Amongst 435 African lion skulls and ten specimens whose origins are likely to be in Africa, five (c. 1%) had DIF (Table 1). Curiously, all African lions with DIF originated from between Tanzania and Zimbabwe, and especially from a relatively small area around Lakes Edward and Albert (central Tanzania – eastern Democratic Republic of Congo) (Appendix 1). In contrast, approximately 46% (26 out of 56) of Indian lion skulls had this characteristic (Table 1).
Table 1. Observations on the presence / absence of the divided infraorbital foramina (DIF) in lion, European cave lion, and tiger.
Two lions from Iran had DIF (Appendix 1). Amongst lions, Iranian and Indian populations are phylogenetically very similar (Barnett et al., 2006a), and customarily have been classified as the same subspecies, P. l. persica (Meyer, 1826), in which DIF therefore occurred in approximately 48% (28 out of 58) of skulls. In the African lion the skulls only had DIF either on the left side (three individuals) or on the right side (two individuals), but in the Asian lion there were seven individuals that had it on both sides (in addition to six left-sided and 13 right-sided specimens). The extinct Barbary lion is suggested to be phylogenetically closer to the Asian lion than to sub-Saharan lions (Barnett et al., 2006a) and yet, amongst the 12 skulls we examined, none had a DIF (Table 1, Appendix 1).
In terms of the frequency of occurrence of DIF, there were statistically significant differences between Asian and African lions (G-test, two tailed, N = 503, df = 1, likelihood ratio χ2 = 108.4, P < 0.001), as well as between Asian and Barbary lions (G-test, two tailed, N = 70, df = 1, likelihood ratio χ2 = 13.9, P < 0.001), whilst a statistically significant difference was not detected between Barbary and sub-Saharan African lions (G-test, two tailed, N = 445, df = 1, likelihood ratio χ2 = 0.3, P = 0.60). In comparison to the lion where DIF occurred in more than 5% of all examined skulls, it occurred only in c. 0.3% (one out of 304) of tiger skulls (lion vs tiger: G-test, two tailed, N = 807, df = 1, likelihood ratio χ2 = 25.0, P < 0.001), and in 13% (one out of eight) of examined skulls of the extinct Pleistocene European cave lion (lion vs. cave lion: G-test, two tailed, N = 511, df = 1, likelihood ratio χ2 = 0.4, P = 0.55).
Divided infraorbital foramen occurred in 45% (5/11) of Indian lion skulls collected in the 19th century, which rose to 67% (10/15) in the early 20th century (pre-1950, including those without recorded collecting dates, yet likely to have been collected during this period as indicated by from their museum register numbers), but this fell to 38% (13/29) post-1950 (Table 2).
Table 2. Observations on the presence / absence of the divided infraorbital foramina (DIF) in Indian lion skulls over time.
However, no statistically significant difference was detected by the G-test at the significant level of 0.05 either between those three periods or between any dyads, although a marginally significant difference was detected between pre- and post-1950 samples (G-test, two tailed, N = 44, df = 1, likelihood ratio χ2 = 3.32, P = 0.069).