Locomotor Adaptations in Plio-Pleistocene Large Carnivores from the Italian Peninsula: Palaeoecological Implications
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Current Zoology 57 (3): 269−283, 2011 Locomotor adaptations in Plio-Pleistocene large carnivores from the Italian Peninsula: Palaeoecological implications Carlo MELORO* Hull York Medical School, The University of Hull, Loxley Building, Cottingham Road Hull HU6 7RX, UK Abstract Mammalian carnivores are rarely considered for environmental reconstructions because they are extremely adaptable and their geographic range is usually large. However, the functional morphology of carnivore long bones can be indicative of lo- comotor behaviour as well as adaptation to specific kind of habitats. Here, different long bone ratios belonging to a subsample of extant large carnivores are used to infer palaeoecology of a comparative sample of Plio-Pleistocene fossils belonging to Italian paleo-communities. A multivariate long bone shape space reveals similarities between extant and fossil carnivores and multiple logistic regression models suggest that specific indices (the brachial and the Mt/F) can be applied to predict adaptations to grass- land and tropical biomes. These functional indices exhibit also a phylogenetic signal to different degree. The brachial index is a significant predictor of adaptations to tropical biomes when phylogeny is taken into account, while Mt/F is not correlated any- more to habitat adaptations. However, the proportion of grassland-adapted carnivores in Italian paleo-communities exhibits a negative relationship with mean oxygen isotopic values, which are indicative of past climatic oscillations. As climate became more unstable during the Ice Ages, large carnivore guilds from the Italian peninsula were invaded by tropical/closed-adapted spe- cies. These species take advantage of the temperate forest cover that was more spread after 1.0 Ma than in the initial phase of the Quaternary (2.0 Ma) when the climate was more arid [Current Zoology 57 (3): 269–283, 2011]. Keywords Carnivora, Long bones, Quaternary, Climate change Although members of Carnivora are literally defined relationship between the morphological variability of by virtue of what they eat, they exhibit a great variabi- long bones shape and the environment occupied by lity also in locomotor adaptations (Ewer, 1973; Taylor, both extant and extinct species. 1989; Van Valkenburgh, 1987). All the elements of the Interestingly, several long bone length ratios of car- appendicular skeleton of carnivores are usually modi- nivores appear to be related with the running perfor- fied in order to maximise locomotor performance which mance (e.g., maximum speed). In particular, metatar- can be remarkable if compared with that exhibited by sal/femur length ratio (= Mt/F) has been intensively other mammals (e.g., the cheetah Acinonyx jubatus can investigated because it can be applied also to the scatter achieve the highest speed ever recorded among extant record of extinct carnivores and their prey (Janis and terrestrial mammals). Such intuitive relationship between Wilhem, 1993). Garland and Janis (1993) revealed that bones and performance is reflected in the external mor- the relationship of such ratio with speed (in large mam- phology of the pelvis, of long bones and other appen- mals) is not an artefact of phylogenetic relatedness even dicular elements like the scapula. It is also useful to if it results not in a straightforward line. Christiansen infer locomotor behaviour in extinct species (Taylor, (1999) confirms that in both carnivores and ungulates 1989; Van Valkenburgh, 1987; Munthe, 1989; Ginsburg, Mt/F co-varies with speed but other long bone ratios can 1999; Argant, 2004; Antón et al., 2005). Accordingly, also be considered as even better descriptor of running Taylor (1989) categorised carnivores for their ability in performance (e.g., Olecranon/Radius length). Carrano running or climbing or digging. These categories are (1999) also demonstrated that long bone indices are reflected also in long bone shape and dimension. The useful for determining locomotor habit in both mam- latter observation allows quantitative analyses, which, mals and dinosaurs. Cursorial species tend to exhibit for carnivores, were firstly performed by Van Valken- longer metatarsal, more slender limb elements and burgh (1985, 1987) in her survey of extant and extinct shorter femora. large carnivore guilds. Her study reveals a complex Samuels and Van Valkenburgh (2008) recently con- Received July 10, 2010; accepted Jan 14, 2011. ∗ Corresponding author. E-mail: [email protected] © 2011 Current Zoology 270 Current Zoology Vol. 57 No. 3 firmed that long bone ratios are useful behavioural pre- 1 Materials and Methods dictors also in rodents that exhibit a remarkable range of locomotion types. Clearly, the analysis of long bone 1.1 Long bones indices proportions is a powerful analytical tool to explore lo- Twenty two extant species of large carnivores be- comotor adaptations in a wide range of vertebrates. longing to families Canidae, Felidae, Hyaenidae and However, they can be also interpreted to elucidate com- Ursidae were considered in order to reconstruct loco- plex behaviours especially in mammalian carnivores. motor behaviour in extinct Italian Plio-Pleistocene large For instance, Lewis (1997) extended the analysis of carnivores. long bone indices to clarify ecological adaptations of Polly (2010) recently demonstrated that eco-morphology African Plio-Pleistocene carnivores. She evidenced a of carnivore communities can be used for environmental difference in eco-morphology between extant African reconstruction. Mean calcaneal gear ratio of extant car- carnivores and Plio-Pleistocene species. The extinct nivore communities correlates with several environ- sabertooth cats (Homotherium, Megantereon and Dinofelis) mental parameters such as precipitation or temperature were prey grapplers. The African Plio-Pleistocene Canis at large geographical scale (all North America). This spp. were more adapted to omnivory and to cursoriality. approach is very promising but it assumes that all Similarly, Meachen-Samuels and Van Valkenburgh members of a carnivore community are represented in a (2009) analysed different ratios from forelimb elements fossil site. This condition is quite rare because of ta- to predict prey size range in extant felids. The study phonomic bias favouring preservation of large taxa clearly shows that forelimb long bone proportions are (Damuth, 1982). Consequently, I restrict my analyses to better predictors of prey size rather than locomotion. large taxa (defined as species bigger than 7 kg) whose Felids adapted to kill large prey exhibit more robust fossil record has been extensively investigated for the humerus and radius at the midshaft and distal epiphyses. Italian peninsula (Raia et al., 2005, 2006a, b, 2007; Nonetheless, felids represent a special case in Carnivora Meloro et al., 2007, 2008). because they are homogenously adapted to hunt verte- For each extant species humerus, radius, femur and brates. This condition rarely applies to different families tibia length (L in cm) measurements were extracted of Carnivora where species tend to exhibit a wider range from the literature (Bertram and Biewener, 1990) and of feeding adaptations (from insectivory to herbivory, combined into the brachial index (BI = radius/humerus Gittleman, 1985; Meiri et al. 2005). length cf. Lewis, 1997) and the tibia/femur index (T/F= Here, I present a survey of long bone indices in a tibia/femur length). subset of both extant and fossil species in order to elu- Data in Janis and Wilhem (1993) and Christiansen cidate eco-morphology of Italian Plio-Pleistocene large (2002) were reviewed to extract for each species meta- carnivore guilds. I focus on the implication of recon- tarsal/femur ratio (Mt/F = metatarsal/femur length). structing locomotor behaviour for palaecological Taken overall, three variables were considered for each reconstructions and, in particular, environmental ones. extant large carnivore: BI, T/F, Mt/F (see Appendix 1). As Lewis (1997) pointed out, some indices like the Even if the number of indices is quite limited, they are brachial (radius/humerus length), can be useful to de- broadly representative of long bone functional mor- scribe the adaptation of a large carnivore for particular phology (Carrano, 1999) and they were selected to cre- habitats (closed, mixed, open savannah). This rela- ate a consistent comparative dataset for the fossil data, tionship will be empirically tested in order to define which are inevitably fragmentary (see next section). for each fossil carnivore particular preference for cer- 1.2 Fossil sample tain biomes. Phylogenetic relatedness among species For extinct Plio-Pleistocene taxa, the latter variables will also be taken into account to validate the statisti- were computed combining measurements directly taken cal models based on the interspecific dataset of extant from museum collections or after an extensive review of Carnivora (Garland et al., 2005). Closely related spe- the Italian and European literature on each fossil large cies tend to resemble each other in several morpho- carnivore (Appendix 2). As the fossils are usually in- logical as well as behavioural traits because of their complete and scattered in space, several long bone in- shared evolutionary history (Blomberg et al., 2003). dices were obtained combining long bone lengths from For this reason, comparative methods are necessary to different localities. When possible, multiple long bone apply when interspecific data are explored for pa- measurements from the same locality