As I’ve been looking at the Sperm Whale skull I thought that I would end the month with a quick review of whale evolution. I have always had an interest in human evolution so I thought it would be useful to know expand my knowledge and link it with my skull of the month!
It was thought that whales had African origins but specimens found in Asia in the 1970s indicated that they arose from the Indian sub-continent. Whales are the descents of land-living animals which have the hippo as their closest living relatives. Both are large, aquatic animals whose features evolved separately. The hippo evolved from their ancestor anthracotheres about 15 million years ago whereas whales evolved 50 million years ago. The first whale like creatures were typical terrestrial mammals with long skulls and carnivorous teeth. The whale ancestor Ambulocetus may have lived a more aquatic lifestyle as it had shorter legs and enlarged hands and feet. Specimens have been discovered in sediments that were once probably an ancient estuary and isotope analysis indicates that they drank both salt and fresh water. Whales evolving after Ambulocetus have higher saltwater isotopes indicating that they spent more and more time in a saltwater environment as generations went on. The position of the nostril also changed over time, moving further back along the snout.
Other areas provide evidence for a terrestrial and mammalian heritage for whales. Studying the developing embryo show that whilst in the womb many whales develop body hair where as living whales have not retained this feature. As mentioned as whales have evolved over time their nostril has changed position however, this can still be seen in the developing embryo. The nostril in the womb develops in the usual mammalian position but migrates to the top of the head as they mature. By studying embryological evidence it has been found that baleen whales have evolved from toothed whales as some baleen embryos develop teeth which disappear before birth.
There’s quite a lot more information out there about whale evolution and I haven’t really gone into much detail here! See below for the sources that I used, plus others which are far more detailed. There is more to whale morphology and locomotion that I haven’t mentioned including the how a whales spine moves in comparison to other marine animals (a whales spine goes up and down rather than side to side!). THere’s also the vestigial hind limbs that can sometimes be found in living whales – yet another line of evidence for a terrestrial ancestry. If you’re interested in the area I would definitely recommend doing some further reading – there’s so much information out there!
Science Daily: http://www.sciencedaily.com/articles/e/evolution_of_cetaceans.htm
The Emergence of Whales (Book): http://books.google.co.uk/books?hl=en&lr=&id=zgWIL6ELoJoC&oi=fnd&pg=PA1&dq=evolution+of+cetaceans&ots=qdL7vIDk3I&sig=lgPjPYd85dxrBzV1sg2u0dWOYuM#v=onepage&q=evolution%20of%20cetaceans&f=false
Understanding Evolution: http://evolution.berkeley.edu/evolibrary/article/evograms_03
Talk Origins: http://www.talkorigins.org/features/whales/
Implications for locomotor evolution of cetaceans: http://www.currentscience.ac.in/Downloads/article_id_079_10_1478_1482_0.pdf
Cetacean Palaeobiology: http://palaeo.gly.bris.ac.uk/palaeofiles/whales/archaeoceti.htm
- Sperm Whale Fossil Vertebrae (beautifullybony.wordpress.com)
- Rise of the Cetacea: Part I – The Pakicetids (scilogs.com)
- How whales made the dramatic evolutionary shift from land to the sea (io9.com)