Eretiscus tonnii – The smallest fossil penguin
Many of the most heralded discoveries of fossil penguins are from giant species. Not all extinct penguins were large, however, and a few were quite tiny. The smallest fossil species yet discovered belongs to a diminutive penguin from the Miocene (about 22 million years ago) of Argentina. George Simpson described this fossil in one of his last scientific publications on fossil penguins in 1981. The first specimen was a tarsometatarsus (that foot bone that keeps popping up in penguin paleontology) and some wing bones have subsequently come to light.
The fossil in question was originally given the genus name Microdytes, meaning “tiny diver”. However, this name is now obsolete because an even tinier diver – a beetle – already had claim on the name “Microdytes“. Beetles have a pesky habit of preoccupying names applied to vertebrates. To be more accurate, vertebrate paleontologists don’t always thoroughly check all taxonomic records before naming new fossils. The most famous example is the case of the theropod dinosaur Syntarsus. This genus name was already occupied by a Malagasy beetle, and so some entomologists took it upon themselves to create a new name for the dinosaur: Megapnosaurus. This translates to “big dead lizard”, a probable sling at the overly generous share of public interest dinosaurs receive compared to beetles. In a zoological wild west, a penguin might be able to bully a beetle out of a prime name. However, that’s not the way things work in the real world. The rule of priority means that the first species to be given a name in a formal scientific publication keeps it. So Microdytes stays with the beetle. The penguin was thus re-christened Eretiscus by Storrs Olson, who first noticed the conflict. The new name means “tiny rower” in reference to the penguins flipper-based locomotion.
Eretiscus was very small. The Little Blue Penguin is the smallest living penguin, reaching only about 1kg in weight – a virtual rubber duck in size (and squeak). At only about 1.5 feet tall, these little guys are less than knee high on most humans. Originally, Eretiscus tonnii was reported as being even smaller. However, only one skeleton of the modern Little Blue was available for comparison when Simpson described the fossil find. The tarsometatarsus of Eretiscus was a millimeter and a half smaller than the tarsometatarsus of that Little Blue skeleton, but other smaller skeletons exist in collections of museums. So the fossil was not the smallest individual penguin ever, but the species may well have been the smallest (we don’t have enough samples to figure out the average). Quibbling over records aside, we can say that small penguins have been around for a long time. They don’t seem to have been very common though. Only a few fossil bones of penguins in the Little Blue size range have been discovered worldwide versus thousands of bones of average size to giant penguins.
Simpson, G.G. 1981. Notes on some fossil penguins, including a new genus from Patagonia. Ameghiniana 18: 266–272.
Olson, S. L. 1986. A Replacement Name for the Fossil Penguin Microdytes Simpson (Aves, Spheniscidae). Journal of Paleontology, 60(3): 785.