English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Zendy Open

Presents the pdf analysis as premium feature

PDF Analysis

Insights

Presents the summarisation as premium feature

Summarisation

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the zaia usage as premium feature

ZAIA

Zendy Tools

Zendy Plus

Presents the access of premium content as premium feature

Premium Content

International audienceAlcidedorbignya 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). Alcidedorbignyais known by exceptionally preserved specimens, which are described here. The two majorspecimens are an almost complete skeleton (MHNC 8372) and a partial skull (MHNC 8399), theformer representing one of the best-preserved fossil placentals from the early Palaeocene and probablythe oldest placental skeleton that is so completely known. These specimens are also the firsteutherian skulls and skeleton ever discovered at Tiupampa, a locality which has yielded numerousmetatherian skulls and partial skeletons. The remarkable preservation of the two skulls allows a detaileddescription of the cranial anatomy with well-identified sutures and foramina, including thoseof the auditory region. Through CT scanning of the skulls, the arterial and venous circulation patternin 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 oldestand earliest diverging North American pantodont (known by skulls and skeletons), from the lateearly Palaeocene (Torrejonian 2 and 3) of New Mexico. Alcidedorbignya is one-third the size, muchmore gracile, and clearly exhibits more plesiomorphic features than Pantolambda. It is also at least3 Ma older. Interesting similarities are also observed between the skull of Alcidedorbignya and several“condylarths”, such as Maiorana, Baioconodon, Arctocyon, and Arctocyonides. The basicraniumof Alcidedorbignya is also similar to that of some extant afrotheres (e.g., Tenrec) or Lipotyphla (e.g.,Solenodon), but most of these similarities may represent placental symplesiomorphies. In fact, thecranial 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 inthis detail. The postcranial skeleton of MHNC 8372 together with some isolated specimens referredto A. inopinata, is compared to adequate morphofunctional models (e.g., Solenodon, Dendrohyrax,Sciurus), which indicates that it was a moderately agile, plantigrade, generalized terrestrial mammalwith 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) andbecause 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)has been undertaken with TNT and Paup 4b10. The matrix includes several stem eutheriansand representatives of the four major clades of Placentalia: Laurasiatheria, Euarchontoglires, Xenarthra,and Afrotheria. Furthermore, because one of the major aims of this analysis is to test possibleclose phylogenetic relationships of Alcidedorbignya inopinata with the five orders of South American“ungulates”, 12 taxa belonging to the Notoungulata, Astrapotheria, Litopterna, Pyrotheria andXenungulata, were included in the matrix. Two analyses were performed: one unconstrained andone with a backbone constraint based on the latest molecular phylogenies. One of the main resultsof these analyses is the high level of homoplasy detected by the low retention index (RI close to 0.5;CI inferior to 0.2), which indicates that half of the similarities present in the matrix are interpretedas homoplasies. Nevertheless, some interesting observations emerge. In both analyses, all membersof Pantodonta are closely related and included in the Placentalia, and the Eocene “cimolestid” taxonDidelphodus, which has been regarded as closely related to pantodonts, is their sister-group. In theconstrained analysis, the Pantodonta are monophyletic and included in the Laurasiatheria; Didelphodusand the pantodonts are clustered with the Tillodontia, either as their sister group or included ina clade also comprising some “condylarths”. In the unconstrained analysis the xenungulate Carodniais included within the Pantodonta as the sister group of Coryphodon, this clade being part of a largebasal polytomy of placental lineages. Both analyses agree with a northern origin of the South Americanpantodont Alcidedorbignya as it is nested within northern taxa. Furthermore, no close relationship ofAlcidedorbignya with South American endemic ungulates is supported, except for pantodont-xenungulateaffinities in the unconstrained analysis. In the constrained analysis the five groups of SouthAmerican endemic “ungulates” are gathered in a single clade included in the laurasiatheres but notdirectly related to pantodonts. Finally, the rather apical position of Alcidedorbignya in both analysesmay be considered as an argument for a pre-K-Pg placental diversification, as this taxon is dated atc. 65 Ma, nearly coincident with the end of the Cretaceous

Alcidedorbignya inopinata, a basal pantodont (Placentalia, Mammalia) from the early Palaeocene of Bolivia: anatomy, phylogeny and palaeobiology