Paleoneurology of stem palaeognaths clarifies the plesiomorphic condition of the crown bird central nervous system.

Lithornithidae, an assemblage of volant Palaeogene fossil birds, provide our clearest insights into the early evolutionary history of Palaeognathae, the clade that today includes the flightless ratites and volant tinamous. The neotype specimen of Lithornis vulturinus, from the early Eocene (approximately 53 million years ago) of Europe, includes a partial neurocranium that has never been thoroughly investigated. Here, we describe these cranial remains including the nearly complete digital endocasts of the brain and bony labyrinth. The telencephalon of Lithornis is expanded and its optic lobes are ventrally shifted, as is typical for crown birds. The foramen magnum is positioned caudally, rather than flexed ventrally as in some crown birds, with the optic lobes, cerebellum, and foramen magnum shifted further ventrally. The overall brain shape is similar to that of tinamous, the only extant clade of flying palaeognaths, suggesting that several aspects of tinamou neuroanatomy may have been evolutionarily conserved since at least the early Cenozoic. The estimated ratio of the optic lobe's surface area relative to the total brain suggests a diurnal ecology. Lithornis may provide the clearest insights to date into the neuroanatomy of the ancestral crown bird, combining an ancestrally unflexed brain with a caudally oriented connection with the spinal cord, a moderately enlarged telencephalon, and ventrally shifted, enlarged optic lobes.

Macroevolutionary drivers of morphological disparity in the avian quadrate.

In birds, the quadrate connects the mandible and skull, and plays an important role in cranial kinesis. Avian quadrate morphology may therefore be assumed to have been influenced by selective pressures related to feeding ecology, yet large-scale variation in quadrate morphology and its potential relationship with ecology have never been quantitatively investigated. Here, we used geometric morphometrics and phylogenetic comparative methods to quantify morphological variation of the quadrate and its relationship with key ecological features across a wide phylogenetic sample. We found non-significant associations between quadrate shape and feeding ecology across different scales of phylogenetic comparison; indeed, allometry and phylogeny exhibit stronger relationships with quadrate shape than ecological features. We show that similar quadrate shapes are associated with widely varying dietary ecologies (one-to-many mapping), while divergent quadrate shapes are associated with similar dietary ecologies (many-to-one mapping). Moreover, we show that the avian quadrate evolves as an integrated unit and exhibits strong associations with the morphologies of neighbouring bones. Our results collectively illustrate that quadrate shape has evolved jointly with other elements of the avian kinetic system, with the major crown bird lineages exploring alternative quadrate morphologies, highlighting the potential diagnostic value of quadrate morphology in investigations of bird systematics.

Tip dating and Bayes factors provide insight into the divergences of crown bird clades across the end-Cretaceous mass extinction.

The origin of crown birds (Neornithes) remains contentious owing to conflicting divergence time hypotheses obtained from alternative sources of data. The fossil record suggests limited diversification of Neornithes in the Late Mesozoic and a substantial radiation in the aftermath of the Cretaceous-Palaeogene (K-Pg) mass extinction, approximately 66 Ma. Molecular clock studies, however, have yielded estimates for neornithine origins ranging from the Early Cretaceous (130 Ma) to less than 10 Myr before the K-Pg. We use Bayes factors to compare the fit of node ages from different molecular clock studies to an independent morphological dataset. Our results allow us to reject scenarios of crown bird origins deep in the Early Cretaceous, as well as an origin of crown birds within the last 10 Myr of the Cretaceous. The scenario best supported by our analyses is one where Neornithes originated between the Early and Late Cretaceous (ca 100 Ma), while numerous divergences within major neoavian clades either span or postdate the K-Pg. This study affirms the importance of the K-Pg on the diversification of modern birds, and the potential of combined-evidence tip-dating analyses to illuminate recalcitrant 'rocks versus clocks' debates.

Comparative morphology of the avian bony columella.

In birds, the columella is the only bony element of the sound conducting apparatus, conveying vibrations of the cartilaginous extracolumella to the fluid of the inner ear. Although avian columellar morphology has attracted some attention over the past century, it nonetheless remains poorly described in the literature. The few existing studies mostly focus on morphological descriptions in relatively few taxa, with no taxonomically broad surveys yet published. Here we use observations of columellae from 401 extant bird species to provide a comprehensive survey of columellar morphology in a phylogenetic context. We describe the columellae of several taxa for the first time and identify derived morphologies characterizing higher-level clades based on current phylogenies. In particular, we identify a derived columellar morphology diagnosing a major subclade of Accipitridae. Within Suliformes, we find that Fregatidae, Sulidae, and Phalacrocoracidae share a derived morphology that is absent in Anhingidae, suggesting a secondary reversal. Phylogenetically informed comparisons allow recognition of instances of homoplasy, including the distinctive bulbous columellae in suboscine passerines and taxa belonging to Eucavitaves, and bulging footplates that appear to have evolved at least twice independently in Strigiformes. We consider phylogenetic and functional factors influencing avian columellar morphology, finding that aquatic birds possess small footplates relative to columellar length, possibly related to hearing function in aquatic habitats. By contrast, the functional significance of the distinctive bulbous basal ends of the columellae of certain arboreal landbird taxa remains elusive.

3D atlas of tinamou (Neornithes: Tinamidae) pectoral morphology: Implications for reconstructing the ancestral neornithine flight apparatus.

Palaeognathae, the extant avian clade comprising the flightless ratites and flight-capable tinamous (Tinamidae), is the sister group to all other living birds, and recent phylogenetic studies illustrate that tinamous are phylogenetically nested within a paraphyletic assemblage of ratites. As the only extant palaeognaths that have retained the ability to fly, tinamous may provide key information on the nature of the flight apparatus of ancestral crown palaeognaths-and, in turn, crown birds-as well as insight into convergent modifications to the wing apparatus among extant ratite lineages. To reveal new information about the musculoskeletal anatomy of tinamous and facilitate development of computational biomechanical models of tinamou wing function, we generated a three-dimensional musculoskeletal model of the flight apparatus of the extant Andean tinamou (Nothoprocta pentlandii) using diffusible iodine-based contrast-enhanced computed tomography (diceCT). Origins and insertions of the pectoral flight musculature of N. pentlandii are generally consistent with those of other extant volant birds specialized for burst flight, and the entire suite of presumed ancestral neornithine flight muscles are present in N. pentlandii with the exception of the biceps slip. The pectoralis and supracoracoideus muscles are robust, similar to the condition in other extant burst-flying birds such as many extant Galliformes. Contrary to the condition in most extant Neognathae (the sister clade to Palaeognathae), the insertion of the pronator superficialis has a greater distal extent than the pronator profundus, although most other anatomical observations are broadly consistent with the conditions observed in extant neognaths. This work will help form a basis for future comparative studies of the avian musculoskeletal system, with implications for reconstructing the flight apparatus of ancestral crown birds and clarifying musculoskeletal modifications underlying the convergent origins of ratite flightlessness.

The influence of fossils in macroevolutionary analyses of 3D geometric morphometric data: A case study of galloanseran quadrates.

In birds and other reptiles, the quadrate acts as a hinge between the lower jaw and the skull and plays an important role in avian cranial kinesis. Though previous studies have qualitatively described substantial variation in quadrate morphology among birds, none have attempted to quantify evolutionary changes in quadrate shape. Here, we investigate geometric evolution of the quadrate in Galloanserae, a major clade of extant birds uniting chicken-like (Galliformes) and duck-like (Anseriformes) fowl. We quantified morphological variation in the quadrate across 50 extant galloanseran species covering all major extant subclades using three-dimensional geometric morphometrics, and performed ancestral shape reconstructions in the context of an up-to-date neornithine phylogeny. We find that our results based only on extant quadrates may overlook plesiomorphic features captured by fossil taxa, resulting in an ancestral state reconstruction for Galloanserae that is seemingly an approximation of the average shape of the extant data set. By contrast, analyses incorporating early fossil galloanseran quadrates (from taxa such as Asteriornis, Presbyornis, and Conflicto) result in ancestral geometric reconstructions more similar to the morphology of extant galliforms, indicating that the quadrate of the last common ancestor of galloanserans may have been more morphologically and functionally similar to those of extant galliforms than to extant anseriforms. These results generally corroborate previous inferences of galloanseran quadrate plesiomorphies and identify several additional plesiomorphic features of the galloanseran quadrate for the first time. Our results illustrate the importance of incorporating fossil taxa into ancestral shape reconstructions and help elucidate important aspects of the morphology and function of the avian feeding apparatus early in crown bird evolutionary history.

Electrical and thermal characterisation of liquid metal thin-film Ga[Formula: see text]O[Formula: see text]-SiO[Formula: see text] heterostructures.

Heterostructures of Ga[Formula: see text]O[Formula: see text] with other materials such as Si, SiC or diamond, are a possible way of addressing the low thermal conductivity and lack of p-type doping of Ga[Formula: see text]O[Formula: see text] for device applications, as well as of improving device reliability. In this work we study the electrical and thermal properties of Ga[Formula: see text]O[Formula: see text]-SiO[Formula: see text] heterostructures. Here, thin-film gallium oxide with thickness ranging between 8 and 30 nm was deposited onto a silicon substrate with a thermal oxide by means of oxidised liquid gallium layer delamination. The resulting heterostructure is then characterised by means of X-ray photoelectron spectroscopy and transient thermoreflectance. The thin-film gallium oxide valence band offset with respect to the SiO[Formula: see text] is measured as 0.1 eV and predicted as [Formula: see text] eV with respect to diamond. The thin-film's out-of-plane thermal conductivity is determined to be 3 ±0.5 Wm[Formula: see text] K[Formula: see text], which is higher than what has been previously measured for other polycrystalline Ga[Formula: see text]O[Formula: see text] films of comparable thickness.

Direct quantification of skeletal pneumaticity illuminates ecological drivers of a key avian trait.

Skeletal pneumaticity is a key feature of extant avian structure and biology, which first evolved among the non-flying archosaurian ancestors of birds. The widespread presence of air-filled bones across the postcranial skeleton is unique to birds among living vertebrates, but the true extent of skeletal pneumaticity has never been quantitatively investigated-hindering fundamental insights into the evolution of this key avian feature. Here, we use microCT scans of fresh, frozen birds to directly quantify the fraction of humerus volume occupied by air across a phylogenetically diverse taxon sample to test longstanding hypotheses regarding the evolution and function of avian skeletal pneumatization. Among other insights, we document weak positive allometry of internal air volume with humeral size among pneumatized humeri and provide strong support that humeral size, body mass, aquatic diving, and the presence or absence of pneumaticity all have independent effects on cortical bone thickness. Our quantitative evaluation of humeral pneumaticity across extant avian phylogeny sheds new light on the evolution and ontogenetic progression of an important aspect of avian skeletal architecture, and suggests that the last common ancestor of crown birds possessed a highly pneumatized humerus.

Reconstructing locomotor ecology of extinct avialans: a case study of Ichthyornis comparing sternum morphology and skeletal proportions.

Avian skeletal morphology is associated with locomotor function, including flight style, swimming and terrestrial locomotion, and permits informed inferences on locomotion in extinct taxa. The fossil taxon Ichthyornis (Avialae: Ornithurae) has long been regarded as highly aerial, with flight similar to terns or gulls (Laridae), and skeletal features resembling foot-propelled diving adaptations. However, rigorous testing of locomotor hypotheses has yet to be performed on Ichthyornis, despite its notable phylogenetic position as one of the most crownward stem birds. We analysed separate datasets of three-dimensional sternal shape (geometric morphometrics) and skeletal proportions (linear measurements across the skeleton), to examine how well these data types predict locomotor traits in Neornithes. We then used this information to infer locomotor capabilities of Ichthyornis. We find strong support for both soaring and foot-propelled swimming capabilities in Ichthyornis. Further, sternal shape and skeletal proportions provide complementary information on avian locomotion: skeletal proportions allow better predictions of the capacity for flight, whereas sternal shape predicts variation in more specific locomotor abilities such as soaring, foot-propelled swimming and escape burst flight. These results have important implications for future studies of extinct avialan ecology and underscore the importance of closely considering sternum morphology in investigations of fossil bird locomotion.

Comparative anatomy of the passerine carpometacarpus helps illuminate the early fossil record of crown Passeriformes.

The hyper-diverse clade Passeriformes (crown group passerines) comprises over half of extant bird diversity, yet disproportionately few studies have targeted passerine comparative anatomy on a broad phylogenetic scale. This general lack of research attention hinders efforts to interpret the passerine fossil record and obscures patterns of morphological evolution across one of the most diverse clades of extant vertebrates. Numerous potentially important crown passeriform fossils have proven challenging to place phylogenetically, due in part to a paucity of phylogenetically informative characters from across the passerine skeleton. Here, we present a detailed analysis of the morphology of extant passerine carpometacarpi, which are relatively abundant components of the passerine fossil record. We sampled >70% of extant family-level passerine clades (132 extant species) as well as several fossils from the Oligocene of Europe and scored them for 54 phylogenetically informative carpometacarpus characters optimised on a recently published phylogenomic scaffold. We document a considerable amount of previously undescribed morphological variation among passerine carpometacarpi, and, despite high levels of homoplasy, our results support the presence of representatives of both crown Passeri and crown Tyranni in Europe during the Oligocene.

Forty new specimens of Ichthyornis provide unprecedented insight into the postcranial morphology of crownward stem group birds.

Ichthyornis has long been recognized as a pivotally important fossil taxon for understanding the latest stages of the dinosaur-bird transition, but little significant new postcranial material has been brought to light since initial descriptions of partial skeletons in the 19th Century. Here, we present new information on the postcranial morphology of Ichthyornis from 40 previously undescribed specimens, providing the most complete morphological assessment of the postcranial skeleton of Ichthyornis to date. The new material includes four partially complete skeletons and numerous well-preserved isolated elements, enabling new anatomical observations such as muscle attachments previously undescribed for Mesozoic euornitheans. Among the elements that were previously unknown or poorly represented for Ichthyornis, the new specimens include an almost-complete axial series, a hypocleideum-bearing furcula, radial carpal bones, fibulae, a complete tarsometatarsus bearing a rudimentary hypotarsus, and one of the first-known nearly complete three-dimensional sterna from a Mesozoic avialan. Several pedal phalanges are preserved, revealing a remarkably enlarged pes presumably related to foot-propelled swimming. Although diagnosable as Ichthyornis, the new specimens exhibit a substantial degree of morphological variation, some of which may relate to ontogenetic changes. Phylogenetic analyses incorporating our new data and employing alternative morphological datasets recover Ichthyornis stemward of Hesperornithes and Iaceornis, in line with some recent hypotheses regarding the topology of the crownward-most portion of the avian stem group, and we establish phylogenetically-defined clade names for relevant avialan subclades to help facilitate consistent discourse in future work. The new information provided by these specimens improves our understanding of morphological evolution among the crownward-most non-neornithine avialans immediately preceding the origin of crown group birds.

Comparison of RT-qPCR and RT-dPCR Platforms for the Trace Detection of SARS-CoV-2 RNA in Wastewater.

We compared reverse transcription-quantitative polymerase chain reaction (RT-qPCR) and RT digital PCR (RT-dPCR) platforms for the trace detection of SARS-CoV-2 RNA in low-prevalence COVID-19 locations in Queensland, Australia, using CDC N1 and CDC N2 assays. The assay limit of detection (ALOD), PCR inhibition rates, and performance characteristics of each assay, along with the positivity rates with the RT-qPCR and RT-dPCR platforms, were evaluated by seeding known concentrations of exogenous SARS-CoV-2 in wastewater. The ALODs using RT-dPCR were approximately 2-5 times lower than those using RT-qPCR. During sample processing, the endogenous (n = 96) and exogenous (n = 24) SARS-CoV-2 wastewater samples were separated, and RNA was extracted from both wastewater eluates and pellets (solids). The RT-dPCR platform demonstrated a detection rate significantly greater than that of RT-qPCR for the CDC N1 and CDC N2 assays in the eluate (N1, p = 0.0029; N2, p = 0.0003) and pellet (N1, p = 0.0015; N2, p = 0.0067) samples. The positivity results also indicated that for the analysis of SARS-CoV-2 RNA in wastewater, including the eluate and pellet samples may further increase the detection sensitivity using RT-dPCR.

Microplastics in the surgical environment.

Atmospheric microplastics (MPs) have been consistently detected within indoor and outdoor air samples. Locations with high human activity are reported to have high MP levels. The aim was to quantify and characterise the MPs present within the surgical environment over a one-week sampling period. MPs were collected in samplers placed around an operating theatre and adjoining anaesthetic room at 12 h intervals. Particles were filtered onto 0.02 µm membranes and analysed using micro-Fourier-transform infrared spectroscopy. The number of MPs identified during the working day sampling period varied, with a mean of 1,924 ± 3,105 MP m-2 day-1 and a range of 0 - 9,258 MP m-2 day-1 observed in the theatre, compared with a mean of 541 ± 969 MP m-2 day-1 and a range of 0 - 3,368 MP m-2 day-1 for the anaesthetic room. Across both rooms and at all sampling points, an increase in levels with a decrease in MP size was observed. Identified particles consisted of mainly fragment shaped MPs (78 %) with polyethylene terephthalate (37 %), polypropylene (25 %), polyethylene (7 %) and nylon (13 %) representing the most abundant polymer types. MPs were not detected in the theatre during non-working hours. The results provide novel information on defining polymer levels and types, in a room environment where the use of single plastics has been regarded as beneficial to practice. These results can inform cellular toxicity studies, investigating the consequences of human MP exposure as well as represent a potentially novel route of exposure for humans for this emerging contaminant of concern, via surgery.

Cretaceous ornithurine supports a neognathous crown bird ancestor.

The bony palate diagnoses the two deepest clades of extant birds: Neognathae and Palaeognathae1-5. Neognaths exhibit unfused palate bones and generally kinetic skulls, whereas palaeognaths possess comparatively rigid skulls with the pterygoid and palatine fused into a single element, a condition long considered ancestral for crown birds (Neornithes)3,5-8. However, fossil evidence of palatal remains from taxa close to the origin of Neornithes is scarce, hindering strong inferences regarding the ancestral condition of the neornithine palate. Here we report a new taxon of toothed Late Cretaceous ornithurine bearing a pterygoid that is remarkably similar to those of the extant neognath clade Galloanserae (waterfowl + landfowl). Janavis finalidens, gen. et sp. nov., is generally similar to the well-known Mesozoic ornithurine Ichthyornis in its overall morphology, although Janavis is much larger and exhibits a substantially greater degree of postcranial pneumaticity. We recovered Janavis as the first-known well-represented member of Ichthyornithes other than Ichthyornis, clearly substantiating the persistence of the clade into the latest Cretaceous9. Janavis confirms the presence of an anatomically neognathous palate in at least some Mesozoic non-crown ornithurines10-12, suggesting that pterygoids similar to those of extant Galloanserae may be plesiomorphic for crown birds. Our results, combined with recent evidence on the ichthyornithine palatine12, overturn longstanding assumptions about the ancestral crown bird palate, and should prompt reevaluation of the purported galloanseran affinities of several bizarre early Cenozoic groups such as the 'pseudotoothed birds' (Pelagornithidae)13-15.

Fossil basicranium clarifies the origin of the avian central nervous system and inner ear.

Among terrestrial vertebrates, only crown birds (Neornithes) rival mammals in terms of relative brain size and behavioural complexity. Relatedly, the anatomy of the avian central nervous system and associated sensory structures, such as the vestibular system of the inner ear, are highly modified with respect to those of other extant reptile lineages. However, a dearth of three-dimensional Mesozoic fossils has limited our knowledge of the origins of the distinctive endocranial structures of crown birds. Traits such as an expanded, flexed brain, a ventral connection between the brain and spinal column, and a modified vestibular system have been regarded as exclusive to Neornithes. Here, we demonstrate all of these 'advanced' traits in an undistorted braincase from an Upper Cretaceous enantiornithine bonebed in southeastern Brazil. Our discovery suggests that these crown bird-like endocranial traits may have originated prior to the split between Enantiornithes and the more crownward portion of avian phylogeny over 140 Ma, while coexisting with a remarkably plesiomorphic cranial base and posterior palate region. Altogether, our results support the interpretation that the distinctive endocranial morphologies of crown birds and their Mesozoic relatives are affected by complex trade-offs between spatial constraints during development.

Alloy Partitioning Effect on Strength and Toughness of κ-Carbide Strengthened Steels.

Alloy partitioning during heat treatment in a lightweight precipitation hardened steel was investigated using transmission electron microscopy and atom probe tomography. The mechanical properties are discussed as a function of the effect of solution treatment temperature and aging time, giving rise to variations in chemical modulation. A wrought lightweight steel alloy with a nominal composition of Fe-30Mn-9Al-1Si-1C-0.5Mo (wt. %) was solution-treated between 1173-1273 K and aged at 773 K. Lower solution treatment temperatures retained a finer grain size and accelerated age hardening response that also produced an improved work hardening behavior with a tensile strength of -1460 MPa at 0.4 true strain. Atom probe tomography indicated these conditions also had reduced modulation in the Si and Al content due to the reduced aging time preventing silicon from diffusing out of the κ-carbide into the austenite. This work provides the framework for heat-treating lightweight, age hardenable steels with high strength and improved energy absorption.

Record-Low Thermal Boundary Resistance between Diamond and GaN-on-SiC for Enabling Radiofrequency Device Cooling.

The implementation of 5G-and-beyond networks requires faster, high-performance, and power-efficient semiconductor devices, which are only possible with materials that can support higher frequencies. Gallium nitride (GaN) power amplifiers are essential for 5G-and-beyond technologies since they provide the desired combination of high frequency and high power. These applications along with terrestrial hub and backhaul communications at high power output can present severe heat removal challenges. The cooling of GaN devices with diamond as the heat spreader has gained significant momentum since device self-heating limits GaN's performance. However, one of the significant challenges in integrating polycrystalline diamond on GaN devices is maintaining the device performance while achieving a low diamond/GaN channel thermal boundary resistance. In this study, we achieved a record-low thermal boundary resistance of around 3.1 ± 0.7 m2 K/GW at the diamond/Si3N4/GaN interface, which is the closest to theoretical prediction to date. The diamond was integrated within ∼1 nm of the GaN channel layer without degrading the channel's electrical behavior. Furthermore, we successfully minimized the residual stress in the diamond layer, enabling more isotropic polycrystalline diamond growth on GaN with thicknesses >2 µm and a ∼1.9 µm lateral grain size. More isotropic grains can spread the heat in both vertical and lateral directions efficiently. Using transient thermoreflectance, the thermal conductivity of the grains was measured to be 638 ± 48 W/m K, which when combined with the record-low thermal boundary resistance makes it a leading-edge achievement.

Ecological selectivity and the evolution of mammalian substrate preference across the K-Pg boundary.

The Cretaceous-Paleogene (K-Pg) mass extinction 66 million years ago was characterized by a worldwide ecological catastrophe and rapid species turnover. Large-scale devastation of forested environments resulting from the Chicxulub asteroid impact likely influenced the evolutionary trajectories of multiple clades in terrestrial environments, and it has been hypothesized to have biased survivorship in favour of nonarboreal lineages across the K-Pg boundary. Here, we evaluate patterns of substrate preferences across the K-Pg boundary among crown group mammals, a group that underwent rapid diversification following the mass extinction. Using Bayesian, likelihood, and parsimony reconstructions, we identify patterns of mammalian ecological selectivity that are broadly similar to those previously hypothesized for birds. Models based on extant taxa indicate predominant K-Pg survivorship among semi- or nonarboreal taxa, followed by numerous independent transitions to arboreality in the early Cenozoic. However, contrary to the predominant signal, some or all members of total-clade Euarchonta (Primates + Dermoptera + Scandentia) appear to have maintained arboreal habits across the K-Pg boundary, suggesting ecological flexibility during an interval of global habitat instability. We further observe a pronounced shift in character state transitions away from plesiomorphic arboreality associated with the K-Pg transition. Our findings are consistent with the hypothesis that predominantly nonarboreal taxa preferentially survived the end-Cretaceous mass extinction, and emphasize the pivotal influence of the K-Pg transition in shaping the early evolutionary trajectories of extant terrestrial vertebrates.

A recessive PRDM13 mutation results in congenital hypogonadotropic hypogonadism and cerebellar hypoplasia.

The positive regulatory (PR) domain containing 13 (PRDM13) putative chromatin modifier and transcriptional regulator functions downstream of the transcription factor PTF1A, which controls GABAergic fate in the spinal cord and neurogenesis in the hypothalamus. Here, we report a recessive syndrome associated with PRDM13 mutation. Patients exhibited intellectual disability, ataxia with cerebellar hypoplasia, scoliosis, and delayed puberty with congenital hypogonadotropic hypogonadism (CHH). Expression studies revealed Prdm13/PRDM13 transcripts in the developing hypothalamus and cerebellum in mouse and human. An analysis of hypothalamus and cerebellum development in mice homozygous for a Prdm13 mutant allele revealed a significant reduction in the number of Kisspeptin (Kiss1) neurons in the hypothalamus and PAX2+ progenitors emerging from the cerebellar ventricular zone. The latter was accompanied by ectopic expression of the glutamatergic lineage marker TLX3. Prdm13-deficient mice displayed cerebellar hypoplasia and normal gonadal structure, but delayed pubertal onset. Together, these findings identify PRDM13 as a critical regulator of GABAergic cell fate in the cerebellum and of hypothalamic kisspeptin neuron development, providing a mechanistic explanation for the cooccurrence of CHH and cerebellar hypoplasia in this syndrome. To our knowledge, this is the first evidence linking disrupted PRDM13-mediated regulation of Kiss1 neurons to CHH in humans.

Disentangling the avian altricial-precocial spectrum: Quantitative assessment of developmental mode, phylogenetic signal, and dimensionality.

The altricial-precocial spectrum describes patterns of variation in avian developmental mode that greatly influence avian life histories. Appraising a given species' position on this spectrum is therefore fundamental to understanding patterns of avian life history evolution. However, evaluating avian developmental mode remains a relatively subjective task reliant on untested assumptions, including the notion that developmental strategies are distributed along a single dimension of statistical variation. Here, we present a quantitative multivariate framework that objectively discriminates among meaningfully different modes of avian development. We gathered information on seven hatchling and post-hatching traits for up to 4000 extant bird species, and find that most traits related to developmental mode show high phylogenetic signal and little intraclade variation, allowing unknown values to be reliably interpolated. Principal component analyses (PCAs) of these traits illustrate that most variation in hatchling state can be quantified along one dimension of trait space. However, our PCAs also reveal an important second dimension explaining variation in post-hatching behavior, enabling factors related to hatchling state and post-hatching behavior to be disentangled. In order to facilitate future macroevolutionary studies of variation in avian developmental strategies, as well as explorations of covariation between developmental mode and other aspects of avian biology, we present PC scores for 9993 extant avian species.