Minusculodelphis minimus: an Insectivorous Jaskhadelphyid Metatherian From Eocene Paleogene Brazil

Taxonomy, affinities, and paleobiology of the tiny metatherian mammal Minusculodelphis, from the early Eocene of South America

Authors:

Olivieria et al

Abstract:

With less than 3 g of estimated body mass, the early Eocene Minusculodelphis minimus Paula Couto (Mammalia, Metatheria, Jaskhadelphyidae) is one of the smallest mammals, living or extinct. It has alternatively been regarded as a didelphid or a derorhynchid “ameridelphian,” or even as an eometatherian marsupial. Here, we describe a new species of Minusculodelphis coming from the same locality (Itaboraí Quarry, Brazil) and age (Itaboraian age) of the type species of the genus. It differs from M. minimus in its larger size and several dental characters. The new species offers data on the upper dentition and femur, which are unknown in the type species. Compared to other Paleogene metatherians, Minusculodelphis shows closer relationships with Jaskhadelphys, from the early Paleocene of Tiupampa, Bolivia, as well as with Kiruwamaq, from the late Eocene-early Oligocene of Perú. A cladistic analysis places all three genera within the family Jaskhadelphyidae (Metatheria, Order indet.), which includes small to tiny, insectivorous-like metatherians. We argue that insectivory (soft insects) is the best-supported diet for both species of Minusculodelphis, and that the most probable microhabitat for them was the understorey or leaf litter of tropical, rain forested environments.

Dryolestidan Cladotherian Paurodon valens was a Tithonian Jurassic Golden Mole Parallel

Ontogeny and taxonomy of Paurodon valens (Mammalia, Cladotheria) from the Upper Jurassic Morrison Formation of USA. (pdf)

Authors:

Averianov et al

Abstract:

Several basal cladotherian taxa previously referred to the “Paurodontidae” (Dryolestida) from the Upper Jurassic Morrison Formation of Wyoming, U.S.A. represent ontogenetic and individual variation of one single taxon, Paurodon valens Marsh, 1887 (=Archaeotrigon brevimaxillus Simpson, 1927, syn. n.; = Pelicopsis dubius Simpson, 1927, syn. n.; = Archaeotrigon distagmus Simpson, 1929, syn. n.; = Araeodon intermissus Simpson, 1937, syn. n.; = Foxraptor atrox Bakker et Carpenter, 1990, syn. n.). P. valens is characterized by prolonged dental replacement, including late eruption of m4 (and m5 as individual variation) and a time gap between shedding of dp2 and eruption of p2, which can be lost in aged individuals. By a shortened dentary and mandibular symphysis, two-three simple premolariform teeth, and four molariform teeth with tall trigonid and small talonid, P. valens is strinkingly similar to the modern golden moles (Chrysochloridae), particularly to Amblysomus hottentotus. This similarity suggests that P. valens was specialized on consuming earth worms in contrast to a more insectivorous diet characteristic for other dryolestidans.

Mammalian Insectivores (and Marsupial!) From Miocene Neogene Germany

Insectivore palaeoecology. A case study of a Miocene fissure filling in Germany

Authors:

Kleitmann et al

Abstract:

Many Miocene localities yielded considerable numbers of eulipotyphlan fossils. The group as a whole is generally considered to be indicative for humid environments, but little is known about the preferences of specific taxa. We discuss the insectivores found in the German fissure filling Petersbuch 28, including an insectivorous marsupial, in an attempt to refine the knowledge of the preferred environments of insectivores. For this, we compared the assemblage in quantitative analyses with other insectivore assemblages of similar age. Our results show that, in full accordance with previous hypotheses, dimylids, most moles and shrews were shown to be indicators for humid environments, like swamps or humid forests, whereas the hedgehogs, the moles Desmanodon and Theratiskos and the shrew Oligosorex were more common in dryer environments.

Jurassic Mammals Kuehneotherium, Morganucodon Were Specialist, not Generalist Insectivores

Dietary specializations and diversity in feeding ecology of the earliest stem mammals

Authors:

Gill et al

Abstract:

The origin and radiation of mammals are key events in the history of life, with fossils placing the origin at 220 million years ago, in the Late Triassic period1. The earliest mammals, representing the first 50 million years of their evolution and including the most basal taxa, are widely considered to be generalized insectivores. This implies that the first phase of the mammalian radiation—associated with the appearance in the fossil record of important innovations such as heterodont dentition, diphyodonty and the dentary–squamosal jaw joint —was decoupled from ecomorphological diversification. Finds of exceptionally complete specimens of later Mesozoic mammals have revealed greater ecomorphological diversity than previously suspected, including adaptations for swimming, burrowing, digging and even gliding, but such well-preserved fossils of earlier mammals do not exist1, and robust analysis of their ecomorphological diversity has previously been lacking. Here we present the results of an integrated analysis, using synchrotron X-ray tomography and analyses of biomechanics, finite element models and tooth microwear textures. We find significant differences in function and dietary ecology between two of the earliest mammaliaform taxa, Morganucodon and Kuehneotherium—taxa that are central to the debate on mammalian evolution. Morganucodon possessed comparatively more forceful and robust jaws and consumed ‘harder’ prey, comparable to extant small-bodied mammals that eat considerable amounts of coleopterans. Kuehneotherium ingested a diet comparable to extant mixed feeders and specialists on ‘soft’ prey such as lepidopterans. Our results reveal previously hidden trophic specialization at the base of the mammalian radiation; hence even the earliest mammaliaforms were beginning to diversify—morphologically, functionally and ecologically. In contrast to the prevailing view this pattern suggests that lineage splitting during the earliest stages of mammalian evolution was associated with ecomorphological specialization and niche partitioning.