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The skeletons of birds are universally described as lightweight as a result of selection for minimizing the energy required for flight. From a functional perspective, the weight (mass) of an animal relative to its lift-generating surfaces is a key determinant of the metabolic cost of flight. The evolution of birds has been characterized by many weight-saving adaptations that are reflected in bone shape, many of which strengthen and stiffen the skeleton. Although largely unstudied in birds, the material properties of bone tissue can also contribute to bone strength and stiffness. In this study, I calculated the density of the cranium, humerus and femur in passerine birds, rodents and bats by measuring bone mass and volume using helium displacement. I found that, on average, these bones are densest in birds, followed closely by bats. As bone density increases, so do bone stiffness and strength. Both of these optimization criteria are used in the design of strong and stiff, but lightweight, manmade airframes. By analogy, increased bone density in birds and bats may reflect adaptations for maximizing bone strength and stiffness while minimizing bone mass and volume. These data suggest that both bone shape and the material properties of bone tissue have played important roles in the evolution of flight. They also reconcile the conundrum of how bird skeletons can appear to be thin and delicate, yet contribute just as much to total body mass as do the skeletons of terrestrial mammals.

How ecological opportunity relates to diversification is a central question in evolutionary biology. However, there are few empirical examples of how ecological opportunity and morphological innovation open new adaptive zones, and promote diversification. We analyse data on diet, skull morphology and bite performance, and relate these traits to diversification rates throughout the evolutionary history of an ecologically diverse family of mammals (Chiroptera: Phyllostomidae). We found a significant increase in diversification rate driven by increased speciation at the most recent common ancestor of the predominantly frugivorous subfamily Stenodermatinae. The evolution of diet was associated with skull morphology, and morphology was tightly coupled with biting performance, linking phenotype to new niches through performance. Following the increase in speciation rate, the rate of morphological evolution slowed, while the rate of evolution in diet increased. This pattern suggests that morphology stabilized, and niches within the new adaptive zone of frugivory were filled rapidly, after the evolution of a new cranial phenotype that resulted in a certain level of mechanical efficiency. The tree-wide speciation rate increased non linearly with a more frugivorous diet, and was highest at measures of skull morphology associated with morphological extremes, including the most derived Stenodermatines. These results show that a novel stenodermatine skull phenotype played a central role in the evolution of frugivory and increasing speciation within phyllostomids.

1. In vertebrates, bite force is a measure of whole organism performance that is associated with both cranial morphology and dietary ecology. Mechanistic studies of bite force production have identified morphological features associated with bite force, and linked bite force with diet, but this approach has rarely been used in mammals. 2. Mammals are a good system with which to investigate the function of the feeding apparatus because of the relative simplicity of their skulls and their high dietary diversity. Phyllostomid bats are one of the most trophically and morphologically diverse groups of mammals, but we know little about the relative importance of biomechanical variables in producing bite force or how these variables vary with diet. 3. We combined in vivo measurements of bite force with assessments of muscular and bony morphology to build and validate a model describing the mechanics of bite force production in 25 species of bats. We used this model to investigate how bats with different diets vary in biomechanical parameters that contribute to bite force. In addition to traditional dietary categories, we used a functional definition of diet that reflects the mechanical demands (hardness) of the food items in the natural diet. 4. Our model provided good predictions of in vivo bite forces and highlighted behavioural variation that is inherent in the in vivo data. The temporalis generates the highest moment about the temporomandibular joint (TMJ) axis, but the moment generated by the masseter is the most important variable in explaining variation among species. The dietary classification based on the hardness of the diet was more effective than traditional dietary categories in describing biomechanical differences among groups. The temporalis generated the highest proportion of the moment about the TMJ axis in species with very hard and hard diets, the masseter was most important for species with soft diets, and the medial pterygoid was most important for species with liquid diets. 5. Our results highlight the utility of combining a modelling approach with in vivo data when conducting ecomorphological studies, and the importance of ecological classifications that reflect functional importance of performance traits.

Head direction (HD) cells discharge based on an animal’s directional heading. Computational models propose that a ring-attractor network across the connections between the lateral mammillary (LMN) and dorsal tegmental nuclei (DTN) underlies the signal’s generation. These models contain neurons that encode either HD or angular head velocity (AHV), but also require cells that are sensitive to both parameters conjunctively (HD + AHV). Here we identify both types of HD cells in the LMN and DTN of female rats, with one population sensitive to AHV (both symmetric and asymmetric), and the other population insensitive to AHV. Notably, many HD + AHV cells are also sensitive to the animal’s linear head-speed (LHS). In contrast, anterodorsal thalamic HD cells are rarely sensitive to AHV or LHS. These findings demonstrate that the requisite HD + AHV cell is present in areas that generate the HD signal and supports the view that a ring attractor network underlies its generation in mammals. The mechanisms generating the head direction cell signal in rats are not fully understood. Here, two distinct types of head direction cells in the lateral mammillary and dorsal tegmental nuclei were identified: one type is angular head velocity independent, while the second type depends on the animal’s angular head velocity.

Previously known only from isolated teeth and lower jaw fragments recovered from the Cretaceous and Palaeogene of the Southern Hemisphere, the Gondwanatheria constitute the most poorly known of all major mammaliaform radiations. Here we report the discovery of the first skull material of a gondwanatherian, a complete and well-preserved cranium from Upper Cretaceous strata in Madagascar that we assign to a new genus and species. Phylogenetic analysis strongly supports its placement within Gondwanatheria, which are recognized as monophyletic and closely related to multituberculates, an evolutionarily successful clade of Mesozoic mammals known almost exclusively from the Northern Hemisphere. The new taxon is the largest known mammaliaform from the Mesozoic of Gondwana. Its craniofacial anatomy reveals that it was herbivorous, large-eyed and agile, with well-developed high-frequency hearing and a keen sense of smell. The cranium exhibits a mosaic of primitive and derived features, the disparity of which is extreme and probably reflective of a long evolutionary history in geographic isolation. The gondwanatherians were mammals known only from teeth and some jaw fragments that lived in the southern continents alongside dinosaurs; here the entire cranium of a bizarre and badger-sized fossil mammal from the Cretaceous of Madagascar shows that gondwanatherians were related to the better-known multituberculates, a long-lived and successful group of now-extinct rodent-like mammals. Anatomy of a Gondwana mammal The gondwanatheres were mammals that lived the southern continents alongside the dinosaurs during the Late Cretaceous and early Paleocene. Known only from a few teeth and some jaw fragments, their appearance and evolutionary relationships remained obscure. The entire skull of a bizarre and badger-sized fossil mammal from the Cretaceous of Madagascar changes all that. Although almost certainly highly derived — as one would expect from a member of the unique endemic island fauna of Madagascar at that time — Vintana is clearly a gondwanathere. The anatomy of the herbivorous, large-eyed and agile creature shows that gondwanatheres were related to the better-known multituberculates, a long-lived and successful group of (now also extinct) rodent-like mammals.

The Jamaican flower bat Phyllonycteris aphylla is categorized as Critically Endangered on the IUCN Red List. It is endemic to Jamaica and formerly known only from Stony Hill Cave, where there are an estimated c. 500 individuals. Previously declared extinct twice, its rediscovery in 2010 at Stony Hill Cave marked new hope for the conservation of this important species. Although little is known about its ecology, the species is presumed to be a cave-obligate rooster and to rely exclusively on so-called hot caves, which are defined by high ambient temperatures and low air quality. In March–April 2023, we surveyed bats at seven caves throughout Jamaica. At two of these, Green Grotto Caves, St. Ann, and Rock Spring Caverns, St. Mary, we captured both male and pregnant female P. aphylla. At Green Grotto Caves, we captured 24 P. aphylla, and 66 at Rock Spring Caverns. We believe Rock Spring Caverns to be one of the largest known roosts of P. aphylla. Neither of these sites are hot caves as both are moderated by flowing water, although warmer chambers may be more important to this bat than to other species. Further monitoring of these populations and continued exploration of other potential roosts are vital for the protection of this species.

The loss of previously adaptive traits is typically linked to relaxation in selection, yet the molecular steps leading to such repeated losses are rarely known. Molecular studies of loss have tended to focus on gene sequences alone, but overlooking other aspects of protein expression might underestimate phenotypic diversity. Insights based almost solely on opsin gene evolution, for instance, have made mammalian color vision a textbook example of phenotypic loss. We address this gap by investigating retention and loss of opsin genes, transcripts, and proteins across ecologically diverse noctilionoid bats. We find multiple, independent losses of short-wave-sensitive opsins. Mismatches between putatively functional DNA sequences, mRNA transcripts, and proteins implicate transcriptional and post-transcriptional processes in the ongoing loss of S-opsins in some noctilionoid bats. Our results provide a snapshot of evolution in progress during phenotypic trait loss, and suggest vertebrate visual phenotypes cannot always be predicted from genotypes alone. Bats are famous for using their hearing to explore their environments, yet fewer people are aware that these flying mammals have both good night and daylight vision. Some bats can even see in color thanks to two light-sensitive proteins at the back of their eyes: S-opsin which detects blue and ultraviolet light and L-opsin which detects green and red light. Many species of bat, however, are missing one of these proteins and cannot distinguish any colors; in other words, they are completely color-blind. Some bat species found in Central and South America have independently lost their ability to see blue-ultraviolet light and have thus also lost their color vision. These bats have diverse diets – ranging from insects to fruits and even blood – and being able to distinguish color may offer an advantage in many of their activities, including hunting or foraging. The vision genes in these bats, therefore, give scientists an opportunity to explore how a seemingly important trait can be lost at the molecular level. Sadier, Davies et al. now report that S-opsin has been lost more than a dozen times during the evolutionary history of these Central and South American bats. The analysis used samples from 55 species, including animals caught from the wild and specimens from museums. As with other proteins, the instructions encoded in the gene sequence for S opsin need to be copied into a molecule of RNA before they can be translated into protein. As expected, S-opsin was lost several times because of changes in the gene sequence that disrupted the formation of the protein. However, at several points in these bats’ evolutionary history, additional changes have taken place that affected the production of the RNA or the protein, without an obvious change to the gene itself. This finding suggests that other studies that rely purely on DNA to understand evolution may underestimate how often traits may be lost. By capturing ‘evolution in action’, these results also provide a more complete picture of the molecular targets of evolution in a diverse set of bats.

The morphology of the nasal cavity in mammals with a good sense of smell includes features that are thought to improve olfactory airflow, such as a dorsal conduit that delivers odours quickly to the olfactory mucosa, an enlarged olfactory recess at the back of the airway, and a clear separation of the olfactory and respiratory regions of the nose. The link between these features and having a good sense of smell has been established by functional examinations of a handful of distantly related mammalian species. In this paper, we provide the first detailed examination of olfactory airflow in a group of closely related species that nevertheless vary in their sense of smell. We study six species of phyllostomid bats that have different airway morphologies and foraging ecologies, which have been linked to differences in olfactory ability or reliance. We hypothesize that differences in morphology correlate with differences in the patterns and rates of airflow, which in turn are consistent with dietary differences. To compare species, we make qualitative and quantitative comparisons of the patterns and rates of airflow through the olfactory region during both inhalation and exhalation across the six species. Contrary to our expectations, we find no clear differences among species in either the patterns of airflow through the airway or in rates of flow through the olfactory region. By and large, olfactory airflow seems to be conserved across species, suggesting that morphological differences appear to be driven by other mechanical demands on the snout, such as breathing and feeding. Olfactory ability may depend on other aspects of the system, such as the neurobiological processing of odours that work within the existing morphology imposed by other functional demands on the nasal cavity.

Several finite element models of a primate cranium were used to investigate the biomechanical effects of the tooth sockets and the material behavior of the periodontal ligament (PDL) on stress and strain patterns associated with feeding. For examining the effect of tooth sockets, the unloaded sockets were modeled as devoid of teeth and PDL, filled with teeth and PDLs, or simply filled with cortical bone. The third premolar on the left side of the cranium was loaded and the PDL was treated as an isotropic, linear elastic material using published values for Young's modulus and Poisson's ratio. The remaining models, along with one of the socket models, were used to determine the effect of the PDL's material behavior on stress and strain distributions under static premolar biting and dynamic tooth loading conditions. Two models (one static and the other dynamic) treated the PDL as cortical bone. The other two models treated it as a ligament with isotropic, linear elastic material properties. Two models treated the PDL as a ligament with hyperelastic properties, and the other two as a ligament with viscoelastic properties. Both behaviors were defined using published stress–strain data obtained from in vitro experiments on porcine ligament specimens. Von Mises stress and strain contour plots indicate that the effects of the sockets and PDL material behavior are local. Results from this study suggest that modeling the sockets and the PDL in finite element analyses of skulls is project dependent and can be ignored if values of stress and strain within the alveolar region are not required.

Bone morphogenetic protein (BMP) adenoviral vectors for the induction of osteogenesis are being developed for the treatment of bone pathology. However, it is still unknown which BMP adenoviral vector has the highest potential to stimulate bone formation in vivo . In this study, the osteogenic activities of recombinant human BMP-2, BMP-4, BMP-6, BMP-7, and BMP-9 adenoviruses were compared in vitro , in athymic nude rats, and in Sprague–Dawley rats. In vitro osteogenic activity was assessed by measuring the alkaline phosphatase activity in C2C12 cells transduced by the various BMP vectors. The alkaline phosphatase activity induced by 2 × 10 5  PFU/well of BMP viral vector was 4890 × 10 −12  U/well for ADCMVBMP-9, 302 × 10 −12  U/well for ADCMVBMP-4, 220 × 10 −12  U/well for ADCMVBMP-6, 45 × 10 −12  U/well for ADCMVBMP-2, and 0.43 × 10 −12  U/well for ADCMVBMP-7. The average volume of new bone induced by 10 7  PFU of BMP vector in athymic nude rats was 0.37±0.03 cm 3 for ADCMVBMP-2, 0.89±0.07 cm 3 for ADCMVBMP-4, 1.02±0.07 cm 3 for ADCMVBMP-6, 0.24±0.05 cm 3 for ADCMVBMP-7, and 0.63±0.07 cm 3 for ADCMVBMP-9. In immunocompetent Sprague–Dawley rats, no bone formation was demonstrated in the ADCMVBMP-2, ADCMVBMP-4, and ADCMVBMP-7 groups. ADCMVBMP-6 at a viral dose of 10 8  PFU induced 0.10±0.03 cm 3 of new bone, whereas ADCMVBMP-9 at a lower viral dose of 10 7  PFU induced more bone, with an average volume of 0.29±0.01 cm 3 .