Thursday, 17 December 2009
......is up to his knees in viscous mud as a ferric smell permeates the air, watching you stand there with a comforting cup of tea, a pack of biscuits and an alluring smile on your face which has not yet been finished by your eyes. Who are you?
Wednesday, 16 December 2009
Had I been allowed to write in my usual self-indulgent style, my essay may have started something like this:
The iconic fossil ammonite, elegantly simple in outward morphology, provides lucid prose for palaeontologists perusing what lays written in the rocks. Their Mesozoic ubiquity, with a characteristic evolutionary pace (which appears geologically hasty, almost eager) renders them excellent index fossils. The gradual evolution their lithified remains display is the bread and butter of biostratigraphy, facilitating dating for even shy, phlegmatic geologists.
As it stands, that is not what I wrote, here is my essay:
The Applied Palaeontology of Ammonites
The iconic ammonites are a group of cephalopods of Subclass Ammonoidea which are invaluable in their application in palaeontology. ‘Ammonites’ is the vernacular term (after Order Ammonitida) for the Mesozoic forms of Ammonoidea, a Subclass which spans approximately 325 Ma from the Devonian to the Cretaceous. The major use of ammonoids lies in biostratigraphy where they are regularly used for zoning the rocks in which they are found, particularly the Mesozoic forms which have allowed for zones to be erected equivalent to less than a million years.
Good index fossils need to have a wide distribution with high abundance, a high rate of evolution and be easily identified; all of which are characteristics of the ammonoids. Shortly after their first appearance in the Devonian, the ammonoids rapidly spread world-wide (House, 1981) and maintained this distribution until their demise in the K/T extinction. They are ubiquitous, particularly in Mesozoic strata, rendering them a highly effective tool for stratigraphy in the field. Although some orders, such as Order Phylloceratida, display little evolution over millions of years (Clarkson, 1998), the vast majority of ammonites show the characteristic rapid morphological change and high speciation rate preferred in index fossils. The identification of an ammonite (excluding heteromorphic ammonoids) is relatively easy, hence their iconic status, and they can easily be used to quickly identify whether the rock is Palaeozoic or Mesozoic with little inspection by an amateur.
The ammonoids display many evolutionary trends and diverse morphological characters readily identifiable in single specimens which allow for their specificity in dating rocks. Ammonoids are commonly found preserved as internal moulds which display the sutures between septa and shell. Fossils with preserved suture lines demonstrate a clear stratigraphical trend from the relatively simple Devonian and Carboniferous sutures, to the extremely complex and flamboyant Mesozoic sutures. Changes in sutures can be used to quickly differentiate between the two eras; Palaeozoic ammonoids have generally zigzagged sutures, whereas Mesozoic ammonites possessed sutures with complex lobes and saddles. Although some ammonoids do not easily fit into this trend – some Permian ammonoids have similar sutures to Mesozoic ammonites – these deviations can be identified using other morphological characters, allowing suture morphology to be utilised for high stratigraphical accuracy when studied in detail and can also be used in the study of ontogeny.
A famous example of a useful lineage of ammonites in biostratigraphy is the Jurassic Family Cardioceratidae, which spanned 20 Ma and can be traced through 28 zones and 62 subzones. They have been described in monospecific assemblages, making them easily identifiable, and they rapidly diversified, allowing for many easily observed trends and accurate dating. These include easily identified changes in the compression of the whorl, in rib shape and in the ornamentation of the keel.
During the Mesozoic, the abundance and diversity of ammonites has even allowed for accurate stratigraphy during extinctions in conjunction with other techniques (Guex et al, 2004).
Aside from biostratigraphy, their global distribution and rapid diversification has allowed ammonites to be used in determining the position of continents during continental drift (Kennedy et al, 1975) along with facilitating the dating of these events.
Ammonites form a group with a basic common shell plan along with a propensity for fossilisation, exceptional diversity, rapid evolutionary change and wide distribution, making them easily recognisable and one of the most useful fossil groups for application in biostratigraphy to a high degree of resolution; they are an invaluable tool for any palaeontologist studying the Palaeozoic and Mesozoic.
Clarkson, E.N.K. (1998). Invertebrate Palaeontology and Evolution (4th ed.). Oxford: Blackwell Science.
Guex, J., Bartolini, A., Atudorei, V., & Taylor, D. (2004). High-resolution ammonite and carbon isotope stratigraphy across the Triassic-Jurassic boundary at New York Canyon (Nevada) [Electronic version]. Earth and Planetary Science Letters, 225(1-2), 29-41.
House, M.R. (1981). Early Ammonoids in Space and Time. In M.R. House, & J.R. Senior (Eds.), The Ammonoidea. The Evolution, Classification, Mode of Life, and Geological Usefulness of a Major Fossil Group (pp. 359-367). London: Systematics Association Special Volume No. 18, Academic Press.
Kennedy, W.J., & Cooper, M. (1975). Cretaceous ammonite distributions and the opening of the South Atlantic [Electronic version]. Journal of the Geological Society, 131(3), 283-288.
Note: there is something bizarre going on in the references which I can't seem to alter.
In 1972 a landmark paper was published in ‘Models in Paleobiology’ titled, “Punctuated Equilibria: an alternative to phyletic gradualism.” The paper, by Stephen Jay Gould and Niles Eldredge, was in many ways nothing new, yet at the same time purported to challenge many long cherished ideas in evolutionary biology. Over the years it has simultaneously been embraced and reviled by scientists, and consistently distorted by creationists.
In many ways Eldredge and Gould had simply connected the dots between different lines of evidence and come to conclusions. They took common knowledge from biostratigraphy and combined it with known models of speciation used by neontologists (those that study living organisms). Here they saw that species appeared in a geologically abrupt time and persisted unchanged for most of their duration. At the time biology and palaeontology were only beginning to overlap, so Eldredge and Gould were the first to realise that the pattern they perceived in the fossil record was exactly what should be expected if Ernst Mayr’s peripatric speciation model were applied to the fossil record.
During peripatric speciation a small group becomes peripherally isolated from the main population. Gene flow between the two populations stops, allowing the two to accumulate separate mutations. Smaller populations can evolve more rapidly, and as they are small they are unlikely to yield fossils. When the isolated group is reintroduced to he larger population, if sufficient time has passed they will no longer be able to interbreed – they have become a new species. Over geologic time this appears sudden.
So why the fuss if these were well established views? Creationist distortions aside, Gould and Eldredge were interested in some of the implications of the theory. They changed ideas of tempo and mode in evolution; they challenged the way we think of natural selection; they raised the possibility of unknown mechanisms; and often claimed to separate micro- and macro-evolution. These were strong boasts which led to years of feuding and bickering among scientists.
The punctuational aspect of ‘punk eek’ (or evolution by jerks as some used to call it) has received the most attention from detractors. It was also one of the main focuses (at first) of Gould and Eldredge, as they loudly proclaimed that Darwinian orthodoxy had been challenged. The first to protest often misunderstood. Many biologists interpreted rapid to mean saltation, where a new species is born instantly from an old one. Creationists also made this mistake and believed they had new evidence of instantaneous creation. Both were mistaken; rapid on a geological timescale means at least tens of thousands of years.
Many ‘phyletic gradualists’ rightly pointed out that a straw man of gradualism had been erected and defeated. No gradualist believes that evolution occurs at a strict pace (Dawkins 1986). Even Darwin had made comments that sound a lot like punctuated equilibria; discussing his tree diagram he said, “But I must here remark that I did not suppose that the process ever goes on so regularly as is represented in the diagram, though in itself made somewhat irregular, nor that it goes on continuously; it is far more probable that each form remains for long periods unaltered, and then again undergoes modification.”
Many biologists tried to ignore punctuated equilibria, focussing on the tempo aspects and dismissing them. An analogy using gears is apt, as evolution can change gears, even becoming so slow as to allow stasis (evolutionary biologists have words like bradytely, horotely and tachytely to describe pace). Is this dismissal valid? Not completely, but to dismiss only the attacks on gradualism evidence is needed. Gould himself (1993) acknowledged that it is a ‘complement to phyletic gradualism’ as gradualism has been documented in groups from microfossils (Macleod 1991) to mammals (Gingerich 1976, Chaline & Laurin 1986).
One of the best examples of punctuations as gradualistic was found by Stephen Jay Gould (1996). He was fortunate to find numerous shells of the Bahamian land snail Cerion, in a single mudflat, the equivalent to a single bedding plane in strata. Using geochemical methods he was able to date the shells; when put in order they showed a gradual, microevolutionary trend spanning 20,000 years.
The other main aspect of punk eek is stasis, the equilibrium aspect of the model. The authors had developed a little motto, “stasis is data” to remind themselves of the importance of this observation. One of Gould’s harshest critics, Jeffrey S. Levinton, agreed with this observation, stating, “This is…the issue of stasis, which I believe to be the legitimate problem spawned by the punctuated equilibrium model.” (1988).
Stasis had previously been dismissed as a lack of data, a situation which has changed a lot since 1972. Stasis is not a lack of evolution; it is a ‘wobble’ or fluctuation around means, with no substantial change (no broader than the range of geographic variation in modern species) and no directional evolution.
There are some issues with empirical verification of stasis, though it is widely acknowledged as occurring. Fossil species are morphospecies, that is they are identified by morphology and only that which fossilises. Substantial phenotypic change can occur without being detectable in the fossil record. Similarly, neontologists often discover new species through genetic testing; practically impossible with fossils. Conversely, intraspecific variation, functional polymorphisms and ontogenic variation may all be wrongly identified as separate species. Despite these possibilities, comparisons suggest that it is not too big an issue for interpreting stasis (Jackson and Cheetham 1994) as the bias is against punk eek.
Some biologists tried to explain stasis away using stabilising selection in unchanging environments. Stabilising selection removes the extremes of a population, keeping it centred around the mean. However, this could not explain stasis through climatic change (Cronin 1985, Prothero and Heaton 1996, Prothero 1999). Many possible explanations for stasis including a homeostatic mechanism resisting selection (a controversial view of Gould’s which fit with some of his other views), habitat tracking (Eldredge), constraints (Lieberman), normalising clade selection (G. L. Williams) and turnover pulses (Vrba) have all been suggested.
Gould and Eldredge originally tried claiming that all change was focussed around speciation events, a position they later changed. Douglas Futuyma (1987) gave strong insight into what may be occurring, “In the absence of isolation, differentiation is broken down by recombination. Given reproductive isolation, however, a species can retain its distinctive complex of characters as its spatial distribution changes along with that of its habitat or niche… Although speciation does not accelerate evolution within populations, it provides morphological changes with enough permanence to be registered in the fossil record. Thus, it is plausible to expect many evolutionary changes in the fossil record to be associated with speciation.”
Palaeontologists in recent years acknowledge punctuated equilibrium as a valid model of long term occurrences, one among many including phyletic gradualism and punctuated anagenesis (Jackson and Cheetham 1999). The main ‘controversial aspects focussed on are the potential decoupling of macro and microevolution; changes in understanding of levels of selection; and the prevalence of selection.
From Futuyma’s insight it is hard to see how punctuated equilibrium could potentially split micro and macro evolution, though this was a genuine early problem. It all depends on whether speciation is caused by more than simple isolation. Punctuated equilbirum presents the possibility of species selection and species sorting, and as most change is ‘tied up’ during speciation, this form of selection gains more prominence, therefore meaning that micro changes cannot be easily extrapolated as such selection would be ignored. Modern focus on speciation is on whether natural selection or genetic drift is more dominant (recent research though is favouring natural selection) therefore raising the possibility that natural selection is not responsible for all diversity (a less common view favoured by Gould).
Gould’s statement in 1993 is still a worthy interpretation, saying, “[Punctuated equilibria’s] most important implications remain the recognition of stasis as a meaningful and predominant pattern within the history of species, and in the recasting of macroevolution as the differential success of certain species (and their descendants) within clades.”
I have hopefully presented a brief and accessible explanation of punctuated equilibria, whilst clearing up any misconceptions. ‘Punk eek’ (or ‘eck’ to some) has changed a lot in the past 3 decades, yet still manages to provoke interesting debate (which is sadly misunderstood by the lay public). Gould believed it to be a “useful extension of evolutionary theory” which can clearly be seen once understood.
Benton, M.J. & Pearson, P.N. (2001). Speciation in the fossil record. Trends in Ecology & Evolution. 16, 405-411.
Chaline, J. & Laurin, B. (1986) Phyletic gradualism in a European Plio-Pleistocene Mimomys lineade (Arvicolidae, Rodentia). Paleobiology. 12(2), 203-216.
Chaline, J., Laurin, B., Brunet-Lecomte, P. & Viriot, L. (1993) Morphological trends and rates of evolution in arvicolids (arvicolidae, rodentia): Towards a punctuated equilibria/disequilibria model. Quaternary International. 19, 27-39.
Cheetham, A.H. (2001) Evolutionary stasis vs. change. In: Briggs D.E.G. & Crowther, P.R. (eds) Palaeobiology II. pp. 137-142. Blackwell Publishing,
Cronin, T.M. (1985) Speciation and stasis in marine ostracoda: climatic modulation of evolution. Science. 227, 60-63.
Dawkins, R. (1986) The blind watchmaker.
Futuyma, D.J. (1987). On the role of species in anagenesis. The American Naturalist. 130, 465-473.
Gingerich, P.D. (1976) Paleontology and phylogeny; patterns of evolution at the species level in early Tertiary mammals. American Journal of Science. 276, 1-28.
Goodfriend, G.A. & Gould, S.J. (1996). Paleontology and chronology of two evolutionary transitions by hybridization in the Bahamian land snail Cerion. Science. 274, 1894-1897.
Gould, S.J. and Eldredge, N. (1972) Punctuated equilibria: an alternative to phyletic gradualism. In: T.J.M. Schopf, ed. Models in paleobiology. pp. 82-115. Freeman, Cooper and Co.,
Gould, S.J. and Eldredge, N. (1993) Punctuated equilibrium comes of age. Nature 366, 223-227.
Jackson, J.B.C. & Cheetham, A.H. (1999) Tempo and mode of speciation in the sea. Trends in Ecology and Evolution. 14, 72-77.
Kellog, D.E. & Hays, J.D. (1975). Microevolutionary patterns in late Cenozoic radiolaria. Paleobiology. 1, 150-160.
Lazarus, D. (1983). Speciation in pelagic protista and its study in the planktonic microfossil record: a review. Paleobiology. 9(4), 327-340.
Lazarus, D.B. (2001) Speciation and morphological change. In: Briggs D.E.G. & Crowther, P.R. (eds) Palaeobiology II. pp. 133-137. Blackwell Publishing,
Levinton, J. (1988). Genetics, paleontology, and macroevolution.
Cambridge University Press, . Cambridge
Macleod, N. (1991) Punctuated anagenesis and the importance of stratigraphy to paleobiology. Paleobiology. 17(2), 167-188.
Malmgren, B.A. & Kennett, J.P. (1981) Phyletic gradualism in a late Cenozoic planktonic foraminiferal lineage; DSDP Site 284, southwest Pacific. Paleobiology. 7, 230-240.
Mayr, E. (1963). Animal species and evolution.
Prothero, D.R. & Heaton, T.H. (1996). Faunal stability during the Early Oligocene climatic crash. Palaeogeography, Paleoclimatology, Palaeoecology. 127, 257-283.
Prothero, D.R. (1999). Does climatic change drive mammalian evolution? GSA Today. 9, 1-7.
Sheldon, P.R. (1987). Parallel gradualistic evolution of Ordovician trilobites. Nature. 330, 561-563.
Wei, K. & Kennett, J.P. (1988). Phyletic gradualism and punctuated equilibrium in the late Neogene planktonic foraminiferal clade Globoconella. Paleobiology. 14, 345-363.
Friday, 21 August 2009
Cetacea, the order that includes whales, dolphins and porpoises, has justifiably captured the imagination for millennia, from the scourge of Jonah to Moby Dick; Monstro the Great to Free Willy; we live in awe of them. It is common knowledge that dolphins show high intelligence and that blue whales (Balaenoptera musculus) are the largest animals to ever have lived, whales break more records than this; the sperm whale (Physeter catodon) can dive for longer and deeper than any mammal (10,000 ft); blue whales and fin whales (Balaenoptera physalus) produce the loudest sound in the animal kingdom (188 decibels); male humpback whales (Megaptera novaeangliae) produce the longest and most complex songs of any animal (up to 9 themes in half an hour, which it repeats for several days).
The plausibility of whale evolution has long been a source of fascination for scientists; and ridicule by creationists. Darwin speculated, to his own embarrassment, in the early editions of The Origin of Species:
In North America the black bear was seen by Hearne swimming for hours with widely open mouth, thus catching, like a whale, insects in the water. Even in so extreme a case as this, if the supply of insects were constant, and if better adapted competitors did not already exist in the country, I can see no difficulty in a race of bears being rendered, by natural selection, more aquatic in their structures and habits, with larger and larger mouths, till a creature was produced as monstrous as a whale.
Such speculation was justifiably rejected and whale evolution remained unsupported by tangible fossil evidence until recent decades. Who can forget Duane Gish’s comical “mer-cow” example of a half-cow, half-fish transition which he termed an “udder failure”? Bizarrely, cetaceans are still at the brunt of creationist attacks, when in actuality they present a wealth of evidence for evolution, not the supposed dearth.
First of all, is such a transition possible? Is a semi-aquatic life possible for a mammal? Visit any zoo or watch any good wildlife documentary (I recommend The Life of Mammals by David Attenborough) and you will find dozens of examples of different stages of amphibious life in extant mammals.
Mammals returning to the sea face many key problems: mammals need to keep warm, which aquatic life makes difficult; efficient movement requires different modifications to land movement; breathing air is difficult in the sea; giving live birth proves difficult under water. These obstacles have been conquered by both whales and many other mammals, but why bother? Food is often the key, and for whales in particular a niche was open; the mosasaurs, plesiosaurs and ichthyosaurs of the Mesozoic had all recently gone extinct, also meaning a lack of predation.
Living mammals provide examples of different stages of aquatic adaptation. In freshwater, the Desman (Desmana moschata and Galemys pyrenaicus) is an insectivore related to moles which has developed a flexible trunk-like snout for a snorkel, long dense fur for warmth and is a very effective swimmer. It remains tied to land as it is too buoyant to dive for long and must eat what it catches on land.
Sea otters (Enhydra lutris) spend all of their lives at sea, using their webbed toes for efficient propulsion. To keep warm they have the densest fur of any mammal, with more hairs in one square centimetre than any human has on their head, they even blow air into it for insulation. Sea otters mate in the sea and wrap themselves in kelp to stop from floating away whilst sleeping (they remain territorial).
Sea lions (of genera Eumetopias, Zalophus, Otaria, Neophoca and Phocarctos) take things further, with paddle-like front legs and back legs which are highly effective flippers yet still allow them to clumsily move on land. They have a lot of blubber and feed their young milk which is 30% fat in order to rapidly return to sea. They still give birth on land and have external ears.
Seals (of family Phocidae) lack the external ears, making them more streamlined. Their hind legs are shorter and cannot aid walking – they have to bounce around or slide when on land to give birth. Seals can stay submerged for up to 20 minutes.
All of these examples show different stages in adapting to the sea. Further discussion on each could be given, also including the fascinating manatees, but the point here is simply that a semi aquatic life is possible and therefore can lead to a fully aquatic one. Now onto the evidence from whales, but first, hippos.
Hippos (Hippopotamus amphibius) spend most of their time in the water and have many key adaptations to such a lifestyle. Their main sensory organs (eyes, ears and nose) are all atop their head allowing them to keep the rest of the body submerged; they are also able to tightly close them underwater. Mating occurs under water and the babies are born and suckle there too, even swimming before walking. A novel hippo adaptation is the secretion of their own sunscreen to prevent sunburn. I mentioned the hippopotamus last because molecular data shows them to be the closest relative of the cetaceans.
These extant examples show that it was at least possible and the molecular data should confirm that it did happen, but that is not enough for most, the fossils need discussing. We must confirm that it did happen with the visual tangibility that only fossils can provide; DNA often seems too abstract.
First comes Indohyus, an ancient artiodactyl the size of a raccoon. Dated to 48 million years ago it is not the ancestor of whales, but has features of the ears and teeth which are shared only by modern whales. It likely resembles the ancestor of whales and was partly aquatic, as evidenced by the denser bones and isotopic extractions from the teeth.
Next we turn to the famous Pakicetus from 52 million years ago. Pakicetus lacked the diving specialisations of modern whales and had intermediate teeth between mesonychids and archaeocetes. This ancestral whale was found in river sediments bordering an ancient sea, fitting for such a transition.
In this rapid trip through fossil whales (which does no justice to the evidence and misses some recent finds including the remingtonocetids such as Kutchicetus, the protocetid Maiacetus which gave birth on land, and many more) we turn to another famous fossil, Ambulocetus. Fifty million years ago the sea lion sized Ambulocetus spent most of its time in shallow water using flippers which still had vestigial hooves. The most important feature of Ambulocetus is the spine – it was highly flexible, allowing for up and down undulations which led to the distinctive locomotive style of all cetaceans.
Many fossils show more progression, such as Dalanistes with its still fully functional limbs with webbed feet and its long snout. Both Indocetus and Rodhocetus (46.5 mya) were partly terrestrial (though very limited) and highly agile in the water. The nostrils of Rodhocetus had moved back – the start of the transition to the blowhole. Other fossils showing more progression include Takracetus and Gaviocetus (both have vestigial hind limbs) and more will undoubtedly be found.
On the whale side of the transition are Basilosaurus and Dorudon from 40 mya. Both had short necks and their blowholes were atop the skull. They also had tiny hind limbs, useless for land locomotion yet still present. These were around 2 foot long on a 50 foot whale and included all the usual hind limb bones including the patella and phalanges.
The fossils show an incredible sequence, one which stretches incredulity to doubt (I recommend looking at them and not relying on my short descriptions). This brief overview gave only a glimpse, the fossils, when studied in more detail, show how almost every unique whale feature evolved, from the blowhole to their locomotion. In almost all cases this required modification of existing traits. As fossils are discussed so often when covering whale evolution I will turn to other lines of evidence.
One of my favourite pieces of evidence for evolution is the presence of pseudogenes, and whales do not disappoint. The olfactory receptor (OR) genes are an important and fascinating group of genes, the elucidation of which won the Nobel Prize for Axel and Buck in 2004.
The OR genes originated from a single gene which has been duplicated repeatedly and altered slightly each time. Their number correlates with the strength of the sense of smell of the animal (an unusual occurrence with genes). A brief look at them in a variety of species is illuminating. Many ‘primitive’ fish have 2 sets of OR genes, lobe finned fish use only one of these sets, homologous to the set used in terrestrial animals. Fish have just a handful of OR genes, amphibians tend to have more, reptiles even more so and mammals can have over 1,000. Already a sequence has emerged.
Looking at mammals more closely, those that rely heavily on smell, such as the mouse or dog, have the full complement of OR genes, all in use. Our own sense of smell is a lot weaker, using only around 400 OR genes. We still carry around 800 OR genes – half have become pseudogenes and are inactive. This coincides with our dependence on colour vision, relying less on smell (which usually leads into another of my favourite examples of evolution).
With this information a prediction can be made. If cetaceans evolved from terrestrial mammals they should have hundreds of OR genes, though as their nose is now a blowhole they should largely be inactive. A look at the dolphin genome shows that 80% of their OR genes are inactive. They also resemble the usual mammalian OR genes. This makes proper sense only in light of the theory of evolution.
Pseudogenes are the genetic equivalent of vestigial traits, which whales also have. Whales famously have a vestigial pelvis and thigh bones which serve little to no purpose except as a pointer to their evolutionary heritage. Occasionally (1 in 500) whales have atavistic legs which protrude outside the body wall, many containing leg bones, some even having feet and toes!
The most exciting discoveries being made in current evolutionary biology come from the study of embryological development and the pathways taken. In a 24 day old spotted dolphin (Stenella attenuata) embryo there is a well developed hind limb bud, only slightly smaller than the forelimb bud. By 48 days the hind limb buds have mostly been reabsorbed whilst the forelimbs continue to develop into flippers. Baleen whales, which are toothless, develop embryonic teeth which are also reabsorbed before birth.
Another example is present in human development too. Foetal humans of around 6 months develop fine, downy hair called lanugo. Lanugo is shed around a month before birth in humans, whereas other apes retain it. Foetal whales also develop lanugo and shed it before birth. These embryonic examples hint at their descent from four-limbed, fur covered ancestors.
More detailed study has been done into the genetic basis of the embryological development of cetaceans, proving to be most illuminating.
Whales still have the main genes used in limb formation (Shh, the Fgfs and Hand2) though the regulation has changed. A loss of the genes would not be possible (it would hinder other areas of development) so their activation was selectively reduced. The changes have been pinpointed to the expression of Hand2, being expressed in the forelimb and not the hind, forming no zone of polarising activity (ZPA) for that limb, thus halting formation. The evidence suggests this shutting off occurred approximately 34 mya.
At the same time the limbs were lost there was a change in vertebral patterning. Hox expression (Hoxd) appears to have altered both features, effecting Shh and Hand2 expression. Not only can we observe fossils, development also shows exactly which mutations may have occurred.
Whales and other cetaceans are not only awe inspiring to observe, they also provide incredible evidence and insights into evolution. The small amount presented here scratches the surface and displays a confluence of disparate evidences from various separate disciplines which are made sense of by the theory of evolution.
References and recommended reading (in non-scientific format):
The Encyclopedia of Animals - published by Weldon Owen (2008).
The Life of Mammals (DVD) – David Attenborough (2002).
Why Evolution is True – Jerry Coyne (2009).
Evolution: What the Fossils Say and Why It Matters – Donald Prothero (2007).
Hooking Leviathan By Its Past, from Dinosaur in a Haystack: Reflections in Natural History – Stephen Jay Gould (1995). http://www.stephenjaygould.org/ctrl/gould_leviathan.html
Your Inner Fish – Neil Shubin (2008).
The Origin of Whales and the Power of Independent Evidence: http://lsrhs.net/departments/science/faculty/bernasconib/Bio%201/Bio1%20homework/Evolution/whales.content.pdf
Inclusion of Cetaceans Within the Order Artiodactyla Based on Phylogenetic Analysis of Pancreatic Ribonuclease Genes: http://www.springerlink.com/content/467ktrklk4utdctk/
Molecular evidence for the inclusion of cetaceans within the order Artiodactyla: http://mbe.oxfordjournals.org/cgi/content/abstract/11/3/357
Molecular evidence from Retroposons that whales form a clade within even-toed ungulates: http://www.lacertilia.com/creationist_critiques/PDFs/Shimamura_etal_1997.pdf
Skeletons of terrestrial cetaceans and the relationship of whales to artiodactyls: http://www.nature.com/nature/journal/v413/n6853/abs/413277a0.html
From Land to Water: the Origin of Whales, Dolphins, and Porpoises: http://www.springerlink.com/content/whn1654v74t64301/
Whales originated from aquatic artiodactyls in the Eocene epoch of India: http://www.nature.com/nature/journal/v450/n7173/full/nature06343.html
Fossil Evidence for the Origin of Aquatic Locomotion in Archaeocete Whales: http://www.sciencemag.org/cgi/content/abstract/sci;263/5144/210
Vestibular evidence for the evolution of aquatic behaviour in early cetaceans: http://www.nature.com/nature/journal/v417/n6885/abs/417163a.html
New Protocetid Whale from the Middle Eocene of Pakistan: Birth on Land, Precocial Development, and Sexual Dimorphism: http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0004366
A remarkable case of external hind limbs in a humpback whale: http://digitallibrary.amnh.org/dspace/handle/2246/4849
Limbs in whales and limblessness in other vertebrates: mechanisms of evolutionary and developmental transformation and loss: http://whitelab.biology.dal.ca/lb/Bejder%20and%20Hall.pdf
The olfactory receptor gene repertoires in secondary-adapted marine vertebrates: evidence for reduction of the functional proportions in cetaceans: http://rsbl.royalsocietypublishing.org/content/3/4/428.abstract
Whale limb evolution:
Sound transmission in archaic and modern whales: Anatomical adaptations for underwater hearing: http://www3.interscience.wiley.com/journal/114265699/abstract?CRETRY=1&SRETRY=0
Eocene evolution of whale hearing: http://www.nature.com/nature/journal/v430/n7001/abs/nature02720.html
Wednesday, 8 April 2009
What is Comical Design?
The theory of Comical Design (CD theory) holds that certain amusing features of the universe, of living things and even the mechanical world are best explained by a cause with a sense of humour, not by natural means. Through the study and analysis of an entity’s appearance, a CD theorist is able to determine whether various natural entities are the product of chance, natural law, comical design, or some combination thereof. Such research involves observing the types of laughter produced when comical agents are viewed. Comical design has applied this scientific method to detect design in irreducibly hilarious biological structures, with prime examples in nature being the infamous duck-billed platypus of the animal kingdom and natural organic phallic entities (NOPEs) such as trees shaped like penises. In the mechanical world the same applies, with the Robin Reliant being undeniably irreducibly hilarious.
Is comical design a scientific theory?
Yes. The scientific method is commonly described as a four-step process involving observations, hypothesis, experiments, and conclusion. Comical design begins with the observation that hysterical agents produce complex and specified humour (CASH). CD theorists hypothesize that if a natural or mechanical object was comically designed, it will contain high levels of CASH. Scientists then perform experimental tests upon these objects to determine if they contain complex and specified humour. One easily testable form of CASH is irreducible hilarity, which can be discovered by experimentally watching the aforementioned entities and other observers to see if any form of side-splitting takes place. When CD researchers find irreducible hilarity in biology or machinery, they conclude that such structures were designed.
Who supports CD theory?
Here at the centre of comical knowledge (COCK) we are looking for scientists to aid in our research. A PhD is not necessary, nor a Masters or any form of degree or qualification. Break away from the fear of supporting the obviously flawed and humourless Darwinism. This group has been created to spread the theory of comical design so that all may become aware of the hilarity which is so obviously caused only by design. Donations in the form of pictures or videos pertaining to entities befitting of the descriptions above will be appreciated muchly.
Tuesday, 7 April 2009
The desire to start this blog came about mostly because I spend an inordinate, almost indecent, amount of time on Facebook discussion boards discussing evolution. It is getting to the point now where I wish I could answer every inane point with a single word, but sadly that is impossible (until I get some psychic superpowers). My original plan to get myself out of having to say much was to follow the footsteps of Whit Grey, who made the leap onto Youtube making videos teaching about evolution and debunking creationist nonsense under the name DonExodus2. This felt like the natural route for me to take, as I have much experience in film production, enough to make some flashy videos at least. Sadly though, I have no computer of my own (this is my sister's) and no camera.
Fortunately I love writing and intend to do as much as I can, so here I get to practice. I will continue to discuss on Facebook for inspiration, allowing me to be reminded of things which need clearing up. I could use other people's words, but I like my own. I will address creationist misconceptions about evolution, sometimes debunking their arguments; I will discuss how evolution works, though I promise to try to be original; I will blog on some random things (who doesn't?); I will discuss religion, mostly with regards to its relationship with science, but also other topics; and I will possibly post some creative writing too.
I hope you enjoy and I hope I stick to my plan.