Teratornis
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| Teratornis merriami Fossil range: Early Pleistocene - Late Pleistocene |
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 Teratornis
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Fossil
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| Teratornis merriami L. H. Miller, 1909 |
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Pleistogyps rex L. H. Miller, 1910 |
Teratornis merriami (Merriam's Teratorn) was a huge North American teratorn, with a wingspan of around 3.5 to 3.8 meters (11 to 12 feet), a wing area of 17.5 square meters, standing an estimated 75 cm tall and weighing about 15 kg. It was somewhat larger than the extant Andean Condor and nearly two times as heavy as the Californian Condor. A closely related species, the Aiolornis, was about 40% larger and lived at an earlier time; it was formerly known as Teratornis incredibilis, but is distinct enough to be placed in its own genus.
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[edit] Physical characteristics
T. merriami is the best-known of the teratorns. A large number of fossil and subfossil bones, representing more than 100 individuals, have been found in locations in California, southern Nevada, Arizona, and Florida, though most are from the Californian La Brea Tar Pits. All remains but one Early Pleistocene partial skeleton from the Leisey Shell Pit near Charlotte Harbor, Florida (which may represent a different species or a subspecies) date from the Late Pleistocene, with the youngest remains dating from the Pleistocene-Holocene boundary.
The finger bones are fused as in all modern birds; however, part of the index finger forms a shelf which aided in bearing the load of long and stout primaries, which enabled the bird to utilize strong upcurrents. The legs were similar to an Andean Condor's, but stouter, and the feet were able to hold prey items for tearing off pieces, but not able to exert a very forceful grip such as in birds of prey. Its wing loading was not much larger than a Californian Condor's, and Merriam's Teratorn should have been able to take off by simply jumping and beating its wings under most circumstances. (Campbell & Tonni, 1983). Indeed, it seems to have been better-adapted for that than for utilizing a short run into the wind from an elevated location as condors do, as its legs are proportionally smaller and its stride less than in these (Fisher, 1945).
[edit] Ecology and extinction
T. merriami generally lived in a manner similar to modern-day condors, although its larger bill suggests that it was a more active predator. Smaller prey up to the size of a small rabbit would probably be swallowed more or less whole, while carrion would have been fed on in a manner similar to condors or vultures. The large number of finds in the La Brea Tar Pits were usually considered to be from teratorns which were attracted by Pleistocene megafauna that became stuck in the viscous asphalt trying to drink from pools of water that gathered on the surface and died, with the teratorns subsequently falling victim to the sticky deposits too. Merriam's Teratorn probably played an important role in opening up the body cavities of carcasses for smaller birds like eagles and ravens which are also known to have frequented the locality, as mammalian predators, being unable to fly, could hardly reach most carcasses without getting mired in the asphalt themselves.
However, there were also true vultures present in the area at that time, and unlike them, T. merriami was also well-adapted to hunt for smaller animals which are also known to have utilized the pools. Analysis of the skull and bill shapes suggests that fish may have constituted a major part of its diet (Hertel, 1995). Taking into account the strong legs, stout claws, and a gripping power not quite as developed as in eagles, this makes it rather likely that Merriam's Teratorn would have hunted for aquatic prey in the manner of an osprey, which also provides a neat explanation as to how such large numbers of powerful, well-flying birds could have become stuck in the asphalt.
The species probably became extinct as the climatic shifts at the end of the last ice age led to widespread ecological alterations and prey scarcity, exacerbated by human hunting and increasing influence on habitat; generally , most large land animals disappeared and the altered precipitation patterns seriously affected populations of aquatic vertebrates. Despite being a better hunter than the Californian Condor, it still was inferior as a predator of small prey to hawks and eagles. The higher population density and more flexible diet of the condor probably ensured that it survived, while T. merriami did not. Recent isotopic studies suggest that the California Condor was able to survive the extinction of the megafauna because it also scavenged dead marine mammals off the Pacific Coast. The terratorn relied more heavily upon the carrion of land mammals and therefore could not survive their extinction.
[edit] Interaction with humans
T. merriami is the largest species of flying bird that was encountered alive by man. The initial reaction was probably one of awe, but as bones found in Amerindian middens[citation needed] show, the bird was not considered sacred enough not to be hunted. On the other hand, the species was probably large and possibly predatory enough to consider human infants food, albeit certainly not on a regular basis. After the species became extinct, its memory perhaps persisted to form a major foundation for the Thunderbird myths. When the largest flying bird ever seen alive by human beings was no more, it was transformed into a supernatural creature.[citation needed]
[edit] References
- Campbell, Kenneth E. Jr. & Tonni, E. P. (1983): Size and locomotion in teratorns. Auk 100(2): 390-403 PDF fulltext
- Fisher, Harvey I. (1945): Locomotion in the Fossil Vulture Teratornis. American Midland Naturalist 33(3): 725-742. doi:10.2307/2421186 (First page image)
- Hertel, Fritz (1995): Ecomorphological indicators of feeding behavior in Recent and fossil raptors. Auk 112(4): 890-903. PDF fulltext
- Miller, Loye H. (1909): Teratornis, a new avian genus from Rancho La Brea. University of California Publications, Bulletin of the Department of Geology 5: 305-317.
