More than 500 totally different shark species roam Earth’s oceans: from zippy little cookie-cutter sharks, to the iconic nice white, to nightmarish goblin sharks, to 25-foot-long, filter-feeding basking sharks. And evidently the present equilibrium of shark species we see in the present day arose after the Cretaceous–Paleogene mass extinction occasion 66 million years in the past, in keeping with new analysis.
In the Cretaceous Period (between 142 million and 66 million years in the past), an order of sharks known as Lamniformes commanded the seas. Also referred to as mackerel sharks, trendy lamniform sharks embrace the nice white, thresher, and mako.
But by learning the various shapes of a whole lot of historic, fossilized shark enamel, researchers discovered that Carcharhiniformes shark variety—the greatest shark order in the present day that features hammerheads, tiger sharks, and extra—exploded after the end-Cretaceous mass extinction, whereas many lamniform sharks went extinct.
That steadiness remains to be what we see in in the present day’s waters: carcharhiniform dominance with a lightweight sprinkling of lamniforms. Other orders of sharks embrace Hexanchiformes (frilled and cow sharks), Pristiophoriformes (noticed sharks), and Heterodontiformes (bullhead sharks).
“This is an interesting and nuanced study that adds context to the end-Cretaceous mass extinction event among two major lineages of sharks,” Neil Aschliman, an evolutionary biologist at St. Ambrose University who wasn’t concerned with the new analysis, instructed Gizmodo.
“Studying fossil sharks is both a curse and a blessing,” Aschliman continued. “Whole specimens are extremely rare because the cartilaginous skeletons of these animals don’t readily fossilize. Sharks continually produce and shed fossil-ready teeth throughout their lifetime. Because of this treasure trove of teeth, we have a solid understanding of when in the geological record different groups of sharks have originated and gone extinct.”
The researchers measured the various shapes of 597 historic shark enamel from round the world courting again between 72 million and 56 million years in the past. The means tooth form modified—taller or shorter, broader or extra needle-like—allow them to map out the post-extinction shark variety, as famous in the Current Biology paper printed on Thursday.
Curiously, after the extinction occasion, lamniform sharks that had huge, triangle-shaped enamel died out, whereas carcharhiniforms with that very same tooth sort thrived.
That disparity may very well be attributable to altering meals sources after the extinction, Mohamed Bazzi, lead examine writer and paleontologist at Uppsala University in Sweden, instructed Gizmodo. Lamniform sharks probably ate a variety of squid and marine reptiles, however lots of these died out. Small bony fishes, on the different hand, began to swarm the seas, a lot to the delight of the carcharhiniform sharks that preyed upon them.
This dynamic could have been the foundation for an evolutionary timeline resulting in in the present day’s shark variety, Bazzi mentioned.
Understanding that timeline might even be helpful for holding in the present day’s sharks from going extinct. That extinction threat is severe, as we overfish oceans and contribute to world warming. Today, over 50 p.c of shark species are both endangered, threatened, or near-threatened, the researchers famous.
“By exploring changes in their diversity over millions of years, we might be able to assess the importance of various contributors—such as temperature, sea-level, and prey-availability—as key drivers of shark evolution,” Bazzi instructed Gizmodo. “Sharks fulfill a very delicate but important ecological role. Their demise may have terrible consequences for the health and stability of whole marine food-webs. They are also remarkable creatures that capture the public imagination, though they are sadly misunderstood.”