Your browser doesn't support javascript.
loading
Mostrar: 20 | 50 | 100
Resultados 1 - 20 de 44
Filtrar
Mais filtros










Base de dados
Intervalo de ano de publicação
1.
PeerJ ; 10: e13342, 2022.
Artigo em Inglês | MEDLINE | ID: mdl-35677394

RESUMO

Background: The Plesiosauria (Sauropterygia) are secondary marine diapsids. They are the only tetrapods to have evolved hydrofoil fore- and hindflippers. Once this specialization of locomotion had evolved, it remained essentially unchanged for 135 Ma. It is still controversial whether plesiosaurs flew underwater, rowed, or used a mixture of the two modes of locomotion. The long bones of Tetrapoda are functionally loaded by torsion, bending, compression, and tension during locomotion. Superposition of load cases shows that the bones are loaded mainly by compressive stresses. Therefore, it is possible to use finite element structure analysis (FESA) as a test environment for loading hypotheses. These include muscle reconstructions and muscle lines of action (LOA) when the goal is to obtain a homogeneous compressive stress distribution and to minimize bending in the model. Myological reconstruction revealed a muscle-powered flipper twisting mechanism. The flippers of plesiosaurs were twisted along the flipper length axis by extensors and flexors that originated from the humerus and femur as well as further distal locations. Methods: To investigate locomotion in plesiosaurs, the humerus and femur of a mounted skeleton of Cryptoclidus eurymerus (Middle Jurassic Oxford Clay Formation from Britain) were analyzed using FE methods based on the concept of optimization of loading by compression. After limb muscle reconstructions including the flipper twisting muscles, LOA were derived for all humerus and femur muscles of Cryptoclidus by stretching cords along casts of the fore- and hindflippers of the mounted skeleton. LOA and muscle attachments were added to meshed volumetric models of the humerus and femur derived from micro-CT scans. Muscle forces were approximated by stochastic iteration and the compressive stress distribution for the two load cases, "downstroke" and "upstroke", for each bone were calculated by aiming at a homogeneous compressive stress distribution. Results: Humeral and femoral depressors and retractors, which drive underwater flight rather than rowing, were found to exert higher muscle forces than the elevators and protractors. Furthermore, extensors and flexors exert high muscle forces compared to Cheloniidae. This confirms a convergently evolved myological mechanism of flipper twisting in plesiosaurs and complements hydrodynamic studies that showed flipper twisting is critical for efficient plesiosaur underwater flight.

2.
Sci Rep ; 12(1): 5546, 2022 04 01.
Artigo em Inglês | MEDLINE | ID: mdl-35365703

RESUMO

Ichthyopterygia is a major clade of reptiles that colonized the ocean after the end-Permian mass extinction, with the oldest fossil records found in early Spathian substage (late Olenekian, late Early Triassic) strata in the western USA. Here, we describe reptilian remains found in situ in the early Spathian Neocolumbites insignis ammonoid zone of South Primorye in the Russian Far East. Specimen NSM PV 23854 comprises fragmentary axial elements exhibiting a combination of morphological characteristics typical of Ichthyopterygia. The cylindrical centra suggest that the specimen represents a basal ichthyopterygian, and its size is comparable to that of Utatsusaurus. Specimen NSM PV 24995 is represented by a single limb bone, which is tentatively identified as an ichthyopterygian humerus. With a body length of approximately 5 m estimated from the humeral length, NSM PV 24995 represents one of the largest specimens of early Spathian marine reptiles known to date. Such size variation among the earliest ichthyopterygians might suggest an explosive diversification in size immediately after the end-Permian mass extinction. Both vertebrae and humerus specimens exhibit an extremely cancellous inner structure, suggesting a high degree of aquatic adaptation in ichthyopterygians, despite their short history of evolution in the ocean.


Assuntos
Evolução Biológica , Fósseis , Animais , Extremo Oriente , Filogenia , Répteis/anatomia & histologia
3.
Science ; 374(6575): eabf5787, 2021 Dec 24.
Artigo em Inglês | MEDLINE | ID: mdl-34941418

RESUMO

Body sizes of marine amniotes span six orders of magnitude, yet the factors that governed the evolution of this diversity are largely unknown. High primary production of modern oceans is considered a prerequisite for the emergence of cetacean giants, but that condition cannot explain gigantism in Triassic ichthyosaurs. We describe the new giant ichthyosaur Cymbospondylus youngorum sp. nov. with a 2-meter-long skull from the Middle Triassic Fossil Hill Fauna of Nevada, USA, underscoring rapid size evolution despite the absence of many modern primary producers. Surprisingly, the Fossil Hill Fauna rivaled the composition of modern marine mammal faunas in terms of size range, and energy-flux models suggest that Middle Triassic marine food webs were able to support several large-bodied ichthyosaurs at high trophic levels, shortly after ichthyosaur origins.


Assuntos
Evolução Biológica , Tamanho Corporal , Cetáceos/anatomia & histologia , Fósseis , Répteis/anatomia & histologia , Animais , Organismos Aquáticos , Cetáceos/fisiologia , Simulação por Computador , Dieta , Ecossistema , Cadeia Alimentar , Filogenia , Répteis/classificação , Répteis/fisiologia , Crânio/anatomia & histologia , Vertebrados/anatomia & histologia , Vertebrados/fisiologia
4.
Anat Rec (Hoboken) ; 304(3): 570-583, 2021 03.
Artigo em Inglês | MEDLINE | ID: mdl-32484294

RESUMO

Here we describe the histology and microanatomy of vertebral centra of the iconic pelycosaur-grade synapsids Edaphosaurus boanerges and Dimetrodon spp. Vertebrae from different axial positions and, in the case of Dimetrodon, from different ontogenetic stages were selected. For the histological description, we produced histological petrographic thin sections ground to a thickness of 50-80 µm of the vertebrae in the sagittal and transversal cutting planes. After the preparation process, the thin sections were examined under transmitted and cross-polarized light in a polarized microscope. The analyzed vertebrae reveal similar bone tissues, where both taxa have cortical parallel-fibered bone (PFB). PFB and lamellar bone (LB) forms in the cancellous part. However, in juvenile Dimetrodon, woven-fibered bone (WFB) is also deposited and shows a high degree of vascularity. This suggests that Dimetrodon had slightly faster bone growth than Edaphosaurus, which is mainly made of PFB and LB and shows poorly developed vascular canals. In addition, one specimen of Dimetrodon displays the preservation of an ossified notochord, which can be assumed to be indicative of how the intervertebral tissues were developed. Historically, evidence of how the joint between Dimetrodon vertebral centra was built was lacking until this specimen appeared. If the notochord ran persistently through the vertebrae, it would have possibly increased the stiffness of the vertebral column and would have affected the limbs and locomotion. Furthermore, the organization of trabeculae and relative thickness of the vertebral cortex gives insights into how the animals were adapted to their habitat.


Assuntos
Fósseis , Lagartos/anatomia & histologia , Coluna Vertebral/anatomia & histologia , Animais , Ecossistema , Texas
5.
RSC Adv ; 11(13): 7552-7563, 2021 Feb 10.
Artigo em Inglês | MEDLINE | ID: mdl-35423242

RESUMO

Porphyrins are macrocyclic tetrapyrrole derivatives that are widely distributed in nature. They are often complexed with a metal ion located in the center of the ring system and may be modified by various substituents including additional rings, or by ring opening, which leads to a plethora of different functions. Due to their extended conjugated aromatic ring system, porphyrins absorb light in the visible range and therefore show characteristic colors. Well-known natural porphyrins include the red-colored heme present in hemoglobin, which is responsible for blood oxygen transport, and the chlorophylls in some bacteria and in plants which are utilized for photosynthesis. Porphyrins are mostly lipophilic pigments that display relatively high chemical stability. Therefore, they can even survive hundreds of millions of years. The present review article provides an overview of natural porphyrins, their chemical structures, and properties. A special focus is put on porphyrins discovered in the fossil record. Examples will be highlighted, and information on their chemical analysis will be provided. We anticipate that the development of novel analytical methods with increased sensitivity will prompt new discoveries of porphyrins in fossils.

6.
Sci Rep ; 10(1): 14106, 2020 08 24.
Artigo em Inglês | MEDLINE | ID: mdl-32839497

RESUMO

The intervertebral disc (IVD) has long been considered unique to mammals. Palaeohistological sampling of 17 mostly extinct clades across the amniote tree revealed preservation of different intervertebral soft tissue types (cartilage, probable notochord) seen in extant reptiles. The distribution of the fossilised tissues allowed us to infer the soft part anatomy of the joint. Surprisingly, we also found evidence for an IVD in fossil reptiles, including non-avian dinosaurs, ichthyosaurs, plesiosaurs, and marine crocodiles. Based on the fossil dataset, we traced the evolution of the amniote intervertebral joint through ancestral character state reconstruction. The IVD evolved at least twice, in mammals and in extinct diapsid reptiles. From this reptilian IVD, extant reptile groups and some non-avian dinosaurs independently evolved a synovial ball-and-socket joint. The unique birds dorsal intervertebral joint evolved from this dinosaur joint. The tuatara and some geckos reverted to the ancestral persisting notochord.


Assuntos
Cartilagem/fisiologia , Dinossauros/anatomia & histologia , Fósseis/anatomia & histologia , Disco Intervertebral/anatomia & histologia , Répteis/anatomia & histologia , Jacarés e Crocodilos/anatomia & histologia , Animais , Aves/anatomia & histologia , Vértebras Cervicais/anatomia & histologia , Disco Intervertebral/fisiologia , Lagartos/anatomia & histologia , Vértebras Lombares/anatomia & histologia , Paleontologia/métodos
7.
J Anat ; 237(6): 1151-1161, 2020 12.
Artigo em Inglês | MEDLINE | ID: mdl-32707603

RESUMO

Temnospondyli are commonly believed to have possessed four digits in the manus and five in the pes. However, actual finds of articulated autopodia are extremely rare. Therefore, an articulated, slightly incomplete forelimb skeleton with preserved manus of Metoposaurus krasiejowensis from the Late Triassic of Poland is important in providing new details about the structure and ossification sequence in the temnospondyl limb. The most important observation is the presence of five metacarpals in this specimen. This allows reconstructing the manus as pentadactyl. The number of phalanges and the distribution of distal articulation facets allow reconstruction of the digit formula as (2?)-3-3-(3?)-(2?). The well-developed fifth digit suggests that the Metoposaurus manus shows a unique ossification sequence: the reduction or late ossification of the first digit conforms to the amniote-frog pattern, and the early development of the second and third digit makes Metoposaurus similar to salamanders. Based on the distribution of pentadactyly vs. tetradactyly in the temnospondyl manus, the number of digits was not phylogenetically constrained in temnospondyls, similar to today's amphibians.


Assuntos
Anfíbios/anatomia & histologia , Evolução Biológica , Membro Anterior/anatomia & histologia , Animais , Fósseis , Filogenia , Polônia
8.
PeerJ ; 7: e7658, 2019.
Artigo em Inglês | MEDLINE | ID: mdl-31720095

RESUMO

The sauropterygian clade Plesiosauria arose in the Late Triassic and survived to the very end of the Cretaceous. Plesiosauria evolved the greatest species diversity of any marine reptile clade, attaining a global distribution. Plesiosauria consist of two clades, Rhomaleosauridae and Neoplesiosauria. Basal Neoplesiosauria have long necks with at least 30 cervicals, but show qualitative osteological evidence for a stiff neck. Here we quantify neck mobility in lateral, ventral, and dorsal directions based on finite element modeling of neck vertebrae from the Middle Jurassic plesiosaur Cryptoclidus eurymerus. We model the mobility in a single motion segment, consisting of two adjacent cervical vertebrae and the joints connecting them. Based on the model with a maximum intervertebral spacing of 3 mm, we find that in Cryptoclidus, the maximum angle of lateral deflection in the motion segment was 2°. The maximum angle of ventral deflection was 5° and of dorsal deflection was 5°. When these values are multiplied by the number of cervical vertebrae, it becomes apparent that neck mobility was limited in all directions. The maximum angle of total lateral deflection in the neck was 67°. The maximum angle of total ventral deflection was 148° and of total dorsal deflection was 157°. This raises the question of the function of such a long, multi-segment but immobile neck. We posit that the long neck served in hydrodynamic and visual camouflage, hiding the bulk of the body from the small but abundant prey, such as schooling fish and squid. Neck immobility may have been advantageous in withstanding strong hydrodynamic forces acting on the neck during predatory strikes.

9.
PeerJ ; 7: e8022, 2019.
Artigo em Inglês | MEDLINE | ID: mdl-31763069

RESUMO

Plesiosaurs are a prominent group of Mesozoic marine reptiles, belonging to the more inclusive clades Pistosauroidea and Sauropterygia. In the Middle Triassic, the early pistosauroid ancestors of plesiosaurs left their ancestral coastal habitats and increasingly adapted to a life in the open ocean. This ecological shift was accompanied by profound changes in locomotion, sensory ecology and metabolism. However, investigations of physiological adaptations on the cellular level related to the pelagic lifestyle are lacking so far. Using vascular canal diameter, derived from osteohistological thin-sections, we show that inferred red blood cell size significantly increases in pistosauroids compared to more basal sauropterygians. This change appears to have occurred in conjunction with the dispersal to open marine environments, with cell size remaining consistently large in plesiosaurs. Enlarged red blood cells likely represent an adaptation of plesiosaurs repeated deep dives in the pelagic habitat and mirror conditions found in extant marine mammals and birds. Our results emphasize physiological aspects of adaptive convergence among fossil and extant marine amniotes and add to our current understanding of plesiosaur evolution.

10.
Sci Rep ; 9(1): 4424, 2019 03 14.
Artigo em Inglês | MEDLINE | ID: mdl-30872623

RESUMO

One of the fossil record's most puzzling features is the absence of preserved eggs or eggshell for the first third of the known 315 million year history of amniote evolution. Our meagre understanding of the origin and evolution of calcareous eggshell and amniotic eggs in general, is largely based on Middle Jurassic to Late Cretaceous fossils. For dinosaurs, the most parsimonious inference yields a thick, hard shelled egg, so richly represented in the Late Cretaceous fossil record. Here, we show that a thin calcareous layer (≤100 µm) with interlocking units of radiating crystals (mammillae) and a thick shell membrane already characterize the oldest known amniote eggs, belonging to three coeval, but widely distributed Early Jurassic basal sauropodomorph dinosaurs. This thin shell layer strongly contrasts with the considerably thicker calcareous shells of Late Jurassic dinosaurs. Phylogenetic analyses and their Sinemurian age indicate that the thin eggshell of basal sauropodomorphs represents a major evolutionary innovation at the base of Dinosauria and that the much thicker eggshell of sauropods, theropods, and ornithischian dinosaurs evolved independently. Advanced mineralization of amniote eggshell (≥150 µm in thickness) in general occurred not earlier than Middle Jurassic and may correspond with a global trend of increase in atmospheric oxygen.


Assuntos
Evolução Biológica , Dinossauros/anatomia & histologia , Casca de Ovo/anatomia & histologia , Ovos/análise , Filogenia , Animais , Fósseis
11.
Nat Commun ; 9(1): 4741, 2018 11 09.
Artigo em Inglês | MEDLINE | ID: mdl-30413693

RESUMO

Vertebrate hard tissues consist of mineral crystallites within a proteinaceous scaffold that normally degrades post-mortem. Here we show, however, that decalcification of Mesozoic hard tissues preserved in oxidative settings releases brownish stained extracellular matrix, cells, blood vessels, and nerve projections. Raman Microspectroscopy shows that these fossil soft tissues are a product of diagenetic transformation to Advanced Glycoxidation and Lipoxidation End Products, a class of N-heterocyclic polymers generated via oxidative crosslinking of proteinaceous scaffolds. Hard tissues in reducing environments, in contrast, lack soft tissue preservation. Comparison of fossil soft tissues with modern and experimentally matured samples reveals how proteinaceous tissues undergo diagenesis and explains biases in their preservation in the rock record. This provides a target, focused on oxidative depositional environments, for finding cellular-to-subcellular soft tissue morphology in fossils and validates its use in phylogenetic and other evolutionary studies.


Assuntos
Fósseis , Compostos Heterocíclicos/química , Especificidade de Órgãos , Polímeros/química , Proteínas/química , Vertebrados/metabolismo , Animais , Reagentes para Ligações Cruzadas/química , Dinossauros , Matriz Extracelular/metabolismo , Oxirredução , Análise Espectral Raman
12.
Curr Biol ; 28(19): R1160-R1163, 2018 10 08.
Artigo em Inglês | MEDLINE | ID: mdl-30300605

RESUMO

The quadrupedal Sauropods - the biggest dinosaurs to walk the Earth - evolved from bipedal ancestors. Two new early sauropodomorphs from South Africa and Argentina indicate that very large, flexed-limbed sauropodomorphs coexisted with early columnar-limbed sauropods for 20 million years.


Assuntos
Dinossauros/anatomia & histologia , Animais , Argentina , Evolução Biológica , Extremidades , África do Sul
13.
PeerJ ; 6: e5144, 2018.
Artigo em Inglês | MEDLINE | ID: mdl-30002976

RESUMO

The cuticle layer consisting mainly of lipids and hydroxyapatite (HAp) atop the mineralized avian eggshell is a protective structure that prevents the egg from dehydration and microbial invasions. Previous ornithological studies have revealed that the cuticle layer is also involved in modulating the reflectance of eggshells in addition to pigments (protoporphyrin and biliverdin). Thus, the cuticle layer represents a crucial trait that delivers ecological signals. While present in most modern birds, direct evidence for cuticle preservation in stem birds and non-avian dinosaurs is yet missing. Here we present the first direct and chemical evidence for the preservation of the cuticle layer on dinosaur eggshells. We analyze several theropod eggshells from various localities, including oviraptorid Macroolithus yaotunensis eggshells from the Late Cretaceous deposits of Henan, Jiangxi, and Guangdong in China and alvarezsaurid Triprismatoolithus eggshell from the Two Medicine Formation of Montana, United States, with the scanning electron microscope (SEM), electron probe micro-analysis (EPMA), and Raman spectroscopy (RS). The elemental analysis with EPMA shows high concentration of phosphorus at the boundary between the eggshell and sediment, representing the hydroxyapatitic cuticle layer (HAp). Depletion of phosphorus in sediment excludes the allochthonous origin of the phosphorus in these eggshells. The chemometric analysis of Raman spectra collected from fossil and extant eggs provides further supportive evidence for the cuticle preservation in oviraptorid and probable alvarezsaurid eggshells. In accordance with our previous discovery of pigments preserved in Cretaceous oviraptorid dinosaur eggshells, we validate the cuticle preservation on dinosaur eggshells through deep time and offer a yet unexplored resource for chemical studies targeting the evolution of dinosaur nesting ecology. Our study also suggests that the cuticle structure can be traced far back to maniraptoran dinosaurs and enhance their reproductive success in a warm and mesic habitat such as Montana and southern China during the Late Cretaceous.

14.
PeerJ ; 6: e4955, 2018.
Artigo em Inglês | MEDLINE | ID: mdl-29892509

RESUMO

Background: Plesiosaurs are marine reptiles that arose in the Late Triassic and survived to the Late Cretaceous. They have a unique and uniform bauplan and are known for their very long neck and hydrofoil-like flippers. Plesiosaurs are among the most successful vertebrate clades in Earth's history. Based on bone mass decrease and cosmopolitan distribution, both of which affect lifestyle, indications of parental care, and oxygen isotope analyses, evidence for endothermy in plesiosaurs has accumulated. Recent bone histological investigations also provide evidence of fast growth and elevated metabolic rates. However, quantitative estimations of metabolic rates and bone growth rates in plesiosaurs have not been attempted before. Methods: Phylogenetic eigenvector maps is a method for estimating trait values from a predictor variable while taking into account phylogenetic relationships. As predictor variable, this study employs vascular density, measured in bone histological sections of fossil eosauropterygians and extant comparative taxa. We quantified vascular density as primary osteon density, thus, the proportion of vascular area (including lamellar infillings of primary osteons) to total bone area. Our response variables are bone growth rate (expressed as local bone apposition rate) and resting metabolic rate (RMR). Results: Our models reveal bone growth rates and RMRs for plesiosaurs that are in the range of birds, suggesting that plesiosaurs were endotherm. Even for basal eosauropterygians we estimate values in the range of mammals or higher. Discussion: Our models are influenced by the availability of comparative data, which are lacking for large marine amniotes, potentially skewing our results. However, our statistically robust inference of fast growth and fast metabolism is in accordance with other evidence for plesiosaurian endothermy. Endothermy may explain the success of plesiosaurs consisting in their survival of the end-Triassic extinction event and their global radiation and dispersal.

15.
Biol Lett ; 14(5)2018 05.
Artigo em Inglês | MEDLINE | ID: mdl-29794006

RESUMO

The toothless beak of modern birds was considered as an adaption for feeding ecology; however, several recent studies suggested that developmental factors are also responsible for the toothless beak. Neontological and palaeontological studies have progressively uncovered how birds evolved toothless beaks and suggested that the multiple occurrences of complete edentulism in non-avian dinosaurs were the result of selection for specialized diets. Although developmental biology and ecological factors are not mutually exclusive, the conventional hypothesis that ecological factors account for the toothless beak appears insufficient. A recent study on dinosaur incubation period using embryonic teeth posited that tooth formation rate limits developmental speed, constraining toothed dinosaur incubation to slow reptilian rates. We suggest that selection for tooth loss was a side effect of selection for fast embryo growth and thus shorter incubation. This observation would also explain the multiple occurrences of tooth loss and beaks in non-avian dinosaur taxa crownward of Tyrannosaurus Whereas our hypothesis is an observation without any experimental supports, more studies of gene regulation of tooth formation in embryos would allow testing for the trade-off between incubation period and tooth development.


Assuntos
Bico/embriologia , Evolução Biológica , Aves/embriologia , Dinossauros/embriologia , Animais , Fósseis , Filogenia , Dente/embriologia
16.
Biol Lett ; 14(1)2018 01.
Artigo em Inglês | MEDLINE | ID: mdl-29298825

RESUMO

Air sacs are an important component of the avian respiratory system, and corresponding structures also were crucial for the evolution of sauropod dinosaur gigantism. Inferring the presence of air sacs in fossils so far is restricted to bones preserving internal pneumatic cavities and foramina as osteological correlates. We here present bone histological correlates for air sacs as a new potential identification tool for these elements of the respiratory system. The analysis of several avian and non-avian dinosaur samples revealed delicate fibres in secondary trabecular and secondary endosteal bone that in the former case (birds) is known or in the latter (non-avian dinosaurs) assumed to have been in contact with air sacs, respectively. The bone histology of this 'pneumosteal tissue' is markedly different from those regions where muscles attached presenting classical Sharpey's fibres. The pneumatized bones of several non-dinosaurian taxa do not exhibit the characteristics of this 'pneumosteum'. Our new histology-based approach thus can be instrumental in reconstructing the origin of air sacs among dinosaurs and hence for our understanding of this remarkable evolutionary novelty of the respiratory system.


Assuntos
Sacos Aéreos , Evolução Biológica , Osso e Ossos/anatomia & histologia , Dinossauros/anatomia & histologia , Dinossauros/classificação , Fósseis/anatomia & histologia , Sistema Respiratório/anatomia & histologia , Animais , Aves/anatomia & histologia
17.
Sci Adv ; 3(12): e1701144, 2017 12.
Artigo em Inglês | MEDLINE | ID: mdl-29242826

RESUMO

Secondary marine adaptation is a major pattern in amniote evolution, accompanied by specific bone histological adaptations. In the aftermath of the end-Permian extinction, diverse marine reptiles evolved early in the Triassic. Plesiosauria is the most diverse and one of the longest-lived clades of marine reptiles, but its bone histology is least known among the major marine amniote clades. Plesiosaurians had a unique and puzzling body plan, sporting four evenly shaped pointed flippers and (in most clades) a small head on a long, stiffened neck. The flippers were used as hydrofoils in underwater flight. A wide temporal, morphological, and morphometric gap separates plesiosaurians from their closest relatives (basal pistosaurs, Bobosaurus). For nearly two centuries, plesiosaurians were thought to appear suddenly in the earliest Jurassic after the end-Triassic extinctions. We describe the first Triassic plesiosaurian, from the Rhaetian of Germany, and compare its long bone histology to that of later plesiosaurians sampled for this study. The new taxon is recovered as a basal member of the Pliosauridae, revealing that diversification of plesiosaurians was a Triassic event and that several lineages must have crossed into the Jurassic. Plesiosaurian histology is strikingly uniform and different from stem sauropterygians. Histology suggests the concurrent evolution of fast growth and an elevated metabolic rate as an adaptation to cruising and efficient foraging in the open sea. The new specimen corroborates the hypothesis that open ocean life of plesiosaurians facilitated their survival of the end-Triassic extinctions.


Assuntos
Osso e Ossos/anatomia & histologia , Fósseis , Filogenia , Répteis/anatomia & histologia , Esqueleto/anatomia & histologia , Adaptação Fisiológica , Animais , Organismos Aquáticos , Evolução Biológica , Alemanha , Oceanos e Mares , Análise de Componente Principal , Répteis/fisiologia
18.
PeerJ ; 5: e3706, 2017.
Artigo em Inglês | MEDLINE | ID: mdl-28875070

RESUMO

Protoporphyrin (PP) and biliverdin (BV) give rise to the enormous diversity in avian egg coloration. Egg color serves several ecological purposes, including post-mating signaling and camouflage. Egg camouflage represents a major character of open-nesting birds which accomplish protection of their unhatched offspring against visually oriented predators by cryptic egg coloration. Cryptic coloration evolved to match the predominant shades of color found in the nesting environment. Such a selection pressure for the evolution of colored or cryptic eggs should be present in all open nesting birds and relatives. Many birds are open-nesting, but protect their eggs by continuous brooding, and thus exhibit no or minimal eggshell pigmentation. Their closest extant relatives, crocodiles, protect their eggs by burial and have unpigmented eggs. This phylogenetic pattern led to the assumption that colored eggs evolved within crown birds. The mosaic evolution of supposedly avian traits in non-avian theropod dinosaurs, however, such as the supposed evolution of partially open nesting behavior in oviraptorids, argues against this long-established theory. Using a double-checking liquid chromatography ESI-Q-TOF mass spectrometry routine, we traced the origin of colored eggs to their non-avian dinosaur ancestors by providing the first record of the avian eggshell pigments protoporphyrin and biliverdin in the eggshells of Late Cretaceous oviraptorid dinosaurs. The eggshell parataxon Macroolithus yaotunensis can be assigned to the oviraptor Heyuannia huangi based on exceptionally preserved, late developmental stage embryo remains. The analyzed eggshells are from three Late Cretaceous fluvial deposits ranging from eastern to southernmost China. Reevaluation of these taphonomic settings, and a consideration of patterns in the porosity of completely preserved eggs support an at least partially open nesting behavior for oviraptorosaurs. Such a nest arrangement corresponds with our reconstruction of blue-green eggs for oviraptors. According to the sexual signaling hypothesis, the reconstructed blue-green eggs support the origin of previously hypothesized avian paternal care in oviraptorid dinosaurs. Preserved dinosaur egg color not only pushes the current limits of the vertebrate molecular and associated soft tissue fossil record, but also provides a perspective on the potential application of this unexplored paleontological resource.

19.
J Anat ; 230(2): 325-336, 2017 02.
Artigo em Inglês | MEDLINE | ID: mdl-27813090

RESUMO

Although it is generally assumed that herbivores have more voluminous body cavities due to larger digestive tracts required for the digestion of plant fiber, this concept has not been addressed quantitatively. We estimated the volume of the torso in 126 terrestrial tetrapods (synapsids including basal synapsids and mammals, and diapsids including birds, non-avian dinosaurs and reptiles) classified as either herbivore or carnivore in digital models of mounted skeletons, using the convex hull method. The difference in relative torso volume between diet types was significant in mammals, where relative torso volumes of herbivores were about twice as large as that of carnivores, supporting the general hypothesis. However, this effect was not evident in diapsids. This may either reflect the difficulty to reliably reconstruct mounted skeletons in non-avian dinosaurs, or a fundamental difference in the bauplan of different groups of tetrapods, for example due to differences in respiratory anatomy. Evidently, the condition in mammals should not be automatically assumed in other, including more basal, tetrapod lineages. In both synapsids and diapsids, large animals showed a high degree of divergence with respect to the proportion of their convex hull directly supported by bone, with animals like elephants or Triceratops having a low proportion, and animals such as rhinoceros having a high proportion of bony support. The relevance of this difference remains to be further investigated.


Assuntos
Evolução Biológica , Tamanho Corporal , Carnívoros/anatomia & histologia , Trato Gastrointestinal/anatomia & histologia , Herbivoria , Imageamento Tridimensional/métodos , Animais , Dinossauros , Mamíferos
20.
PLoS One ; 11(7): e0158448, 2016.
Artigo em Inglês | MEDLINE | ID: mdl-27391607

RESUMO

Mid-diaphyseal cortical bone tissue in humeri of Nothosaurus spp. consists of coarse parallel-fibered bone, finer and higher organized parallel-fibered bone, and lamellar bone. Vascular canals are mainly arranged longitudinally and radially in a dominantly radial system. Blood vessels are represented by simple vascular canals, incompletely lined primary osteons, and fully developed primary osteons. Nothosaurus spp. shows a variety of diaphyseal microanatomical patterns, ranging from thick to very thin-walled cortices. In the early Anisian (Lower Muschelkalk), small- and large-bodied Nothosaurus spp. generally exhibit bone mass increase (BMI). In the middle to late Anisian (Middle Muschelkalk) small-bodied nothosaurs retain BMI whereas larger-bodied forms tend to show a decrease in bone mass (BMD). During the latest Anisian to early Ladinian (Upper Muschelkalk), small- and few large-bodied nothosaurs retain BMI, whereas the majority of large-bodied forms exhibit BMD. The stratigraphically youngest nothosaurs document five microanatomical categories, two of which are unique among marine amniotes: One consists of a very heterogeneously distributed spongy periosteal organization, the other of very thin-walled cortices. The functional significance of the two unique microanatomical specializations seen in large-bodied nothosaurs is the reduction of bone mass, which minimizes inertia of the limbs, and thus saves energy during locomotion. Transitions between the various microanatomical categories are rather gradual. Our results suggest that small-bodied Nothosaurus marchicus and other, not further assignable small-bodied nothosaurs seem to have been bound to near-shore, shallow marine environments throughout their evolution. Some large-bodied Nothosaurus spp. followed the same trend but others became more active swimmers and possibly inhabited open marine environments. The variety of microanatomical patterns may be related to taxonomic differences, developmental plasticity, and possibly sexual dimorphism. Humeral microanatomy documents the diversification of nothosaur species into different environments to avoid intraclade competition as well as competition with other marine reptiles. Nothosaur microanatomy indicates that knowledge of processes involved in secondary aquatic adaptation and their interaction are more complex than previously believed.


Assuntos
Dinossauros/anatomia & histologia , Osteon/anatomia & histologia , Periósteo/anatomia & histologia , Tíbia/anatomia & histologia , Animais , Densidade Óssea/fisiologia , Dinossauros/fisiologia , Periósteo/fisiologia , Tíbia/fisiologia
SELEÇÃO DE REFERÊNCIAS
DETALHE DA PESQUISA
...