Penguins are flightless marine birds that have inhabited this planet for at least 65 millions of years, according to experts. Scientists wonder the changes that occurred throughout the evolution of this group, its causes and implications. Within this context, Claudia Tambussi, principal researcher, and Federico Degrange, assistant researcher, conducted studies on this issue at the Centro de Investigaciones de Ciencias de la Tierra (CICTERRA CONICET-UNC) [Earth Sciences Research Centre].
Three years ago, on the Marambio Island of the Antarctic, Claudia Tambussi and other researchers from the Museo de La Plata [Museum of La Plata] found two of the three skulls known in the continent so far. The objective was to reconstruct the brain and other sensory structures through tomographies. The study focused on the analysis of these organs to deduce the olfactory, auditory and visual capacities and draw a comparison with the current Antarctic penguins. The results were published on the cover of the scientific magazine Journal of Vertebrate Paleontology.
In Antarctica, there are fossils of these birds that date from 32 millions of years ago, apart from the current specimens. In the intermediate space between these two periods, there is no evidence of anything at all. And it was just around 32 millions of years ago that the dramatic climate change and glaciations’ processes began in Antarctica, so it is possible that the old penguins either might have migrated –in this case their descendants could be somewhere else- or become extinct. Therefore, the ones that inhabit the Antarctica now do not bear any relationship to those ones. Besides, they do not have any relationship neither with the Patagonian nor with the Chilean ones, but they resemble those of New Zealand.
“The old Antarctic penguin’s appearance was similar to the current ones. If we had the chance to find one alive now, we would not hesitate to identify it with that group of birds despite some differences such as its long beak and the possibility of having red plumage on the chest, according to some studies of a specimen of the same time found in Peru”, the researcher describes.
Furthermore, scientists explained that their body plan was practically the same as the current penguins so capacities and similar habits can be inferred. “The oval body, as a rugby ball, is ideal to swim and dive. Among vertebrates, there are only few that have this shape, and among the living birds, only the penguins. The latter ones, according to fossil remains, used to have that shape 32 millions of years ago”, Degrange affirms. Maybe, 60 millions of years ago, these characteristics have not been equal, they might have even been able to fly, but this is still being debated.
As the researchers studied shapes of the brain, cerebellum, ear and olfactory bulbs from the fossils, the team could compare them with the current ones and draw some conclusions. “Firstly, we found that 32 millions of years ago the penguins did not fly, they dived, but they maintained to day the brain of a flying bird”, Tambussi explains. In this regard, it is surprising to know the great development of the visual abilities of both current penguins as well as the old ones, a typical feature of the flying birds.
“The fossils revealed that the neuro-anatomy of the penguins kept on changing even 30 millions of years after having lost the ability to fly through mechanisms such as the expansion of the areas of the brain related to the visual capacity and the reduction of the olfactory bulbs, still in progress”, Daniel Ksepka, one of the authors of the research who works at the Bruce Museum in the USA, explains. In this way one of the differences the scientists found in the evolution of penguins, from their flying ancestors to the current ones that are fully divers, is that there was a remarkable loss of olfactory ability. “Birds generally have a limited sense of smell, except for the seabirds that although they do not reach the level of the mammals, it is more developed and these birds can identify some chemicals dissolved in the water that are useful to find their prey”, Degrange comments. “Somehow, the selection of visual abilities prevailed whereas the olfactory ones were lost”, Tambussi describes.
Another change identified by the researchers was related to the internal ear and it is associated to the ear and its auditory abilities. “The ear of the oldest penguis is more robust than the current ones, but we do not know which could be its functional difference. Nevertheless, just as the current ones, the old penguins could identify low frequency sounds – those ones whose wave is longer so it weakens less when it travels on the air – such as the AM radio. This is a typical characteristic of animals that communicate among themselves, and mainly in the case of birds that live in colonies”, Degrange explains. So this allows us to determine that they have always been gregarious, a hypothesis that is strengthen through the fact that there is great number of penguins’ fossils in the same place.
Finally, as regards the brain, it shows some changes in the layout of the structures. However, the analysis of the brain, the sense organs and the rest of the structures found in the skull showed that the current penguins as well as the old ones have a great development of the proprioceptive capacities. These allow animals to have a self-perception in relation to the surroundings so when they are moving, for instance diving, they can keep their eyes on a target that also moves, without losing stability. “Therefore we can infer, once more, that old penguins were able to dive and they already had one part of their life in the continent and other in the underwater environment”, Tambussi explains.
- By Mariela López Cordero – CCT, CONICET Córdoba
- About the study
- TAMBUSSI Claudia P., principal researcher at the CONICET (CICTERRA, CONICET-UNC)
- Degrange Federico J, assistant researcher at the CONICET (CICTERRA, CONICET-UNC)
- Ksepka Daniel, Bruce Museum, Greenwich, ConneticutT, USA