scholarly journals Foreflipper and hindflipper muscle reconstructions of Cryptoclidus eurymerus in comparison to functional analogues: introduction of a myological mechanism for flipper twisting

PeerJ ◽  
2021 ◽  
Vol 9 ◽  
pp. e12537
Author(s):  
Anna Krahl ◽  
Ulrich Witzel
Keyword(s):  
Late Cretaceous ◽  
Late Triassic ◽  
Crown Group ◽  
The Past ◽  
Pelvic Muscles ◽  
Muscle Functions

Background Plesiosaurs, diapsid crown-group Sauropterygia, inhabited the oceans from the Late Triassic to the Late Cretaceous. Their most exceptional characteristic are four hydrofoil-like flippers. The question whether plesiosaurs employed their four flippers in underwater flight, rowing flight, or rowing has not been settled yet. Plesiosaur locomotory muscles have been reconstructed in the past, but neither the pelvic muscles nor the distal fore- and hindflipper musculature have been reconstructed entirely. Methods All plesiosaur locomotory muscles were reconstructed in order to find out whether it is possible to identify muscles that are necessary for underwater flight including those that enable flipper rotation and twisting. Flipper twisting has been proven by hydrodynamic studies to be necessary for efficient underwater flight. So, Cryptoclidus eurymerus fore- and hindflipper muscles and ligaments were reconstructed using the extant phylogenetic bracket (Testudines, Crocodylia, and Lepidosauria) and correlated with osteological features and checked for their functionality. Muscle functions were geometrically derived in relation to the glenoid and acetabulum position. Additionally, myology of functionally analogous Chelonioidea, Spheniscidae, Otariinae, and Cetacea is used to extract general myological adaptations of secondary aquatic tetrapods to inform the phylogenetically inferred muscle reconstructions. Results A total of 52 plesiosaur fore- and hindflipper muscles were reconstructed. Amongst these are flipper depressors, elevators, retractors, protractors, and rotators. These muscles enable a fore- and hindflipper downstroke and upstroke, the two sequences that represent an underwater flight flipper beat cycle. Additionally, other muscles were capable of twisting fore- and hindflippers along their length axis during down- and upstroke accordingly. A combination of these muscles that actively aid in flipper twisting and intermetacarpal/intermetatarsal and metacarpodigital/metatarsodigital ligament systems, that passively engage the successive digits, could have accomplished fore-and hindflipper length axis twisting in plesiosaurs that is essential for underwater flight. Furthermore, five muscles that could possibly actively adjust the flipper profiles for efficient underwater flight were found, too.

Revised stratigraphy of the Mesozoic rocks of southern Cyprus

1980 ◽  
Vol 117 (6) ◽  
pp. 547-563 ◽  
Author(s):  
R. E. Swarbrick ◽  
A. H. F. Robertson
Keyword(s):  
Oceanic Crust ◽  
Continental Margin ◽  
Late Cretaceous ◽  
Sedimentary Cover ◽  
Igneous Rocks ◽  
Late Triassic ◽  
Metamorphic Rocks ◽  
Southern Cyprus

SummaryRecent resurgence of interest in the Mesozoic rocks of SW and southern Cyprus necessitates redefinition of the Mesozoic sedimentary and igneous rocks in line with modern stratigraphical convention. Two fundamentally different rocks associations are present, the Troodos Complex, not redefined, a portion of late Cretaceous oceanic crust, and the Mamonia Complex, the tectonically dismembered remnants of a Mesozoic continental margin. Based on earlier work, the Mamonia Complex is divided into two groups, each subdivided into a number of subsidiary formations and members. The Ayios Photios Group is wholly sedimentary, and records the evolution of a late Triassic to Cretaceous inactive continental margin. The Dhiarizos Group represents Triassic alkalic volcanism and sedimentation adjacent to a continental margin. Several other formations not included in the two groups comprise sedimentary mélange and metamorphic rocks. The Troodos Complex possesses an in situ late Cretaceous sedimentary cover which includes two formations of ferromanganiferous pelagic sediments, radiolarites and volcaniclastic sandstones. The overlying Cainozoic calcareous units are not redefined here.

The Origin of Dinosaurs and the Beginning of the Age of Dinosaurs

1989 ◽  
Vol 2 ◽  
pp. 7-21
Author(s):  
Kevin Padian
Keyword(s):  
Terrestrial Ecosystems ◽  
Early Jurassic ◽  
The Other ◽  
Late Triassic ◽  
Relevant Paper ◽  
The Past ◽  
General Account ◽  
Extensive Information ◽  
The Times

What are dinosaurs? What features characterize them? Who were their closest relatives? What were the times like when the dinosaurs first evolved? How did their appearance change the balance of diversity in terrestrial ecosystems? During the past decade we have come to know much more about these topics than ever before. What follows is only a brief review. For more extensive information, readers are referred to the chapters in Padian (1986a), particularly the Introduction, on questions of the Late Triassic - Early Jurassic transition; and to Gauthier (1984, 1986) on the characteristics of dinosaurs and their relations. Because this is meant to be a general account, like the other papers in this book, it is impossible to cite every worker, discovery, or relevant paper in the field, and some personal judgments must be exercised.

Dinosaur Architectural Adaptations for a Gymnosperm-Dominated World

2000 ◽  
Vol 6 ◽  
pp. 183-208
Author(s):  
David E. Fastovsky
Keyword(s):  
Late Cretaceous ◽  
Middle Jurassic ◽  
Vascular Plants ◽  
Late Triassic ◽  
Time Interval ◽  
Paraphyletic Group

The middle jurassic through Cretaceous was the heyday of gymnosperms. Gymnosperms—a paraphyletic group of seed-bearing, non-flowering vascular plants including conifers, ginkgos, seed ferns, cycads, and cycadeoids—comprised as much as 80% of global floras throughout this time interval. Even the much-heralded rise of angiosperms in the mid- to Late Cretaceous did little to shake the Mesozoic dominance among terrestrial floras of gymnosperms (in particular, conifers; see Tiffney, 1997). By the end of the Cretaceous, angiosperms comprised—depending upon whose estimate is being used—somewhere between 40 and 60% of the world's floras (Lidgard and Crane, 1988; Tiffney, 1997), leaving plenty of ecospace available for gymnosperms. The lower part of Figure 1, redrawn from Tiffney (1997), documents the flux of the major groups of plants throughout the Late Triassic-through-latest Cretaceous interval. The figure reaffirms that in the Mesozoic, gymnosperms were the floral force to be reckoned with.

Morphology, anatomy, phylogenetics and distribution of fossil and extant Trochodendraceae in the Northern Hemisphere

2020 ◽  
Author(s):  
Steven R Manchester ◽  
Zlatko Kvaček ◽  
Walter S Judd
Keyword(s):  
Northern Hemisphere ◽  
Late Cretaceous ◽  
Morphological Characters ◽  
Basal Part ◽  
Parsimony Analysis ◽  
Crown Group ◽  
Modern Species ◽  
The Family ◽  
New Material ◽  
Fossil Fruit

Abstract We present the oldest known occurrences of crown-group Trochodendraceae based on new material from the Palaeocene of Wyoming, USA. Two genera are recognized, Trochodendron and Eotrochion gen. nov. The fossil fruit of Trochodendron infernense sp. nov. is represented by a pedicellate, apically dehiscent capsular fruit composed of nine follicle-like units, each bearing a persistent convex style. The basal part is ornamented with numerous raised stamen scars. From the same deposits, Eotrochion is represented by infructescences, fruits and associated leaves. The infructescences are racemes of numerous apically dehiscent capsules, each with c. 14–16 styles, each with an underlying nectary and receptacles lacking stamen scars, but possessing a prominent perianth scar. A phylogenetic assessment of the modern species, plus representatives of four extinct genera of fossil Trochodendraceae based on available morphological characters, yields a favoured topology of Trochodendron(Eotrochion(Concavistylon kvacekii(C. wehrii (Pentacentron, Tetracentron)))). A parsimony analysis of currently available characters indicates that C. wehrii renders Concavistylon non-monophyletic. Accordingly, we transfer it to Paraconcavistylon gen. nov., characterized by pendent, rather than erect infructescences. We also reconsider the extinct Nordenskioeldia (Late Cretaceous to Miocene), the prior placement of which in Trochodendraceae has been challenged, and we consider it to fall outside the crown group of the family.

Phylogenies and angiosperm diversification

Paleobiology ◽  
1993 ◽  
Vol 19 (2) ◽  
pp. 141-167 ◽  
Author(s):  
James A. Doyle ◽  
Michael J. Donoghue
Keyword(s):  
Early Cretaceous ◽  
Phylogenetic Trees ◽  
Sister Group ◽  
Late Triassic ◽  
Tectonic Activity ◽  
Crown Group ◽  
Extrinsic Factors ◽  
Angiosperm Diversification ◽  
Stem Lineage ◽  
Cladistic Analyses

Approaches to patterns of diversification based on counting taxa at a given rank can be misleading, even when all taxa are monophyletic. Such “rank-based” approaches are unable to reflect a hierarchy of evolutionary events because taxa of the same rank cannot be nested within one another. Phylogenetic trees specify an order of origination of characters and clades and can therefore be used in some cases to test hypotheses on causal relationships between characters and changes in diversity. “Tree-thinking” also clarifies discussions of the age of groups, by distinguishing between splitting of the stem-lineage from its sister group and splitting of the crown-group into extant clades.Cladistic evidence that Pentoxylon, Bennettitales, and Gnetales are the sister group of angiosperms implies that the angiosperm line (angiophytes) existed by the Late Triassic. The presence of primitive members of five basic angiosperm clades indicates that the crown-group (angiosperms) had begun to diversify by the mid-Early Cretaceous (Barremian-Aptian), but not necessarily much earlier. The greatest unresolved issue raised by cladistic analyses concerns the fact that the angiosperm tree can be rooted in two almost equally parsimonious positions. Trees rooted near Magnoliales (among “woody magnoliids”) suggest that the angiosperm radiation may have been triggered by the origin of intrinsic traits, e.g., a fast-growing, rhizomatous habit in the paleoherb and eudicot subgroup. However, trees rooted among paleoherbs, which are favored by rRNA data, imply that these traits are basic for angiosperms as a whole. This could mean that the crown-group originated not long before its radiation, or, if it did originate earlier, that its radiation was delayed due to extrinsic factors. Such factors could be a trend from environmental homogeneity and stability in the Jurassic to renewed tectonic activity and disturbance in the Early Cretaceous. Potentially relevant pre-Cretaceous fossils cannot be placed with confidence, but may be located along the stem-lineage (stem angiophytes); their generally paleoherb-like features favor the paleoherb rooting. The history of angiophytes may parallel that of Gnetales: some diversification of the stem-lineage in the Late Triassic, near disappearance in the Jurassic, and vigorous radiation of the crown-group in the Early Cretaceous.

Species composition of the Late Cretaceous eutherian mammal Paranyctoides Fox

2013 ◽  
Vol 50 (7) ◽  
pp. 693-700 ◽  
Author(s):  
Marisol Montellano-Ballesteros ◽  
Richard C. Fox ◽  
Craig S. Scott
Keyword(s):  
North America ◽  
Species Composition ◽  
Central Asia ◽  
Late Cretaceous ◽  
Geographic Range ◽  
Eutherian Mammal ◽  
The Past ◽  
Central Asian ◽  
Dinosaur Park Formation ◽  
Eutherian Evolution

Although the known record of Mesozoic eutherian mammals has been significantly enriched in recent years, early eutherian evolution is still not well understood. Among the more controversial of Mesozoic eutherians is Paranyctoides Fox, which was described in 1979 from the Judithian Dinosaur Park Formation, Alberta, Canada. It is a rare taxon and therefore has been identified in only a few other North American Late Cretaceous local faunas since. Within the past decade, dental and gnathic remains discovered in Central Asia have also been referred to Paranyctoides, thereby expanding the geographic range of the genus substantially and making it the only Late Cretaceous eutherian ostensibly occurring in both continents. As a result of our detailed study of Paranyctoides, however, we find that the Central Asian species lack the diagnostic characters of Paranyctoides and must be referred to other taxa. We conclude that this genus was limited to North America, ranging from Aquilan to Lancian time, and accordingly we recognize as valid only the following species: Paranyctoides sternbergi (Judithian, Alberta), P. maleficus (Aquilan, Alberta), Paranyctoides Wahweap sp. A and sp. B (Judithian, Utah), Paranyctoides Kaiparowits sp. A and sp. B (Judithian, Utah). Another purported species of Paranyctoides, P. megakeros, from the Lancian of Wyoming, is a junior synonym of Alostera saskatchewanensis.

scholarly journals A new stem turtle from the Middle Jurassic of Scotland: new insights into the evolution and palaeoecology of basal turtles

2008 ◽  
Vol 276 (1658) ◽  
pp. 879-886 ◽  
Author(s):  
Jérémy Anquetin ◽  
Paul M Barrett ◽  
Marc E.H Jones ◽  
Scott Moore-Fay ◽  
Susan E Evans
Keyword(s):  
Middle Jurassic ◽  
Late Jurassic ◽  
Evolutionary History ◽  
Sister Group ◽  
Late Triassic ◽  
Sister Group Relationship ◽  
New Taxon ◽  
Crown Group ◽  
History Of ◽  
Isle Of Skye

The discovery of a new stem turtle from the Middle Jurassic (Bathonian) deposits of the Isle of Skye, Scotland, sheds new light on the early evolutionary history of Testudinata. Eileanchelys waldmani gen. et sp. nov. is known from cranial and postcranial material of several individuals and represents the most complete Middle Jurassic turtle described to date, bridging the morphological gap between basal turtles from the Late Triassic–Early Jurassic and crown-group turtles that diversify during the Late Jurassic. A phylogenetic analysis places the new taxon within the stem group of Testudines (crown-group turtles) and suggests a sister-group relationship between E. waldmani and Heckerochelys romani from the Middle Jurassic of Russia. Moreover, E. waldmani also demonstrates that stem turtles were ecologically diverse, as it may represent the earliest known aquatic turtle.

scholarly journals The significance of zircon U-Pb ages in the Ba river basin to the timing of major tectonic stages of Kontum massif

2019 ◽  
Vol 41 (2) ◽  
pp. 105-115 ◽  
Author(s):  
Doan Dinh Hung ◽  
Yukiyasu Tsutsumi ◽  
Toshifumi Komatsu ◽  
Nguyen Hoang ◽  
Nguyen Ba Hung ◽  
...  
Keyword(s):  
River Basin ◽  
Late Cretaceous ◽  
Age Groups ◽  
Age Dating ◽  
Middle Permian ◽  
Late Triassic ◽  
Mountain Ranges ◽  
Tectonic Events ◽  
Deformation Processes ◽  
Formation And Evolution

Ba River originates from the Ngoc Linh mountain ranges, NW of Kontum massif and flows into the East Sea from the Da Rang estuary. The Ba River basin (Da Rang river) is considered as the means of transport and storage of products from the Kontum massif resulted following weathering, erosion or deformation processes either by natural causes or the regional thermo-tectonic events. A total of 122 zircon grains separated from the Ba River basin sediments are selected for U-Pb isotopic age dating by LA-ICP-MS method. Among the 122 samples, 114 are concordant, forming 3 major age groups, including middle-Late Cretaceous (105–85 Ma), Middle Permian - Late Triassic (270–211 Ma), Late Ordovician - Early Silurian (455–424 Ma). A few samples show ages scattering from 1470 to 970 Ma (Mesoproterozoic), and one sample shows a value of 2383±24 Ma (Paleoproterozoic). The acquired U-Pb zircon ages may reflect 3 major thermo- tectonic stages in the formation and evolution of the Kontum Massif from the Early Paleoproterozoic till middle-Late Cretaceous, with the most significant time being Middle Permian (270 Ma)-Late Triassic (211 Ma) (97 over 122 samples, e.g., 79,5%), corresponding to the period of convergence, collision and orogeny of the Indosinian block.  

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