View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by Servicio de Difusión de la Creación Intelectual Inferring habitat and feeding behaviour of early Miocene notoungulates from Patagonia GUILLERMO H. CASSINI, MANUEL MENDOZA, SERGIO F. VIZCAI´NO AND M. SUSANA BARGO Cassini, G.H., Mendoza, M., Vizcaı´no, S.F. & Bargo, M.S. 2011: Inferring habitat and feeding behaviour of early Miocene notoungulates from Patagonia. Lethaia,Vol.44, pp. 153–165. Notoungulates, native fossil mammals of South America, have been usually studied from a taxonomic point of view, whereas their palaeobiology has been largely neglected. For example, morpho-functional or eco-morphological approaches have not been rigorously applied to the masticatory apparatus to propose hypothesis on dietary habits. In this study, we generate inferences about habitat and feeding preferences in five Santacrucian genera of notoungulates of the orders Typotheria and Toxodontia using novel computer techniques of knowledge discovery. The Santacrucian (Santa Cruz Formation, late-early Miocene) fauna is particularly appropriate for this kind of studies due to its taxonomic richness, diversity, amount of specimens recorded and the quality of preservation. Over 100 extant species of ungulates, distributed among 13 families of artiodactyls and peris- sodactyls, were used as reference samples to reveal the relationships between craniodental morphology and ecological patterns. The results suggest that all Santacrucian notoungu- lates present morphologies characteristic of open habitats’ extant ungulates. Although the Toxodontia exhibits the same morphological pattern of living mixed-feeders and grazers, the Typotheria shows exaggerated traits of specialized grazer ungulates. h Cra- niodental morphology, ecomorphology, fossil ungulates, knowledge discovery, South America. Guillermo H. Cassini [[email protected]], Divisio´n Paleontologı´a Vertebrados, Museo de La Plata, Paseo del Bosque s ⁄ n, B1900FWA La Plata, Argentina; Manuel Men- doza [[email protected]], Centro Oceanogra´fico de Murcia, Instituto Espan˜ol de Oceanografı´a. Varadero 1, E-30740 San Pedro del Pinatar, Murcia, Spain; Sergio F. Viz- caı´no [[email protected]] and M. Susana Bargo [[email protected]], Divisio´n Paleontologı´a Vertebrados, Museo de La Plata, Paseo del Bosque s ⁄ n, B1900FWA La Plata, Argentina; manuscript received on 17 ⁄ 02 ⁄ 2010; manuscript accepted on 07 ⁄ 05 ⁄ 2010. Notoungulata constitutes the most abundant and their inferred general appearance and the grinding diverse clade of endemic South American ungulates, pattern of molar crowns (Ameghino 1907; Scott 1912; both taxonomically and morphologically (Simpson Bond 1999). Typotheres are small-to-medium size 1936; Patterson & Pascual 1972; Cifelli 1993). No- mammals, mostly described as rodent-like in overall toungulates are recorded throughout the Cenozoic, form, although different families resemble living from the late Palaeocene to the late Pleistocene capybaras (Mesotheriidae), hares (Hegetotheriidae), (Bondesio 1986; Croft 1999). The group reaches its hyraxes (Interatheriidae) and small deer (Ameghino greatest taxonomic richness (at the genus level) during 1889; Sinclair 1909; Bond et al. 1995; Croft 1999; Re- the Palaeogene, gradually diminishing throughout the guero et al. 2007). Neogene with forms that become progressively more In both toxodonts and typotheres, there is an specialized, until their extinction by the late Pleisto- apparent tendency to evolve from generalized masti- cene–early Holocene (see Bond et al. 1995). catory apparatus with complete dentition, without Following Billet (2010), the clade comprises two diastema and brachyodont cheek teeth, to very spe- monophyletic groups: Toxodontia and Typotheria – cialized forms including, for instance, hypertrophied plus the basal notoungulate family Henricosborniidae, incisors, simplified crown patterns and ever-growing and a clade comprising Notostylops as the sister group (hypselodont) cheek teeth (Ameghino 1887, 1894; of Pyrotheria (before considered as a separate order). Scott 1937; Simpson 1967; Cifelli 1985). Some phylo- Toxodonts include large (i.e. above 44 kg, sensu Mar- genetic studies suggest that hypselodonty probably tin & Steadman 1999) to very large animals (including evolved at least four times within the Notoungulata – strictly megammamals, i.e. 1000 kg or more), and are in the Toxodontidae, Interatheriidae, Mesotheriidae sometimes compared with hippos or rhinos, due to and Hegetotheriidae (Croft & Weinstein 2008). The DOI 10.1111/j.1502-3931.2010.00231.x Ó 2010 The Authors, Journal compilation Ó 2010 The Lethaia Foundation 154 Cassini et al. LETHAIA 44 (2011) palaeobiological implications of this morphological Santa Cruz beds (350 and 550 kg respectively), only diversity and the relationship between form and being surpassed by the astrapothere Astrapotherium function have not been analysed rigorously before, (1000 kg), whereas Adinotherium is rather smaller and the dietary inferences have been mostly limited (120 kg). Nesodon, Adinotherium and Homalodothe- to broad generalizations. rium species have complete dentition without dia- The Santacrucian mammalian fauna (Santa Cruz stema and large masseteric and temporal muscles Formation, late–early Miocene) along the Atlantic attachment areas. Nesodon and Adinotherium have coast of southern Patagonia is particularly appropri- hypertrophied lateral incisors and high-crowned of ate for this kind of study due to its taxonomic rich- finite growth cheek teeth (protohypsodonty, sensu ness, diversity, amount of specimens recorded and Mones 1982). The Santacrucian Typotheria are quality of preservation (see Vizcaı´no et al. 2006, small-sized animals represented by Protypotherium, 2010; and references therein). Among notoungulates, Interatherium (Interatheriidae; Fig. 1C, D),Hegetothe- the Toxodontia are represented by three genera: Nes- rium and Pachyrukhos (Hegetotheriidae; Fig. 1E, F). odon, Adinotherium (Toxodontidae, Nesodontinae; Calculating body masses as decribed above, Hegeto- Fig. 1A, B) and Homalodotherium (Homalodotherii- therium and Pachyrukhos are respectively the largest dae). Calculating body mass using the mean of out- (14 kg) and the smallest (2.8 kg) examples. put of the allometric equations for ‘all ungulates’ Among interatheriids, Protypotherium species (4.5 proposed by Janis (1990a), Homalodotherium and kg for the smaller Protypotherium attenuatum and Nesodon areamongthelargestungulatesfromthe approximately 8.5 kg for the largest Protypotherium AC D E B F Fig. 1. Skull and mandible of Santacrucian notoungulates genera included in this study. Toxodontids: A, Nesodon MPM-PV 3659; B, Adino- therium MPM-PV 3532 and 3666. Typotheres: C, Protypotherium AMNH 9868; D, Interatherium MPM-PV 3471; E, Hegetotherium MPM-PV 3526; and F, Pachyrukhos AMNH 9219. Scale bar 10 cm. LETHAIA 44 (2011) Notoungulate habitat and diet 155 australe)arelargerthanInteratherium (3.5 kg). Artiodactyls and Perissodactyls were also achieved by Interatheriids include species with complete dentition notoungulates. and without diastema or hypertrophied incisors. The Principle of Actualism is applied, assuming Thus,theirincisorsareallthesamewidth.Inhegeto- that some biomechanical laws have constrained in the theriids, the upper and lower central incisors are same manner the evolution of the craniodental struc- hypertrophied, and the lateral incisors and canines ture of these three taxonomic groups, leading to the are atrophied, resulting in a functional diastema in convergence of common morphological patterns. Hegetotherium, and an anatomical diastema with However, when the phylogenetic legacy is different, missing teeth in Pachyrukhos. In all these taxa, cheek and the starting morphology varies, the same biome- teeth are high-crowned and ever-growing (eu- chanical laws can be upheld with different strategies, hypsodonty, sensu Mones 1982), and the masseteric associated to different morphological patterns. muscle areas of attachment are larger than the tem- poral ones. All genera analysed in this study have been tradi- Material and methods tionally considered mostly herbivores. Following Scott (1937), and based primarily on the high-crowned Abbreviations cheek teeth, they were considered inhabitants of open plains and other open-habitat, eating mostly grasses AMNH: American Museum of Natural History, New (Patterson & Pascual 1968; Cifelli 1985; Billet et al. York,USA;MACN:MuseoArgentinodeCiencias 2009). Bond (1986) and Tauber (1997b) also sup- Naturales ‘Bernardino Rivadavia’, Buenos Aires, ported the grazers hypothesis based on the degree of Argentina; MLP: Museo de La Plata, La Plata, Argen- hypsodonty and incisor morphology. With reference tina; MPM-PV: Museo Regional Provincial Padre ‘M. to Nesodon and Adinotherium, Madden (1997) pro- J. Molina’, Rı´o Gallegos, Argentina; YPM-PU: Yale posed that the most complex molar crowns would Peabody Museum, New Haven, USA. have provided great shearing ability among toxodont- ids allowing them to break down the grasses more eas- Data ily. However, Townsend & Croft (2008) using a micro-wear approach for three genera of Santacrucian Forty-seven specimens of notoungulates from the notoungulates disagreed the preceding dietary infer- Santa Cruz Formation (late-early Miocene) were anal- ences. They conclude that Nesodon imbricatus was a ysed. Only specimens with no or little apparent defor- leaf browser that focused more on hard browsing,