[PaleoMammalogy • 2023] the Pliocene Marsupial Ambulator keanei gen. nov. (Marsupialia: Diprotodontidae) from inland Australia and its Locomotory Adaptations

 Ambulator keanei (Stirton, 1967)

in van Zoelen, Camens, Worthy et Prideaux. 2023.  

DOI: 10.1098/rsos.230211 

 twitter.com/Zoelenotherium

Abstract

Diprotodontids were the largest marsupials to exist and an integral part of Australian terrestrial ecosystems until the last members of the group became extinct approximately 40 000 years ago. Despite the frequency with which diprotodontid remains are encountered, key aspects of their morphology, systematics, ecology and evolutionary history remain poorly understood. Here we describe new skeletal remains of the Pliocene taxon Zygomaturus keanei from northern South Australia. This is only the third partial skeleton of a late Cenozoic diprotodontid described in the last century, and the first displaying soft tissue structures associated with footpad impressions. Whereas it is difficult to distinguish Z. keanei and the type species of the genus, Z. trilobus, on dental grounds, the marked cranial and postcranial differences suggest that Z. keanei warrants genus-level distinction. Accordingly, we place it in the monotypic Ambulator gen. nov. We, also recognize the late Miocene Z. gilli as a nomen dubium. Features of the forelimb, manus and pes reveal that Ambulator keanei was more graviportal with greater adaptation to quadrupedal walking than earlier diprotodontids. These adaptations may have been driven by a need to travel longer distances to obtain resources as open habitats expanded in the late Pliocene of inland Australia.

Keywords: megafauna, Pliocene, Australia, fossil marsupials, Diprotodontidae, cranial and postcranial morphology

 

 Reassembled partial skeleton Ambulator keanei (SAMA P54742) with silhouette.

Systematic palaeontology

Class: Mammalia Linnaeus, 1758 

Superorder: Marsupialia Illiger, 1811 

Order: Diprotodontia Owen, 1877  

Superfamily: Diprotodontoidea Archer & Bartholomai, 1978 

Family: Diprotodontidae Gill, 1872 

Genus: Ambulator gen. nov.

 

Ambulator keanei (Stirton, 1967) comb. nov.

 Genus Etymology: ‘Ambulator’ is Latin for ‘walker’. This is in reference to the taxon's many postcranial adaptations that to plantigrade, graviportal walking. The gender of the genus is masculine.

 

 Species etymology: Named for Mr Vincent P. Keane, who provided heavy equipment for the excavations in the Tirari Desert in 1962 conducted by Ruben A. Stirton, Paul F. Lawson, Richard H. Tedford and Michael O. Woodburne. 

 Holotype: SAMA P13844, partial lower mandible with both ascending rami missing; right and left I1; left and right P3; left M1; right M4, partial maxilla containing left M2–M4. Collected by R. A. Stirton in 1962.

 Type locality: Keane Quarry, Lake Palankarinna, South Australia. Palankarinna Local Fauna, 3.9 Ma.

Conclusion: 

We describe the first postcranial material known for Ambulator keanei. This is only the fourth species of post-Miocene diprotodontid for which postcranial material has been described and includes the first three-dimensional description of the footpad morphology for the family. We found that Am. keanei expresses the earliest evidence for specialized graviportal locomotion within diprotodontids, suggesting that it may have been relatively vagile, which may correlate with late Pliocene grassland expansion. We also found evidence that the phalanges of graviportal diprotodontids were not used in weight bearing during locomotion. Systematic comparisons of established diprotodontid taxa indicate that inclusion of postcranial morphology in phylogenetic analyses is needed in order to resolve both species- and the higher-level taxonomy for the Diprotodontidae. Rare, well-preserved skeletal and soft tissue material found in the Main Body of the Tirari Formation indicates considerable potential for discovery of additional material. Future efforts should target collecting more vertebrate material from this formation. This may lead to not only a better understanding of marsupial diversity but a better understanding of the faunal change of Australia through time.

Jacob D. van Zoelen, Aaron B. Camens, Trevor H. Worthy and Gavin J. Prideaux. 2023. Description of the Pliocene Marsupial Ambulator keanei gen. nov. (Marsupialia: Diprotodontidae) from inland Australia and its Locomotory Adaptations. Royal Society Open Science. DOI: 10.1098/rsos.230211 

 twitter.com/Zoelenotherium/status/1663824958848638976

[PaleoMammalogy • 2023] A Macroevolutionary Pathway to Megaherbivory

in Sanisidro, Mihlbachler & Cantalapiedra, 2023.

 DOI: 10.1126/science.ade1833 

 twitter.com/Canta_Lab

Abstract

Several scenarios have been proposed to explain rapid net size increases in some early Cenozoic mammalian lineages: sustained and gradual directional change, successive occupation of adaptive zones associated with progressively larger body sizes, and nondirectional evolution associated with branching events in combination with higher diversification potential of the larger lineages. We test these hypotheses in brontotheres, which are among the first radiations of mammals that consistently evolved multitonne sizes. Body-mass evolution in brontotheres mainly occurred during speciation and had no preferential direction. Long-term directional change stemmed from the higher survival of larger lineages in less-saturated herbivore guilds. Our study emphasizes the role of differential species proliferation in explaining the long-term phenotypic trends observed in the fossil record, which are more than an accumulation of steady microevolutionary changes.

Editor’s summary: 

After the extinction of large dinosaurs at the end of the Cretaceous, many mammals underwent a rapid increase in size. Several hypotheses for this change have been put forward, with much debate about the drivers. Sanisidro et al. looked at the record of body size in brontotheres, large herbivorous mammals from the Eocene that experienced orders of magnitude changes in size. The authors saw no evidence for directional selection, but instead found a pattern of increased survival of larger species caused by reduced competition with other herbivores in their niches. Thus, over time, the increase in body size in these mammals was caused by the macroevolutionary process of species sorting. —Sacha Vignieri

Oscar Sanisidro, Matthew C Mihlbachler and Juan L Cantalapiedra. 2023. A Macroevolutionary Pathway to Megaherbivory. SCIENCE. 380, 6645; 616-618. DOI: 10.1126/science.ade1833

  twitter.com/Canta_Lab/status/1656720984617934850

  phys.org/news/2023-05-differential-species-proliferation-key-evolutionary.html

[PaleoMammalogy • 2021] Paraceratherium linxiaense • An Oligocene Giant Rhino (Perissodactyla: Paraceratheriidae) provides insights into Paraceratherium Evolution

  Paraceratherium linxiaense

Deng, Lu, Wang, Flynn, Sun, He & Chen, 2021

DOI: 10.1038/s42003-021-02170-6

Abstract

As one of the largest land mammals, the origin and evolution of the giant rhino Paraceratherium bugtiense in Pakistan have been unclear. We report a new species Paraceratherium linxiaense sp. nov. from northwestern China with an age of 26.5 Ma. Morphology and phylogeny reveal that P. linxiaense is the highly derived species of the genus Paraceratherium, and its clade with P. lepidum has a tight relationship to P. bugtiense. Based on the paleogeographical literature, P. bugtiense represents a range expansion of Paraceratherium from Central Asia via the Tibetan region. By the late Oligocene, P. lepidum and P. linxiaense were found in the north side of the Tibetan Plateau. The Tibetan region likely hosted some areas with low elevation, possibly under 2000 m during Oligocene, and the lineage of giant rhinos could have dispersed freely along the eastern coast of the Tethys Ocean and perhaps through some lowlands of this region.

Holotype (HMV 2006) of Paraceratherium linxiaense sp. nov.
Skull: a lateral view; b ventral view; c dorsal view; d anterior view; e occipital view. Mandible: f, h lateral view and medial view of left ramus, respectively; g occlusal view. Skull and mandible share the scale bar, but both anterior and nuchal views have an independent scale bar.

Systematic paleontology

Perissodactyla Owen, 1848 

Paraceratheriidae Osborn, 1923

Paraceratherium Forster-Cooper, 1911

Paraceratherium linxiaense sp. nov.

Diagnosis: Paraceratherium linxiaense possesses features that characterize the genus, such as a giant body size, long premaxillae with anterior ends extending downward, separated parietal crests, high condyle compared to the height of nuchal surface, lower inferior border of the posttympanic process than the condyle, roughly horizontal anterior part of symphysis, and downward turning cone-shaped I1. It is more derived than other species within this genus in having a larger body size, deeper nasal notch above M2, much higher occipital part and posterior end of zygomatic arch, and smaller upper incisor I1. The lower margin of the horizontal mandibular ramus is concave under the diastema, and small i1 extends anteriorly and horizontally. The dental formula is 1.0.3.3/1.0.3.3. P2 is semimolarized, while P3 and P4 are submolarized. The metaconule connects with the ectoloph and the anterior point of the hypocone in moderate wear; the antecrochet is moderate; the lingual border of the protocone is rounded on molars; and the ecto-posterior corner of the protolophid is angular on p3 and p4. The atlas has an expanded transverse foramen and a dumb-bell shaped vertebral fossa.

Age: IVPP locality LX1808 is faunally and paleomagnetically dated to the middle of chron C8r with an estimated age of 26.5 million years ago (Ma) in the late Oligocene (Fig. 5).

Type horizon of Paraceratherium linxiaense sp. nov.
Exposures of fluvial and lacustrine sediments of the Linxia Basin (LX 1808) at the type locality of this new species (HMV 2006, yellow square) and where the axis and thoracic vertebrae were also found in Wangjiachuan Village, Dongxiang County, Gansu Province, China. 
Type locality of Paraceratherium linxiaense sp. nov.
Map showing the giant rhino fossil locality of the Linxia Basin in Wangjiachuan Village, Dongxiang County, Gansu Province, China.

 Type locality of Paraceratherium linxiaense sp. nov.
Map showing the giant rhino fossil locality of the Linxia Basin in Wangjiachuan Village, Dongxiang County, Gansu Province, China.

 

Tao Deng, Xiaokang Lu, Shiqi Wang, Lawrence J. Flynn, Danhui Sun, Wen He and Shanqin Chen. 2021. An Oligocene Giant Rhino provides insights into Paraceratherium Evolution. Communications Biology. 4: 639. DOI: 10.1038/s42003-021-02170-6

[PaleoMammalogy • 2021] Nesorhinus gen. nov. • A New Rhinoceros Clade from the Pleistocene of Asia sheds light on Mammal Dispersals to the Philippines

in Antoine, Reyes, Amano, ... et Ingicco, 2021. 

 

 DOI: 10.1093/zoolinnean/zlab009 

 twitter.com/Noel_Amano 

 

Abstract

Rhinoceroses are among the most endangered mammalian species today. Their past diversity is well documented from the Eocene onward, although their evolutionary history is far from being fully understood. Here, we elucidate the systematic affinities of a Pleistocene rhinoceros species represented by a partial skeleton from 709 ± 68 kya archaeological deposits in Luzon Island, Philippines. We perform a comprehensive phylogenetic analysis, including all living species and a wide array of extinct rhinocerotid species. We confirm the early split between Elasmotheriinae and Rhinocerotinae at c. 35.5 Mya and constrain the divergence between recent Asian and African rhinoceroses at c. 24 Mya, with contrasting phenotypic evolutionary rates in Diceroti and Rhinoceroti. Dental features reveal the existence of an unsuspected Asian Pleistocene clade, referred to as Nesorhinus gen. nov.. It includes the rhinoceros from the Philippines and another extinct species from Taiwan, N. hayasakai. Nesorhinus is the sister-group to a cluster comprising Dicerorhinus and Rhinoceros. Our phylogenetic results strongly suggest an island-hopping dispersal for Nesorhinus, from the Asian mainland towards Luzon via Taiwan by the Late Miocene or later, and Pleistocene dispersals for representatives of Rhinoceros. Nesorhinus philippinensis would be the first perissodactyl species supporting the island-rule hypothesis, with decreased body weight and limb-bone robustness.

Keywords: evolutionary trends, island biogeography, island fauna, Mammalia, megafauna, morphological phylogenetics, morphological systematic

Pierre-Olivier Antoine, Marian C. Reyes, Noel Amano, Angel P. Bautista, Chun-Hsiang Chang, Julien Claude, John De Vos and Thomas Ingicco. 2021. A New Rhinoceros Clade from the Pleistocene of Asia sheds light on Mammal Dispersals to the Philippines. Zoological Journal of the Linnean Society. zlab009.  DOI: 10.1093/zoolinnean/zlab009

  twitter.com/Noel_Amano/status/1396085838920957954

    

[PaleoMammalogy • 2020] Environmental Drivers of Megafauna and Hominin Extinction in Southeast Asia

 

A savannah in Middle Pleistocene Southeast Asia. 

 foreground: stegodon, hyenas, and Asian rhinos (Rhinoceros).

 background: water buffalo can be seen at the edge of a riparian forest

in Louys & Roberts, 2020. 

DOI: 10.1038/s41586-020-2810-y

 Illustration: Peter Schouten  

Abstract

Southeast Asia has emerged as an important region for understanding hominin and mammalian migrations and extinctions. High-profile discoveries have shown that Southeast Asia has been home to at least five members of the genus Homo. Considerable turnover in Pleistocene megafauna has previously been linked with these hominins or with climate change, although the region is often left out of discussions of megafauna extinctions. In the traditional hominin evolutionary core of Africa, attempts to establish the environmental context of hominin evolution and its association with faunal changes have long been informed by stable isotope methodologies. However, such studies have largely been neglected in Southeast Asia. Here we present a large-scale dataset of stable isotope data for Southeast Asian mammals that spans the Quaternary period. Our results demonstrate that the forests of the Early Pleistocene had given way to savannahs by the Middle Pleistocene, which led to the spread of grazers and extinction of browsers—although geochronological limitations mean that not all samples can be resolved to glacial or interglacial periods. Savannahs retreated by the Late Pleistocene and had completely disappeared by the Holocene epoch, when they were replaced by highly stratified closed-canopy rainforest. This resulted in the ascendency of rainforest-adapted species as well as Homo sapiens—which has a unique adaptive plasticity among hominins—at the expense of savannah and woodland specialists, including Homo erectus. At present, megafauna are restricted to rainforests and are severely threatened by anthropogenic deforestation.

 

Biogeography, Biological anthropology, Ecosystem ecology, Environmental impact, Palaeontology

Artist’s reconstruction of a savannah in Middle Pleistocene Southeast Asia. In the foreground Homo erectus, stegodon, hyenas, and Asian rhinos are depicted. Water buffalo can be seen at the edge of a riparian forest in the background. 

  Illustration: Peter Schouten 

Julien Louys and Patrick Roberts. 2020. Environmental drivers of megafauna and hominin extinction in Southeast Asia. Nature. DOI: 10.1038/s41586-020-2810-y

Past Tropical Forest Changes Drove Megafauna and Hominin Extinctions

New biochemical research shows significant turnovers in Southeast Asian environments and animals during the Pleistocene

shh.mpg.de/1873324/past-tropical-forest-changes-drove-megafauna-and-hominin-extinctions

phys.org/news/2020-10-tropical-forest-drove-megafauna-hominin.html

    

[Paleontology • 2020] Extinction of eastern Sahul Megafauna coincides with Sustained Environmental Deterioration

 Sahul Megafauna

in Hocknull, Lewis, Arnold, et al., 2020. 

  DOI: 10.1038/s41467-020-15785-w

natureecoevocommunity.nature.com
theconversation.com

Abstract
Explanations for the Upper Pleistocene extinction of megafauna from Sahul (Australia and New Guinea) remain unresolved. Extinction hypotheses have advanced climate or human-driven scenarios, in spite of over three quarters of Sahul lacking reliable biogeographic or chronologic data. Here we present new megafauna from north-eastern Australia that suffered extinction sometime after 40,100 (±1700) years ago. Megafauna fossils preserved alongside leaves, seeds, pollen and insects, indicate a sclerophyllous forest with heathy understorey that was home to aquatic and terrestrial carnivorous reptiles and megaherbivores, including the world’s largest kangaroo. Megafauna species diversity is greater compared to southern sites of similar age, which is contrary to expectations if extinctions followed proposed migration routes for people across Sahul. Our results do not support rapid or synchronous human-mediated continental-wide extinction, or the proposed timing of peak extinction events. Instead, megafauna extinctions coincide with regionally staggered spatio-temporal deterioration in hydroclimate coupled with sustained environmental change.

Fig. 2: Summary of field sites and diversity of fossil remains from South Walker Creek (QML1420).
a Aerial map of main South Walker Creek fossil sites SW9, SWJ and SW3 with downstream site SWCC indicated by arrow. Megafauna taxa recovered from each site indicated by numbered silhouette: 1. Pallimnarchus sp. 2. ‘Quinkana’ sp., 3. Crocodylus sp. cf. C. porosus, 4. Varanus priscus, 5. Varanus sp. (large), 6. Dromaius sp., 7. Diprotodon optatum, 8. Phascolonus gigas, 9. Sedophascolomys sp. cf. S. medius, 10. Thylacoleo sp., 11. Palorchestes sp., 12. Macropus sp. (giant), 13. Protemnodon sp., 14. Notamacropus sp. (giant), 15. Osphranter sp. cf. O. rufus, 16. sthenurine.
b Stratigraphic section A–Aʹ crossing through SW9, SWJ and SW3 (indicated by dashed line in (a)). Quaternary (Qa) alluvial sediment overlies dipping basement Permo-Triassic Rewan Group (Rw) bedrock (vertical exaggeration 5×).
 Fossil deposit surface expression at SW9 (c), SW3 (d) and SWCC (e). Summary of the diverse fossil remains recovered from SWC sites. ...

Fig. 2: Summary of field sites and diversity of fossil remains from South Walker Creek (QML1420).
 Fossil deposit surface expression at SW9 (c), SW3 (d) and SWCC (e). Summary of the diverse fossil remains recovered from SWC sites (see Supplementary Note 1 for detailed descriptions): f
 leaves and bivalves in situ at SW9; g Goodeniaceae seed; h Velesunio wilsoni bivalve; i insect elytron (?Curculionidae); j Pallimnarchus sp. osteoderm; k Crocodylus sp. cf. C. porosus osteoderm; isolated crocodile teeth from l Pallimnarchus, m Crocodylus sp. and n ‘Quinkana’; o Varanus priscus tooth; p Macropus sp. (giant) tibia in situ at SW9; q Varanus priscus dorsal vertebra; associated appendicular elements from Thylacoleo sp., r metacarpal, s phalange and t fibula; u Diprotodon optatum right dentary; v Macropus sp. (giant) humerus with crocodile puncture marks (indicated by arrows); w Articulated pelvis and caudal vertebrae of Phascolonus gigas from SW9; x associated hind limb of juvenile Protemnodon sp. from SW9.

Scale bars equal 1 mm in (g, i); 5 mm in (h, j–t, v, x); 10 mm in (u); and 50 mm in (w).

Life and Death in Tropical Australia, 40,000 years ago. Pallimnarchus stalks the world’s largest kangaroo at the edge of a drying billabong. Two Megalania fight over the carcass of Diprotodon optatum whilst another giant kangaroo, standing at 3m tall, reaches for the freshest leaves to eat. In the distance, the sun beats down on the Mt. Britton range, a silent witness to the extinctions yet to unfold.

Illustration: Ryan Bargiel, Vlad Konstantinov, Andrey Atuchin & Scott Hocknull © Queensland Museum (2020).

natureecoevocommunity.nature.com

       


Scott A. Hocknull, Richard Lewis, Lee J. Arnold, Tim Pietsch, Renaud Joannes-Boyau, Gilbert J. Price, Patrick Moss, Rachel Wood, Anthony Dosseto, Julien Louys, Jon Olley and Rochelle A. Lawrence. 2020. Extinction of eastern Sahul Megafauna coincides with Sustained Environmental Deterioration. Nature Communications. 11, 2250. DOI: 10.1038/s41467-020-15785-w

Life and death in tropical Australia, 40,000 years ago. natureecoevocommunity.nature.com/users/366107-scott-hocknull/posts/61740-megafauna-extinction

theconversation.com/humans-coexisted-with-three-tonne-marsupials-and-lizards-as-long-as-cars-in-ancient-australia-138534

https://blog.qm.qld.gov.au/2020/05/18/discovering-the-worlds-largest-kangaroo-part-2-in-the-lab

    

     

     

[PaleoMammalogy • 2019] Causes and Consequences of Pleistocene Megafaunal Extinctions as Revealed from Rancho La Brea Mammals

 the hunting behavior of La Brea carnivores, including saber-toothed cats, dire wolves, and coyotes.  

in DeSantis, Crites, Feranec, et al., 2019. 

 DOI: 10.1016/j.cub.2019.06.059

Illustration: Mauricio Antón 

Highlights:

• Sabertooth cats and dire wolves were not in competition for similar prey

• Sabertooth cats scavenged more intensively during cooler intervals

 • Coyote diets were substantially affected by the extinction of megafauna

• Rancho La Brea fossils reveal that diets of carnivorans are not always conserved

Summary

The fossils preserved in the Rancho La Brea “tar” seeps in southern California span the past ∼50,000 years and provide a rare opportunity to assess the ecology of predators (e.g., the American lion, sabertooth cats, cougars, dire wolves, gray wolves, and coyotes), including clarifying the causes and consequences of the terminal Pleistocene extinction event. Here, a multi-proxy approach elucidates dietary responses of carnivorans to changing climates and megafaunal extinctions. Using sample sizes that are unavailable anywhere else in the world, including hundreds of carnivoran and herbivore specimens, we clarify the paleobiology of the extinct sabertooth cats and dire wolves—overturning the idea that they heavily competed for similar prey. Canids (especially the dire wolf) consumed prey from more open environments than felids, demonstrating minimal competition for prey throughout the latest Pleistocene and largely irrespective of changing climates, including just prior to their extinction. Coyotes experienced a dramatic shift in dietary behavior toward increased carcass utilization and the consumption of forest resources (prey and/or plant resources) after the terminal Pleistocene megafaunal extinction. Extant predators’ ability to effectively hunt smaller prey and/or utilize carcasses may have been a key to their survival, especially after a significant reduction in megafaunal prey resources. Collectively, these data suggest that dietary niches of carnivorans are not always static and can instead be substantially affected by the removal of top predators and abundant prey resources.

 Keywords: Canis, Carnivora, diet, dental microwear, mammals, paleoecology, Pleistocene, Rancho La Brea, Smilodon, stable isotopes

 the hunting behavior of La Brea carnivores, including saber-toothed cats, dire wolves, and coyotes.

Illustration: Mauricio Antón

 Larisa R.G. DeSantis, Jonathan M. Crites, Robert S. Feranec, Kena Fox-Dobbs, Aisling B. Farrell, John M. Harris, Gary T. Takeuchi and Thure E. Cerling. 2019. Causes and Consequences of Pleistocene Megafaunal Extinctions as Revealed from Rancho La Brea Mammals.  Current Biology. DOI: 10.1016/j.cub.2019.06.059

Intense look at La Brea Tar Pits explains why we have coyotes, not saber-toothed cats phys.org/news/2019-08-intense-la-brea-tar-pits.html via @physorg_com

Saber-tooth surprise: Fossils redraw picture of the fearsome big cat
 on.natgeo.com/2M29oUu via @NatGeoScience