Here is a lovely little creature from Sri Lanka, Pettalus cf. cimiciformis, a member of the same lineage that includes the daddy longlegs we’re all familiar with. You could call it a daddy longlegs too, but its legs aren’t particularly long (plus it’s tiny–the size of a sesame seed.)
It may not seem like much, but it poses a fascinating riddle. It belongs to a family of daddy longlegs called Petallidae. Below is a map of where other species of Petallidae can be found. They seem to be scattered randomly across the world. But petallids are terrible at dispersing. Their ranges are small (usually less than fifty miles). And they live only on ancient continent crust. Petallids live on Sri Lanka and on Madagascar. But they live on none of the young volcanic islands in between–or anywhere else in the world, for that matter. So they couldn’t have swum or flown to their farflung locations. Yet DNA evidence clearly shows that the petallids all descend from a common ancestor. So, how did they get there? The answer lies below the fold…
Here is a picture of the southern hemisphere about 150 million years ago. Ever since the continents formed, they have been drifting slowly across the surface of the planet. Back in the Jurassic Period, South America, Africa, Antarctica, India, and Australia were all welded together. So were a few islands, such as Madagascar and Sri Lanka. And the current ranges of petallids, so fragmented today, appear to have covered the southern part of this vanished supercontinent. The lineage first evolved there, slowly spread out across a continuous landmass, and then rode across the planet on drifting continents.
The journeys of animals and plants are the subject of one of science’s lesser known branches, historical biogeography. I’ve always thought its obscurity was a shame, because it can do such a remarkable job of illuminating the history of the planet through a comparison of living things. Much to my surprise, stumpy daddy longlegs are turning out to be among the best guides to that history. The full story can be found in my article in tomorrow’s New York Times, plus an even more detailed map. (Two papers in press can be found here and here.)
Update: I’ve also posted the article on my web site.
Go Further
Animals
- Octopuses have a lot of secrets. Can you guess 8 of them?
- Animals
- Feature
Octopuses have a lot of secrets. Can you guess 8 of them? - This biologist and her rescue dog help protect bears in the AndesThis biologist and her rescue dog help protect bears in the Andes
- An octopus invited this writer into her tank—and her secret worldAn octopus invited this writer into her tank—and her secret world
- Peace-loving bonobos are more aggressive than we thoughtPeace-loving bonobos are more aggressive than we thought
Environment
- Listen to 30 years of climate change transformed into haunting musicListen to 30 years of climate change transformed into haunting music
- This ancient society tried to stop El Niño—with child sacrificeThis ancient society tried to stop El Niño—with child sacrifice
- U.S. plans to clean its drinking water. What does that mean?U.S. plans to clean its drinking water. What does that mean?
- Food systems: supporting the triangle of food security, Video Story
- Paid Content
Food systems: supporting the triangle of food security - Will we ever solve the mystery of the Mima mounds?Will we ever solve the mystery of the Mima mounds?
History & Culture
- Strange clues in a Maya temple reveal a fiery political dramaStrange clues in a Maya temple reveal a fiery political drama
- How technology is revealing secrets in these ancient scrollsHow technology is revealing secrets in these ancient scrolls
- Pilgrimages aren’t just spiritual anymore. They’re a workout.Pilgrimages aren’t just spiritual anymore. They’re a workout.
- This ancient society tried to stop El Niño—with child sacrificeThis ancient society tried to stop El Niño—with child sacrifice
- This ancient cure was just revived in a lab. Does it work?This ancient cure was just revived in a lab. Does it work?
Science
- The unexpected health benefits of Ozempic and MounjaroThe unexpected health benefits of Ozempic and Mounjaro
- Do you have an inner monologue? Here’s what it reveals about you.Do you have an inner monologue? Here’s what it reveals about you.
- Jupiter’s volcanic moon Io has been erupting for billions of yearsJupiter’s volcanic moon Io has been erupting for billions of years
- This 80-foot-long sea monster was the killer whale of its timeThis 80-foot-long sea monster was the killer whale of its time
Travel
- How to plan an epic summer trip to a national parkHow to plan an epic summer trip to a national park
- This town is the Alps' first European Capital of CultureThis town is the Alps' first European Capital of Culture
- This royal city lies in the shadow of Kuala LumpurThis royal city lies in the shadow of Kuala Lumpur
- This author tells the story of crypto-trading Mongolian nomadsThis author tells the story of crypto-trading Mongolian nomads