Labels:text | font | paper | publication | document OCR: The discovery of fossil dinosaur eggs and nests in the Gobi Desert, Mongolia, in 1923 gave scientists the first real proof that dinosaurs hatched from eggs. Other reptiles (animals that have waterproof skin and lay eggs) and birds (animals that have feathers) also hatch from eggs. Since 1923, other finds have been made in many parts of the world, most notably in Montana, in 1978. Scientists have been able to study the remains of the eggs and nests and work out how dinosaurs may have developed throughout their lives, and how they tended their young. ALTRICIAL YOUNG The discovery of nest sites has given scientists an insight into the early life of dinosaurs. At nest sites in Montana, fossilized clutches of eggs and hatchlings belonging to Maiasaura have been discovered that indicate the young of some dinosaur species were born in a less advanced state than others. The hatchlings of Maiasaura appear to have had poorly formed limb joints. This suggests that Maiasaura young were altricial, which means that they were poorly developed on hatching. They would have stayed in the nest, cared for by adults, until they were old enough to leave. In this way, they would have been like present-day altricial birds, such as blackbirds, which are hatched nearly naked and with their eyes closed. They are dependent on their parents for food and warmth, and are confined to the nest. PRECOCIAL YOUNG Clutches of Troodon eggs and hatchlings discovered at nest sites in Montana hinted that the young were hatched in an advanced state. The fossil hatchlings had well-formed limb joints. This suggested that Troodon young were precocial, which means that they were well-developed on hatching. They might have been reasonably self-sufficient - able to look for their own food. This is comparable to present-day precocial birds, such as ducks, which are hatched with a covering of down and with their eyes open. They leave the nest immediately and learn skills and behavior patterns from their parents rapidly, through a process called "imprinting." NESTING AND EGG-LAYING Dinosaurs such as Maiasaura probably made their nests by making a mound of earth, and scooping a hollow in the top of it. Most female dinosaurs then laid their eggs in circles, but without the eggs touching one another. Some hadrosaurs (duck-billed dinosaurs) laid their eggs in a spiral, the first egg in the center of the scoop and the rest coiling around it. Female dinosaurs then put sand or vegetation around the eggs to protect them and to keep them warm, or possibly to prevent them from overheating in the sun. NESTING COLONIES The study of discovered nest sites has also revealed that Maiasaura, and possibly other dinosaurs, returned to the same nesting sites year after year. This behavior is also displayed by present-day birds. Within the nesting sites, Maiasaura built their nests approximately 9 m (30 ft) apart. This is the same length as the Maiasaura dinosaur itself. By nesting in colonies like this, Maiasaura could depend on numbers as a defense against many different predatory dinosaurs that would steal eggs, kill hatchlings, or kill individual adults.
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