Late Oligocene mousebird converges on parrots in skull morphology

Abstract

A new fossil stem group representative of Coliiformes (mousebirds) with a remarkable skull morphology is described from the late Oligocene of Germany. Oligocolius psittacocephalon sp. nov. for the first time preserves the skull of a post‐Eocene fossil mousebird. This exhibits a combination of skull features unknown from any other bird and converges on the skull of parrots in that the beak is separated from the cranium by a marked nasofrontal hinge and in that the interorbital part of the frontal bones is very wide. In addition, the mandible of the new species exhibits long retroarticular processes, which are unexpected because unlike in other coliiform birds exhibiting this feature, the short beak was probably not used for probing in substrate. It is hypothesized that the retroarticular processes of O. psittacocephalon instead served for a particular wide and forceful opening of the beak. Eight large fruit stones are situated in the area of the digestive tract of the new species. Preservation of most of these in a well‐delimited cluster in the region of the upper oesophagus suggests that, unlike in modern mousebirds, O. psittacocephalon had a crop. The new fossil shows that late Oligocene European stem group Coliiformes significantly differed from their extant relatives in morphology and probably also in feeding ecology.

A new specimen of the Early Eocene Masillacolius brevidactylus and its implications for the evolution of feeding specializations in mousebirds (Coliiformes)

“…2B) forms a marked shelf-like lip as in extant mousebirds. Unlike in living mousebirds and Oligocolius (Mayr, 2013), however, an eminentia articularis is absent and further unlike in extant Coliiformes, the processus lateralis does not form a marked, dorsally directed process.…”

“…Such processes are now known from the Early Eocene Chascacocolius oscitans, Chascacocolius cacicirostris, and M. brevidactylus, and from the Late Oligocene Oligocolius brevitarsus (Houde and Olson, 1992;Mayr, 2005Mayr, , 2013; this study; note that the asterisk symbol designating taxa with known skulls in Mayr, 2013: fig. 5 should have been assigned to Celericolius acriala and not to M. brevidactylus; the scale bar in Mayr, 2013: fig. 1 furthermore denotes 10 mm, and not 5 mm as erroneously stated).…”

“…A phylogenetic analysis was performed based on the character matrix of Mayr (2013), with the same settings as in this latter study. The following six character scorings were added or modified: character 2 (bill approximately one-half of total skull length): scored as present (0) for M. brevidactylus; character 4 (eminentia articularis of quadrate): scored as absent (0) for M. brevidactylus and Sandcoleus copiosus; character 5 (mandible with processus retroarticularis blade-like and elongated to approximately one-sixth of the skull length): scored as present (1) for M. brevidactylus; character 26 (configuration of foramina vascularia proximalia): scored as (0) for M. brevidactylus (two foramina present) and as (2) for Selmes absurdipes (single foramen on lateral side of shaft).…”

“…One of these is represented by the Sandcoleidae (Sandcoleus, Anneavis, Eoglaucidium), which distinctly differ from other stem group Coliiformes in various skeletal features (Houde and Olson, 1992;Mayr, 2009). All non-sandcoleid stem group Coliiformes belong to a clade that also includes the crown group representatives (Ksepka and Clarke, 2010;Mayr, 2009Mayr, , 2013Mayr and Mourer-Chauviré, 2004). These birds are characterized by an elongated and slender tarsometatarsus and a large, shield-like discus pygostyli.…”

Phylogenetically vetted and stratigraphically constrained fossil calibrations within Aves

“…Fossil Record of Coliiformes. A relatively continuous temporal record is now recognized following the first appearance of Coliiformes, with fossils recovered from Early Eocene horizons in the Willwood Formation (early Wasatchian ~54 Ma; Houde and Olson, 1992), the Early Eocene Green River Formation (~51.5 Ma; Houde and Olson, 1992;Ksepka and Clarke, 2010c), Middle Eocene Bridger Formation (~48 Ma; Houde and Olson, 1992), Middle Eocene Messel Formation (~47 Ma; Mayr and Peters, 1998;Peters, 1999;Mayr, 2000a), multiple Late Eocene horizons at Quercy (Mourer-Chauviré, 1988b) the latest Eocene Florissant Formation , and the Early Oligocene Frauenweilerand Late Oligocene Enspel deposits of Germany (Mayr, 2000b(Mayr, , 2013b (Figure 10). Mousebirds are also represented by a suite of fossil taxa from younger Neogene deposits.…”