Archive for October 2009
Scientific study of extinct penguins started exactly 150 years ago, when the first paper on a fossil specimen was published. The bone itself was actually collected a few years earlier, from a beach near Kakanui, a settlement on the east coast of the South Island of New Zealand. The Maori place name Kakanui means “noisy parrot”, preumably a reference to wide parrot populations that have sadly since been extirpated from the area. According to official accounts, the fossil was “found by a native in the limestone of Kakaunui [sic], and was brought to Mr. Mantell imbedded to some extent in a matrix which was readily recognizable as that particular limestone”. Unfortunately, this rather vague account leaves many important facts out. Some are of historic interest only – the name of the pioneering discoverer of the first penguin not even been recorded. Of more serious concern to paleontologists is the geological context. Without knowing what rocks the fossil came from, we lose information about the age of the fossil, the environment the penguin lived in, and the context of fossilization. These data are important – paleontologists often say that when the locality of a fossil is unknown, half of its information content is lost. Where was “that particular limestone”? This question is difficult to answer, but it may be a resolvable issue. I’ll write about this in a later post.
Moving back to the fossil itself, it quickly left Otago. Like many of the earliest fossils from New Zealand, it was spirited away to England for study. This was standard practice in colonial times – for example, the first described moa bones ended up in London in the possession of Sir Richard Owen, a renowned anatomist best known for coining the name “Dinosauria”. The fossil penguin bone we are interested in ended up in the possession of Thomas Henry Huxley, a formidable biologist who earned the nickname Darwin’s Bulldog for his vociferous defense of the theory of evolution during its earliest years.
It was instantly clear to Huxley that the bone represented an extinct species of penguin. First of all, it was larger than the same bone in even the biggest living penguin species, the Emperor Penguin (Aptenodytes forsteri). Second, many of the details of the bone differed. In living birds, the bones that form the base of the three toes fuse together into one. These bones are separated by deep grooves in living penguins, but not so in the fossil. One of the openings for blood vessels of the foot seen in living penguins was also missing, and the ridges of bone that guide the tendons used to flex the toes are arranged in a different manner. All these differences indicated a penguin that was distantly related to our modern species, so a new species name was proposed: Palaeeudyptes antarcticus. Palaeeudyptes translates roughly to “ancient true diver” and antarcticus refers to the southern latitude at which the fossil was recovered. He published the scientific paper making this name valid in 1859.
In reality, the fossil itself is not much to look at. Nonetheless, though much more complete penguin fossils have been found since, the Palaeeudyptes antarcticus holotype received pride of place as the starting point of comparison for subsequent discoveries. Since the original paper by Huxley, the fossil was visited by famous paleontologist George Gaylord Simpson, one of the architects of the “New Synthesis” of evolution, New Zealand’s Brian Marples, author of ground-breaking early studies of fossil penguins, and many other luminaries. Casts reside today in the American Museum of Natural History, Smithsonian Institution, Otago Museum, and many other museums.
Unresolved questions still surround this precious relic. Some are related to its legacy for taxonomy, the science of classification. Formal codes of taxonomic nomenclature dictate the way in which new species (living or fossil) are named. These help avoid a chaotic situation where the same species goes by different names in different regions or multiple species are inadvertently given the same name. Among the rules are the diagnosis of the species and the designation of a holotype. The holotype is a single specimen chosen to represent the species – the standard by which to compare all other exemplars. Obviously, the specimen selected to be the holotype is typically the “best” available – well-preserved, showing the distinctive characters of the species clearly, lacking any trace of injury, illness or damage. However, in paleontology complete skeletons are rare or completely unknown for many species, so often a less desirable specimen must be chosen for the holotype. In the case of Palaeeudyptes, only one foot bone was originally available, and so the taxonomic fate of the species became forever tied to this single bone.
At the time Palaeeudyptes antarcticus was named, no other fossil penguins were formally described in the scientific literature. Diagnosis was simple, because no living penguin tarsometatarsus closely resembled that of Palaeeudyptes antarcticus. But now, about 50 different fossil penguin species have been discovered and we know that many different species had a foot like that of Palaeeudyptes antarcticus. A lot of fossils from all around the world have been shoehorned into the species Palaeeudyptes antarcticus over the years because of these similarities, but this would mean a single species of penguin survived for tens of millions of years and spread throughout New Zealand, Australia and Antarctica. Essentially, a house of cards was built – rough guesses were made that other leg bones from new fossil sites belonged to Palaeeudyptes antarcticus because the foot bones were somewhat similar, then flipper bones were assigned to the species because they were from the same general area, then somewhat similar flipper bones from a new area were assigned to the species and so on. We now know this was just an artifact of misidentifying fossils and over-extrapolating, because analyses of the evolutionary relationships have shown that some of these fossils are only distantly related to the original Palaeeudyptes antarcticus and need to be given their own species names. These differences would probably have been recognized much earlier if there had been more than one bone to compare to.
This post is dedicated to profiling one of the most impressive fossil penguins yet discovered: Icadyptes salasi – a giant, spear-beaked penguin from the Eocene.
Peruvian paleontologists discovered the first Icadyptes specimen in marine sediments from the Otuma Formation, deposited about 36 million years ago. The name “Icadyptes” refers to the Department of Ica, the Peruvian state where the fossil was found and “salasi” honors Rodolfo Salas, a renowned Peruvian paleontologist. Tiny shells from pelagic planktonic organisms and scales from fish related to anchovies and sardines show us that this penguin was buried in relatively deep waters off the ancient shoreline of Peru. The penguin may have been foraging for prey when it died, or the carcass could have drifted out from shallower waters and then sank to the bottom. Because the bones are beautifully preserved and many still connected as in life, there was probably not a very long interval between death and burial.
For a long time, paleontologists have known at least some fossil penguins had long, strongly built beaks quite distinct from the generally stubby bill of most living species. Bits and pieces of penguin skulls had been recovered from rocks in Antarctica, New Zealand and South America. Icadyptes is important because it provides the first complete example of one of these spear-beaked penguin skulls. Penguin bones are pretty resistant to destruction compared to typical birds bones, because they are extremely solid (unlike the hollow bones of “normal” birds like gulls or pigeons). This has resulted in thousands of penguin bones making it into the fossil record. But most of these bones are from the flipper or hindlimb – more delicate parts of the skeleton such as the skull and the sternum (breastbone) are frequently lost even in the best-preserved specimens. So until Icadyptes was discovered, we had little idea what the skull of a giant penguin looked like.
Incredible might be the best word to describe it. The beak is remarkably long, making up nearly two-thirds of the skull. In terms of construction, it really is more like a spear than a modern penguin beak.
Many of the skull bones that remain separate in living penguins – such as parts of the premaxillae and palatines – are fused together into a solid structure. Rather than having a hooked tip like the beak of modern penguins, the beak ended in a point. Finally, the texture of the beak suggests the soft tissue overlying the bone was of a different form than modern penguins. Today’s penguins have a very thick outer coating – the rhamphotheca, that covers their beaks. This makes the beak thicker than would be obvious from the bony portion alone. Icadyptes has unusual texturing on the bony beak, a network of shallow grooves for the blood vessels that nutrify the rhamphotheca.
This patterning is almost identical to the patterning in living frigatebirds, boobies and gannets – all birds with a very thin, layered, tightly fitted rhamphotheca. Impressions on the bone thus suggest Icadyptes may have had a similar beak covering – a thin sheath rather than a thick horny covering.
Together, all of these features strongly indicate a unique feeding strategy for Icadyptes. Storrs Olson and Andrzeg Myrcha hypothesized that giant penguins probably fed by spearing prey, rather than capturing prey between the upper and lower jaws. Icadyptes supports this idea – this penguin surely struck fear into Eocene fish and squid.
One final revelation from the Icadyptes holotype specimen is that although the beak was very long, the skull as a whole was disproportionately small compared to the total body size. Because the hindlimbs and most of the vertebrae are missing, it is impossible to precisely reconstruct the total size of Icandyptes. We do now, however, that it was far larger than even the Emperor Penguin, probably close to 5 feet standing higher and significantly heavier than a similar sized human. Skull length is easily outstips that of even the largest living penguins, but the difference between the flipper bones is even greater. With the small head atop the bulky body, Icadyptes probably looked like a linebacker penguin without its helmet.
Penguins have been around for a long time – far longer than humans. The first penguins appeared at least 60 million years ago. Whether we would instantly recognize these primitive penguins as members of the same family as today’s lovable diving birds is debatable. In many ways they were very similar to living penguins – they had flipper-like wings, stood and walked in much the same way as today’s penguins on short, stumpy legs with a flat-footed posture, and were certainly flightless in air but capable of efficient “underwater flight”. There were also marked differences – these early penguins had longer necks, a more flexible and less-flattened flipper and unique beak shapes. What their feathers, color patterns and life habits were like remain mysterious in many ways, but we can piece together many aspects of how they lived with fossil evidence and observations of living seabirds.
This blog will attempt to provide a tour of the incredible diversity of penguins – both extinct and living – and report on new scientific findings from the paleontological, systematic and biological literature that provide insight into penguin evolution.