Tuesday, July 26, 2016

[PaleoOrnithology • 2016] Mioneophron longirostris • A New Old World Vulture from the late Miocene of China sheds light on Neogene shifts in the past Diversity and Distribution of the Gypaetinae

Mioneophron longirostris 
 Li, Clarke, Zhou & Deng, 2016
 DOI: 10.1642/AUK-15-240.1 

Neogene fossils of Old World vultures (Aegypiinae and Gypaetinae) are known from both Old World and New World records. There are no extant Old World vultures in the Americas today, although a large diversity of Gypaetinae is known from Miocene to late Pleistocene records. Despite a comparatively large number of North American gypaetine fossils, complete specimens have rarely been reported from Eurasia and Africa. We describe the exceptional skeleton of a new gypaetine vulture from the late Miocene deposits of the Linxia Basin in northwestern China. The specimen is the oldest record of Gypaetinae from Eurasia or Africa. A reexamination of the geographic and temporal distribution of most Old World vultures from Neogene deposits indicates a diverse radiation, coincident with early- to mid-Miocene grassland expansion for Gypaetinae. Although the diversification of Aegypiinae has been linked to the transition from C3 to C4 grassland, Gypaetinae diversification predates that transition in both North America and Asia. A shift in the known latitudinal distribution is also noted. Neogene records of Old World vultures are found primarily in mid- and high-latitude regions of North America and Eurasia as well as in the middle and low latitudes of Eurasia and Africa. With very few records in the middle to late Miocene, a latitudinal distribution similar to that of extant species is first seen in the early Pliocene. The new fossil provides further temporal constraints on avian subclade diversification. It is also consistent with an emerging pattern of profound recent shifts in avian diversity and distribution more generally.

Keywords: extinction, fossil, Gypaetinae, Linxia, Old World vulture


AVES Linnaeus, 1758
ACCIPITRIDAE Vieillot, 1816
Gypaetinae Vieillot, 1816

Mioneophron longirostris, gen. et sp. nov. (Figures 1–4)

Holotype: HMV 1877: A nearly complete skeleton (Figure 1) preserved in yellow-brownish siltstone with carbonate cementation. The proximal right tarsometatarsus and distal left tarsometatarsus have been rearranged after collection (illustrated as dark gray regions in Figure 1). Some bones have been fabricated and others recomposed in a wrong position (e.g., pedal digits). The left distal humerus is reconstructed with plaster and the proximal right tarsometatarsus appears to be a proximal tibiotarsal fragment, without any definite clue to its affinity. The position of the hallux opposite of where it should be in the right pes is one indication that the pedal digits were recomposed.

Locality and horizon: The holotype was collected from Baihua Village, Zhuangheji Town, Guanghe County, in Gansu Province, northwestern China (Figure 5: star), in the Upper Miocene Liushu Formation, Linxia Basin. All currently known fossil birds in the Linxia Basin are from the same unit, which is characterized by a distinct matrix lithology (Deng et al. 2013). The bird fossils have been acquired from local farmers and collectors. The holotype specimen is archived in the Hezheng Paleozoological Museum, Gansu Province, China.

Etymology: The genus name, “Mioneophron,” references the Miocene age and the proposed affinity of the new specimen with Neophron. The adjectival species name, longirostris, references an elongate rostrum.

Diagnosis: Mioneophron longirostris can be differentiated from all other gypaetine and aegypiine vultures by the unique presence of a combination of the following features: a long and narrow rostrum with small oval-shaped nares (Figure 1), a well-projected and globose humeral head and distinct caudal ridge on the margin of the deltopectoral crest, a much longer ulna than tibiotarsus (ratio = 1.45), and a distinct groove between the dorsal iliac ridges (Figure 2).

Systematic placement of the new species

The new species shares several features with gypaetine vultures, including the relatively weakly projected transverse nuchal crest on the basicranium as well as the broad humeral deltopectoral crest. It also has fewer cervical vertebrae (14, vs. 15–17 in Aegypiinae; Rich 1980, Holdaway 1994), and the postacetabular ilia are incompletely fused to the sacrum (Figure 4; Jollie 1976, 1977a, 1977b, 1977c), both of which are features consistent with gypaetine vultures. However, Mioneophron has a wider deltopectoral crest than aegypiine vultures, a deeper humeral capital incisure, a gentler bicipital crest, and a shorter mandibular symphysis. Furthermore, unlike in aegypiine vultures, no pneumatic foramina are present on the proximal surface of the pisiform process of the carpometacarpus (Manegold et al. 2014). The medial hypotarsal crest is slightly higher than that of the lateral one in the cranial view, whereas in Aegypius, Trigonoceps, and Torgos the 2 hypotarsal crests are very similar in height.

 Zhiheng Li, Julia A. Clarke, Zhonghe Zhou and Tao Deng. 2016. A New Old World Vulture from the late Miocene of China sheds light on Neogene shifts in the past diversity and distribution of the Gypaetinae.  The Auk. 133(4); 615-625. DOI: 10.1642/AUK-15-240.1

RESUMEN: Los fósiles del Neógeno de buitres del Viejo Mundo (Aegypiinae y Gypaetinae) se conocen de localidades en el Viejo y el Nuevo Mundo. Actualmente no existen buitres del Viejo Mundo en las Américas, aunque se conoce una gran diversidad de Gypaetinae a partir de registros del Mioceno al Pleistoceno tardío. A pesar de un número comparativamente grande de fósiles de Gypaetinae en Norte América, los reportes de especímenes completos en Eurasia y África son raros. En este trabajo describimos el esqueleto excepcional de un nuevo buitre gypaetino de los depósitos del Mioceno tardío de la cuenca Linxia en el noreste de China. El espécimen es el registro más viejo de Gypaetinae de Eurasia o África. La reevaluación de la distribución geográfica y temporal de la mayoría de los buitres del Viejo Mundo en depósitos del Neógeno indica una radiación diversa que coincide con la expansión de las praderas durante el Mioceno temprano a medio. Aunque la diversificación de Aegypiinae ha sido relacionada con la transición de praderas C3 a praderas C4, la diversificación de Gypaetinae precede esa transición en Norte América y Asia. También notamos un cambio en la distribución latitudinal. Los registros del Neógeno de buitres del Viejo Mundo se encuentran principalmente en regiones de latitud media y alta en Norte América y Eurasia, y también en regiones de latitud media y baja en Eurasia y África. Con tan pocos registros en el Mioceno medio a tardío, una distribución latitudinal similar a la de las especies actuales sólo se ve inicialmente en el Plioceno temprano. El nuevo fósil impone más restricciones temporales en la diversificación de subclados de aves. También es consistente con un patrón emergente de cambios profundos recientes en la diversidad y distribución de las aves en general.

Palabras clave: buitres del Viejo Mundo, extinción, fósil, Gypaetinae, Linxia