by Nataly H. Aranzamendi
Millions of years ago, the world was a very different place from what we see now. Colossal giants wandered through planet Earth and many of them were quite different from the animals that remain today. However a group of flightless birds was already represented: the prehistoric penguins.
When did penguins appear?
George G. Simpson¹, an important paleontologist and geologist, classified ancient penguins in three groups: Palaeeudyptinae, Paraptenodytinae, and Palaeospheniscinae. He originally recognized about a dozen species, but since then there are new additions to the family tree of penguins nearly every year.
Based on previous DNA and fossil evidence, the possible dates for the earliest ancestor of penguins were originally calculated to date back 40 million years ago. However, recent evidence² has expanded those dates backwards and changed what we know about the presence of penguins. The oldest penguins might just date back to 60 million years ago during the early Cenozoic or late Cretaceous periods. This is 20 million years older than previously thought — and when dinosaurs were wandering the Earth!
Photo Credit: By Discott – Own work, CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=59535142
Did they look like their surviving relatives?
The ancestors of penguins were slightly different from extant species. The oldest penguins probably had already lost their typical bird plumage, but their semi-rigid flipper — which helps them to swim in the ocean and gives them their hydrodynamic shape — was not totally transformed in all species.
An agreement among scientists seems to be the fact that there were some prehistoric penguins that reached big sizes. This was inferred from fossil records and particularly recorded for the oldest groups. For example, the largest fossil penguin was Anthropornis nordenskjoeldi, a penguin that could have reached almost two meters tall. This species lived around 33-45 million years ago. Another fossil found recently in New Zealand² was likely of a similar size as Anthropornis. Thus, big penguins were not uncommon. Nonetheless, a decline in body size occurred for the later groups³.
Two species of the genera Kairuku4 that lived in New Zealand in the late Oligocene (23-34 million years ago) depict some morphological differences between them and extant (currently living) species. Those penguins already showed the typical upright penguin posture, as well as long flippers and short, thick legs and feet. However, their bodies were much more slender than penguins of today and their bills much longer.
Prehistoric penguins shared the same distribution as their current relatives. They were found in the Southern Hemisphere including Antarctica. Fossil records of extinct penguins have been found in Antarctica, New Zealand, Australia, Argentina, Chile, Peru and South Africa.
Places where fossils were found show a relatively high penguin diversity, which possibly peaked at the late Eocene and early Oligocene. A high penguin diversity was probably related to the expansion of cold waters and the change in favorable conditions for diversification5 that followed the separation of continents from Antarctica.
In the late Paleocene, Antarctica and the surrounding continents were in very different geographic positions from where they are located today. Australia and South America were closer to Antarctica but increasingly shifted northwards and separated more and more from the frozen continent. Such events probably had a big influence in the biogeography of penguins. Isolation from the old continent and new climatic conditions most likely provided optimal conditions that made diversification of species possible.
However, continental species did not remain completely isolated, since DNA evidence has shown us that multiple independent dispersal events could have occurred. In Australia, for example, new species of penguins arrived to the continent at different historical times³. Besides the fact that Australia hosted several species of penguins, currently there is only one species left there, the Little penguin.
Based on the later example and extensive fossil record, it seems that penguin diversity was high everywhere but declined during more recent periods. Why penguin diversity plummeted is still a mystery although several factors could have contributed. Perhaps the appearance of potential competitors like cetaceans (dolphins, porpoises and whales) and pinnipeds (seals and sea lions) displaced them and/or deprived them of food. Another hypothesis is that environmental conditions continued changing and food became scarcer.
In any case, the constant exploration and finding of new fossils will probably keep increasing our knowledge of the penguin family tree. Similarly, the advancement of technology and improvement of data based on DNA analyses will keep providing information of the exact time when prehistoric gigantic penguins were wandering our planet.
1 Simpson, G.G. 1946. Fossil penguins. Bulletin of the American Museum of Natural History, 87 (1): 1-100, figs. 1-33. New York.
2 Mayr, G., De Pietri, V. L., & Scofield, R. P. (2017). A new fossil from the mid-Paleocene of New Zealand reveals an unexpected diversity of world’s oldest penguins. The Science of Nature, 104(3-4), 9.
3 Park T, Fitzgerald EMG, Gallagher SJ, Tomkins E, Allan T (2016) New Miocene Fossils and the History of Penguins in Australia. PLOS ONE 11(4): e0153915
4 Ksepka, D.T., Fordyce, R.E., Ando, T. and Jones, C.M. (2012). «New fossil penguins (Aves, Sphenisciformes) from the Oligocene of New Zealand reveal the skeletal plan of stem penguins». Journal of Vertebrate Paleontology 32 (2): 235-254
5 Acosta Hospitaleche, C. I. A., Griffin, M., Asensio, M., Cione, A. L., & Tambussi, C. P. (2013). Middle Cenozoic penguin remains from the Patagonian Cordillera. Andean Geology vol.40 no.3 set. 2013