On the development of the chondrocranium and the histological anatomy of the head in perinatal stages of marsupial mammals

An overview of the literature on the chondrocranium of marsupial mammals reveals a relative conservatism in shape and structures. We document the histological cranial anatomy of individuals representing Monodelphis domestica, Dromiciops gliroides, Perameles sp. and Macropus eugenii. The marsupial chondrocranium is generally characterized by the great breadth of the lamina basalis, absence of pila metoptica and large otic capsules. Its most anterior portion (cupula nasi anterior) is robust, and anterior to it there are well-developed tactile sensory structures, functionally important in the neonate. Investigations of ossification centers at and around the nasal septum are needed to trace the presence of certain bones (e.g., mesethmoid, parasphenoid) across marsupial taxa. In many adult marsupials, the tympanic floor is formed by at least three bones: alisphenoid (alisphenoid tympanic process), ectotympanic and petrosal (rostral and caudal tympanic processes); the squamosal also contributes in some diprotodontians. The presence of an entotympanic in marsupials has not been convincingly demonstrated. The tubal element surrounding the auditory tube in most marsupials is fibrous connective tissue rather than cartilage; the latter is the case in most placentals recorded to date. However, we detected fibrocartilage in a late juvenile of Dromiciops, and a similar tissue has been reported for Tarsipes. Contradictory reports on the presence of the tegmen tympani can be found in the literature. We describe a small tegmen tympani in Macropus. Several heterochronic shifts in the timing of development of the chondocranium and associated structures (e.g., nerves, muscles) and in the ossification sequence have been interpreted as largely being influenced by functional requirements related to the altriciality of the newborn marsupial during early postnatal life. Comparative studies of chondocranial development of mammals can benefit from a solid phylogenetic framework, research on non-classical model organisms, and integration with imaging and sectional data derived from computer-tomography.Fil: Sánchez Villagra, Marcelo R.. Universitat Zurich; SuizaFil: Forasiepi, Analia Marta. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Provincia de Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Universidad Nacional de Cuyo. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales; Argentin

A new Megatheriinae skull (Xenarthra, Tardigrada) from the pliocene of northern venezuela – Implications for a giant sloth dispersal to central and North America

A skull of a ground sloth from the Pliocene San Gregorio Formation documents a northern neotropical occurrence of a megatheriine that addresses issues on intraspecific variation and biogeography. The new specimen is broadly similar in size and morphology to that of Proeremotherium eljebe from the underlying Codore Formation in the Urumaco Sequence, differing in several features such as a longer basicranial area and a more posteriorly projected basioccipital between the condyles. The living sloths species of Bradypus and Choloepus do not have unequivocal anatomical features that indicate sexual dimorphism. Nevertheless, fossil sloths may have shown such dimorphism, and speculations on this subject are part of the considerations that can be made when allocating fragmentary fossils (e.g., in the new skull the presence of a long sagittal crest could indicate a male individual and the absence of an extended crest in Proeremotherium eljebe a female one). We speculate that as early as the late middle Miocene, two main lines of Megatheriinae had clearly separated in two geographic areas, one in the rising Andean area and one at low latitudes on the lowlands of central and northern South America.Fil: Carlini, Alfredo Armando. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Departamento Científico de Paleontología de Vertebrados; ArgentinaFil: Brandoni, Diego. Provincia de Entre Ríos. Centro de Investigaciones Científicas y Transferencia de Tecnología a la Producción. Universidad Autónoma de Entre Ríos. Centro de Investigaciones Científicas y Transferencia de Tecnología a la Producción. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Centro de Investigaciones Científicas y Transferencia de Tecnología a la Producción; ArgentinaFil: Sánchez, Rodolfo. Museo Paleontológico de la Alcaldia de Urumaco; VenezuelaFil: Sánchez Villagra, Marcelo R.. Universitat Zurich; Suiz

In the spotlight—Established researcher

With whom and where did you study? My undergraduate study in Biology was at Universidad Simón Bolívar in Caracas. After a year of fieldwork and diverse laboratory experiences, I went for a PhD at Duke University, with a thesis on marsupial mammal cranial development and evolution. I had two coadvisors: Kathleen Smith (comparative ontogenetics) and Richard Kay (paleontological work). This was followed by my Habilitation under my mentor Wolfgang Maier in Tübingen (Germany), where I worked on diverse topics of mammalian ontogeny and learned to teach on the comparative anatomy of diverse Deuterostomia groups. During my job at the Natural History Museum in London, I learned about modularity from hosting Anjali Goswami as a postdoc; from many paleontologists there and in Zurich I was inspired to contribute to “developmental paleontology.” What got you interested in biology? When did you know EvoDevo was for you? I came to Biology with a fascination for exploring the natural world; evolution provided an explanation to my questions on origins. My first interest was in reconstructing evolutionary trees, and for that solving homology questions required the ontogenetic perspective. Exposure to EvoDevo ideas came from readings at graduate school at Duke on the neural crest, heterochrony, evolutionary novelties, and others—there I learned that EvoDevo was not just about Hox genes, and I became inspired by Pere Alberch's papers. I started to use the sequence heterochrony approach following the work of Kathleen Smith, Mike Richardson, and others, as this allowed me to examine developmental evolution with a comparative approach that did not require perfectly timed series and thus could be more inclusive in taxonomic sampling. When I learned about palaeohistology from my then postdoc Torsten Scheyer in Zurich, I realized that one could directly address matters of growth and life history in fossils, in addition to an approach based on phylogenetic bracket considerations. For my work on animal domestication, I saw the chance to bring a comparative ontogenetic perspective, and here the insights gained on neural crest development by detailed experimental studies in the work of Rich Schneider and others inform much of what we discussed about patterns of morphological diversification. What do you see as the major challenges of EvoDevo? I hope that EvoDevo embraces genuinely comparative ontogenetic research as a part of it, and that technological advances continue to contribute with discoveries but do not determine what can be funded or published, as EvoDevo remains a question-driven discipline as opposed to one driven by methods. Macroevolutionary questions that can be addressed only from a developmental perspective should continue to be part of a broad and pluralistic EvoDevo, as well as the explanation of phenotypic variation among populations within a species. I imagine that the examination of neglected groups of organisms or of organ systems will provide unanticipated insights on the amazing variation in developmental evolution. It will be a challenge for the EvoDevo community to be inclusive in that it can be practiced by people across the world given the differential access to resources. Maybe some of the research in Eco-EvoDevo will serve to better understand environmental issues faced by humanity, but I suspect it is more likely that EvoDevo will be more about satisfying human intellectual curiosity

Claude Lévi-Strauss as a humanist forerunner of cultural macroevolution studies

Cross-cultural studies of humans using methods developed in evolutionary biology and comparative linguistics are flourishing. ‘Cultural macroevolution’ has great potential to address fundamental questions of cultural transformation and human history. However, this field is poorly integrated with core cultural anthropology, although both aim in part at addressing similar issues. Claude Lévi-Strauss established a comparative approach searching for universals and documentation of diversity to bring understanding to cultural phenomena. Recognizing the nomothetic nature of Lévi-Strauss’ work, his abstraction and modelling, provides an example within anthropology of the search for universals and the study of big data, akin to cultural macroevolution studies. The latter could benefit, beyond the sophisticated analyses of big data mined from ethnographic work, from the integration with the intellectual legacy and practice of core anthropology and thus propitiate the synergistic interaction of disciplines. Attempts at rapprochement of disciplines from the natural sciences that lack pluralism and present a narrow view are deemed examples of ‘Wilson's effect’

Timing of organogenesis support basal position of turtles in the amniote tree of life

Background: The phylogenetic position of turtles is the most disputed aspect in the reconstruction of the land vertebrate tree of life. This controversy has arisen after many different kinds and revisions of investigations of molecular and morphological data. Three main hypotheses of living sister-groups of turtles have resulted from them: all reptiles, crocodiles + birds or squamates + tuatara. Although embryology has played a major role in morphological studies of vertebrate phylogeny, data on developmental timing have never been examined to explore and test the alternative phylogenetic hypotheses. We conducted a comprehensive study of published and new embryological data comprising 15 turtle and eight tetrapod species belonging to other taxa, integrating for the first time data on the side-necked turtle clade. Results: The timing of events in organogenesis of diverse character complexes in all body regions is not uniform across amniotes and can be analysed using a parsimony-based method. Changes in the relative timing of particular events diagnose many clades of amniotes and include a phylogenetic signal. A basal position of turtles to the living saurian clades is clearly supported by timing of organogenesis data. Conclusion: The clear signal of a basal position of turtles provided by heterochronic data implies significant convergence in either molecular, adult morphological or developmental timing characters, as only one of the alternative solutions to the phylogenetic conundrum can be right. The development of a standard reference series of embryological events in amniotes as presented here should enable future improvements and expansion of sampling and thus the examination of other hypotheses about phylogeny and patterns of the evolution of land vertebrate development

The Paleozoic and Mesozoic vertebrate record of Venezuela: An overview, summary of previous discoveries and report of a mosasaur from the La Luna Formation (Cretaceous)

Most reports of Paleozoic and Mesozoic vertebrates from Venezuela are anecdotical, with few detailed descriptions of mostly ‘fish' groups. Synapsids (e.g., mammals) are totally unknown, and dinosaurs are only reported from the La Quinta Formation. At least 14 formally recognized geological formations contain fossil vertebrates, most from the Central and Western parts of the country. In the Devonian there is a significant contrast between the vertebrates of Venezuela and Colombia and those of more southern parts of South America. Marine reptiles are present in a few localities in western Venezuela, and are very fragmentary, with one exception. A mosasaur from the Cretaceous La Luna Formation, reported here for the first time, is the most complete vertebrate (tetrapod) from the Cretaceous of Venezuela, and includes a partial skull and a few postcranial remain

Evolutionary and developmental aspects of phalangeal formula variation in pig-nose and soft-shelled turtles (Carettochelyidae and Trionychidae)

In order to examine the evolution of the phalangeal formula in a diverse clade of turtles, including hyperphalangy as a rare condition in this group, we studied 210 specimens representing all extant genera of Trionychidae and their sister taxon, Carettochelyidae. Both groups consist of highly aquatic species with elongated autopods that are either paddle-like (Trionychidae) or transformed to flippers (Carettochelyidae). Phalangeal formulae were obtained mostly by radiographs of alcohol-preserved or dry specimens, as well as by direct counts from skeletons. All trionychids and Carettochelys are pentadactylous, but their phalangeal formulae differ. Carettochelys exhibits the turtle-plesiomorphic state (manus and pes: 2-3-3-3-3), with no variation in adults. Trionychids exhibit intraspecific variation, ranging from 2-3-3-3-2 to 2-3-3-6-5 for the manus, and from 2-3-3-3-2 to 2-3-3-5-3 for the pes. The extant Carettochelys as well as the Middle Eocene Allaeochelys crassesculpta are characterized by an elongation of phalanges, whereas trionychids consistently have shorter phalanges. All trionychid genera exhibit some degree of hyperphalangy in digits IV and V, in both the manus and pes. Phalanges of the clawed digits I-III are very robust compared to phalanges of the non-clawed digits IV and V. The latter contribute significantly to the enlargement of the paddle by their additional phalanges. We hypothesize that this phalangeal pattern is coupled with prolongation of growth processes in the non-clawed digits. The differences in autopod morphology between carettochelyids and trionychids reflect different locomotor patterns related to different natural histories (elongated flippers for high-speed escape in the mainly herbivorous Carettochelys; broad paddles for rapid turns during hunting in the mainly carnivorous trionychids). The autopod of Pelodiscus sinensis is proposed as an experimental model to examine the developmental basis of adult autopod variatio

Why are There Fewer Marsupials than Placentals? On the Relevance of Geography and Physiology to Evolutionary Patterns of Mammalian Diversity and Disparity

Placental mammals occupy a larger morphospace and are taxonomically more diverse than marsupials by an order of magnitude, as shown by quantitative and phylogenetic studies of several character complexes and clades. Many have suggested that life history acts as a constraint on the evolution of marsupial morphology. However, the frequent circumvention of constraints suggests that the pattern of morphospace occupation in marsupials is more a reflection of lack of ecological opportunity than one of biases in the production of variants during development. Features of marsupial physiology are a potential source of biases in the evolution of the group; these could be coupled with past macroevolutionary patterns that followed conditions imposed by global temperature changes. This is evident at the K/Pg boundary and at the Eocene/Oligocene boundary. The geographic pattern of taxonomic and morphological diversity in placental clades mirrors that of extant placentals as a whole versus marsupials: placentals of northern origin are more diverse those of southern one and include the clades that are outliers in taxonomic (rodents and bats) and ecomorphological (whales and bats) richnes