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in category paleontology

190 results found. For more information, click each entry to expand.

181: Morphometric Analysis of Lungfish Endocasts Elucidates Early Dipnoan Palaeoneurological Evolution
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Posted 15 Sep 2021

Morphometric Analysis of Lungfish Endocasts Elucidates Early Dipnoan Palaeoneurological Evolution
182 downloads bioRxiv paleontology

Alice M Clement, Tom J Challands, Richard Cloutier, Laurent Houle, Per E Ahlberg, Shaun P Collin, John A Long

Lungfish (Dipnoi) are lobe-finned fish (Sarcopterygii) that have persisted for over 400 million years from the Devonian Period to present day. They are the extant sister group to tetrapods and thus have the ability to provide unique insight into the condition of the earliest tetrapods as well as their own evolutionary history. The evolution of their dermal skull and dentition is relatively well understood, but this is not the case for the central nervous system. While the brain itself has very poor preservation potential and is not currently known in any fossil lungfish, substantial indirect information about it and associated structures such as the inner ears can be obtained from the cranial endocast. However, before the recent development of X-ray tomography as a palaeontological tool, these endocasts could not be studied non-destructively, and few detailed studies were undertaken. Here we describe and illustrate the endocasts of six Palaeozoic lungfishes (Iowadipterus halli, Gogodipterus paddyensis, Pillararhynchus longi, Griphognathus whitei, Orlovichthys limnatis, and Rhinodipterus ulrichi) from tomographic scans. We combine these with six previously described lungfish endocasts (4 fossil and 2 recent taxa), also based on tomographic studies, into a 12-taxon data set for multivariate morphometric analysis using 17 variables. We find that the olfactory region appears to be more highly plastic than the hindbrain, and undergoes significant elongation in several taxa. Further, while the semicircular canals covary as an integrated module, the utriculus and sacculus of the inner ear instead vary independently of each other. The functional and phylogenetic implications of our findings are discussed.

182: Bioerosion traces and borings in the Upper Devonian vertebrate remains from the Holy Cross Mountains, Poland Bioerosion in fish remains
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Posted 24 Jul 2021

Bioerosion traces and borings in the Upper Devonian vertebrate remains from the Holy Cross Mountains, Poland Bioerosion in fish remains
159 downloads bioRxiv paleontology

Piotr Szrek, Patrycja G. Dworczak, Olga Wilk

Among the hundreds of collected Devonian vertebrate macrofossils in the Holy Cross Mountains, placoderms dominate and provide data on their morphology, distribution and taphonomy. So far 17 out of more than 500 studied specimens have revealed bones with surfaces covered by sediment-filled trace fossils. The traces have been made on the vertebrate remains before their final burial. The borings, oval in cross-section, include dendroidal networks of shallow tunnels or short, straight or curved individual scratches and grooves, which frequently create groups on the both sides of the bones. ?Karethraichnus isp. from Kowala and ?Osteocallis isp. from Wietrznia are the oldest record of these ichnogenera. Sedimentological clues indicate a shallow water environment, probably from the slope below the storm wave base.

183: The scratch-digging lifestyle of the Permian "microsaur" Batropetes as a model for the exaptative origin of jumping locomotion in frogs
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Posted 27 Sep 2021

The scratch-digging lifestyle of the Permian "microsaur" Batropetes as a model for the exaptative origin of jumping locomotion in frogs
137 downloads bioRxiv paleontology

Maren Jansen, David Marjanović

Recent studies have shown that the Triassic stem-frog Triadobatrachus lacked the ability to jump off, but nonetheless had the forelimb strength to withstand the impact of landing from a jump. We propose a hypothesis to resolve this pseudoparadox: the strengthened forelimbs are former adaptations to forelimb-based digging that later made jumping possible by exaptation. Micro-CT data from a skeleton of Batropetes palatinus reveal thin cortical bone, confirming Batropetes as terrestrial. Combining adaptations to walking and digging, confirmed by statistical analyses, Batropetes is thought to have searched for food in leaf litter or topsoil. We interpret Batropetes as having used one forelimb at a time to shove leaf litter aside. Batropetes may thus represent an analog or possibly a homolog of the digging stage that preceded the origin of Salientia. We discuss the possibility of homology with the digging lifestyles of other "microsaurs" and other amphibians.

184: Three new Cenomanian conifers from El Chango (Chiapas, Mexico) offer a snapshot of the geographic mosaic of the Mesozoic conifer decline
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Posted 03 Sep 2021

Three new Cenomanian conifers from El Chango (Chiapas, Mexico) offer a snapshot of the geographic mosaic of the Mesozoic conifer decline
134 downloads bioRxiv paleontology

Ixchel Gonzalez-Ramirez, Sergio RS Cevallos-Ferriz, Carl Rothfels

Premise of study: El Chango is a recently discovered quarry that contains extremely well preserved fossils. The Cenomanian age of the locality corresponds to a time when the global flora was transitioning from gymnosperm- to angiosperm-dominated, yet conifers predominate in this locality. These fossils thus provide a rare opportunity to understand the replacement of conifers by angiosperms as the dominant group of plants. Methods: We collected material from El Chango in annual expeditions (2010 to 2014). We selected the three most abundant and best preserved conifer morphotypes and conducted a total-evidence (i.e., including molecular and morphological data) phylogenetic analysis of a sample of 72 extant conifer species plus the three fossils. We use these results to inform our taxonomic decisions. Results: We obtained four equally most-parsimonious trees (consistency index = 44.1%, retention index = 78.8%). Despite ambiguous relationships among some extant taxa, the three fossil conifers had the same phylogenetic position in all four most parsimonious trees; we describe these species as new: Sequoiadendron helicalancifolium sp. nov. (Cupressaceae), and Microcachrys rhomboidea sp. nov. and Dacrydium bifoliosus sp. nov (Podocarpaceae). The ecosystem is interpreted as a coastal humid mixed forest. Conclusions: Our findings contribute to the understanding of Cenomanian equatorialregions, and support the hypothesis of a geographically and ecologically structured rise of angiosperms, with conifers remaining dominant in brackish-water and angiosperms becoming dominant in freshwater-ecosystems. These fossils fill in gaps in the evolutionary history of lineages like Microcachrys, which we demonstrate occurred in the Northern hemisphere before becoming restricted to its current range (Tasmania).

185: Belemnite phylogeny and decline during the mid-Cretaceous
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Posted 12 Oct 2021

Belemnite phylogeny and decline during the mid-Cretaceous
113 downloads bioRxiv paleontology

Kevin Stevens

Belemnites are common fossil coleoid cephalopods of the Mesozoic. They began to diversify in the Triassic-Early Jurassic and maintained this diversity until the early Early Cretaceous. During the mid-Cretaceous, they declined in diversity and distribution, being restricted to only the Boreal and Austral Realm since the Turonian. Here, I present the first cladistic analysis of belemnite phylogeny, spanning taxa representative of the whole diversity and stratigraphic range of the group. This analysis shows that the usually applied subdivision of all belemnites into "Belemnitina" and "Belemnopseina" is not supported. A newly identified clade, the Pseudoalveolata, is suggested here. Pseudoalveolate belemnites represent the last remaining belemnites after the Aptian. Oceanic anoxia and warming are likely the main cause of the mid- Cretaceous belemnite decline, resulting in the Aptian-Albian dominance of the warm-adapted pseudoalveolate genus Neohibolites. The rise of teleost fish diversity during the mid- Cretaceous is discussed and its relevance for belemnite evolution. Some teleosts (e.g., Enchodus) might have taken over the mesopredator niches left by belemnites during the mid- Cretaceous, being better adapted to warming seas. Belemnites were not able to recover their earlier widespread distribution and diversity and the last remaining, disjunctly distributed families, the northern Belemnitellidae and southern Dimitobelidae, became extinct at the K/Pg-boundary.

186: Orientations of Mistaken Point fronds indicate morphology impacted ability to survive turbulence
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Posted 11 Sep 2021

Orientations of Mistaken Point fronds indicate morphology impacted ability to survive turbulence
107 downloads bioRxiv paleontology

Philip B. Vixseboxse, Charlotte G. Kenchington, Frances S. Dunn, Emily G. Mitchell

The Ediacaran organisms of the Mistaken Point E surface have provided crucial insight into early animal communities, including how they reproduced, the importance of Ediacaran height and what the most important factors were to their community dynamics. Here, we use this iconic community to investigate how morphological variation between eight taxa affected their ability to withstand different flow conditions. For each of Beothukis, Bradgatia, Charniodiscus procerus, Charniodiscus spinosus, Plumeropriscum, Primocandelabrum and Fractofusus we measured the orientation and length of their stems (if present) and their fronds. We statistically tested each taxon's stem and frond orientation distributions to see whether they displayed a uniform or multimodal distribution. Where multimodal distributions were identified, the stem/frond length of each cohort was tested to identify if there were differences in size between different orientation groups. We find that Bradgatia and Thectardis show a bimodal felling direction, and infer that they were felled by the turbulent head of the felling flow. In contrast, the frondose rangeomorphs including Beothukis, Plumeropriscum, Primocandelabrum, and the arboreomorphs were felled in a single direction, indicating that they were upright in the water column, and were likely felled by the laminar tail of the felling flow. These differences in directionality suggests that an elongate habit, and particularly possession of a stem, lent greater resilience to frondose taxa against turbulent flows, suggesting that such taxa would have had improved survivability in conditions with higher background turbulence than taxa like Bradgatia and Thectardis, which lacked a stem and which had a higher centre of mass, which may have fared better in quieter water conditions.

187: The response of Oligo-Miocene bivalve fauna of the Kutch Basin (western India) to regional changes in tectonics and climate
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Posted 09 Sep 2021

The response of Oligo-Miocene bivalve fauna of the Kutch Basin (western India) to regional changes in tectonics and climate
102 downloads bioRxiv paleontology

Saurav Dutta, Devapriya Chattopadhyay

Tectonic changes have influenced the evolution of the marine community by changing the seaway configuration over time. Two such tectonic events during Oligo-Miocene, the closure of the Tethyan seaway leading to separation of the Arabian sea from proto-Mediterranean (~19 Ma) and significant uplift of the Tibetan plateau marking the initiation of the monsoon (~16 Ma), represent a classic case of tectonic shift influencing the regional environment of the Indian subcontinent. We investigated the taxonomic and body-size response of ~2000 marine bivalve individuals from 11 time-constrained shellbeds of the Kutch basin from three formations, Maniyara Fort (Chattian), Khari Nadi (Aquitanian), and Chhasra (Burdigalian-Langian), representing a time span of ~9 Ma (24.4-15 Ma). Principal coordinate analyses show a distinct species composition for Oligocene Maniyara Fort formation, differing substantially from the younger Miocene formations implying the possible effect of biogeographic separation due to the Tethyan closure. The absence of signature proto-Mediterranean taxa in Oligocene shellbeds also supports a limited faunal exchange as early as ~24.4Ma. Maximum likelihood estimation (MLE) analyses of richness and body size, however, reveal a dominantly conservative behavior supporting a stasis model without a strong directional trend through time. The absence of any persistent directional change in either diversity, body size, or species composition during an interval between ~17.2 Ma to ~15.7 Ma, an interval that has been claimed to have experienced the initiation of monsoon, points to the limited influence of this phenomena on the shallow marine ecosystem. Our results support limited faunal exchange due to the Tethyan closure and demonstrate little influence of the Himalayan upliftment on the evolutionary tempo of the Oligo-Miocene marine bivalves of the Kutch basin.

188: Relationships between the hard and soft dimensions of the nose in Pan troglodytes and Homo sapiens reveal the nasal protrusions of Plio-Pleistocene hominids
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Posted 18 Oct 2021

Relationships between the hard and soft dimensions of the nose in Pan troglodytes and Homo sapiens reveal the nasal protrusions of Plio-Pleistocene hominids
80 downloads bioRxiv paleontology

Ryan M. Campbell, Gabriel Vinas, Maciej Henneberg

By identifying similarity in bone and soft tissue covariation patterns in hominids, it is possible to produce facial approximation methods that are compatible with more than one species of primate. In this study, we conducted an interspecific comparison of the nasomaxillary region in chimpanzees and modern humans with the aim of producing a method for predicting the nasal protrusions of ancient Plio-Pleistocene hominids. We addressed this aim by first collecting and performing regression analyses of linear and angular measurements of nasal cavity length and inclination in modern humans ( Homo sapiens; n = 72) and chimpanzees ( Pan troglodytes ; n = 19), and then by performing a set of out-of-group tests. The first test was performed on two subjects that belonged to the same genus as the training sample, i.e., Homo ( n = 1) and Pan ( n = 1), and the second test, which functioned as an interspecies compatibility test, was performed on Pan paniscus ( n = 1), Gorilla gorilla ( n = 3), Pongo pygmaeus ( n = 1), Pongo abelli ( n = 1), Symphalangus syndactylus ( n = 3), and Papio hamadryas ( n = 3). We identified statistically significant correlations in both humans and chimpanzees with slopes that displayed homogeneity of covariation. Joint prediction formulae were found to be compatible with humans and chimpanzees as well as all other African great apes, i.e., bonobos and gorillas. The main conclusion that can be drawn from this study is that regression models for approximating nasal projection are homogenous among humans and African apes and can thus be reasonably extended to ancestors leading to these clades.

189: Linking host plants to damage types in the fossil record of insect herbivory
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Posted 05 Nov 2021

Linking host plants to damage types in the fossil record of insect herbivory
48 downloads bioRxiv paleontology

Sandra R Schachat, Jonathan L. Payne, C. Kevin Boyce

Studies of insect herbivory on fossilized leaves tend to focus on a few, relatively simple metrics that are agnostic to the distribution of insect damage types among host plants. More complex metrics that link particular damage types to particular host plants have the potential to address additional ecological questions, but such metrics can be biased by sampling incompleteness due to the difficulty of distinguishing the true absence of a particular interaction from the failure to detect it---a challenge that has been raised in the ecological literature. We evaluate a range of methods for characterizing the relationships between damage types and host plants by performing resampling and subsampling exercises on a variety of datasets. We found that the components of beta diversity provide a more valid, reliable, and interpretable method for comparing component communities than do bipartite network metrics. We found the rarefaction of interactions to be a valid, reliable, and interpretable method for comparing compound communities. Both of these methods avoid the potential pitfalls of multiple comparisons. Lastly, we found that the host specificity of individual damage types is challenging to assess. Whereas some previously used methods are sufficiently biased by sampling incompleteness to be inappropriate for fossil herbivory data, alternatives exist that are perfectly suitable for fossil datasets with sufficient sample coverage.

190: On the dynamics of spatial updating
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Posted 28 Oct 2021

On the dynamics of spatial updating
28 downloads bioRxiv paleontology

Jean Blouin, Jean-Philippe Pialasse, Laurence Mouchnino, Martin Simoneau

Most of our knowledge on the human neural bases of spatial updating comes from fMRI studies in which recumbent participants moved in virtual environments. As a result, little is known about the dynamic of spatial updating during real body motion. Here, we exploited the high temporal resolution of electroencephalography (EEG) to investigate the dynamics of cortical activation in a spatial updating task where participants had to remember their initial orientation while they were passively rotated about their vertical axis in the dark. After the rotations, the participants pointed towards their initial orientation. We contrasted the EEG signals with those recorded in a control condition in which participants had no cognitive task to perform during body rotations. We found that the amplitude of the P1N1 complex of the rotation-evoked potential (RotEPs) (recorded over the vertex) was significantly greater in the Updating task. The analyses of the cortical current in the source space revealed that the main significant task-related cortical activities started during the N1P2 interval (136-303 ms after rotation onset). They were essentially localised in the temporal and frontal (supplementary motor complex, dorsolateral prefrontal cortex, anterior prefrontal cortex) regions. During this time-window, the right superior posterior parietal cortex (PPC) also showed significant task-related activities. The increased activation of the PPC became bilateral over the P2N2 component (303-470 ms after rotation onset). In this late interval, the cuneus and precuneus started to show significant task-related activities. Together, the present results are consistent with the general scheme that the first task-related cortical activities during spatial updating are related to the encoding of spatial goals and to the storing of spatial information in working memory. These activities would precede those involved in higher order processes also relevant for updating body orientation during rotations linked to the egocentric and visual representations of the environment.

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