Tuesday, November 5, 2013

A giant fossil platypus

Artist's reconstruction of the giant platypus Obdurodon
tharalkooschild
.  The tooth on which it was based is
shown in the upper-right corner.  Reconstruction and
illustration by Peter Schouten.  Image source.
I can't help but laugh about the fact that one of the top science news stories today is about a giant platypus.  I wasn't kidding when I said yesterday that there was not much news to report on.  Apparently, the latest issue of the Journal of Vertebrate Paleontology reports the find of a tooth belonging to a huge ancient platypus in Australia, termed Obdurodon tharalkooschild (JVP requires a subscription to read, but you can read the summaries at Fox News or Science Daily).

The poor platypus has been the subject of many jokes, appearing to be a cross between a duck and several rodent- or weasel-like mammals.  Some people facetiously claim that it was a mistake made by God during the creation process, while others think it should be the final proof that shuts down the evolutionary tree of life.  How is the platypus viewed scientifically?

First, let's address the question of reconstructing an entire animal from a tooth.  This is done surprisingly often in paleontology, because single bones are much more common than complete skeletons.  Teeth are particularly hard and resistant to weathering, so they are often the only remnants left of ancient creatures.  How accurate are such reconstructions, though?  If we are dealing with an entirely unknown animal, then much of it is left to the imagination.  Typically, a new bone is compared to the bones of known animals, and the creature in question is assumed to be somewhat similar to its closest counterpart.  This is why one of the first dinosaurs discovered, Iguanadon, was originally depicted as a gigantic iguana, because its tooth was similar to that of an iguana's.  It wasn't until many complete skeletons were found in a coal mine in Belgium that scientists developed a more complete and accurate picture of what this and other dinosaurs really looked like.  In the case of Obdurodon, our giant platypus, the tooth that was found closely resembles those of other fossil platypi, the skeletons of which resemble the modern platypus, though the modern one does not have any teeth.  It is assumed that tooth and body size are approximately proportional, so the size of the new tooth implies that the creature it belonged to was about a meter long.  Teeth tend to be very useful for diagnosing mammals, so there is little doubt that Obdurodon belongs in the platypus family, but there is currently no way to know for sure how similar it actually looked to the modern platypus.

Now, how does the platypus fit into the creationist and evolutionary models?  It is generally recognized as a mammal, yet it has a ducklike bill and lays eggs.  This odd combination of characters is not troublesome for creationists, who believe that the platypus was specially created by God and is not "related" to any other creatures.  It was apparently created with teeth, but over time those were lost.  Evolutionists are not particularly troubled by the platypus either, however.  Platypi are classified in a group of mammals called "monotremes," the only living members of which are the platypus and echidna.  It is believed that monotremes split from other mammals very early in the mammalian line, before the reptilian egg-laying attribute was lost.  The other mammals then evolved to give rise to marsupials and placental mammals (Some scientists believe that monotremes split from marsupials after the marsupial-placental divide, but most hold to the former model).  The resemblance of the bill to that of a duck is attributed to convergent evolution, the idea that an anatomical structure will evolve separately in unrelated creatures if it is effective in its use.

The fossil record of monotremes is quite sparse.  Interestingly, most monotreme fossils are extremely recent, with only a handful found in Mesozoic rocks (attributed to the time of the dinosaurs in the evolutionary timeline, and considered late-stage Flood deposits by creationists).  Mammals are thought to have evolved in the Late Triassic, around 225 million years ago, at about the same time as the first dinosaurs.  If monotremes arose early in mammalian evolution, they should appear in the fossil record around this time, yet the first widely-recognized monotreme does not appear until the Cretaceous, ~115 million years later.  Even then, there are only a few scattered specimens before the Cenozoic, when mammals took their turn after the extinction of the dinosaurs.

Yet, if monotremes and other mammals were created at the same time as dinosaurs, according to creationists, why are they so sparse in the Mesozoic rocks?  To be honest, I have not yet heard a completely satisfactory answer to this question, though there are a few hypotheses:

  1. Mammals are generally faster and smarter than reptiles, so they were able to escape the floodwaters longer than dinosaurs and were therefore buried later.  I do not particularly like this explanation, because there is little evidence to suggest that mammals are so much faster and smarter than reptiles as to lead to such definitive separation in the fossil record.  Plus, there are plenty of slow and stupid mammals, and plenty of dinosaurs seem to have been quick and intelligent.  I find this explanation very unconvincing.
  2. Mammals occupied higher elevations in the pre-Flood world, while dinosaurs occupied lower elevations near shorelines, so dinosaurs were buried first, and mammal remains were either never buried or quickly eroded from the top of the stratigraphic column.  This explanation, I admit, comes largely from my own mind, adapted from similar explanations from others.  Dinosaurs are frequently found in deposits that are interpreted as shorelines or floodplains, which typically occur in low-lying areas.  Mammals, meanwhile seem to be more suited to higher, cooler climates, given their fur and warm-bloodedness.  It stands to reason, then, that each group had their own geographical niche in the pre-Flood ecosystem.  The dinosaurs were therefore hit first by the floodwaters and buried with only a few small mammals, and the larger mammals were either not buried (but still died) or were buried briefly and eroded by the receding waters.  Today's mammal-bearing rocks are generally ascribed to post-Flood events by creationists, though it is not completely out of the question that they were the last layers to be deposited in the Flood itself.
  3. Mammals, along with angiosperms (flowering plants), comprised an entirely separate ecosystem on a separate continent that was lost during the Flood or that no longer bears accessible fossiliferous rocks.  This idea was proposed to me by a creationist paleontologist (whose name escapes me at the moment) at a creation conference in Rapid City.  While it seems quite radical at first, I believe this hypothesis merits consideration.  What if the Garden of Eden was on this continent, and it was quite literally destroyed during the Flood, sucked down into the mantle, possibly?  Or what if it is buried under the Antarctic ice sheet?
As I said, none of these explanations satisfactorily answer the question, in my opinion.  However, questions will always abound.  The more we learn, the less we realize we know.  There seems to be an infinite amount of information to learn about creation, but that should be expected from an infinite Creator.

1 comment:

  1. Today I learned:
    Knuckles, Sonic the Hedgehog's foe/friend, is an echidna.

    ReplyDelete