Geometric morphometrics reveals sex-differential shape allometry in a spider

Common scientific wisdom assumes that spider sexual dimorphism (SD) mostly results from sexual selection operating on males. However, testing predictions from this hypothesis, particularly male size hyperallometry, has been restricted by methodological constraints. Here, using geometric morphometrics (GMM) we studied for the first time sex-differential shape allometry in a spider (Donacosa merlini, Araneae: Lycosidae) known to exhibit the reverse pattern (i.e., male-biased) of spider sexual size dimorphism. GMM reveals previously undetected sexdifferential shape allometry and sex-related shape differences that are size independent (i.e., associated to the y-intercept, and not to size scaling). Sexual shape dimorphism affects both the relative carapace-to-opisthosoma size and the carapace geometry, arguably resulting from sex differences in both reproductive roles (female egg load and male competition) and life styles (wandering males and burrowing females). Our results demonstrate that body portions may vary modularly in response to different selection pressures, giving rise to sex differences in shape, which reconciles previously considered mutually exclusive interpretations about the origins of spider SDThe fieldwork was financially supported by the Ministerio de Ciencia e Innovación and the Consejo Superior de Investigaciones Científicas to CFM (022/2007). JML is endorsed by project CGL2013-42643-

‘Dinosaur-bird’ macroevolution, locomotor modules and the origins of flight

S.M.N. is supported by a FPI-UAM 2019 predoctoral grant from the Autonomous University of Madrid. This research was partially funded by project CGL2013-42643P from MINECO (Spain) and PGC2018-094955-A100 from MICIU (Spain). This work is a contribution of the CIPb-UAM research group and the PMMV team (Paleoclimatology, Macroecology and Macroevolution of Vertebrates) as part of the UCM-910607 research group. We thank to all the organizing committee of the 4th International Meeting of Early-stage Researchers in Palaeontology for inviting us to participate in the Special Issue “Young Solutions to Old Issues: Discoveries in Palaeontology Research”. Funding Open Access funding provided thanks to the CRUE-CSIC agreement with Springer Natu

Variación morfológica y alometría de las vértebras precloacales en el ofidio daboia russelli (viperidae)

Understanding the variation of the ophidian vertebral morphology is an essential tool in snake paleobiology, but so far this field remains hardly investigated. A major problematic is the still scarce knowledge about the basis of homogeneity of intracolumnar shape variation along the vertebrae of the precloacal region in these animals. For instance, this variation can be overwhelmingly low in cases such as in vipers, for which it seems almost impossible to describe a concrete regionalization of the precloacal region without ambiguity. This study has applied geometric morphometrics to analyze if the shape variation of the vertebrae of the precloacal vertebrae of an adult specimen of Daboia russelli allows differentiating any sort of parcellation within the column of this organism. We have also explored if size is associated with the organization of vertebral shape along the axial skeleton. The multivariate analyses showed that the main pattern of vertebral shape variation in D. russelli concerns the neural spine and the hypapophysis, whereas the shape of the vertebral centrum appears to be nearly invariant along the series. Our analysis also showed that the precloacal region can be sudivided into two portions that merge in a transitional boundary of largest vertebrae in the middle of the column. From this middle region towards the distal ends of the column vertebrae become smaller changing their shapes in two antithetical waysFunds provided by the project CGL2009-11838 BTE and a FPU grant (AP2007-00904; MICINN) to I. Sarri

On the importance of examining the relationship between shape data and biologically meaningful variables. An example studying allometry with geometric morphometrics.

Geometric morphometrics (GM) is a tool for the statistical analysis of shape on Cartesian landmark coordinates. However, because GM studies commonly focus on the description of morphological trends within shape space (or morphospace), the predictive power of multivariate statistics to understand morphological change remains underutilized. Here we show the protocols to study allometry in 3D with these tools on a postnatal growth series of the domestic chicken. We contrast three approaches: a ?traditional? one in which size variables are compared statistically, a Principal Components Analysis on size and shape scores (Procrustes  form space), and a multivariate regression. In the latter  approach we further used three different independent factors  inherently related to ontogeny: skull centroid size, body weight, and age of the specimens. The results clearly stress the importance of studying shape change in relation to different causal factors (i.e., with regressions), demonstrating that, indeed, any independent variable or variables that make biological sense can be used to understand morphological change with GM.Fil: Marugán-Lobón, Jesús. Universidad Autónoma de Madrid. Facultad de Ciencias; España;Fil: Blanco-Miranda, David. Universidad Autónoma de Madrid. Facultad de Ciencias; España;Fil: Chamero Macho, Beatriz. Universidad Autónoma de Madrid. Facultad de Ciencias; España; Provincia del Chubut. Fundación Egidio Feruglio. Museo Paleontológico;Fil: Martín-Abad, Hugo. Universidad Autónoma de Madrid. Facultad de Ciencias; España

The consequences of craniofacial integration for the adaptive radiations of Darwin’s finches and Hawaiian honeycreepers

© 2020, The Author(s), under exclusive licence to Springer Nature Limited. The diversifications of Darwin’s finches and Hawaiian honeycreepers are two text-book examples of adaptive radiation in birds. Why these two bird groups radiated while the remaining endemic birds in these two archipelagos exhibit relatively low diversity and disparity remains unexplained. Ecological factors have failed to provide a convincing answer to this phenomenon, and some intrinsic causes connected to craniofacial evolution have been hypothesized. The tight coevolution of the beak and the remainder of the skull in diurnal raptors and parrots suggests that integration may be the prevalent condition in landbirds (Inopinaves). This is in contrast with the archetypal relationship between beak shape and ecology in Darwin’s finches and Hawaiian honeycreepers, which suggests that the beak can adapt as a distinct module in these birds. Modularity has therefore been proposed to underpin the adaptive radiation of these groups, allowing the beak to evolve more rapidly and freely in response to ecological opportunity. Here, using geometric morphometrics and phylogenetic comparative methods in a broad sample of landbird skulls, we show that craniofacial evolution in Darwin’s finches and Hawaiian honeycreepers seems to be characterized by a tighter coevolution of the beak and the rest of the skull (cranial integration) than in most landbird lineages, with rapid and extreme morphological evolution of both skull regions along constrained directions of phenotypic space. These patterns are unique among landbirds, including other sympatric island radiations, and therefore counter previous hypotheses by showing that tighter cranial integration, not only modularity, can facilitate evolution along adaptive directions

Soft-tissue and dermal arrangement in the wing of an Early Cretaceous bird: Implications for the evolution of avian flight

Despite a wealth of fossils of Mesozoic birds revealing evidence of plumage and other soft-tissue structures, the epidermal and dermal anatomy of their wing’s patagia remain largely unknown. We describe a distal forelimb of an enantiornithine bird from the Lower Cretaceous limestones of Las Hoyas, Spain, which reveals the overall morphology of the integument of the wing and other connective structures associated with the insertion of flight feathers. The integumentary anatomy, and myological and arthrological organization of the new fossil is remarkably similar to that of modern birds, in which a system of small muscles, tendons and ligaments attaches to the follicles of the remigial feathers and maintains the functional integrity of the wing during flight. The new fossil documents the oldest known occurrence of connective tissues in association with the flight feathers of birds. Furthermore, the presence of an essentially modern connective arrangement in the wing of enantiornithines supports the interpretation of these primitive birds as competent fliersSupport and funds were provided by the projects CGL2009-1183 BTE and CGL-2013-42643-P, Juntas de Comunidades de Castilla-La Mancha and by donations from Mrs. Gretchen Augustyn to the Dinosaur Institute of the Natural History Museum of Los Angeles Count

Quantitative analysis of morphometric data of pre-modern birds: phylogenetic versus ecological signal

Birds are one of the most diverse clades of extant terrestrial vertebrates, a diversity that first arose during the Mesozoic as a multitude of lineages of pre-neornithine (stem) birds appeared but did not survive into the Cenozoic Era. Modern birds (Neornithes) inhabit an extensive array of ecologically distinct habitats and have specific and varied foraging strategies. Likewise, the morphological disparity among Mesozoic lineages appears to underscore a significant degree of ecological diversity, yet attempts to determine lineage specific ecologies have mainly been limited to superficial narratives. In recent years, numerous studies have used various morphometric proxies to interpret the paleoecology of Mesozoic bird lineages, but largely without evaluating the interplay between ecological and phylogenetic signals. Moreover, most studies of this sort transform the original data into logarithms to control dimensionality, underestimating the biases induced upon such transformations. The goal of this study is to quantitatively address the ecomorphology of crown-group Neornithes using a dense sample of raw forelimb and hindlimb measurements, and to examine if such results can be used to infer the ecologies of Mesozoic bird lineages. To that end, scaling of limb measurements and ecological data from modern birds was assessed statistically using phylogenetic comparative methods, followed by the inclusion of fossil taxa. A strong relationship was recovered between humerus and hindlimb allometric scaling and phylogeny. Our results indicate that while some ecological classes of modern birds can be discriminated from each other, phylogenetic signature can overwhelm ecological signal in morphometric data, potentially limiting the inferences that can be made from ecomorphological studies. Furthermore, we found differential scaling of leg bones among Early Cretaceous enantiornithines and ornithuromorphs, a result hinting that habitat partitioning among different lineages could be a pervasive phenomenon in avian evolutio

Diversity and evolution of the Confuciusornithidae: Evidence from a new 131- million-year-old specimen from the Huajiying Formation in NE China

The Huajiying Formation contains the earliest deposits of the Jehol Biota, representing the world’s second oldest avifauna. This avifauna includes the early confuciusornithid Eoconfuciusornis zhengi, the oldest occurrence of this clade and one of the earliest divergences of pygostylian birds. Although E. zhengi shows unique traits, the holotype’s immature age makes comparisons with the better known Confuciusornis sanctus problematic. As a result, the taxonomic validity of E. zhengi is controversial. We describe a small, osteologically adult confuciusornithid from the same deposits as E. zhengi. The new fossil is most similar to E. zhengi but also shares traits with the stratigraphically younger Confuciusornis. The humerus of the new fossil is straighter and more slender, and bears a less dorsally-developed deltopectoral crest compared with similarly-sized and smaller specimens of Confuciusornis. The morphology of the humerus is intermediate between E. zhengi and Confuciusornis and its proximal portion is pierced by a small deltopectoral foramen, absent in the holotype of E. zhengi. However, this foramen is much smaller than in any other confuciusornithid. Shape analyses (geometric morphometrics) of the humerus of confuciusornithids of different ages and representatives of other basal avians and closely-related non-avian theropods supports our observations and indicate that the humeral differences between the holotype of E. zhengi and the new specimen are not easily explained as ontogenetic variation within a single species. However, the limited number of early confuciursornithids does not allow us to confidently interpret such differences as interspecific. Nonetheless, these analyses support the morphological distinctiveness of the early confuciusornithids from the Huajiying Formation and suggest a stepwise acquisition of the unique humeral morphology of ConfuciusornithidaeGN is supported by a PG Scholarship/Studentship from The Alumni Foundation, University of Bristol, UK. JML is supported by the Spanish MINECO, Project CGL-2013-42643. Innovative Team Program of the Beijing Academy of Science and Technology, the Beijing Millions of Talents Project in the New Century, the National Natural Science Foundation of China (No. 41602006), and theBeijing Natural Science Foundation (No. 5174032) provided funding for this researc