What Drove the Giant Marsupial Predators (sparassodontans) of South America to Extinction?

Extinction of South American sparassodontans (Metatheria): environmental fluctuations or complex ecological processes?

Authors:

Lópes-Aguirre et al

Abstract:

Sparassodontans are a diverse but now extinct group of metatherians that were apex predators in South America during most of the Cenozoic. Studying their decline has been controversial mainly due to the scarcity of the fossil record, and different methodological approaches have led to contradictory hypotheses. In an effort to explore questions about their extinction, we developed a novel multi-model statistical approach to analyse all of the currently available data at a continental scale. Using multiple regression analysis and new advances in beta diversity analysis, we used all currently available fossil data at a continental scale to test four competing hypotheses to account for the decline of sparassodontans: competition with placental carnivorans, competition with avian phorusrhacids, non-competitive ecological interactions, and environmental fluctuations. Our results show that the sparassodontan extinction was a gradual process with species disappearing throughout the Cenozoic. Multiple regression analysis supported non-competitive ecological interactions as the best extinction model. Native South American ungulates, African migrants (caviomorph rodents and platyrrhine primates) and didelphimorphians were the groups with the highest statistical significance. Sparassodontan beta diversity increased between South American Land Mammal Ages after the Paleocene–Eocene boundary. Our results demonstrate that ecological modelling techniques illuminate aspects of extinction processes whilst mitigating the limitations of the fossil record. Our study suggests that non-competitive ecological interactions could have been the main driver for sparassodontan extinction rather than, as commonly assumed, a result of competition and/or abiotic fluctuations.

Microleo attenboroughi: a Fossil Marsupial Carnivore From Miocene Neogene Australia

It weighed a little more than that 20-ounce bottle of Mountain Dew on your desk and is named after one of the giants in nature broadcasting: Meet the pocket-sized marsupial lion that you wish you could have met for real 19 million years ago.

Microleo attenboroughi is the latest fascinating fossil to emerge from northern Australia, which earlier this year gave us the hypercarnivore Whollydooleya tomnpatrichorum (go on, just say that name aloud. You know you want to). Researchers unearthed M. attenboroughi at the fossiliferous Riversleigh UNESCO World Heritage Site and dated the animal to about 19 million years ago, when the area was a lush rainforest.

Named in honor of beloved broadcaster Sir David Attenborough (also arguably the world’s most famous naturalist and, come on, the guy everyone wishes would turn up at a dinner party), this mini-marsupial got his academic debut this week in the online, open-access Palaeontologia Electronica.

link.

Therian Mammals Started an Ecomorphical Evolutionary Radiation PRIOR to the Extinction of the Dinosaurs

Therian mammals experience an ecomorphological radiation during the Late Cretaceous and selective extinction at the K–Pg boundary

Authors:

Grossnickle et al

Abstract:

It is often postulated that mammalian diversity was suppressed during the Mesozoic Era and increased rapidly after the Cretaceous–Palaeogene (K–Pg) extinction event. We test this hypothesis by examining macroevolutionary patterns in early therian mammals, the group that gave rise to modern placentals and marsupials. We assess morphological disparity and dietary trends using morphometric analyses of lower molars, and we evaluate generic level taxonomic diversity patterns using techniques that account for sampling biases. In contrast with the suppression hypothesis, our results suggest that an ecomorphological diversification of therians began 10–20 Myr prior to the K–Pg extinction event, led by disparate metatherians and Eurasian faunas. This diversification is concurrent with ecomorphological radiations of multituberculate mammals and flowering plants, suggesting that mammals as a whole benefitted from the ecological rise of angiosperms. In further contrast with the suppression hypothesis, therian disparity decreased immediately after the K–Pg boundary, probably due to selective extinction against ecological specialists and metatherians. However, taxonomic diversity trends appear to have been decoupled from disparity patterns, remaining low in the Cretaceous and substantially increasing immediately after the K–Pg extinction event. The conflicting diversity and disparity patterns suggest that earliest Palaeocene extinction survivors, especially eutherian dietary generalists, underwent rapid taxonomic diversification without considerable morphological diversification.

More Delightful Extinct Marsupial Mammals From Riversleigh World Heritage site in Australia

Riversleigh World Heritage site in Australia is a who's who of weird extinct animals. It is a limestone cave packed with huge number of skeletons, leftovers of poor creatures that have got accumulated over the course of millions of years.

Scientists have found fossils of the Thingodonta from its depths. Thingodonta is a woodpecker-like marsupial that gnawed bugs out of tree bark using its teeth. They have discovered proof of an extinct tusked kangaroo relative, with the scientific name Balbaroo fangaroo.

They've dug out the leftovers of drop crocs, ancient crocodiles that killed their prey by making them fall out of trees. And they came across the gigantic Dromornis, also called ‘Demon Duck of Doom’, which is 10 feet tall and is one of the world’s biggest birds.

Scientists now said that they have a tiny, but quite strange new creature to include in the collection. The latest creature is malleodectes mirabilis, or ‘wondrous hammer biter’, which is a ferret-sized cousin of present day Tasmanian devils that survived on escargot diet.

In a statement, University of New South Wales paleontologist Mike Archer, the main author of a study on the fossil appeared in Scientific Reports, said that Malleodectes mirabilis was an extremely weird mammal, odd in its own way just like a koala or kangaroo.

The creatures had massive, hammer-like premolars that let them eat entire snails, including shell and all. The researchers haven’t seen such characteristics in a mammal before.

link.

"Australian" Marsupials in Paleogene South America?

On The existence of non-microbiotherian Australidelphian marsupials (Diprotodontia) in the Eocene of Patagonia

Authors:

Lorente et al

Abstract:

A diverse assemblage of extinct mammals of early–middle Eocene age (Ypresian–Lutetian boundary) come from the Patagonian localities of La Barda and Laguna Fría around Paso del Sapo in northwestern Chubut Province (Argentina). Metatherians are well represented, mostly by dental remains of ‘Didelphimorphia’, Paucituberculata, Sparassodonta, Microbiotheria, and Polydolopimorphia. Here we analyse three calcanea and one astragalus referable to the same, indeterminate taxon, from La Barda, showing the fusion of their ectal and sustentacular facets. This facet arrangement characterizes the Australidelphia, a marsupial clade represented by Microbiotheria from South America and Antarctica, plus all Australasian lineages. Other australidelphian features shown by these tarsals include: in the calcanea, a reduced peroneal process and a tripartite cuboid facet; in the astragalus, a round, very small astragalar head in relation to the body; a convex trochlea with a half for the tibia and half, in slightly lower position, for the fibula. Their size and other anatomical features suggest that the new tarsals cannot be referred to the Microbiotheria. Phylogenetic analysis suggests that the La Barda taxon lies within the Australidelphia, and that it is either closely related or belongs to, the Diprotodontia. The existence of advanced australidelphians in Patagonia adds further evidence of the close relationship between Patagonia, Antarctica, and Australia during the Late Cretaceous – early Palaeogene.

Did Placentals and Marsupials Diverge 170 Million Years ago Starting at the Aalenian/Bajocian Jurassic?

The Interrelationships of Placental Mammals and the Limits of Phylogenetic Inference

Authors:

Tarver et al

Abstract:

Placental mammals comprise three principal clades: Afrotheria (e.g. elephants and tenrecs), Xenarthra (e.g. armadillos and sloths) and Boreoeutheria (all other placental mammals), the relationships among which are the subject of controversy and a touchstone for debate on the limits of phylogenetic inference. Previous analyses have found support for all three hypotheses, leading some to conclude that this phylogenetic problem might be impossible to resolve, due to the compounded effects of Incomplete Lineage Sorting (ILS) and a rapid radiation. Here we show, using a genome scale nucleotide dataset, microRNAs, and the reanalysis of the three largest previously published amino-acid datasets, that the root of Placentalia lies between Atlantogenata and Boreoeutheria. Although we found evidence for ILS in early placental evolution, we are able to reject previous conclusions that the placental root is a hard polytomy that cannot be resolved. Reanalyses of previous datasets recover Atlantogenata + Boreoeutheria and show that contradictory results are a consequence of poorly fitting evolutionary models; instead, when the evolutionary process is better-modelled, all datasets converge on Atlantogenata. Our Bayesian molecular clock analysis estimates that marsupials diverged from placentals 157-170 Ma, crown Placentalia diverged 86-100 Ma, and crown Atlantogenata diverged 84-97 Ma. Our results are compatible with placental diversification being driven by dispersal rather than vicariance mechanisms, postdating early phases in the protracted opening of the Atlantic Ocean.

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.

The Phylogenetics of 5 Mammals From Aptian/Albian Cretaceous Texas and Oklahoma

Taxonomic revision of tribosphenic mammals from the Lower Cretaceous Antlers Formation of Texas and Oklahoma, USA.

Author:

Averianov

Abstract:

There are five taxa of tribosphenic mammals in the Early Cretaceous Antlers Formation of Texas and Oklahoma, USA: a basal stem therian (Kermackia texana), stem therians near the eutherian-metatherian dichotomy (Holoclemensia texana and Pappotherium pattersoni), and stem marsupials (Atokatheridium boreni and Oklatheridium szalayi). K. texana has a primitive therian postcanine formula with three molars, replacement of p5, M3 with low protocone and no conules, lower molars with a large trigonid angle, oblique protocristid, paraconid smaller than metaconid (except m3), strong distal metacristid, narrow talonid, small talonid basin, and small entoconid (absent on m3). H. texana also has replacement in the fifth premolar locus and three molars. It is more derived in having a larger protoconal region with higher protocone and conules present, lack of distal metacristid, smaller trigonid angle, transverse protocristid, and wide talonid with larger talonid basin. It is similar to Eutheria by having M1 with reduced ectoflexus, semimolariform p5, and low trigonid angle with transverse protocristid. Holoclemensia cannot be referred to Eutheria because of the lack of the second rank postvallum/prevallid shear and unwinged conules. P. pattersoni (=Slaughteria eruptens) has replacement in the fifth premolar position, premolariform p5, and three molars (symplesiomorphies for Theria). It is more derived than Holoclemensia in having a wider and shorter talonid. Pappotherium is similar to Eutheria in having a low trigonid angle, transverse protocristid, and the cristid obliqua labial to the protocristid notch. It cannot be attributed to the Eutheria because of the narrow protoconal region, low protocone, small conules lacking internal cristae, postprotocrista not extending labially past the metacone base, and a small talonid basin. Atokatheridium boreni and Oklatheridium szalayi (=O. minax, syn. nov.) have four molars and emphasis on the postvallum/prevallid shear (large metacone on M2, strong postmetacrista, paraconid higher than metaconid). These taxa cannot be attributed to the Deltatheroida because of large protoconal region with winged conules. Oklatheridium is further different from the Deltatheroida in having a wider talonid and better developed entoconid.

Ganguroo robustiter: a new Miocene Neogene Macropodid (kangaroo)

Ganguroo robustiter, sp. nov. (Macropodoidea, Marsupialia), a middle to early late Miocene basal macropodid from Riversleigh World Heritage Area, Australia

Authors:

Cooke et al

Abstract:

Cranial and dental remains of the middle to early late Miocene macropodid kangaroo, Ganguroo robustiter, sp. nov., are described. Postcranial remains of G. robustiter were previously described as referable to G. bilamina. Ganguroo robustiter is more robust (approximately 20% larger) and more derived than G. bilamina and G. bites, in having a larger m4, a well-developed posterolingual ridge and lingual cingulum on P3, a longer P3/p3, and no stylar cusp C on M3–M4. We used previously published data matrices to analyze the phylogenetic relationship of G. robustiter. Both phylogenetic analyses, using craniodental and postcranial characters, place G. robustiter within Macropodidae, as the sister taxon to sthenurines and macropodines. Species of Ganguroo are not found to be monophyletic despite their extreme similarity in character scores. This may be due to the large amount of missing data for G. bilamina and G. bites for which no postcranial remains have been identified. Phylogenetic results are ambiguous, recovering unresolved trees with low bootstrap values, but the generic assignment of these taxa is maintained because they are remarkably similar. Species of Ganguroo may represent a phyletic lineage, with species increasing in size and losing cusp/cuspids on their premolars through time, which appears to coincide with a broader record of changing vegetation and climates through the middle Miocene.

Albian Cretaceous Wyoming and Montana had a Diverse Mammal Population

Tribosphenic mammals from the Lower Cretaceous Cloverly Formation of Montana and Wyoming

Authors:

Cifelli et al

Abstract:

We report a diverse assemblage of tribosphenidan mammals from several localities in the Cloverly Formation (Lower Cretaceous, Albian) of Montana and Wyoming. This unit is of historical significance for yielding well-known dinosaurs (e.g., Deinonychus antirrhopus, Tenontosaurus tilletti) and early mammals (e.g., Gobiconodon ostromi, Montanalestes keeblerorum). We provisionally identify 13 taxa (five of which are formally recognized), including Pappotherium pattersoni, a new species of the deltatheroidan Oklatheridium (O. wiblei, sp. nov.), a eutherian (Montanalestes, previously named), and two new basal tribosphenidans (Argaliatherium robustum, gen. et sp. nov., and Carinalestes murensis, gen. et sp. nov.). An unnamed taxon, represented by associated but almost edentulous dentaries, is interpreted to have had four incisors, a single-rooted canine, three premolars, and four molars, indicating that the metatherian tooth formula was established by the Albian. In addition, an indeterminate lower molar fragment preserving twinned talonid cusps and a buccal postcingulid provides the earliest evidence for Marsupialiformes. We also provide a more detailed description of the associated dentaries (holotype) of Montanalestes keeblerorum. The mammalian fauna from the Cloverly Formation shares several taxa with the roughly contemporaneous Trinity Group of Oklahoma and Texas, an observation that also applies to the dinosaur fauna, suggesting some degree of latitudinal homogeneity among described terrestrial vertebrates in this part of the North American Early Cretaceous.

Lotheridium mengi: a new Deltatheroidan Metatherian Mammal From Upper Cretaceous China

A new Cretaceous Metatherian mammal from Henan, China

Authors:

Bi et al

Abstract:

We report a new deltatheroidan mammal from the Upper Cretaceous of Henna, China. The new taxon, Lotheridium mengi, is based on a nearly complete skull and associated lower jaws with full adult dentition. Deltatheroidans are known mostly from fragmentary specimens from Asia and North America. Previous views on deltatheroidan relationships were diverse, but recent studies favored their metatherian affinity. The new specimen represents the most complete skull known for deltatheroidans and provides additional evidence that deltatheroidans already had the distinctive metatherian dental formula and replacement pattern and several other derived metatherian features, supporting the metatherian status for this clade. The new species also indicates that deltatheroidan mammals were more diverse and had broader geographical distributions than previously thought.

DNA of Extinct Pleistocene Quaternary Macropod (kangaroos, wallabies) Studied

Late Pleistocene Australian Marsupial DNA Clarifies the Affinities of Extinct Megafaunal Kangaroos and Wallabies

Authors:

Llamas et al

Abstract:

Understanding the evolution of Australia’s extinct marsupial megafauna has been hindered by a relatively incomplete fossil record and convergent or highly specialized morphology, which confound phylogenetic analyses. Further, the harsh Australian climate and early date of most megafaunal extinctions (39–52 ka) means that the vast majority of fossil remains are unsuitable for ancient DNA analyses. Here, we apply cross-species DNA capture to fossils from relatively high latitude, high altitude caves in Tasmania. Using low-stringency hybridization and high-throughput sequencing, we were able to retrieve mitochondrial sequences from two extinct megafaunal macropodid species. The two specimens, Simosthenurus occidentalis (giant short-faced kangaroo) and Protemnodon anak (giant wallaby), have been radiocarbon dated to 46–50 and 40–45 ka, respectively. This is significantly older than any Australian fossil that has previously yielded DNA sequence information. Processing the raw sequence data from these samples posed a bioinformatic challenge due to the poor preservation of DNA. We explored several approaches in order to maximize the signal-to-noise ratio in retained sequencing reads. Our findings demonstrate the critical importance of adopting stringent processing criteria when distant outgroups are used as references for mapping highly fragmented DNA. Based on the most stringent nucleotide data sets (879 bp for S. occidentalis and 2,383 bp for P. anak), total-evidence phylogenetic analyses confirm that macropodids consist of three primary lineages: Sthenurines such as Simosthenurus (extinct short-faced kangaroos), the macropodines (all other wallabies and kangaroos), and the enigmatic living banded hare-wallaby Lagostrophus fasciatus (Lagostrophinae). Protemnodon emerges as a close relative of Macropus (large living kangaroos), a position not supported by recent morphological phylogenetic analyses.

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.

Metatherian Mammals Nearly Wiped out by KT/K-Pg Extinction

The origin and early evolution of metatherian mammals: the Cretaceous record

Authors:

Wiliamson et al

Abstract:

Metatherians, which comprise marsupials and their closest fossil relatives, were one of the most dominant clades of mammals during the Cretaceous and are the most diverse clade of living mammals after Placentalia. Our understanding of this group has increased greatly over the past 20 years, with the discovery of new specimens and the application of new analytical tools. Here we provide a review of the phylogenetic relationships of metatherians with respect to other mammals, discuss the taxonomic definition and diagnosis of Metatheria, outline the Cretaceous history of major metatherian clades, describe the paleobiology, biogeography, and macroevolution of Cretaceous metatherians, and provide a physical and climatic background of Cretaceous metatherian faunas. Metatherians are a clade of boreosphendian mammals that must have originated by the Late Jurassic, but the first unequivocal metatherian fossil is from the Early Cretaceous of Asia. Metatherians have the distinctive tightly interlocking occlusal molar pattern of tribosphenic mammals, but differ from Eutheria in their dental formula and tooth replacement pattern, which may be related to the metatherian reproductive process which includes an extended period of lactation followed by birth of extremely altricial young. Metatherians were widespread over Laurasia during the Cretaceous, with members present in Asia, Europe, and North America by the early Late Cretaceous. In particular, they were taxonomically and morphologically diverse and relatively abundant in the Late Cretaceous of western North America, where they have been used to examine patterns of biogeography, macroevolution, diversification, and extinction through the Late Cretaceous and across the Cretaceous-Paleogene (K-Pg) boundary. Metatherian diversification patterns suggest that they were not strongly affected by a Cretaceous Terrestrial Revolution, but they clearly underwent a severe extinction across the K-Pg boundary.

Tsagandelta dashzevegi: a new Carnivorous Deltatheroidan Metatherian From Cenomanian/Campanian Cretaceous Mongolia

A deltatheroidan mammal from the Upper Cretaceous Baynshiree Formation, eastern Mongolia

Authors:

Rougier et al

Abstract:

Deltatheroidans are a specialized group of basal metatherians with a long fossil history and a broad geographic distribution across Asia and North America. The group was among the first Mesozoic mammals known by relatively complete cranial material, recovered from the Gobi Desert by the American Museum expeditions in the 1920s. Deltatheroidans exhibit trends in their dentition towards apparent specializations for carnivory, including strongly developed postmetacrista, pronounced postvallum-prevallid shear, and a reduction of the ultimate molar. While the oldest undisputed deltatheroidans hail from the Early Cretaceous of North America, Upper Cretaceous rocks in central Asia have yielded the best preserved specimens and the bulk of the diversity. Here we describe a new deltatheroidan, Tsagandelta dashzevegi, gen. et sp. nov., from the Upper Cretaceous Baynshiree Formation of eastern Mongolia. This taxon adds to the diversity of the group in central Asia and provides further evidence of uniformity among the Late Cretaceous vertebrate faunas across the Gobi Desert.

Did Giant Short Faced Kangaroos Walk Like Theropods?

Locomotion in Extinct Giant Kangaroos: Were Sthenurines Hop-Less Monsters?

Authors:

Janis et al

Abstract:

Sthenurine kangaroos (Marsupialia, Diprotodontia, Macropodoidea) were an extinct subfamily within the family Macropodidae (kangaroos and rat-kangaroos). These “short-faced browsers” first appeared in the middle Miocene, and radiated in the Plio-Pleistocene into a diversity of mostly large-bodied forms, more robust than extant forms in their build. The largest (Procoptodon goliah) had an estimated body mass of 240 kg, almost three times the size of the largest living kangaroos, and there is speculation whether a kangaroo of this size would be biomechanically capable of hopping locomotion. Previously described aspects of sthenurine anatomy (specialized forelimbs, rigid lumbar spine) would limit their ability to perform the characteristic kangaroo pentapedal walking (using the tail as a fifth limb), an essential gait at slower speeds as slow hopping is energetically unfeasible. Analysis of limb bone measurements of sthenurines in comparison with extant macropodoids shows a number of anatomical differences, especially in the large species. The scaling of long bone robusticity indicates that sthenurines are following the “normal” allometric trend for macropodoids, while the large extant kangaroos are relatively gracile. Other morphological differences are indicative of adaptations for a novel type of locomotor behavior in sthenurines: they lacked many specialized features for rapid hopping, and they also had anatomy indicative of supporting their body with an upright trunk (e.g., dorsally tipped ischiae), and of supporting their weight on one leg at a time (e.g., larger hips and knees, stabilized ankle joint). We propose that sthenurines adopted a bipedal striding gait (a gait occasionally observed in extant tree-kangaroos): in the smaller and earlier forms, this gait may have been employed as an alternative to pentapedal locomotion at slower speeds, while in the larger Pleistocene forms this gait may have enabled them to evolve to body sizes where hopping was no longer a feasible form of more rapid locomotion.

Fieratherium sorex: a new, Unique Oligocene Paleogene Shrew-like Metatherian Mammal From Argentina

A unique, Late Oligocene shrew-like marsupial from western Argentina and the evolution of dental morphology

Authors:

Forasiepi et al

Abstract:

We describe a new metatherian mammal, Fieratherium sorex gen. et sp. nov., found in western Argentina (Quebrada Fiera locality, southern Mendoza Province), in Late Oligocene deposits (Agua de la Piedra Formation, Deseadan age). The only known specimen is a juvenile with fragments of both dentaries, the right maxilla and a fragment of the left premaxilla with dentition. The loci and the number teeth preserved suggest a dental formula of I?3/i3, C1/c1, P3/p3, M?3/m?3. Fieratherium sorex has a convergent shrew-like appearance and a unique combination of features among metatherians and other South American mammals of Palaeogene age, including the well-known faunas of Patagonia. An analysis of its phylogenetic affinities suggests that Fieratherium is the sister-group of the Paucituberculata. As already described by other authors for several mammalian taxa, the mainly Patagonian South American Palaeogene fossil record offers little information to understanding the evolution of northern lineages. Fieratherium may represent a taxon belonging to a lineage that had its origin in Neotropical regions, so far unrecorded in the southern region of South America.

Paleogene (?) Deposits Found in Australia

IN an astounding discovery, palaeontologists think they might have found an even more fossil-rich site in northwest Queensland than the world-renowned Riversleigh World Heritage Area.

The site could become one of the planet’s most important prehistoric places because scientists hope it holds the missing link between the demise of the dinosaurs and the emergence of mammals.

The dig is near Riversleigh but can be accessed only by helicopter or foot.

Renowned palaeontologist Mike Archer initially visited for just a couple of hours two years ago, the first time the area had likely been trod by Europeans.

He had been tipped off by Xtrata employee Ned Stephenson who had been using satellite images to examine landscapes.

ut what has really excited scientists is that the new fossil deposits, dubbed New Riversleigh, are either on or near marine rocks that are about 500 million years old and which have not been below sea level since.

“Theoretically, it means limestone sediment of any age could have accumulated their way back to the dinosaur age,’’ he said. “I’m not interested in dinosaurs but what happened between the age of the dinosaurs and the earliest mammals.’’

This was a dark age of emerging mammal species, roughly from the end of the dinosaurs 65 million years ago to 24 million years ago.

link.

a New Species of Small Sparassodont Metatherian From Miocene Neogene Bolivia

A new species of small-bodied sparassodont (Mammalia, Metatheria) from the middle Miocene locality of Quebrada Honda, Bolivia

Authors:

Engelman et al

Abstract:

The Sparassodonta (Mammalia, Metatheria) are a group of carnivorous mammals that dominated the macropredatory guild of South America during the Cenozoic. Here, we describe a new sparassodont based on a single specimen from the middle Miocene Quebrada Honda local fauna of southern Bolivia. This specimen (UF 27881) does not clearly correspond to any major sparassodont group (e.g., Hathliacynidae, Borhyaenidae, etc.) and represents a morphotype previously unknown among the Sparassodonta. UF 27881 is distinguished from other sparassodonts by its short, broad, borhyaenid-like rostrum and small size, among other features. However, we decline to coin a new name for UF 27881 due to the fragmentary nature of this specimen and the absence of most of its dentition. This specimen suggests that the appearance of the Sparassocynidae and several hypercarnivorous didelphid taxa (including Thylophorops, Thylatheridium, Lutreolina, and Hyperdidelphys) represent an evolutionary response to the decline in small, predatory sparassodont taxa during the late Cenozoic. This study documents new morphological diversity among the Sparassodonta and highlights the value of fossils from traditionally undersampled parts of South America.

South America Hosted Several Cretaceous Relic Mammal Populations at Least into the Miocene Neogene

The bizarre ‘metatherians’ Groeberia and Patagonia, late surviving members of gondwanatherian mammals

Authors:

Chimento et al

Abstract:

Cenozoic mammalian faunas from South America contrast with those of the other continents by the great diversification of metatherian mammals. Among the later, a wide range of morphological disparity have been reported, and several bizarre mammals have been assigned to such clade, based mainly on biogeographical grounds. Outstanding examples of bizarre mammals referred to as Metatheria are the Eocene Groeberia and the Miocene Patagonia. Recent discoveries indicate that South America possessed a more diverse faunal composition than previously thought, and it became evident that many Mesozoic holdovers (e.g. australosphenidans, gondwanatherians and dryolestoids) surpassed the K/T boundary, thus forming part of the Cenozoic faunas. The Cenozoic taxa Patagonia and Groeberia exhibit several similarities with the Gonwanatheria, including rodent-like jaws with enlarged incisives, molariform cheek-teeth, anteriorly extended masseteric fossa and palinal mastication among other features. The inclusion of Gondwanatheria, Patagonia and Groeberia within an abarcative phylogenetic analysis resulted in close phylogenetic relationships among these taxa. Such hypothesis indicates that Cretaceous relics in the Cenozoic of South America were more diversified than previously thought.