Hadrosaurs – Dominant Herbivores of the Cretaceous
Scientists from the University of Utah have published a paper on a superbly preserved skull of a Late dinosaur with 500 teeth Cretaceous duck-billed dinosaur that demonstrates in glorious detail why this group of animals were so successful.
The skull discovered in a remote region of Utah – the Grand Staircase-Escalante National Monument (so remote that it was the last place on the American continent to be mapped), was unearthed by an expedition in 2003, but only properly studied and evaluated by palaeontologists in 2005.
So much fossil material has been found in this part of the United States of America, that palaeontologists have difficulty in recording and studying all their fossil finds. It can be many years after a fossil is found before it is formally described and scientifically studied.
Gryposaurus Dinosaur Skull
The skull has been identified as belonging to an adult Gryposaurus, a member of the Hadrosaurine lineage, distinguished from Lambeosaurines by wide premaxillary rostrums, a cir-cumnarial depression surrounding the external naris, generally an enlarged and bony naris and the presence of a prominent anteromedial process of the maxilla. The species has been described as G. monumentensis, named after the area in which it was found. A number of Campanian species of Gryposaurs are known most have been recovered from the Dinosaur Provincial Park formation of Alberta, Canada.
This remarkable skull has permitted the team from Utah University to closely examine the teeth of Hadrosaurs. This skull has over 300 teeth in the maxilla and dentary, making a very effective grinding surface for crushing and pulping plant material. Another 500 teeth were embedded in the jawbones, ready to erupt and replace any other teeth that became worn.
Dinosaurs are sometimes referred to as “land sharks”. This term is used to describe the way in which Dinosauria teeth are replaced in the jaw in a similar fashion to ray finned fishes such as sharks. If a tooth was lost as the dinosaur was feeding or fighting, another, replacement tooth would erupt through the jaw-line to replace the tooth that had fallen out. In this way, dinosaurs always had an effective biting and grinding surface in their tooth-lined mouths. Humans for example, in contrast to the Dinosauria only have two sets of teeth (child and adult) in their lifetime.
The ability to chew their food very efficiently may have given Ornithopods such as the Hadrosaurs a distinct advantage over other types of herbivorous dinosaur such as the long-necked Sauropods. During the Jurassic geological period, the Sauropods made up a considerable portion of the herbivorous fauna in many ecosystems. However, during the Cretaceous geological period, the Ornithopods came to prominence and began to dominate terrestrial ecosystems.
Ten-metre Long Herbivore
Other bones believed to belong to this species have been unearthed at the dig site and palaeontologists have estimated that this animal could reach lengths of ten metres or more. One palaeontologist, Scott Sampson, commented that this robust animal was the “Arnold Schwarzenegger” of its dinosaur family. The powerful jaws would have enabled these animals to tackle a whole variety of plant food, but further research is required to determine Gryposaurus’s dietary preferences.
Hopefully, some coprolite (fossilised poo) will be found in association with Gryposaurus fossil material. An analysis of this fossil material would provide scientists with some insight into which plants this duck-billed dinosaur actually ate.
Gryposaurus was named after its nasal arch, the name is from the Greek meaning “hook-nosed lizard”. Muscles in the skull enabled the animal to chew food in a similar way to bovines of today (the actual process is different, cows for example grind their jaws from side to side, Hadrosaurs would have ground food in a more up and down motion). The broad beak would have cropped vegetation and the teeth in combination with the animal’s tongue and cheeks would have processed the plant material very effectively. Alternating between a quadrupedal and bipedal stance Gryposaurus could have fed on vegetation from ground level up to about four metres high.
Old “hook nose” would have certainly been an impressive sight, an example of the many wonderful varieties of peculiar looking dinosaur. No plants would have been safe from a herd of them as they wandered the Late Cretaceous plains looking for their next meal. Fossil track ways uncovered by palaeontologists in North America and also in China show that these large plant-eating dinosaurs did move around in large herds. Many genera may also have migrated long distances in order to be able to reach breeding sites or areas which were particularly lush and verdent.
Probably a Very Colourful Dinosaur
Although palaeontologists do not know what duck-billed dinosaurs were, it is likely that many species were very colourful. The bizarre facial ornamentation may have played an important role in species recognition, competition for mates and inter-species rivalry. The enlarged nasal region of Gryposaurus may have played a role in visual display or vocalisation.
Attacked by Tyrannosaurs
The dominant and apex predators in the Late Cretaceous environment of North America were the Tyrannosaurs. It is likely that Tyrannosaurs hunted herds of Gryposaurus. A healthy, full-grown Gryposaurus would have provided formidable opposition for even the most determined meat-eater. It has been speculated that carnivorous dinosaurs hunted in packs, mobbing individuals to bring them down or perhaps selecting an ill or weak member of the herd to attack. Some scientists have estimated that an adult Gryposaurus may have weighed as much as an African elephant – around five tonnes.
With such a powerful battery of teeth in their jaws, coupled with strong jaw muscles, these Hadrosaurine dinosaurs would have made short work of any vegetation that they encountered. They were perfectly adapted to chewing plants but like all the Dinosauria, the Hadrosaurs became extinct around sixty-five million years ago.