Old Earth Ministries Online Dinosaur Curriculum
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Lesson 58 - Hadrosaurid Overview
Hadrosaurids or duck-billed dinosaurs are members of the family Hadrosauridae, and include ornithopods such as Edmontosaurus and Parasaurolophus. They were common herbivores in the Upper Cretaceous Period of what are now Asia, Europe and North America. They have been referred to as the "cows of the Cretaceous." They are descendants of the Upper Jurassic/Lower Cretaceous iguanodontian dinosaurs and had similar body layout. They were ornithischians.
Hadrosaurids are divided into two principal subfamilies. The lambeosaurines (Lambeosaurinae) had hollow cranial crests or tubes, and were generally less bulky. The saurolophines, identified as hadrosaurines in most pre-2010 works (Saurolophinae or Hadrosaurinae), lacked hollow cranial crests (solid crests were present in some forms) and were generally larger.
|Parasaurolophus cyrtocristatus at Field Museum of Natural History (Picture Source)|
The hadrosaurs are known as the duck-billed dinosaurs due to the similarity of their head
In 2009, paleontologist Mark Purnell conducted a study into the chewing methods and diet of hadrosaurids. By analyzing hundreds of microscopic scratches on the teeth of a fossilized Edmontosaurus jaw, the team determined hadrosaurs had a unique way of eating unlike any creature living today. In contrast to a flexible lower jaw joint prevalent in today's mammals, hadrosaurs had a unique hinge between the upper jaws and the rest of its skull. The team found the dinosaur's upper jaws pushed outwards and sideways while chewing, as the lower jaw slid against the upper teeth.
Hadrosaurids were the first dinosaur family to be identified in North America, the first traces being found in 1855-1856 with the discovery of fossil teeth. Joseph Leidy examined the teeth, and erected the genera Trachodon and Thespesius (others included Troodon, Deinodon and Palaeoscincus). One species was named Trachodon mirabilis. Now it seems that the teeth genus Trachodon is a mixture of all sorts of cerapod dinosaurs, including ceratopsids. In 1858 the teeth were associated with Leidy's eponymous Hadrosaurus foulkii, named after the fossil hobbyist William Parker Foulke. More and more teeth were found, resulting in even more (now obsolete) genera.
A second duck-bill skeleton was unearthed, and was named Diclonius mirabilis in 1883 by Edward Drinker Cope, which he incorrectly used in favor of Trachodon mirabilis. But Trachodon, together with other poorly typed genera, was used more widely and, when Cope's famous "Diclonius mirabilis" skeleton was mounted at the American Museum of Natural History, it was labeled as "Trachodont dinosaur". The duck-billed dinosaur family was then named Trachodontidae.
A very well-preserved complete hadrosaurid specimen (Edmontosaurus annectens) was recovered in 1908 by the fossil collector Charles Hazelius Sternberg and his three sons, in Converse County, Wyoming. Analyzed by Henry Osborn in 1912, it has come to be known as the "Trachodon mummy". This specimen's skin was almost completely preserved in the form of impressions.
Lawrence Lambe erected the genus Edmontosaurus ("lizard from Edmonton") in 1917 from a find in the lower Edmonton Formation (now Horseshoe Canyon Formation), Alberta. Hadrosaurid systematics were addressed in a 1942 monograph by Richard Swann Lull and Nelda Wright. They proposed the genus Anatosaurus for several species of dubious genera. Cope's famous mount at the AMNH became Anatosaurus copei. In 1990, Anatosaurus was moved to Edmontosaurus. One former Anatosaurus species was distinct enough from Edmontosaurus to be placed in a separate genus, named Anatotitan, so in 1990 the AMNH mount was re-labelled Anatotitan copei.
Hadrosaurid remains have been found in rocks above the K-T boundary, indicating that some dinosaurs lived on for up to 400,000 years after most dinosaurs became extinct.
One of the most complete fossilized specimens was found in 1999 in Hell Creek Formation of North Dakota and now is nicknamed "Dakota". The hadrosaur fossil is so well preserved that scientists have been able to calculate its muscle mass and learn that it was more muscular than thought, probably giving it the ability to outrun predators such as Tyrannosaurus rex. Unlike the collections of bones found in museums, this mummified hadrosaur fossil comes complete with skin (not merely skin impressions), ligaments, tendons and possibly some internal organs. It is being analyzed in the world's largest CT scanner, operated by the Boeing Company. The machine usually is used for detecting flaws in space shuttle engines and other large objects, but previously none as large as this. Researchers hope the technology will help them learn more about the fossilized insides of the creature. They also found a gap of about a centimeter between each vertebra, indicating that there may have been a disk or other material between them, allowing more flexibility and meaning the animal was actually longer than what is shown in a museum.
The family Hadrosauridae was first used by Edward Drinker Cope in 1869. Since its creation, a major division has been recognized in the group, between the (generally crested) subfamily Lambeosaurinae and (generally crestless) subfamily Saurolophinae (or Hadrosaurinae). Phylogenetic analysis has increased the resolution of hadrosaurid relationships considerably. For more on this topic, please see the Wikipedia page for Hadrosaurid.
While studying into the chewing methods of hadrosaurids in 2009, the paleontologists Vincent Williams, Paul Barrett, and Mark Purnell found that hadrosaurs likely grazed on horsetails and vegetation close to the ground, rather than browsing higher-growing leaves and twigs. This conclusion was based upon the evenness of scratches on hadrosaur teeth, which suggested the hadrosaur used the same series of jaw motions over and over again. As a result, the study determined that the hadrosaur diet was probably made of leaves and lacked the bulkier items such as twigs or stems, which might have required a different chewing method and created different wear patterns. However, Purnell said these conclusions were less secure than the more conclusive evidence regarding the motion of teeth while chewing.
The hypothesis that hadrosaurs were likely grazers rather than browsers appears to contradict previous findings from preserved stomach contents found in the fossilized guts in previous hadrosaurs studies. The most recent such finding before the publication of the Purnell study was conducted in 2008, when a team led by University of Colorado at Boulder graduate student Justin S. Tweet found a homogeneous accumulation of millimeter-scale leaf fragments in the gut region of a well-preserved partially-grown Brachylophosaurus. As a result of that finding, Tweet concluded in September 2008 that the animal was likely a browser, not a grazer. In response to such findings, Purnell said preserved stomach contents are questionable because they do not necessarily represent the usual diet of the animal. The issue remains a subject of debate.
Coprolites (fossilized droppings) of some Late Cretaceous hadrosaurs show that the animals sometimes deliberately ate rotting wood. Wood itself is not nutritious, but decomposing wood would have contained fungi, decomposed wood material and detritus-eating invertebrates, all of which would have been nutritious.
Baby-sized hadrosaur fossils have been documented in the scientific literature. Tiny hadrosaur footprints have been discovered in the Blackhawk Formation of Utah.
In the Dinosaur Park Formation
In 2001 Darren H. Tanke and M. K. Brett-Surman reviewed and described eggshell and hatchling material from the Dinosaur Park Formation of Dinosaur Provincial Park. Eggshell is rare in the Park, being present in only two microfossil sites, both of which are predominated by the preserved shells of invertebrate life. The survival of hadrosaur eggshell fragments in the presence of these invertebrate shells may be result of calcium in the invertebrate shells buffering contemporary acidic water which would have dissolved them. The hadrosaur eggshell fragments "show little to no stream abrasion" suggesting that the material did not originate far from their final burial place in the Park. The authors felt that their newly reported material corroborated the then-recent suggestion that hadrosaurs did not nest exclusively in upland areas, but also areas of lower elevation. Some recovered hadrosaur fossils might actually be from embryos. Hatchling and nestling-sized hadrosaur remains had been falsely considered rare in Dinosaur Park Formation due to bias on the part of collectors seeking larger specimens and sometimes not recognizing what was encountered. Hadrosaurs had been speculated to be upland breeders due to the lack of preserved egg and hatchling material.
However young hadrosaur remains had been previously reported from lowland deposits. Darren Tanke observed that an experienced collector could actually discover multiple juvenile hadrosaur specimens a day. During the 1992 field season a concerted effort was undertaken by the Royal Tyrell Museum to recover the remains of young hadrosaurs. The researchers describe the acquisition that season of 43 specimens as being a success. Most of the recovered fossils were of dentaries missing their teeth, bones from limbs and feet, as well as vertebral centra. The material showed little or none of the abrasion that would have resulted from transport, meaning the fossils were buried near their point of origin. The researchers conclude that this meant that hadrosaurs were nesting in the lowlands of the area represented by the strata containing the fossils and that previous workers hypotheses of lowland hadrosaur breeding were "confirmed." It was the slow dissolution of shells left by clams and snails releasing calcium carbonate into the water that raised the water's pH high enough to prevent the eggshells from dissolving. The no fragment's greatest dimension exceeds one cm. The eggshells' surface has a pebbly texture. Dinosaur Provincial Park eggshell is similar to the eggshells from the Two Medicine and Judith River Formations of Montana as well as eggshell from the Devil's Coulee in southern Alberta.
Most hadrosaur neonate (baby) bones are incomplete due to their small size and vulnerability to the high erosion rates in the Dinosaur Provincial Park. Dentaries are common hadrosaur neonate fossils. Most specimens don't preserve all of the tooth replacement gooves. Most preserve only about ten tooth files.
No neural arches are represented among the vertebrae fossils. Although some limb bones show signs of transport wear, the distances traveled before burial were probably not far as such small bones would be unlikely to survive the great diversity of scavengers and acidic water conditions. The breakdown of tannins from coniferous vegetation would have caused the pH of the waters in the park to be acidic. Dinosaur eggshell is lacking from the bone beds producing the hadrosaur juvenile bones.
The authors concluded that hadrosaurs nested in both upland or lowland area, although described factors influencing the division of breeding locations as unknown. They suggested that "diet, soil conditions, habits, [and] competition" between dinosaur genera might have played roles. Some of the less common hadrosaurs in the Dinosaur Park Formation of Dinosaur Provincial Park like Brachylophosaurus or Parasaurolophus may have had a more upland habitat where they may have nested or fed.
The limbs of the juvenile hadrosaurs are anatomically and proportionally similar to those of adult animals. However, the joints often show "predepositional erosion or concave articular surfaces." Probably due to the cartilaginous cap covering the ends of the bones. The pelvis of a young hadrosaur was similar to that of an older individual.
Daily activity patterns
Comparisons between the scleral rings of several hadrosaur genera (Corythosaurus, Prosaurolophus, and Saurolophus) and modern birds and reptiles suggest that they may have been cathemeral, active throughout the day at short intervals.
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