User:Abyssal/Timeline of Dinosaur Park Formation paleontology

Hadrosaur Hatchlings
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 the 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. Neonate sized Champsosaurus, crocodilians, turtles, ornithomimids, Saurornitholestes, Troodon, tyrannosaurs, possible ankylosaurs, centrosaurines, and hadrosaurs have been documented in the scientific literature. 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. Tiny hadrosaur footprints have been discovered in the Blackhawk Formation of Utah. 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." Most of the shells from the microfossil site are from pisidiid clams, but rarely unionid clams and gastropods are found. It was the slow dissolution of these shells 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. The eggshell is similar to the eggshells from the Two Medicine and Judith River Formations in Montana. Dinosaur eggshell can have different textures on different parts of the egg. Dinosaur Provincial Park eggshell is similar to eggshell from the Devil's Coulee in southern Alberta. Most hadrosaur neonate 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." 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. 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. Bonebeds 23, 28, 47, and 50 yielded "unusually high" numbers of young hadrosaur remains. Certain outcrops of bonebed 50 are "particularly rich," producing around a dozen such fossils a year. Dinosaur eggshell is lacking from the bone beds producing the hadrosaur juvenile bones. Tanke concludes that the abundance of bone in these locations is not due to collecting biases or intensity.

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 represent the remains of individuals who died while migrating through the region. They might also have had a more upland habitat where they may have nested or fed. Tanke and Brett-Surman bemoaned science's lack of knowledge about hadrosaurs from the uplands and those from Campanian strata and northern Alberta.

Info used in

 * Dinosaur Park Formation
 * Hadrosaurs
 * Dinosaur reproduction
 * Pisidiidae
 * Unionidae

Reference

 * Tanke, D.H. and Brett-Surman, M.K. 2001. Evidence of Hatchling and Nestling-Size Hadrosaurs (Reptilia:Ornithischia) from Dinosaur Provincial Park (Dinosaur Park Formation: Campanian), Alberta, Canada. pp. 206-218. In: Mesozoic Vertebrate Life—New Research Inspired by the Paleontology of Philip J. Currie. Edited by D.H. Tanke and K. Carpenter. Indiana University Press: Bloomington. xviii + 577 pp.