Image: Amy Martin
In Brief
- Scientists historically skirted the subject of how dinosaurs had sex, out of modesty and an absence of evidence.
- But studies of the closest living relatives of dinosaurs are providing insights into their probable reproductive anatomy.
- And computer models can test the plausibility of putative mating positions.
More In This Article
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Overview
What Color Were Dinosaurs? [Video]
Adapted from My Beloved Brontosaurus: On the Road with Old Bones, New Science, and Our Favorite Dinosaurs, by Brian Switek, by arrangement with Scientific American/Farrar, Straus and Giroux, LLC. Copyright © 2013 by Brian Switek
I was shuffling through Chicago's O'Hare international airport when I saw it: a magnificent, towering skeleton of a dinosaur. At first I thought it was a mirage created by my travel-addled brain. But the scene did not evaporate as I approached. Pillarlike forelimbs and brawny shoulders supported a long swerve of neck bones leading up to the dinosaur's small, boxy skull, which peered over the top of a banner touting the airport's Wi-Fi, as if looking to the tarmac beyond to check the latest departures and arrivals. I stopped and stared at the behemoth—a replica of Brachiosaurus inherited from the Field Museum in Chicago—mentally filling in the internal organs, muscles and skin of a creature that at 85 feet long is one of the largest dinosaurs ever found. And then a strange thought bubbled up in my mind: How did such a gargantuan animal have sex?
Giddy and tired, I envisioned a pair of amorous Brachiosaurus standing in a clearing in a conifer forest some 150 million years ago during the Jurassic period, each one waiting for the other to make the first move. But try as I might, I couldn't quite figure out the mechanics of what should come next. Could the male rear up to mount the female? Could the female support his weight? Wouldn't her massive tail get in the way? Alas, my flight started boarding, so I had to part ways with the skeleton, but I continued to ponder the mating mystery on the plane. It has captivated me ever since.
Dinosaurs must have had sex to reproduce. As in nearly all modern-day reptiles, males would have deposited sperm inside females, which would later lay fertilized eggs containing developing dinosaur embryos. Yet although scientists have managed to deduce quite a bit about dinosaur biology, the nuts and bolts of dinosaur sex remained largely unknown—in part because studying the sexual behavior of animals was taboo historically and the topic seemed so beyond the reach of science that very little could be said about dinosaur mating with confidence. Not all hope is lost, however. Dinosaur fossils have furnished clues to such intimate details as when during development these reptiles reached sexual maturity and how they attracted mates. Meanwhile studies of birds and crocodilians—the closest living relatives of dinosaurs—hint at what the external reproductive anatomy of dinosaurs looked like. And computer modeling offers the possibility of testing theories about how these giants managed to do the deed itself. Much remains to be discovered, but scientists are slowly drawing back the curtain on dinosaur amour.
Lock and Key
Signs of sex are hard to find in the fossil record of any creature. Among the rare examples are 47-million-year-old turtles that died while copulating and a pair of 320-million-year-old sharks that might have been courting when they were rapidly buried. Sadly no dinosaur skeletons have been found locked in romantic embrace. And not even the most beautifully preserved of these beasts retain remains of their reproductive organs.
For insights into the private parts of these extinct animals, scientists have had to turn to their closest extant relatives: birds and crocodilians. Birds are living dinosaurs, a specialized lineage that evolved around 150 million years ago and continues to thrive today. Crocodilians—a group that includes the alligators, gharials and crocodiles—are the closest living relatives of the group formed by extinct dinosaurs and modern birds. A trait present in both birds and crocodilians is likely to have been present in nonavian dinosaurs as well. One such trait is a cloaca—the single end point for the reproductive, urinary and intestinal tracts in both sexes of birds and crocodilians and probably, by extension, dinosaurs. Thus, an Apatosaurus's genitals would not be visible as it plodded by. Instead they would have been concealed in the cloaca, which would have appeared only as a slit underneath the dinosaur's tail.
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15 Comments
Add CommentI understood that the "hip spike" of Kentrosaurus was actually a shoulder spike - is this no longer the case?
Reply | Report Abuse | Link to thisI was surprised to learn about the "brawny" shoulders of the dinosaur. "Brawny" normally connotes large, strong, muscles. Dinosaurs, in their modern form, don't normally have muscles.
Reply | Report Abuse | Link to thisActually, they may not have. I can not believe I have not seen this mentioned anywhere before either.(a quick google search doesnt seem to show anything obvious either)
Reply | Report Abuse | Link to thisDinosaurs likely fertilized their eggs externally. At least some of them may have anyway. There are different examples today of creatures that externally fertilize eggs. Dinosaur eggs were also highly porous, which is often cited as for gas exchange but also serving the dual purpose of allowing sperm to cross through wouldnt be much of a stetch.
It does seem to fit. I would of course think the details like pore size need to be looked at and what not, but I would have to say this isnt an out there idea.
Nature does often favor simple ways of doing things and the bigger the animals would get(not to mention the spikes), the harder it would be interact. Simply having the eggs get laid and then having the male come up and make a deposit avoids alot of stress.
I am not an expert on the subject by any means, but when things seem to fit...
Nathan Myhrvold scooped you 16 years ago. See his TED7 talk on how dinosaurs have sex.
Reply | Report Abuse | Link to thisAfter having read the article I now ponder as to whether the author has sex.
Reply | Report Abuse | Link to thisAnother of life's great mysteries slowly coming to light. Sleeping a little easier tonight.
Reply | Report Abuse | Link to thisTHANK YOU!THANK YOU!THANK YOU!
Although I am no expert on dinosaur reproduction, I do know a bit about eggs. Especially the challenges of reproducing on land. In order for external reproduction eggs have to be porous enough for sperm to enter, this would also make them very prone to desiccation. So if a dinosaur wanted to fertilize eggs externally they had to oviposit their eggs in very humid conditions, like mud or so. This would also limit the places they are able to reproduce. Amphibians fertilize externally but they do so in water or other moist places. So although I will not say it is impossible that external fertilization took place in dinosaurs, to me it seems highly unlikely.
Reply | Report Abuse | Link to thisThere's also an efficiency point about that. Dinosaur eggs were fairly large. Dispersing sperm efficiently across a large pile of eggs would have been difficult at best and would have risked a large number of nonviable eggs, a waste of energy use especially by the larger reptiles. Amphibians tend to be small and their eggs clustered, allowing sperm to form a cloud around them and enter them opportunistically.
Reply | Report Abuse | Link to thisObviously the scientists are still shy to talk about the details otherwise they would have brought up the Argentinian Lake Duck which It is notable for possessing, in relation to body length, the longest penis of all vertebrates.
Reply | Report Abuse | Link to thisPenises that apparently grow extraordinarily long for breeding season, and mostly wither away in between.
It's so long that to keep it safe inside, the penis has developed a corkscrew like shape that the duck can pull inside like a spring when not in use.
http://dave-littler.livejournal.com/79256.html
If a duck can do that, no doubt probably did something similar, rendering the need to mount each other or get in some other difficult copulatory position unnecessary.
Some dinos could have retained a trait from amphibians and male dinos could have dropped a spermatophore for the lady dino to pick up with her cloaca.
Convenience is also a selling point with this technique as she could store the packet of sperm for later if times weren't right for raising a brood when a irresistible, hot studosaur caught her eye.
THEN there is a third option of the fish, and the way I thought chickens fertilized their eggs when I was like 5 years old.
Eggs are not hermetically sealed. Perhaps dino eggs were permeable enough when initially laid that a male dino could slather them with sperm and fertilize them that way. Only after they were fertilized would their shells harden.
Oh and I almost forgot, large land mammals also possess extraordinarily large as in long penises to enable them to mate.
Reply | Report Abuse | Link to thisPictures of elephants about to mate show their can almost be half the body length of the female.
So ducks aren't the only ones who have giant copulatory organs LOL
OBVIOUSLY LENGTH would have probably been the way dinos compensated for any sort of anatomical obstacle to mating.
NO HALF-EVOLVED DINOSAURS: Just google the title to read this Internet article of mine.
Reply | Report Abuse | Link to thisBabu G. Ranganathan*
B.A. Bible/Biology
Check-out my newest and very popular Internet site: THE SCIENCE SUPPORTING CREATION
Author of popular Internet article, TRADITIONAL DOCTRINE OF HELL EVOLVED FROM GREEK ROOTS
* I have given successful lectures (with question and answer period afterwards) defending creation before evolutionist science faculty and students at various colleges and universities. I've been privileged to be recognized in the 24th edition of Marquis "Who's Who in The East" for my writings on religion and science.
Jacobs86 You're assuming that the pores would have to stay the same size throughout development.
Reply | Report Abuse | Link to thisA short window of time in which the egg had pores large enough for dino sperm to pass and fertilize the egg could have existed.
Fertilization would trigger a process to shrink the pores immediately afterward either through calcium deposition or protein matrix of some sort.
That's all speculation, but for eggs to be laid with extra calcium in the outer layers waiting for fertilization to then be used to minimize the pores is not a big evolutionary feat if there is a need.
Baculum as an assist....anyone expert on bacului?
Reply | Report Abuse | Link to thisCould they have used their long necks and mouths to move sperm?
Reply | Report Abuse | Link to thisbgrnathan While I celebrate your troll-dom, please note:
Reply | Report Abuse | Link to thisevery dinosaur ever discovered was fully evolved.
Evolution is simply a description of the process whereby the chemistry and physics that rule life provides for the continuation of said life.
What is alive at any given moment represent the leftovers, after the scythe of environmental forces slice down that which cannot survive.
If evolution doesn't happen, why are there different flu vaccines every year?