Bucerotidae from the Miocene of Uganda (1 Viewer)

[Fred Ruhe]

Ségolène Riamon, Martin Pickford, Brigitte Senut & Antoine Louchart, 2020

Bucerotidae from the early Miocene of Napak, Uganda (East Africa): The earliest hornbill with a modern‐type beak

Ibis. in press. doi:10.1111/ibi.12907

Abstract: https://onlinelibrary.wiley.com/doi/10.1111/ibi.12907

Hornbills (Bucorvidae and Bucerotidae) are among the most recognizable groups of birds. Their large, curved beak topped by a casque is their most obvious feature. Here, we describe the earliest fossil of a hornbill and more precisely a Bucerotidae, from the early Miocene of Napak. This fossil is a proximal part of a maxilla that can be tentatively assigned to the genus Tockus and which attests to an ancient evolutionary origin of this particular beak shape. The new fossil, as well as several postcranial bones, represent the earliest record of the Bucerotidae dated to about 19 million years ago, and can serve as a calibration point in future molecular phylogenies.

Enjoy,

Fred

 

[Fred Ruhe]

Systematic palaeontology

Order Bucerotiformes Fürbringer, 1888
Family Bucerotidae Rafinesque, 1815
Genus Tockus Lesson, 1830

cf. Tockus sp.


Material

The fossil (NAP XII 8’10) was collected during the 2010 field season of the Uganda Palaeontology Expedition (a Franco-Ugandan cooperative project in Palaeontology). The fossil is a fragment of the proximal part of the maxilla. It is comprised of a sedimentary infilling forming an internal mould which is partially covered with bone (Fig. 1). The bone cortex being very thin in some Bucerotidae, particularly the cranial parts, this explains why bone does not cover all of the natural internal mould of the Napak maxilla. All the Napak fossil specimens are curated at the Uganda Museum, Kampala.


Geological context and age

The fossil NAP XII 8’10 was collected from the Napak fossil deposits, located in the Karamoja region in northeastern Uganda. This geological formation consists of volcano-sedimentary strata, which accumulated on the slopes of the Napak volcano. Ash deposition resulted in rapid burial and played a role in fossil mineralization. Tuffs (volcano-sedimentary rocks formed by consolidation of millimetric volcanic projections, under the action of water) often enhance the preservation of fossils (Hay 1986). Two stratigraphic units have been identified in the deposits; the locality NAP XII being situated in the upper unit, the Napak Member which consists of palaeosols developed on subaerial tuffs (Pickford et al. 1986). The Napak strata were dated to the Lower Miocene, 20-18 Ma (Bishop et al. 1969, Pickford 2002, Y. Sawada et al. unpubl. data). Napak fossil sites have yielded many fossils including Hominoidea and a high diversity of the other Mammalia and Mollusca (Bishop et al. 1969, Senut et al. 2000, Gommery et al. 2002, Pickford 2002, Pickford 2004, Musalizi et al. 2009, Bento Da Costa et al. 2019). The site NAP XII is located on the southern side of the volcano, near a ridge line.

Fred

Figure 1.:
Map of the Napak Volcano, Karamoja and different views of the Napak fossil. (A) Position of the fossiliferous localities at Napak from Pickford et al. (2019). The star symbol corresponds to the site where the fossil was collected. (B,D,F,G) Fossil proximal maxilla NAP XII 8’10. (B,D) lateral view. (F) ventral view. (G) dorsal view. In the photos, the bone is a lighter colour than the background matrix. (C,E) Interpretative line drawing with the areas in grey corresponding to the bone. Scale bars, 10 mm.