The present paper describes a disarticulated skull of Allqokirus australis Marshall & Muizon, 1988, a basal sparassodont (Metatheria, Mammalia) from the early Palaeocene (c. 65 Ma.) of Tiupampa (Bolivia). The specimen includes the rostrum and palate with right premaxilla, both maxillae, left lacrimal, palatines and most upper teeth. The second largest element includes the frontals, the left squamosal, the parietals, the supraoccipital, the basisphenoid, the presphenoid, the alisphenoid, and part of the pterygoids. The nasals, basioccipital and exoccipitals are missing. Other elements are the left petrosal, the right jugal and squamosal, and both dentaries. The elements of the specimen allow for a good reconstruction of the skull, which is thoroughly described and compared to that of other sparassodonts and to the Tiupampa pucadelphyids, Pucadelphys and Andinodelphys. The dental morphology of Allqokirus australis is extremely similar to that of Patene simpsoni from the early Eocene of Itaboraí (Brazil) and presents distinct (although incipient) carnivorous adaptations. Furthermore, some characters of the ear region (e.g. medial process of the squamosal, deep groove for the internal carotid artery at the ventral apex of the petrosal) are also present in most other sparassodonts and in the pucadelphyids from the same locality. A parsimony analysis performed on the basis of a data matrix of 364 characters and 38 taxa placed Allqokirus in a sparassodont clade (the Mayulestidae) that also included Mayulestes and Patene. This family constitutes the sister group of all other sparassodonts. Our analysis also retrieved a large clade composed of the sparassodonts and the pucadelphyids, formally named Pucadelphyda n. superord. This superorder represents the large metatherian carnivorous radiation of the Tertiary of South America, which is first known at Tiupampa, and which started to diversify probably slightly earlier, during the late Cretacous in South America. So far, no representative of Pucadelphyda has been discovered in North America. At Tiupampa, Allqokirus and Mayulestes are the largest metatherians of the fauna and they fill the predaceous mammalian ecological niche. They are the earliest representatives of Sparassodonta, a successful metatherian carnivorous radiation which persisted in South America until the late Pliocene, i.e., during more than 63 Ma.

Alcidedorbignya inopinata Muizon & Marshall, 1987 is a basal pantodont (Placentalia, Mammalia) of small body size, from the early Palaeocene of the Santa Lucia Formation at Tiupampa, Bolivia. Tiupampa is the type locality for the Tiupampan, a South American Land Mammal age (SALMA), which is assigned an age equivalent to the basal Torrejonian 1 of North America (c. 65 Ma). Alcidedorbignya is known by exceptionally preserved specimens, which are described here. The two major specimens are an almost complete skeleton (MHNC 8372) and a partial skull (MHNC 8399), the former representing one of the best-preserved fossil placentals from the early Palaeocene and probably the oldest placental skeleton that is so completely known. These specimens are also the first eutherian skulls and skeleton ever discovered at Tiupampa, a locality which has yielded numerous metatherian skulls and partial skeletons. The remarkable preservation of the two skulls allows a detailed description of the cranial anatomy with well-identified sutures and foramina, including those of the auditory region. Through CT scanning of the skulls, the arterial and venous circulation pattern in the basicranium as well as the bony labyrinth of the inner ear were tentatively reconstructed. A thorough description of the postcranial skeleton of MHNC 8372 is also provided. Among pantodonts, Alcidedorbignya presents the closest morphological similarities with Pantolambda, the oldest and earliest diverging North American pantodont (known by skulls and skeletons), from the late early Palaeocene (Torrejonian 2 and 3) of New Mexico. Alcidedorbignya is one-third the size, much more gracile, and clearly exhibits more plesiomorphic features than Pantolambda. It is also at least 3 Ma older. Interesting similarities are also observed between the skull of Alcidedorbignya and several "condylarths", such as Maiorana, Baioconodon, Arctocyon, and Arctocyonides. The basicranium of Alcidedorbignya is also similar to that of some extant afrotheres (e.g., Tenrec) or Lipotyphla (e.g., 398GEODIVERSITAS • 2015 • 37 (4) Muizon C. de et al. Solenodon), but most of these similarities may represent placental symplesiomorphies. In fact, the cranial anatomy of Alcidedorbignya, beyond the simple thorough description of a basal pantodont, sheds light on the cranial anatomy of placentals from the earliest Paleocene, previously unknown in this detail. The postcranial skeleton of MHNC 8372 together with some isolated specimens referred to A. inopinata, is compared to adequate morphofunctional models (e.g., Solenodon, Dendrohyrax, Sciurus), which indicates that it was a moderately agile, plantigrade, generalized terrestrial mammal with good climbing ability (scansorial) and occasionally capable of standing in a bipedal position. The scutiform ungual phalanges were probably bearing nail-like hooves (or primate-like nails) and because of the absence of claws, fossorial habits are unlikely.A parsimony analysis of a data matrix including 72 taxa and 426 characters (cranial and postcranial...