''Aiolornis incredibilis'' is an extinct species of

teratorn Teratornithidae is an extinct family of very large birds of prey that lived in North and South America from the Late Oligocene to the Late Pleistocene. They include some of the largest known flying birds. Taxonomy Teratornithidae are related ...

bird from the western

United States The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country primarily located in North America. It consists of 50 states, a federal district, five major unincorporated territorie ...

. Only fragmentary remains have been found, which are dated between the Early

Pliocene The Pliocene ( ; also Pleiocene) is the epoch in the geologic time scale that extends from 5.333 million to 2.58Zanclean The Zanclean is the lowest stage or earliest age on the geologic time scale of the Pliocene. It spans the time between 5.332 ± 0.005 Ma (million years ago) and 3.6 ± 0.005 Ma. It is preceded by the Messinian Age of the Miocene Epoch, and fol ...

) and Late

Pleistocene The Pleistocene ( , often referred to as the ''Ice age'') is the geological Epoch (geology), epoch that lasted from about 2,580,000 to 11,700 years ago, spanning the Earth's most recent period of repeated glaciations. Before a change was fina ...

. First described as ''Teratornis incredibilis'' by Howard in 1952 based on a

cuneiform bone There are three cuneiform ("wedge-shaped") bones in the human foot: * the first or medial cuneiform * the second or intermediate cuneiform, also known as the middle cuneiform * the third or lateral cuneiform They are located between the navicu ...

, the species has been moved to the new genus ''Aiolornis'' by Campbell, Scott and Springer in 1999. The generic name is derived from the

ancient Greek Ancient Greek includes the forms of the Greek language used in ancient Greece and the ancient world from around 1500 BC to 300 BC. It is often roughly divided into the following periods: Mycenaean Greek (), Dark Ages (), the Archaic peri ...

words ''aiolus'' and ''ornis''. Aiolus refers to the Greek god of the wind, and ''ornis'' means "bird". The specific name ''incredibilis'' means ‘incredible’. ''A. incredibilis'' is lesser-known than its close relative, ''Teratornis merriami'', even though ''A. incredibilis'' was significantly larger. It presumably became extinct at the same time as the other

megafauna In terrestrial zoology, the megafauna (from Greek μέγας ''megas'' "large" and New Latin ''fauna'' "animal life") comprises the large or giant animals of an area, habitat, or geological period, extinct and/or extant. The most common threshold ...

in North America.

History of discovery

The first ''Aiolornis'' material, described in 1952, was a

found in Smith Creek Cave, White Pine County, which is located 34 miles north of

Baker A baker is a tradesperson who bakes and sometimes sells breads and other products made of flour by using an oven or other concentrated heat source. The place where a baker works is called a bakery. History Ancient history Since grains ha ...

Nevada Nevada ( ; ) is a U.S. state, state in the Western United States, Western region of the United States. It is bordered by Oregon to the northwest, Idaho to the northeast, California to the west, Arizona to the southeast, and Utah to the east. N ...

. The fossil was found to be from the

Quaternary The Quaternary ( ) is the current and most recent of the three periods of the Cenozoic Era in the geologic time scale of the International Commission on Stratigraphy (ICS). It follows the Neogene Period and spans from 2.58 million years ...

, and similarities with ''Teratornis merriami'' were noted in the description, hence the usage of the name ''T. incredibilis'' in the original description of the bird. The specimen was deemed distinct enough to warrant the naming of a new species based on its sheer size and other differences. The

holotype A holotype is a single physical example (or illustration) of an organism, known to have been used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of several ...

specimen (on which the species is based) is around 40% larger than the same bone in ''T. merriami''. In a redescription published in 1999, the species was moved into its own genus, ''Aiolornis'', as ''A. incredibilis''. Prior to this redescription, four additional specimens had been referred to ''T. incredibilis'', although they were not diagnostic. There is also a lack of certainty on whether all of this material actually belongs to ''Aiolornis'', due to the fragmentary nature of the fossils and the large timespan they represent. The fossils include the proximal end of an

ulna The ulna (''pl''. ulnae or ulnas) is a long bone found in the forearm that stretches from the elbow to the smallest finger, and when in anatomical position, is found on the medial side of the forearm. That is, the ulna is on the same side of t ...

, the distal end of a

radius In classical geometry, a radius ( : radii) of a circle or sphere is any of the line segments from its center to its perimeter, and in more modern usage, it is also their length. The name comes from the latin ''radius'', meaning ray but also the ...

, the fragmentary

proximal Standard anatomical terms of location are used to unambiguously describe the anatomy of animals, including humans. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position pro ...

end of a

carpometacarpus The carpometacarpus is a bone found in the hands of birds. It results from the fusion of the carpal and metacarpal bone, and is essentially a single fused bone between the wrist and the knuckles. It is a smallish bone in most birds, generally flatt ...

, and the

anterior Standard anatomical terms of location are used to unambiguously describe the anatomy of animals, including humans. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position prov ...

portion of a beak. The 1999 paper also refers a new bone to the species, a partial

humerus The humerus (; ) is a long bone in the arm that runs from the shoulder to the elbow. It connects the scapula and the two bones of the lower arm, the radius and ulna, and consists of three sections. The humeral upper extremity consists of a roun ...

(upper arm bone). The specimen was collected at Quintin Lake in April 1993, which is located approximately 1 km northeast of Murrieta, Riverside County, California. It differs from that of ''T. merriami'' in multiple aspects. The many differences between ''A. incredibilis'' and ''T. merriami'' supported the erection of the new genus ''Aiolornis'' for the former.

Description

''Aiolornis'' is classified as a

, and its past affiliation with the much better preserved ''Teratornis'' allows for inferences about its appearance. It is usually depicted as a larger version of ''Teratornis''. ''Aiolornis'' differs from ''Teratornis'' in a number of places, most obvious of which is size. Its wingspan is estimated to have been between 5 and 5.5 meters, and its weight at around 23 kg, which make it one of the largest, if not the largest, flight-capable bird from North America. The holotype material differs from that of ''T. merriami'' in a few key ways. For instance, present on the os carpi ulnare of ''Aiolornis'' is a prominent ridge, which forms the end of the facies articularis ulnaris and extends further beyond this, coming close to the attachment point for the ulno-ulnocarpal ligament. This attachment point is also proportionally longer than the same point in ''Teratornis'', and it protrudes more prominently from the bone. The facies articularis ulnaris is also slightly more concave than that of ''Teratornis'', with the dorsal rim lower than the ventral rim. The partial humerus described in the 1999 paper also differs from that of ''T. merriami'' and that of ''Argentavis magnificens'' in a number of ways, but most prominently in the fact that the facies dorsalis is fairly flat for the length of the attachment of the M. latissimus dorsi, becoming slightly convex near its distal end, and that the ''facies posterioris'' and ''facies dorsalis'' meet at a near right angle, with line of insertion of the ''M. latissimus dorsi'' following a well-defined "corner" of the ''margo anteriodorsalis''.

Classification

''Aiolornis'' is classified within Teratornithidae, which is a family in the order

Cathartiformes The order Cathartiformes of raptors or birds of prey includes the New World vultures and the now-extinct Teratornithidae. These raptors are classified by most taxonomic authorities in the order Accipitriformes (which includes the eagles and hawk ...

. The order also includes the extinct and extant

New World vulture The New World vulture or condor family, Cathartidae, contains seven extant species in five genera. It includes five extant vultures and two extant condors found in warm and temperate areas of the Americas. The "New World" vultures were widespread ...

References

External links

Photo of model at Anza-Borrego desert state park
{{Taxonbar, from=Q15707896 Bird genera Pleistocene birds Pliocene birds Pliocene birds of North America Teratornithidae Pleistocene birds of North America Fossil taxa described in 1999