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For dinosaurs, hatching eggs was a long-term commitment.

A nest pinned the parents down to the spot where the eggs were laid. As long as they were incubating their eggs, they couldn't venture off in search of food or to flee predators. And their eggs incubated for a very long time.

That's according to Gregory Erickson, a paleobiologist at Florida State University and the lead author of a new study on dinosaur hatching times in the journal Proceedings of the National Academy of Sciences. Close examination of embryos found fossilized inside their eggs suggests that dinosaurs took as many as six months to hatch - far longer than their closest modern descendants, today's birds.

This long period of development may have been what doomed them, Erickson said. After an asteroid crashed into the earth 66 million years ago, triggering a mass extinction, it would have been harder for slowpoke reproducers like dinosaurs to recover.

"I think it's an important piece for understanding why dinosaurs went extinct," he said.

[Right after an asteroid killed the dinosaurs, life returned to the scene of the crime]

To understand why, we have to rewind a bit, to about 10 million years before the asteroid strike. It's the end of the Cretaceous Period. In what is now Mongolia's Gobi Desert, a clutch of 12 eggs the rough size and shape of potatoes has just been laid by a Protoceratops andrewsi, a relative of the more famous Triceratops. Around the same time, near Alberta, Canada, a duck-billed Hypacrosaurus stebingeri laid a huge egg the size of a volleyball. ("Ridiculous," Erickson said of the almost 10-pound Hypacrosaurus egg.)

While the dinosaurs did whatever it is dinosaurs do while nesting (scientists think some species sat on their nests like birds, while others probably buried their eggs like reptiles), the embryos inside slowly develop. Just before the halfway point of their incubation period, they start to grow teeth.

In humans and reptiles, teeth are formed from dentin, a liquid that gets laid down every day and then mineralizes, forming a hard layer. Over time, the layers build up like tree rings, one for each day the embryo developed.

" You can basically just count those up and figure out how long it took the dentition to form," Erickson said. He wondered if dinosaur embryos might exhibit the same phenomenon. So he talked with scientists at the American Museum of Natural History (which houses the Protoceratops eggs) and the University of Calgary (which has the Hypacrosaurus egg) into letting him sample a small amount of tooth from each fossil.

As soon as he popped his slide under a microscope and saw the telltale dentin layers, "I knew we were in business," Erickson said.

The number of layers let him calculate a conservative estimate of the incubation times for the two species: about three months for the smaller Protoceratops hatchlings, six months for the larger Hypacrosaurus. Most birds' eggs hatch in a fraction of that time (chickens take three weeks, canaries need just 13 days). Even emperor penguin dads, who famously huddle around their eggs for extended periods to protect them from the harsh Antarctic winter, incubate their young for two months at most.

[Scientists believe they've found a 'pregnant' T. rex]

"It's really surprising," Erickson said. "I don't think that people would have entertained the idea that they would have incubated over the better part of the year."

David Varricchio, a paleontologist at Montana State University not involved in the study, was less surprised by the long incubation times, noting that modern reptiles also take a long time to hatch. But the method of calculating incubation periods was a compelling one, he said, and it provides another line of evidence for understanding dinosaurs' lives.

Spending a long time caring for a clutch of eggs probably cramped dinosaur parents' styles. It restricted their habitats to regions where the weather was right for incubating an egg, made migration more difficult, and exposed attending parents to predators, natural disasters and hunger - "all the rigors that go with trying to protect the nest for long periods of time," Erickson said. Basically, this could have been an extreme version of the lengthy parenting depicted in the film "March of the Penguins."

And that probably had consequences when the asteroid struck and wiped out most dinosaurs, along with 75 percent of all life on Earth. If a species was going to survive, it needed to be holding all the right cards when it came to physical and life history attributes. Successful creatures were small and adaptable animals that lived fast and died young. For the ancestors of birds, quick incubation times may have boosted their ability to repopulate and evolve to fill ecological niches left vacant after the disaster.

But dinosaurs were large and probably endothermic (warm blooded), which made them "profligate wasters of energy," Erickson said. They also took a long time to reach sexual maturity. On top of all this, a slow incubation might have been a "black ace" - contributing to long generational times that made it harder for dinosaurs to bounce back.

"Dinosaurs found themselves holding basically a dead man's hand," Erickson said.
Read more: Cheetahs are racing toward extinction How Vera Rubin changed science Dear Science: Could my body include an atom from Shakespeare? Slime molds prove you don't need a brain to learn - or teach - a new trick Drone video captures killer whales eating a shark alive

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Dinosaurs took months to hatch out of their eggs. That may have doomed them.

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For dinosaurs, hatching eggs was a long-term commitment. A nest pinned the parents down to the spot where the eggs were laid. As long as they were incubating their eggs, they couldn't venture off in search of food or to flee predators. And their eggs incubated for a very long time.

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Day 23 - Dinosaur Museum At last we had arrived at the dinosaur museum. Unfortunately we arrived late, so we had just over an hour to see the whole place. I had been here two times previously, and the place has not changed much.

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Researchers have discovered two small dinosaurs together with a lagerpetid, a group of animals that are recognized as precursors of dinosaurs. The discovery made in Brazil and reported in the Cell Press journal Current Biology on November 10 represents the first time that a dinosaur and a dinosaur precursor have ever been found together.

The new lagerpetid (Ixalerpeton) and saurischian dinosaur (Buriolestes) were unearthed from the ~230-million-year-old Carnian Santa Maria Formation -- one of the oldest known rock units including dinosaur fossils anywhere in the world.

"We now know for sure that dinosaurs and dinosaur precursors lived alongside one another and that the rise of dinosaurs was more gradual, not a fast overtaking of other animals of the time," says Max Langer of Brazil's Universidade de São Paulo.

The discovery clearly shows that these animals were contemporaries of each other during the earliest stages of dinosaurs' evolution. The new lagerpetid specimen also preserves the first skull, scapular, and forelimb elements, plus associated vertebrae, known for the group, the researchers report. Tooth evidence also shows that the first dinosaurs most likely fed on "all kinds of small animals, but most probably not plants," Langer says.

Those details help to reveal how dinosaurs acquired some of their characteristic anatomical traits. Their analysis also suggests that Buriolestes is one of the oldest known Sauropodomorpha, the group of long-necked dinosaurs that includes sauropods.

The two new animals have already helped to fill important gaps in the evolution of the key anatomical features of dinosaurs. But Langer and his colleagues aren't done with them yet. They are using CT scans to characterize and describe the animals' anatomy in even greater detail. They also hope to get an even more precise radioisotopic date on the oldest dinosaur-bearing rocks, and the search for more Triassic fossils continues.
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Journal Reference:

Sergio Furtado Cabreira, Alexander Wilhelm Armin Kellner, Sérgio Dias-da-Silva, Lúcio Roberto da Silva, Mario Bronzati, Júlio Cesar de Almeida Marsola, Rodrigo Temp Müller, Jonathas de Souza Bittencourt, Brunna Jul'Armando Batista, Tiago Raugust, Rodrigo Carrilho, André Brodt, Max Cardoso Langer. A Unique Late Triassic Dinosauromorph Assemblage Reveals Dinosaur Ancestral Anatomy and Diet. Current Biology, 2016; DOI: 10.1016/j.cub.2016.09.040

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Dinosaurs' rise was 'more gradual,' new fossil evidence suggests

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Researchers have discovered two small dinosaurs together with a lagerpetid, a group of animals that are recognized as precursors of dinosaurs. The discovery made in Brazil represents the first time that a dinosaur and a dinosaur precursor have ever been found together.

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born in 1819