Morphometric variation in the papionin muzzle and the biochronology of the South African Plio‐Pleistocene karst cave deposits

Abstract

Papionin monkeys are widespread, relatively common members of Plio-Pleistocene faunal assemblages across Africa. For these reasons, papionin taxa have been used as biochronological indicators by which to infer the ages of the South African karst cave deposits. A recent morphometric study of South African fossil papionin muzzle shape concluded that its variation attests to a substantial and greater time depth for these sites than is generally estimated. This inference is significant, because accurate dating of the South African cave sites is critical to our knowledge of hominin evolution and mammalian biogeographic history. We here report the results of a comparative analysis of extant papionin monkeys by which variability of the South African fossil papionins may be assessed. The muzzles of 106 specimens representing six extant papionin genera were digitized and interlandmark distances were calculated. Results demonstrate that the overall amount of morphological variation present within the fossil assemblage fits comfortably within the range exhibited by the extant sample. We also performed a statistical experiment to assess the limitations imposed by small sample sizes, such as typically encountered in the fossil record. Results suggest that 15 specimens are sufficient to accurately represent the population mean for a given phenotype, but small sample sizes are insufficient to permit the accurate estimation of the population standard deviation, variance, and range. The suggestion that the muzzle morphology of fossil papionins attests to a considerable and previously unrecognized temporal depth of the South African karst cave sites is unwarranted.

Ecogeographical and phylogenetic effects on craniofacial variation in macaques

“…Size variation was strongly correlated with facial elongation across macaques; as size increases, a rounded face becomes more elongated. This scaling pattern is probably conserved in the tribe Papionini because a similar pattern was observed in other clades of this tribe, including the genus Papio (Leigh, ), large‐bodied papionins (Frost et al, ), and the entire Papionini tribe (Collard and O'Higgins, ; Singleton, ; Leigh et al, ; Gilbert and Grine, ). This common allometric pattern is largely explained by truncation or extension of a common ontogenetic trajectory (O'Higgins and Collard, ; Leigh et al, ; Leigh, ), suggesting that variation in facial elongation of macaques is largely a passive consequence of body size modifications along a common allometry.…”

Phylogenetic relationships within the Cercocebus–Mandrillus clade as indicated by craniodental morphology: Implications for evolutionary biogeography

“…A direct reading of the fossil record may implicate East Africa as the geographic area of origin for the Mandrillus lineage since the earliest specimens of Soromandrillus are found there at ∼3.4 Ma (Delson and Dean, ; Gilbert, ). However, because the exact placement of Soromandrillus within the lineage is unresolved, the most parsimonious interpretation of the Cercocebus – Mandrillus group's biogeographic origins is currently equivocal with either western equatorial Africa or East Africa being the most likely options (Gilbert, ). If Soromandrillus is regarded as the most primitive member of the broader Cercocebus/Procercocebus + Mandrillus clade, then its presence in East Africa may suggest an origin there.…”

“…We verified the origin of each specimen based on its provenance as to ensure the exclusion of questionable C. galeritus (formerly included in C. agilis ) and C. lunulatus (formerly included in C. atys ) specimens in the data set. Sample sizes of most taxa and characters correspond to the minimum of five to ten individuals suggested by Gilbert and Grine (), but are low for quantitative data of female M. sphinx ( n = 2 specimens) and for qualitative data of C. atys ( n = 2 males and 2 females). Sample sizes, split up per taxon and per character, can be found in the Supporting Information Tables and 2.…”

Letter to the editor: Geochronology and palaeoenvironments of Southern African hominin‐bearing localities—A reply to Wrangham et al., 2009. “Shallow‐water habitats as sources of fallback foods for hominins”

“…A recent example is Morris (2010), who reports the age of the StW 573 fossil from Sterkfontein as at least 2.7 Ma citing Clarke (1998), a paper published before a plethora of recent geochronological work (Partridge et al, 1999(Partridge et al, , 2003Walker et al, 2006; had been undertaken at the site. This misrepresentation leads to further confusion over the likely age of the deposits and mistrust and misunderstanding of wellestablished dating methods (e.g., Gilbert and Grine, 2010). Only recently, through a combination of faunal, palaeomagnetic, electron spin resonance (ESR), and uranium-lead dating have more reliable age estimates for these deposits begun to emerge.…”