The phylogenetic relationships of argyrolagid marsupials

New material of the oldest known argyrolagid marsupial Proargyrolagus bolivianus from the late Oligocene of Bolivia is described. The new specimen preserves previously unknown aspects of the anterior dentition that solve the long-standing homology problem concerning the identity (i2) of the procumbent lower incisors in argyrolagids. This new anatomical information is incorporated into a morphology-based phylogenetic analysis of all extant marsupial families and Argyrolagidae, with the aim of testing the monophyly of Paucituberculata and evaluating the relationships among extant marsupial families. Eleven features support the monophyly of Paucituberculata, the following three unique among Marsupialia: small size of the paraconid, procumbent second lower incisor, and supraoccipital without distinct lambdoid crest resulting in globular form of braincase. Paucituberculata is the sister group of an Australian clade of marsupials that includes Dromiciops, but these results are not robust, as shown by sensitivity analyses. The foramen ovale surrounded completely by the alisphenoid supports the association of Dromiciops with diprotodontians.     

Petrosal bones of metatherian mammals from the Late Palaeocene of Itaboraí (Brazil), and a cladistic analysis of petrosal features in metatherians

Metatherian petrosal bones were recovered from the early Late Palaeocene Itaboraí, Brazil, and are formally described. A cladistic analysis of the distribution of 56 petrosal and basicranial characters among extant and fossil metatherians was conducted, resulting in seven parsimonious trees. Relationships among metatherian ingroup taxa are congruent with current understanding of metatherian phylogeny. Metatheria is diagnosed by eight petrosal synapomorphies: stapedial artery absent in adults; reduced, intramural prootic canal; extrabullar internal carotid artery; inferior petrosal sinus between petrosal, basisphenoid, and basioccipital; cava supracochleare and epiptericum completely separated; reduction of the lateral flange; reduction of the anterior lamina; separation of the jugular foramen from the opening for the inferior petrosal sinus. The Palaeocene taxa Mayulestes , Pucadelphy s, and Andinodelphys from Tiupampa, and Petrosal Type II from Itaboraí are the sister groups of all other South American and Australian metatherians. This analysis confirms previous results showing the South American 'monito del monte' Dromiciops nested within the Australasian radiation. Within this australidelphian clade, Dromiciops is closely related to the dasyurids. The South American Caenolestes appears more closely related to the Australidelphia than to the South American didelphids. The Petrosal Types I, III, IV and V from Itaboraí are the stem taxa of the clade Australidelphia plus Caenolestes . The significant synapomorphies supporting this relationship are: enlargement of the fossa subarcuata that produces a bulbous ventral aspect of the mastoid and loss of post-temporal canal.  Journal compilation © 2007 The Linnean Society of London, Zoological Journal of the Linnean Society , 2007, 150 , 85–115. No claim to original French government works.     

Cranial Morphology of a Pantolestid Eutherian Mammal from the Eocene Bridger Formation,Wyoming, USA: Implications for Relationships and Habitat

Pantolestinae is a eutherian subfamily of mammals whose members are known from the middle early Paleocene through at least the beginning of the Oligocene of North America. They are also known from Europe, and possibly Africa. A lack of information on pantolestine skulls has prevented the use of cranial anatomy in evaluation of this group’s enigmatic higher-level phylogenetic relationships. Conversely, postcranial skeletons are well known and locomotor interpretations based on them are robust. The most complete known skull of a pantolestine, Pantolestes longicaudus (YPM 13525), is described here and compared to potential close fossil relatives and extant mammals. Semicircular canal morphology is used to test locomotor hypotheses. YPM 13525 lacks an ossified bulla. It has a mediolaterally broad basioccipital, a large entoglenoid process, and a deeply incised glaserian fissure of the squamosal, caudal and rostral tympanic processes on the petrosal, a foramen for an internal carotid artery (ICA) that entered the tympanic cavity from a posteromedial position, bony tubes enclosing the main stem and transpromontorial branch of the ICA, a large anterior carotid foramen formed within the basisphenoid, evidence of a stapedial artery ramus superior, a groove on the dorsal aspect of the basisphenoid leading to the piriform fenestra possibly for drainage of the cavernous sinus to an extracranial inferior petrosal sinus, a dorsum sellae with well-developed posterior clinoid processes, a foramen rotundum within the alisphenoid, and a sphenorbital fissure between the alisphenoid and orbitosphenoid. Overall, the morphology is not strikingly similar to any potential close relative and the phylogenetic position of Pantolestinae cannot be estimated without cladistic analysis of a character matrix that includes this new morphology and broadly samples extant and extinct eutherian taxa. Semicircular canal morphology differs from that of two likely terrestrial Paleocene mammals, Aphronorus (another pantolestid) and Eoryctes (a palaeoryctid), suggesting a different, possibly semi-aquatic, lifestyle for Pantolestes.     

新疆准噶尔盆地北缘铁尔斯哈巴合晚渐新世两种啮形类耳区的形态研究

我们曾描述过一块与本文描述的标本产自同一地点和层位、可能为Ａｍｐｈｅｃｈｉｎｕｓ的猬类岩骨标本（孟津等,１９９９）。后来新发现的与牙齿属同一个体的Ａｍｐｈｅｃｈｉｎｕｓ岩骨标本证明我们根据单体岩骨的分类鉴定无误。此例说明,在一定的条件下,耳区标本在某些哺乳动物类群中可以鉴定到属,甚至种。因此在形态学、生物地层学上都有一定的意义,而且会因有关标本的不断积累而越来越重要。本文记述了另外两块产自新疆准噶尔盆地北缘铁尔斯哈巴合晚渐新世地层中的岩骨。有关地层、地点资料及所用术语见孟津等（１９９９）以及其中…     

The petrosal of Omomys carteri and the evolution of the primate basicranium

The first omomyine petrosals, those of Omomys carteri, are described. Omomys probably had a tympanic bulla and canals for the intratympanic carotid circulation derived from the petrosal bone. The stapedial and promontory canals were complete, large and subequal. The posterior carotid foramen entered the bulla posteromedially. The intratympanic portion of the facial nerve was fully enclosed in bone, the stapedius fossa is extrabullar and the parotic fissure is patent. The mastoid was pneumatized from the epitympanic recess and a supracochlear cavity may have been present. The Omomys petrosals exhibit a generic omomyiform morphology, exhibiting no features that can be interpreted as autapomorphies and only one feature shared with adapiforms. The monophyly of Omomyiformes is based on other cranial characters, dental and postcranial characters assessed elsewhere. The similarity of the Shanghuang petrosal to the petrosals of omomyiforms, as well as the ambiguous evidence of its association, suggest that an omomyiform affinity for that petrosal cannot be ruled out.     

Cranial circulation of the pen-tailed tree shrewPtilocercus lowii and relationships of Scandentia

The major cranial arteries and veins are described for a 30-mm crown-rump length fetus of the pen-tailed tree shrewPtilocercus lowii, and comparisons are made with cranial vessels reported in the tree shrewTupaia and with the vascular pattern reconstructed for primitive eutherians.Ptilocercus shares a number of derived features of the cranial circulation withTupaia, which, therefore, represent synapomorphies of tree shrews (Tupaiidae, Scandentia). Included are (1) the enclosure of the intratympanic portion of the internal carotid artery in a bony canal that is floored proximally and distally by the entotympanic and by the petrosal in between, (2) the enclosure of the intratympanic portion of the stapedial artery by the petrosal in a canal on the promontorium and within the epitympanic crest beneath the tympanic roof, (3) the absence of an exit for the arteria diploëtica magna, (4) an alisphenoid canal, (5) a maxillary artery that passes medial to the mandibular nerve beneath foramen ovale, and (6) a laryngeopharyngeal artery. Some of these derived features, however, are also found in certain other eutherians (e.g., numbers 2, 3, and 6 in Euprimates) and, therefore, may be used in future studies to assess the higher-level affinities of Scandentia.     

The origin of the Australasian marsupial fauna and the phylogenetic affinities of the enigmatic monito del monte and marsupial mole.

Alternative hypotheses in higher-level marsupial systematics have different implications for marsupial origins, character evolution, and biogeography. Resolving the position of the South American monito del monte (Order Microbiotheria) is of particular importance in that alternate hypotheses posit sister-group relationships between microbiotheres and taxa with disparate temporal and geographic distributions: pediomyids; didelphids; dasyuromorphians; diprotodontians; all other australidelphians; and all other marsupials. Among Australasian marsupials, the placement of bandicoots is critical; competing views associate bandicoots with particular Australasian taxa (diprotodontians, dasyuromorphians) or outside of a clade that includes all other Australasian forms and microbiotheres. Affinities of the marsupial mole are also unclear. The mole is placed in its own order (Notoryctemorphia) and sister-group relationships have been postulated between it and each of the other Australasian orders. We investigated relationships among marsupial orders by using a data set that included mitochondrial and nuclear genes. Phylogenetic analyses provide support for the association of microbiotheres with Australasian marsupials and an association of the marsupial mole with dasyuromorphs. Statistical tests reject the association of diprotodontians and bandicoots together as well as the monophyly of Australasian marsupials. The origin of the paraphyletic Australasian marsupial fauna may be accounted for by (i) multiple entries of australidelphians into Australia or (ii) bidirectional dispersal of australidelphians between Antarctica and Australia.     

The Skull of <Emphasis Type="Italic">Epidolops ameghinoi</Emphasis> from the Early Eocene Itaboraí Fauna,Southeastern Brazil,and the Affinities of the Extinct Marsupialiform Order Polydolopimorphia

The skull of the polydolopimorphian marsupialiform Epidolops ameghinoi is described in detail for the first time, based on a single well-preserved cranium and associated left and right dentaries plus additional craniodental fragments, all from the early Eocene (53–50 million year old) Itaboraí fauna in southeastern Brazil. Notable craniodental features of E. ameghinoi include absence of a masseteric process, very small maxillopalatine fenestrae, a prominent pterygoid fossa enclosed laterally by a prominent ectopterygoid crest, an absent or tiny transverse canal foramen, a simple, planar glenoid fossa, and a postglenoid foramen that is immediately posterior to the postglenoid process. Most strikingly, the floor of the hypotympanic sinus was apparently unossified, a feature found in several stem marsupials but absent in all known crown marsupials. “Type II” marsupialiform petrosals previously described from Itaboraí plausibly belong to E. ameghinoi; in published phylogenetic analyses, these petrosals fell outside (crown-clade) Marsupialia. “IMG VII” tarsals previously referred to E. ameghinoi do not share obvious synapomorphies with any crown marsupial clade, nor do they resemble those of the only other putative polydolopimorphians represented by tarsal remains, namely the argyrolagids. Most studies have placed Polydolopimorphia within Marsupialia, related to either Paucituberculata, or to Microbiotheria and Diprotodontia. However, diprotodonty almost certainly evolved independently in polydolopimorphians, paucituberculatans and diprotodontians, and Epidolops does not share obvious synapomorphies with any marsupial order. Epidolops is dentally specialized, but several morphological features appear to be more plesiomorphic than any crown marsupial. It seems likely Epidolops that falls outside Marsupialia, as do morphologically similar forms such as Bonapartherium and polydolopids. Argyrolagids differ markedly in their known morphology from Epidolops but share some potential apomorphies with paucituberculatans. It is proposed that Polydolopimorphia as currently recognised is polyphyletic, and that argyrolagids (and possibly other taxa currently included in Argyrolagoidea, such as groeberiids and patagoniids) are members of Paucituberculata. This hypothesis is supported by Bayesian non-clock phylogenetic analyses of a total evidence matrix comprising DNA sequence data from five nuclear protein-coding genes, indels, retroposon insertions, and morphological characters: Epidolops falls outside Marsupialia, whereas argyrolagids form a clade with the paucituberculatans Caenolestes and Palaeothentes, regardless of whether the Type II petrosals and IMG VII tarsals are used to score characters for Epidolops or not. There is no clear evidence for the presence of crown marsupials at Itaboraí, and it is possible that the origin and early evolution of Marsupialia was restricted to the “Austral Kingdom” (southern South America, Antarctica, and Australia).     

The petrosal and inner ear of the Late Jurassic cladotherian mammal Dryolestes leiriensis and implications for ear evolution in therian mammals

Dryolestes leiriensis is a Late Jurassic fossil mammal of the dryolestoid superfamily in the cladotherian clade that includes the extant marsupials and placentals. We used high resolution micro‐computed tomography (µCT) scanning and digital reconstruction of the virtual endocast of the inner ear to show that its cochlear canal is coiled through 270°, and has a cribriform plate with the spiral cochlear nerve foramina between the internal acoustic meatus and the cochlear bony labyrinth. The cochlear canal has the primary bony lamina for the basilar membrane with a partially formed (or partially preserved) canal for the cochlear spiral ganglion. These structures, in their fully developed condition, form the modiolus (the bony spiral structure) of the fully coiled cochlea in extant marsupial and placental mammals. The CT data show that the secondary bony lamina is present, although less developed than in another dryolestoid Henkelotherium and in the prototribosphenidan Vincelestes. The presence of the primary bony lamina with spiral ganglion canal suggests a dense and finely distributed cochlear nerve innervation of the hair cells for improved resolution of sound frequencies. The primary, and very probably also the secondary, bony laminae are correlated with a more rigid support for the basilar membrane and a narrower width of this membrane, both of which are key soft‐tissue characteristics for more sensitive hearing for higher frequency sound. All these cochlear features originated prior to the full coiling of the therian mammal cochlea beyond one full turn, suggesting that the adaptation to hearing a wider range of sound frequencies, especially higher frequencies with refined resolution, has an ancient evolutionary origin no later than the Late Jurassic in therian evolution. The petrosal of Dryolestes has added several features that are not preserved in the petrosal of Henkelotherium. The petrosal characters of dryolestoid mammals are essentially the same as those of Vincelestes, helping to corroborate the synapomorphies of the cladotherian clade in neural, vascular, and other petrosal characteristics. The petrosal characteristics of Dryolestes and Henkelotherium together represent the ancestral morphotype of the cladotherian clade (Dryolestoidea + Vincelestes + extant Theria) from which the extant therian mammals evolved their ear region characteristics. © 2012 The Linnean Society of London, Zoological Journal of the Linnean Society, 2012, 166 , 433–463.     

Ontogenetic and phylogenetic transformations of the vomeronasal complex and nasal floor elements in marsupial mammals

Histological sections and three-dimensional reconstructions of section-series were used to document the anatomy of the vomeronasal complex and other aspects of the ethmoidal region in representatives of 13 families and six orders of marsupial mammals, including for the first time Microbiotheria. The changes during growth of several features were examined in ontogenetic series. Marsupials are very conservative in comparison with eutherians regarding the vomeronasal complex. All have a vomeronasal organ and a nasopalatine duct, have no nasopalatine duct cartilage, have no (or just an incipient) palatine cartilage, and the overall construction of the nasal floor is uniform across species. Most features examined show a high degree of homoplasy (e.g. presence of glandular ridges, isolated dorsal process of the paraseptal cartilage), and their systematic value is confined to low taxonomic levels. Significant ontogenetic changes occur in features usually discussed in the systematic/taxonomic literature. Amongst the didelphids examined, Caluromys philander shows several autapomorphies. It is hypothesized that the opening of the VNO into the upper end of the nasopalatine duct was present in the marsupial groundplan. Most marsupials have a large and horizontal anterior transverse lamina, the plesiomorphic condition, which becomes oblique in diprotodontians. Some features are autapomorphies of well-supported monophyletic groups of marsupials, e.g. the conspicuous internasal communication of perameliformes and the 'tube-like' or ring-shaped paraseptal cartilage of vombatiformes. An outer bar joining the middle (and not the dorsal-most portion) of the paraseptal cartilage characterizes Australasian marsupials and Dromiciops, with the exclusion of perameliformes, and evolved independently in Caluromys philander.     

Relationships Among Families of Diprotodontia (Marsupialia) and the Phylogenetic Position of the Autapomorphic Honey Possum (Tarsipes rostratus)

The Australasian marsupial order Diprotodontia includes ten extant families that are grouped into the suborders Vombatiformes (koalas and wombats), Macropodiformes (kangaroos and allies), and Phalangeriformes (possums and gliders). We investigated interfamilial relationships using mitochondrial 12S rRNA, valine tRNA, and 16S rRNA gene sequences. Our results support the monophyly of both Vombatiformes and Macropodiformes, but not Phalangeriformes. Among possums and gliders, there was strong support for a petauroid clade that includes Pseudocheiridae (ringtail possums), Petauridae (sugar glider, striped possums), Acrobatidae (feathertail possums), and the monotypic family Tarsipedidae, which is represented by the highly specialized and autapomorphic honey possum (Tarsipes rostratus). Other prior hypotheses for the phylogenetic placement of the honey possum were rejected by statistical tests. The inclusion of the honey possum within Petauroidea suggests that derived ultrastructural features of Tarsipes' spermatozoa evolved independently in Tarsipes versus polyprotodont Australasian marsupials.     

Ontogenetic and phylogenetic transformations of the ear ossicles in marsupial mammals

This study is based on the examination of histological sections of specimens of different ages and of adult ossicles from macerated skulls representing a wide range of taxa and aims at addressing several issues concerning the evolution of the ear ossicles in marsupials. Three-dimensional reconstructions of the ear ossicles based on histological series were done for one or more stages of Monodelphis domestica, Caluromys philander, Sminthopsis virginiae, Trichosurus vulpecula, and Macropus rufogriseus. Several common trends were found. Portions of the ossicles that are phylogenetically older develop earlier than portions representing more recent evolutionary inventions (manubrium of the malleus, crus longum of the incus). The onset of endochondral ossification in the taxa in which this was examined followed the sequence; first malleus, then incus, and finally stapes. In M. domestica and C. philander at birth the yet precartilaginous ossicles form a supportive strut between the lower jaw and the braincase. The cartilage of Paauw develops relatively late in comparison with the ear ossicles and in close association to the tendon of the stapedial muscle. A feeble artery traverses the stapedial foramen of the stapes in the youngest stages of M. domestica, C. philander, and Sminthopsis virginiae examined. Presence of a large stapedial foramen is reconstructed in the groundplan of the Didelphidae and of Marsupialia. The stapedial foramen is absent in all adult caenolestids, dasyurids, Myrmecobius, Notoryctes, peramelids, vombatids, and phascolarctids. Pouch young of Perameles sp. and Dasyurus viverrinus show a bicrurate stapes with a sizeable stapedial foramen. Some didelphids examined to date show a double insertion of the Tensor tympani muscle. Some differences exist between M. domestica and C. philander in adult ossicle form, including the relative length of the incudal crus breve and of the stapes. Several differences exist between the malleus of didelphids and that of some phalangeriforms, the latter showing a short neck, absence of the lamina, and a ventrally directed manubrium. Hearing starts in M. domestica at an age in which the external auditory meatus has not yet fully developed, the ossicles are not fully ossified, and the middle ear space is partially filled with loose mesenchyme. The ontogenetic changes in hearing abilities in M. domestica between postnatal days 30 and 40 may be at least partially related to changes in middle ear structures.     

云南兽(三列齿类爬行动物)的耳区结构

本文介绍了以短吻云南兽为代表的一种耳区结构.它表明在三列齿类爬行动物里已经出现有发育的耳蜗壳以及在其内侧通过的颈内动脉等进步性质,听腔亦趋封闭.云南兽的中耳腔外侧出现了一条曲折的骨质外耳道,侧枕骨突外侧明显的沟可能表明方骨后耳膜之存在.     

Relationships among orders and families of marsupials based on 12S ribosomal DNA sequences and the timing of the marsupial radiation

Part of the mitochondrial 12S ribosomal RNA gene was amplified and sequenced for 26 marsupials. Multiple alignments for these sequences as well as seven additional sequences taken from GenBank were obtained using CLUSTAL. PAUP was used for phylogenetic analysis and to obtain random tree-length distributions. Analyses were performed with and without phylogenetic constraints. Our results clearly show that 12S rDNA contains phylogenetic signal at and above the ordinal level and is thus appropriate for addressing phylogenetic questions deep in the mammalian tree. Standard parsimony analyses provide some support for a clade containing diprotodontians, dasyurids,Dromiciops, andNotoryctes; transversion parsimony analysis suggests the possible inclusion of peramelids as well. Within the Diprotodontia, vombatids and phascolarctids cluster together on transversion parsimony and phalangerids may be associated with this clade. The enigmatic tarsipedids are apparently part of a clade that also contains pseudocheirids, petaurids, and acrobatids. The 12S sequences suggest that the origination of extant marsupial orders peaked 15 million years later than the equivalent taxonomic diversification of extant placental orders and may be entirely post-Cretaceous. Families of diprotodontian marsupials originated during the Eocene and early Oligocene, which is consistent with previous single-copy DNA hybridization results.     

The cerebellar paraflocculus and the subarcuate fossa in<Emphasis Type="Italic">Monodelphis domestica</Emphasis> and other marsupial mammals — ontogeny and phylogeny of a brain-skull interaction

The development of the subarcuate fossa and the cerebellar paraflocculus was studied in an ontogenetic series ofMonodelphis domestica Wagner, 1842 The spatial relation between these structures was examined qualitatively in adult specimens of several marsupial taxa. The fossa is first formed without participation of the cerebellar paraflocculus, which fills the fossa first fully and then partially later in development. The correlation between the size of the petrosal lobule of the paraflocculus and the subarcuate fossa in adults is weak. The volume of the subarcuate fossa was measured in 68 specimens representing 19 species of recent marsupials. Its size is negatively allometric with respect to skull size. The didelphids examined (‘large opossums’) have relatively smaller subarcuate fossae than the other marsupials examined, andSarcophilus laniarius is the major outlier, with a very small fossa. Loss of the subarcuate fossa has occurred at least twice in metatherian evolution (some sparassodonts and wombats). All marsupials examined to date, with the exception of wombats, have a differentiated petrosal lobule of the paraflocculus.     

Family-level relationships among the Australasian marsupial "herbivores" (Diprotodontia: Koala, wombats, kangaroos and possums)

The marsupial order Diprotodontia includes 10 extant families, which occupy all terrestrial habitats across Australia and New Guinea and have evolved remarkable dietary and locomotory diversity. Despite considerable attention, the interrelations of these families have for the most part remained elusive. In this study, we separately model mitochondrial RNA and protein-coding sequences in addition to nuclear protein-coding sequences to provide near-complete resolution of diprotodontian family-level phylogeny. We show that alternative topologies inferred in some previous studies are likely to be artifactual, resulting from branch-length and compositional biases. Subordinal groupings resolved herein include Vombatiformes (wombats and koala) and Phalangerida, which in turn comprises Petauroidea (petaurid gliders and striped, feathertail, ringtail and honey possums) and a clade whose plesiomorphic members possess blade-like premolars (phalangerid possums, kangaroos and their allies and most likely, pygmy possums). The topology resolved reveals ecological niche structuring among diprotodontians that has likely been maintained for more than 40 million years.     

Cranial morphology of Aegyptopithecus and Tarsius and the question of the tarsier-anthropoidean clade

New crania of the Oligocene anthropoidean Aegyptopithecus provide a test of the hypothesized tarsier-anthropoidean clade. Three cranial characters shared by Tarsius and some modern anthropoideans (apical interorbital septum, postorbital septum, "perbullar" carotid pathway) were examined. 1) An apical interorbital septum is absent in Aegyptopithecus. A septum does occur in Galago senegalensis (Lorisidae) and Microcebus murinus (Cheirogaleidae), so the presence of a septum is not strong evidence favoring a tarsiiform-anthropoidean clade. 2) In Aegyptopithecus and other anthropoideans, the postorbital septum is formed mainly by a periorbital flange of the zygomatic that extends medially from the lateral orbital margin onto or near the braincase. The postorbital plate of Tarsius is formed by frontal and alisphenoid flanges that extend laterally from the braincase to the zygomatic's frontal process, which is not broader than the postorbital bars of other prosimians. Periorbital flanges evolved in Tarsius for support or protection of the enormous eyes, as suggested by the occurrence of maxillary and frontal flanges that cup portions of the eye but do not separate it from temporal muscles. 3) The internal carotid artery of Aegyptopithecus enters the bulla posteriorly and crosses the anteroventral part of the promontorium. The tympanic cavity was probably separated from the anteromedial cavity by a septum stretching from the carotid channel to the ventrolateral bullar wall. In Tarsius, the carotid pathway is prepromontorial, and a septum stretches from the carotid channel to the posteromedial bullar wall. Quantitative analyses indicate that anterior carotid position has evolved because of erect head posture. The cranium of Oligocene anthropoideans thus provides no support for the hypothesized tarsier-anthropoidean clade.     

THE AUDITORY REGION OF EARLY PALEOCENE PUCADELPHYDAE (MAMMALIA, METATHERIA) FROM TIUPAMPA, BOLIVIA, WITH PHYLOGENETIC IMPLICATIONS

Abstract:  New petrosal bones, assigned to Pucadelphys and Andinodelphys , from the Lower Paleocene of Tiupampa, Bolivia, are described. These remains provide new information on the anatomy of the ear region of these taxa. The re-examination of characters from the petrosal and basicranium shed light on the phylogenetic relationships of the three Tiupampan genera known from complete cranial remains (i.e. Mayulestes , Pucadelphys and Andinodelphys ). The combination of dental, general cranial and basicranial characters led to two alternative hypotheses. The first is that borhyaenoids (including Mayulestes ) are nested within Notometatheria. Pucadelphyds (i.e. Pucadelphys and Andinodelphys ) are the sister group of a clade comprising MHNC 8369 (one isolated petrosal from Tiupampa) and Marsupialia. The second favours the paraphyly of 'borhyaenoids' (i.e. the exclusion of Mayulestes from borhyaenoids) and the polyphyly of 'Notometatheria'. In this case, Mayulestes and borhyaenids represent the stem group of a clade including Asiatic, American and Australian metatherians. This analysis of combined datasets (dental, general cranial and basicranial) highlighted contradictory information in the dental and cranial characters, serving to emphasize that in a large anatomical complex like an entire skull mosaic evolution of the characters is likely.