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Phylogeny of the – morphological reconstruction of evolutionary relationships among extant and Xenarthrans

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Morphology-based investigations of the phylogenetic relationships among extant and fossil xenarthrans

TIMOTHY J. GAUDIN AND H. GREGORY MCDONALD

Resumen de la fauna eocena de Messel en Alemania. Virtual­ mente todas las reconstrucciones recientes de la filo­ En un grupo como el de los Xenarthra, en el que la di­ genia de los perezosos apoyan el origen difiletico de los versidad conocida de formas extinguidas excede por dos generos arboricolas vivientes, pero difieren en las mucho la de las vivientes, aquellos analisis morfologicos hipotesis de relaciones con diferentes taxones fosiles. que incorporen taxones fosiles aumentan su importan­ Un comprehensivo analisis reciente ubica a Bradypus cia al mejorar nuestra comprension de la filogenia. En como el taxon hermano de los restantes perezosos y este estudio se revisan las investigaciones morfologicas reune a Choloepus con los megaloniquidos extingui­ recientes sobre filogenia de los xenartros. Se resaltan dos. Este estudio corrobora la monofilia de las familias las areas de amplio consenso, induyendo la monofilia Nothrotheriidae, , y de Xenarthra, de cada uno de sus tres subgrupos prin­ , apoya la alianza de notroteridos, mega­ cipales [, Vermilingua, Phyllophaga (= Tardi­ teridos y megaloniquidos en un dado Megatheriodea grada 0 Folivora)] y de los [Vermilingua + Phy­ y, dentro de este ultimo grupo, reune a notroteridos Hophaga]. Tambien se revisan los estudios recientes de y megateridos en un dado Hamado Megatheria. Las las relaciones supraordinales del grupo, asi como los relaciones entre estas familias de perezosos, particu­ amilisis filogeneticos dentro de los Cingulata, Vermi­ larmente Mylodontidae y Megalonychidae, asi como lingua y PhyHophaga. Las afinidades de Xenarthra con la taxonomia alfa de todos los xenartros, requieren de otros grupos de mamiferos placentarios aun gene ran nuevos estudios. controversias y requieren de mas investigaciones. Den­ tro de los Cingulata aun son poco comprendidas la ta­ Resumo xonomia y la filogenia de los gliptodontes y se requie­ ren mas estudios, aunque los analisis recientes prove en Em urn grupo como 0 dos Xenarthra, em que a diversi­ nueva informacion sobre la sistematica de este grupo. dade conhecida de formas extintas excede com muito a Un estudio dadistico confirma hipotesis filogeneticas vivente, os estudos morfologicos que incorporam tax­ previas sobre las relaciones entre extingui­ ons fosseis aumentam sua importancia, ao melhorar dos y vivientes, pampaterios y gliptodontes, induyendo nossa compreensao da filogenia. Nesse estudo, revisam­ la monofilia de los eufractinos vivientes y un dado que se os estudos morfologicos recentes sobre a filogenia reune a gliptodontes y pampaterios y la posicion basal dos xenartros. Resaltam-se as areas de amplo consenso, de los dasipodinos dentro de los Cingulata. Sin em­ induindo 0 monofiletismo de Xenarthra, de urn de seus bargo, no sostiene la monofilia de los armadillos como tres sub-grupos [Cingulata, Vermilingua, Phyllophaga un todo 0 de los tolipeutinos, eutatinos y eufractinos. (= Tardigrada ou Folivora) e dos Pilosa [Vermilingua + Con respecto a los Vermilingua, las relaciones entre los Phyllophaga]. Tambem, revisam-se os estudos recentes miembros indiscutidos del grupo no produce contro­ das relayoes supra-ordinarias do grupo, assim como as versias, pero existe un gran desacuerdo sobre la ubi­ analises filogeneticas dentro dos Cingulata, Vermilin­ cacion de Eurotamandua, el presunto oso hormiguero gua e Phyllophaga. As afinidades de Xenarthra como

24 Phylogenetic relationships among extant and fossil xenarthrans 25

""'--- , _, ,~x <; '~~,,_~.'-.: . '.~ ~ PHYLLOPHAGA CINGULATA VERMILINGUA (= TARDIGRADA)

Figure 3.1. Cladogram depicting the relation­ ship among the three suborders of Xenarthra: Cingulata, Vermilingua, and Phyllophaga (= Tardigrada or Folivora). The alliance of anteat­ PILOSA ers and in a monophyletic Pilosa to the exclusion of armored xenarthrans has been supported by a wide variety of subsequent mor­ phological and molecular studies (see Introduc­ tion). depicted across the top, from left to right: (, SA), Chaeto­ phractus (hairy ), Myrmecophaga (giant ), Choloepus (two-toed ), Megath­ erium (pleistocene, SA). Modified from Gaudin (2003). Abbreviations: SA = . outros grupos de mamiferos placentarios ainda geram ultimo grupo, reune os notroteriideos e megateriideos controversias e requerem mais estudos. Urn estudo em urn dado chamado Megatheria. As relac;:6es entre dadistico confirma hip6teses filogeneticas previas sobre estas familias de preguic;:as, particularmente ­ as relac;:6es entre tatus extintos e viventes, pampaterios tidae e Megalonychidae, assim como a taxonomia alfa e gliptodontes, induindo 0 monofiletismo dos eufracti­ de todos os xenartros, requer novos estudos. nos viventes, e urn dado que reune os gliptodontes e pampaterios, e a posic;:ao basal dos dasipodinos dentro Introduction dos Cingulata. Apesar disso, nao sustenta 0 monofile­ tismo dos tatus como urn to do, ou dos tolipeutinos, eu­ Historically, the roots of systematic analysis in biol­ tatinos e eufractinos. Com respeito aos Vermilingua, as ogy lie in comparative studies of organismal morphol­ relac;:6es entre os membros indiscutiveis do grupo nao ogy. Linnaeus (1758) based his great Systema Naturae produz controversias, mas existe urn grande desacordo on similarities in overall form among the organisms sobre a posic;:ao de Eurotamandua, 0 presumido taman­ he surveyed. The systematists and taxonomists of the dua da fauna eocenica de Messel na Alemanha. Virtual­ eighteenth and nineteenth centuries who constructed mente todas as reconstruc;:6es recentes da filogenia das much of the basic of living and extinct xen­ preguic;:as ap6iam uma origem difiletica dos dois gene­ arthrans did so on the basis of morphology (much ros de preguic;:as arboricolas viventes, contudo diferem of this early literature is reviewed in Hoffstetter 1958, sobre as hipoteticas relac;:6es com diferentes taxons f6s­ 1982; Glass 1985; Wetzel 1985a). Individual species and seis. Uma analise recente posiciona Bradypus como 0 higher-level taxa have been recognized using external taxon-irmao das preguic;:as rest antes e reune Choloepus morphological or skeletal characteristics, be they living com os megaloniquideos extintos. Esse estudo cor­ (Wetzel 1985a) or extinct (Hoffstetter 1958). The various rob ora 0 monofiletismo das familias Nothrotheriidae, groupings and sub groupings within Xenarthra were Megatheriidae, Megalonychidae e Mylodontidae, ap6ia established largely on the basis of skeletal and dental a alianc;:a de notroteriideos, megateriideos e megalo­ traits (appendix 3.1, figure 3.1): the Cingulata, the ar­ niquideos em urn dado Megatherioidea e, dentro deste mored xenarthrans, which bear a carapace formed by 26 T. J. Gaudin and H. G. McDonald

a mosaic of dermal ossifications and epidermal scales, should continue to playa vital role in improving our can be divided into armadillos, with their peglike teeth, knowledge of the phylogenetic history ofXenarthra. and pampatheres, with enlarged bilobate teeth, both of Recent advances in the study of xenarthran phylog­ which have imbricating osteoderms that allow flexibil­ eny utilizing both morphological and molecular in­ ity in the carapace, and the , with their very vestigations have been reviewed by Garcia (2003) and peculiar trilobate teeth and immobile carapaces; the Gaudin (2003). In addition, a separate chapter (Delsuc Vermilingua or , which have tubular, edentu­ and Douzery this volume) treats recent developments lous skulls; and the Phyllophaga (= Tardigrada or Foliv­ in the use of mitochondrial and nuclear gene sequences ora), including the living tree sloths and extinct ground to examine relationships of extant xenarthrans. There­ sloths, which share a hypselodont herbivorous denti­ fore, in this chapter we will focus on morphology-based tion and a characteristic reduced dental formula with investigations of phylogeny that have been published a maximum of five upper and four lower teeth in each subsequent to Gaudin (2003), while also considering half of the jaw (Gaudin 1999a). Armadillos, anteaters, pertinent earlier studies that have laid the groundwork and sloths were originally placed in different groups by for our current understanding of the phylogeny of the Linnaeus, with armadillos assigned to his Bestiae along group. We will follow the basic outline of Gaudin's with pigs, some insectivores, and opossums, whereas (2003) review. First, we will consider issues related to anteaters and sloths were allocated to Bruta along with the supraordinal relationships of Xenarthra. Several , manatees, and pangolins. Nevertheless, these aspects of xenarthran phylogeny are well established in three very disparate types of were eventually the published literature (Delsuc et al. 2002; Delsuc et al. united into a single order because they share a suite 2003; Garcia 2003; Gaudin 2003, 2004a; Rose et al. 2005; of unique and unusual morphological characteristics Gaudin and Wible 2006) and need not be treated in de­ (Gaudin 1999a; McDonald 2003b; Rose et al. 2005; ap­ tail here. These include the monophyly ofXenarthra as pendix 3.1), among them the feature for which the or­ a whole and the monophyly of each of the three major der was named, the xenarthrous intervertebral articula­ subgroups, Cingulata, Vermilingua and Phyllophaga, as tions (Gaudin 1999b). well as the monophyly of the Pilosa, a clade that unites The advent of modern cladistic techniques has fa­ sloths and anteaters to the exclusion of cingulates (ap­ cilitated improvements in our detailed understanding pendix 3.1, figure 3.1). However, we will review studies of xenarthran phylogeny, as has the development of that investigate phylogenetic relationships within each molecular systematic analyses. As discussed in O'Leary of the three primary subgroups. (1999) and O'Leary and Geisler (1999), morphology­ based phylogenetic analyses are able to incorporate a Supraordinal relationships much broader taxonomic sample than molecular stud­ ies because of the inclusion of fossil taxa, but at the cost Morphology-based studies of mammalian phylogeny of limited character sampling, being restricted almost over the past several decades have tended to place entirely to osteological characters, particularly if the Xenarthra in a remote position within Placentalia, for fossil record is to be included. Xenarthra is unusual (but example, as the sister taxon to other placentals (Epi­ not unique) among mammalian orders in the sense that theria), although perhaps allied with certain extant or it includes a well-known and tremendously diverse ra­ extinct groups like pangolins (Order Pholidota) and diation of extinct taxa, including more than 150 genera Palaeanodonta (Novacek and Wyss 1986; Novacek (McKenna and Bell 1997), but only 14 extant genera and 1992). Placement of the Xenarthra as the sister group 31 extant species (Gaudin 2003). Two major groups, the to the other placentals was first advocated by early glyptodonts and pampatheres, have no modern repre­ cladistic morphological studies (McKenna 1975). The sentatives and sloths are only minimally represented (2 Xenarthra/Epitheria dichotomy has been criticized by extant genera with 6 species). Thus, systematic stud­ other morphologists (Rose and Emry 1993; Gaudin et ies that consider only extant taxa are likely to be par­ al. 1996), and both morphological and molecular work ticularly susceptible to taxonomic sampling problems has failed to support the xenarthran/pholidotan clade such as long-branch attraction (Hillis 1998). Therefore, (Rose and Emry 1993; Delsuc et al. 2002; Rose et al. morphological studies of xenarthran phylogeny, espe­ 2005). However, recent molecular studies generally fa­ cially those that examine a wide variety of extinct taxa, vor a remote position of Xenarthra among placentals. Phylogenetic relationships among extant and fossil xenarthrans 27

Xenarthra has been identified as one of the four primary bivorous pampatheres and glyptodonts (figure 3.2; see placental clades, along with Afrotheria, Laurasiatheria, also Fernicola et al. this volume). Gaudin (2003) points and Euarchontoglires (Madsen et al. 2001; Delsuc et al. out that armadillos are the most diverse clade of liv­ 2002; Springer et al. 2004). The relationships among ing xenarthrans and have the oldest fossil record, yet these four clades are not well resolved, although either study of their relationships, and indeed the phylogeny Xenarthra or Afrotheria, or a clade uniting the two, is of all cingulates, has been largely neglected until re­ typically placed at the base of the placental tree (Mad­ cently. The work by Delsuc et al. (2002, 2003), using sen et al. 2001 Delsuc et al. 2002; Springer et al. 2004). nuclear and mitochondrial DNA sequences, has done Recently, two studies of higher-level mammalian much to rectify the situation for extant armadillos, al­ relationships have been published that include rep­ though data for the fairy armadillo Chlamyphorus are resentatives of Xenarthra and employ morphological as yet unavailable. Morphology-based investigations of characters either exclUSively (Luo and Wible 2005) or cingulate relationships, however, especially those that in combination with molecular characters (Asher et consider extinct taxa, remain scarce, with one or two al. 2003). Interestingly, neither supports a basal posi­ noteworthy exceptions. tion for Xenarthra within Placentalia. Luo and Wible The systematics of the diverse and formerly abundant (2005) sampled only a small number of extant placen­ assemblage of extinct glyptodonts are the least studied tal taxa, along with a variety of extinct basal eutheri­ and least understood among any of the major groups ans. Nevertheless, xenarthrans along with carnivorans of cingulates. Glyptodonts have been subdivided into formed a crown clade, exclusive of extant representa­ various subfamilies and tribes based primarily on char­ tives from Glires and Lipotyphla (Luo and Wible 2005). acters relating to ornamentation of the carapace and the In Asher et al. (2003), when morphological characters structure of the caudal armor, along with selected fea­ alone were considered, Xenarthra formed a clade with tures of the cranial and postcranial skeleton. However, aardvarks and pangolins that in turn was part of a large there is no consensus as to their taxonomy at any level basal placental multichotomy in the strict consensus and certainly little phylogenetic analysis of the relation­ tree. However, when molecular characters were added, ships among the various taxa. Paula Couto (1979) listed Xenarthra was not only pulled apart from pholidotans four subfamilies: Propalaehoplophorinae; Hoplophori­ and tubulidentates in the strict consensus trees, it was nae, with the tribes Palaeohoplophorini, Plohophorini, pulled into a crown clade including afrotherians and Hoplophorini, Panochthini, Lomaphorini, Neothora­ laurasiatherians and excluding members of a para­ cophorini, and Neuryurini; Doedicurinae; and Glypto­ phyletic stem group of Euarchontoglires (Asher et al. dontinae. In their study of the ear region of cingulates, 2003). Patterson et al. (1989) recognized the same four sub­ It is worth reiterating that the morphological data families: Propalaehoplophorinae, Sclerocalyptinae (= of Asher et al. (2003) supported a close relationship Hoplophorinae), Glyptodontinae, and Doedicurinae, between Pholidota and Xenarthra-in fact, it resulted but with fewer tribes, as the Sclerocalyptinae was not in a sister-group relationship between the pangolin subdivided into tribes and the Doedicurinae included Manis and the vermilinguan Tamandua, thus only the Panochthini and Doedicurini. It should be resulting in a nonmonophyletic Xenarthra. However, noted that their work focused primarily on descriptive when molecular data were added, this relationship fell anatomy of the ear region and that most of the study apart. Pholidotans were not included in the Luo and concerned armadillos. Only two glyptodonts, Plohoph­ Wible (2005) study. Clearly, consensus concerning the orus (= Hoplophractus) and Eleutherocercus, were ex­ surpraordinal relationships of Xenarthra has not been amined. Neither of the above taxonomies recognized achieved, and more investigation of this question is the enigmatiC subfamily Glyptatelinae, which first ap­ warranted. peared in the middle Eocene (Mustersan) and survived into at least the middle Pleistocene (Irvingtonian) of Relationships within Cingulata in the form of Pachyarmatherium (Downing and White 1995, Vizcaino, Rinderknecht, Cingulata encompasses the extant armadillos as well as and Czerwonogora 2003). In contrast, McKenna and a large radiation of extinct forms, including not only Bell (1997) divided the Glyptodontidae into five sub­ a wide variety of fossil armadillos, but also the her- families: the Glyptatelinae and the four subfamilies 28 T. J. Gaudin and H. G. McDonald

recognized by Paula Couto (1979) and Patterson et al. 3.2). Nevertheless, many of the conclusions of the study (1989). The primary difference was that only two of are startling when compared to previous work. In the the subfamilies were subdivided into tribes, with the phylogeny of Gaudin and Wible (2006), the armadillos Hoplophorinae having the largest number, including (sensu lato) are paraphyletic, with the clade including the Hoplophorini, Lomaphorini, Palaehoplophorini, pampatheres and glyptodonts as a crown group nested Plohophorini, Panochthini, and Neuryurini. The within the armadillo radiation (figure 3.2). The tolyp­ Glyptodontinae was subdivided into two tribes, the eutine clade of extant armadillos recovered by Delsuc Glyptodontini for South American forms and Glypto­ et al. (2002,2003) was not obtained in any of Gaudin theriini for the North American genus Glyptotherium. and Wible's (2006) analyses. Lastly, Gaudin and Wible's The tribe Neothoracophorini was also recognized but (2006) study fails to unite extinct forms traditionally not placed in any subfamily. placed in the Euphractinae with the extant euphractine These earlier classifications have been contradicted clade, arranging them instead in a paraphyletic assem­ in a number of important respects by the recent phy­ blage that includes both extinct "euphractines" and eu­ logenetic studies of Fernicola (2005). Fernicola (2005) tatines, making both groups polyphyletic (figure 3.2). conducted a cladistic analysis based upon 84 cranio­ Gaudin and Wible (2006) acknowledge that their dental characters in 12 genera. His results analysis is based on a restricted character base (ap­ are summarized by Fernicola et al. (this volume), but pendix 3.l), and call for the addition of postcranial or it is worth noting here that the monophyly of several soft-tissue data to further refine our understanding of of the traditional subfamilies is not supported by his cingulate phylogeny. Certainly a total-evidence analy­ work. Indeed, his results reinforce the observation that sis of cingulate phylogeny, combining morphological glyptodonts are the one group within Xenarthra most and molecular data, would also be a valuable contribu­ requiring intensive study and revision, with regard to tion to the systematic literature on this group. A more both taxonomy and phylogeny. complete understanding of cingulate phylogeny will Among the cingulates the only broad, morphology­ ultimately be an invaluable enhancement of ongoing based cladistic study of the group's phylogeny is that studies of anatomical and functional evolution among of Gaudin and Wible (2006, figure 3.2). Gaudin and armored xenarthrans (e.g., Hill 2004; Kalthoff 2004; Wible (2006) examined the craniodental morphology Vizcaino, Farina et al. 2004; Fernicola 2005; Fernicola of a wide diversity of living and extinct armadillos, et al. this volume; Vizcaino et al. this volume). including all 9 extant genera, 3 genera of eutatine ar­ madillos, 4 genera of extinct euphractine armadillos, Relationships within Vermilingua the extinct genera Stegotherium and Peltephilus, and a single representative each from the pampatheres (Vas­ Recent analyses have reached a consensus concern­ sallia) and glyptodonts (Propalaehoplophorus). Their ing the relationships among undoubted vermilin­ results are congruent with other, earlier investigations guans. Both morphological (Gaudin and Branham of cingulate phylogeny in a number of respects. Like 1998; Gaudin 2003) and molecular studies (Delsuc et Patterson et al. (1989) and Engelmann (1985), they rec­ al. 2002, 2003) support the alliance of the extant gen­ ognize a close relationship between pampatheres and era Tamandua and Myrmecophaga in a monophyletic glyptodonts (figure 3.2). Their alliance of Stegotherium clade (), with the third extant genus with the extant long-nosed armadillos (Dasypus) like­ Cyclopes placed in a separate group (). wise echoes the conclusions of Patterson et al. (1989) Moreover, there is broad agreement on the affinities and Engelmann (1985), and the remote placement of of the South American fossil anteaters-the the horned armadillo Peltephilus as the sister group to Protamandua and Mio- Neotamandua allied other cingulates (figure 3.2) is reminiscent of earlier with myrmecophagids, and the Pliocene Palaeomyr­ classifications (e.g., Hoffstetter 1958) where Peltephi­ midon allied with Cyclopes (Gaudin 2003; see also Mc­ Ius was placed in its own family. The conclusions of Donald et al. this volume). The consensus breaks down, Gaudin and Wible (2006) are also congruent with the however, when the affinities of the putative European molecular analyses of Delsuc et al. (2002,2003) in rec­ anteater Eurotamandua are considered. ognizing the monophyly of the extant euphractine ar­ Eurotamandua derives from the middle Eocene madillos and in placing Dasypus on a separate branch Messel deposits of central Germany and was initially from other armadillos at the base of the clade (figure assigned to the Vermilingua (Storch 1981), making it Glyptodonts -t Pampatheres ~.. r--'·"',,-,,- jIIII ~ ~ ... -Extinct--~~ L-:2 - / E~~:::=c~me~~

jIIII

~. Extant Euphractines !III

jIIII

!III - jIIII ) Tolypeutines

!III - Dasypodines Peltephilus

Figure 3.2. Cladogram summarizing relationships within the Cingulata, as proposed by Gaudin and Wible (2006). Animals depicted at the right of the figure, starting at the top: (Pleistocene, SA), Chaetophractus (hairy armadillo), Tolypeutes (three-banded armadillo), Dasypus (long-nosed armadillo). Skulls depicted in left lateral view at the far right of the figure, starting at the top: Propalaehoplophorus (Miocene, SA), Holmesina (Pleistocene, SA and NA), Proeutatus (Miocene, SA), Eu­ phractus (yellow armadillo), Tolypeutes, Dasypus, Peltephilus (Miocene, SA). figures of Glyptodon, Chaetophractus, and Tolypeutes from Gaudin (2003). Abbreviations: NA = North America, SA = South America. 30 T. 1. Gaudin and H. G. McDonald

the only early xenarthran known from out­ studies are detailed elsewhere (Garcia 2003; Gaudin side South America. Subsequent authors have argued 2003, 2004a; see also Delsuc and Douzery this volume), that Eurotamandua is not a true vermilinguan, but is and will not be discussed further here. more properly placed within Xenarthra as the sister The most comprehensive of the recent morphology­ taxon of Pilosa, outside Xenarthra as the sister taxon to based investigations is that of Gaudin (2004a; figure Palaeanodonta, or even in its own order, distinct from, 3.3). Employing an extensive dataset of craniodental but distantly related to, Xenarthra and Palaeanodonta characters examined in 33 extinct and extant sloth (Rose et al. 2005). In the most recent review of the mat­ genera, including representatives of each of the major ter (Rose et al. 2005), the authors themselves could sloth families as well as a wide variety of xenarthran not agree on the proper phylogenetic allocation of this outgroup taxa, Gaudin (2004a) was able to investigate taxon, with one author favoring ties to the Vermilingua, such questions as the monophyly or diphyly of the two and the other three suggesting close relationship either extant tree sloth genera and the relationships among to Palaeanodonta or to the earliest pangolin Eomanis. and within the various sloth families. Gaudin's (2004a) Indeed, several phylogenetic analyses carried out by one results strongly support the diphyly of the tree sloths of us (Gaudin 2004b, 2005) would tend to strengthen (figure 3.3), an idea previously proposed by Patterson this latter claim. Nevertheless, it seems unlikely that a and Pascual (1972) and further developed by Webb convincing case can be made for the affinities of this (1985a). Gaudin (2004a) positioned Bradypus as the enigmatic taxon in the absence of a more comprehen­ sister taxon to all other sloths (a clade termed "Eutardi­ sive phylogenetic analysis that includes representatives grada"), in contrast to both Patterson and Pascual's and from each of the major families within Pholidota, Pa­ Webb's studies, where Bradypus was considered closely laeanodonta, and Xenarthra, and possibly other non­ allied with the megatheres. Gaudin's (2004a) results edentate placental mammals. are, however, congruent with those of Patterson and Pascual (1972) and Webb (1985a) in the placement of Relationships within Phyllophaga Choloepus within the family Megalonychidae, a clade that includes the extinct Antillean sloths (figure 3.3). By far the most active area for morphology-based in­ Although the detailed relationships among tree sloths vestigations of xenarthran phylogeny has been among and ground sloths advocated by Gaudin (2004a) dif­ the extinct and extant sloths. In the past decade nu­ fer from those proposed in other recent morphological merous studies have examined relationships within and (White and MacPhee 2001; Pujos 2002) and molecular among the various sloth families using morphological analyses (Poinar et al. 1998, 2003; Greenwood et al. 2001; (Perea 1992; Gaudin 1995, 2004a; De Iuliis 1996; White Hofreiter et al. 2003), it is significant that all of them and MacPhee 2001; McDonald and Muizon 2002; Mc­ support the diphyly of tree sloths. Gaudin's (2004a) Donald and Perea 2002; Pujos 2002, 2006; Muizon et phylogeny also corroborates the monophyly of the al. 2003, 2004a; see also McDonald and De Iuliis this three extinct families of ground sloths, the Mylodonti­ volume; Pujos this volume) and molecular characters dae, Megatheriidae, and Nothrotheriidae, as well as the (Hoss et al. 1996; Poinar et al. 1998, 2003; Greenwood Megalonychidae (figure 3.3). Megatheriids, nothroth­ et al. 2001; Hofreiter et al. 2003). The latter group of eriids, and megalonychids are joined in a monophyletic papers is remarkable for both its inclusion of ancient clade Megatherioidea, within which Megatheriidae and DNA sequence data from extinct sloths, and, what is Nothrotheriidae form a monophyletic grouping termed equally important, the lack of agreement among the re­ the Megatheria (figure 3.3). A variety of Santacrucian sults of the various studies. This is no doubt attributable (early-middle Miocene) taxa traditionally labeled to both the fragmentary nature of the recovered DNA "nothrotheres" are removed to the base of the Mega­ sequences and the extremely limited taxonomic sample therioidea, although one of these taxa, Eucholoeops, is available for molecular study, which has included only recognized as a basal megalonychid (Gaudin 2004a). two extinct genera representing two separate families, A number of Gaudin's (2004a) phylogenetic conclu­ the nothrotheriid from North America sions are consistent with the findings of other recent and the mylodontid Mylodon from South America, morphological studies. McDonald and Muizon (2002) along with a sample recovered from a coprolite (Hof­ and Muizon et al. (2003, 2004a) support the recogni­ reiter et al. 2003) that currently cannot be assigned to tion of a monophyletic family Nothrotheriidae for the a described genus or species. The conclusions of these late Miocene-Pleistocene nothrotheres, and within that ~ MEGALONYCHIDAE ~ ~ including Choloepus ~ ~ ~~ -- MEGATHERIIDAE aft? ~~ . . . ;( - I NOTHROTHERIIDAE ~ MEGATHERIA ~ ~ 111----- :;: Basal Megatherioids ~ MEGATHERIOIDEA

\ ------MYLODONTIDAE - EUTARDIGRADA

Bradypus

Figure 3.3. Cladogram summarizing relationships within the Phyllophaga (= Tardigrada or Folivora), as proposed by Gaudin (2004a). Sloths are divided into four monophyletic families: Megalonychidae, Megatheriidae, Nothrotheriidae, and Mylodon­ tidae. The relationship of certain basal, mostly Santacrucian megatherioid sloths, to the three main megatherioid families (Megalonychidae, Megatheriidae, and Nothrotheriidae) is not unambiguously resolved. The extant 8radypus is placed as the sister taxon to all other sloths, whereas extant Ch%epus is incorporated into the family Megalonychidae. Animals depicted at the right of the figure from top to bottom: Ch%epus (two-toed sloth), (Pleistocene, SA), 8radypus (three-toed sloth). Skulls depicted in left lateral view at the far right of the diagram, from top to bottom: (Pleistocene, WI), Ch%epus, (Pleistocene, SA and NA), Nothrotheriops (Pleistocene, NA), Hapa/ops (Miocene, SA), Paramy/odon (Pleistocene, NA), 8radypus. Skull and animal figures from Gaudin (2003, 2004a). Abbreviations: NA = North America, SA = South America, WI = West Indies. 32 T. J. Gaudin and H. G. McDonald

family, the close relationship between the North Amer­ 1992) sloths. These studies demonstrate that there is ican Pleistocene genus Nothrotheriops and the South still much to learn about the phylogeny of sloths, a fact American Pleistocene genus . Indeed, readily admitted by Gaudin (2004a) in the conclusion Muizon et al. (2004a) provide a formal diagnosis for the to his study. Questions still needing additional study newly recognized family. White and MacPhee (2001) include the within-group phylogenetic relationships of confirm the diphyly of the modern tree sloths and the mylodontids and megalonychids and the detailed rela­ close relationship between extant Choloepus and small­ tionships of the extant tree sloths to the various groups bodied Antillean megalonychids. Their phylogenetic of extinct sloths. An analysis that incorporates post­ conclusions were based on an analysis of cranial and cranial skeletal characters, or soft tissue or molecular postcranial skeletal characters in a limited array of sloth characters, alongside Gaudin's (2004a) extensive matrix taxa, and their analysis did not include any megalony­ of craniodental features, should also prove valuable in chid taxa from South America such as Pliomorphus. further elucidating the phylogenetic history of sloths. This may explain why their results differ from those of Gaudin (2004a) in a number of important respects. Conclusions For example, their study does not yield a monophyletic Megalonychidae, but instead splits the Antillean radia­ Because of the disparities between the extinct and ex­ tion of megalonychids into distinct large-bodied and tant radiations in Xenarthra, with known fossil forms small-bodied clades, suggesting two separate dispersal greatly outnumbering the depauperate extant assem­ events of this family into the Caribbean islands. Their bIage, morphology-based investigations of phylog­ recognition of two distinct clades within the Antil­ eny that can account for this extinct diversity take on lean radiation of sloths is reminiscent of Kraglievich's particular importance. Morphological studies have so (1923) taxonomy, in which (the largest of far failed to achieve a consensus concerning the su­ the Antillean sloths) was placed in a distinct subfam­ praordinal relationships of Xenarthra, either among ily (Megalocninae) whereas Microcnus (a small-bodied themselves or with molecular studies. The latest mor­ form) and other Antillean sloths were assigned to the phological studies do not support a remote position Ortotherinae. of Xenarthra within Placentalia, however, and offer at Gaudin's (2004a) cladogram also closely parallels best equivocal support for a relationship between Xen­ some of the relationships of the mylodontine mylo­ arthra and Pholidota and/or Palaeanodonta. Within donts derived by Perea (1992). The two studies cannot Xenarthra, support for the monophyly of three major be directly compared as Perea utilized a number of gen­ subgroups, Cingulata, Vermilingua, and Phyllophaga, era (e.g., Sphenotherus, Promylodon, Ranculcus, Mega­ is consistently achieved, and there is robust support for bradys and Prolestodon) not incorporated by Gaudin, the alliance of the latter two groupings into a monophy­ and likewise Gaudin utilized some genera (e.g., Thino­ letic clade Pilosa. badistes and ) not included by Perea. In Among cingulates, the recent study by Gaudin and addition, Perea (1992) based his analysis solely on the Wible (2006) throws doubt on several traditional phy­ mandible because this is the only element available for logenetic hypotheses, but is consistent with previous some taxa; hence he was limited to a smaller number studies, including molecular ones, in a number of re­ of characters. Despite all these differences, the two spects, such as support of a monophyletic grouping of cladograms are congruent at a number of places. In glyptodonts and pampatheres and of extant euphrac­ both analyses Mylodon is the sister taxon to the other tine armadillos and its recognition of dasypodine ar­ genera, followed by Pleurolestodon, then , madillos as a separate and basal cingulate group. The with as the most derived member of the My­ systematics of glyptodonts is poorly known, although lodontinae. recent work by Fernicola (2005; see also Fernicola et al. Several of the studies cited above deal in more de­ this volume) holds promise for improving our phyloge­ tail with taxa given only superficial consideration by netic understanding of this group. Gaudin (2004a), including detailed, species-level phy­ Relationships within Vermilingua are broadly agreed logenies of megatheriid (De Iuliis 1996; Pujos 2002, upon, with the exception of the position of the puta­ 2006; see also Pujos this volume), scelidotheriine tive European anteater genus Eurotamandua. Strong (McDonald and Perea 2002), and mylodontine (Perea disagreements persist in the literature over the proper Phylogenetic relationships among extant and fossil xenarthrans 33 allocation of this taxon, whether to Vermilingua, to viting us to contribute this review. We are grateful to Palaeanodonta, to Pholidota, or to its own order. Only Julia Morgan Scott for producing almost all of the draw­ a comprehensive phylogenetic analysis incorporating ings used in this paper. We also wish to thank the edi­ representative taxa from all these groups is likely to tors and Susana Bargo and John Wible for their careful convincingly resolve this issue. critique of the manuscript. Tim Gaudin's work on this A comprehensive analysis of sloth phylogeny by study was supported by NSF RUI Grant DEB 0107922. Gaudin (2004a) is consistent with other recent morpho­ logical and molecular studies in affirming the diphyletic Appendix 3.1. Synapomorphies of Xenarthra and origin of the modern tree sloths. More controversial is major subgroups. his allocation of Choloepus to the Megalonychidae and Bradypus to a position as the sister taxon to all other Terminology for cranial anatomy follows Wible and sloths. Gaudin's (2004a) results also recognize a mono­ Gaudin (2004). Notations by the present authors are phyletic grouping Megatherioidea including megathe­ set off in square brackets [ J. riid, nothrotheriid, and meglonychid sloths to the exclu­ sion of mylodontids, and within megatherioids a close Xenarthra association between megatheriids and nothrotheriids. Engelmann (1985)-(1) xenarthrous intervertebral articula­ Gaudin's (2004a) recognition of a distinct family Noth­ tions [see Gaudin 1999b below]; (2) fusion of ischium to rotheriidae for late Miocene-Pleistocene nothrotheres anterior caudal vertebrae; (3) dermal ossicles in skin; (4) is consistent with other recent studies. However, there reduction of dentition [see McDonald 2003b below]; (5) remains much to learn about the relationships within placement of infraorbital canal entirely lateral to body of each of the sloth families. Additional phylogenetic is­ maxilla; (6) development of secondary scapular spine on sues unaddressed or unresolved by Gaudin's (2004a) the posterior margin of the scapula; (7) presence of m. study include the relationship to other sloths of Pseu­ rectus thoracis lateralis; (8) presence of m. pterygo-tym­ doglyptodon (Engelmann 1987; Wyss et al. 1990), Ente­ panicus; (9) presence of extensive retia mirabile in limbs; (10) paired post-renal venae cavae. lops (Pascual 1960), or the subfamily Schismotheriinae, Gaudin (1995)-(11) dorsoventrally elongate ectotympanic a grouping recognized by McKenna and Bell (1997) as bone; (12) presence of the pterygoid bone in the bony comprising eight genera of pre-Pliocene sloths, among wall of the tympanic cavity; (13) reduction of the antero­ them the ever-popular root taxon . All schis­ posterior length of the postglenoid region of the skull; motheriines were formerly considered to be early noth­ (14) participation of the entotympanic in the rim of the rotheres. Do they represent a true monophyletic clade jugular foramen; (15) entotympanic/pterygoid contact; or are they only an artificial paraphyletic taxon created (16) absence of ectotympanic/alisphenoid contact; (17) as a by-product of the more intensive study of the Plio­ fusion of distal tympanohyal to mastoid. Pleistocene forms? Gaudin et al. (1996)-(18) stapedial artery lost in adults. Lastly, it should be noted that there remains a critical Reiss (1997)-(19) m. mylohyoideus originates from den­ need for more alpha-level taxonomy in all xenarthran taries, basicranium, and soft palate; (20) anterior digas­ groups, as the validity of many of the genera and spe­ tric m. contributes to m. sternomandibularis; (21) trans­ cies described in the past requires serious reexamina­ verse m. stylopharyngeus enters soft palate. tion. There is no doubt that oversplitting of taxa at both Gaudin (1999b)-(22) wide zygapophyseal facets in poste­ the genus and species level has resulted in the true di­ rior thoracic vertebrae; (23) enlarged metapophyses; (24) versity of fossil xenarthrans being hidden in a plethora enlarged anapophyses in posterior thoracic and lumbar vertebrae; (25) medial and lateral zygapophyseal facets in of names that lack any biological reality. If our under­ post-diaphragmatic vertebrae [modification of (1) from standing of the phylogenetic history of the Xenarthra is Engelmann (1985)]; (26) xenarthrous articulations be­ to improve, any future analysis will require the inclu­ tween metapophysis and anapophysis [modification of sion of more taxonomically valid taxa. (1) from Engelmann (1985)]. McDonald (2003b )-(27) reduction or loss of premaxillary Acknowledgments teeth [modification of (4) from Engelmann (1985)]; (28) loss of deciduous dentition [modification of (4) from En­ We thank Jim Loughry and Sergio Vizcaino for their gelmann (1985)]; (29) reduction or loss of work in organizing and editing this volume, and for in- [modification of (4) from Engelmann (1985)]; (30) pres- 34 T. J. Gaudin and H. G. McDonald

ence of ventral articular processes on the sternebrae that lers connected by movable bands [there are also typically form complex synovial articulations with the sternal ribs; movable bands around the tail). (31) ossified sternal ribs that bear articular facets for one Gaudin (2004a)-(14) posterior teeth covered laterally by another and one or two articular heads for the sterne­ the ascending ramus of the mandible; (15) nearly vertical brae; (32) loss of fibular/calcaneal contact; (33) proximal posterior edge of the condylar process of the mandible; phalanges of manus and pes proximo distally compressed; (16) anterior edge of nasals evenly convex; (17) occipital (34) presence of a large palmar sesamoid or falciform in condyles positioned immediately posterior to condyloid the tendon of the m. flexor digitorum profundus. foramina. Gaudin (2004a)-(35) septomaxilla present; (36) facial Wible and Gaudin (2004)-(18) presence of a canal or fo­ exposure of lacrimal larger than orbital exposure; (37) ramen for the auricular ramus of the vagus nerve; (19) posterior upper teeth slant labially, posterior lower teeth carotid foramen between the basisphenoid and the pe­ inclined lingually; (38) ossified larynx. trosal; (20) cavum supracochleare is open ventrally; (21) Wible and Gaudin (2004)-(39) multiple foramina for the Glaserian fissure lies adjacent to the foramen ovale; (22) major, accessory, and minor palatine nerves and vessels; hypoglossal foramen lies ventral to the jugular foramen; (40) loss of alisphenoid canal; (41) a caudal palatine fo­ (23) incisive foramen lies within, or nearly within, the ramen that includes the minor palatine nerve and ves­ premaxilla; (24) presence of at least two mental foram­ sels; (42) absence of inferior petrosal sinus foramen; (43) ina; (25) piriform fenestra confluent with the carotid reduction or loss of foramen for the ramus superior of foramen; (26) presence of double posterior openings of the stapedial artery; (44) hiatus Fallopii absent; (45) lac­ the posttemporal canal, the lower entirely within the pe­ rimal foramen on the face; (46) mandibular foramen at trosal; (27) sphenopalatine and caudal palatine foramina the level of the alveolar plane; (47) absence of mastoid confluent. foramen; (48) absence of stapedial artery groove; (49) Gaudin and Wible (2006)-(28) occipital height greater closed stylomastoid foramen; (50) rostral opening of the than or equal to its width; (29) occipital artery travel­ pterygoid canal visible in lateral view below the sphenor­ ing in a groove on the occiput extending dorsal to the bital fissure; (51) an extrabullar internal carotid artery. posttemporal foramen; (30) width of the external nares Rose et al. (2005)-(52) loss ofinterparietal; (53) presence of much greater than their height; (31) external nasal ap­ a well-developed entotympanic; (54) anteroposteriorly erture inclined anteroventrally in lateral view; (32) an­ expanded ribs; (55) reduction in the number of lumbar terior portion of the nasoturbinal lying medial to the vertebrae; (56) tendency to incorporate caudal vertebrae nasal/maxillary or premaxillary suture; (33) rectangular in the sacrum; (57) scapula with elevated spine and elon­ occipital condyles. gate acromion. Pilosa Cingulata Engelmann (1985)-(1) scapular fenestra [= "coracoid fo­ Engelmann (1985)-(1) modification of dermal ossicles into ramen") immediately above the coracoid process of the flattened, interlocking plates [= "scutes"); (2) fusion of scapula; (2) concave articular surface for the navicular axis to one or more cervical vertebrae; (3) fusion of tibia on the astragalar head; (3) posterior displacement of and fibula; (4) development of a lateral keel on the radial the kidneys into the pelvic cavity; (4) testes positioned articulation of the humeral trochlea; (5) greater trochan­ within the pelvic cavity; (5) expanded epitympanic sinus ter of femur extends proximal to the head; (6) loss of the within the squamosal; (6) reduction or loss of the post­ foramen rotundum [probably represents a fusion of the glenoid foramen; (7) jugular foramen recessed above and foramen rotundum and sphenorbital fissure); (7) pres­ behind the petrosal, entotympanic and/or tympanohyal; ence of pronounced postglenoid fossa; (8) loss of pars (8) presence of a femoral head to the m. flexor cruris late­ intermedia of hypophysis. ralis; (9) incomplete zygomatic arch; (10) loss ofthe pars Gaudin (1995)-(9) enlarged paroccipital process; (10) gle­ tuberalis of the hypophysis. noid fossa of squamosal posterodorsally inclined. Gaudin (1995)-(11) subarcuate fossa directly dorsal to in­ Gaudin (1999b)-(ll) xenarthrous articulations between ternal auditory meatus; (12) enlarged jugular foramen; anapophysis and ribs in thoracic vertebrae, between an­ (13) glenoid fossa of squamosal bounded by lateral shelf; apophysis and transverse processes in lumbar vertebrae. (14) entotympanic!mastoid contact. McDonald (2003b)-(12) homodont dentition; (13) devel­ Gaudin and Branham (1998)-(15) lacrimal foramen with opment of a carapace that includes a cephalic shield and prominent lateral walls; (16) absence of metacromion of in all but glyptodonts includes pectoral and pelvic buck- scapula; (17) fourth metacarpal longest metacarpal; (18) Phylogenetic relationships among extant and fossil xenarthrans 35

sustentacular and navicular facets of astragalus conflu­ maxilla; (34) pterygoids exposed in hard palate [modi­ ent. fication of (3) from Engelmann (1985)]; (35) pterygoid Gaudin (2004a)-(19) angular process of mandible with without hamulus or free standing descending lamina; medially inflected tip; (20) lateral edges of mandibular (36) infraorbital foramina exposed in ventral view; (37) spout convergent anteriorly in dorsal view; (21) nasotur­ zygomatic process of squamosal strongly reduced, :s; 5% binal and maxilloturbinal subequal in length; (22) jugal basonasallength. loosely attached to skull; (23) separate foramen rotun­ Rose et al. (2005)-(38) elongate, tubular skull; (39) keratin­ dum; (24) nuchal crest does not overhang occiput pos­ ized region of stomach for grinding up ingested insects. teriorly. Wible and Gaudin (2004)-(25) Glaserian fissure well sepa­ Phyllophaga rated from the foramen ovale; (26) incisive foramen Engelmann (1985)-(1) presence of paired perforations elongate; (27) maxillary foramen visible in ventral view; in the lumbar vertebral centra; (2) presence of a large, (28) optic canal positioned ventrally in the orbitosphe­ asymmetrically developed intravertebral [= "rhachid­ noid; (29) absence of an anterior opening of the orbito­ ian"] vein; (3) inclusion of the optic foramen within the temporal canal. opening for the sphenorbital fissure; (4) reduction of the medial trochlea of the tibial articular surface of the as­ Vermilingua tragalus. Engelmann (1985)-(1) loss of teeth; (2) elongate muzzle; (3) Gaudin (1995)-(5) posterior crus of ectotympanic attached posteriorly extended pterygoids [see Gaudin and Bran­ to squamosal/mastoid bridge; (6) anteroposterior length ham (1998), Gaudin (2004a)]; (4) ossified auditory bulla; of entotympanic greater than ectotympanic; (7) mastoid (5) flattened ribs. exposed in depression between exoccipital and nuchal Gaudin (1995)-(6) entotympanic reduced; (7) pterygOid crests; (8) mastoid with weak lateral exposure; (9) sty­ enlarged to form medial bony wall of tympanic cavity; lomastoid canal directed posteroventrally; (10) internal (8) musculotubal canal exits tympanic cavity posterome­ carotid artery sulcus saddle-shaped; (ll) glenoid fossa of dially; (9) musculotubal canal directed posteroventrally; squamosal bounded by medial shelf; (12) entotympanic (10) arteria diploetica magna enters sidewall of brain­ takes the form of a vertical plate attached dorsally to the case. promontorium of the petrosal, with a horizontal medial Reiss (1997)-(11) jaw adductors weak; (12) loss of m. sty­ expansion lying dorsal to the internal carotid artery; (13) loglossus; (13) loss of tongue insertion of m. hyloglos­ entotympanic with lateral process that contacts tympa­ sus; (14) loss of tongue insertion of m. palatoglossus; (15) nohyal; (14) tympanohyal directed ventrally and some­ compound m. sternoglossus present. what posteriorly; (15) presence of a groove connecting Gaudin and Branham (1998)-(16) dorsal process of pre­ the stylomastOid foramen and posttemporal foramen. maxilla erect, compressed anteroposteriorly; (17) small Gaudin (1999b)-(16) weak development of anapophyses in exposure of maxilla in orbit; (18) frontal/parietal suture posterior thoracic and lumbar vertebrae. well anterior to glenOid; (19) temporal lines diverge pos­ McDonald (2003b)-(17) presence of caniniform teeth in teriorly, widely separated from nuchal crest; (20) hard which lower tooth occludes with the posterior surface palate extends posteriorly to the back of the tympanic of the upper; (18) tubercular facets on ribs concave; cavity [modification of (3) from Engelmann (1985)]; (21) (19) presence of acromiocoracoid arch (absent in extant subarcuate fossa large, deep; (22) basicranial/basifacial sloths). axis slightly curved [concave ventrally]; (23) mandibular Gaudin (2004a)-(20) the maximum ventral extent of the symphysis strongly downturned ventrally; (24) anterior entotympanic and ectotympanic roughly equivalent; (21) edge of spinous process of axis extends forward to level entotympanic forms the lateral wall and roof of the sul­ of dens; (25) prehensile tail present; (26) entepicondylar cus for the internal carotid artery, and has a medial ridge notch present; (27) intercondylar fossa of femur wider forming at least part of the medial wall of the sulcus; (22) than lateral condyle; (28) tibial sesamoid bone [= "pre­ teeth characterized by a large core of well-vascularized hallux"] present; (29) prominent lateral tuberosity pres­ modified orthodentine; (23) presence of a posterior ex­ ent on proximal fifth metatarsal. ternal opening of the mandibular canal near the junction Gaudin (2004a)-(30) mandibular condyle hooks laterally of the ascending and horizontal rami of the mandible; in dorsal view; (31) mandibular symphysis very short, (24) presence of a large posteriorly or posteroventrally <10% of maximum mandibular length; (32) mandibular directed process on the proximal end of the stylohyal; symphysis anteroventrally inclined; (33) palate elongate (25) presence of a rugose palate, marked by numerous and narrow, widened at base of zygomatic processes of pits and grooves; (26) presence of a large pterygoid ex- 36 T. J. Gaudin and H. G. McDonald

posure in the roof of the nasopharynx; (27) presence of a broad, deep descending lamina of the pterygoid, typically with a semicircular ventral margin. [Gaudin (2004a) lists the above features as unique characters of sloths, but lists at least 20 more unambiguous synapomorphies of sloths in his appendix 4J Rose et al. (2005)-(28) five upper, four lower teeth; (29) ju­ gal with large ascending and descending processes; (30) proximal radius circular; (31) ilium flared laterally; (32) thorax elongated and rigid. The Biology of the Xenarthra

Edited by Sergio F. Vizcaino and W. J. Loughry

University Press of Florida Gainesville/Tallahassee/Tampa/Boca Raton Pensacola/OrJando/Miami/Jacksonville/Ft. Myers/Sarasota

{> f? ~ ~ fb " 6'-- "6 \ 1 D .- J 16 S"-I Bibliography

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