DIETARY EVALUATIONS AND PALEOECOLOGY OF AN EXTINCT GIRAFFID (GIRAFFOKERYX PUNJABIENSIS) FROM SIWALIKS OF PAKISTAN.
The dietary preferences and paleoecology of Giraffokeryx punjabiensis Pilgrim 1910 an extinct giraffid species from Chinji Formation of Potwar Siwaliks of Pakistan have been investigated by incorporating mesowear-I mesowear-II and hypsodonty methods. The mesowear patterns of Giraffokeryx punjabiensis are very much consistent with the browsers as well as seasonal mixed feeders whereas hypsodonty index (1.31 0.06) categorizes it within the browsers. Comparison of the results from these research tools suggest that the extinct giraffid reflects diverse dietary spectra ranging from browsers to seasonal mixed feeders and shows no affinities with grazers. The coexistenceof G. punjabiensis with its mammalian paleocommunity reveals the persistence of mosaics of diverse habitats ranging from tropical evergreen forest to subtropical ones closed seasonal woodlands to wooded savannas.
Key words: hypsodonty Miocene mesowear ungulates Sivatherines biostratigraphy.
The dietary preferences of large herbivorous mammals including giraffids can be evaluated on the basis of mesowear I II and hypsodonty studies (Solounias and Semprebon 2002; Damuth and Janis 2011). The mesowear-I method is based on two major attributes named buccal cusp shape (either the paracone or metacone) and cusp relief developed by attrition and abrasion for estimating average life long diet of ungulates (Kaiser and Solounias 2003; Franz-Odendaal and Solounias 2004). Mesowear-II method combines the two variables such as cusp shape and occlusal relief (of mesowear-I) as a single variable and then mesowear scorings are scaled by relating them with a mesowear ruler" (Mihlbachler et al. 2011). Hypsodonty is recognized as morphological proxy to interpret feeding adaptations and habitat inference in large herbivorous mammals (Fortelius et al. 2003; Stromberg 2006).
The diet of extinct Giraffidae was browse as in extant giraffes. The notion about the extinct giraffids as traditional browsers was changed when Solounias et al. (1988) found that the Samotherium boissieri Major 1888 (an extinct giraffid from the Miocene of Samos Greece) was known to be mixed feeder to grazer. The premaxillary shape and dental microwear analyses showed that the diets of extinct Giraffidae were highly heterogeneous (e.g.) the Bramatherium megacephalum (Lydekker 1878) and Sivatherium giganteum Falconer and Cautley 1835 (Sivatheriinae) were grazers.
The Giraffinae and Palaeotraginae Pilgrim 1911 also showed browsing mixed feeding and grazing diet. Furthermore Okapia johnstoni (Sclater 1901) (the okapi) the second and very rare living species of Giraffidae is a fruit-dominated browser instead of being regular browser whereas the Giraffa camelopardalis (Gmelin 1788) is designated as a leaf-dominated browser (Solounias and Semprebon 2002). Studies on premaxillary shape and dental microwear also revealed that the Sivatheriinae Palaeotragus primaevus Churcher 1970 and Helladotherium duvemoyi Gaudry 1860 were committed browsers whereas Giraffokeryx punjabensis Pilgrim 1910 was a mixed feeder (Solounias and Moelleken 1993; Solounias et al. 2000). Other studies on dietary evaluations of herbivores including giraffids from Middle Miocene of Pakistani Siwaliks was based solely on general comparisons with their extant analogues (e.g. Barry et al. 2002; Badgley et al. 2008; Samiullah et al. 2012). Considering this approach
Barry et al. (2002) and Badgley et al. (2008) assumed that the Giraffokeryx punjabiensis was a browser similar to living giraffes whereas Samiullah et al. (2012) proposed its dietary spectrum ranging from a browser to a mixed feeder. During the last two decades however several approaches have been developed for dietary evaluations of fossil mammals. We have presently evaluated in detail the dietary adaptations of a Siwalik Sivathere; Giraffokeryx punjabiensis based on mesowear-I mesowear-II and hypsodonty index hoping to achieve better resolution than from mesowear-I and previous dietary inferences since it gives a very precise average life long diet of the species. Exploration of dietary adaptations in ungulate remains provide information concerning paleoecological conditions of individual species and ultimately of terrestrial paleocommunities of mammals (Kaiser et al. 2000).
Abbreviations GCUPC= Govt. College University Lahore Paleontological Collection ca= Circa H= crown height W= crown width l= left r= right M= upper molar m= lower molar Ma= mega annum MN= Mein Zones HI= Hypsodonty Index MS= mesowear scale N= number of samples.
MATERIALS AND METHODS
Specimens (molar teeth) of Giraffokeryx punjabiensis unearthed from the Chinji Type locality and Bin Mir Khatoon (Chinji Formation) of Pakistan were examined. The HI was calculated based on the metrics of completely unworn seven m3sfollowing Janis (1988). Seventeen M2s were selected for mesowear analysis following Fortelius and Solounias (2000) and Mihlbachler et al. (2011). The mesowear method is based on two variables namely cusp shape and occlusal relief and were determined by direct observation and the percentage of teeth with high/low cusps and sharp/round/blunt cusps was calculated for the species. The variables were then plotted against HI as recommended by Fortelius and Solounias (2000). The cusp sharpness and degree of relief are dependent variables. Higher occlusal relief tends to be sharper as compared to low relief cusps and cusps with zero relief are obviously blunt. Hence old mesowear
(Mesowear Type I) were treated as a single variable (Mesowear Type II) during which cusp apices are continuously assigned to stages ranging from the sharpest cusps displaying highest relief to the bluntest cusps showing lowest relief. Mesowear scorings were digitized by relating them with a mesowear ruler" designed by Mihlbachler et al. (2011). Having recorded the mesowear scorings the percentages for each variable were calculated which in turn were examined by hierarchical cluster analyses using PAST version 14 software to evaluate the dietary and habitat interpretations of the studied taxon.
Mesowear analysis: The mesowear signatures of Giraffokeryx punjabiensis reflect affinities with extant browsers and mixed feeders.
Table.1. Absolute and relative mesowear scorings of upper M2s of Giraffokeryx punjabiensis Pilgrim 1910.
###Cusp relief###Cusp shape###Cusp relief###Cusp shape
The living analogues for browsers are a giraffid; Giraffa camelopardalis Linnaeus (1758) and a cervid; Capreolus capreolus Linnaeus (1758). The extant analogues for mixed feeders are Tragelaphus imberbis (Blyth 1869) and Procavia capensis Pallas (1766) (Table 1 Appendix 2).
The graphical representation indicates that the Giraffokeryx punjabiensis may be placed within the dietary spectrum of browsers and seasonal mixed feeders. As regards cusp shape the specimens have 36.84% round cusps 63.15% sharp and 0% blunt cusps (Table 1 Fig.2). Bivariate plots of Mesowear results for Giraffokeryx punjabiensis versus mesowear variable outlined by Fortelius and Solounias (2000) for extant species of ungulates were prepared. Hypsodonty Index: Hypsodonty index shows that Giraffokeryx punjabiensis is a brachydont browser. Nevertheless it is somewhat more hypsodont than the living brachydont giraffe Giraffa camelopardalis (HI= 1.2) (Janis 1988). The Hypsodonty Index (HI) for Giraffokeryx punjabiensis calculated here is 1.31 0.06 (n=6) (Appendix 1). The purpose of incorporation of hypsodonty index (HI) is primarily to evaluate the mesowear results and to compare with its extant analogues i.e. Giraffa camelopardalis Okapia johnstoni for drawing ecomorphic inferences. The HI of 1.31 0.06 is utilized for Giraffokeryx punjabiensis in all bivariate representations (Appendix 1). The graphical representation indicates that the Giraffokeryx punjabiensis is placed within the dietary spectrum of browsers (Figs. 4-7 A B C).
Mesowear: Although cusp relief in the extant giraffe G. camelopardalis and Giraffokeryx punjabiensis are similar yet the cusp shape markedly differs. As regards numbers Giraffa camelopardalis shows 74% sharp and 26% round shaped cusps (Fortelius and Solounias 2000) as compared to the less marked pattern in Giraffokeryx punjabiensis (63.15% sharp 36.84% round) (Table 1 Fig.2). Bivariate representations of mesowear variables show that diet of G. punjabiensis was different from that of the living giraffes. The species under study is analogous to Tragelaphus imberbis (Blyth 1869) and Procavia capensis Pallas (1766). Consequently the diet of G. punjabiensis seems to be most consistent with browsers and seasonal mixed feeders. It indicates no evidence for a pure grazer (Table 1 Fig. 2).
Hypsodonty study: The HI (1.31 0.06) for Giraffokeryx punjabiensis suggests its placement within the brachydont browsers. Considersing Janis (1988) Damuth and Janis (2011) hypsodonty interpretations Giraffokeryx punjabiensis may be categorized within the dietary spectrum of two sub-types of brachyodont browsers such as regular browsers (BB) and high level browsers (HB). Furthermore the HI of Giraffokeryx punjabiensis is similar to the average for four regular browsers (BB); Odocoileus virginianus Hylochoerus minertzhageni Mazama mazama americana Choeropsis liberiensis and three high-level browsers (HB); Alces alces (Erxleben 1777) Litocranius walleri and Okapia johnstoni. Having compared the HI and body size/mass of Giraffokeryx punjabiensis to the previously published HI and body size of 127 species of extant ungulates (Janis 1988) G. punjabiensis HI seems most similar to that of its multiple extant analogues i.e. one cervid;
Alces alces (Linnaeus 1758) (moose) a giraffid; Okapia johnstoni (Sclater 1901) (okapi) a Hippopotamid; Choeropsis liberiensis (Morton 1849) (pygmy hippos) a suid; Hylochoerus minertzhageni (Thomas 1904) (giant forest hog) (Janis 1988). The Alces alces and Okapia johnstoni have been classified by Janis (1988) as high-level browsers (HB) while Choeropsis liberiensis and Hylochoerus minertzhageni as regular browsers (BB) and Muntiacus reevesi as mixed feeders in closed habitats (MFC). Both of the regular and high level browsers have body weights nearly equivalent to the estimated body weight for G. punjabiensis (233 kg) by Barry et al. (2002). Comparison of the results from these research techniques reveals that the G. punjabiensis is categorized within the dietary spectra of browsers as well as seasonal mixed feeders and shows no affinities with grazers (Table 1 Fig. 2 Appendix 2).
Biostratigrphy and Paleoecology: The Giraffokerycinae appeared sporadically in the Chinji beds of the Siwaliks (Bhatti et al. 2007). Giraffokeryx punjabiensis has been documented from several localities of Siwalik late Middle Miocene (Bhatti 2005) occupying a long geo- chronologic ranges from Western Europe to Indian subcontinent (Bohlin 1926; Bosscha-Erdbrink 1977; Gentry et al. 1999). G. punjabiensis in association with Listriodon pentapotamiae Conohyus sindiensis Gaindatherium browni Brachypotherium fatehjangense Sivapithecus sp. and Deinotherium pentapotamie are considered to be zonal marker elements of Chinji Formation (Sarwar 1977; Barry et al. 2002). The Chinji fauna is in favor of Middle Miocene age because the comparison of the material with several representatives of the fauna indicates a Middle Miocene age (Pilgrim 1937 1939; Heissig 1972).The faunal assemblage contains elements significant enough to be compared with Astaracian of Europe and
Greco-Iranian Province spanning from middle Miocene to earliest Late Miocene (Khan et al. 2011). It shows overlapping of temporal ranges with that of the Chinji stratotype which correspond to the MN6 as well as MN7/8 (Heissig 1972; Colbert 1935; Pickford and Morales 2003).
The dietary preferences of giraffes provide a baseline for interpretation of their ecology. The reconstruction of palaeoecology of ungulate remains is largely dependent on their palaeodietary inferences (Bibi and Gulec 2008). The great diversity of the ungulate paleocommunity reveals the predominance of forest frugivores/selective browsers browsers and browsing mixed feeders during Middle Miocene to earliest Late Miocene of Siwaliks in Pakistan (Badgley et al. 2005 2008). Frugivores/selective browsers and browsers are indicators of tropical evergreen forest to subtropical one whereas browsing mixed feeders are markers of woodlands and wooded savannas (Janis 1988; Damuth and Janis 2011).The coexistence of G. punjabiensis with mammalian paleocommunity suggests the persistence of mosaics of diverse habitats ranging from tropical evergreen forests to subtropical ones closed and seasonal woodlands to woodedsavannas.
Conclusions: Mesowear signatures in association with HI indicated that the diet of G. punjabiensis was most consistent with browsers as well as seasonal mixed feeders. G. punjabiensis was not an exclusively browser or grazer. Rational for the abrasion-attrition gradients within the mixed feeding adaptation is that the Middle Miocene mammalian assemblage is represented by a diverse populations or cohorts of organisms that accumulated over 3.9 Ma (ca.14.2-10.3 Ma) and it is most likely that animals died at different intervals of the year and therefore had paleodiets which varied seasonally. The paleoecology of studied taxon reveals the persistence of mosaics of diverse habitats ranging from tropical evergreen forests to subtropical ones closed and seasonal woodlands to wooded savannas.This study contributes to the understanding of evolution of dietary preferences and paleoecology among Siwalik Sivatherines.
Acknowledgments: We are grateful to Raja Jan Raja Khalid Mehmood and Raja Tahir from Dhok Mori Mothan Muhammad Ajaib Shaukat Ali and Wajid Ali from Dhok Bin Mir Khatoon for immense help during field work and hospitality. This study was funded by Higher Education Commission (HEC) of Pakistan.
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|Publication:||Journal of Animal and Plant Sciences|
|Date:||Oct 31, 2014|
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