445 Million Years Old (and Still Having Sex on the Beach)
Posted by Richard Conniff on December 12, 2011
The Harvard entomologist, photographer, and writer Piotr Naskrecki has a beautiful new book out from University of Chicago Press. It’s called Relics: Travels in Nature’s Time Machine. Here’s the publisher’s description:
Naskrecki begins by defining the concept of a relic—a creature or habitat that, while acted upon by evolution, remains remarkably similar to its earliest manifestations in the fossil record. Then he pulls back the Cambrian curtain to reveal relic after eye-popping relic: katydids, ancient reptiles, horsetail ferns, majestic magnolias, and more, all depicted through stunning photographs and first-person accounts of Naskrecki’s time studying them and watching their interactions in their natural habitats.
And here’s an excerpt:
First came the big females. Nearly all had males in tow. In the dimming light we could see spiky tails of hundreds more as they tumbled in the waves, trying to get to the dry land. By the time the sun fully set, the beach was covered with hundreds of glistening, enormous animals. Females dug in the sand, making holes to deposit their eggs, nearly four thousand in a single nest, while the males fought for the privilege of fathering the embryos. Fertilization in horseshoe crabs is external, and often multiple males share the fatherhood of a single clutch. Equipped with a pair of big compound eyes (plus eight smaller ones) capable of seeing the ultraviolet range of the light spectrum, male horseshoe crabs are very good at locating females even in the melee of waves, sand, and hundreds of other males. Scientists studying this behavior suspected at first that males might be attracted by female pheromones, but as it turns out they rely solely on their excellent vision. They do make mistakes, however, and it is not rare to find males forming chains, which disperse as soon as a real female shows up.
Watching the drama of the mass spawning of horseshoe crabs is to me as close to a religious experience as I will ever get. My heart seems to slow down and a natural calmness helps me momentarily forget all the ills of the world. As strange and distant as horseshoe crabs may seem, these majestic organisms remind me that we share the same evolutionary heritage. Although our paths to what we are now diverged early, humans and horseshoe crabs at some point shared the same ancestor. It was a very long time ago. Horseshoe crabs have been around longer than most groups of organisms that surround us now. In the fossil deposits of Manitoba, the recent discovery of an interesting little creature named Lunataspis aurora proves that horseshoe crabs quite similar to modern forms were already present in the Ordovician, 445 million years ago. By the time the first dinosaurs started terrorizing the land in the Triassic (about 245 million years ago), horseshoe crabs were already relics of a bygone era. And yet they persisted. Dinosaurs came and went, the polarity and climate of Earth changed many times over, but horseshoe crabs slowly plowed forward. Yet during this time they changed surprisingly little. Species from the Jurassic were so similar to modern forms that I doubt I would notice anything unusual if one crawled in front of me on the beach in Delaware. Somehow horseshoe crabs had stumbled upon a lifestyle and morphology so successful that they were able to weather changes to our planet that wiped out thousands of seemingly more imposing lineages (dinosaurs and trilobites immediately come to mind). But despite claims to the contrary by creationists and other lunatics, they kept evolving. Modern horseshoe crabs, limited to three species in Southeast Asia and one in eastern North America, differ in many details from their fossil relatives. We know, for example, that many, if not most, fossil horseshoe crabs lived in fresh water, often in shallow swamps overgrown with dense vegetation, and some might have even been almost entirely terrestrial.
You can buy the book here.