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The sex lives of dinosaurs

A paleontologist finds human insights in ancient mating behavior

Globe Staff photo Illustration

Let’s face it: If sex hadn’t existed in the animal kingdom long before Homo sapiens, humans wouldn’t be here at all. So it’s odd that our understanding of how sexual reproduction worked in the pre-human world is mostly limited to lurid speculation—like a recent Daily Mail article about dinosaur mating called “The joy of T-Rex,” which made the Internet go wild.

As far as real science goes, however, we still know very little about when sex began, who was doing it, and how exactly they went about it. Paleontologist John A. Long hopes to change that. His work over the past decade has focused largely on the ancient evolution of sex, starting with his 2007 discovery of a 380-million-year-old fossilized placoderm fish from the Devonian period with a tiny fish embryo and umbilical cord inside it: the first pregnant mother in the fossil record. That discovery, in northern Australia, pushed the known date of internal fertilization back by about 200 million years and suggested a whole new prehistory for copulatory sex—even before the evolutionary transition from sea life to land life about 5 million years later.


Using fossil data along with his knowledge of the bizarre quirks of modern animal sexual behavior, Long has amassed a number of startling theories about ancient animal copulation in his new book, “Dawn of the Deed: The Prehistoric Origins of Sex.” But his main purpose in writing about primitive fish penises and dinosaur sex positions, he writes, is to help modern humans understand our own peculiar sexual behavior—much of which harks back to extremely ancient history.

Long, who was born and spent most of his professional career in Australia, is now the vice president of research and collections at Los Angeles’s Natural History Museum; his previous books include “Frozen in Time” and “The Rise of Fishes.” He spoke to Ideas by phone from Los Angeles.


IDEAS: So what is the point of sex, evolutionarily speaking? And how long has it existed on this planet?

LONG: Sex probably evolved way back in single cells, over 2 billion years ago, simply because, when the whole population is more genetically homogenous, it’s fairly easily to be susceptible to changes in the environment or disease. By mixing your genetic makeup, by sharing the DNA, you have more variable offspring, which are capable of dealing with a wider range of challenges in the natural world.

IDEAS: When did copulation between invertebrates, sex as we think of it today, begin?

LONG: In 2007 [I discovered] a 380-million-year-old fossil fish from a site in northern Australia....I noticed some strange little bones inside the bigger fish. And we realized that there was an embryo, and later on it revealed an umbilical cord attached to it, and we absolutely confirmed beyond doubt that we had a mother with an unborn embryo inside it. And this pushed back the origin of live birth by nearly 200 million years, based on previous fossils. The most important thing was that it signaled to us that these fish weren’t laying eggs and spawning in the water, like most fish do today, that they had a complex form of copulation in order to reproduce....The act that we know and love goes right back to these early fish, which were the very first of our lineage to develop male and female differences.


IDEAS: What was sex like among these early fish?

LONG: The earliest known male sexual organs for copulation, which occur in these ancient placoderm fishes, were actually covered by bone. So we have “claspers” in sharks, which are soft cartilaginous rubbery structures. But these things had bony plates covering them with spikes and hooks. So it would’ve been a very delicate affair. But we know it worked, because these sorts of placoderms occur as fossils everywhere around the world at this time. They were definitely doing something right, even if it would’ve been cumbersome and awkward.

IDEAS: Was it fun?

LONG: We all know today that mammals, reptiles, birds, all experience some degree of pleasure through sex. So when did that start, is the question? I only postulate that as an idea, I don’t have any evidence or proof. But unless it was enjoyable to do...I can’t think why they would’ve done it in the first place.

IDEAS: How is the ancient evolution of sex connected to human development?

LONG: For me one of the big revelations of [writing my book] was discovering papers that link the beginning of limbs to the beginnings of reproductive organs. Because that fits in beautifully with my fish back in the Devonian, because the reproductive organs are actually part of the hind pelvic fins, which would eventually evolve into legs in all higher vertebrates....I like to say that I’ve spent my life studying ancient fossil fish, but it’s really because it’s the beginning of the human body plan.


IDEAS: What does knowing about the ancient history of sex help us understand about modern-day sex on this planet?

LONG: It basically shows that there’s nothing that humans do that hasn’t been done before one way or another in the animal kingdom...every kind of bizarre sexual activity that you can mention is part of the reproductive strategy of some given species....So when we think of dividing human sexuality in terms of what’s natural and so on, I think we need to look at the animal kingdom more carefully before we judge others.

Britt Peterson is a writer in Washington, D.C.