10 Paleoecology of the Paucituberculata and Microbiotheria (Mammalia, Marsupialia) from the late Early Miocene of Patagonia Mar/a Alejandro Alu!ilo, Edgardo Ortiz-JaureguizaT, anti Adriana M. Candela Abstract ami li sis de los result ados de las mas as corporales y [a This chapter presents a paleoecological an alysis of non­ dietas, se reconocieran diversos nichos ecologicos: camivorous Sanlacrucian marsupials of the orders Paucituber­ pequen os a medianos insectivoros. pequenos a medianos culara and Microbiothelia. Different ecological niches are insecliv oros~ fru g i v oros y medianos a grandes ft1Jgiv oros. infen-ed [Tom estimates of bcx:Iy mass, diet, and iocomOior Nuestros resultados nos pemliten coneluir qu e lo s Pauej­ behavior. Body masses were estimated using a regression tu berculata y los Microbiothe ria de la FOlmaci6n Santa analysis based on living marsupials. Possible dietary prefer­ Cruz constituyen ull agregado ecologicamente diverso ences were explored by an analys is of the developmeut ofmolar que habit6 zonas boscosas. desarrolladas bajo un clima shearing crests. Inferences about locomotor behaviors of some calid o y con lIu vias estac ionales. ESlas zonas habrian spec ies with we ll -preserved postcran iaJ skeletal remains were ofrecido una amplia diversidad de recursos fanlo espa­ deJived from a publ is hed morphofunctional analysis. From the ciale!-. como troficos para los diversos ni chos ecologicos wide range of estimat.ed body masses and diet several niches de los marslipiaies no carn lvoros. Nuestfa reconstrucci6n were infened: small- to medium-sized insecti vores, small- to paleoambiental es compatible con la ex isrencia de hetero­ medium-sized insectivore-frugivores, and medium- to large­ geneidad arnbie nl al dmante el Sanl<lCfUCenSe, inferencia sized fmgi vores. According to our results, Paucituberclilata and est" deri vada de otras indicadores climatico-ambien l<lles. Microbiothelia of thc Sant..'1 Cruz FonnatiQJl conStilule an eco­ logically diverse assemblage tbat inhabited forested habitats, developed under w<um temperanlres and seasonaj rainfall. 10.1 Introduction These fores ted habitats could have supported severn] nnn-car­ During the Cenozoic, a high diversity of mctatherians occupied nivorous marsupi~ 1 niches, offering diverse resources both in a broad range of ecological niches jn South America. This the spatial dimensions and ill the lrophic ones. array included medium 1"0 IMge carnivorous and camivorous­ omnivorous (i.e. Sparassodonra; Prevosti e/ aI., Chapter [I ). Resumen small granivorous (e.g. poJydolopimOlphian ArgyroJagoidea; En eS le capitulo se presenta un ana lisis paleoecologico de Goin el a/.. in press), and several small to medium insectivorous los mars upiales no carn ivoros del Santacrucense pertene­ and i.nsec ti vorolis- flUgiv oro u ~ species (e.g. didelphimorphian cientes a los 6rdenes P,Hlcitubercul ata y Microbiothe ri a. Didelphidae, Paucituberculata; Gain (!( al., in press, Dumont Para establecer los dislinlos nichos ecologicos se anali ­ el aI., 2000). All of the larger taxa are now extinct, and a fe\~ zaron las masas corporales, dietas y eS lJ"<t tegia<; locomo­ of the small- to medium-sized insecti vorous, insec ti vorous-­ loras. El tamafio cO'lx)ral fue es ti mado a partir de una recta fmgivorous, and carnivorous tax a (microbi otherians, pauciru­ de re grcsion liuear obtenida a partir de marsupiales berculatans. and didelphids) surv ive to the presenl. actu aJes. Las pos ibles preferencias dietarias fu eron explor­ Pallcituberculata and Microbiotheria are two major adas medi ante un anaJi 5is del grado de desalToll o de las crestas cortantes de los molares. L1.s estrategias Marsupialia clades (Fig. 10.1). As a result of all current locomotoras, en el easo de aqllelJas especies que poseen ph y l oge Jli e~ (e.g. Amrine-Madsen el 01. , 2003; Horovitz amI un esqueleto postcraneano bien preservado, fu eron infer­ Sanchez· ViUagra , 2003; Phillips cf aI., 2006; Asher ef al., 2001: id as a partir de un amili sis morfofunciona1. A partir del Nilsson el al., 2004; Beck, 2008; Meredith el 01., 20081. there is consensus on Ihe close affinities between (he extruu microbiotheriid Dromiciops gliroides and the A ustralasian Early Miocelle Paleobiology ill Paragonia: Hi.~h - Loli f llde marsupials (Ausu'alidelphia; Szalay, 1982. 1994). However, Paleocommunities of {he Sama Cmz Forma/ioll, ed. Sergio F. Vizcaino, Ri chard F. Kay and M. Susana Bargo. Published by the posilion of D. gfiroides within AustralicJ elphia js srill Cam bridge Uni vt:rsil Y Press. (C' C<l mbridge Universit y Press 2012. con t rove r ~ i a J (Nilson et 01., 20JO). On the other hand, mo~ : 156 Paleoec% RY of Santacrucian Pauciruherculata alld Microhiotheria 157 ,--------_________ Monol rem ~l~ 1l1e fossiJ record of Paucitubercul a[a and M icrobiotheria ,--_----------- -- Vmcelesfes indicates that these marsupials had a wid er geographic Euthaflll disllibution and hi gher taxonomic di versity than those of ,------------ DeJlellleriClum the present (Abell o, 2007; G01n ef al., in press) . The oldest· ,-_________ Pucadff/phys known Paucituberculata and Microbiotheria date from the ,--------- CMolph lll1 orpllta Paleocene and include fonns such as the paucituberculatan ,-______ Paucltubercullta Bardalestes Goin , Candela, Abello and Oli veira, 2009 ,-____ Oas ywomorphla (ltaboraian Age, Argentina; Goin el al. , in pres s) and the ,-___ Pernmella microbiotherian Mirand.arheriw71 (Paula Couto, 1952) from Microbiother/a Brazil (Itaboraian Age; Goi n e( al. , in press). Bolh groups Diprolodon tJa achieved their hi ghest taxo nomi c di versity in the Early Mi ocene Colhuehuapian ~nd Santacrucian Ages, but the Fig. 10.1. Phylogenetic Iree showing the relationships of li ving marsupial oruers (modified from HoroviTz and Srinchez~ Villagra. 2003 ). in fe n'ed cladogenetic events that gave rise to the Miocene fOims seem to hav e OCC UlTed during the Oligocene (Abello, phylogenetic studies based on molecular or combined data 2007; Goin el al. , 2010). By the Early Miocene, micro­ (e.g. , Nilson et al., 2004; Asher et aI., 2004; Beck, 2008; biotherians are represented by nine species belonging to Meredith ef 0/., 2008), as well as some morphological Microbiotheriidae. At [he same time, paucitu berculatans studies based on cranial , postcranial, and soft tissue are represented for 23 species gro uped among Caenol estj­ anatomy (Horovitz and Sanchez· Villagra, 2003), indici:lte dae, Pi chipilidae, Palaeothenti dae, and Abderitidae. that Paucituberculata is the sister group of Au stralidelphia. Despite the abundant representation of small marsup ia ls Microbi otherialls and pallcituberculatans are poorly (parti cularly paucituberculatans) in the Early Miocene represented in presenl.day ecosyste ms (Flores, 2006a, b; (Bown "nd Fl eagle, 1993; Abello, 2007), they are mainly PatterSo n, 2007; Patterso n and Rogers, 2007). The only known by mandibular and max illalY remains and isolated extant microbiotherian is the so-called "monito del mome" leeth. Consequently, the reconstructions of cerrain paleo­ (Dromiciops gliroides), a small insectivorous marsupi al ecological aspects (e.g_ body size, diet) have been de rived endemic to the temperate forests of so uthern Chi Ie and from the sLud y of dental remains. Argentina, associated wi th (he southern beech forests Several ecological niches have been identified among (Nothofagus) and South American mountain bamboos Paucituberculala (Dumont el 01., 2(00): small insectiv ores (Chusquea) (Hershkovitz. 1999). Dromiciops gLiroides is (Caenolestid ae and Pichipilic1ae), small· to medium-size lhe only South American marsupial reported to exhibit deep inseclivore- fru givores (Palaeotb entidae), and small- to torpor or hibemation (Greer, 1966; Bozinovic el al., 2004). medium·size frugivores (AbdeliLidae). As yet only two speci· In the summer season thi s species is acti ve during the mens including postcrartial and cranial rem ai ns are reported ni ght, being a common mammal of the understory stratum for Pancituberculata (Abello and Candela, 2010). These were (Rodriguez-Cabal et al .. 2008) . referred (0 two palaeothentid species, Palaeothentes minu.ru.s The living Paucituberculata include fi ve species th at Ameghino, L887 and Paloeolhentes lemoinei Ameghino, are grouped in the genera Caeno/estes, Lestoros, and 1887 , from the late Early Miocene (Santa Cruz Fonnation). RhYllcholestes, all belonging 10 Caenolestidae ("shrew oppo· Curso-saltatorial locomotor srrategies were in ferred for both sum s"). This clade has a disjunct Andean distribution that species (Abello and Candela, 20 I 0). ranges from Venezuela Lo northern Pem (Caenolestes; In this chapter we summarize previous paleoecological Albuja and Patterson, 1996), central Pem and Bolivia studies of Sanl acrucian Paucituberculala, and present the (ustoros inca; Anderson , 1997; Ramirez er ol., 2(07) and results of a new paleoecological analysis of Santacrllcian southern Chile and Argen tin a (Rhyncholestes; Patterson and Microbiotheria. Additionally, we evaluate the paleoenviron­ Gallardo, 1987; Birney et aI. , 1996). Caeno1estids have a mental significance of non-carnivorous Miocene marsupials. wide latitudinal and al tirudinal (up to 4000 meters above sea level) di stribution . spanning several biomes including 10.2 Santacrucian pattcituberculatans Paramo, Montane foresl, and Valdi vian forest. Extant caeno­ and microbiotherians Ie..<;tids are small shrew·sized marsupials, which inh abit moist and dense vegetated microhabitaLs