Dinosaur eggs and babies
Every dinosaur hatched from an egg. Fossil nests, eggs and embryos tell us how long eggs took to hatch, whether parents looked after their young, and why even giant dinosaurs started life in fairly small eggs.
Many kinds of dinosaur eggs
Dinosaur eggs range from round, like a grapefruit, to long and narrow. Most had hard shells with calcium in them, but a fossil nest of Protoceratops studied in 2020 shows its eggs had soft shells, like some turtle eggs, so they rarely fossilised.[1][2]
Some places hold enormous numbers of eggs: an ancient beach in north-eastern Spain preserves about 300,000 fossil dinosaur eggs.[1]
Slower to hatch than bird eggs
Embryo teeth lay down one growth line a day, a bit like tree rings. In 2017 scientists counted these lines in embryos still inside their eggs and found that Protoceratops eggs took at least about 83 days to hatch, and those of the duck-billed Hypacrosaurus at least about 171 days.[2][3]
That is several times longer than bird eggs of a similar size, and closer to reptiles. Eggs that take so long are at great risk from predators and bad weather.[3]
Did parents care for their young?
In the late 1970s in Montana, scientists found many duck-billed dinosaur nests close together, with young that had already grown past hatching size but were still in the nests. They named the dinosaur Maiasaura, "good mother lizard", and the site became known as Egg Mountain.[4]
Citipati, a bird-like dinosaur from Mongolia, is known from fossils sitting on nests of eggs with the arms spread over them, the same posture as a brooding bird. So at least some dinosaurs looked after their eggs.[5]
Giants from small eggs
Even the largest known dinosaur eggs are smaller than those of the elephant bird, an extinct giant bird from Madagascar. An egg cannot get too big: the larger it is, the thicker the shell must be to stay strong, yet the embryo inside still needs oxygen through tiny pores in the shell.[1]
So a long-necked dinosaur that would grow over 20 m long started life in an egg no bigger than some giant birds' eggs, and had to grow thousands of times heavier before it was adult.[6]
Sources and further reading
More articles
- How dinosaur footprints form
- Why we say "dinosaur fossils", not "dinosaur bones"
- How do we know how old a dinosaur is?
- The first dinosaur fossils (in the world and in Thailand)
- How dinosaurs get their names
- How many Thai dinosaurs are there, and where were they found?
- Are birds really dinosaurs?
- The day the dinosaurs disappeared
- Animals people think are dinosaurs, but aren't
- Jurassic Park: how much of it is true?
- How do we know what colour dinosaurs were?
- How did long-necked dinosaurs get so big?