Ostrich expansion into India during the Late Pleistocene: Implications for continental dispersal corridors

Palaeogeography, Palaeoclimatology, Palaeoecology 417 (2015) 80–90

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Ostrich expansion into India during the Late Pleistocene: Implications for continental dispersal corridors James Blinkhorn a,⁎, Hema Achyuthan b, Michael D. Petraglia c a b c

UMR5199 PACEA, Université de Bordeaux, Avenues de Facultes, Cedex Pessac, France Department of Geology, Anna University, Chennai 600 025, India School of Archaeology, Research Laboratory for Archaeology and the History of Art, University of Oxford, Oxford OX1 3QY, United Kingdom

a r t i c l e

i n f o

Article history: Received 2 July 2014 Received in revised form 14 October 2014 Accepted 21 October 2014 Available online 27 October 2014 Keywords: Dispersal India Katoati Late Pleistocene Stable isotope Struthio

a b s t r a c t New evidence is presented for the earliest occurrence of ostrich (Struthio sp.) in India during the Late Pleistocene along with a synthesis on the evidence for ostrich populations in the subcontinent. Direct dating of ostrich eggshell using Accelerator Mass Spectrometry (AMS) radiocarbon methods on excavated samples from Katoati, Rajasthan, India is supported by Optically Stimulated Luminescence (OSL) dating of associated sediments to demonstrate the arrival of ostrich in India before 60 thousand years ago (ka). In addition, the first stable isotope studies on ostrich eggshell from India have been conducted, yielding a new form of palaeoenvironmental proxy data for the Late Pleistocene. The geographic expansion of ostrich into India corresponds with the distribution of Sahel-like environments, bordering but not substantially colonising endemic Indian vegetation zones. The dispersal of ostrich into India marks a rare introduction of megafauna into the subcontinent during the Late Pleistocene, the longevity of which spans a period more than 40 ka. The timespan and range of this colonisation indicate the availability and exploitation of suitable habitats in India. The continental dispersal of ostrich into India during the Late Pleistocene offers useful insights into the debate surrounding the dispersal of modern humans, and contrasts with the hypothesized coastal movement of Homo sapiens into India. © 2014 Elsevier B.V. All rights reserved.

1. Introduction Broad continuity in the presence of megafauna can be observed in the Indian subcontinent throughout the Middle Pleistocene and extending into the Late Pleistocene (Roberts et al., 2014). The Pakistani Siwalik formations yield repeated evidence for the presence of Struthionidae (family of flightless ratite birds), spanning the Middle Miocene to Middle Pleistocene (Dennell, 2004; Patnaik et al., 2009b; Stern et al., 1994). However, a significant change in the distribution of Struthiodiae is evident in the Late Pleistocene, becoming absent in the Himalayan forelands and instead appearing in western and central India for the first time (Andrews, 1911; Badam, 2005; Bidwell, 1910). The timing of this significant range expansion is poorly constrained and has yet to be set within the broader context of Late Pleistocene faunal dynamics and their relationship with palaeoenvironmental changes. The only osteological remains of Struthiodiae from South Asia were collected from unspecified Siwalik strata and described as a new species, Struthio asiaticus, by Milne-Edwards (1871) on the basis of size differences with the extant African ostrich, Struthio camelus. A metric study of these specimens noted that despite presenting a more robust neck, the Siwalik specimens were comparable in form ⁎ Corresponding author. Tel.: +33 5 40 00 25 45. E-mail address: [email protected] (J. Blinkhorn).

http://dx.doi.org/10.1016/j.palaeo.2014.10.026 0031-0182/© 2014 Elsevier B.V. All rights reserved.

and size with a large male specimen of S. camelus (Davies, 1880). Further description by Lydekker (1884) suggested that the stouter neck of the Siwalik specimen should be considered as within the realm of individual variation, rather than at a species level, thus suggesting S. asiaticus be treated as a ‘preliminary’ taxon. Since this time, a number of osteological remains and, more problematically, eggshell specimens, have been attributed to S. asiaticus spanning from the Pliocene to the Late Pleistocene and ranging from South Africa to East Asia (Kurochkin et al., 2010; Manegold et al., 2013; Mikhailov, 1991; Mourer-Chauviré and Geraads, 2008), making it the most widespread species in the genus Struthio. Osteological studies of specimens attributed to S. asiaticus are noted to be between 20 and 50% more robust than contemporary African ostrich, although not necessarily taller (MourerChauviré and Geraads, 2008). In contrast to the paucity of osteological remains, ostrich eggshells (OES) have been recovered from a number of contexts in the Siwalik Range (Dennell, 2005; Stern et al., 1994) and in the Indian peninsula (Badam, 2005). Ratite eggshells with aepyornithoid-type pore patterns are reported from the Upper Miocene Dhok Pathan formations near Hasnot (Patnaik et al., 2009b; Sauer, 1972), and a range of sites in the Siwalik formations dating between 11.35 and 1.25 million years ago (Ma) (Stern et al., 1994). Eggshells with struthionid-type pore patterns are found in younger Siwalik deposits ranging in age from 2.24 to 0.5 Ma (Stern et al., 1994) and at a number of sites in the Indian states of

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Rajasthan, Uttar Pradesh, Madhya Pradesh and Maharashtra dating between N43 and 18 thousand years ago (ka) (Badam, 2005). More detailed description of eggshell morphology and putative taxonomic affiliations of these OES samples have been restricted to the Late Pleistocene samples (Sahni et al., 1990). The earliest samples examined, from Ken River (Uttar Pradesh), were considered as “practically indistinguishable” from egg-shell of modern Somali ostrich (S. camelus molydophanes) (Andrews, 1911; Bidwell, 1910), though noted as thicker than contemporary examples, with more recent studies reaching the same conclusions based upon wider sampling from the Indian peninsula (Sahni et al., 1990). The extinction of Late Pleistocene Struthio sp. from India has been briefly discussed (e.g. Badam, 2005) yet the timing and potential causes for their expansion into western and central India has not be addressed. Pertinent to this are patterns of climatic amelioration during the Late Pleistocene that may have permitted the extension of favourable habitats for ostrich from their endemic regions into India. Here, evidence is presented for the earliest dated Late Pleistocene Struthio samples from western India, which is placed in its palaeoenvironmental context along with all known samples of Struthiodiae from South Asia. Factors that may have affected this Late Pleistocene expansion are discussed. 2. Materials and methods Ostrich eggshell has been recovered from both surface and excavated contexts at Katoati, Rajasthan, India. OES fragments have been recovered from six sites, labelled KAT1–5 and JFL2. The excavation of a 4.5 m trench at KAT1 yielded two pieces of OES. The two pieces were recovered in 10 mm screens from sediment excavated at a depth of 3.4 m from surface in horizon S4 (Fig. 1) (Blinkhorn et al., 2013). At KAT2 a cluster of OES was observed eroding from an exposed sediment sequence below the contact between two distinct geological units, homologous with S2 and S3 at KAT1. Shallow excavation (ca 10 cm) identified three discrete clusters of OES fragments embedded in the

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lower sediment deposits (S3) (Fig. 1), overlying a thin, laterally extensive pebble horizon. Further exploration at exposures of this pebble horizon resulted in the recovery of three OES samples from S3 deposits at sites KAT3, KAT4 and KAT5. Inspection of an exposed sediment sequence yielded a single piece of OES from site JFL2, which was recovered from an aeolian deposit between a thin, upper and thick, lower gravel horizon (Blinkhorn et al., 2013). Individual fragment thickness of OES from all sites was measured using digital callipers. A total of nine OES samples were submitted and processed for AMS radiocarbon dating. Eight samples were processed in the Oxford Radiocarbon Accelerator Unit (ORAU). These samples were sandblasted in aluminium oxide powder, etched in ~0.2 M HCl for 2 min, rinsed in distilled water and dried prior to acid hydrolysis for producing CO2 for graphitisation for AMS dating and mass spectrometer analysis (see Bronk-Ramsey et al., 2002, 2004a, 2004b for further details). One of four samples recovered from KAT2 was analysed by Prof. Jay Quade, University of Arizona, Tucson. Additional dating has been undertaken at KAT2 using Optically Stimulated Luminescence (OSL). OSL samples were recovered from sediment deposits ca 5 cm above and below the excavated OES deposits at KAT2, relating to units S2 (above) and S3 (below) from KAT1, and submitted to the Wadia Institute of Himalayan Geology for analysis (see Supplementary information for methodology). Mass spectrometer analysis of 12 OES samples (including seven samples analysed by ORAU) was undertaken without physical or chemical abrasion of the surface. Subsamples of OES pieces were selected and rinsed in ethanol to remove any adhering sediments prior to crushing in an agate pestle and mortar and drying at 40 °C. Oxygen and carbon stable isotopic results were obtained using a VG Isogas Prism II mass spectrometer with an on-line VG Isocarb common acid bath preparation system. Each sample was reacted with purified phosphoric acid (H3PO4) at 90 °C with the liberated carbon dioxide cryogenically distilled prior to admission to the mass spectrometer. Both oxygen and carbon isotopic ratios are reported relative to the VPDB international standard. Calibration was against the in-house

Fig. 1. Excavated sediment sequences at KAT1 (left) and KAT2 (right; not to scale) illustrating the sediment context for horizons bearing OES and associated OSL dates.

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NOCZ Carrara Marble standard with a reproducibility of better than 0.2%. Stable isotope ratios are expressed using the notation as difference in parts per thousand (permil, ‰) relative to the standard, calculated as δ‰([Rsample / Rstandard] −1) × 1000, where R = 13C/12C or 18O/16O.

OES beads post-dates the Last Glacial Maximum (LGM). However, it may be anticipated that numerous other previously dated samples would return older dates if subject to the same pre-treatment protocols and AMS dating methods that have been employed at Katoati.

3. Results 3.1. Ostrich eggshell thickness and form Thirty-six measurements of OES thickness indicate a mean thickness of 2.27 mm, with a range between 2.13 and 2.38 mm. This range matches closely with the reported thicknesses of samples from the Indian peninsula, including from Ken River (2.4 mm) (Andrews, 1911) and from the sites of Ledkheri, Chandresal and Anjar (2.1 to 2.2 mm) (Sahni et al., 1990). Collectively, these samples are all notably larger than a single measurement of 1.7 mm from a sample from Pakistan (Grellet-Tinner, 2006), but substantially smaller than aepyornithoidtype OES from the Dhok Pathan formation at Hasnot with a mean of 2.76 mm (range = 2.5 to 2.9 mm) (Patnaik et al., 2009b). Pores are concentrated in spherical to sub-spherical pits (Fig. 2) matching descriptions of previously studied Late Pleistocene OES from the Indian peninsula (Sahni et al., 1989, 1990), and appear analogous in form to the pore structures of S. camelus molydophanes (Sahni et al., 1989, 1990) and descriptions of S. asiaticus (Mourer-Chauviré and Geraads, 2008). 3.2. Dating The results of direct dating of OES samples from Katoati are presented in Table 1, together with a compilation of all previous dates for OES in the Late Pleistocene of South Asia. Our results show that the application of AMS radiocarbon dating methods have returned the oldest directly dated evidence for the presence of Struthio in Late Pleistocene India. The minimum ages returned for two of the oldest samples from KAT1 occur below OSL ages indicating an age of change in depositional environment at Katoati at ca 60 ka (Blinkhorn et al., 2013). This indicates that the OES from KAT1 predates this change in depositional environment and is therefore older than 60 ka. In addition, they overly a horizon dated to 77 ± 18 ka, restricting the likely maximum age of these specimens to late MIS 5 or MIS 4. The chronometric evidence provides robust support for the earlier age estimate from KAT2 (N 59.9 ka), and for the overall antiquity of all samples analysed, which occur at the limit of AMS radiocarbon range. The ages of the four samples from KAT2 either predate or fall within the error range of the OSL date associated with S3 sediments at the site (38 ± 6 ka), which corroborates the antiquity of the samples, clearly indicating that they are not related with the younger (21 ± 3 ka) S2 sediments (see Table 2). The dating results from KAT3 (52.1 ± 1.1 ka) and KAT4 (45.1 ± 0.5 ka) also derived from the upper part of S3 sediment deposits, yielding similar age estimates. The single sample collected from JFL2, occurring in a slightly different sediment sequence, returned an age of 45.3 ± 0.6 ka. We present the eight oldest directly dated samples of OES from India. Our findings support similar evidence for the antiquity of OES from gravel deposits of the Surajkund formation at Hathnora 1 (Patnaik et al., 2009a). At Hathnora 1 samples of OES pieces were found in association with an equid and a bovid tooth, which were ESR dated to 61.6 ka and 62.8 ka respectively; a third, reworked tooth from the same sediment context was dated to 131 ka. As a result, the maximum age of the sediment context, and therefore the OES, is ca 62 ka. This corroborates the antiquity of previously dated samples for which only minimum age estimates could be returned, including at Mehtakheri (Mishra, 1995), Nagda (Agrawal et al., 1991) and Ramgada (Ramnagar) (Kumar et al., 1990). Elsewhere, OES samples have been dated between N42 and 22 ka, with the exception of Khapardkhera, where charcoal associated with an archaeological horizon containing

Fig. 2. Photographs of OES from Katoati, matching descriptions of other OES from India, Struthio camelus molydophanes (Sahni et al., 1989, 1990) and some descriptions of Struthio asiaticus (Mourer-Chauviré and Geraads, 2008) showing: a) the exterior surface exhibiting pore structures concentrated into pits; b) a close up of a single pore pit; and c) the interior surface morphology.

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Table 1 The results of AMS radiocarbon dating of OES samples from Katoati, Rajasthan, synthesised with other dated OES samples from India. Site

Lab no.

Method

Material

Date

(±)

Ref

Hathnora 1 Hathnora 1 KAT1-23b KAT2-a KAT1-23a KAT3 KAT2-e JFL2 KAT4 KAT2 Mehtakheri Chandresal Chandresal KAT2-c Nagda Ramgada (Ramnagar) Bori Patne Morgaon Khapardkhera

FT42 FT39 OxA-25898 OxA-25899 OxA-25897 OxA-25902 OxA-25901 OxA-19407 OxA-25903 AA 96726 AA 8463 Grn 10638 Grn 10639 OxA-25900 PRL-854 PRL-1196 AA 8461 Grn 7200 AA 8846 A 9446

ESR ESR AMS C14 AMS C14 AMS C14 AMS C14 AMS C14 AMS C14 AMS C14 AMS C14 AMS C14 C14 C14 AMS C14 C14 C14 AMS C14 C14 AMS C14 C14

Equid tooth Bovid tooth OES OES OES OES OES OES OES OES OES OES OES OES OES OES OES OES OES Charcoal

62,800 61,600 N62,000 N59,900 N57,900 52,100 49,500 45,350 45,100 N45,000 N41,900 38,000 36,550 35,210 N31,000 N31,000 30,000 25,000 22,485 15,680

9000 900

Patnaik et al. (2009a) Patnaik et al. (2009a) Blinkhorn et al. (2013) This article Blinkhorn et al. (2013) This article This article Blinkhorn et al. (2013) This article This article Mishra (1995) Mishra (1995) Mishra (1995) This article Agrawal et al. (1991) Kumar et al. (1990) Mishra et al. (2003) Sali (1985) Mishra et al. (2003) Mishra et al. (2003)

3.3. Stable isotopes The results of the first stable isotope analyses of Late Pleistocene OES in India are presented in Table 3 and Fig. 3. The isotopic composition of OES is characterised as a “snap-shot” of diet, averaged over 3–5 days, with breeding occurring after the rainy season when sufficient nutrient stores have been acquired (Johnson et al., 1998). As non-obligate drinkers, a range of fractionation processes within either surface or plant water sources as well as physiological responses of ostrich to humidity may affect oxygen isotope data preserved in OES, suggesting that these results may be best used only as a qualitative measure of palaeoclimate (Johnson et al., 1998). δ18O results from the Katoati sites can be readily separated into three groups. The majority of samples range between −0.5‰ and 0.5‰, whereas the two samples from the KAT1 excavated sequence show a large step in enrichment of δ18O, returning results of ~ 6‰, and a similarly large step is observed with KAT3-a, returning results of ~12‰. As a result, it can be suggested that the majority of samples relate to eggs produced during more humid conditions, with those from KAT1 and KAT3-a indicating increasing aridity. Carbon isotope results from OES appear to directly reflect the isotopic composition of the diet, with an enrichment of ~16‰ (Johnson et al., 1998; Ségalen et al., 2006) such that a pure C3 diet would produce an average δ13C of −9.5‰ and a pure C4 diet would return results of 4.2‰. Ostriches show a slight preference for C3 shrubs and select against some vegetation (Johnson et al., 1998), which could relate to requirement for plant water intake where surface water supplies are not available. Overall, the results from most samples indicate that the estimated ostrich diets at Katoati show relatively equal proportions of C3 and C4 input with δ13C of −2 to −3.5‰ relating to a slight bias toward C3 consumption forming 51.1 to 55.6% of consumed vegetation. The results from KAT3-a are substantially different, indicating a pure C3 diet. The carbon isotope results of samples that were physically and chemically abraded match well, although not exactly, with un-abraded samples suggesting that potential contamination from secondary carbonate

1100 800 650 500

700 600 220

420 200 320/310 440/415

sources has been effectively limited. Overall, no clear diachronic trends in isotopic composition are evident in this Late Pleistocene sample. When compared to isotope results from earlier Siwalik Struthionidae (Stern et al., 1994), it is evident that the majority of results from Katoati occupy a tight range within that observed in the Quaternary period (Fig. 2). Oxygen isotope results from Katoati, which indicated increased aridity (KAT1-23a; KAT1-23b; KAT3-a), extend beyond the typical range observed in Indian ratite populations. Instead, these match results from a limited number of aepyornithoid-type Pliocene specimens. This may represent aridity experienced at an individual, rather than population-wide, scale. Similarly, only the carbon isotope results from KAT3-a extend beyond the variability observed in ratite δ13C‰ from the Siwalik Quaternary sequence, but within the range of Miocene samples, again potentially the result of individual scale variation. 3.4. Geographic distribution The distribution of sites with OES in South Asia is presented in Fig. 4. This illustrates a clear spatial distinction between the range of Late Pleistocene sites in the Indian peninsula and the earlier Siwalik sites. The majority of Late Pleistocene occurrences of OES in India occur in the Chambal and Narmada valleys, associated with the Malwa Plateau of west-central India. Fewer sites are reported from the Tapi valley and between the headwaters of the Krishna and Bhima Rivers on the Deccan Plateau in south-central India. A small number of sites, including Katoati, are notable in that they are not located in the immediate vicinity of one of the subcontinents large drainage basins. Nevertheless, the landscape at Katoati indicates that the excavated sites occur at the edge of a braided stream network that may have ultimately fed into the Luni River. Three sites located in Kachchh, Gujarat are located close to smaller fluvial regimes in near-coastal locations. Sites bearing OES are reported both in lowland or wide valley floor contexts, as well as within regions displaying more relief, occurring at the edge of different watersheds. In contrast, Pliocene to Middle Pleistocene OES sites are

Table 2 OSL ages and supporting De and dose rate data for the sediment samples from KAT2. Lab sample

Field sample

U (ppm)

Th (ppm)

K (%)

Mean De (Gy)

Least De (Gy)

Wt. mean De (Gy)

Dose rate (Gy/ka)

Mean age (ka)

Least age (ka)

Wt. mean age (ka)

LD-1099 LD-1100

KAT2–above KAT2–below

1.5 1.9

11.6 13.5

1.3 1.3

48 ± 5 98 ± 19

42 ± 1 79 ± 7

46 ± 5 93 ± 13

2.2 ± 0.1 2.4 ± 0.2

21 ± 3 40 ± 8

19 ± 1 32 ± 4

21 ± 3 38 ± 6

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Table 3 Results of stable isotope studies of OES samples from Rajasthan. Sample

δ13C‰

δ13C‰a

δ18O‰

Age (BP)

KAT1-23a KAT1-23b KAT2-a KAT2-b KAT2-c KAT2-d KAT2-e KAT2-f KAT2b KAT3-a KAT3-b KAT4 KAT5

−3.277 −3.413 −2.902 −2.948 −2.969 −3.095 −2.655 −2.904 −2.57 −9.917 −3.311 −3.015 −2.921

−5.1 −4.1 −3.9

6.057 6.391 0.173 −0.007 0.139 −0.062 −0.538 0.338 −0.086 11.937 0.218 0.038 0.058

N57,900 N62,000 N59,900

−2.8 −2.8

−9.9 −2.6

35,210 ± 220 49,500 ± 800 N45,000 52,100 ± 1100 45,100 ± 500

a Carbon isotope results reported from physically and chemically abraded samples produced during AMS radiocarbon dating at the University of Oxford. b Stable isotope results reported from sample dated at the University of Arizona.

restricted to the foothills of the Himalaya and the Siwalik ranges and occur in the upper reaches of the Indus drainage system. Despite the occurrence of Late Pleistocene OES in a wide variety of landscape contexts, their distribution appears geographically limited, predominately associated with the Malwa Plateau and associated drainage systems. Occupation of the Deccan Plateau is significantly more limited to a cluster of sites close to Pune, Mahrashtra, and a single site at the watershed of the Tapi River. Combined, these sites present a

SW–NE trend, although Katoati, the Kachchh sites, Ken River and Shindi are clear exceptions to this. The earliest dated examples of OES in India, dating between N 60 and 35 ka at Katoati and Hathnora, appear in river systems that flow to the west/south-west. The concentration of sites on the Malwa Plateau that are associated with eastward flowing drainage networks mostly dates between N 40 and N 30 ka, with the exception of Khapardkhera, which dates to 16 ka. The dated sites from the Deccan Plateau, also relating to eastward flowing river systems, are younger than both of these groups, dating to 30–22 ka. 4. Discussion The presence of ostrich in Late Pleistocene India appears to be restricted both temporally and spatially, and marks a significant change in geographic range compared to the Miocene to Middle Pleistocene. The earliest evidence for ostrich in Late Pleistocene India occurs in contexts dating to N60 ka, in MIS 4, at the margins of the Thar Desert and the westward draining Narmada basin. While ostriches are present at Katoati and the Narmada basin during MIS 3, the range of ostrich expands in this period to include the Malwa Plateau. With the onset of MIS 2, evidence for ostrich is only found on the north western Deccan Plateau. Only a single example of ostrich, at Khapardkhera, on the Malwa Plateau, is known from India post-dating the LGM. In order to further assess the timing and nature of ostrich expansion into India, it is necessary to situate these findings in broader context. 4.1. Chronology The presence of ostrich in India currently appears restricted from MIS 4 to MIS 2 (N 60–16 ka). The earliest dated evidence for ostrich, occurring before 60 ka (MIS 4), stretches beyond the range of traditional radiocarbon methods, although earlier dates from Katoati are suggested by OSL dating. Therefore the use of dating methods, such as OSL, is necessary to corroborate the antiquity of the samples. As this has typically not been the case in South Asia, expansion of ostrich into western and central India prior to MIS 4 cannot be precluded. Nevertheless, both environmental evidence and ecological evidence reviewed below may further support the appearance of ostrich in western and central India during MIS 4. Khaparkeda presents the only evidence for the survival of ostrich in India b20 ka. The regional extinction of ostrich from India is suggested to have occurred across the LGM, perhaps resulting from extreme climatic pressure and increased competition and human predation (see below). The presence of numerous OES samples dating to before the LGM and the scarcity of similar samples dating after the LGM support the suggestion of significant collapse of ostrich populations at this time, which ultimately leads to their regional extinction. Based on examples of Struthio extirpation in North Asia (Janz et al., 2009) and numerous megafaunal taxa at a global scale (Koch and Barnosky, 2006), an alternative hypothesis may suggest the regional extinction of ostrich around the Pleistocene–Holocene boundary with the return to interglacial climates. However, as yet there is no evidence to support continuity of ostrich populations in India into the Holocene, and the unique, mosaic nature of Indian habitats may indicate that the global collapse of megafaunal diversity ca 10 ka is not a suitable analogy (Roberts et al., 2014). 4.2. Taxonomy

Fig. 3. Stable oxygen and carbon isotope results of un-abraded Late Pleistocene OES samples from KAT1 to KAT5 compared with Pliocene to Middle Pleistocene samples from Siwalik sites illustrating (top) the relationship between isotope values and (bottom) stable isotope variability through time. The carbon isotope results from Katoati overlap with other Pleistocene Siwalik samples, indicating a greater focus on C4 plant resources, whereas oxygen isotope results from Katoati show greater overlap with some Miocene samples, indicating greater aridity.

The Late Pleistocene ostrich population represented by OES in the Indian peninsula can be most securely referred to as Struthio sp. In their comparison of OES samples from Late Miocene and Pliocene of East Africa and Namibia, Harrison and Msuya (2005) identify a pattern of decreasing shell thickness and pore diameter and increasing pore density through time between Struthio karingarbensis (shell thickness = 2.9–3.2; pore density = 2.2/cm2; pore diameter = 2.7 mm; age range = 6.5–4.2 Ma), Struthio kakesiensis (shell thickness =

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Fig. 4. Geographic distribution of OES sites in South Asia.

2.5–4.4 mm, mean = 3.2; pore density = 4.6/cm2; pore diameter = 2.5 mm; age range = 4.5–3.6 Ma), Struthio daberasensis (shell thickness = 1.7–2.6 mm; mean = 2.3; pore density = 4–5/cm2; pore diameter = 2.2 mm; age range = 6.5–3 Ma) and S. camelus (shell thickness = 1.5–2.8 mm; mean = 2.1; pore density = 10.8/cm2; pore diameter = 1 mm; age range = 3.8 Ma to present). It is worth noting that dated OES from Siwalik deposits bearing struthionid-type morphotypes only overlaps chronologically with S. camelus. OES comparable to S. camelus molydophanes associated with osteological remains identified as S. asiaticus in Late Pliocene deposits at Ahl al Oughlam, Morocco, exhibit a shell thickness (2.3 to 2.7 mm; mean = 2.54 mm) that overlaps the range of S. daberasensis but a greater pore density (10–20/cm2) comparable to S. camelus, thus fitting the broad trend (Mourer-Chauviré and Geraads, 2008). The decreased shell thickness in the Late Pleistocene ostrich population in India with high pore density continues this African trend. However, while the

thickness range overlaps with S. asiaticus samples from Ahl al Oughlam, the Indian samples are notably thinner. The occurrence of OES in Central and East Asia shares some similarities with South Asia. The recovery of aepyornithoid-type eggshells from Miocene deposits followed by struthionid forms appearing in the Pliocene deposits in Mongolia and reported as Struthiolithus (Sauer, 1972) parallel the records from the Siwalik Range. Notably, the samples, originally reported as Struthiolithus, exhibit thinner shells than their African counterparts, ranging between 1.8 and 2.4 mm. In addition, the struthionid-type eggshells exhibit needle point pores rather than pore-pits observed in the contemporary African sample. A rich collection of Upper Pleistocene specimens dated using C14 methods are reported from China, Mongolia and Transbaikal Russia (Janz et al., 2009; Kurochkin et al., 2010). Further descriptions of their morphology (i.e. shell thickness, pore structure and density) are required before meaningful comparison can be made with the South Asian sample.

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The direct ancestry and taxonomic affiliation of Late Pleistocene Struthio in western and central India is difficult to assess based on ootaxonomy alone, particularly as a number of potential source populations exist. They may represent descendants of the Siwalik populations, a more widespread population of S. asiaticus that extends from the Siwalik Range to Morocco and potentially including South Africa, more recent Struthio populations found within this range, such as those known from Arabia (Potts, 2001) including Late Pleistocene samples from the Mundafan depression (Crassard et al., 2013), or of shared source population with Central and East Asian Struthio populations. While it may not be possible to identify which source population, and therefore which taxon, expanded into western and central India in the Late Pleistocene, it is possible to explore why this expansion occurred.

4.3. Neogene and Quaternary habitats of Struthiodiae in South Asia Significant changes to the geographic and ecological makeup of South Asia have occurred since the earliest known appearance of ostrich, and particularly in the mountainous northern region which has yielded all evidence for ostrich prior to the Late Pleistocene. Himalayan orogeny and associated changes to Eurasian climate systems, particularly the evolution of the Asian monsoons, are likely to have had significant impacts upon ostrich populations. Studies of Himalayan exhumation rates indicate a decrease in monsoonal intensity after 10 Ma, following the mid-Miocene climatic optimum, followed by an enhanced monsoon system after 4 Ma (Clift et al., 2008). Isotopic studies of pedogenic carbonates have indicated a sharp change to C4 dominated ecologies in the Late Miocene (Cerling et al., 1997; Quade and Cerling, 1995), but more recent studies have suggested lateral variability in floral gradients prior to C4 expansions and greater heterogeneity in floral change (Behrensmeyer et al., 2007; Morgan et al., 2009). Similarly the expansion of C4 flora has a notable but complex effect on faunal isotopic signatures (Barry et al., 2002; Morgan et al., 1994). Two distinct phases in Siwalik OES isotope chemistry can clearly be identified. Mid-Miocene samples older than ca 9 Ma, exclusively comprising specimens with aepyornithoid-type pore patterns, present a strong C3 signature associated with relatively humid conditions. Pleistocene samples, predominately comprising specimens with struthionid-type pore patterns, present a strong C4 signature associated with relatively humid conditions. Limited sample size prevents a clear characterisation of Late Miocene and Pliocene OES isotope chemistry, although the carbon isotope signature is intermediate between the range of the mid-Miocene and Pleistocene groups whereas the oxygen isotope signature indicates increased aridity in contrast to both. These results broadly corroborate existing trends identified in other isotope archives, particularly highlighting the appearance of C4 plants in the Siwaliks and their exploitation by Pleistocene ostrich populations. The apparent synchronicity of the appearance of a C4 signature in OES isotope chemistry and the appearance of struthionid-type pore patterns may indicate that the appearance of new ostrich populations in the Siwalik sequence was related to wide ranging ecological reconfiguration. However, the continuity of specimens with aepyornithoid-type pore patterns that substantially overlaps the appearance of C4 flora and OES with struthionid-type pore patterns suggests that existing ostrich populations were not rapidly replaced. In this context, the Late Pleistocene expansion of ostrich into western and central India exhibits the exploitation of a similar resource base with earlier Pleistocene ostrich populations, focused upon C4 habitats. Extirpation of Siwalik ostrich populations may have been the result of changing relief, environments, impacts of climate change on seasonality or a combination of these factors, and identifying which factor may have been dominant in this process is beyond resolution of data available. However, these Siwalik habitats differed significantly in their geographic structure and climatic seasonality from the regions of western

and central India into which ostrich populations expanded during the Late Pleistocene. 4.4. Geographic and palaeoenvironmental context of Late Pleistocene ostrich expansion in western and central India Given the known distribution of Struthiodiae spanning the Miocene– Pleistocene, and the geographical and ecological makeup of north India and Pakistan, the Late Pleistocene expansion of ostrich into western and central India is most likely to have been the result of dispersals from the north-west of the subcontinent. Indeed, the NW–SE cline noted in the dated occurrences of OES in western and central India appears to support this. Geographic and environmental conditions in the Thar Desert, marking the most north-westerly extremity of the Late Pleistocene ostrich range in India, are therefore critical to understanding the timing and nature of ostrich expansions. An expansion into the Thar Desert, whether eastwards from Africa and Arabia or southeast-wards from the Siwalik Range, requires a crossing of the Indus River. A GIS model of eastward dispersal routes across southern Asia, based on least cost surface models, indicates the Indus as a major barrier, indicating that any expansions would likely be directed into the interior of the Thar Desert to be capable of traversing these river systems (Field et al., 2007). Increased humidity experienced across southern Asia during MIS 5 would have provided an important context both for population expansion and an increased potential for river systems to prevent major changes to geographic ranges. While the Indus may have been a major physical barrier to dispersals, it is likely to have also acted as a refugium for flora and fauna alike during periods of increased aridity, such as MIS 4, delivering a constant supply of water from the Himalaya through landscapes lacking direct precipitation. In this context, the Indus corridor provides the most likely direct source for ostrich expansions into western and central India. Indeed, during glacial conditions such as MIS 4, changes to river channel morphology in the mid and lower Indus valley modulated by varying flow and sediment supply may have provided the most suitable conditions for the crossing of this physical barrier. This provides the immediate context for the appearance of Late Pleistocene ostrich in India. The Thar Desert provides the best recorded evidence for Late Pleistocene environmental change in South Asia and suggests that humid conditions were present for much of MIS 3, with evidence for faltering fluvial systems and the onset of dune mobility occurring by 35 ka (see Blinkhorn, in press). During this period of faltering humidity in MIS 3, ostrich appear to successfully expand to the majority of its known range in India, encompassing all dated sites within and to the north of the Narmada valley. The occurrence of ostrich in Arabia in this time period has also been recently reported, dating to 49.8 ka and N50 ka (Crassard et al., 2013). Increasing aridity occurs during the period leading up to the LGM, evident in the onset of sand dune mobility commencing in the central Thar Region and extending to the mouth of the Narmada. It is during the transition between MIS 3 and 2 and prior to the LGM that the geographic range of ostrich in India reaches its southernmost extent on the north-west Deccan Plateau. Only the site of Kharpakeda indicates the limited continuity of ostrich populations on the Marwa Plateau across the LGM. Fig. 5 presents the distribution of OES sites in India plotted with modelled rainfall during peak humidity in MIS 5 (which may also serve as an appropriate analogy for early MIS 3 given the presence of terrestrial proxies directly indicating humid conditions) and during the LGM (a suitable, but more arid analogue for MIS 4). The earliest evidence for Late Pleistocene ostrich in India, at Katoati, occurs when increased aridity in the Thar Desert would have presented arid environments that may have depressed other faunal populations. Increasing aridity between MIS 3 and 2 may have extended arid and semi-arid habitats to the east of the Thar Desert, while eventually prohibiting occupation of the expanding extreme arid desert. The majority of OES sites in India are located in regions that have experienced arid to

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Fig. 5. (Left) Distribution of OES sites in India plotted with modelled annual rainfall during the last interglacial (MIS 5) (Otto-Bliesner et al., 2006) and (right) distribution of OES sites in India plotted with modelled annual rainfall during the LGM (Braconnot et al., 2007).

semi-arid climates between MIS 4 and 2, with little indication for the colonisation of sub-humid to humid regions of the subcontinent. Similarly, Janz et al. (2009) have suggested that the Late Pleistocene expansion of Struthio populations in Central Asia may reflect a strengthening summer monsoon. Recent models of vegetation changes across southern Asia (Boivin et al., 2013) offer a useful context in which to situate the dispersal of ostrich into South Asia. Fig. 6 illustrates the known distribution of ostrich in India plotted on modelled vegetation from MIS 5 (which may also serve as an analogy for humid phases of MIS 3) and MIS 4 (which may be analogous to periods of increasing aridity in MIS 3 and 2). On the enhanced humidity model, a corridor of Sahel-like vegetation is evident across southern Asia and encircling the arid core of the Thar Desert. Katoati, alongside five other undated sites, occurs at the interface between this Sahel corridor and a mosaic of tropical savannah/woodland grass. The Marwa Plateau sites also appear predominately at a vegetative boundary, between tropical savannah/ woodland grass mosaics and dry tropical woodland habitats. However, on the heightened aridity model, these sites also cluster at the boundary between Sahel and tropical savannah/woodland grass mosaics. The heterogeneous habitats of the Indian subcontinent appear to have been critical to the continuity of large faunal taxa in India. Faunal records from the Billasurgum caves, south India suggest that 20 of 21 large animal species have remained present in the Indian subcontinent over the Late Pleistocene, with the disappearance of Theropithecus marking the only example of extinction (Roberts et al., 2014).

Nevertheless, a number of species, such as wild ass and Indian rhinoceros, now only appear in restricted distributions within the Indian subcontinent (Roberts et al., 2014). Fragmentation and spatial redistribution of India's habitat mosaic appear to have played a critical role in faunal mobility and long term continuity in the region (Roberts et al., 2014). The arrival of ostrich in western and central India before 60 ka appears to have occurred during such a period of habitat redistribution. The high levels of mobility of the ostrich populations may have been critical to effectively exploit changing habitat boundaries and compete with Indian fauna, particularly with the extension of Sahel-like vegetation in the region. Nevertheless, there is little evidence to suggest the successful ostrich colonisation of endemic Indian habitats. It remains unclear what caused the regional extinction of ostrich from India, although the lack of an endemic source population, competition for marginal resources and increased predation from Indian fauna over the LGM, as well as exploitation by rapidly growing modern human populations may all have played some role. 4.5. The importance of ostrich expansion into India for the human dispersal debate The ostrich is one of two megafaunal species known to have expanded into western and central India during the Late Pleistocene, the other being Homo sapiens. The dispersal of ostrich into western and central India before 60 ka offers an important opportunity to assess a number of aspects of the modern human dispersal debate. Meanwhile, the

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Fig. 6. Distribution of OES sites in India plotted with modelled vegetation in (left) MIS 5 and (right) MIS 4, analogous to humid and arid phases in MIS 3–2 respectively (following Boivin et al., 2013).

demographic expansion of human populations within India may be significant in explaining the regional extinction of ostrich, either through predation or indirect impacts upon regional ecology. The appearance of ostrich in Late Pleistocene India prior to 60 ka occurs before the time frame suggested by some for the appearance of modern humans in India, between 60 and 50 ka (e.g. Mellars et al., 2013). The argument for a dispersal of modern humans after 60 ka favours a rapid coastal dispersal in to India on account of advanced technological and social adaptations, with a timeframe based on mtDNA evidence (Mellars et al., 2013). Ostrich expansions into India during the Late Pleistocene indicate that continental routes of dispersal into India were also possible. Predation of ostrich and use of OES by contemporary and prehistoric human populations indicate significant geographic overlap of humans and ostriches in Sahel-like and savannah habitats (Cooper et al., 2009). This suggests that the continental routes of expansion exploited by ostrich populations prior to 60 ka, focused upon Sahel-like and savannah habitats, may also have been habitable to human populations and offer an alternative dispersal route to those proposed by coastal models. Ostrich beads and symbolic pieces play a role in the identification of behavioural modernity in the archaeological record, both in Africa (e.g. d'Errico and Stringer, 2011) and in South Asia (James and Petraglia, 2005; Mellars et al., 2013). The presence of OES beads, and fragments incised with hatched patterns, such as at Patne (Sali, 1985), is suggested to support a dispersal of human populations associated with these material behaviours at the onset of MIS 3 (Mellars et al., 2013). Yet, alternate models argue for earlier expansions of modern humans into South Asia during MIS 5 (see Blinkhorn and Petraglia,

2014), possibly preceding the arrival of ostrich. Resolving the timeframe of the earliest expansion of ostrich into western and central India is therefore critical to assess whether OES may have been available to human populations throughout MIS 5. An earlier arrival of human populations would preclude the use of OES, and the appearance of symbolic material culture produced using OES may indicate regional innovations in response to local demographic and environmental pressures (Petraglia et al., 2009) rather than an innate feature of modern human behaviour. Nevertheless, ostriches appear to have been recorded, albeit rarely, in the rich corpus of rock art known from South Asia, such as at the site of Firengi, south of Bhopal (Badam, 2005). Evidence for ostrich regional extinction prior to the Holocene supports the suggestion that rock art was being created in India during the late phases of the Late Pleistocene (Taçon et al., 2010). If the extension of Sahel-like vegetation across South Asia was a key factor in the dispersal of both ostrich and humans, potential dispersals of both taxa during MIS 5 should be considered based on available palaeoenvironmental reconstructions. However, modern humans appear to have been uniquely successful in expanding beyond these Sahel-like habitats, to which ostriches appear restricted. The successful adaptation of modern humans to new habitats and changing environments may have also impacted upon the regional extinction of ostrich. Overlapping factors of environmental deterioration and demographic expansion appear to have provided a context for technological innovation around the MIS 3–2 boundary, associated with the emergence of more efficient hunting technologies and the earliest evidence for human-modified OES (Petraglia et al., 2009). Whether through direct predation of ostrich and their eggs, or more indirect ecological impacts

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on increasingly fragmented habitats, the growing population of modern humans in South Asia is likely to have been a factor contributing to the regional extinction of ostrich from India. 5. Summary Our results of direct dating of OES samples from Katoati, along with dating of their sedimentary context, present the first robust evidence to indicate a significant Late Pleistocene range expansion of ostrich in India before 60 ka. By synthesising these results with existing reports and placing them within their palaeoenvironmental and ecological contexts, a restricted timespan for the occurrence of ostrich expansion into the Indian peninsula, limited to MIS 3–2, has been demonstrated. The range of Late Pleistocene ostrich in India now appears to track the margin of Sahel-like habitats, with limited evidence to suggest any extensive colonisation of regions with endemic Indian vegetation. The dispersal of ostrich into India during the Late Pleistocene is notable in the context of long-term stability in the diversity of mega-fauna in the region, as well as potential analogies for the more successful dispersals of modern humans. Acknowledgments The fieldwork was supported by the Emslie Horniman Scholarship (Royal Anthropological Institute, London) awarded to JB. AMS radiocarbon dating at ORAU was funded by the NERC Radiocarbon Facility (2011/2/16) awarded to MP and JB. JB is supported by a Fondation Fyssen Post-Doctoral Fellowship. MP is supported by a grant from the European Research Council (no. 295719). We thank Jay Quade (University of Arizona) for AMS dating an OES sample from KAT2, Peter Ditchfield (University of Oxford) for facilitating the stable isotope analysis, and N. Suresh (Wadia Institute of Himalayan Studies, Dheradun) for dating the OSL samples from KAT2 and providing the methodology and figures reported in SI. JB and HA thank the Anna University for their support and facilities. We thank Francesco d'Errico for Fig. 2. We would like to thank the editor, F. Surlyk, and the anonymous reviewers whose comments have improved our manuscript. Appendix A. Supplementary data Supplementary data to this article can be found online at http://dx. doi.org/10.1016/j.palaeo.2014.10.026. References Agrawal, D.P., Kusumgar, S., Yadava, M., 1991. Physical research laboratory radiocarbon date list VI. Radiocarbon 33, 329–344. Andrews, C.W., 1911. Note on some fragments of the fossil egg-shell of a large struthious bird from Southern Algeria, with some remarks on some pieces of the egg-shell of an ostrich from Northern India. Verhandlungen V Internationale Ornithologie Kongress, Berlin, 1910, pp. 169–174. Badam, G.L., 2005. A note on the ostrich in India since the Miocene. Man Environ. 30, 97–104. Barry, J.C., Morgan, M.E., Flynn, L.J., Pilbeam, D., Behrensmeyer, A.K., Raza, S.M., Khan, I.A., Badgley, C., Hicks, J., Kelley, J., 2002. Faunal and environmental change in the late Miocene Siwaliks of northern Pakistan. Paleobiology 28, 1–71. Behrensmeyer, A.K., Quade, J., Cerling, T.E., Kappelman, J., Khan, I.A., Copeland, P., Roe, L., Hicks, J., Stubblefield, P., Willis, B.J., Latorre, C., 2007. The structure and rate of late Miocene expansion of C4 plants: evidence from lateral variation in stable isotopes in paleosols of the Siwalik Group, northern Pakistan. Geol. Soc. Am. Bull. 119, 1486–1505. Bidwell, E., 1910. Remarks on some fragments of egg shell from a fossil ostrich in India. Ibis IV, 759–761. Blinkhorn, J., 2014. Late Middle Palaeolithic surface sites occurring on dated sediment formations in the Thar Desert. Quat. Int. http://dx.doi.org/10.1016/j.quaint.2014.01.027 (in press). Blinkhorn, J., Petraglia, M.D., 2014. Assessing Models for the dispersal of modern humans to South Asia. In: Dennell, R., Porr, M. (Eds.), Southern Asia, Australia and the Search for Human Origins. Cambridge University Press, Cambridge, pp. 64–75. Blinkhorn, J., Achyuthan, H., Petraglia, M., Ditchfield, P., 2013. Middle Palaeolithic occupation in the Thar Desert during the Upper Pleistocene: the signature of a modern human exit out of Africa? Quat. Sci. Rev. 77, 233–238.

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