Earliest evidence for fruit consumption and potential seed dispersal by birds

Chicago Archaeopteryx informs on the early evolution of the avian bauplan

Here we report on the nearly complete and uncrushed 14th specimen of Archaeopteryx. Exceptional preservation and preparation guided by micro-computed tomographic data make this one of the best exemplars of this iconic taxon, preserving important data regarding skeletal transformation and plumage evolution in relation to the acquisition of flight during early avian evolution. The ventrolaterally exposed skull reveals a palatal morphology intermediate between troodontids1 and crownward Cretaceous birds2,3. Modifications of the skull reflect the shift towards a less rigid cranial architecture in archaeopterygids from non-avian theropods. The complete vertebral column reveals paired proatlases and a tail longer than previously recognized. Skin traces on the right major digit of the hand suggest that the minor digit was free and mobile distally, contrary to previous interpretations4. The morphology of the foot pads indicates that they were adapted for non-raptorial terrestrial locomotion. Specialized inner secondary feathers called tertials5,6 are observed on both wings. Humeral tertials are absent in non-avian dinosaurs closely related to birds, suggesting that these feathers evolved for flight, creating a continuous aerodynamic surface. These new findings clarify the mosaic of traits present in Archaeopteryx, refine ecological predictions and elucidate the unique evolutionary history of the Archaeopterygidae, providing clues regarding the ancestral avian condition.

Common developmental origins of beak shapes and evolution in theropods

Vertebrate beaks show a remarkable diversity of forms, epitomized by birds and non-avian theropods. Few studies have investigated how underlying developmental processes influence beak shape. The power cascade is a model of growth describing the log-log linear relationship of the beak radius with distance from the tip. We measured beak and toothed snout shapes in 127 species across 120 families of extant birds and extinct non-avian theropods and found that 95% followed the power cascade model. Ancestral state estimation suggests that the power cascade constitutes a fundamental growth pattern of the theropod rostrum, and perhaps all vertebrate rostra. The morphospace defined by the power cascade shows how bird beak shape explores the geometries associated with ecological specializations while adhering to the growth model. We show that the power cascade influences the macroevolutionary exploration of rostrum morphospace, enabling extant birds to inhabit all components of Earth's biosphere.

Direct evidence of frugivory in the Mesozoic bird Longipteryx contradicts morphological proxies for diet

Diet is one of the most important aspects of an animal's ecology, as it reflects direct interactions with other organisms and shapes morphology, behavior, and other life history traits. Modern birds (Neornithes) have a highly efficient and phenotypically plastic digestive system, allowing them to utilize diverse trophic resources, and digestive function has been put forth as a factor in the selectivity of the end-Cretaceous mass extinction, in which only neornithine dinosaurs survived.1 Although diet is directly documented in several early-diverging avian lineages,2 only a single specimen preserves evidence of diet in Enantiornithes, the dominant group of terrestrial Cretaceous birds.3 Morphology-based predictions suggest enantiornithines were faunivores,4,5,6 although the absence of evidence contrasts with the high preservation potential and relatively longer gut-retention times of these diets. Longipteryx is an unusual Early Cretaceous enantiornithine with an elongate rostrum; distally restricted dentition7; large, recurved, and crenulated teeth8; and tooth enamel much thicker than other paravians.9 Statistical analysis of rostral length, body size, and tooth morphology predicts Longipteryx was primarily insectivorous.4,5 Contrasting with these results, two new specimens of Longipteryx preserve gymnosperm seeds within the abdominal cavity interpreted as ingesta. Like Jeholornis, their unmacerated preservation and the absence of gastroliths indicate frugivory.10 As in Neornithes,11 complex diets driven by the elevated energetic demands imposed by flight, secondary rostral functions, and phylogenetic influence impede the use of morphological proxies to predict diet in early-diverging avian lineages.

Synthetic analysis of trophic diversity and evolution in Enantiornithes with new insights from Bohaiornithidae

Enantiornithines were the dominant birds of the Mesozoic, but understanding of their diet is still tenuous. We introduce new data on the enantiornithine family Bohaiornithidae, famous for their large size and powerfully built teeth and claws. In tandem with previously published data, we comment on the breadth of enantiornithine ecology and potential patterns in which it evolved. Body mass, jaw mechanical advantage, finite element analysis of the jaw, and traditional morphometrics of the claws and skull are compared between bohaiornithids and living birds. We find bohaiornithids to be more ecologically diverse than any other enantiornithine family: Bohaiornis and Parabohaiornis are similar to living plant-eating birds; Longusunguis resembles raptorial carnivores; Zhouornis is similar to both fruit-eating birds and generalist feeders; and Shenqiornis and Sulcavis plausibly ate fish, plants, or a mix of both. We predict the ancestral enantiornithine bird to have been a generalist which ate a wide variety of foods. However, more quantitative data from across the enantiornithine tree is needed to refine this prediction. By the Early Cretaceous, enantiornithine birds had diversified into a variety of ecological niches like crown birds after the K-Pg extinction, adding to the evidence that traits unique to crown birds cannot completely explain their ecological success.

Patterns of variation in fleshy diaspore size and abundance from Late Triassic-Oligocene

Vertebrate-mediated seed dispersal is a common attribute of many living plants, and variation in the size and abundance of fleshy diaspores is influenced by regional climate and by the nature of vertebrate seed dispersers among present-day floras. However, potential drivers of large-scale variation in the abundance and size distributions of fleshy diaspores through geological time, and the importance of geographic variation, are incompletely known. This knowledge gap is important because fleshy diaspores are a key mechanism of energy transfer from photosynthesis to animals and may in part explain the diversification of major groups within birds and mammals. Various hypotheses have been proposed to explain variation in the abundance and size distribution of fleshy diaspores through time, including plant-frugivore co-evolution, angiosperm diversification, and changes in vegetational structure and climate. We present a new data set of more than 800 georeferenced fossil diaspore occurrences spanning the Triassic-Oligocene, across low to mid- to high palaeolatitudes. We use this to quantify patterns of long-term change in fleshy diaspores, examining the timing and geographical context of important shifts as a test of the potential evolutionary and climatic explanations. We find that the fleshy fruit sizes of angiosperms increased for much of the Cretaceous, during the early diversification of angiosperms from herbaceous ancestors with small fruits. Nevertheless, this did not cause a substantial net change in the fleshy diaspore size distributions across seed plants, because gymnosperms had achieved a similar size distribution by at least the Late Triassic. Furthermore, gymnosperm-dominated Mesozoic ecosystems were mostly open, and harboured low proportions of specialised frugivores until the latest Cretaceous, suggesting that changes in vegetation structure and plant-frugivore co-evolution were probably not important drivers of fleshy diaspore size distributions over long timescales. Instead, fleshy diaspore size distributions may be largely constrained by physical or life-history limits that are shared among groups and diversify as a plant group expands into different growth forms/sizes, habitats, and climate regimes. Mesozoic gymnosperm floras had a low abundance of fleshy diaspores (<50% fleshy diaspore taxa), that was surpassed by some low-latitude angiosperm floras in the Cretaceous. Eocene angiosperm floras show a mid- to high latitude peak in fleshy fruit abundance, with very high proportions of fleshy fruits that even exceed those seen at low latitudes both in the Eocene and today. Mid- to high latitude proportions of fleshy fruits declined substantially over the Eocene-Oligocene transition, resulting in a shift to more modern-like geographic distributions with the highest proportion of fleshy fruits occurring in low-latitude tropical assemblages. This shift was coincident with global cooling and the onset of Southern Hemisphere glaciation, suggesting that rapid cooling at mid- and high latitudes caused a decrease in availability of the climate conditions most favourable for fleshy fruits in angiosperms. Future research could be focused on examining the environmental niches of modern fleshy fruits, and the potential effects of climate change on fleshy fruit and frugivore diversity.

Intra-gastric phytoliths provide evidence for folivory in basal avialans of the Early Cretaceous Jehol Biota

Angiosperms became the dominant plant group in early to middle Cretaceous terrestrial ecosystems, coincident with the timing of the earliest pulse of bird diversification. While living birds and angiosperms exhibit strong interactions across pollination/nectivory, seed dispersal/frugivory, and folivory, documentation of the evolutionary origins and construction of that ecological complexity remains scarce in the Mesozoic. Through the first study of preserved in situ dietary derived phytoliths in a nearly complete skeleton of the early diverging avialan clade Jeholornithidae, we provide direct dietary evidence that Jeholornis consumed leaves likely from the magnoliid angiosperm clade, and these results lend further support for early ecological connections among the earliest birds and angiosperms. The broad diet of the early diverging avialan Jeholornis including at least fruits and leaves marks a clear transition in the early evolution of birds in the establishment of an arboreal (angiosperm) herbivore niche in the Early Cretaceous occupied largely by birds today. Morphometric reanalysis of the lower jaw of Jeholornis further supports a generalized morphology shared with other herbivorous birds, including an extant avian folivore, the hoatzin.

Neontological and paleontological congruence in the evolution of Podocarpaceae (coniferales) reproductive morphology

Introduction

Podocarpaceae are a diverse, primarily tropical conifer family that commonly produce large leaves and highly reduced, fleshy seed cones bearing large seeds. These features may result from relatively recent adaptation to closed-canopy angiosperm forests and bird-mediated seed dispersal, although determining precisely when shifts in leaf and seed cone morphology occurred is difficult due to a sparse fossil record and relatively few surviving deep lineages.

Methods

We compare the fossil record of Podocarpaceae with results from ancestral state reconstruction methods and correlated character models using neontological data and a previously published molecular time-tree.

Results

Ancestral state reconstructions suggest that small leaves, small seeds, and multi-seeded cones are ancestral in crown Podocarpaceae, with reduced cones bearing few seeds appearing in the Early Cretaceous and the correlated evolution of large leaves and large seeds occurring from the Late Cretaceous onwards. The exact timing of these shifts based on neontological data alone are poorly constrained, however, and estimates of leaf and seed size are imprecise.

Discussion

The fossil record is largely congruent with results based on the molecular time-tree, but provide important constraints on the range of leaf and seed sizes that were present in Cretaceous Podocarpaceae and the time by which changes in cone morphology and seed size likely occurred. We suggest in particular that reduced seed cones appeared in the Early Cretaceous and are linked to the contemporaneous diversification of small bodied avialans (birds), with shifts to larger seed sizes occurring after the Cretaceous in association with the spread of closed-canopy angiosperm forests.

Cranial osteology and palaeobiology of the Early Cretaceous bird Jeholornis prima (Aves: Jeholornithiformes)

Jeholornis is a representative of the earliest-diverging bird lineages, providing important evidence of anatomical transitions involved in bird origins. Although ~100 specimens have been reported, its cranial morphology remains poorly documented owing to poor two-dimensional preservation, limiting our understanding of the morphology and ecology of the key avian lineage Jeholornithiformes, in addition to cranial evolution during the origin and early evolution of birds. Here, we provide a detailed description of the cranial osteology of Jeholornis prima, based primarily on high-quality, three-dimensional data of a recently reported specimen. New anatomical information confirms the overall plesiomorphic morphology of the skull, with the exception of the more specialized rostrum. Data from a large sample size of specimens reveal the dental formula of J. prima to be 0–2–3 (premaxillary–maxillary–dentary tooth counts), contrary to previous suggestions that the presence of maxillary teeth is diagnostic of a separate species, Jeholornis palmapenis. We also present evidence of sensory adaptation, including relatively large olfactory bulbs in comparison to other known stem birds, suggesting that olfaction was an important aspect of Jeholornis ecology. The digitally reconstructed scleral ring suggests a strongly diurnal habit, supporting the hypothesis that early-diverging birds were predominantly active during the day.