Laelaps

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Scotland did not have much to offer 19-year-old Andrew Geddes Bain. Both his parents had died when he was a child, and even though he was educated his job prospects were few. When his uncle, Lieutenant Colonel William Geddes, left for South Africa in 1816 young Andrew decided to go with him to the British empire’s southern frontier.

Once he arrived there, Bain found work where he could. He worked as a saddler, an explorer, an ivory trader, a soldier, and a road-builder, but in 1837 Bain read a book that would inspire him to look a little bit closer at the rugged landscape around him. That book was Charles Lyell’s influential Principles of Geology.

Just like young Charles Darwin, Bain was smitten with Lyell’s work. It allowed him to see the traces of lost worlds right beneath his feet, and his job as a road builder gave him the perfect opportunity to see in the field what Lyell had described in print. Bain’s newfound interest would prove to be a boon to British scientists back home.

While he was searching the dusty, shrub-flecked landscape of the Karoo desert for fossils one day in 1838, Bain discovered a skull unlike any he had seen before. The creature had a short, turtle-like head complete with a beak, but instead of being toothless it possessed two large tusks that jutted down from the upper jaw. It was a fantastic find, and its relatively good state of preservation made it all the more spectacular. Many fossils from the Karoo were crushed, distorted, extremely fragile, and encased in nearly impenetrable sandstone.

Bain said the skull represented a “bidental” animal, but he did not have the background in anatomy to fully comprehend what he had found. To find out, Bain sent the skull to the Geological Society in England in 1844. The London academics were astonished. Bain’s “bidental” creature was not quite like any other known animal, living or fossil, and the Society sent Bain a £20 reward for his “judicious course” of action. Encouraged by the warm reception of the distant scholars, Bain started shipping more fossils and acted as the “man in the field” for London’s cadre of professional naturalists.

While the rest of Bain’s fossils were en route South Africa, the task of describing the enigmatic skull fell to England’s most eminent comparative anatomist, Richard Owen. Clearly the skull had belonged to some kind of reptile, Owen surmised, but it did not correspond to any type of lizard, crocodile, or lizard that he knew of. This creature, which he named Dicynodon for the two enlarged canines sticking out from the upper jaw, was a chimera the consisted of both mammalian and reptilian parts. It straddled what had thought to have been a well-defined boundary in the order of life, and the ever-pious Owen could not help but think that the bizarre nature of Dicynodon spoke to “a power transcending the trammels of the scientific system.”

The discovery of Dicynodon was just the beginning. South Africa proved to be unexpectedly fossil-rich, and Owen became the unofficial interpreter of the colony’s prehistory. By the late 1850′s Owen had seemingly everyone who ventured into the field, from laborers to visiting politicians, funneling fossils back to England for him to scrutinize. Even Prince Alfred, who visited South Africa in 1860, returned home with two more Dicynodon skulls for Owen to add to his ever-expanding collection. His annoyance at the hubbub over Darwin’s evolutionary theory aside, Owen has at the height of his scientific power.

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As it turned out, Dicynodon was not an isolated anomaly. The fossil flood inundated Owen with a collection of “reptilian” skulls that also possessed mammalian traits, like differentiated kinds of teeth in different parts of the jaw. Rather than deny these strange amalgamations of features Owen celebrated them by giving the new forms names like Galesaurus (“weasel reptile”), Cynochampsa (“dog crocodile”, called Diademodon today), Lycosaurus (“wolf reptile”, see image to the left), and Tigrisuchus (“tiger crocodile”). By Owen’s estimate these fossils showed that sometime in the distant past reptiles began to converge of the mammal body type, an interpretation that was difficult for other naturalists to challenge.

Owen had a corner on the Karoo fossil market. If a significant specimen was found, chances were it was sent right to him, and so pervading was his reach that paleontologists who later visited the Karoo lamented that almost all the best specimens were already in Owen’s stores. This was made all the more intolerable by Owen’s jealous love for “his” fossils. Owen was a powerful and ornery figure who full-well knew his own brilliance. He would be the one to translate the secrets of prehistoric South Africa, and anyone who wanted to use specimens sent to Owen would require the blessing of the imposing figure.

Despite his rejection of Darwin’s particular theory of evolution by natural selection, however, Owen did not entirely reject the idea that the Karoo fossils might have something to say about evolution. They were clearly approaching the mammalian “grade” and therefore, in Owen’s view, superior to any of the dim-witted, cold-blooded reptiles that inhabited the modern world. Why this “upward” evolutionary trend was reversed, though, Owen could not say, nor could he square Darwin’s or Lamarck’s theories of evolution with the degenerative trend he saw.

Today, however, we know that Dicynodon and the other “mammal-like reptiles” Owen described were not reptiles at all. They were synapsids from late Permian and early Triassic (or between about 265 to 250 million years old), creatures that lived long after the ancestors of modern reptiles split off from the rest of the amniote evolutionary tree but before the first “true” mammals evolved. While Dicynodon and its kin may have looked reptilian, they were truly more closely related to mammals, and they fit snugly within the evolutionary framework that Darwin proposed.

Comments

  1. #1 Greg Laden
    September 24, 2009

    Nice writeup

    These are cool fossils. I’ve had the opportunity to see and handle some at the exTransvaal Museum, where my friend Francais Thackeray has been studying them.

  2. #2 Pierce R. Butler
    September 24, 2009

    Aw shucks. On reading the headline, I had hopes this post was about the vice-president.

    *sigh*

  3. #3 Mike Keesey
    September 24, 2009

    I am hoping that in my lifetime the term “stem-mammals” completely eclipses “mammal-like reptiles”.

  4. #4 Vasha
    September 24, 2009

    Nitpick: you should avoid using the word “chimera” in the sixth paragraph, since nowadays, referring to fossils, that word means a supposed individual erroneously put together from pieces of more than one species.

  5. #5 Laelaps
    September 24, 2009

    Pierce; I am not sure whether having a Dicynodon for vice-president would result in more gaffes or less…

    Mike; Agreed. I am going to be doing my part on that front in an upcoming project. I only used it here to contrast the old understanding with the new one. Details soon.

    Vasha; A fair point, but I think artistic license covers my usage. :) I will try to be more aware of that in the future, though.

  6. #6 Greg Laden
    September 25, 2009

    Vasha: Or, a ghostshark!

  7. #7 johannes
    September 25, 2009

    Pierce; I am not sure whether having a Dicynodon for vice-president would result in more gaffes or less…

    Only one heart-attack away from the end of cynodont rule ;-)