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sex, dinosaurs, and placoderms

by Donald Prothero, Apr 10 2013

A review of The Dawn of the Deed: The Prehistoric Origins of Sex, by John A. Long (University of Chicago Press, Chicago, 2012).

As I mentioned in last week’s post, we all know that subjects like sex and dinosaurs are guaranteed to get the public’s attention and interest, no matter what story you want to promote. Paleontologist and author Dr. John A. Long (formerly the Vice-President of Research and Collections at the Natural History Museum of Los Angeles County, but now back home in Australia as the Strategic Professor in Palaeontology at Flinders University in Adelaide) has cleverly woven a story about the wild sex lives of the animals kingdom as a hook to talk about his own research into the fossil fish (especially an extinct group called placoderms), which show the first evidence of internal fertilization, the oldest known vertebrate embryos, and the first copulatory structures.

One would think that a story about small extinct placoderms in nodules from the deserts of Western Australia would be a hard sell for a popular book, but Long pulls off the feat with aplomb. The heart of the book is filled with Long’s excitement about this research as he finds and uncovers these amazingly 3D fish fossils from the nodules of the Gogo beds, then compares them with fossils described from collections elsewhere in the world. He soon discovers that mysterious structures that were misidentified or ignored by previous fish paleontologists are actually pelvic claspers (long rodlike structures also found in the pelvic fins of modern sharks to aid them in copulation with females). Then he and his colleagues discover traces of tiny bones inside an adult placoderm that were misidentified as their last meal, but turn out to be embryos. We follow Long’s story as he works on this research until is it is accepted to be published in top journals like Nature. The discovery gets global coverage, and Long even takes part in big media events with a live uplink between the announcement in Australia and Queen Elizabeth of England (in a chapter called “Announcing Fossil Sex to the Queen”).

Surrounding this story of Long’s research into the earliest fish sex are chapters that review some of the wild and bizarre sexual practices among living animals. We find out all about how erotic asphyxiation works (first discovered in hanging victims that orgasmed  and ejaculated as they died), the prevalence of homosexual behavior in many groups of animals, and why certain ducks have the longest penises among any groups of vertebrates (longer than their entire body). In the final few chapters, Long reviews the evidence for the evolution of sex from the first sexually-reproducing organisms, to the incredible sexual feats of the arthropods. These include male barnacles, which have a penis eight times longer than their bodies, to the story of how the male bedbug stabs the body cavity of the female with his knife-like penis, and leaves the sperm packet inside her body, to the familiar accounts of how female praying mantises eat the male as he is copulating with her, and he keeps at it and does even better at copulation even though his head is gone. Long describes some of the bizarre sexual behavior of fishes, from the grunion running on the beach, to the deep-sea fish where the males attach to females and then degenerate into sperm organs and nothing more.There is a vivid account of sexual behavior in mammals, from the rough sex practiced by dolphin and orcas (the males will use their long penises in surprising ways), to the various types of sperm competition where one male secretes a plug in the female after copulation, but other males have penises which can remove the plug and replace the competitor’s sperm.

And of course, the million-dollar question: how did dinosaurs do it? Long begins with the story about how the first dinosaur leg bone fossil ever discovered was described as “Scrotum humanum” by Richard Brookes in 1763. He describes the legendary accounts of how eccentric British paleontologist Beverly Halstead demonstrated dinosaur mating behavior on the stage during a professional talk (something I heard about when I was a graduate student), showed slides of himself in the full Monty to demonstrate the proportions of the human penis, and had illustrations showing copulating dinosaurs in children’s books. Long discusses the practices of male lizards and snakes which have hemipenes (a penis forked into two branches, which pop out of their cloaca when inflated like a rubber glove turning inside out). Based on the types of sexual dimorphism seen in dinosaurs and the behaviors of their closest relatives, the birds and crocodiles, Long concludes that dinosaur males must have had a single penis (not hemipenes, or cloacal kissing), and probably copulated with males mounted behind (as do turtles and crocodilians). But as several other authors have also shown, this poses a problem for large sauropods, who would be putting their enormous weight largely on their two hind legs and whose heads must have stayed down during copulation or else they would have passed out from the difficulty of getting the blood all the way up to their brains if they raised their necks!

In short, Long’s book is a lively and uninhibited account of sexual behavior throughout the animal kingdom, and how we can learn about past sexual behavior from the fossil record. Unless you are prudish and can’t stand reading such material, the entire book is a short fun read that will keep your interest from beginning to end. As Jared Diamond wrote in his review of the book, “You are now holding a compromise between a book that you should carry hidden inside an opaque bag, and a sober, respectable scientific treatise. It’s a deliciously written account of the evolution of sex, in all its bizarre manifestations. Read, blush, and enjoy!”

2 Responses to “sex, dinosaurs, and placoderms”

  1. Adrian Morgan says:

    I can’t resist a little cheer at the fact of Flinders University — my university, in that I went there and also still live nearby — being mentioned on SkepticBlog. Yay! :-) Haven’t heard of John A Long before, though.

  2. DevoutCatalyst says:

    My 2011 copy is titled ‘Hung Like an Argentine Duck: a journey back in time to the origins of sexual intimacy’. Glad to see it reviewed here.