Dorling Kindersley/Science Source
BRISBANE, AUSTRALIA —Typically taller than four elephants and heftier than a jet airliner, sauropods are among the most famous of the dinosaurs. But scientists may have been wrong about one of their key features. Instead of lizardlike lips, the behemoths sported beaks akin to those of birds or turtles, researchers report here today at the annual meeting of the Society of Vertebrate Paleontology. The dinos may have used these beaks, which encased large numbers of long, peglike teeth, to harvest the vast quantities of vegetation they required to reach record sizes.
The research helps to answer a long-standing mystery, says study author Kayleigh Wiersma, a paleontologist at the University of Bonn in Germany. Since the 1930s, long rows of isolated sauropod teeth—still perfectly arranged in the position they would have been in the mouth during life—have been found embedded as fossils in rocks, but with not a scrap of fossil bone encasing them. “There must have been something holding them in place,” she says. “Otherwise they would have been scattered all around the dig site.”
Wiersma and her University of Bonn co-author, Martin Sander, first hinted at the possibility of a gum or beak structure in 2017. That was based on an analysis of two skulls of Camarasaurus. Now, they have studied seven sets of isolated tooth rows from a variety of sauropod species, including German “dwarf” sauropod Europasaurus, as well the groups that include well-known species such as Diplodocus, Brachiosaurus, and Apatosaurus.
The scientists report the likely presence of beaks in many of these species. The finding is based on seven fossils of isolated rows of up to 40 teeth, as well as a detailed analysis of the skulls and teeth of Camarasaurus and Europasaurus. The teeth fossils in these species typically show surface wear only about 50% of the way down to the jaw, Wiersma says. That indicates the teeth were once deeply embedded in a “rhamphotheca,” or beaklike structure made of keratin (which also forms our hair and nails, as well as bird beaks and feathers). Existing reconstructions of sauropod faces would have left the tooth roots exposed and the teeth too loosely attached to the skull, the authors say. In Camarasaurus and Europasaurus the pair also found tiny pits in the surface bone of the jaw, which may indicate the presence of blood vessels that once nourished beak tissue.
Wiersma and Sander speculate that beaks may have held exposed teeth tightly in place and provided stability as the dinos munched their way through vast quantities of ferns, conifers, and other prehistoric plant matter.
“You can’t have teeth exposed to that degree and not have any protection,” says Steve Salisbury, a paleontologist who works on sauropods at the University of Queensland here. “It seems likely there would have been some sort of tissue that enclosed the base at least and provided some buffer from the outside world.”
There is no modern analog to compare the beaks with, however, as no living species possesses both a beak and teeth, as some dinosaurs did. Beaks are already known in many other dinosaur groups—including Triceratops, Stegosaurus, duck-billed hadrosaurs, and dome-headed Pachycephalosaurus—as the bony bases of the beaks are preserved in fossils.
Given that living birds, some prehistoric crocodiles, and early relatives of dinosaurs called silesaurids also have beaklike structures, the ancestors of this entire group may have had beaks, says Darren Naish, a paleontologist at the University of Southampton in the United Kingdom. “But I don’t think we would have expected sauropods to have beaks,” he adds. It’s a “whole new look.”
Source: Science Mag