How Many Babies Did Dinosaurs Have? And Other Questionable Prehistoric Parenting Practices

It’s a complex topic, and one we can explore in part by looking to the closest living relatives of these extinct animals that are still alive today, something known as phylogenetic bracketing. We can also look to fossil evidence for answers, and some questions? Well, sometimes it’s just common sense.

Dinosaur babies: A numbers game

We know for a fact that juvenile dinosaurs had an extremely high mortality rate.

Jay Balamurugan

“Baby animals are not the most stable of things,” said Walking With Dinosaurs’ palaeoartist Jay Balamurugan at a press screening. “If you’ve ever watched baby sea turtles going into the ocean in any other documentary, baby dinosaurs were kind of like that. They would [have hatched] in huge numbers. Loads of eggs being laid, loads of dinosaurs hatching, because of the high mortality.”

“We know for a fact that juvenile dinosaurs had an extremely high mortality rate. There are lots of dangers in the prehistoric world as there are today. We know of dinosaurs that have been preserved because they fall into things like quicksand. We know of dinosaurs that have been quite literally squashed under foot of other dinosaurs, we’ve found some that have just been pancakes. There are lots and lots of perils in the ancient world, dinosaurs would have fallen victim to many of those, and we have quite a lot of them in the fossil record.”

 

Many species play the numbers game, producing lots of eggs in the hopes that even one might make it to adulthood and pass on their genes to the next generation. What that specific number might be changes depending on the dinosaur species, but there does seem to be a pattern between degrees of parental care and egg numbers.

How many eggs did dinosaurs lay?

Theropods were typically laying between 10 and 20 eggs per nest, explained PhD student Becky Lakin to Emily Osterloff for the Natural History Museum, London. They include Allosaurus, a meat-eater and protective parent that likely guarded its eggs and hatchlings. We may even have discovered an example of brood parasitism in an Allosaurus nest that contained the eggs of an ancient crocodilian. It’s possible, says Lakin, that this crafty croc might have benefited from the dedicated daycare an unwitting Allosaurus could provide its young while it swam off and got on with other things.

Sitting on top of a nest was an option for some smaller dinosaurs, and we have fossil evidence of a dinosaur sitting on its eggs like a bird. However, it would’ve been a costly practice as they were forced to sit there all day, a near-literal sitting duck. Other dinosaurs couldn’t sit on their eggs because, put simply, they would’ve squished their young into an omelette before any predators got a chance to have a look in. 

Dinosaur egg incubation

This is certainly the case for the multiple-ton Sauropods, but we’ve found evidence that suggests they found other ways to keep their eggs warm.  As Dr Darren Naish explains in the below video from Prehistoric Planet 2, we’ve found evidence of female Sauropods digging out trenches with their legs. Shielded from view and the elements, it created a more stable environment for their eggs. 

It’s even thought that some dinosaurs may have used rotting vegetation as a heat source for developing offspring by building mounds of it like compost on top of nursery mounds. We see this behavior today in a living dinosaur (read: bird) – a kind of turkey in Australia that can keep its eggs warm for around 7 weeks using manky old plant matter.

Titanosaurs weren’t that bothered about looking after their young.

Dr Susannah Maidment

Sauropods living in what we now know as Argentina appear to have borrowed heat from Earth for cooking up some babies. Fossilized remains of their nests have been found near thermal springs, and the same volcanic activity that keeps them hot may have been acting like a free incubator for dinosaurs. In India, layers of dinosaur eggs have been found between layers of lava, demonstrating that the practice was being repeated for centuries. A smart move on the part of the mother, but one that seems to have been her parting gift to her offspring.

“Titanosaurs weren’t that bothered about looking after their young,” said Dr Susannah Maidment to IFLScience at the Natural History Museum, London, opening of their Patagotitan gallery. “They sort of dropped them and went, very casual attitude. They would have made their nursing mounds on the ground, laid the eggs and maybe covered them and then off they went and that was it for parental care.”

Parental care and egg numbers

We see that lack of parental care reflected in Sauropod egg numbers, which Lakin says could have been in the region of 100 per nest. For babies like Isisaurus, their parents were probably long-gone by the time they were ready to go in search of food out in the faraway forests, and it’s here that the “safety in numbers” idea really kicks in.

“The babies probably hatched out and may have lived together in a kind of herd when they were hatchlings,” said Maidment. “They must have grown incredibly rapidly so you can imagine something that was hatching out of an egg [a bit smaller than a football] and growing to be the largest terrestrial vertebrae ever to walk the earth – it must have grown incredibly fast.”

Many of these animals would have died when they were much younger from disease or from predation.

Dr Susannah Maidment

“We don’t really know how long they lived. It’s really quite difficult to tell because that sort of information requires cutting up the bones and you can imagine why people don’t like you cutting up their very precious dinosaur bones to examine them. We think maybe around 50 years or 60 years, something like that for the very maximum, but, of course, many of these animals would have died when they were much younger from disease or from predation and things like that.”

That means that making it out of their prehistoric nurseries may have involved occasionally watching your siblings get slurped up by Rajasaurus, but each species’ behavioral adaptations gave them a fighting chance to be strong enough to make it in the big wide world. We often have a habit of looking back on dinosaur behavior through the lens of our mammalian ways, but it’s thought many species actually behaved more like some birds and reptiles in it being the dads that put the real shift in. Just check out “The River Dragon”, Spinosaurus the super-dad.