The placement of the head that minimizes online memory: a complex systems approach

It is well known that the length of a syntactic dependency determines its online memory cost. Thus, the problem of the placement of a head and its dependents (complements or modifiers) that minimizes online memory is equivalent to the problem of the minimum linear arrangement of a star tree. However, how that length is translated into cognitive cost is not known. This study shows that the online memory cost is minimized when the head is placed at the center, regardless of the function that transforms length into cost, provided only that this function is strictly monotonically increasing. Online memory defines a quasi-convex adaptive landscape with a single central minimum if the number of elements is odd and two central minima if that number is even. We discuss various aspects of the dynamics of word order of subject (S), verb (V) and object (O) from a complex systems perspective and suggest that word orders tend to evolve by swapping adjacent constituents from an initial or early SOV configuration that is attracted towards a central word order by online memory minimization. We also suggest that the stability of SVO is due to at least two factors, the quasi-convex shape of the adaptive landscape in the online memory dimension and online memory adaptations that avoid regression to SOV. Although OVS is also optimal for placing the verb at the center, its low frequency is explained by its long distance to the seminal SOV in the permutation space.Comment: Minor changes (language improved; typos in Eqs. 5, 6 and 13 corrected

Polyhedral Surface Approximation of Non-Convex Voxel Sets and Improvements to the Convex Hull Computing Method

In this paper we introduce an algorithm for the creation of polyhedral approximations for objects represented as strongly connected sets of voxels in three-dimensional binary images. The algorithm generates the convex hull of a given object and modifies the hull afterwards by recursive repetitions of generating convex hulls of subsets of the given voxel set or subsets of the background voxels. The result of this method is a polyhedron which separates object voxels from background voxels. The objects processed by this algorithm and also the background voxel components inside the convex hull of the objects are restricted to have genus 0. The second aim of this paper is to present some improvements to our convex hull algorithm to reduce computation time

Minimizing Unsatisfaction in Colourful Neighbourhoods

Colouring sparse graphs under various restrictions is a theoretical problem of significant practical relevance. Here we consider the problem of maximizing the number of different colours available at the nodes and their neighbourhoods, given a predetermined number of colours. In the analytical framework of a tree approximation, carried out at both zero and finite temperatures, solutions obtained by population dynamics give rise to estimates of the threshold connectivity for the incomplete to complete transition, which are consistent with those of existing algorithms. The nature of the transition as well as the validity of the tree approximation are investigated.Comment: 28 pages, 12 figures, substantially revised with additional explanatio

Reevaluation of species concepts of uppermost cretaceous unionidae (mollusca: bivalvia) : Hell Creek formation, Montana, U.S.A.

Species are the basic units of life relative to taxonomy, and a practical definition of species is imperative to paleontology in order to promote reproducible, unambiguous criteria for accurately interpreting past species relationships. The need for a well-defined rubric for identifying species is evident in the freshwater mussel assemblage (Family Unionidae) in the Hell Creek Formation. The Hell Creek Formation unionid species were first described by Whitfield in 1903 and 1907. His descriptions were often based on differences of a single trait. In 197 6, Russell reevaluated the original species descriptions, I but still based the classification of species on only a few qualitative morphologic differences. These previous species diagnoses did not incorporate phenetics (based on morphologic similarity) or cladistics (based on evolutionary relationships). As a result, the assignment of morphologically similar specimens to previously defined species is sometimes problematic. Additionally, without more knowledge, certain species may not clearly be considered distinct. The goal of this study is to reevaluate four sister species sets in order to assess their validity as species using an analytical approach instead of relying on the traditional qualitative approach. Species diagnosis on the basis of a single trait or very few traits, as employed in the previous species descriptions, is not likely adequate to support the classification as distinct species or to show the relationships among species. To test the validity of species in the Hell Creek Formation, an extensive database of quantitative and qualitative character traits was constructed to be applied to various quantitative models. The morphological distinction of each species was ascertained by using discriminant and cluster analyses. The species distinction based on evolutionary relationships was also tested using cladistic methods. Comparing morphologic differences without quantitative analysis, all eight species display significant morphologic differences, implying that they are discrete species. Discriminant analysis distinguished all eight species on the basis of quantitative traits; however, many sister species were indistinguishable solely on the basis of qualitative traits. Cluster analysis displayed apparent structure in the dendrogram that loosely applied to eight distinct species, but in some cases, there was substantial intermixing of specimens otherwise assigned to the recognized species observed in the clusters. Cladistics displayed minimal resolution in the phylogenetic relationships between species and was not able to distinguish between sisters species on the basis of the criteria given. The results herein suggest that each species is distinct on the basis of their morphology as shown by species comparison with and without quantitative models. Interpretation of the evolutionary relationships among the species shows that each sister species set is closely related, but within the sister sets, the species are phylogenetically indistinguishable

Using Phylogenetic Analysis To Diagnose Freshwater Molluscan Species In The Judith River Formation Of Hill And Fergus Counties, Montana, With Notes On Depositional Environments And Quality Of Preservation

The Judith River Formation has a long history of study, from Meek and Hayden’s expeditions in the 1850s to E. D. Cope’s searches for new dinosaur species. More recently, the Judith River Formation receives a plethora of research in paleontology and geology. Despite this, little work has been done on the freshwater molluscan fauna found within. The purpose of this study was to create a method where accurate species diagnoses become possible, and to create a launching point for future work in the Judith River Formation. Freshwater mollusk specimens were collected from shell beds in the Judith River Formation at the type area in the Missouri River Breaks (Fergus County), and near Rudyard, Montana (Hill County). Specimens were then separated by general morphology and measured for select character traits (e.g. convexity of whorls). Photos of Judith River Formation type specimens were taken at the National Museum of Natural History at the Smithsonian Institution and subsequently measured for the same character traits. A table was created which listed possible character traits for the freshwater mollusk types and each possible outcome was given a code (e.g. 0, 1, 2) for analysis. Then using trait codes assigned to each type species and comparing them to trait codes assigned to collected specimens, species identifications were made. This methodology allows for a more quantitative method of species diagnoses. Accomplishing this is essential to additional cladistical work in the Judith River Formation as better material becomes available. Depositional environment of localities sampled was derived from autecological and lithologic data. This will be beneficial to both paleontologists and geologists for future work in the Judith River Formatio

A new small-bodied azhdarchoid pterosaur from the Lower Cretaceous of England and its implications for pterosaur anatomy, diversity and phylogeny

BACKGROUND: Pterosaurs have been known from the Cretaceous sediments of the Isle of Wight (southern England, United Kingdom) since 1870. We describe the three-dimensional pelvic girdle and associated vertebrae of a small near-adult pterodactyloid from the Atherfield Clay Formation (lower Aptian, Lower Cretaceous). Despite acknowledged variation in the pterosaur pelvis, previous studies have not adequately sampled or incorporated pelvic characters into phylogenetic analyses. METHODOLOGY/PRINCIPAL FINDINGS: The new specimen represents the new taxon Vectidraco daisymorrisae gen. et sp. nov., diagnosed by the presence of a concavity posterodorsal to the acetabulum and the form of its postacetabular process on the ilium. Several characters suggest that Vectidraco belongs to Azhdarchoidea. We constructed a pelvis-only phylogenetic analysis to test whether the pterosaur pelvis carries a useful phylogenetic signal. Resolution in recovered trees was poor, but they approximately matched trees recovered from analyses of total evidence. We also added Vectidraco and our pelvic characters to an existing total-evidence matrix for pterosaurs. Both analyses recovered Vectidraco within Azhdarchoidea. CONCLUSIONS/ SIGNIFICANCE: The Lower Cretaceous strata of western Europe have yielded members of several pterosaur lineages, but Aptian pterosaurs from western Europe are rare. With a pelvis length of 40 mm, the new animal would have had a total length of c. 350 mm, and a wingspan of c. 750 mm. Barremian and Aptian pterodactyloids from western Europe show that small-bodied azhdarchoids lived alongside ornithocheirids and istiodactylids. This assemblage is similar in terms of which lineages are represented to the coeval beds of Liaoning, China; however, the number of species and specimens present at Liaoning is much higher. While the general phylogenetic composition of western European and Chinese communities appear to have been approximately similar, the differences may be due to different palaeoenvironmental and depositional settings. The western Europe pterodactyloid record may therefore be artificially low in diversity due to preservational factors

Interspecific variation in the limb long bones among modern rhinoceroses—extent and drivers

International audienceAmong amniotes, numerous lineages are subject to an evolutionary trend toward body mass and size increases. Large terrestrial species may face important constraints linked to weight bearing, and the limb segments are particularly affected by such constraints due to their role in body support and locomotion. Such groups showing important limb modifications related to high body mass have been called "graviportal." Often considered graviportal, rhinoceroses are among the heaviest terrestrial mammals and are thus of particular interest to understand the limb modifications related to body mass and size increase. Here, we present a morphofunctional study of the shape variation of the limb long bones among the five living rhinos to understand how the shape may vary between these species in relation with body size, body mass and phylogeny. We used three dimensional geometric morphometrics and comparative analyses to quantify the shape variation. Our results indicate that the five species display important morphological differences depending on the considered bones. The humerus and the femur exhibit noticeable interspecific differences between African and Asiatic rhinos, associated with a significant effect of body mass. The radius and ulna are more strongly correlated with body mass. While the tibia exhibits shape variation both linked with phylogeny and body mass, the fibula displays the greatest intraspecific variation. We highlight three distinct morphotypes of bone shape, which appear in accordance with the phylogeny. The influence of body mass also appears unequally expressed on the different bones. Body mass increase among the five extant species is marked by an increase of the general robustness, more pronounced attachments for muscles and a development of medial parts of the bones. Our study underlines that the morphological features linked to body mass increase are not similar between rhinos and other heavy mammals such as elephants and hippos, suggesting that the weight bearing constraint can lead to different morphological responses

The Comparative Osteology of the Petrotympanic Complex (Ear Region) of Extant Baleen Whales (Cetacea: Mysticeti)

Anatomical comparisons of the ear region of baleen whales (Mysticeti) are provided through detailed osteological descriptions and high-resolution photographs of the petrotympanic complex (tympanic bulla and petrosal bone) of all extant species of mysticete cetaceans. Salient morphological features are illustrated and identified, including overall shape of the bulla, size of the conical process of the bulla, morphology of the promontorium, and the size and shape of the anterior process of the petrosal. We place our comparative osteological observations into a phylogenetic context in order to initiate an exploration into petrotympanic evolution within Mysticeti.The morphology of the petrotympanic complex is diagnostic for individual species of baleen whale (e.g., sigmoid and conical processes positioned at midline of bulla in Balaenoptera musculus; confluence of fenestra cochleae and perilymphatic foramen in Eschrichtius robustus), and several mysticete clades are united by derived characteristics. Balaenids and neobalaenids share derived features of the bulla, such as a rhomboid shape and a reduced anterior lobe (swelling) in ventral aspect, and eschrichtiids share derived morphologies of the petrosal with balaenopterids, including loss of a medial promontory groove and dorsomedial elongation of the promontorium. Monophyly of Balaenoidea (Balaenidae and Neobalaenidae) and Balaenopteroidea (Balaenopteridae and Eschrichtiidae) was recovered in phylogenetic analyses utilizing data exclusively from the petrotympanic complex.This study fills a major gap in our knowledge of the complex structures of the mysticete petrotympanic complex, which is an important anatomical region for the interpretation of the evolutionary history of mammals. In addition, we introduce a novel body of phylogenetically informative characters from the ear region of mysticetes. Our detailed anatomical descriptions, illustrations, and comparisons provide valuable data for current and future studies on the phylogenetic relationships, evolution, and auditory physiology of mysticetes and other cetaceans throughout Earth's history