Manthi et al.—Giant Pleistocene lion from East Africa


Table 3. Results of pairwise t-tests for difference of means of the three comparative samples. All tests were two-tailed and for equal variances except the test incorporating P. atrox and the variables PL and BL, which were for unequal variances. The null hypothesis is that means were equal and significant p-values indicate that the hypothesis is overturned. Values of p are shown below the diagonals and the significance level above the diagonals. NS=not significant; for other abbreviations, see Material and Methods.


LP3 P. leo


P. spelaea P. atrox


LP4 P. leo


P. spelaea P. atrox


PL P. leo


P. spelaea P. atrox


P. spelaea P. atrox


BL P. leo


P. leo —


p≪0.0001 p≪0.0001


—


P≪0.0001 P≪0.0001


—


p=0.0284 p≪0.0001


—


P=0.000204 P≪0.0001


P. spelaea ***


—


p=0.511 ***


—


P=0.797 *


—


p=0.852 ***


— P=0.540


P. atrox ***


NS —


*** NS —


*** NS —


*** NS —


standard deviations from the mean of our sample of modern lion, so the specimen cannot be reasonably attributed to the modern form. Alternatively, the great size of KNM-ND 59673 can be accounted for in three ways: (1) it represents an extinct species distinct from, but closely related to, Panthera leo; (2) it represents the result of body size tracking climate change in the Middle and Late Pleistocene, but does not represent a distinct population or subspecies; (3) it represents an extinct, distinct population or subspecies that was substantially larger than any modern population or subspecies within P. leo. None of these alternatives can be definitively ruled out.


However, alternative 1 must be considered very unlikely given the fossil record of lions in Africa, as summarized in Yamaguchi et al. (2004). Fossil lions dating back as far as 2 Ma are mor- phologically indistinguishable from modern lions (Werdelin and Lewis, 2005, 2013; Werdelin and Peigné, 2010; Werdelin and Dehghani, 2011) and, except for KNM-ND 59673, fall within the size range of the modern species, taking into account


its entire geographic range. The fossil record is notoriously fickle, but any extinct and much larger species would be expected to have a significant temporal extent (measured in hundreds of thousands of years at least), and although sampling in the latest Middle and Late Pleistocene is comparatively poor, that of the East African (and particularly Kenyan) early Pleis- tocene is quite good, which makes it unlikely that a such a distinct species of lion would have left no trace in the known fossil record. With regard to alternative 2, the work of Klein (1986)


showed that there is some change in m1 size (the proxy used for body size) with latitude in modern lions, with lions at high latitude (and colder climate) being somewhat larger than lions living closer to the equator. The difference is slight, however (~3%; see Klein, 1986, fig. 17). In the present case, the differ- ence in BL is >40% and it is highly unlikely that climate dif- ferences between present-day Kenya and that of 200,000 years ago could explain such a large difference. This is especially true because the age of the Natodomeri lion specimen places it close to the end of Marine Isotope Stage 7, at a time when climate was cooler than today but still far from glacial. It could be argued


311


that P3 and P4 length differ much less from extant lions than BL in KNM-ND 59673, and thus that skull size might be more susceptible to size increase with cold climate than dental size. Our data do indeed show allometry, in that BL increases faster than LP4 with increasing size (slope of reduced major axis regression 1.641 for log10 data). However, even with this allo- metry accounted for, a modern lion with LP3 of 38.3mmwould be expected to have a BL of ~300–310mm, not the 380mmthat is the case with the specimen under study. We thus consider a purely climate-driven explanation for the great size of the specimen unlikely. Alternative 3, although not at present susceptible to proof,


seems the most plausible of the three. Phylogeographic studies of extant lion (Barnett et al., 2014; Bertola et al., 2016) indicate that extant lion haplotypes diversified 120.2–384.8 ka, which brackets the date for the Natodomeri lion. If the mean diver- gence estimate of 244.8 ka is correct (Bertola et al., 2016:fig. 3), the Natodomeri lion could hypothetically represent a haplotype that was sister taxon to all extant lion haplotypes. Interestingly, Natodomeri lies in the overlap between the two major haplo- groups (‘north’ and ‘south’) of Bertola et al. (2016). Therefore, alternative but somewhat less likely hypotheses are that the Natodomeri lion was sister taxon to all extant lions within either the ‘south’ group of Bertola et al. (2016), the diversification of which is dated to 90.3–300.6 ka (mean: 189.2 ka) or the ‘north’ group, dated to 71.6–239.7 ka (mean: 147.6 ka). As noted, fossils from the late Middle and Late Pleistocene


are poorly documented in eastern Africa and since a genetically distinct population or subspecies could be temporally quite ephemeral the likelihood that it would be sampled is much reduced from that of a species. That such a population may have existed could be due to greater biomass of megafauna in the late Middle and Late Pleistocene than at present, sustaining a population of very large lions. Occurrence of abundant mega- fauna, such as the giant buffalo Syncerus antiquus (Duvernoy, 1851) (see Faith, 2014 for a discussion of Late Pleistocene extinctions in Africa) at this time may also have led to the evolution of a larger lions to exploit this resource more exten- sively than today.


Conclusions


This paper describes KNM-ND 59673, from the late Middle Pleistocene of Natodomeri, northeastern Kenya, the partial skull of a lion of much greater size than any alive today. This skull represents the first indication of the existence of a population of giant lions in the late Middle and Late Pleistocene of eastern Africa, perhaps occasioned by the presence of greater mega- faunal biomass than today. The find of KNM-ND 59673 reminds us that the Middle


and Late Pleistocene of eastern Africa are still poorly studied and that surprises will still occur as sampling improves.


Acknowledgments


We thank the Government of Kenya for permission to work at Natodomeri. We also thank the National Museums of Kenya for supporting this project. The Turkana County administration and the Turkana people in the Natodomeri area provided invaluable


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