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5/2/15 Cover

Wild Things

The weird and wonderful in the natural world

Sarah Zielinski

Wild Things

Wild Things

Your toy stegosaurus may be a girl

toy stegosaurus

This toy stegosaurus isn’t a wholly accurate reproduction of the species. But based on the shape of its plates, it may be more like a female than a male of its species, a new study suggests.

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Are your toy dinosaurs boys or girls? One Science News editor decided her plush stegosaurus was male and named him Franklin. It was as good a guess as any since there’s really no way to tell a dinosaur’s gender just by looking at it. Even paleontologists can’t always determine gender. Female dinosaurs that were pregnant when they died had a specific type of bone tissue (and sometimes eggs inside), but dinos without that tissue could have been either males or (nonpregnant) females.

A new study, however, proposes that at least one species of dino, Stegosaurus mjosi, did have distinct gender differences in morphology. In this species, the big, bony plates that distinguish a stegosaur may have differed in shape between males and females.

This is the conclusion of an undergraduate project by Evan Saitta, now a grad student at the University of Bristol in England. Saitta examined nearly a dozen S. mjosi fossil specimens, including five new ones that had been found together in a quarry near Grass Range, Mont. He published his findings April 22 in PLOS ONE.

S. mjosihad two forms, he found. Some individuals had plates that were tall, skinny and pointy. Others had plates that were shorter, rounder and wider. Other than the plates, the bones of the animals were so similar that they must have come from the same species. And all the individuals were adults, so the plate shapes didn’t differ according to maturity. The most likely explanation for the different morphologies, Saitta reasoned, was that they came from different sexes.

But which was the male and which was the female? There was none of that special bone tissue or any eggs to definitively mark any of the dinos as females. So Saitta made some deductions based on anatomical differences in modern bovids — large herbivores including antelopes and bison that could be a stegosaur stand-in. In bovids, males tend to have large ornamentation. If that was also true in S. mjosi, then the male fossils are the ones with the larger, rounder plates.

If these two morphs truly belonged to the same species and represent different sexes, then this would be one of the first cases of sexual dimorphism found in a non-avian dinosaur. It’s something that’s pretty common in animals today (and in avian dinos, like cardinals), but it’s been hard to find in dino fossils.

What this means in your house, though, is that you probably can tell the gender of your toy stegosaurus. If it’s got wide, round plates across its back, your dino is probably a boy. If those plates are tall and pointy, you’ve got a girl.

Editor's note: This post was updated on April 22 to note that this would be one of the first, not the first, cases of sexual dimorphism in a non-avian dinosaur.

Animals,, Oceans

Growth of mining on land may promote invasions at sea

By Sarah Zielinski 7:46pm, April 21, 2015
Ballast water taken in to keep ships stable could, when discharged elsewhere, release species that become invasive in their new homes.
Ecosystems,, Ecology

Before you plant this spring, consider the birds

By Sarah Zielinski 10:00am, April 20, 2015
A study of Chicago neighborhoods finds that the plants in private yards influence the variety of birds that live in the area.

How many manatees live in Florida?

By Sarah Zielinski 4:30pm, April 15, 2015
The most recent official count reports more than 6,000 manatees in Florida waters, but a new estimate may give a better picture of the population.

Flight delayed: There’s a coyote on the runway

By Sarah Zielinski 9:00am, April 14, 2015
A new study tallies up airport incidents involving carnivores and finds coyotes are the biggest threat.
Animals,, Oceans

Tiny sea turtles are swimmers, not drifters

By Sarah Zielinski 12:00pm, April 9, 2015
Young green and Kemp’s ridley sea turtles moved in different directions than instruments set adrift in the sea, which shows the animals were swimming.
Animals,, Ecology,, Climate

Eggs and other land foods won’t feed polar bears

By Sarah Zielinski 9:00am, April 5, 2015
Polar bears will not be able to survive on land by eating birds, eggs and vegetation, a new review concludes.
Animals,, Conservation

How human activities may be creating coywolves

By Sarah Zielinski 8:00am, April 1, 2015
Endangered red wolves will mate with coyotes when their partners are killed, which often happens because of human activities, a new study finds.
Animals,, Conservation

‘If you build it they will come’ fails for turtle crossings

By Sarah Zielinski 2:00pm, March 25, 2015
Turtles and snakes barely used an ecopassage built to make their movements safer. Scientists blame poor fencing that failed to keep them off the roadway.
Animals,, Conservation

Conservationists should make friends with hunters

By Sarah Zielinski 1:22pm, March 20, 2015
A survey of outdoor enthusiasts in rural New York finds that both hunters and birdwatchers are likely to engage in conservation behaviors, such as donating money.

Evidence of ‘yeti’ probably came from a Himalayan black bear

By Sarah Zielinski 2:21pm, March 17, 2015
Last year, a genetic analysis revealed two hairs from an unknown species of bear in Asia. A new study finds that they belong to rare Himalayan black bears.
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