Winter has taken a firm grip on Montana, snow is falling and the birding has slowed as it is the in-between time – fall migrants have long since passed and winter irruptives have not appeared yet. During this time of year, I spend a lot of time inside near the fire thinking about birds and devouring any associated scraps of related information. I began to think about the evolution of birds, and came across some rather intriguing information. Dare I say it is knowledge of epic portions? Do you realize that there were huge birds at one time that soared in the skies and terrorized upon the ground? I mean they were truly gigantic. Some of these species weighed hundreds of pounds, while others possessed house-length wingspans. These birds fascinate me, and I have decided to dedicate a series of posts and (possibly) videos to these great birds of Earth’s past.
The family, Teratornithidae, which persisted from the Miocene through Pleistocene epochs, had wings with such load-bearing properties, that a bird, in all likelihood, could simply spread its wings into the wind and be lifted skyward. They are typically depicted as scavengers that closely resemble modern New World vultures, although we are discovering that the case may be that teratorns were effective predators. These raptors once soared over the expanses of the Americas, and only recently come to the end of evolution’s road.
Imagine roaming across the prairies of Pleistocene era North America, and a cold, black shadow envelops around you. This huge shadow is coming from high above, where a lone Aiolornis incredibilis (largest North American teratorn) soars overhead. Primal fear wells up from the deepest pit of your stomach as you scramble for any scrap of cover. The wings stretch nearly 18 feet from tip to tip as they hold the 50 pound predator airborne. Its huge, flesh-tearing bill slices through the air as it wheels around for one more pass. The eyes pierce the landscape looking for the tell-tale brown lump of the some hapless mammal on the horizon. These food items may have, actually, been alive at the time of their being swallowed whole as the bill morphology and stout legs may indicate it was a hunter rather than a passive scavenger. Although typically illustrated with feather-less heads of today’s vultures (both Old and New World), the crowns of teratorns may have actually been covered with feathers.
By far, the most well-known of the teratorns is Teratornis merriami, a massive raptor with wingspans commonly achieving spans of 12 feet. Teratornis merriami was larger than any existing Andean Condor and double the size of the California Condor, which it was distantly related. This particular teratorn has been excavated from the world famous La Brea Tar Pits, where it is a common fossil. Scavenging may be have been an important part of its diet, which is indicated by all the specimens coming from the tar pits. An unlucky animal would become entrapped by the sticky ooze and succumbed to death in the black goo. A teratorn would happen across the body and proceed to land near it, only to become another victim of the tar pits itself. In geologic terms, this particular teratorn become extinct only a relative blink of the eye ago. As the last Ice Age drew nearer to its inevitable termination, the ecology of North America began to radically change. The climates and habitats that once supported mega-fauna were changing, and that situation coupled with arrival of the ultimate predator, humans, lead to the demise of the mega-fauna. The teratorns were along for this extinction ride as well.
Although North America had its own massive teratorns, the most incredible member of this family that is known to science is the ridiculous Argentavis magnificens, the largest flying bird ever known to exist. All of its fossils were excavated in Argentina. Its wingspan comes in at whopping ~23 feet with an estimated body weight of 150 lb. Imagine a single wide trailer gliding overhead, and you get some sense of the massiveness of Argentavis magnificens. This species was pushing the physical limits of avian flight. It walked the fine line from effective soaring bird and evolutionary disaster. More likely than not, it would use wind-blown perches with considerable drop-offs to attain flight as it leaned out into the void. Its heaviness probably indicates that Argentavis magnificens had a scavenging ecological role rather than the active hunter abilities of its relatives in North America.
Hunter S. Thompson said that “with the right kinds of eyes, one could see the high watermark,” and I would like to think that someday atop some lonely ridgeline, I might just be able to squint my eyes just so and see the shadow of a massive teratorn race across the rocky crags.