''Aiolornis incredibilis'' is an extinct species of teratorn bird from the western

United States The United States of America (USA), also known as the United States (U.S.) or America, is a country primarily located in North America. It is a federal republic of 50 U.S. state, states and a federal capital district, Washington, D.C. The 48 ...

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

Pliocene The Pliocene ( ; also Pleiocene) is the epoch (geology), epoch in the geologic time scale that extends from 5.33 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 f ...

) and Late

Pleistocene The Pleistocene ( ; referred to colloquially as the ''ice age, Ice Age'') is the geological epoch (geology), epoch that lasted from to 11,700 years ago, spanning the Earth's most recent period of repeated glaciations. Before a change was fin ...

. First described as ''Teratornis incredibilis'' by Howard in 1952 based on a cuneiform bone, 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 classical antiquity, ancient world from around 1500 BC to 300 BC. It is often roughly divided into the following periods: Mycenaean Greek (), Greek ...

words ''aiolus'' and ''ornis''. Aiolus refers to the Greek god of the wind, and ''ornis'' means "bird". The

specific name Specific name may refer to: * in Database management systems, a system-assigned name that is unique within a particular database In taxonomy, either of these two meanings, each with its own set of rules: * Specific name (botany), the two-part (bino ...

''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 zoology, megafauna (from Ancient Greek, Greek μέγας ''megas'' "large" and Neo-Latin ''fauna'' "animal life") are large animals. The precise definition of the term varies widely, though a common threshold is approximately , this lower en ...

in North America.

History of discovery

The first ''Aiolornis'' material, described in 1952, was a cuneiform bone found in Smith Creek Cave, White Pine County, which is located 34 miles north of

Baker A baker is a tradesperson who baking, bakes and sometimes Sales, 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 histo ...

Nevada Nevada ( ; ) is a landlocked state in the Western United States. It borders Oregon to the northwest, Idaho to the northeast, California to the west, Arizona to the southeast, and Utah to the east. Nevada is the seventh-most extensive, th ...

. 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), as well as the current and most recent of the twelve periods of the ...

, 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 (Latin: ''holotypus'') is a single physical example (or illustration) of an organism used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of s ...

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 or ulnar bone (: ulnae or ulnas) is a long bone in the forearm stretching from the elbow to the wrist. It is on the same side of the forearm as the little finger, running parallel to the Radius (bone), radius, the forearm's other long ...

, the distal end of a

radius In classical geometry, a radius (: radii or radiuses) of a circle or sphere is any of the line segments from its Centre (geometry), center to its perimeter, and in more modern usage, it is also their length. The radius of a regular polygon is th ...

, the fragmentary

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

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 fla ...

, and the

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

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

humerus The humerus (; : humeri) 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 (bone), radius and ulna, and consists of three sections. The humeral upper extrem ...

(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 teratorn, 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 also includes the extinct and extant

New World vulture Cathartidae, known commonly as New World vultures or condors, are a family (biology), family of birds of prey consisting of seven extant species in five genus, genera. It includes five extant vultures and two extant condors found in the Americas. ...

s. Teratornithidae has only been included in a single phylogenetic analysis, published by Steven Emslie in 1988. The analysis was conducted using cranial characters of various taxa within the order

Ciconiiformes Storks are large, long-legged, long-necked wading birds with long, stout bills. They belong to the family Ciconiidae, and make up the order Ciconiiformes . Ciconiiformes previously included a number of other families, such as herons and ibise ...

, with a specific focus on Vulturidae (

Cathartidae Cathartidae, known commonly as New World vultures or condors, are a family of birds of prey consisting of seven extant species in five genera. It includes five extant vultures and two extant condors found in the Americas. They are known as "New W ...

). This analysis included ''Teratornis merriami'' as a representative of Teratornithidae, and found the group to be just outside of Vulturidae.

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