scholarly journals Heterochronic Shifts Mediate Ecomorphological Convergence in Skull Shape of Microcephalic Sea Snakes

2019 ◽  
Vol 59 (3) ◽  
pp. 616-624 ◽  
Author(s):  
Emma Sherratt ◽  
Kate L Sanders ◽  
Amy Watson ◽  
Mark N Hutchinson ◽  
Michael S Y Lee ◽  
...  
Keyword(s):  
Morphological Changes ◽  
Shape Variation ◽  
Micro Computed Tomography ◽  
Trophic Specialization ◽  
Evolutionary Patterns ◽  
Dietary Specialization ◽  
Geometric Morphometric ◽  
Sea Snakes ◽  
Morphometric Methods ◽  
Cranial Shape

Abstract Morphological variation among the viviparous sea snakes (Hydrophiinae), a clade of fully aquatic elapid snakes, includes an extreme “microcephalic” ecomorph that has a very small head atop a narrow forebody, while the hind body is much thicker (up to three times the forebody girth). Previous research has demonstrated that this morphology has evolved at least nine times as a consequence of dietary specialization on burrowing eels, and has also examined morphological changes to the vertebral column underlying this body shape. The question addressed in this study is what happens to the skull during this extreme evolutionary change? Here we use X-ray micro-computed tomography and geometric morphometric methods to characterize cranial shape variation in 30 species of sea snakes. We investigate ontogenetic and evolutionary patterns of cranial shape diversity to understand whether cranial shape is predicted by dietary specialization, and examine whether cranial shape of microcephalic species may be a result of heterochronic processes. We show that the diminutive cranial size of microcephalic species has a convergent shape that is correlated with trophic specialization to burrowing prey. Furthermore, their cranial shape is predictable for their size and very similar to that of juvenile individuals of closely related but non-microcephalic sea snakes. Our findings suggest that heterochronic changes (resulting in pedomorphosis) have driven cranial shape convergence in response to dietary specializations in sea snakes.

scholarly journals Trophic specialization drives morphological evolution in sea snakes

2018 ◽  
Vol 5 (3) ◽  
pp. 172141 ◽  
Author(s):  
Emma Sherratt ◽  
Arne R. Rasmussen ◽  
Kate L. Sanders
Keyword(s):  
Body Length ◽  
Body Shape ◽  
Morphological Changes ◽  
Morphological Evolution ◽  
Ecological Factors ◽  
Trophic Specialization ◽  
Dietary Specialization ◽  
Sea Snake ◽  
Sea Snakes ◽  
Specialist Predators

Viviparous sea snakes are the most rapidly speciating reptiles known, yet the ecological factors underlying this radiation are poorly understood. Here, we reconstructed dated trees for 75% of sea snake species and quantified body shape (forebody relative to hindbody girth), maximum body length and trophic diversity to examine how dietary specialization has influenced morphological diversification in this rapid radiation. We show that sea snake body shape and size are strongly correlated with the proportion of burrowing prey in the diet. Specialist predators of burrowing eels have convergently evolved a ‘microcephalic’ morphotype with dramatically reduced forebody relative to hindbody girth and intermediate body length. By comparison, snakes that predominantly feed on burrowing gobies are generally short-bodied and small-headed, but there is no evidence of convergent evolution. The eel specialists also exhibit faster rates of size and shape evolution compared to all other sea snakes, including those that feed on gobies. Our results suggest that trophic specialization to particular burrowing prey (eels) has invoked strong selective pressures that manifest as predictable and rapid morphological changes. Further studies are needed to examine the genetic and developmental mechanisms underlying these dramatic morphological changes and assess their role in sea snake speciation.

scholarly journals Comparing skull formation of the Hungarian (Hortobágy) Zackel sheep breed by geometrics morphometrics

2015 ◽  
pp. 29-33
Author(s):  
Zsuzsanna Csóri ◽  
András Gáspárdy ◽  
András Jávor
Keyword(s):  
Morphological Changes ◽  
Time Change ◽  
Carpathian Basin ◽  
Sheep Breed ◽  
Geometric Morphometric ◽  
The Past ◽  
Morphometric Methods ◽  
Skull Formation ◽  
Over Time

This work seeks to explore the morphological changes of the Hungarian (Hortobágy) Zackel sheep's skull, which occurred in the past 50–70 years. In this study, we compared individuals skull forms by geometric morphometric methods. The origin of the breed is not known, we do not know when entering the Carpathian Basin. Therefore, the comparison involved the only known early archaeological findings. We have shown that there is no difference between each period colour variations, but over time change has occurred in the skull formation of the breed.

Larval anatomy of Andean tadpoles of Telmatobius (Anura: Ceratophryidae) from Northwestern Argentina

Zootaxa ◽  
2008 ◽  
Vol 1938 (1) ◽  
pp. 40-60 ◽  
Author(s):  
M. FLORENCIA VERA CANDIOTI
Keyword(s):  
Intraspecific Variation ◽  
Characteristic Pattern ◽  
Species Discrimination ◽  
Shape Variation ◽  
Geometric Morphometric ◽  
Northwestern Argentina ◽  
Preliminary Results ◽  
Internal Morphology ◽  
Morphometric Methods ◽  
Interspecific And Intraspecific Variation

In this paper I study the oral, buccopharyngeal, and musculoskeletal configuration in tadpoles of nine Telmatobius species from Northwestern Argentina (T. atacamensis, T. ceiorum, T. laticeps, T. oxycephalus, T. pinguiculus, T. pisanoi, T. cf. schreiteri, T. scrocchii, and T. stephani; N = 30, Gosner stages 31–36). Specimens were prepared according to standard clearing and staining protocols; additionally, I applied landmark and outline-based geometric morphometric methods in order to quantify shape variation in chondrocrania, hyobranchial skeletons, and suprarostral cartilages. Although preliminary, results show a marked morphological uniformity on the analyzed levels, and overlapping interspecific and intraspecific variation, which renders species discrimination difficult. Some distinctive traits for the genus are bicuspidate buccal spurs, peculiar arrangement of buccal roof and floor papillae, tetrapartite suprarostral, adrostral cartilages, a lateral slip of the m. subarcualis rectus II-IV invading branchial septum IV, and a characteristic pattern of muscles inserted on the diaphragm. The conservative larval internal morphology in this genus could be explained by a recent speciation and a development possibly characterized by the postmetamorphic appearance of specific features.En este trabajo estudio la morfología oral, bucofaríngea y musculoesquelética de larvas de nueve especies de Telmatobius del Noroeste argentino (T. atacamensis, T. ceiorum, T. laticeps, T. oxycephalus, T. pinguiculus, T. pisanoi, T. cf. schreiteri, T. scrocchii y T. stephani; N = 30, estadios de Gosner 31–36). Los especímenes se prepararon siguiendo protocolos clásicos de transparentación y coloración diferencial; adicionalmente, apliqué métodos de morfometría geométrica basada en landmarks y contornos para cuantificar la variación de formas en condrocráneos, esqueletos hiobranquiales y cartílagos suprarostrales. Aunque de carácter preliminar, los resultados muestran una notable uniformidad morfológica en los niveles analizados, y una variación intraespecífica que se superpone con la interespecífica, dificultando la distinción entre especies. Algunos rasgos distintivos del género son un par de espolones bucales bífidos, un arreglo particular de las papilas del techo y piso bucales, suprarostral tetrapartito, adrostrales, un haz del m. subarcualis rectus II-IV invadiendo el septo branquial IV, y un patrón aparentemente característico de los músculos insertos en el diafragma. La morfología larval interna conservadora en el género podría explicarse por una especiación reciente y un desarrollo posiblemente caracterizado por la aparición postmetamórfica de los rasgos específicos.

scholarly journals The Utility of Geometric Morphometrics to Elucidate Pathways of Cichlid Fish Evolution

2011 ◽  
Vol 2011 ◽  
pp. 1-8 ◽  
Author(s):  
Michaela Kerschbaumer ◽  
Christian Sturmbauer
Keyword(s):  
Geometric Morphometrics ◽  
Evolutionary Biology ◽  
Body Shape ◽  
Cichlid Fish ◽  
Anatomical Landmarks ◽  
Trophic Specialization ◽  
Geometric Morphometric ◽  
The Family ◽  
Morphometric Methods ◽  
Head Morphology

Fishes of the family Cichlidae are famous for their spectacular species flocks and therefore constitute a model system for the study of the pathways of adaptive radiation. Their radiation is connected to trophic specialization, manifested in dentition, head morphology, and body shape. Geometric morphometric methods have been established as efficient tools to quantify such differences in overall body shape or in particular morphological structures and meanwhile found wide application in evolutionary biology. As a common feature, these approaches define and analyze coordinates of anatomical landmarks, rather than traditional counts or measurements. Geometric morphometric methods have several merits compared to traditional morphometrics, particularly for the distinction and analysis of closely related entities. Cichlid evolutionary research benefits from the efficiency of data acquisition, the manifold opportunities of analyses, and the potential to visualize shape changes of those landmark-based methods. This paper briefly introduces to the concepts and methods of geometric morphometrics and presents a selection of publications where those techniques have been successfully applied to various aspects of cichlid fish diversification.

scholarly journals Integration and diversity of the caviomorph mandible (Rodentia: Hystricomorpha): assessing the evolutionary history through fossils and ancestral shape reconstructions

2019 ◽  
Vol 188 (1) ◽  
pp. 276-301 ◽  
Author(s):  
Alicia Álvarez ◽  
Marcos D Ercoli ◽  
Diego H Verzi
Keyword(s):  
Evolutionary History ◽  
Middle Eocene ◽  
Morphological Changes ◽  
Feeding Habits ◽  
Shape Variation ◽  
Phylogenetic Structure ◽  
Geometric Morphometric ◽  
History Of ◽  
Life Habits ◽  
Functional Units

Abstract Caviomorph rodents constitute a highly diverse clade of Neotropical mammals. They are recorded since at least the late Middle Eocene and have a long and complex evolutionary history. Using geometric morphometric data, we analysed the variation in mandibular shape of this clade through integration analyses, allometry and shape optimizations onto a phylogenetic tree of 104 extant and extinct species. The analyses of shape variation revealed a strong influence of phylogenetic structure and life habits. A remarkable allometric effect was observed for specific mandibular traits. Morphological changes occurring in the alveolar and muscular functional units were moderately associated. Interestingly, the coordinated evolution of these two functional units was decoupled in the clade of extant abrocomids. A sequential and nearly synchronic acquisition of convergent traits has occurred in chinchillids and derived cavioids since at least the early Middle Oligocene, probably derived from grass-feeding habits or similar adaptations to other abrasive items. Convergences between fossorial taxa evolved in two main events through the Oligocene and middle Late Miocene. Morphological analysis of the fossil representatives allowed a better understanding of the timing of trait acquisitions during the evolutionary history of caviomorphs and its relationship with global and regional palaeoenvironmental changes.

scholarly journals Beyond the carapace: skull shape variation and morphological systematics of long-nosed armadillos (genus Dasypus)

PeerJ ◽  
2017 ◽  
Vol 5 ◽  
pp. e3650 ◽  
Author(s):  
Lionel Hautier ◽  
Guillaume Billet ◽  
Benoit de Thoisy ◽  
Frédéric Delsuc
Keyword(s):  
Morphological Variation ◽  
Distinct Species ◽  
Morphological Characters ◽  
Molecular Data ◽  
Shape Variation ◽  
Micro Computed Tomography ◽  
Dasypus Novemcinctus ◽  
Skull Morphology ◽  
Geometric Morphometric ◽  
Skull Shape

Background The systematics of long-nosed armadillos (genus Dasypus) has been mainly based on a handful of external morphological characters and classical measurements. Here, we studied the pattern of morphological variation in the skull of long-nosed armadillos species, with a focus on the systematics of the widely distributed nine-banded armadillo (Dasypus novemcinctus). Methods We present the first exhaustive 3D comparison of the skull morphology within the genus Dasypus, based on micro-computed tomography. We used geometric morphometric approaches to explore the patterns of the intra- and interspecific morphological variation of the skull with regard to several factors such as taxonomy, geography, allometry, and sexual dimorphism. Results We show that the shape and size of the skull vary greatly among Dasypus species, with Dasypus pilosus representing a clear outlier compared to other long-nosed armadillos. The study of the cranial intraspecific variation in Dasypus novemcinctus evidences clear links to the geographic distribution and argues in favor of a revision of past taxonomic delimitations. Our detailed morphometric comparisons detected previously overlooked morphotypes of nine-banded armadillos, especially a very distinctive unit restricted to the Guiana Shield. Discussion As our results are congruent with recent molecular data and analyses of the structure of paranasal sinuses, we propose that Dasypus novemcinctus should be regarded either as a polytypic species (with three to four subspecies) or as a complex of several distinct species.

Ontogeny and geographic variation of a new species of the corynexochine trilobite Zacanthopsis (Dyeran, Cambrian)

2009 ◽  
Vol 83 (4) ◽  
pp. 524-547 ◽  
Author(s):  
Melanie J. Hopkins ◽  
Mark Webster
Keyword(s):  
Geographic Variation ◽  
Species Delimitation ◽  
Pairwise Comparison ◽  
Species Level ◽  
Shape Variation ◽  
Geometric Morphometric ◽  
East Central ◽  
Morphometric Methods ◽  
Cambrian Trilobite ◽  
A New Species

Assessment of ontogenetic and geographic variation can have substantial influence on species delimitation and thereby on perceived patterns of species-level morphological variation and diversity in space and time. Here we describe the ontogeny and intraspecific variation of the early Cambrian trilobite, Zacanthopsis palmeri n. sp., based on silicified material from east-central Nevada, USA. Zacanthopsis palmeri is the oldest documented Cambrian corynexochine to shift from possessing a fused rostal-hypostomal plate to a functional hypostomal suture in mature specimens during ontogeny. Six geographically distinct samples of mature Z. palmeri from a single silicified limestone bed traceable over tens of kilometers in east-central Nevada permit exploration of geographic variation within this species using geometric morphometric methods. No one sample encompasses all of the shape variation expressed by Z. palmeri and several geographically segregated samples show some degree of morphological separation in pairwise comparison. Nonetheless, these samples are not qualitatively or quantitatively different from one another when all samples are taken into account. The degree of variation within Z. palmeri is similar in magnitude to the differences between other species in the genus known from much less material.

scholarly journals 3D Digitization in Functional Morphology: Where is the Point of Diminishing Returns?

2019 ◽  
Vol 59 (3) ◽  
pp. 656-668 ◽  
Author(s):  
Sharlene E Santana ◽  
Jessica H Arbour ◽  
Abigail A Curtis ◽  
Kathryn E Stanchak
Keyword(s):  
Functional Morphology ◽  
Three Dimensional ◽  
Comparative Morphology ◽  
Micro Computed Tomography ◽  
Evolutionary Patterns ◽  
Geometric Morphometric ◽  
Critical Dimensions ◽  
Contrast Enhanced Ct ◽  
2D Data ◽  
3D Digitization

Abstract Modern computational and imaging methods are revolutionizing the fields of comparative morphology, biomechanics, and ecomorphology. In particular, imaging tools such as X-ray micro computed tomography (µCT) and diffusible iodine-based contrast enhanced CT allow observing and measuring small and/or otherwise inaccessible anatomical structures, and creating highly accurate three-dimensional (3D) renditions that can be used in biomechanical modeling and tests of functional or evolutionary hypotheses. But, do the larger datasets generated through 3D digitization always confer greater power to uncover functional or evolutionary patterns, when compared with more traditional methodologies? And, if so, why? Here, we contrast the advantages and challenges of using data generated via (3D) CT methods versus more traditional (2D) approaches in the study of skull macroevolution and feeding functional morphology in bats. First, we test for the effect of dimensionality and landmark number on inferences of adaptive shifts during cranial evolution by contrasting results from 3D versus 2D geometric morphometric datasets of bat crania. We find sharp differences between results generated from the 3D versus some of the 2D datasets (xy, yz, ventral, and frontal), which appear to be primarily driven by the loss of critical dimensions of morphological variation rather than number of landmarks. Second, we examine differences in accuracy and precision among 2D and 3D predictive models of bite force by comparing three skull lever models that differ in the sources of skull and muscle anatomical data. We find that a 3D model that relies on skull µCT scans and muscle data partly derived from diceCT is slightly more accurate than models based on skull photographs or skull µCT and muscle data fully derived from dissections. However, the benefit of using the diceCT-informed model is modest given the effort it currently takes to virtually dissect muscles from CT scans. By contrasting traditional and modern tools, we illustrate when and why 3D datasets may be preferable over 2D data, and vice versa, and how different methodologies can complement each other in comparative analyses of morphological function and evolution.

scholarly journals A new, three-dimensional geometric morphometric approach to assess egg shape

PeerJ ◽  
2018 ◽  
Vol 6 ◽  
pp. e5052 ◽  
Author(s):  
Marie R.G. Attard ◽  
Emma Sherratt ◽  
Paul McDonald ◽  
Iain Young ◽  
Marta Vidal-García ◽  
...  
Keyword(s):  
Three Dimensional ◽  
Linear Measurement ◽  
Future Research ◽  
Species Variation ◽  
Shape Variation ◽  
Micro Computed Tomography ◽  
Finite Elements Analysis ◽  
Geometric Morphometric ◽  
Egg Shape ◽  
Precise Representation

This paper proposes a new methodology to quantify patterns of egg shape variation using geometric morphometrics of three-dimensional landmarks captured on digitally reconstructed eggshells and demonstrates its performance in capturing shape variation at multiple biological levels. This methodology offers unique benefits to complement established linear measurement or two-dimensional (2D) contour profiling techniques by (i) providing a more precise representation of eggshell curvature by accounting for variation across the entire surface of the egg; (ii) avoids the occurrence of correlations from combining multiple egg shape features; (iii) avoids error stemming from projecting a highly-curved three-dimensional (3D) object into 2D space; and (iv) enables integration into 3D workflows such as finite elements analysis. To demonstrate, we quantify patterns of egg shape variation and estimate morphological disparity at multiple biological levels, within and between clutches and among species of four passerine species of different lineages, using volumetric dataset obtained from micro computed tomography. The results indicate that species broadly have differently shaped eggs, but with extensive within-species variation so that all four-focal species occupy a range of shapes. Within-species variation is attributed to between-clutch differences in egg shape; within-clutch variation is surprisingly substantial. Recent comparative analyses that aim to explain shape variation among avian taxa have largely ignored potential biases due to within-species variation, or use methods limited to a narrow range of egg shapes. Through our approach, we suggest that there is appreciable variation in egg shape across clutches and that this variation needs to be accounted for in future research. The approach developed in this study to assess variation in shape is freely accessible and can be applied to any spherical-to-conical shaped object, including eggs of non-avian dinosaurs and reptiles through to other extant taxa such as poultry.

scholarly journals Arothron: An R package for geometric morphometric methods and virtual anthropology applications

2021 ◽  
Author(s):  
Profico Antonio ◽  
Buzi Costantino ◽  
Castiglione Silvia ◽  
Melchionna Marina ◽  
Piras Paolo ◽  
...  
Keyword(s):  
R Package ◽  
Geometric Morphometric ◽  
Morphometric Methods ◽  
Virtual Anthropology
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