Perudyptes – Fossil penguins at the equator!
When penguins at the equator are mentioned, half the time people think it is a joke. What more ludicrous image than the tuxedoed denizens of the Antarctic ice sheets lounging about with tropical drinks on a sun-baked beach? In fact, several living species of penguins inhabit equatorial waters today. The Humbolt penguin (Spheniscus homboldti) occupies the coastlines of Peru, Ecuador and Chile reaching almost to the line, and Galapagos penguins (Spheniscus mendiculus) mock our preconceptions by happily swimming right across the equator daily. The latter are the only penguin species that naturally occurs in the Northern Hemisphere – by about a few hundred yards.
Still, penguins near the equator are remarkable, and still more amazing is the thought of these birds reaching the line during “Greenhouse Earth” conditions. During the first half of the Cenozoic Era, the world was significantly hotter than today, with global temperatures averaging 5+ degrees Celsius higher. Penguins were long thought to have reached low latitudes only after global cooling during the second half of the Cenozoic, when temperatures began approaching today’s averages. One fossil changed these theories.
Perudyptes devriesi is an amazing fossil because it shows penguins were already thriving in equatorial waters by the middle of the Eocene Epoch, about 42 million years ago. The penguin itself is quite a gem in terms of preservation quality. Over 42 million years, a lot of bad things can happen to a fossil and often very little is left by the time paleontologists find it. Salt crystals embedded in bone and matrix, long dormant in the dry climate, begin to erupt from fossils from the deserts of Peru when they come into contact with the more humid air of Lima where the national museum is located. Aside from the normal chipping away of rock and gluing fragile pieces, fossils have to be soaked in water to dissolve these crystals before they damage the bones. Luckily, the Perudyptes fossil was rescued just in time. It was collected by Peruvian paleontologist extraordinaire Mario Urbina and studied by a large international team (Julia Clarke, Marcelo Stucchi, Mario Urbina, Norberto Giannini, Sara Bertelli, Yanina Narvaez and Clint Boyd) which I had the privilege to be a part of.
Perudyptes still has its skull (rare in fossil penguins) as well as some major bones of the wing, pelvis and foot. Such completeness gives us a much better idea of where the species fits in the penguin tree and how it swam and ate. The genus name Perudyptes means “Peruvian diver”, and the species name devriesi honors Tom DeVries, an invertebrate paleontologist who has done decades of fine work mapping the fossil bearing strata of Peru and studying the mollusks that evolved in the region over the past 50 million years. Perudyptes devriesi would have been close to the size of a King Penguin – larger than most of the penguins alive today, but nowhere near the size of “giant” species like Icadyptes salasi. I’ll provide more details on the osteology of this penguin a few posts down the road.
The discovery of Perudyptes means penguin spread very rapidly from their ancestral range (probably New Zealand based on the occurrence there of the oldest and most primitive penguin fossils). In fact, by the end of the Eocene, penguins had reached Antarctica, Australia, and South America – all the major landmasses they now occupy except for South Africa. This task may have been easier for early penguins than it would be today. The continents of the Southern Hemisphere were much closer together – Australia and Antarctica were actually still connected. Later in the Cenozoic, tectonic forces would rift these last remnants of the supercontinent Gondwana apart, with profound climactic consequences and major effects on ocean circulation. By that time penguins where already well-established throughout the southern oceans. We don’t know for sure whether they had reached all the minor islands they occupied (except in cases where the island in question had not yet been born out of the volcanic depths), but almost certainly they also had firm foothold on most of the habitable coasts – a fast rise to success.
You can read more about Perudyptes devriesi in the paper below. More is on the way. A much longer monograph on the morphology and phylogenetic significance of this species is coming in a few months from Julia Clarke and myself, and will be freely available from the American Museum of Natural History Bulletin.
References: Clarke, J.A., D.T. Ksepka, M. Stucchi, M. Urbina, N. Giannini, S. Bertelli, Y. Naraez and C. Boyd. 2007. Paleogene equatorial penguins challenge the proposed relationship between biogeography, diversity, and Cenozoic climate change. Proceedings of the National Academy of Sciences 104: 11545-11550.