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.

A humerus (wing bone) from Eretiscus tonnii

References:

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.

On the Feet of Penguins

Penguin feet are very distinct.  Perhaps the most important bone in terms of giving penguins their cachet with the public is the tarsometatarsus (the ever-present foot bone).  Thanks to their almost comically short feet, penguins move on land with an endearing waddling gait rather than with the more serious step of birds with longer, more gracile legs.  Aside from length, another major difference between the feet of penguins and those of most other birds is that penguins have a very tiny hallux, or first toe.  Most birds have four toes, instead of the five typical of mammals like ourselves. A few have only three  toes (for example, some kingfishers) and the ostrich is unique in having only two.  In most living birds, the first toe quite large and is modified for perching.  It is reversed, facing the opposite direction as the remaining three toes, to help grasp branches more firmly.  In some aquatic birds, the first toe is connected to the second toe by a web which makes the foot a more efficient paddle.

Penguins certainly don’t perch.  They also don’t paddle with their feet, instead using their flippers to propel themselves through the water.  Penguin feet are made for walking and steering.  These birds, although much more graceful at sea, are quite capable of marching across challenging terrain.  Adelie Penguins can march up to 100 kilometers (about 60 miles) across sea ice to get to their breeding grounds.  Penguins can also jump surprising distances. The aptly named rockhopper penguins can maneuver dangerously jagged stacks of wave-beaten rocks on windswept islands by bounding from one to another with striking skill.  Penguin feet may not be good for running or perching in trees, but they are well designed for this type of workload.  The tarsometatarsus and phalanges (small bones of the toes) are wrapped in a thick layer of blubbery fat to cushion them, and covered with rough, thick scales to stand up to wear and help gain purchase on slippery surfaces. Steering is the other locomotory task of the penguin foot.  If you have a chance to observe penguins swimming through a glass divider at an aquarium or zoo, pay attention to their feet.  They employ their feet like little rudders, angling them to help control their dive direction.

The fossil record shows us that penguins have developed a more compact foot over time.  Waimanu, the oldest known fossil penguin, has a relatively short tarsometatarsus by the standards of flying birds, but it cuts an elegant figure compared to the squat tarsometatarsus of living penguins.  We see a more square shape and some shortening in the Eocene penguins from Seymour Island.  By the Oligocene (25 million years ago) most of the penguins preserved in the fossil record have a foot of modern proportions. So far, no fossil has preserve the hallux.  This suggests that even the oldest penguins already had a very small hallux, as such a tiny bone can easily be lost during the fossilization process or even go unrecognized during fossil collection and preparation.  Aside from being a bit of trivia, many ornithologists consider the fact that both Procellariiformes (tubenose seabirds like albatrosses and petrels) and penguins have a miniscule hallux to be strong evidence linking these two groups of birds to a common ancestor.

An articulated foot from a dried-up skeleton of a Galapagos penguin, showing the tiny first toe.

Penguins Chasing a Butterfly

None are fossil penguins, but this is too good not to share:

Megadyptes waitaha – The last penguin to go extinct

Island birds have undergone some of the most fascinating radiations in evolutionary history, producing such wonders as the “toothed” Moa-Nalo ducks (Chelychelynechen, Thambetochen and Ptaiochen) of Hawaii and the enormous nine foot tall Elephant Birds (Aepyornis) of Madagascar. Island birds have also been devastated by human exploitation. The Dodo (Raphus), once an inhabitant of Mauritius, is an icon of extinction. Sadly, the Dodo is only the most well-known member of this club. Giant moa were hunted to extinction in New Zealand. Dozens of unique birds including Moa-Nalos, flightless ibises and nectar-feeding songbirds were wiped off the Hawaiian Islands following the arrival of humans. Today, many of the native bird species of Guam are severely endangered by predation by invasive snakes, introduced by humans.

Penguins were long thought to have been exempt from this fate. Because they can retreat to the sea where they are difficult to capture, penguins are somewhat less vulnerable to hunting than many other types of birds, particularly other flightless ones. Although historically harassed by humans in many ways, no penguin species was thought to have been wiped out until a very recent discovery. A team of researchers in New Zealand and Australia rounded up subfossil bones from archeological sites from the South Island of New Zealand ranging from 200 to 1500 years in age. They extracted ancient DNA from the bones and compared the sequences to other collected from live Yellow-Eyed Penguins (and museum specimens of the same species). The findings were startling – a wide genetic distance was uncovered separating the pre-1500s mainland penguin bones from post-1500s bones. The younger bones belong to the modern Yellow-Eyed Penguin (Megadyptes antipodes), and their DNA sequences cluster with samples from living individuals and subfossil bones of the species from outside the mainland. However, DNA from the pre-1500s subfossil bones from the mainland don’t cluster with the Yellow-eyed Penguin samples. DNA evidence suggests a distinct species of penguin was living on the South Island of New Zealand. This conclusion is backed up by careful comparisons of the bones, which demonstrates size and shape differences outside the range of normal variation seen in living Yellow-Eyed Penguins. The newly recognized, recently extinct species was named Megadyptes waitaha by the team.

Bones of the living Yellow-Eyed Penguin Megadyptes antipodes (left side of each pair) and the recently extinct Megadyptes waitaha (right side of each pair).

Dating of the fossil deposits suggests that Megadyptes waitaha survived all the way up to the time of colonization, overlapping with the fist human settlers to arrive from Polynesia. Direct evidence from associated artifacts shows that humans actively hunted these penguins, and the circumstantial evidence from timing strongly points to overexploitation as the proximal cause of their extinction. A second interesting finding of this study is that the modern Yellow-eyed Penguin seems to have benefited from the extinction of Megadyptes waitaha. Comparisons of the morphology of subfossil penguin bones, along with DNA extraction, reveals that in the 1500s the Yellow-eyed Penguin was restricted to sub-Antarctic islands such as the Auklands. During this same time period, Megadyptes waitaha inhabited a wide swath of the east coast of the South Island. Flash forward to 1800, and Megadyptes waitaha is nowhere to be found anywhere. Yellow-eyed Penguins crop up nearly everywhere that Megadyptes waitaha used to be. The timing suggests that as hunting patterns shifted, prime penguin real estate vacated by Megadyptes waitaha was reclaimed by Megadyptes antipodes.

So, Megadyptes waitaha is now a ghost on our collective consciences. These bones are something to think of when penguin populations suffer from oil spills, rampaging stray dogs, or overdeveloped beaches. There were at least 20 species of penguins when humans first appeared, and now we have 19 species left to enjoy and protect.

References:

Boessenkool, S.; Austin, J.J.; Worthy, T.H.W.; Scofield R.P.; Cooper, A.; Seddon, P.J.; Waters, J.M. 2009. Relict or colonizer? Extinction and range expansion of Penguins in southern New Zealand. Proceedings of the Royal Society of London B 276:815-821.

James, H.F. and Olson, S.L. 1991. Descriptions of thirty-two new species of birds from the Hawaiian Islands: Part 2. Passeriformes. Ornithological Monographs, 46: 1-88.

Olson, S.L. and James, H.F. 1991. Descriptions of thirty-two new species of birds from the Hawaiian Islands: Part 1. Non-Passeriformes. Ornithological Monographs, 45: 1-88.