''Mirarce'' (meaning "wonderful winged messenger") is a genus of enantornithe

bird Birds are a group of warm-blooded vertebrates constituting the class Aves (), characterised by feathers, toothless beaked jaws, the laying of hard-shelled eggs, a high metabolic rate, a four-chambered heart, and a strong yet lightweig ...

from the

Late Cretaceous The Late Cretaceous (100.5–66 Ma) is the younger of two epochs into which the Cretaceous Period is divided in the geologic time scale. Rock strata from this epoch form the Upper Cretaceous Series. The Cretaceous is named after ''creta'', ...

Utah Utah ( , ) is a state in the Mountain West subregion of the Western United States. Utah is a landlocked U.S. state bordered to its east by Colorado, to its northeast by Wyoming, to its north by Idaho, to its south by Arizona, and to it ...

. It contains a single species, ''M. eatoni''.Science News
Mirarce eatoni: Newly-Discovered Cretaceous Bird Lived Among Dinosaurs, Was Strong Flier
November 13, 2018. It was similar in size to modern

turkeys The turkey is a large bird in the genus ''Meleagris'', native to North America. There are two extant turkey species: the wild turkey (''Meleagris gallopavo'') of eastern and central North America and the ocellated turkey (''Meleagris ocellat ...

Discovery

In 1992, in Utah, USA, paleontologist Howard Hutchison discovered fossilized remains of an enantiornithine bird. For a long time they have not been described; they were sometimes figured under the unofficial name of "

Kaiparowits The Paiute Indian Tribe of Utah is a federally recognized tribe of Southern Paiute and Ute Indians in southwestern Utah. Reservation The Paiute Indian Tribe of Utah (PITU) has a reservation composed of ten separate parcels of land, located in fo ...

enantiornithine". The holotype, UCMP 139500, is well preserved in three dimensions. It consists of a partial postcranial skeleton without a skull, including 3 cervical and 2 thoracic vertebrae, a

pygostyle Pygostyle describes a skeletal condition in which the final few caudal vertebrae are fused into a single ossification, supporting the tail feathers and musculature. In modern birds, the rectrices attach to these. The pygostyle is the main compone ...

, a

furcula The (Latin for "little fork") or wishbone is a forked bone found in most birds and some species of non-avian dinosaurs, and is formed by the fusion of the two pink clavicles. In birds, its primary function is in the strengthening of the thoracic ...

, the

xiphoid process The xiphoid process , or xiphisternum or metasternum, is a small cartilaginous process (extension) of the inferior (lower) part of the sternum, which is usually ossified in the adult human. It may also be referred to as the ensiform process. Bo ...

of the

sternum The sternum or breastbone is a long flat bone located in the central part of the chest. It connects to the ribs via cartilage and forms the front of the rib cage, thus helping to protect the heart, lungs, and major blood vessels from injury. Sha ...

, a fragment of the left scapula and a

coracoid A coracoid (from Greek κόραξ, ''koraks'', raven) is a paired bone which is part of the shoulder assembly in all vertebrates except therian mammals (marsupials and placentals). In therian mammals (including humans), a coracoid process is prese ...

, the humerus, ulna, and radius with fragments of the manus, several fused fragments of the pelvic girdle, and some elements of the hind limbs. It is the most complete enantiornithine found in North America. In 2018, the fossil was named and described by a group of paleontologists led by Jesse Atterholt. The generic name is made up of the Latin ''mirus''; beautiful, "for an impressive level of preservation and morphological details," with the addition of the name of Arke ( Ἄρκη \ Arkē ), the winged messenger of the Titans of Greek mythology - "for evidence pointing to an improved vehicle of this kind." The species name ''eatoni'' given in honor of Jeffrey Eaton in recognition of the decades of scientific work done on the Kaiparowits formation and the study of its fossil specimens.

Description

''Mirarce eatoni'' was a large turkey-sized bird. Skeletal morphology indicates that at the time of death, the individual was adult. All the surviving elements of the bones show complete fusion. The bones of the forelimbs deserve special attention. The humerus of the bird is short and strong. The left ulna was preserved as a mineral cast of the internal cavity with several small fragments of fossilized bone surface. Two folded spots preserved on the posterior edge of the bone body are interpreted as quill knobs. These elongated folds are located along the length of the bone. Despite the fact that bone fragments do not allow measuring the size of each tubercle, determining the distance between them or estimating the number of secondary feathers, their very presence on the fossil is a very significant fact, as this is the first time the structure has been found in enantiornithines.

Phylogeny

''Mirarce'' was found to be a member of Avisauridae, close to '' Avisaurus'' itself.

Paleoecology

''Mirarce'' fossils have been found in the

Kaiparowits Formation The Kaiparowits Formation is a sedimentary rock formation found in the Kaiparowits Plateau in Grand Staircase–Escalante National Monument, in the southern part of Utah in the western United States. It is over 2800 feet (850 m) thick, and is ...

of western North America, which dates to the late

Campanian The Campanian is the fifth of six ages of the Late Cretaceous Epoch on the geologic timescale of the International Commission on Stratigraphy (ICS). In chronostratigraphy, it is the fifth of six stages in the Upper Cretaceous Series. Campani ...

age of the

Cretaceous The Cretaceous ( ) is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of ...

References

Late Cretaceous birds of North America Avisaurids Fossil taxa described in 2018 {{paleo-bird-stub