scholarly journals Slow and steady: the evolution of cranial disparity in fossil and recent turtles

2016 ◽  
Vol 283 (1843) ◽  
pp. 20161881 ◽  
Author(s):  
Christian Foth ◽  
Walter G. Joyce
Keyword(s):  
Global Warming ◽  
Geometric Morphometrics ◽  
Fossil Record ◽  
Habitat Destruction ◽  
Late Triassic ◽  
Diverse Group ◽  
Two Dimensional ◽  
Global Patterns ◽  
A Minor

Turtles (Testudinata) are a diverse group of amniotes that have a rich fossil record that extends back to the Late Triassic, but little is known about global patterns of disparity through time. We here investigate the cranial disparity of 172 representatives of the turtle lineage and their ancestors grouped into 20 time bins ranging from the Late Triassic until the Recent using two-dimensional geometric morphometrics. Three evolutionary phases are apparent in all three anatomical views investigated. In the first phase, disparity increases gradually from the Late Triassic to the Palaeogene with only a minor perturbation at the K/T extinct event. Although global warming may have influenced this increase, we find the Mesozoic fragmentation of Pangaea to be a more plausible factor. Following its maximum, disparity decreases strongly towards the Miocene, only to recover partially towards the Recent. The marked collapse in disparity is likely a result of habitat destruction caused by global drying, combined with the homogenization of global turtle faunas that resulted from increased transcontinental dispersal in the Tertiary. The disparity minimum in the Miocene is likely an artefact of poor sampling.

The nasal cavity of two traversodontid cynodonts (Eucynodontia, Gomphodontia) from the Upper Triassic of Brazil

2021 ◽  
pp. 1-16
Author(s):  
Arymathéia Santos Franco ◽  
Rodrigo Temp Müller ◽  
Agustín G. Martinelli ◽  
Carolina A. Hoffmann ◽  
Leonardo Kerber
Keyword(s):  
Nasal Cavity ◽  
Fossil Record ◽  
Nasal Septum ◽  
Internal Surface ◽  
Nasolacrimal Duct ◽  
Upper Triassic ◽  
Late Triassic ◽  
Southern Brazil ◽  
Dorsal Region ◽  
Left And Right

Abstract Traversodontidae is a group of Triassic herbivorous/omnivorous cynodonts that represents the most diversified lineage within Cynognathia. In southern Brazil, a rich fossil record of late Middle/mid-Late Triassic cynodonts has been documented, with Exaeretodon riograndensis Abdala, Barberena, and Dornelles, 2002 and Siriusgnathus niemeyerorum Pavanatto et al., 2018 representing two abundant and well-documented traversodontids. The present study provides a comparative analysis of the morphology of the nasal cavity, nasal recesses, nasolacrimal duct, and maxillary canals of both species using computed tomography, highlighting the changes that occurred in parallel to the origin of mammaliaforms. Our results show that there were no ossified turbinals or a cribriform plate delimiting the posterior end of the nasal cavity, suggesting these structures were probably cartilaginous as in nonmammaliaform cynodonts. Both species show lateral ridges on the internal surface of the roof of the nasal cavity, but the median ridge for the attachment of a nasal septum is absent. Exaeretodon riograndensis and S. niemeyerorum show recesses on the dorsal region of the nasal cavity, which increase the volume of the nasal cavity, potentially enhancing the olfactory chamber and contributing to the sense of smell. On the lateral sides of the nasal cavity, the analyzed taxa show a well-developed maxillary recess. Although E. riograndensis and S. niemeyerorum have roughly similar nasal cavities, in the former taxon, the space between the left and right dorsal recesses of the nasal cavity is uniform along its entire extension, whereas this space narrows posteriorly in S. niemeyerorum. Finally, the nasolacrimal duct of S. niemeyerorum is more inclined anteroposteriorly than in E. riograndensis.

scholarly journals Competitive Diels–Alder and ene addition of N-arylmaleimides to 7-dehydrocholesteryl acetate

1992 ◽  
Vol 70 (11) ◽  
pp. 2730-2744 ◽  
Author(s):  
William J. Leigh ◽  
Donald W. Hughes ◽  
D. Scott Mitchell
Keyword(s):  
Molecular Mechanics ◽  
Nmr Spectra ◽  
Benzene Solution ◽  
Diels Alder ◽  
Spectroscopic Techniques ◽  
Two Dimensional ◽  
A Minor ◽  
C Nmr ◽  
Alder Adduct ◽  
Ene Addition

Thermolysis of N-phenyl, N-para-biphenyl, and N-para, para′-terphenylmaleimide with 7-dehydrocholesteryl acetate in benzene solution at 200 °C yields mixtures of four cycloadducts in relative yields that are essentially independent of the maleimide substituent. The three major products are those of ene addition to C7 of the steroid with abstraction of the proton at C9 or C14. The α-endo-Diels-Alder adduct is formed as a minor product. The structures of the adducts have been elucidated on the basis of one- and two-dimensional 1H and 13C NMR spectroscopic techniques, including homonuclear 1H decoupling, NOE, 1H–1H COSY, heteronuclear 1H–13C shift correlation, and TOCSY 2-D experiments, and the results of molecular mechanics (MMX) calculations. The combination of these techniques has made it possible to almost completely assign the 1H and 13C NMR spectra for two of the ene adducts and the Diels–Alder adduct from reaction of 7-dehydrocholesteryl acetate with N-phenyl maleimide.

Going with the flow: global warming and the challenge of sustaining river ecosystems in monsoonal Asia

2007 ◽  
Vol 7 (2) ◽  
pp. 69-80 ◽  
Author(s):  
D. Dudgeon
Keyword(s):  
Global Warming ◽  
Human Impacts ◽  
Habitat Destruction ◽  
Dispersal Ability ◽  
Suitable Habitat ◽  
Hydrologic Alteration ◽  
Ecological Processes ◽  
Ecosystem Integrity ◽  
River Ecosystems ◽  
The Rich

River ecosystems in monsoonal Asia are experiencing human impacts to the detriment of the rich biodiversity they support. Threats include hydrologic alteration, pollution, habitat destruction, overexploitation, and invasive exotic species. Global warming will cause further changes to river ecosystems, and may act synergistically with other threat factors. Significant upward or northward range adjustments by the freshwater biota will be necessary to cope with rising temperatures, but there will be significant constraints upon dispersal ability and availability of suitable habitat for many organisms. Global warming will exacerbate existing impacts of hydrologic alteration because of the adaptive human responses that will be engendered by changes in climate and runoff, particularly dams constructed for hydropower generation, flood protection, water storage, and irrigation. The consequences of further hydrologic alteration and habitat fragmentation will be profound, since almost all ecological processes, material transfers and life-cycle events in the rivers of monsoonal Asia are mediated or controlled by flow. Thus a change in the timing or amounts of flow changes everything. Collaborative research to determine the environmental allocation of water flow needed to maintain ecosystem integrity and sustain biodiversity in the human-dominated rivers of monsoonal Asia should be a priority for ecologists, engineers and water-resource managers.

Perspectives on the Evolution and Diversification of the Diatoms

2007 ◽  
Vol 13 ◽  
pp. 1-12 ◽  
Author(s):  
Matthew L. Julius
Keyword(s):  
Molecular Clock ◽  
Fossil Record ◽  
Early Jurassic ◽  
Late Triassic ◽  
Evolutionary Relationships ◽  
Data Sets ◽  
Diatom Species ◽  
Generic Level ◽  
Existing Data

The understanding of diatom evolution has progressed greatly over the last two decades. Existing data sets have been reanalyzed, new data sets have been generated, and new tools have been employed. Hindering progress is the seemingly endless number of diatom species remaining to be described and relative small number of investigators active in the field. This problem is further confounded by the dramatic reorganization of generic level classification in the group. Despite these problems, many conclusions can be made about prior hypotheses concerning the group's development. Most notably, the origin of the diatoms can be bracketed between the Late Triassic and Early Jurassic using fossil record and molecular clock estimates. This combination of techniques has also provided consensus and clarification to the origin and duration of specific lineages enhancing our understanding of the group's diversification, early ecology, and evolutionary relationships.

On the Origin of Stiffening in Biopolymers

2005 ◽  
Vol 874 ◽  
Author(s):  
Erik Van der Giessen ◽  
Teun Koeman ◽  
Teun Van Dillen ◽  
Patrick Onck
Keyword(s):  
Network Model ◽  
Finite Strain ◽  
Strain Analysis ◽  
Large Strains ◽  
Minor Effect ◽  
Two Dimensional ◽  
Thermally Induced ◽  
Small Strains ◽  
Dimensional Network ◽  
A Minor

AbstractStrain stiffening of protein networks is explored by means of a finite strain analysis of a two-dimensional network model of cross-linked semiflexible filaments. The results show that stiffening is caused by non-affine network rearrangements that govern a transition from a bending dominated response at small strains to a stretching dominated response at large strains. Thermally-induced filament undulations only have a minor effect; they merely postpone the transition.

Taxonomic review of two fossil crocodylians from the Cenozoic of South America and its implications for the crocodylian fauna of the continent

Zootaxa ◽  
2019 ◽  
Vol 4656 (3) ◽  
pp. 475-486
Author(s):  
GIOVANNE M. CIDADE ◽  
DANIEL FORTIER ◽  
ASCANIO DANIEL RINCÓN ◽  
ANNIE SCHMALTZ HSIOU
Keyword(s):  
South America ◽  
Fossil Record ◽  
Middle Miocene ◽  
Taxonomic Status ◽  
Junior Synonym ◽  
Diverse Group ◽  
Taxonomic Review ◽  
Nomen Dubium ◽  
Extant Species ◽  
The World

The crocodylomorph fauna of the Cenozoic of South America is one of the richest and most diverse in the world. The most diverse group within that fauna is Alligatoroidea, with nearly all of its species belonging to the Caimaninae clade. Many of the fossil alligatoroid species from the Cenozoic of South America were proposed based on very incomplete remains, and as a result their validity requires revision. Two such species are Balanerodus logimus Langston, 1965, from the middle Miocene of Colombia and Peru, and Caiman venezuelensis Fortier & Rincón, 2012, from the Pliocene-Pleistocene of Venezuela. This study has performed a thorough review of the taxonomic status of these two alligatoroid species, concluding that B. logimus is a nomen dubium and that Ca. venezuelensis is a junior synonym of the extant species Ca. crocodilus. This review offers a significantly more accurate scenario for alligatoroid diversity in the Cenozoic of South America in different epochs such as the Miocene and Pleistocene. Additionally, the record of Ca. crocodilus from the Pleistocene of Venezuela is the first fossil record that can be assigned to this species. 

scholarly journals A new tetracyclic diterpenoid from the seeds of Euphorbia lathyris

2020 ◽  
Vol 44 (5-6) ◽  
pp. 322-325
Author(s):  
Lie-Feng Ma ◽  
Yue Zhang ◽  
Xuan Zhang ◽  
Meng-Jia Chen ◽  
Zha-Jun Zhan ◽  
...  
Keyword(s):  
Mass Spectrometry ◽  
Nuclear Magnetic Resonance ◽  
High Resolution ◽  
Spectroscopic Data ◽  
Resonance Spectroscopy ◽  
Ionization Mass ◽  
Two Dimensional ◽  
Detailed Interpretation ◽  
A Minor ◽  
Euphorbia Lathyris

Eupholathone, a minor diterpenoid with an unusual tetracyclic skeleton, was obtained from the seeds of Euphorbia lathyris, along with two known lathyrane diterpenoids, euphorbia factors L2 and L3. The structure of eupholathone was elucidated by detailed interpretation of its spectroscopic data, especially two-dimensional nuclear magnetic resonance spectroscopy and high-resolution electrospray ionization mass spectrometry.

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