Archive for January 2010
How long have penguins been around? I suspect that most people would respond that they seem relatively young, in the grand scheme of things. Penguins are so unique, and they seem particularly modern because of their constant presence in ads and movies. There is also that constant mental association with icy environments that makes it hard to picture them along a steamy Paleocene coastline.
Waimanu is currently the oldest known penguin, and it is an ancient taxon indeed. The rocks containing the Waimanu manneringi holotype skeleton are an astounding 61.6 million years old, far and away the oldest to produce penguin bones. A close relative, the smaller Waimanu tuatahi is found in rocks 58-60 million years old. To put this in perspective, these penguins lived just 4-5 million years after the mass extinction that killed off the dinosaurs (except for birds of course).
The first fossils of this taxon were collected almost 20 years ago by Al Mannering, in whose honor the first species is named. Both come from the Waipara Greensand, a unit of sedimentary rocks laid down in nearshore waters during the Paleocene in present down North Canterbury. During the Paleocene, this area of the South Island of New Zealand was submerged, and penguins, plankton and shellfish often became entombed in the dark sandy sediments upon death. Millions of years later, these rocks and their trove of fossils were exposed as tectonic forces lifted the ancient seafloor up to the sun and the Waipara River cut away the overlying layers.
These early penguins inherited a world in which a reset button had been firmly pressed. It was warm, rather homogenous in temperature across most of the latitudinal gradient, and most importantly, nearly every major niche was hung generously with “help wanted” signs. For much of the Mesozoic, dinosaurs dominated terrestrial ecosystems and large marine reptiles occupied the aquatic tetrapod predator niche. Mosasaurs, plesiosaurs and pliosaurs swam the seas worldwide. But at the end of the Cretaceous, an asteroid impact wiped out all of these groups. Even sharks were decimated, though of course some survived to re-supply our oceans and imaginations with toothed nightmares.
This extinction spelled opportunity for many groups. Mammals radiated into the void left by dinosaurs, and some dinosaurs got a new opportunity. The volant (flying) ancestors of penguins had a window in which the seas were free of largely free of competitors and low on predators. This was a perfect time to drop flight altogether. By 60million years ago, Waimanu manneringi and Waimanu tuatahi, two closely related species, had reached this critical stage in penguin evolution.
Waimanu is both amazingly penguin-like and amazingly primitive. Waimanu manneringi was a healthy size, about halfway between a King Penguin and an Emperor Penguin in standing height, while Waimanu tuatahi was a bit smaller, about 2 1/2 feet (80cm) tall. Waimanu manneringi is only known from a single hindlimb and pelvis, while specimens of Waimanu tuatahi is much more complete – multiple specimens together combine to give us almost the entire skeleton. From head to toe, the skeleton of Waimanu combines primitive and derived characters. The skull exhibits the long, narrow beak seen in other early fossil penguins rather than a stubbier modern penguin beak. The flipper is much shorter than the wing of a flighted bird, but significantly longer relative to the body than in living penguins (indicating it would have a lower wing load). The bones are also more flattened than flighted birds but less flattened than living penguins, which have highly compressed bones to form a more knife-like wing profile. In the hindlimb, Waimanu is very close to modern penguins. The shape of the limb bones indicate an upright posture like modern penguins employ, and the feet are short and stubby. So Waimanu walked like a penguin on land, swam like a less-efficient penguin in the water, and probably ate the same basic foods (perhaps a little fish heavy). There is a lot more to say about these fascinating species, but I will await some upcoming work by the Waimanu team to cover that story.
In closing, I should point out that the title of this post is actually a bit inaccurate. Waimanu manneringi is in fact the oldest penguin we know of. But, it is highly unlikely it was actually the first penguin. The rock record is incomplete, and there is a roughly 10 million year gap between Waimanu tuatahi and the next oldest penguin fossil, showing we are missing big pieces of penguin history – probably on both sides of the 60 million year mark.
The closest relatives of penguins that are alive today are the Procellariiformes, the group that includes albatrosses and petrels. These birds are commonly called tubenoses because their nostrils take the form of short tubes instead of flat openings. Most likely, the penguin lineage and the tubenose lineage split off from one another and started on their own evolutionary paths deeper in time, perhaps even during the Cretaceous Period. At this deep split, the birds heading off along the evolutionary trajectories to modern penguins and modern petrel probably looked a lot more like a petrel than a penguin – certainly volant (capable of flight) and probably with a similar ecology to some modern tubenose birds. Whether we would call the bird on the penguin side of the split a “penguin” is debatable – it would probably be very hard for us to recognize a fossil penguin in the rock record until, like Waimanu, they evolved a flightless lifestyle. So, pending the discovery of a mind-bending fossil of a flying penguin, we’ll let Waimanu revel in its place in the sun.
There is a lot more about Waimanu here.
References: Slack, K.E., C.M. Jones, T. Ando, G.L. Harrison, R.E. Fordyce, U. Arnason, and D. Penny. 2006. Early Penguin Fossils, Plus Mitochondrial Genomes, Calibrate Avian Evolution. Molecular Biology and Evolution 23: 1144-1155.
Dr. Brian J. Marples was one of the great contributors to the study of penguin evolution during the 20th century. Marples was a true polymath, one of the all-purpose scientists of yesteryear who are so rare today. He studied and published on many disparate topics including spiders from throughout the South Pacific, the life habits of New Zealand birds, the circulatory systems of fish, extinct whale brain endocasts, and of course fossil penguins.
Marples actually found many of the penguin fossils he studied while searching for spiders, the main focus of much of his life’s work. A spider expert, he had a particular interest in trapdoor spiders. These spiders are common in rocky environments, including greensand and limestone cliffs (like those above). These spiders inhabit burrows with home-made “doors” that they leap from to ambush and capture passing prey. Traveling around the vicinity of Duntroon, a settlement in the South Island, Marples collected trapdoor spiders in jars as he worked on mapping their geographical distributions and describing their anatomy. In the process, he regularly ran into fossil bone – often from penguins and whales. According to accounts (see link below), he and his students often livened up the Duntroon Hotel’s bar after collecting expeditions. I’ve lifted my feet to the fire in the same staff lounge Marples no doubt frequented at the University, but I can only guess at the boisterous activities generated by placing pints on top of the table and jars of spiders underneath.
The fossils collected from the Duntroon cliffs revolutionized our understanding of ancient penguins. Previously, many fossil penguin bones had been collected but associated skeletons from individual animals were very rare. Marples penguins gave us the first glimpse at what the skeletons large Oligocene penguins of 25 million years past might have looked like whole (with the notable exception that nearly all the skull bones were lost). In paleontology, it is common practice to name newly discovered species in honor of someone who has contributed to the discovery or study of that species – for example the person who found the fossil, a volunteer who helped with the field or museum work, or a respected expert on the group of interest. Marples has been recognized three times in this manner.
Interestingly, Dr, Marples himself actually described the fossils that bear his name. It is of course in bad taste (and in fact forbidden) to name a fossil after yourself. Marples certainly did not attempt such a crass act. At the time he found the penguins, he believed two of them belonged to the already-named species Palaeeudyptes antarcticus and Platydyptes novaezealandiae, and that the third represented a new species of the South American genus Palaeospheniscus – Palaeospheniscus novaezealandiae. This later turned out to be an overly conservative interpretation. The first two fossils were later found to be distinct species and the third found not to belong in the genus Palaeospheniscus.
George Gaylord Simpson later changed the genus name to Marplesornis (“Marples’ bird”) in recognition of these differences, and in honor of Marples’ contributions to penguin paleontology. The other two fossils also bear Marples-based species honorifics – Pierce Brodkorb dubbed one set of large penguin fossils from the Burnside Mudstone Quarry near Otago University Palaeeudyptes marplesi and Simpson named a smaller set of remains from cliffs of Duntroon Platydyptes marplesi. Palaeeudyptes marplesi was a large, stout fellow though unfortunately we have only a few limb bones and vertebrae. Platydyptes marplesi, seen below, was a moderate sized penguin with really wide flipper bones – the genus name means “wide diver” and has turned out to be one of the more common penguins of the Oligocene of New Zealand. A unique arrangement of the articulation between the wing and shoulder suggests it was a strong underwater flier, but the mechanics are still under study.
Marplesornis novaezealandiae is perhaps the most interesting of the three species. According to analyses of fossil penguin relationships, Marplesornis represents the last lineage of penguins to branch off the evolutionary tree before the radiation of modern penguins began. This penguin was about the size of a living King Penguin and had large spaces for the jaw muscles on the back of the skull, like modern penguins that eat fish. It supports the hypothesis that only once modern penguins had evolved did the group begin experimenting with more krill-heavy planktonic diets.
So, those are the three penguins. For more on spiders and other facets of Dr. Marple, check out the Vanished World website: http://www.vanishedworld.co.nz/spiders.htm