Meng Chen, Caroline A. E. StrÃmberg, and Gregory P. Wilson (2019)
Assembly of modern mammal community structure driven by Late Cretaceous dental evolution, rise of flowering plants, and dinosaur demise.
Proceedings of the National Academy of Sciences (advance online publication)
Amazing fossil discoveries over the last 30 years have led to the paleontological consensus that some Mesozoic mammaliaforms underwent ecomorphological diversification in the midst of dinosaurs. However, the ecological structure of Mesozoic mammaliaform communities remains unclear. Here, we quantify the ecological structure of extinct and extant small-bodied mammaliaform communities aiming to identify evolutionary and ecological drivers that have influenced those communities through time. We used body size, diet, and locomotion of constituent species to plot ecospace occupation and calculate ecological richness and disparity of those communities. We propose that the interplay of Late Cretaceous dental evolution, the rise of angiosperms, and competition with other vertebrates were critical in shaping the ecological structure of small-bodied mammaliaform communities through time.
The long-standing view that Mesozoic mammaliaforms living in dinosaur-dominated ecosystems were ecologically constrained to small size and insectivory has been challenged by astonishing fossil discoveries over the last three decades. By studying these well-preserved early mammaliaform specimens, paleontologists now agree that mammaliaforms underwent ecomorphological diversification during the Mesozoic Era. This implies that Mesozoic mammaliaform communities had ecological structure and breadth that were comparable to todayâs small-bodied mammalian communities. However, this hypothesis remains untested in part because the primary focus of most studies is on individual taxa. Here, we present a study quantifying the ecological structure of Mesozoic mammaliaform communities with the aim of identifying evolutionary and ecological drivers that influenced the deep-time assembly of small-bodied mammaliaform communities. We used body size, dietary preference, and locomotor mode to establish the ecospace occupation of 98 extant, small-bodied mammalian communities from diverse biomes around the world. We calculated ecological disparity and ecological richness to measure the magnitude of ecological differences among species in a community and the number of different eco-cells occupied by species of a community, respectively. This modern dataset served as a reference for analyzing five exceptionally preserved, extinct mammaliaform communities (two Jurassic, two Cretaceous, one Eocene) from Konservat-LagerstÃtten. Our results indicate that the interplay of at least three factors, namely the evolution of the tribosphenic molar, the ecological rise of angiosperms, and potential competition with other vertebrates, may have been critical in shaping the ecological structure of small-bodied mammaliaform communities through time.
Kailah M. Thorn, Mark N. Hutchinson, Michael Archer & Michael S. Y. Lee (2019)
A new scincid lizard from the Miocene of Northern Australia, and the evolutionary history of social skinks (Scincidae: Egerniinae).
Journal of Vertebrate Paleontology Article e1577873
The Egerniinae (formerly the Egernia group) is a morphologically diverse clade of skinks comprising 61 extant species from eight genera, spread across Australia, New Guinea, and the Solomon Islands. The relatively large size and robustness of many egerniines has meant that they fossilize more readily than other Australian skinks and have been more frequently recorded from paleontological excavations. The Riversleigh World Heritage Area of northeastern Australia has yielded multiple egerniine fossils, but most are isolated jaw elements, and only one taxon ('Tiliqua' pusilla) has been formally described. Articulated remains recently recovered from the mid-Miocene AL90 site (14.8 Ma) at Riversleigh are here described as Egernia gillespieae and represent the first opportunity to describe the morphology of a significant portion of a single individual of a fossil member of the Egerniinae. We include this fossil and 'T.' pusilla in an integrated analysis of morphology and published molecular data to assess their relationships and to provide calibration points for the timing of the egerniine radiation. Our calibrated tree combining molecular and morphological data suggests that the modern Australian radiation dates to the end of the Eocene (34.1 Ma). Both fossils are within the Australian crown clade Egerniinae: Egernia gillespieae is placed close to species of the living genus Egernia, whereas 'Tiliqua' pusilla likely sits basal to the divergence of the clade inclusive of Tiliqua and Cyclodomorphus. The fossils thus provide direct evidence that the Australian radiation of the Egerniinae was well underway by the mid-Miocene.
Menelia VasilopoulouâKampitsi, Jana Goyens,Â Simon Baeckens, Raoul Van Damme & Peter Aerts (2019)
Habitat use and vestibular system's dimensions in lacertid lizards.
Journal of Anatomy (advance online publication)
The vestibular system is crucial for movement control during locomotion. As the dimensions of the vestibular system determine the fluid dynamics of the endolymph and, as such, the system's function, we investigate the interaction between vestibular system size, head size and microhabitat use in lizards. We grouped 24 lacertid species in three microhabitat types, we acquired threeâdimensional models of the bony vestibular systems using microâcomputer tomography scanning, and we performed linear and surface measurements. All vestibular measurements scale with a negative allometry with head size, suggesting that smaller heads house disproportionally large ears. As the sensitivity of the vestibular system is positively related to size, a sufficiently large vestibular system in smallâheaded animals may meet the sensitivity demands during challenged locomotion. We also found that the microhabitat affects the locomotor dynamics: lizards inhabiting open microhabitats run at higher dimensionless speeds. On the other hand, no statistical relationship exists between dimensionless speed and the vestibular system dimensions. Hence, if the vestibular size would differ between microhabitats, this would be a direct effect (i.e. imposed, for instance, by requirements for manoeuvring, balance control, etc.), rather than depending on the lizardsâ intrinsic running speed. However, we found no effect of the microhabitat on the allometric relationship between head and vestibular system size. The finding that microhabitat is not reflected in the vestibular system size (hence sensitivity) of the lacertids in this study is possibly due to spatial constraints of the skull.
Martin QvarnstrÃm, Stavros Anagnostakis, Anders Lindskog, Udo Scheer, Vivi Vajda, Bo W. Rasmussen, Johan Lindgren & Mats E. Eriksson (2019)
Multiâproxy analyses of Late Cretaceous coprolites from Germany.
Lethaia (advance online publication)
A total of 462 coprolites from three localities exposing Upper Cretaceous deposits in the MÃnster Basin, northwestern Germany, have been subjected to an array of analytical techniques, with the aim of elucidating ancient trophic structures and predatorâprey interactions. The phosphatic composition, frequent bone inclusions, size and morphology collectively suggest that most, if not all, coprolites were produced by carnivorous (predatory or scavenging) vertebrates. The bone inclusions further indicate that the coprolite producers preyed principally upon fish. Putative host animals include bony fish, sharks and marine reptiles â all of which have been previously recorded from the MÃnster Basin. The presence of borings and other traces on several coprolites implies handling by coprophagous organisms. Remains of epibionts are also common, most of which have been identified as the encrusting bivalve Atreta. Palynological analyses of both the coprolites and host rocks reveal a sparse assemblage dominated by typical Late Cretaceous dinoflagellates, and with subâordinate fern spores, conifer pollen grains and angiosperm pollen grains. The dinoflagellate key taxon Exochosphaeridium cenomaniense corroborates a Cenomanian age for the Plenus Marl, from which most studied coprolites derive. The findings of this study highlight the potential of a multiâproxy approach when it comes to unravelling the origin, composition and importance of coprolites in palaeoecosystem analyses.
Sam M. Slater, Richard J. Twitchett, Silvia Danise & Vivi Vajda (2019)
Substantial vegetation response to Early Jurassic global warming with impacts on oceanic anoxia.
Nature Geoscience (advance online publication)
Rapid global warming and oceanic oxygen deficiency during the Early Jurassic Toarcian Oceanic Anoxic Event at around 183 Ma is associated with a major turnover of marine biota linked to volcanic activity. The impact of the event on land-based ecosystems and the processes that led to oceanic anoxia remain poorly understood. Here we present analyses of sporeâpollen assemblages from PliensbachianâToarcian rock samples that record marked changes on land during the Toarcian Oceanic Anoxic Event. Vegetation shifted from a high-diversity mixture of conifers, seed ferns, wet-adapted ferns and lycophytes to a low-diversity assemblage dominated by cheirolepid conifers, cycads and Cerebropollenites-producers, which were able to survive in warm, drought-like conditions. Despite the rapid recovery of floras after Toarcian global warming, the overall community composition remained notably different after the event. In shelf seas, eutrophication continued throughout the Toarcian event. This is reflected in the overwhelming dominance of algae, which contributed to reduced oxygen conditions and to a marked decline in dinoflagellates. The substantial initial vegetation response across the Pliensbachian/Toarcian boundary compared with the relatively minor marine response highlights that the impacts of the early stages of volcanogenic global warming were more severe for continental ecosystems than marine ecosystems.
New issue of Bollettino della SocietÃ Paleontologica Italiana 58Â isÂ devoted to the Italian geo-palaeontological record of major turnovers in the history of life and is in open access:
Papers that may be of interest:
R. Posenato (2019)
The end-Permian mass extinction (EPME) and the Early Triassic biotic recovery in the western Dolomites (Italy): state of the art.Â
Bollettino della SocietÃ Paleontologica Italiana 58: 11-34
The Dolomites (Southern Alps, Italy) represent a key-area to study the biotic and environmental events connected to the end-Permian mass extinction (EPME) and the Early Triassic biotic recovery of shallow-marine ecosystems. Geological and palaeontological researches on these events began since in the early 19th century. The contributions of these studies to the stratigraphic setting, dating, intensity, pattern and causes of the EPME and Early Triassic biotic recovery are outlined herein. After almost two centuries of research, our present undestanding suggests the following multi-steps scenario. The EPME occurred during a short extinction interval, which started at the base of transgressive oolitic beds of the Tesero Member (Werfen Formation, latest Changhsingian). The early phase lasted only a few millennia. It caused a dramatic drop of fossil abundance and diversity and the extinction of about 65% of existing genera, including the large-sized brachiopods and molluscs. The second phase affected the sparse stenotopic marine organisms, most had survived within microbial communities, and finished just above the Permian/ Triassic boundary a few thousand years after the first phase. Stressed environmental conditions, recorded by low diversified benthic assemblages dominated by disaster taxa, lasted up to the lower Olenekian Campil Member (Werfen Fm.). The early biotic recovery phase, recorded by the reappearance of stenotopic organisms and an increase in biodiversity occurred about 1.3 Myr after the EPME witnessed in the Tirolites cassianus beds of the Val Badia Member.
N. Preto, M.Bernardi, J. Dal Corso, P. Gianolla, E. Kustatscher, G. Roghi & M. Rigo (2019)
The Carnian Pluvial Episode in Italy: History of the research and perspectives.
Bollettino della SocietÃ Paleontologica Italiana 58: 35-49
The Carnian Pluvial Episode (CPE) was a perturbation of the Late Triassic climate that had a strong impact on marine and terrestrial ecosystems. The CPE is still a relatively neglected episode if compared to the other global ecosystem turnovers of the Mesozoic. Nevertheless, the CPE is synchronous with a major biological turnover, with both extinction among many marine and terrestrial groups and, remarkably, one of the most important evolutionary phases in the entire history of Life. The first significant radiation of dinosaurs, the spread of conifers and bennettitaleans, the first common occurrence of calcareous nannofossils, and the first reefs built by scleractinian corals all occurred during or soon after the CPE. Furthermore, the first common occurrence of amber dates to the CPE. Ammonoids and conodonts, the two most important groups for the biostratigraphy of the Triassic, were also subject to a significant turnover. Many localities in Italy had a primary role for the understanding of the CPE, and still represent benchmarks for new studies. Some of these localities are paradigmatic examples of the geological and biotic processes that were occurring during this interval of geologic time, and should be designated as geosites. While recent studies on the CPE focused on identifying the episode globally, and far from the best studied regions of Western Tethys and the European continent, the Italian CPE localities could still provide a wealth of information on this event, especially concerning the evolution of shallow marine and terrestrial groups. Indeed, the best deep-water record of the CPE (Pignola, Basilicata), the most expanded and complete shallow water successions (Raibl area, Friuli-Venezia Giulia), the most prolific amber sites and the best preserved reef associations (Dolomites, Veneto) all occur in Italy.
Silva I. Premoli (2019)
The Cretaceous/Palaeogene Boundary: Italian souvenirs for the youngest of the "Big Five" extinctions.Â
Bollettino della SocietÃ Paleontologica Italiana 5:, 73-75.
The aim of this contribution is to provide a brief introduction to the Italian section of the Bottaccione gorge, near Gubbio, and its bearing to the understanding of the end Cretaceous event. I provide an historical account of the main contributions that built the fundamental background knowledge to the famous hypothesis of an extraterrestrial cause for the extinction event, which was originally formulated grounding on observations and specimens collected in this section.
A. Montanari & R. Coccioni (2019)
The serendipitous discovery of an extraterrestrial iridium anomaly at the Cretaceous-Palaeogene boundary in Gubbio and the rise of a far-reaching theory.Â
Bollettino della SocietÃ Paleontologica Italiana 58: 77-83.
It is not so frequent that in a scientific investigation using a deductive approach, an unforeseen result leads to a new hypothesis, which grows stronger through the same deductive approach of investigation, and eventually becomes a theory leading to a paradigm shift. The theory that a catastrophic impact of an extraterrestrial object, a comet or an asteroid, on the Earth caused a global mass extinction at the end of the Cretaceous Period strongly challenged the Lyellian paradigm of gradualism/uniformitarianism. In the 1980s, a nonconformist theory sprouted from the serendipitous discovery of an iridium anomaly in an inconspicuous clay layer marking the Cretaceous-Palaeogene boundary in the pelagic succession of Gubbio and opened the way to forty years of heated debates and thousands of scientific publications in the most disparate fields of Earth and planetary sciences. With this paper, our intention is to recount the scientific background, which led to the formulation of this theory.