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Results 41 through 60 out of 190

in category paleontology

 

41: Inferring lifestyle for Aves and Theropoda: a model based on curvatures of extant avian ungual bones

Savannah E. Cobb, William I Sellers

1,207 downloads (posted 10 Jan 2019)

Claws are involved in a number of behaviours including locomotion and prey capture, and as a result animals evolve claw morphologies that enable these functions. Past authors have found geometry of the keratinous sheath of the claw to correlate with mode of life for extant birds and squamates; this relationship has frequently been cited to infer lifestyles for Mesozoic theropods including Archaeopteryx. However, claw sheaths rarely fossilize and are prone to deformation; past inferences are thus compromised. As the ungual phalanx within the claw is relatively resistant to deformation and more commonly preserved in the fossil record, geometry of this bone would provide a more useful metric for paleontological analysis. In this study, ungual bones of 108 birds and 5 squamates were imaged using X-ray techniques and a relationship was found between curvatures of the ungual bone within the claw of pedal digit III and four modes of life; ground-dwelling, perching, predatory, and scansorial; using linear discriminant analysis with Kappa equal to 0.69. Our model predicts arboreal lifestyles for certain key taxa Archaeopteryx and Microraptor and a predatory ecology for Confuciusornis. These findings demonstrate the utility of our model in answering questions of palaeoecology, the theropod-bird transition, and the evolution of avian flight.

https://rxivist.org/papers/41351
https://doi.org/10.1101/517375

42: Palaeobiological inferences based on long bone epiphyseal and diaphyseal structure - the forelimb of xenarthrans (Mammalia)

E. Amson, J.A. Nyakatura

1,201 downloads (posted 13 May 2018)

Trabecular architecture (i.e., the main orientation of the bone trabeculae, their relative number, mean thickness, spacing, etc.) has been shown experimentally to adapt with extreme accuracy and sensitivity to the loadings applied to the bone during life. However, the potential of trabecular parameters used as a proxy for the mechanical environment of an organism's organ to help reconstruct the lifestyle of extinct taxa has only recently started to be exploited. Furthermore, these parameters are rarely combined to the l...

https://rxivist.org/papers/30111
https://doi.org/10.1101/318121

43: Reconstructing the ecology of a Jurassic pseudoplanktonic megaraft colony

Aaron W. Hunter, David Casenove et al.

1,191 downloads (posted 04 Mar 2019)

Pseudoplanktonic crinoid megaraft colonies are an enigma of the Jurassic. They are among the largest in-situ invertebrate accumulations ever to exist in the Phanerozoic fossil record. These megaraft colonies and are thought to have developed as floating filter-feeding communities due to an exceptionally rich relatively predator free oceanic niche, high in the water column enabling them to reach high densities on these log rafts. However, this pseudoplanktonic hypothesis has never actually been quantitatively tested and ...

https://rxivist.org/papers/45272
https://doi.org/10.1101/566844

44: The first fossil skull of an anteater (Vermilingua, Myrmecophagidae) from northern South America, a taxonomic reassessment of Neotamandua and a discussion of the myrmecophagid diversification

Kevin Jiménez-Lara, Jhon González

1,179 downloads (posted 07 Oct 2019)

The evolutionary history of the South American anteaters, Vermilingua, is incompletely known as consequence of the fragmentary and geographically biased nature of the fossil record of this group. Neotamandua borealis is the only recorded extinct species from northern South America, specifically from the Middle Miocene of La Venta area, southwestern Colombia. A new genus and species of myrmecophagid for La Venta, Gen. et sp. nov., is here described based on a new partial skull. Additionally, given that the co-occurrent s...

https://rxivist.org/papers/62701
https://doi.org/10.1101/793307

45: Dental abscesses on the maxilla of a two million-year-old early Homo specimen

Ian Towle, Joel D Irish

1,148 downloads (posted 01 Apr 2019)

Abscesses and other periapical lesions are found in abundance in recent archeological samples, yet are scarce in the fossil hominin record. Periapical voids commonly develop after exposure of a tooth's pulp chamber and are commonly associated with heavy crown wear, trauma or caries. In this study, all available maxilla and mandible fragments from the South African fossil hominin collections were studied, including specimens assigned to Homo naledi, Paranthropus robustus, Australopithicus africanus, A. sediba and early H...

https://rxivist.org/papers/47494
https://doi.org/10.1101/595595

46: A Late Cretaceous Lonchodectid?

Carlos Albuquerque

1,128 downloads (posted 20 Dec 2019)

A pterosaur ulnar specimen (NZMS CD 467) from the Mangahouanga Stream of New Zealand s North Island has been first described by Wiffen et al 1988. Assumed to belong to a Santanadactylus-like pterosaur, this taxon has not since been extensively described, with only a few tentative claims that it represents an azhdarchid. Here, I re-examine the specimen and compare it to other pterodactyloid taxa, noting peculiar features such as its plug-like (obdurate) ulnar end. Christened Parirau ataroa, this taxon is found to be a lo...

https://rxivist.org/papers/69431
https://doi.org/10.1101/2019.12.17.879783

47: Community stability and selective extinction during Earth's greatest mass extinction

Peter D Roopnarine, Kenneth D Angielczyk

1,097 downloads (posted 01 Feb 2015)

We modelled the resilience and transient dynamics of terrestrial paleocommunities from the Karoo Basin, South Africa, around the Permian-Triassic mass extinction. Using recently refined biostratigraphic data that suggest two pulses of extinction leading up to the Permian-Triassic boundary, we show that during times of low extinction, paleocommunities were no more stable than randomly assembled communities, but they became stable during the mass extinction. Modelled food webs before and after the mass extinction have low...

https://rxivist.org/papers/30137
https://doi.org/10.1101/014688

48: Bilateral Asymmetry of the Forearm Bones as Possible Evidence of Antemortem Trauma in the StW 573 Australopithecus Skeleton from Sterkfontein Member 2 (South Africa)

A.J. Heile, Travis Rayne Pickering et al.

1,068 downloads (posted 05 Dec 2018)

The 3.67-million-year-old StW 573 Australopithecus skeleton is important for the light it sheds on the paleobiology of South African species of that genus, including, as discussed here, how the possible pathology of the specimen informs our understanding of Australopithecus behavior. The StW 573 antebrachium exhibits bilateral asymmetry, with significantly more longitudinally curved left forearm bones than right. Arguing from a comparative perspective, we hypothesize that these curvatures resulted from a fall onto a hyp...

https://rxivist.org/papers/38071
https://doi.org/10.1101/486076

49: Root caries on a Paranthropus robustus third molar from Drimolen

Ian Towle, Alessandro Riga et al.

1,066 downloads (posted 12 Mar 2019)

Objectives Dental caries is often perceived as a modern human disease. However, their presence is documented in many early human groups, various non-human primates and, increasingly, our hominin ancestors and relatives. In this study we describe an antemortem lesion on the root of a Paranthropus robustus third molar from Drimolen, South Africa, which likely represents another example of caries in fossil hominins. Materials and Methods The molar, DNH 40, is dated to 2.0–1.5 Ma and displays a lesion on the mesial root su...

https://rxivist.org/papers/45878
https://doi.org/10.1101/573964

50: A multiscale view of the Phanerozoic fossil record reveals the three major biotic transitions

Alexis Rojas, Joaquin Calatayud et al.

1,058 downloads (posted 06 Dec 2019)

The hypothesis of the Great Evolutionary Faunas is a foundational concept of macroevolutionary research postulating that three global mega-assemblages have dominated Phanerozoic oceans following abrupt biotic transitions. Empirical estimates of this large-scale pattern depend on several methodological decisions and are based on approaches unable to capture multiscale dynamics of the underlying Earth-Life System. Combining a multilayer network representation of fossil data with a multilevel clustering that eliminates the...

https://rxivist.org/papers/68080
https://doi.org/10.1101/866186

51: Dental caries in human evolution: frequency of carious lesions in South African fossil hominins

Ian Towle, Joel D Irish et al.

1,035 downloads (posted 02 Apr 2019)

Caries frequencies in South African fossil hominins were observed and compared with other hominin samples. Species studied include Paranthropus robustus, Homo naledi, Australopithecus africanus, early Homo and A. sediba. Teeth were viewed macroscopically with Micro-CT scans used to confirm lesions. Position and severity of each lesion were also noted and described. For all South African fossil hominin specimens studied, 16 have carious lesions, six of which are described for the first time in this study. These are from ...

https://rxivist.org/papers/47571
https://doi.org/10.1101/597385

52: Characterizing the body morphology of the first metacarpal in the Homininae using 3D geometric morphometrics

Jonathan Morley, Ana Bucchi et al.

1,030 downloads (posted 01 May 2020)

Objectives: Extinct hominins can provide key insights into the development of tool use, with the morphological characteristics of the thumb of particular interest due to its fundamental role in enhanced manipulation. This study quantifies the shape of the first metacarpals' body in the extant Homininae and some fossil hominins to provide insights about the possible anatomical correlates of manipulative capabilities. Materials and methods: The extant sample includes MC1s of modern humans (n=42), gorillas (n=27) and chimp...

https://rxivist.org/papers/81892
https://doi.org/10.1101/2020.04.30.070326

53: Micro-XRF study of the troodontid dinosaur Jianianhualong tengi reveals new biological and taphonomical signals

Jinhua Li, Rui Pei et al.

986 downloads (posted 08 Sep 2020)

Jianianhualong tengi is a key taxon for understanding the evolution of pennaceous feathers as well as troodontid theropods, and it is known by only the holotype, which was recovered from the Lower Cretaceous Yixian Formation of western Liaoning, China. Here, we carried out a large-area micro-X-Ray fluorescence (micro-XRF) analysis on the holotypic specimen of Jianianhualong tengi via a Brucker M6 Jetstream mobile XRF scanner. The elemental distribution measurements of the specimen show an enrichment of typical bones cou...

https://rxivist.org/papers/99995
https://doi.org/10.1101/2020.09.07.285833

54: Assesssing the role of humans in Greater Antillean land vertebrate extinctions: new insights from Cuba

Johanset Orihuela, Lázaro W. Viñola et al.

984 downloads (posted 28 Jan 2020)

The Caribbean archipelago is a hotspot of biodiversity characterized by a high rate of extinction. Recent studies have examined these losses, but the causes of the Antillean Late Quaternary vertebrate extinctions, and especially the role of humans, are still unclear. Current results provide support for climate-related and human-induced extinctions, but often downplaying other complex bio-ecological factors that are difficult to model or to detect from the fossil and archaeological record. Here, we discuss Caribbean vert...

https://rxivist.org/papers/72161
https://doi.org/10.1101/2020.01.27.922237

55: Stabilization of cultural innovations depends on population density: testing an epidemiological model of cultural evolution against a global dataset of rock art sites and climate-based estimates of ancient population densities. Short title: Cultural epidemiology: the case of rock art

Richard Walker, Anders Eriksson et al.

976 downloads (posted 16 Jul 2019)

Demographic models of human cultural evolution have high explanatory potential but weak empirical support. Here we use a global dataset of rock art sites and climate and genetics-based estimates of ancient population densities to test a new model based on epidemiological principles. The model focuses on the process whereby a cultural innovation becomes endemic in a population. It predicts that this cannot occur unless population density exceeds a critical value. Analysis of the data, using a Bayesian statistical framewo...

https://rxivist.org/papers/55927
https://doi.org/10.1101/705137

56: Dispersal ability predicts evolutionary success among mammalian carnivores

Soren Faurby, L. Werdelin et al.

971 downloads (posted 05 Sep 2019)

Understanding why some clades contain more species than others is a major challenge in evolutionary biology, and variation in dispersal ability and its connection to diversification rate may be part of the explanation. Several studies have suggested a negative relationship between dispersal capacity and diversification rate among living mammals. However, this pattern may differ when also considering extinct species, given known extinction biases. The colonization of new areas by various lineages may be associated with b...

https://rxivist.org/papers/59915
https://doi.org/10.1101/755207

57: A unique predator in a unique ecosystem: modelling the apex predator from the late cretaceous crocodyliform-dominated fauna in brazil

Felipe C. Montefeltro, Stephan Lautenschlager et al.

964 downloads (posted 15 Nov 2019)

Theropod dinosaurs were relatively scarce in the Late Cretaceous ecosystems of southeast Brazil. Instead, hypercarnivorous crocodyliforms known as baurusuchids were abundant and probably occupied the ecological role of apex predators. Baurusuchids exhibited a series of morphological adaptations hypothesised to be associated with this ecological role, but quantitative biomechanical analyses of their morphology have so far been lacking. Here, we employ a biomechanical modelling approach, applying finite element analysis (...

https://rxivist.org/papers/66340
https://doi.org/10.1101/843334

58: Kinematics of wings from Caudipteryx to modern birds

Yaser Saffar Talori, Jing-Shan Zhao et al.

962 downloads (posted 16 Aug 2018)

This study seeks to better quantify the parameters that drove the evolution of flight from non-volant winged dinosaurs to modern birds. In order to explore this issue, we used fossil data to model the feathered forelimb of Caudipteryx, the most basal non-volant maniraptoran dinosaur with elongate pennaceous feathers that could be described as forming proto-wings. In order to quantify the limiting flight factors, we created three hypothetical wing profiles for Caudipteryx representing incrementally larger wingspans, whic...

https://rxivist.org/papers/17328
https://doi.org/10.1101/393686

59: The record of Deinotheriidae from the Miocene of the Swiss Jura Mountains (Jura Canton, Switzerland)

Fanny Gagliardi, Olivier Maridet et al.

950 downloads (posted 10 Aug 2020)

The Miocene sands of the Swiss Jura Mountains, long exploited in quarries for the construction industry, have yielded abundant fossil remains of large mammals. Among Deinotheriidae (Proboscidea), two species, Prodeinotherium bavaricum and Deinotherium giganteum, had previously been identified in the Delemont valley, but never described. A third species, Deinotherium levius, from the locality of Charmoille in Ajoie, is reported herein for the first time in Switzerland. These occurrences are dated from the middle to the L...

https://rxivist.org/papers/93949
https://doi.org/10.1101/2020.08.10.244061

60: Common species link global ecosystems to climate change

Bjarte Hannisdal, Kristian Agasøster Haaga et al.

949 downloads (posted 15 Mar 2016)

Common species shape the world around us, and changes in their commonness signify large-scale shifts in ecosystem structure and function. Dominant taxa drive productivity and biogeochemical cycling, in direct interaction with abiotic components of the Earth system. However, our understanding of the dynamic response of ecosystems to global environmental changes in the past is limited by our ability to robustly estimate fossil taxonomic richness, and by our neglect of the importance of common species. To rectify this, we ...

https://rxivist.org/papers/30134
https://doi.org/10.1101/043729