its describers, it is not a bird. Credit: Emily Willoughby Wikimedia (CC BY-SA 4.0)

One of the topics surrounding dinosaurs that often gets more than its fair share of attention is how they became extinct. While the event of their disappearance is so often the dramatic coda of books and documentaries, it might be surprising to know that the extinction of the dinosaurs is usually one of the least interesting questions out there to many paleontologists. Not only do we actually have a fairly good idea as to what happened at the end of the Cretaceous to cause such a big die-off, most of us in the paleontology world are much more concerned about how dinosaurs lived and evolved than how they died out.

Of course, not all the dinosaurs are extinct. Birds are just a group of feathery theropod dinosaurs that managed to pull through to the present day, and it’s much more tantalizing to ponder how modern birds were able to survive when all their close cousins died out. There’s all sorts of wonderful fossil birds filling in the spectrum between non-avian dinosaurs (those that aren’t classified as birds) and todays modern bird species. Some of these were really weird, like the fully aquatic four-foot tall “Hesperornis” with its wingless body, powerful swimming legs, and toothed beak. There was also a group of prehistoric birds called the enantiornithines, or ‘opposite ‘birds’. Despite having clawed wings and toothed beaks, these prehistoric birds were capable of flight, lived in trees, and probably would have looked very similar to today’s modern birds, which we call the neornithines. This lifestyle may have actually led to the downfall of most fossil birds. 
In a recent study published in “Current Biology”, Daniel Field and colleagues determined that at the time of the end-Cretaceous extinction, a significant amount of tree cover around the world was destroyed by the effects of the meteorite impact. This was determined by studying tree pollen in the late Cretaceous and noticing there was a significant drop in tree abundance during the time of the extinction event. This spelled bad news for most birds at the time, including the enantiornithines who were so dependent on living in trees for survival. 
However, the authors point out that the early neornithines, the ancestors of today’s birds, spent most of their time on the ground, finding food and shelter in the underbrush. Low-lying plants such as ferns and shrubs weren’t as badly affected by the meteorite disaster, and research by the Philip J. Currie Dinosaur Museum’s own Derek Larson has indicated that early modern birds were well adapted to eating seeds in the undergrowth. Here they were able to hunker down and survive, while the rest of the dinosaurs around them died out in the rapid environmental change. 
After the meteor event filtered out the creatures not destined for survival in the Paleocene world, the neornithines were quick to spread and diversify. Once the early modern birds had the skies to themselves, it didn’t take them long to branch out from meek ground-dwellers into the myriad of specialized forms we see today. It goes to show that today’s birds aren’t just beautiful to watch, they’re also hardened survivors and worthy successors of the dinosaur lineage. 
Reference: Field et al., Early Evolution of Modern Birds Structured by Global Forest Collapse at the End-Cretaceous Mass Extinction, Current Biology (2018),