Ecological Disparity Research Articles

The oldest semi-aquatic beaver in the world and a new hypothesis for the evolution of locomotion in Castoridae.

The North American rodent fossil record includes hundreds of species representing both an incredible taxonomic diversity and great ecological disparity. Although it is during the Oligocene that taxonomic diversity first peaks, it is not until the Miocene, almost 10 Myr later, that many ecologies, particularly locomotory ecologies, are recorded. Here, I present a new Oligocene-aged species of beaver from Montana, Microtheriomys articulaquaticus sp. nov., which represents the oldest semi-aquatic rodent in North America and the oldest amphibious beaver in the world, pushing the advent of semi-aquatic ecology in beavers by 7 Myr. I also provide morphological data supporting a terrestrial ecology for the sister taxon to Castoridae. Together with existing data, these findings lead to a new hypothesis for the evolutionary ecology of castorids whereby swimming was exapted from burrowing during the Oligocene. This evolution of semi-aquatic locomotion may have taken place in North America instead of Eurasia. It started in small beavers with gigantism achieved only much later. Indeed, body size evolution in castoroids follows a directional drift. Beavers obey Cope's rule, a selection for larger size over time that appears associated with semi-aquatic ecology and may well explain their low modern diversity.

Bridging macroecology and macroevolution in the radiation of sigmodontine rodents.

Investigations of phenotypic disparity across geography often ignore macroevolutionary processes. As a corollary, the random null expectations to which disparity is compared and interpreted may be unrealistic. We tackle this issue by representing, in geographical space, distinct processes of phenotypic evolution underlying ecological disparity. Under divergent natural selection, assemblages in a given region should have empirical disparity higher than expected under an evolutionarily oriented null model, whereas the opposite may indicate constraints on phenotypic evolution. We gathered phylogenies, biogeographic distributions, and data on the skull morphology of sigmodontine rodents to discover which regions of the Neotropics were more influenced by divergent, neutral, or constrained phenotypic evolution. We found that regions with higher disparity than expected by the evolutionary-oriented null model, in terms of both size and shape, were concentrated in the Atlantic Forest, suggesting a larger role for divergent natural selection there. Phenotypic disparity in the rest of South America, mainly the Amazon basin, northeastern Brazil, and Southern Andes, was constrained-lower than predicted by the evolutionary model. We also demonstrated equivalence between the disparity produced by randomization-based null models and constrained-evolution null models. Therefore, including evolutionary simulations into the null modeling framework used in ecophylogenetics can strengthen inferences on the processes underlying phenotypic evolution.

Subaqueous foraging among carnivorous dinosaurs

Secondary aquatic adaptations evolved independently more than 30 times from terrestrial vertebrate ancestors1,2. For decades, non-avian dinosaurs were believed to be an exception to this pattern. Only a few species have been hypothesized to be partly or predominantly aquatic3-11. However, these hypotheses remain controversial12,13, largely owing to the difficulty of identifying unambiguous anatomical adaptations for aquatic habits in extinct animals. Here we demonstrate that the relationship between bone density and aquatic ecologies across extant amniotes provides a reliable inference of aquatic habits in extinct species. We use this approach to evaluate the distribution of aquatic adaptations among non-avian dinosaurs. We find strong support for aquatic habits in spinosaurids, associated with a marked increase in bone density, which precedes the evolution of more conspicuous anatomical modifications, a pattern also observed in other aquatic reptiles and mammals14-16. Spinosaurids are revealed to be aquatic specialists with surprising ecological disparity, including subaqueous foraging behaviour in Spinosaurus and Baryonyx, and non-diving habits in Suchomimus. Adaptation to aquatic environments appeared in spinosaurids during the Early Cretaceous, following their divergence from other tetanuran theropods during the Early Jurassic17.

Morphology mirrors trophic niche in a freshwater amphipod community

Abstract Amphipod crustaceans are ubiquitous in temperate freshwaters, where they radiated multiple times in a broad range of habitats. This has led to significant morphological and ecological disparity. However, a limited knowledge of functional morphology and its relation to ecology has often led to the view that freshwater amphipods are omnivorous shredders. Herein, we hypothesise that trophic differentiation is related to functional morphology in a sympatric assemblage of three species belonging to three widespread families: Crangonyctidae, Gammaridae, and Niphargidae. We quantified seasonal diet composition by examining gut contents, and measured 42 functional morphological traits. Our results reveal a clear trophic and morphological differentiation among these sympatric species. The carnivorous Niphargus valachicus exhibited predatory traits exemplified by a smaller molar surface and stomach length, and larger/longer grasping, locomotory, and sensory appendages in comparison to the herbivorous Gammarus dacicus. The third species, Synurella ambulans, was omnivorous given its intermediate diet and morphology. We did not find consistent evidence for seasonal diet variation, except for the summer and winter diet of G. dacicus. The observed niches stretched along a broad trophic spectrum, indicating that even small riverine amphipod communities can exhibit significant functional disparity. The apparent connection between morphology and diet is similar to that observed in other crustaceans, strengthening our mechanistic understanding of the niche–morphology link. However, the generality of these conclusions needs to be tested on larger species datasets.

Patterns of skeletal integration in birds reveal that adaptation of element shapes enables coordinated evolution between anatomical modules.

Birds show tremendous ecological disparity in spite of strong biomechanical constraints imposed by flight. Modular skeletal evolution is generally accepted to have facilitated this, with distinct body regions showing semi-independent evolutionary trajectories. However, this hypothesis has received little scrutiny. We analyse evolutionary modularity and ecomorphology using three-dimensional data from across the entire skeleton in a phylogenetically broad sample of extant birds. We find strongly modular evolution of skeletal element sizes within body regions (head, trunk, forelimb and hindlimb). However, element shapes show substantially less modularity, have stronger relationships to ecology, and provide evidence that ecological adaptation involves coordinated evolution of elements across different body regions. This complicates the straightforward paradigm in which modular evolution facilitated the ecological diversification of birds. Our findings suggest the potential for undetected patterns of morphological evolution in even well-studied groups, and advance the understanding of the interface between evolutionary integration and ecomorphology.

A polyvalent and universal tool for genomic studies in gastropod molluscs (Heterobranchia)

Molluscs are the second most diverse animal phylum and heterobranch gastropods present ~ 44,000 species. These comprise fascinating creatures with huge morphological and ecological disparity. Such great diversity comes with even larger phylogenetic uncertainty and many taxa have been largely neglected in molecular assessments. Genomic tools have provided resolution to deep cladogenic events but generating large numbers of transcriptomes/genomes is expensive and usually requires fresh material. Here we leverage a target enrichment approach to design and synthesize a probe set based on available genomes and transcriptomes across Heterobranchia. Our probe set contains 57,606 70mer baits and targets a total of 2,259 ultra-conserved elements (UCEs). Post-sequencing capture efficiency was tested against 31 marine heterobranchs from major groups, including Acochlidia, Acteonoidea, Aplysiida, Cephalaspidea, Pleurobranchida, Pteropoda, Runcinida, Sacoglossa, and Umbraculida. The combined Trinity and Velvet assemblies recovered up to 2,211 UCEs in Tectipleura, up to 1,978 in Nudipleura, and up to 1,927 in Acteonoidea, the latter two being the most distantly related taxa to our core study group. Total alignment length was 525,599 bp and contained 52% informative sites and 21% missing data. Maximum-likelihood and Bayesian inference approaches recovered the monophyly of all orders tested as well as the larger clades Nudipleura, Panpulmonata, and Euopisthobranchia. The successful enrichment of diversely preserved material and DNA concentrations demonstrate the polyvalent nature of UCEs, and the universality of the probe set designed. We believe this probe set will enable multiple, interesting lines of research, that will benefit from an inexpensive and largely informative tool that will, additionally, benefit from the access to museum collections to gather genomic data.

Evolution of ecospace occupancy by Mesozoic marine tetrapods

AbstractEcology and morphology are different, and yet in comparative studies of fossil vertebrates the two are often conflated. The macroevolution of Mesozoic marine tetrapods has been explored in terms of morphological disparity, but less commonly using ecological‐functional categories. Here we use ecospace modelling to quantify ecological disparity across all Mesozoic marine tetrapods. We document the explosive radiation of marine tetrapod groups in the Triassic and their rapid attainment of high ecological disparity. Late Triassic extinctions led to a marked decline in ecological disparity, and the recovery of ecospace and ecological disparity was sluggish in the Early Jurassic. High levels of ecological disparity were again achieved by the Late Jurassic and maintained during the Cretaceous, when the ecospace became saturated by the Late Cretaceous. Sauropterygians, turtles and ichthyosauromorphs were the largest contributors to ecological disparity. Throughout the Mesozoic, we find that established groups remained ecologically conservative and did not explore occupied or vacant niches. Several parts of the ecospace remained vacant for long spans of time. Newly evolved, radiating taxa almost exclusively explored unoccupied ecospace, suggesting that abiotic releases are needed to empty niches and initiate diversification. In the balance of evolutionary drivers in Mesozoic marine tetrapods, abiotic factors were key to initiating diversification events, but biotic factors dominated the subsequent generation of ecological diversity.

Pycnodont fishes (Actinopterygii, Pycnodontiformes) from the Upper Cretaceous (lower Turonian) Akrabou Formation of Asfla, Morocco

The Upper Cretaceous (upper Cenomanian–middle Turonian) Akrabou Formation of Asfla, southeast Morocco is renowned for exceptionally preserved, often three-dimensional bony and cartilaginous fish fossils. Teleosts, rare holosteans and chondrichthyans are well known from the so-called ‘Goulmima ichthyological assemblage’, however pycnodonts (Actinopterygii, Pycnodontiformes) have received scant attention and remain undescribed until now. Five nominal species are recognised in the assemblage, including two new forms: Neomesturus asflaensis gen. et sp. nov. and Paranursallia cavini sp. nov. The Italian genus Polazzodus is reported in Morocco for the first time. Specimen taphonomy is examined in the context of substrate consistency and oxygenation of an outer shelf carbonate platform setting. Diversity and ecological disparity of the Goulmima assemblage is revised in regard to trophic partitioning with durophagy seemingly more diverse than previously recognised. Comparisons with other pycnodont-bearing horizons of similar age demonstrate strong faunal affinities between the Asfla pycnodonts and those in the western Tethys and South Atlantic.

Phylogeography of the ‘cosmopolitan’ orb-weaverArgiope trifasciata(Araneae: Araneidae)

AbstractFew spider species show truly cosmopolitan distributions. Among them is the banded garden spider Argiope trifasciata, which is reported from six continents across major climatic gradients and geographical boundaries. In orb-weaver spiders, such global distributions might be a result of lively dispersal via ballooning. However, wide distributions might also be artefactual, owing to our limited understanding of species taxonomy. To test the hypothesis that A. trifasciata might be a complex of cryptic species with more limited geographical ranges, we investigated the biogeographical structure and evolutionary history of A. trifasciata through a combination of time-calibrated phylogenetic analyses (57 terminals and three genes), ancestral range reconstruction and species delimitation methods. Our results strongly suggest that A. trifasciata as currently defined is not a single species. Its populations fall into five reciprocally monophyletic clades that are genetically distinct and have evolutionary origins in the Plio-Pleistocene. These clades are confined to East Asia, temperate Australia, Hawaii, the New World and the Old World (Africa and most of the Palaearctic). Our results provide the basis for future investigation of morphological and/or ecological disparity between the populations that are likely to represent species, in addition to examinations of the attributes and dispersal modes of these species.

Estimating urban greenness index using remote sensing data: A case study of an affluent vs poor suburbs in the city of Johannesburg

The importance of urban green space has over the years grown into an indispensable component of green infrastructure incorporated in urban planning and design as investment to promote the well-being of city dwellers. The continuous advancement in remote sensing spatial and spectral resolutions has made it possible to effectively map and evaluate urban green space for better management. The urban greenness index between the affluent suburb of Rosebank in the north and the poor Township of Soweto in the south, of Johannesburg city was assessed and compared to determine the environmental quality between the two areas. The total above ground biomass (AGB) of the two predominantly occurring street trees, Jacaranda mimosifolia and Platanus x acerifolia in Rosebank was estimated using existing allometric equations for the respective species. An equation was derived from the correlation of normalized difference vegetation index (NDVI) values extracted from SPOT 6 image and AGB of Rosebank. The same equation was then used to extrapolate and estimate the AGB of Soweto. The results showed that Rosebank had the lowest total AGB of approximately 113,179 ton, while that of Soweto was approximately 504,400 ton. However, the greenness index of Rosebank (83%) was greater than in Soweto (14%), indicating a pattern of ecological disparity between the two areas. These findings could be useful for designing a sound urban planning and policy formulation for the city of Johannesburg.

A re-evaluation of the Chaetothyriales using criteria of comparative biology

Chaetothyriales is an ascomycetous order within Eurotiomycetes. The order is particularly known through the black yeasts and filamentous relatives that cause opportunistic infections in humans. All species in the order are consistently melanized. Ecology and habitats of species are highly diverse, and often rather extreme in terms of exposition and toxicity. Families are defined on the basis of evolutionary history, which is reconstructed by time of divergence and concepts of comparative biology using stochastical character mapping and a multi-rate Brownian motion model to reconstruct ecological ancestral character states. Ancestry is hypothesized to be with a rock-inhabiting life style. Ecological disparity increased significantly in late Jurassic, probably due to expansion of cytochromes followed by colonization of vacant ecospaces. Dramatic diversification took place subsequently, but at a low level of innovation resulting in strong niche conservatism for extant taxa. Families are ecologically different in degrees of specialization. One of the clades has adapted ant domatia, which are rich in hydrocarbons. In derived families, similar processes have enabled survival in domesticated environments rich in creosote and toxic hydrocarbons, and this ability might also explain the pronounced infectious ability of vertebrate hosts observed in these families. Conventional systems of morphological classification poorly correspond with recent phylogenetic data. Species are hypothesized to have low competitive ability against neighboring microbes, which interferes with their laboratory isolation on routine media. The dataset is unbalanced in that a large part of the extant biodiversity has not been analyzed by molecular methods, novel taxonomic entities being introduced at a regular pace. Our study comprises all available species sequenced to date for LSU and ITS, and a nomenclatural overview is provided. A limited number of species could not be assigned to any extant family.

Reconstructing the archosaur radiation using a Middle Triassic archosauriform tooth assemblage from Tanzania.

Following the Permo–Triassic mass extinction, Archosauriformes—the clade that includes crocodylians, birds, and their extinct relatives outside crown Archosauria—rapidly diversified into many distinct lineages, became distributed globally, and, by the Late Triassic, filled a wide array of resource zones. Current scenarios of archosauriform evolution are ambiguous with respect to whether their taxonomic diversification in the Early–Middle Triassic coincided with the initial evolution of dietary specializations that were present by the Late Triassic or if their ecological disparity arose sometime after lineage diversification. Late Triassic archosauriform dietary specialization is recorded by morphological divergence from the plesiomorphic archosauriform tooth condition (laterally-compressed crowns with serrated carinae and a generally triangular lateral profile). Unfortunately, the roots of this diversification are poorly documented, with few known Early­–Middle Triassic tooth assemblages, limiting characterizations of morphological diversity during this critical, early period in archosaur evolution. Recent fieldwork (2007–2017) in the Middle Triassic Manda Beds of the Ruhuhu Basin, Tanzania, recovered a tooth assemblage that provides a window into this poorly sampled interval. To investigate the taxonomic composition of that collection, we built a dataset of continuous quantitative and discrete morphological characters based on in situ teeth of known taxonomic status (e.g., Nundasuchus, Parringtonia: N = 65) and a sample of isolated teeth (N = 31). Using crown heights from known taxa to predict tooth base ratio (= base length/width), we created a quantitative morphospace for the tooth assemblage. The majority of isolated, unassigned teeth fall within a region of morphospace shared by several taxa from the Manda Beds (e.g., Nundasuchus, Parringtonia); two isolated teeth fall exclusively within a “Pallisteria” morphospace. A non-metric multidimensional scaling ordination (N = 67) of 11 binary characters reduced overlap between species. The majority of the isolated teeth from the Manda assemblage fall within the Nundasuchus morphospace. This indicates these teeth are plesiomorphic for archosauriforms as Nundasuchus exhibits the predicted plesiomorphic condition of archosauriform teeth. Our model shows that the conservative tooth morphologies of archosauriforms can be differentiated and assigned to species and/or genus, rendering the model useful for identifying isolated teeth. The large overlap in tooth shape among the species present and their overall similarity indicates that dietary specialization lagged behind species diversification in archosauriforms from the Manda Beds, a pattern predicted by Simpson’s “adaptive zones” model. Although applied to a single geographic region, our methods offer a promising means to reconstruct ecological radiations and are readily transferable across a broad range of vertebrate taxa throughout Earth history.

A possible case of inverted lifestyle in a new bivalved arthropod from the Burgess Shale.

The origin of the arthropod carapace, an enlargement of cephalic tergites, can be traced back to the Cambrian period. However, its disparity and evolution are still not fully understood. Here, we describe a new ‘bivalved’ arthropod, Fibulacaris nereidis gen. et sp. nov., based on 102 specimens from the middle Cambrian (Wuliuan Stage) Burgess Shale, Marble Canyon area in British Columbia's Kootenay National Park, Canada. The laterally compressed carapace covers most of the body. It is fused dorsally and merges anteriorly into a conspicuous postero-ventrally recurved rostrum as long as the carapace and positioned between a pair of backwards-facing pedunculate eyes. The body is homonomous, with approximately 40 weakly sclerotized segments bearing biramous legs with elongate endopods, and ends in a pair of small flap-like caudal rami. Fibulacaris nereidis is interpreted as a suspension feeder possibly swimming inverted, in a potential case of convergence with some branchiopods. A Bayesian phylogenetic analysis places it within a group closely related to the extinct Hymenocarina. Fibulacaris nereidis is unique in its carapace morphology and overall widens the ecological disparity of Cambrian arthropods and suggests that the evolution of a ‘bivalved' carapace and an upside-down lifestyle may have occurred early in stem-group crustaceans.

The pre-Pleistocene fossil thylacinids (Dasyuromorphia: Thylacinidae) and the evolutionary context of the modern thylacine.

The thylacine is popularly used as a classic example of convergent evolution between placental and marsupial mammals. Despite having a fossil history spanning over 20 million years and known since the 1960s, the thylacine is often presented in both scientific literature and popular culture as an evolutionary singleton unique in its morphological and ecological adaptations within the Australian ecosystem. Here, we synthesise and critically evaluate the current state of published knowledge regarding the known fossil record of Thylacinidae prior to the appearance of the modern species. We also present phylogenetic analyses and body mass estimates of the thylacinids to reveal trends in the evolution of hypercarnivory and ecological shifts within the family. We find support that Mutpuracinus archibaldi occupies an uncertain position outside of Thylacinidae, and consider Nimbacinus richi to likely be synonymous with N. dicksoni. The Thylacinidae were small-bodied (< ~8 kg) unspecialised faunivores until after the ~15–14 Ma middle Miocene climatic transition (MMCT). After the MMCT they dramatically increase in size and develop adaptations to a hypercarnivorous diet, potentially in response to the aridification of the Australian environment and the concomitant radiation of dasyurids. This fossil history of the thylacinids provides a foundation for understanding the ecology of the modern thylacine. It provides a framework for future studies of the evolution of hypercarnivory, cursoriality, morphological and ecological disparity, and convergence within mammalian carnivores.

Assembly of modern mammal community structure driven by Late Cretaceous dental evolution, rise of flowering plants, and dinosaur demise

The long-standing view that Mesozoic mammaliaforms living in dinosaur-dominated ecosystems were ecologically constrained to small size and insectivory has been challenged by astonishing fossil discoveries over the last three decades. By studying these well-preserved early mammaliaform specimens, paleontologists now agree that mammaliaforms underwent ecomorphological diversification during the Mesozoic Era. This implies that Mesozoic mammaliaform communities had ecological structure and breadth that were comparable to today's small-bodied mammalian communities. However, this hypothesis remains untested in part because the primary focus of most studies is on individual taxa. Here, we present a study quantifying the ecological structure of Mesozoic mammaliaform communities with the aim of identifying evolutionary and ecological drivers that influenced the deep-time assembly of small-bodied mammaliaform communities. We used body size, dietary preference, and locomotor mode to establish the ecospace occupation of 98 extant, small-bodied mammalian communities from diverse biomes around the world. We calculated ecological disparity and ecological richness to measure the magnitude of ecological differences among species in a community and the number of different eco-cells occupied by species of a community, respectively. This modern dataset served as a reference for analyzing five exceptionally preserved, extinct mammaliaform communities (two Jurassic, two Cretaceous, one Eocene) from Konservat-Lagerstätten. Our results indicate that the interplay of at least three factors, namely the evolution of the tribosphenic molar, the ecological rise of angiosperms, and potential competition with other vertebrates, may have been critical in shaping the ecological structure of small-bodied mammaliaform communities through time.

Siphonariid development: Quintessential euthyneuran larva with a mantle fold innovation (Gastropoda; Panpulmonata).

Recent phylogenetic revisions of euthyneuran gastropods ("opisthobranchs" and "pulmonates") suggest that clades with a planktotrophic larva, the ancestral life history for euthyneurans, are more widely distributed along the trunk of the euthyneuran tree than previously realized. There is some indication that the planktotrophic larva of euthyneurans has distinctive features, but information to date has come mainly from traditional "opisthobranch" groups. Much less is known about planktotrophic "pulmonate" larvae. If planktotrophic larvae of "pulmonates" share unique traits with those of "opisthobranchs," then a distinctive euthyneuran larval-type has been the developmental starting template for a spectacular amount of evolved morphological and ecological disparity among adult euthyneurans. We studied development of a siphonariid by preparing sections of larval and postmetamorphic stages for histological and ultrastructural analysis, together with 3D reconstructions and data from immunolabeling of the larval apical sensory organ. We also sought a developmental explanation for the unusual arrangement of shell-attached, dorso-ventral muscles relative to the mantle cavity of adult siphonariids. Adult siphonariids ("false limpets") have a patelliform shell but their C-shaped shell muscle partially embraces a central mantle cavity, which is different from the arrangement of these components in patellogastropods ("true limpets"). It is not obvious how shell muscles extending into the foot become placed anterior to the mantle cavity during siphonariid development from a veliger larva. We found that planktotrophic larvae of Siphonaria denticulata are extremely similar to previously described, planktotrophic "opisthobranch" larvae. To emphasize this point, we update a list of distinctive characteristics of planktotrophic euthyneuran larvae, which can anchor future studies on the impressive evolvability of this larval-type. We also describe how premetamorphic and postmetamorphic morphogenesis of larval mantle fold tissue creates the unusual arrangement of shell-muscles and mantle cavity in siphonariids. This result adds to the known postmetamorphic evolutionary innovations involving mantle fold tissue among euthyneurans.

New highly pachyostotic nothosauroid interpreted as a filter-feeding Triassic marine reptile.

Two well-preserved specimens of a new eosauropterygian from the Upper Triassic of Central Spain are attributed to a new taxon, Paludidraco multidentatus gen. et sp. nov. It is a member of Simosauridae that presents several exclusive characters suggesting a highly specialized trophic adaptation. This discovery increases the already high ecological disparity of the Triassic marine reptiles.

Fuzzy ecospace modelling

Abstract Quantitative ecospace models are a numerical approach to comparing the functional structure of different ecosystems on macroevolutionary time‐scales, by quantifying the distribution of functional ecological traits. Ecospace modelling has historically been restricted to a combination of visual interpretation and quantification via metrics such as mean sum of ranges. We argue that comparing ecosystem function in this way overlooks critical information about degrees of overlap and redundancy, and potentially misrepresents the role of “empty ecospace” in driving macroevolution. Fuzzy ecospace modelling (FEM) places conventional ecospace modelling within a fuzzy set‐theoretic framework, wherein functional groups are learned from the dataset, creating models which are sensitive to overlap and the role of empty ecospace. Fuzzy ecospace modelling is a machine learning program which quantifies functional ecological similarity, and uses this information to classify new taxa. It creates functional groups using a Gower dissimilarity coefficient‐based approach to the k‐medoids algorithm, and uses fuzzy discriminant analysis to classify the taxa present in another ecosystem into these clusters, based on minimal Gower dissimilarity with a fuzzy threshold. This has the effect of quantifying the similarity between these ecosystems in terms of their functional groups, accounting for total redundancy, partial redundancy/novelty and total novelty. By using fuzzy membership functions, FEM can classify taxa which are highly ecologically dissimilar (outliers with respect to all functional groups), taxa which are fully redundant (100% similarity to those in a given functional group) and taxa in‐between, which represent degrees of niche overlap. This can be used to compare the functional groups present in different ecosystems (as well as their degrees of overlap), and as a metric approach to comparing total ecological disparity. These results can be used to test models of the role of empty ecospace in macroevolutionary trends, or to investigate how ecosystems respond to global perturbations. Furthermore, it allows us to define numerically the concept of empty ecospace for n‐dimensional datasets. A cluster‐based approach to the quantification of ecospace allows for a numerical estimate of niche overlap, a value particularly difficult to quantify in fossil contexts.

Ecological disparity is more susceptible to environmental changes than familial taxonomic richness during the Cretaceous in the Alpstein region (northeastern Switzerland)

Studies of global palaeoecology through time usually ignore regional details. Such regional studies on palaeoecology are required to better understand both regional- and global-scale palaeoecolgical changes. We analyzed the palaeoecolgy of a Cretaceous sedimentary sequence in the Alpstein (cantons of Appenzell Ausserrhoden, Appenzell Innerrhoden and St. Gallen, northeastern Switzerland), which covers from the Barremian to Cenomanian stage. Two diversity indices of familial taxonomic richness and ecological disparity (ecospace occupation) with the trophic nucleus concept were employed in order to document changes in palaeocommunities through time. Our results illustrate that taxonomic richness did not change dramatically, while distinct changes occurred in ecospace occupation through time. The changes in ecospace utilization likely root in fluctuations in water depth and ocean temperature. In addition to these changes in sea level and temperature, our results suggest that water depth was higher in the eastern part of the Alpstein region. Ecospace occupation was moderately diverse through time, which is likely linked with the favorable conditions such as moderate water depth, which made the region habitable for a range of organisms. Only during the late Barremian, the sea was maybe too shallow, thus preventing highly diverse associations. Statistical tests indicate that the chronological changes of familial taxonomic richness and ecological disparity are decoupled and that the ecological disparity is more highly variable in response to environmental changes than familial taxonomic richness.

A new odontocete (toothed cetacean) from the Early Miocene of Peru expands the morphological disparity of extinct heterodont dolphins

A key step in the evolutionary history of Odontoceti (echolocating toothed cetaceans) is the transition from the ancestral heterodont condition – characterized by the presence of double-rooted cheek teeth bearing accessory denticles – to the homodont dentition displayed by most extant odontocete species. During the last few decades, new finds and the reassessment of specimens in collections revealed an increased morphological disparity amongst the Oligo–Miocene heterodont odontocetes. Based on a partly articulated skeleton from late Early Miocene (Burdigalian, 18.8–18.0 Ma) beds of the Chilcatay Formation (Pisco Basin, Peru), we describe a new genus and species of heterodont odontocete, Inticetus vertizi, in the new family Inticetidae. This large dolphin is characterized by, amongst other things, a long and robust rostrum bearing at least 18 teeth per quadrant; the absence of procumbent anterior teeth; many large, broad-based accessory denticles in double-rooted posterior cheek teeth; a reduced ornament of dental crowns; the styliform process of the jugal being markedly robust; a large fovea epitubaria on the periotic, with a correspondingly voluminous accessory ossicle of the tympanic bulla; and a shortened tuberculum of the malleus. Phylogenetic analyses (with and without molecular constraint; with and without down-weighting of homoplastic characters) yielded contrasting results, with Inticetus falling either as a stem Odontoceti or as an early branching member of a large Platanistoidea clade. With its large size, robust rostrum and unusual dental morphology, and the absence of conspicuous tooth wear, Inticetus increases the morphological and ecological disparity of Late Oligocene–Early Miocene heterodont odontocetes. Finally, this new taxon calls for caution when attempting to identify isolated cetacean cheek teeth, even at the suborder level.http://zoobank.org/urn:lsid:zoobank.org:pub:5B306B49-EB1B-42F9-B755-B0B05B4F938F