TAXONOMY & NOMENCLATURE * *How Do We Know This? Like living animals, fossil remains of once-living animals
classified and grouped according to their relationships
each other and to their ancestors.
(Campbell et al 1999)(Campbell & Tonni 1980, 1983) (Campbell & Tonni 1980) (Chatterjee et al 2007) (Howard 1963, 1972) (Miller 1909)
Describer (Date):Teratornis merriami (Miller 1909) Ailornis incredibilis (Howard 1952, new combination by Campbell) Cathartornis gracilis (Miller 1910) Argentavis magnificens (Campbell & Toni 1980)
Teratorns originally placed in family of Vultures (Cathartidae) because of hooked beak and condor-like skeleton of Teratornis merriami (Miller 1909)
In 1981 and 1983 Campbell suggested T. merriami was not a vulture or a scavenger, but an active predator capable of hunting and walking with features common to both storks and vultures as well as unique features of neither group.
In 1999 Campbell revised the taxonomy of T. incredibilis and placed it in a new genus, Ailornis.
In 2007 paleontologists said Argentavis and other teratorns are related to storks (Ciconiidae) and New World vultures (Vulturidae) and belonged in the order Ciconiiformes with other long-legged wading/walking/soaring birds. (Chatterjee et al 2007)
Much current discussion about which modern and fossil birds belong in this order, considering recent genetic studies.
An ancestral teratorn (Argentavis magnificens) known from Miocene rocks (about 6 million years old) in Argentina (Campbell & Tonni 1980)
Teratorns probably originated in South America.
Ailornis incredibilis (known previously as Teratornis incredibilis) fossils found from 3-4 million years ago to about 20,000 years ago; this long time span suggests Ailornis is actually more than one species.
(Campbell et al 1999)
Cathartornis gracilis is known from only two leg bones at Late Pleistocene La Brea deposits; it may not be distinct from T. merriami. (Campbell & Tonni 1983)
Oldest North American records for T. merriami are from the Anza-Borrego Desert in California from Pliocene and Pleistocene rocks. (Howard 1963, 1972).
Also over 100 specimens from Late Pleistocene California's Rancho La Brea asphalt deposits.
No members of the teratorn family survived Pleistocene times; they have been extinct for at least 10,000 years.
DISTRIBUTION & HABITAT * *How Do We Know This? Scientists use knowledge of the earth's rocks, global plate tectonic movements,
and the chemical process of fossilization
to make sense of fossil distribution patterns and ancient habitats.
(Campbell & Tonni 1981) (Chatterjee et al 2007)(Palmqvist & Vizcaíno 2003) (Rhys 1980)
Argentavis magnificens known from central and northwestern Argentina.
T. merriami known from about 105 specimens from Rancho La Brea,California, plus Florida, New Mexico,
Cathartornisgracilis known only from Rancho La Brea, California
Ailornis incredibilis found in southern California and Nevada
Argentavis: This bird, the largest of the teratorns may have depended on updrafts and thermals to stay aloft (Chatterjee et al 207)
Argentavis may have evolved in South America along with the evolution of open grasslands and the rise of the Andes.(Rhys 1980)
(Chatterjee et al 2007)
Habitat may have been a large plain like southern Patagonia today (savanna with distinct dry season) (Campbell & Tonni 1981) with areas of mountain ranges or high ground for nesting and taking off. (Palmqvist & Vizcaíno 2003) (Chatterjee et al 2007)
Home range estimated at 542 km sq
(Palmqvist & Vizcaíno 2003)
Teratornis merriami occupied habitats that were less open, with coastal shrub and woodlands in California
PHYSICAL CHARACTERISTICS* *How Do We Know This? Careful study of fossil bone or tooth anatomy yields much exact information
about placement and strength of muscles, tendons, ligaments, nerves, and blood vessels.
In rare cases, skin and hair impressions or actual skin or hair is preserved.
Body weight is more difficult to gauge because fat leaves no impression on the skeleton.
(Chatterjee et al 2007) (Campbell & Tonni 1983) (Campbell et al 1999)
Estimated Body Weight:T. merriami 13.7kg (30.2 lb) (Campbell & Tonni 1983). Slightly heavier than living California condors Ailornis incredibilis 23 kg (50 lb)
Argentavis magnificens 70 kg (154 lb); 7 times
heavier than California condor (Chatterjee et al 2007))
Estimated Wingspan:T. merriami 3.5-4m (11.5-13.1 ft) Ailornis incredibilis: 5.0-5.5 m (16.4-18 ft)
Argentavis magnificens 6-8 m (19.7-26.3 ft)
Large soaring predatory birds with stout legs, long toes, with the last digits moderately curved and blunt (not used for holding prey as in hawks or eagles). Pelvis resembles a stork's; they were adept walkers on the ground, but not good runners. (Campbell & Tonni 1983)
Other Physical Characteristics
Wing bones have features of condors and also pelicans and Bald Eagles (Campbell & Tonni 1983) (Hertel 1995).
Sutures between some skull bones are not tightly fused; this may help teratorns swallow large and struggling prey (Campbell & Tonni 1981).
This is one reason paleontologists do not think they had scavenging habits.
A sharp hooked bill known for T. merriami; skull of Argentavis not known.
BEHAVIOR & ECOLOGY* *How Do We Know This? Since direct observation of a fossil animal's behavior isn't possible, paleontologists
comparison and contrast with living animals for guidance. Tracks can sometimes
reveal further clues.
(Campbell & Tonni 1981) (Chatterjee et al 2007) (Palmqvist & Vizcaíno 2003)
Teratornis merriami capable of walking well and stalking but not running (Campbell & Tonni 1981)
More adapted for moving on the ground than condors. (Campbell & Tonni 1981)
Of all the teratorns, Argentavis probably was the least agile because of its very large size.
Argentavis probably behaved more like vultures than the other teratorns (Palmqvist & Vizcaíno 2003)
Probably was too large to be a strong flyer but could soar and glide efficiently at speeds of 67 km/h (42 mph)(Chatterjee et al 2007)
Estimated dives of 241 km/h (150 mph) (Chatterjee et al 2007)
Vultures, for comparison, soar about 61km/h (38 mph)
Argentavis would have had trouble taking off on level ground because of its great size
By running down a slope into a very slight headwind, takeoff possible (using albatrosses' technique) (Chatterjee et al 2007)
Couldn't take off by running on level ground - not enough wing power.
Teratornis merriami would have had a soaring/cruising speed of 57 km/h (
35 mph) (Chatterjee et al 2007)
Hertel (1995) observed that there were many more species of Pleistocene daytime raptors in western North America than are found today, and there were twice as many scavenger birds as today,
There numbers possible because of greater diversity and abundance of prey species
DIET & FEEDING* *How Do We Know This? Clues to fossil mammals' diets come from teeth,skull shape,
from fossil dung and gut contents, from
lab analysis of oxygen
in bone and teeth,
looking at diets of similar modern animals.
(Campbell & Tonni 1981,1983) (Chatterjee et al 2007) (Hertel 1995)(Palmqvist & Vizcaíno 2003)
Teratorns were predatory carnivores (Campbell & Tonni 1981) and possibly opportunistic scavengers (Hertel 1995)
Probably hunted in daytime, using thermals for flight. (Chatterjee et al 2007)
Possible killing techniques suggested by one researcher include flicking prey sharply to the ground.(Campbell & Tonni 1981).
The beak of T. merriami was not strong enough to kill by biting. (Campbell & Tonni 1981).
The huge teratorn Argentavis could kill sizeable prey with its large beak.(Chatterjee et al 2007)
A study by Hertel (1995) suggested teratorns were fish-eaters, specializing in plucking fish from the surface of water with their beaks, although Campbell (1981) says they weren't agile enough to capture aquatic prey on the wing.
Argentavis magnificens could have swallowed hare-sized prey in one gulp. (Campbell & Tonni 1983)
Estimated to have eaten 5-10 kg of meat daily (Palmqvist & Vizcaíno 2003)
Armadillos, rodent-like mammals, possums, and capybara may have been food for this large teratorn.
Both Argentavis and Teratornis merriami had similar feeding mechanisms (Campbell 1981)
T. merriami prey hypothesized to be lizards, snakes, small and medium-sized mammals, birds. (Campbell & Tonni 1983)
T. merriami grasped prey with hooked bill
Very mobile (kinetic) skull bones helped teratorns hold and swallow struggling prey without damage to themselves.
REPRODUCTION & DEVELOPMENT * *How do We Know This? Isotope studies of elements present in fossil bones
about timing of reproductive stresses.
Clues to stages of development come from tooth
replacement patterns in mammals and closure of sutures
in vertebrate skull and limb bones.
(Palmqvist & Vizcaíno 2003)
Argentavis estimates calculated by comparison with similar sized modern raptors with long breeding cycles and small clutches.
(Palmqvist & Vizcaíno 2003)
Breeding every two years
Incubation of eggs: 64 days
One or two hatchlings every two years
Nestlings for 230 days
Long period of time to reach maturity, like albatross or frigate birds - at least 10 years.
The largest teratorns probably had a long life span, due to their large size. (Palmqvist & Vizcaíno 2003)
Causes of death not known but assumed to be lack of food, disease, parasites, predation by other raptors or owls, and accidents, much like modern birds of prey (Palmqvist & Vizcaíno 2003)
DISEASES AND PATHOLOGY*
*How do We Know This? Abnormalities in fossil bones may show
evidence of arthritis, cancer, nutritional stress, fractures and more.
Important Web Resources (including where to view fossils in museums):