Whale Evolution in the Fossil Record

"...The evidence is absolutely conclusive that they [cetaceans] were not originally aquatic in habit, but are derived from terrestrial mammals of fairly high organisation, belonging to the placental division of the class, - animals in which a hairy covering was developed, and with sense organs, especially that of smell, adapted for living on land; animals, moreover, with four completely developed limbs on the type of the higher vertebrate, and not of that of fishes." - Flower, W. H. 1883. "On whales, past and present and their probable origins II", Nature, vol. 28, pp. 226-30. "The whales and porpoises together form a great order of animals known as the order Cetacea, all the members of which are most admirably adapted for an exclusively aquatic life. Nevertheless, the details of their anatomy (rudiments of hind-limbs, &c.) conclusively prove that they are the descendants of beasts which were quadrupeds fitted to live upon the earth's surface. But although the fossil remains of countless Cetacea have been entombed, yet the transitional forms are still amongst "missing links" of Nature." - London Quarterly Review 1886, pp. 275-284. Before any cetacean transitional forms were found (except for Basilosaurids), anatomists concluded that the modern forms must be derived from terrestrial, quadrupedal mammals. The hypothesis meant that transitional forms linking these aquatic mammals with their terrestrial ancestors must have previously lived, died and some should have fossilized. This is a prediction which can be tested. If cetaceans really did descend from terrestrial quadrupeds, than forms intermediate between them should be found in geological strata. You argue that that what if these forms were merely intermediate not because they are closely genealogically related to modern cetaceans, but merely mimic the transition due to convergent evolution. It is impossible to conclusively determine whether or not this the case, but there is some evidence that indicates that it is not an example of convergent evolution. Firstly, the first appearance archaeocetes ('archaic whales') precedes modern cetaceans in the fossil record exactly where they should to be if they are ancestral. If modern cetaceans appeared before the first appearance of archaeocetes in the geological strata, then it would definitely be a case of convergent evolution. Secondly, in some cases, the apparent transition of certain characters is very gradual and continuous. For instance, let's take a look at some transitions that have taken place: 1) Freshwater osmoregulation to seawater osmoregulation (i.e. the ability to drink seawater). 2) The nostrils (external nares) posteriorly migrating from the tip of the snout (rostrum) to the the vertex of the head (forming a blowhole). 3) The reduction of the semicircular canals relative to body size. I have already brought up the first and third transitions, with the former having an intermediate stage (Ambulocetus) and the latter being discontinuous, but appearing in early semi-aquatic cetaceans. The second transition, however, is actually presented by some fine transitional fossils that form a gradual series. The external nares being located posteriorly from the tip of the rostrum is a very useful aquatic adaptation as it allows the cetaceans to breath without having to lift their face out of the water. Below is a figure showing a gradual series of steps in "nasal drift" which begins at the tip of snout and migrates posteriorly. There are even more fossils which are intermediate with respect to external nare position between some of the fossils shown below (but I will not show due to the size of the image): Note: All the fossil craniums are the same size for comparison purposes only. There is dramatic variation in size, especially between the first and last cetacean in the series. In addition to this, you can see that I took different photos, drawings and schematic diagrams from different sources. Also, the fossils do not represent a lineal line of descent, but are interpreted as evolutionary "cousins". The external nares are highlighted in red. It should also be noted that during early embryological development of cetaceans, the nostrils initially form at the tip of the snout and then later migrates posteriorly up towards the vertex of the head. The characters mentioned are only but a few of the traits which unite archaeocetes with modern whales. I mentioned the sigmoid process and the involucrum because they are simple, distinct and unique features of cetaceans, but there are much more complex and subtle features that are shared between archaeocetes with modern whales. Modern whales are unique in that their mandibular foramen is quite large when compared to non-cetaceans. I will let Thewissen & Bajpai (2001) explain why this is the case: "In all mammals, including cetaceans, the nerves and blood vessels of the lower teeth travel through a canal called the mandibular foramen on the medial, or inner, side of the lower jaw. In odontocetes, this foramen covers the entire depth of the mandible and is much larger than is necessary for a simple conduit for nerve and vessels. Indeed the foramen has become part of the whale's hearing apparatus: It houses a fat pad, which extends posteriorly to the middle ear. Sounds are received by the lower jaw and are then transmitted by this fat pad to the middle ear. The posterior side of the mandible, with its fat pad, is the most sound-sensitive area of a modern odontocete, more sensitive than the area of the ear itself." Here are to figures from Thewissen & Bajpai (2001) and Nummela et al. (2007): This shows that Pakicetids had small mandibular foramens like non-ceataceans while Ambulocetids, Remingtonicetids, Protocetids (includuing Maiacetus inuus) and Basilosaurids have enlarged mandibular foramens like modern cetaceans. There is a difference between making predictions from a model and later observing those predictions and finding observations that are consistent with the model, but they were never predicted in the first place. The former exercise actually puts your model to the test; you are so confident that the model is valid that you are willing to “put it on the line”, in a manner of speaking. While the latter exercise can be evidence for a model, it’s not as strong because all that is being done is post hoc rationalization. Once again, these intermediate fossils are evidence for the hypothesis that cetaceans descended from terrestrial mammals because they were predicted to exist in the fossil record a century beforehand. The hypothesis was tested and confirmed because these intermediates have been observed in the fossil record. Your competing hypotheses that you are bringing forth are a post hoc analyses, where you are not predicting anything, but instead coming up with other explanations that are just consistent with the evidence. I don’t normally like to quote young-earth creationists because I don’t like it when creationists misquote scientists. However, I will quote paleontologist Dr. Kurt Wise because I think his position is quite clear: “Darwin’s fourth expectation - of stratomorphic series - has been confirmed by such examples as the early bird series, the tetrapod series, the whale series, the various mammal series of the Cenozoic (for example, the horse series, the camel series, the elephant series, the pig series, the titanothere series, etc.), the Cantius and Plesiadapus primate series, and the hominid series. Evidence for not just one but for all three of the species level and above types of stratomorphic intermediates expected by macroevolutionary theory is surely strong evidence for macroevolutionary theory. Creationists therefore need to accept this fact. It certainly cannot be said that traditional creation theory expected (predicted) any of these fossil finds.” You notice in the summary below that some parts of the intermediates are missing or analyses are yet to be done on them. You can make predictions about these unknown features. If an oxygen isotope analysis is ever done on Maiacetus inuus, I predict that its oxygen isotopic composition will have a high oxygen-18 abundance. If the another Ambulocetid fossil is ever found with the auditory bulla completely preserved, it will have a sigmoid process present. Below is a summary of the presence/absence of cetacean/marine traits in some archaeocetes: Pakicetids (e.g. Pakicetus) Sigmoid process: present Involucrum: present Three-fold reduction in semicircular canal radii: absent Capacity to osmoregulate in seawater: absent Enlarged mandibular foramen: absent Remingtonocetids (e.g. Remingtoncetus) Sigmoid process: present Involucrum: present Three-fold reduction in semicircular canal radii: present Capacity to osmoregulate in seawater: present Enlarged mandibular foramen: present Ambulotocetids Sigmoid process: unknown Involucrum: present Three-fold reduction in semicircular canal radii: unknown Capacity to osmoregulate in seawater: present Enlarged mandibular foramen: present Maiacetus inuus Sigmoid process: present Involucrum: present Three-fold reduction in semicircular canal radii: unknown Capacity to osmoregulate in seawater: unknown Enlarged mandibular foramen: present Durodon atrox Sigmoid process: present Involucrum: present Three-fold reduction in semicircular canal radii: present Capacity to osmoregulate in seawater: present Enlarged mandibular foramen: presentNotes:The second quote in the previous round from me is attributed to Richard Dawkins.If you wish for any of the sources for the claims I have made, please don't hesitate to request them.