South American Marsupials Research Articles

A new vertebrate ichnological association sheds light on the small metatherian record of the Middle Miocene in South America

Vertebrate ichnological associations recorded in Middle Miocene successions were unknown in South America. During that time, South America was isolated from other continents and had a unique endemic fauna and flora. The lower Vinchina succession occurred between 15.6 and 12.7 Ma and records the footprints of highly specialized mammals, reptiles, and birds for the first time. To identify all footprint producers, we focused on anatomical traits of the appendicular skeleton represented on the footprints together with body size estimations of the producers as body mass and the apparent trunk length (GAD). Carnivoripeda sudamericana nov. isp. reveals a weasel-like producer of ∼1 kg and a trunk length of 19–26 cm most likely attributed to metatherian carnivores (Sparassodonta). They represent the oldest carnivore footprints in South America. Small bipedal rodent-like mammals of ∼280 g using a jumping gait (Morphotype A) are interpreted as produced by highly specialized South American marsupials, argyrolagids, whose footprints were unknown until now. Other mammalian footprints recorded are Tacheria troyana most likely produced by dinomyid caviomorph rodents. They represent animals of ∼16 kg and a trunk length of 48–55 cm, like living dinomyids. Subcircular to oval structures (Morphotype B) seems to be produced by medium-sized ungulates, while stepping in cohesive and plastic soupy sediments. cf. Chelonipus torquatus suggests small freshwater turtles (Chelidae or Podocnemididae), of ∼400 g consistent with a trackmaker of carapace size of ∼9 cm. Aviadactyla vialovi was most likely produced by a small shorebird (Scopolacidae) of ∼40 g. All footprints are preserved on crevasse splay deposits of anastomosing fluvial systems together with meniscate feeding (Taenidium barretti) and simple dwelling trace fossils (Palaeophycus tubularis) produced by insects and are an example of the Scoyenia Ichnofacies.

Molecular Phylogeny of Cryptonanus (Didelphidae: Thylamyini): Evidence for a recent and complex diversification in South American open biomes

Systematic revisions of South American marsupials have contributed to our knowledge about genus and species diversity in the last decades, including studies of the most recently described genus Cryptonanus (Didelphidae), currently comprising four recognized species. Herein we provide the first phylogeny for these mouse opossums based on comprehensive sampling, including representatives from all nominal taxa, encompassing most of the geographic distribution of the genus while also extending its known range. The taxonomic status of Cryptonanus species was explored by analyses of multiple mitochondrial and nuclear DNA markers to assess phylogenetic relationships and to provide divergence time estimates, species delimitations and biogeographical hypotheses. Cryptonanus monophyly remained highly supported despite the inclusion of abundant new data from more than a hundred specimens, comprising 10 independent evolutionary lineages. Species-complexes within valid nominal taxa reveal higher species richness in the genus. Based on divergence estimates from a dated phylogeny, we suggest that Cryptonanus diversified along the Quaternary, with speciation events occurring well into the Pleistocene. The best supported biogeographical hypothesis endorses speciation by vicariance and subset speciation across open formations in shaping the evolutionary history of this didelphid genus, strongly associated with dry tropical landscapes of South America.

Continental assessment of South American marsupial conservation priorities: A methodological approach using a spatially explicit conservation indicator

The distributional range of South American marsupials is the response to evolutionary history, geology and climate, resulting in a chorology characteristic of each taxon. We integrated information for each species using the global conservation status given by the International Union for Conservation of Nature (IUCN), plus the taxonomic singularity, and the chorotype using an explicit conservation indicator: the pixel conservation value (PCV). We generated a map of South America with 0.5° × 0.5° grids, where we ranked areas with different conservation values (PCVs), analyzed their overlap with protected areas and human pressure, and tested their use with a recent disturbance (fires during August 2019) at a continental scale. The highest PCVs were found in the Andean region from Perú to northern Argentina, and in Brazil between the Paranaense Forest and the Cerrado ecoregions. Only 21.5% of the total PCV area was protected, with 60% to 0% of PCV areas protected. When human pressure and conservation scenarios were analyzed, 99.9% of all pixels are under some kind of pressure, with 33.3% and 66.7% under high and low pressure, respectively. We present comparative information between areas, and show examples of the usefulness of this indicator to quantitatively evaluate the impact of environmental disturbances on their conservative value.

Variability and variation in Rhyncholestes raphanurus Osgood (Paucituberculata, Caenolestidae)

BackgroundCaenolestids are a group of poorly known South American marsupials with a restricted distribution in Páramo and Subpáramo environments of the Andes from Colombia and western Venezuela to Bolivia (represented by the genera Caenolestes and Lestoros), and Valdivian rainforest in southern Chile (including a separate population in Chiloé Island) and Argentina, where a single species lives: the Long-nosed shrew opossum (Rhyncholestes raphanurus). The objectives of this work were to analyze the intraspecific variability of R. raphanurus, which includes an anatomical description of the skull and dentition, describe its geographic variation, test for sexual dimorphism, and assess potential differences between continental and Island populations.MethodsLinear Mossimann-transformed variables were used to assess sexual differences within a large population (La Picada), compare sexes within other continental populations, and in a separate analysis, compare continental from Island samples. A full model Principal Components Analysis was performed to assess differences between males and females of the continental and Island populations. A thorough description of the skull and teeth of the species and comparisons with other living Caenolestidae is presented.ResultsRhyncholestes raphanurus presents little geographic variation, even between Island and continental populations. Similarly, we found no significant difference between sexes of this species in cranial and dental measurements. We provide a detailed description of cranial morphology and its variation, and also, the first description of the occipital bones, which haven’t been previously described for any Paucituberculata.ConclusionsComparative studies of continental and Chiloé Island specimens support the treatment of R. raphanurus as a single valid species, especially since morphologic and morphometric differences fall within the extremes of continental populations. The morphology of R. raphanurus clearly separates this genus from other extant Caenolestidae, and in a much greater degree than the differences found between Lestoros and Caenolestes.

Resistance of South American opossums to vWF-binding venom C-type lectins

Opossums in the clade Didelphini are well known to be resistant to snake venom due to endogenous circulating inhibitors which target metalloproteinases and phospholipases. However, the mechanisms through which these opossums cope with a variety of other damaging venom proteins are unknown. A protein involved in blood clotting (von Willebrand Factor) has been found to have undergone rapid adaptive evolution in venom-resistant opossums. This protein is a known target for a subset of snake venom C-type lectins (CTLs), which bind it and then induce it to bind platelets, causing hemostatic disruption. Several amino acid changes in vWF unique to these opossums could explain their resistance; however, experimental evidence that these changes disrupt venom CTL binding was lacking. We used platelet aggregation assays to quantify resistance to a venom-induced platelet response in two species of venom-resistant opossums (Didelphis virginiana, Didelphis aurita), and one venom-sensitive opossum (Monodelphis domestica). We found that all three species have lost nearly all their aggregation response to the venom CTLs tested. Using washed platelet assays we showed that this loss of aggregation response is not due to inhibitors in the plasma, but rather to the failure of either vWF or platelets (or both) to respond to venom CTLs. These results demonstrate the potential adaptive function of a trait previously shown to be evolving under positive selection. Surprisingly, these findings also expand the list of potentially venom tolerant species to include Monodelphis domestica and suggest that an ecological relationship between opossums and vipers may be a broader driver of adaptive evolution across South American marsupials than previously thought.

Intraspecific variability inLestoros inca(Paucituberculata, Caenolestidae), with reports on dental anomalies and eruption pattern

Abstract Caenolestids are a group of poorly known South American marsupials with a restricted distribution in paramo and subparamo environments of the Andes from Colombia and western Venezuela to Bolivia (represented by the genera Caenolestes and Lestoros), and in Valdivian rain forest in southern Chile and Argentina where a single species (Rhyncholestes raphanurus) lives. The Incan shrew opossum, Lestoros inca, lives in mountains of southern Peru and extreme northwestern Bolivia. Despite being common in trapping surveys, little is known of its cranial and dental intraspecific variability, tooth eruption pattern, and dental anomalies. The objective of this work was to analyze the intraspecific variability of L. inca, which includes an anatomical description of the skull and dentition and analysis of clinal variation, tooth eruption patterns, and dental anomalies. The eruption pattern found in L. inca confirms the sequence P3 → m4 → p3 → M4 as the general pattern for living paucituberculatans. Missing teet...

Analysis of dental homologies and phylogeny of Paucituberculata (Mammalia: Marsupialia)

The Paucituberculata is an endemic group of South American marsupials, recorded from the early Cenozoic up to the present. In this report, the most comprehensive phylogenetic analysis of Paucituberculata to date is presented. Fifty-seven terminal species were scored for 74 new and re-examined characters. Homologies of dental characters used in previous systematic studies were critically reviewed to evaluate their inclusion in the analysis. Phylogenetic results corroborated two major paucituberculatan clades, Palaeothentoidea and Caenolestoidea, and the main palaeothentoid groupings: Pichipilidae, Palaeothentidae, and Abderitidae. Taxon sampling and reinterpretations of molar cusp and crest homologies played an important role in the generation of new phylogenetic hypotheses. The main differences with respect to previous phylogenies were focused on palaeothentoid relationships: Palaeothentes boliviensis and Pilchenia lucina are not members of Palaeothentidae but instead clustered with Pilchenia intermedia and P. antiqua, forming the sister-group of a Palaeothentidae + Abderitidae clade, and Titanothentes simpsoni, previously considered a palaeothentine, is nested within the Acdestinae clade. Based on the time-calibrated phylogeny, the following stages in the paucituberculatan evolutionary history are suggested: origin of the group, in the Paleocene to early Eocene at the latest, split of Caenolestoidea and Palaeothentoidea clades during the late early to middle Eocene, evolutionary radiation of palaeothentid and abderitid lineages near the Oligocene–Eocene boundary, and decreased diversity and extinction of palaeothentoids during the middle Miocene. © 2013 The Linnean Society of London, Biological Journal of the Linnean Society, 2013, 109, 441–465.

Revision of the family Listropsoralgidae Fain, 1965 (Acariformes: Sarcoptoidea)—skin parasites of marsupials and rodents

The family Listropsoralgidae Fain, 1965 (Acariformes: Sarcoptoidea) is represented by the permanent skin ectoparasites associated with the South American and Australian marsupials (12 species) and the South American rodents of the family Echimyidae (1 species). The phylogenetic relationships of these mites (12 ingroup and 2 outgroup species) are reconstructed on the basis of the maximum parsimony (MP) and Bayesian analyses (BA) of 76 morphological characters. MP analysis confirmed monophyly of the listropsoralgid genera, the strict consensus of 18 trees generated by MP has the following pattern: Petauralges (Listropsoralgoides, Didelphialges, Listropsoralges) with poor resolution among species of the genus Listropsoralges. The same tree was generated by BA. Both successive and implied weighting strategies resulted in 7 MP trees: Petauralges (Listropsoralgoides (Didelphialges (Listropsoralges))). The relationships between species of the genus Listropsoralges received the poorest resolution: L. caenolestes (L. monodelphis, L. vossi, L. faini, L. brevisetosa (L. thylamys (L. marmosa-L. caluromys))). The host-parasite relationships of listropsoralgids are briefly discussed. The family Listropsoralgidae is taxonomically revised and to date includes 13 species in 4 genera. Six species and one genus are described as new: Listropsoralges brevisetosus sp. n. from Marmosa murina (Didelphimorphia: Didelphidae) from Peru, Listropsoralges similis sp. n. from Caluromys derbianus (Didelphidae) from Panama, Listropsoralges thylamys sp. n. from Thylamys venustus (Didelphidae) from Bolivia, Listropsoralges vossi sp. n. from Monodelphis domestica (Didelphidae) from Brazil, Listropsoralges caenolestes sp. n. from Caenolestes fuliginosus (Paucituberculata: Caenolestidae) from Ecuador, and Didelphialges metachirus gen. n., sp. n. from Metachirus nudicaudatus (Didelphidae) from Peru. The female of Listropsoralges faini Bochkov and Wauthy, 2009 is described for the first time.

An ‘ameridelphian’ marsupial from the early Eocene of Australia supports a complex model of Southern Hemisphere marsupial biogeography

Recent molecular data strongly support the monophyly of all extant Australian and New Guinean marsupials (Eomarsupialia) to the exclusion of extant South American marsupials. This, together with available geological and fossil evidence, has been used to argue that the presence of marsupials in Australia is simply the result of a single dispersal event from South America during the latest Cretaceous or Palaeocene, without subsequent dispersals between the two continents. Here, I describe an isolated ankle bone (calcaneus) of a metatherian from the early Eocene Tingamarra Local Fauna in northeastern Australia. Strikingly, this specimen, QM F30060, lacks the 'continuous lower ankle joint pattern' (CLAJP), presence of which is a highly distinctive apomorphy of the marsupial clade Australidelphia, which includes Eomarsupialia, the living South American microbiotherian Dromiciops and the Tingamarran fossil marsupial Djarthia. Comparisons with a range of marsupials and stem-metatherians strongly suggest that the absence of the CLAJP in QM F30060 is plesiomorphic, and that this specimen represents the first unequivocal non-australidelphian ('ameridelphian') metatherian known from Australia. This interpretation is confirmed by phylogenetic analyses that place QM F30060 within (crown-group) Marsupialia, but outside Australidelphia. Based on these results, the distribution of marsupials within Gondwana cannot be explained by simply a single dispersal event from South America and Australia. Either there were multiple dispersals by marsupials (and possibly also stem-metatherians) between South America and Australia, in one or both directions, or, alternatively, there was a broadly similar metatherian fauna stretching across southern South America, Antarctica and Australia during the Late Cretaceous-early Palaeogene.

Relationships of South American marsupials (Didelphimorphia, Microbiotheria and Paucituberculata) and hard ticks (Acari: Ixodidae) with distribution of four species of Ixodes

Relationships of South American marsupials (Didelphimorphia, Microbiotheria and Paucituberculata) and hard ticks (Acari: Ixodidae) with distribution of four species of Ixodes

Relationships of South American marsupials (Didelphimorphia, Microbiotheria and Paucituberculata) and hard ticks (Acari: Ixodidae) with distribution of four species of Ixodes

Historical information shows that South American marsupials are irrelevant hosts for South American hard ticks (Ixodidae Murray) of the genera Haemaphysalis Koch, Rhipicephalus Koch and Dermacentor Koch. Twenty two Amblyomma Koch species were occasionally found on Didelphimorphia Gill, but some records are doubtful (i.e., A. dissimile Koch, 1844) and only A. fuscum Neumann, 1907 appears to be a relevant parasite of this type of host. Twelve species of Ixodes Latreille were determined on these hosts, although one of them, I. longiscutatus Boero, 1944, is probably misidentified. Four species, I. amarali Fonseca, 1935b, I. loricatus Neumann, 1899, I. luciae Sénevet, 1940 and I. venezuelensis Kohls, 1953 are usual parasites of Didelphimorphia. These species (I. venezuelensis excluded) have adult ticks feeding mostly on Didelphidae Gray, and sub-adult ticks feeding mostly on Didelphidae and several species of sigmodontine rodents. All parasitic stages of I. venezuelensis were recorded from Didelphimorphia although rodents are also of importance for its life cycle. Records from marsupials and nonmarsupial hosts show that I. amarali is established in eastern Brazil, and I. venezuelensis in Venezuela, Colombia, Panama and Costa Rica. The alleged southernmost record of I. luciae in Central Argentina was found to be erroneous and its southern limit is located in northwestern Argentina and its way northwards includes Bolivia, Peru, western Brazil, French Guiana, Surinam, Trinidad & Tobago, Panama, Guatemala, Belize and southern Mexico with unconfirmed but probably valid records for Ecuador, Colombia, Costa Rica, Nicaragua and Honduras. The distribution of I. loricatus has been historically considered to range from southern Argentina to southern Mexico but southernmost and northernmost records are now considered doubtful along with Venezuelan populations for this tick, while the only records for Panama and Colombia were based on wrong tick identifications. Bona fide populations of I. loricatus range from central-eastern Argentina and southern Uruguay to Paraguay up to north-eastern Brazil. Dromiciops gliroides Thomas, the only member of Microbiotheria Ameghino is the exclusive host of Ixodes neuquenensis Ringuelet, 1947. There is only one record of tick infestation (Ixodes jonesae Kohls, Sonenshine & Clifford, 1969) of Paucituberculata Ameghino, indicating that these marsupials are of no apparent importance for maintenance of South American hard ticks. We speculate that the species of Ixodes feeding on Didelphimorphia and Sigmodontinae Wagner are a clade derived from ancestors feeding exclusively on Didelphidae that radiated after the invasion of South America by Sigmodontinae or their ancestors. Ixodes neuquenensis (established in south-western South America) is considered a relatively new species that radiated from Ixodes parasites of Sigmodontinae invaders in southern South America.

Tracking Marsupial Evolution Using Archaic Genomic Retroposon Insertions

Author SummaryEver since the first Europeans reached the Australian shores and were fascinated by the curious marsupials they found, the evolutionary relationships between the living Australian and South American marsupial orders have been intensively investigated. However, neither the morphological nor the more recent molecular methods produced an evolutionary consensus. Most problematic of the seven marsupial groups is the South American species Dromiciops gliroides, the only survivor of the order Microbiotheria. Several studies suggest that Dromiciops, although living in South America, is more closely related to Australian than to South American marsupials. This relationship would have required a complex migration scenario whereby several groups of ancestral South American marsupials migrated across Antarctica to Australia. We screened the genomes of the South American opossum and the Australian tammar wallaby for retroposons, unambiguous phylogenetic markers that occupy more than half of the marsupial genome. From analyses of nearly 217,000 retroposon-containing loci, we identified 53 retroposons that resolve most branches of the marsupial evolutionary tree. Dromiciops is clearly only distantly related to Australian marsupials, supporting a single Gondwanan migration of marsupials from South America to Australia. The new phylogeny offers a novel perspective in understanding the morphological and molecular transitions between the South American and Australian marsupials.

Molecular characterization of an ancient Hepatozoon species parasitizing the ‘living fossil’ marsupial ‘Monito del Monte’ Dromiciops gliroides from Chile

The Microbiotheriid Dromiciops gliroides, also known as ‘Monito del Monte’, is considered to be a threatened species and the only living representative of this group of South American marsupials. During the last few years, several blood samples from specimens of ‘Monito del Monte’ captured at Chiloe island in Chile have been investigated for blood parasites. Inspection of blood smears detected a Hepatozoon species infecting red blood cells. The sequences of DNA fragments corresponding to small subunit ribosomal RNA gene revealed two parasitic lineages belonging to Hepatozoon genus. These parasite lineages showed a basal position with respect to Hepatozoon species infecting rodents, reptiles, and amphibians but are phylogenetically distinct from Hepatozoon species infecting the order Carnivora. In addition, the Hepatozoon lineages infecting D. gliroides are also different from those infecting other micro-mammals living in sympatry, as well as from some that have been described to infect an Australian species of bandicoot. The potential vector of this parasite appears to be the host-specific tick Ixodes neuquenensis because the sequencing of a long amplicon determined the presence of one of the two lineages found in the marsupial. © 2009 The Linnean Society of London, Biological Journal of the Linnean Society, 2009, 98, 568–576.

Abdominal muscle and epipubic bone function during locomotion in Australian possums: Insights to basal mammalian conditions and eutherian‐like tendencies in Trichosurus

Mammals have four hypaxial muscle layers that wrap around the abdomen between the pelvis, ribcage, and spine. However, the marsupials have epipubic bones extending anteriorly into the ventral hypaxial layers with two additional muscles extending to the ventral midline and femur. Comparisons of South American marsupials to basal eutherians have shown that all of the abdominal hypaxials are active bilaterally in resting ventilation. However, during locomotion marsupials employ an asymmetrical pattern of activity as the hypaxial muscles form a crosscouplet linkage that uses the epipubic bone as a lever to provide long-axis support of the body between diagonal limb couplets during each step. In basal eutherians, this system shifts off the femur and epipubic bones (which are lost) resulting in a shoulder to pelvis linkage associated with shifts in both the positions and activity patterns of the pectineus and rectus abdominis muscles during locomotion. In this study, we present data on hypaxial function in two species (Pseudocheirus peregrinus and Trichosurus vulpecula) representing the two major radiations of possums in Australia: the Pseudocheiridae (within the Petauroidea) and the Phalangeridae. Patterns of gait, motor activity, and morphology in these two Australian species were compared with previous work to examine the generality of 1) the crosscouplet lever system as the basal condition for the Marsupialia and 2) several traits hypothesized to be common to all mammals (hypaxial tonus during resting ventilation, ventilation to step synchrony during locomotion, and bilateral transversus abdominis activity during locomotor expiration). Our results validate the presence of the crosscouplet pattern and basic epipubic bone lever system in Australian possums and confirm the generality of basal mammalian patterns. However, several novelties discovered in Trichosurus, reveal that it exhibits an evolutionary transition to intermediate eutherian-like morphological and motor patterns paralleling many other unique features of this species.

Chulpasia and Thylacotinga, late Paleocene-earliest Eocene trans-Antarctic Gondwanan bunodont marsupials: New data from Australia

A new marsupial from the early Eocene Tingamarra Local Fauna of southeastern Queensland, Australia, is named and referred to Chulpasia Crochet and Sigé, 1993, a genus otherwise known from early Tertiary deposits of Peru. This taxon, Chulpasia jimthorselli nov. sp., differs in upper molar morphology only in minor details from the Peruvian type species Chulpasia mattaueri and is almost identical in size. New materials referable to the Tingamarra marsupial Thylacotinga bartholomaii Archer, Godthelp and Hand are also described. Species of Chulpasia and Thylacotinga share many striking derived as well as plesiomorphic dental features that allow recognition of a new monophyletic subfamily, Chulpasiinae. Its familial relationships are in doubt, but members of the subfamily could have provided the ancestral stock for Rosendolops and other early Tertiary South American polydolopimorphian marsupials. This is the first evidence that a Gondwanan genus of therian land mammals spanned South America, Antarctica and Australia during the early Tertiary. The very close similarity between the Peruvian and Australian fossils (and suggested short time span between their stratigraphic occurrences) provides further paleontological support for a trans-Antarctic land connection between South America and Australia extending well into the early Paleogene.

Cone visual pigments in two species of South American marsupials

Marsupials are largely confined to Australasia and to Central and South America. The visual pigments that underlie the photosensitivity of the retina have been examined in a number of species from the former group where evidence for trichromatic colour vision has been found, but none from the latter. In this paper, we report the cone opsin sequences from two nocturnal South American marsupial species, the gray short-tailed opossum, Monodelphis domestica, and the big-eared opossum, Didelphis aurita. Both are members of the Order Didelphimorphia (American opossums). For both species, only two classes of cone opsin were found, an SWS1 and an LWS sequence, and in vitro expression showed that the peak sensitivity of the SWS1 pigment is in the UV. Analysis of the Monodelphis genome confirms the absence of other classes of cone visual pigment genes. The SWS1 and LWS genes with 4 and 5 introns respectively, show the same exon–intron structure as found for these genes in all other vertebrates. The SWS1 gene shows a conserved synteny with flanking genes. The LWS gene is X-linked, as in all therian mammals so far examined, with a locus control region 1.54 kb upstream.

Physical map of two tammar wallaby chromosomes: A strategy for mapping in non-model mammals

Marsupials are especially valuable for comparative genomic studies of mammals. Two distantly related model marsupials have been sequenced: the South American opossum (Monodelphis domestica) and the tammar wallaby (Macropus eugenii), which last shared a common ancestor about 70 Mya. The six-fold opossum genome sequence has been assembled and assigned to chromosomes with the help of a cytogenetic map. A good cytogenetic map will be even more essential for assembly and anchoring of the two-fold wallaby genome. As a start to generating a physical map of gene locations on wallaby chromosomes, we focused on two chromosomes sharing homology with the human X, wallaby chromosomes X and 5. We devised an efficient strategy for mapping large conserved synteny blocks in non-model mammals, and applied this to generate dense maps of the X and 'neo-X' regions and to determine the arrangement of large conserved synteny blocks on chromosome 5. Comparisons between the wallaby and opossum chromosome maps revealed many rearrangements, highlighting the need for comparative gene mapping between South American and Australian marsupials. Frequent rearrangement of the X, along with the absence of a marsupial XIST gene, suggests that inactivation of the marsupial X chromosome does not depend on a whole-chromosome repression by a control locus.

Dental anomalies in Dromiciops gliroides (Microbiotheria, Microbiotheriidae), Caenolestes fuliginosus and Rhyncholestes raphanurus (Paucituberculata, Caenolestidae)

Dental anomalies are described after analyzing series of skulls and mandibles of three species of South American marsupials: the monito del monte (Dromiciops gliroides), the silky shrew-opossum (Caenolestes fuliginosus) and the Chilean shrew-opossum (Rhyncholestes raphanurus). The anomalies are classified into three categories: (1) supernumerary or missing teeth in normal positions of the dental series, (2) morphological anomalies like teeth fusion or anomalous crown shape, and (3) presence of teeth in unusual positions. Cusp fusion and supernumerary teeth at the end of the toothrow have been observed predominantly in D. gliroides. A tendency to find supernumerary or missing teeth is observed between the procumbent incisors and the second lower premolars in caenolestids. Possible causes for these anomalies and their morphofunctional value are discussed. A comparison with other marsupials is presented and discussed. Isolation of local populations and its effects on genetic drift processes might explain the high percentage of dental anomalies.

Marsupial uncoupling protein 1 sheds light on the evolution of mammalian nonshivering thermogenesis

Brown adipose tissue expressing uncoupling protein 1 (UCP1) is responsible for adaptive nonshivering thermogenesis giving eutherian mammals crucial advantage to survive the cold. The emergence of this thermogenic organ during mammalian evolution remained unknown as the identification of UCP1 in marsupials failed so far. Here, we unequivocally identify the marsupial UCP1 ortholog in a genomic library of Monodelphis domestica. In South American and Australian marsupials, UCP1 is exclusively expressed in distinct adipose tissue sites and appears to be recruited by cold exposure in the smallest species under investigation (Sminthopsis crassicaudata). Our data suggest that an archetypal brown adipose tissue was present at least 150 million yr ago allowing early mammals to produce endogenous heat in the cold, without dependence on shivering and locomotor activity.

Population characteristics of Dromiciops gliroides (Philippi, 1893), an endemic marsupial of the temperate forest of Patagonia

The only living representative of Microbiotheriidae, one of the oldest lineages of marsupials (Marshall 1978), is Dromiciops gliroides (Philippi, 1893, monito del monte). This marsupial is endemic to the northern portion of the temperate forest of Patagonia, between 361 and 431 South in Chile and Argentina, where it dwells mainly in old-growth Nothofagus forest (Hershkovitz 1999; Saavedra and Simonetti 2001; Lobos et al. 2005). Morphological, chromosomal and molecular studies suggest that this marsupial shares more phylogenetic affinity with the Australian marsupials (Diprotodontia) than with other South American marsupials (Didelphidae) (Kirsch et al. 1997; Nilsson et al. 2004). Recent research suggests that the monito del monte may disperse seeds of 80% of the flora with fleshy fruits, in addition to its role as the sole disperser of the keystone mistletoe Tristerix corymbosus (Amico and Aizen 2000; Amico et al. unpubl.). This role makes this marsupial essential for preservation of biodiversity of the temperate forest of Patagonia. In spite of the potential key role of monito del monte in the temperate forest of Patagonia, little is known about its population