Zoological Journal of the Linnean Society

Understanding behavioral differences between non-native and closely related endangered species could be important to aid conservation management. In volume 169 of Zoology, Bels et al. (2025) reported on their comparison of display-action-patterns (DAP) between native Iguana delicatissima and non-native iguanas present on islands of the Guadeloupe Archipelago in the Caribbean Lesser Antilles. Here, we address conceptual and methodological concerns about their work and reanalyze their data given our proposed corrections, primarily a literature-informed adjustment of their "species" category. We additionally utilize online videos from South American mainland I. iguana populations, from where the non-native iguanas in the Guadeloupe Archipelago originate, to better understand the different DAPs between native and non-native iguanas in the Guadeloupe Archipelago. Significant differences in DAP characteristics among "species" categories (native I. delicatissima, non-native iguanas, and hybrids) show that Bels et al. (2025) oversimplified their data analyses by merging all non-native populations into one group. This result indicates the presence of behavioral variation among subpopulations within widely hybridizing iguanid populations, which has been poorly studied. Additionally, videos from mainland populations across two major mitochondrial clades of Iguana iguana show that non-native iguanas on Guadeloupe retained DAP characteristics of those populations from which they originate. We discuss these findings in light of the proposed hypotheses put forward by Bels et al. (2025), of which two can be excluded. Overall, our reanalysis shows that studies focusing on characteristics within settings of complex hybridization in diverse species should acknowledge this complexity.

Nematodes belonging to the Cystidicolidae Skrjabin, 1946 constitute more than 23 genera of 111 recognized species in fish from many habitats including the deep-sea, continental shelves, estuarine and freshwater habitats. The taxonomy of many species within the Cystidicolidae is unsettled due to their small size and correspondingly small morphological characters requiring use of scanning electron microscopy and supported more recently by molecular studies. The type species, Ascarophis morrhuae Van Beneden, 1870, which belongs to one of the first described and most speciose cystidicolid genera with 46 species, is based on a two-sentence description of a single female specimen from an Atlantic cod, Gadus morhua, presumably captured off the coast of Belgium in the North Sea (Van Beneden, 1870). New material was collected/examined from Atlantic cod and haddock, Melanogrammus aeglefinus, from Iceland and the North Sea and specimens present in the Natural History Museum, London were also studied. Based on these materials, A. morrhuae is morphologically redescribed and the first DNA sequences of this species are provided, it is differentiated from other Ascarophis species present in the North Atlantic and previous records are reviewed. This information provides a foundation for taxonomic and phylogenetic reconsideration of all cystidicolid nematodes and related families.

Incilius marmoreus inhabits an extensive range along the Pacific Coast of Mexico and a smaller allopatric region in the State of Veracruz, exhibiting an unusual distribution among herpetofauna. Gunther (1901) classified the Pacific coastal toads Bufo argillaceus and B. lateralis as conspecific with Incilius [Bufo] marmoreus, which has its type locality in Veracruz. Here, we adopt a multidisciplinary approach to reevaluate the phylogeography and taxonomy of I. marmoreus by gathering and analyzing morphological data and conducting phylogenetic and population genetic analyses from genome-wide SNP data. Our results uphold the current taxonomy by concurring with Gunther (1901). Our phylogenetic and population genetic analyses suggest that I. marmoreus from Veracruz are closely related to those from Oaxaca whilst coalescent analyses recovered a north-south split along the Pacific Coast estimated to have occurred [~]0.86 Mya followed by a shallow east-west split in the southern lineage that separates the Pacific coastal populations and the allopatric population in Veracruz [~]0.33 Mya. This species displays marked morphological and genetic diversity throughout its range, but this variation appears to be consistent with gene flow across contiguous populations rather than the existence of independent evolutionary lineages. The processes leading to the geographic isolation of the population on the coast of Veracruz remain uncertain, but we hypothesize that climatic and vegetation changes in the Late Pleistocene may have played a role.

Astyanax Baird & Girard, 1854 is a widely distributed and species-rich genus of Acestrorhamphidae, whose abundant populations in Neotropical basins play a crucial ecological role at the trophic level. Taxonomic uncertainties persist within the genus, as seen in Astyanax sp. (formerly designated as A. fasciatus) from the Magdalena basin in Colombia. Concerns about its genetic status are heightened due to ecological threats posed by hydroelectric dams, from habitat loss to river connectivity. We isolated and characterized 17 microsatellite loci to assess the population genetics of this species in a broad sample from the middle and lower sections of the Cauca River, now interrupted by the Ituango dam. Furthermore, a multidisciplinary approach integrating phylogenetic analyses of mitochondrial (COI) and nuclear (rag2) markers with geometric morphometric analyses was employed to evaluate potential cryptic diversity within Astyanax sp. Microsatellites revealed two genetic groups in the studied area, strongly supported as distinct lineages by phylogenetic analyses. Unexpectedly, one of these lineages of Astyanax sp. was recovered in an unresolved clade with samples of A. microlepis and allopatric samples of A. viejita from the Maracaibo Lake basin. Each genetic group showed high genetic diversity, but also evidence of recent bottleneck events and significant-high values of inbreeding. Morphometric analyses provided evidence of significant phenotypic differentiation among A. microlepis, Astyanax sp. 1 (Asp1), and Astyanax sp. 2 (Asp2). Morphological patterns ranged from the robust profile of A. microlepis to the streamlined shape of Astyanax sp. 2 (Asp2), with Astyanax sp. 1 (Asp1) displaying intermediate traits and localized differences in head length and fin placement. Statistical support from permutation tests and a high overall classification accuracy (95.65%) underscore the existence of distinct morphospecies, suggesting that phenotypic differentiation is well-established, despite the complex evolutionary history of the group. This study suggests the presence of cryptic diversity within Astyanax sp. and provides valuable genetic information for the conservation and management of their populations in the Magdalena basin.

Uintatheres, mammals belonging to the extinct order Dinocerata, are among the most recognizable of all Paleogene ([~]66 - 23 Ma) organisms. Unmistakable for their bizarre skulls with multiple pairs of horns and saber-like upper canines, uintatheres have captivated paleontologists since the late nineteenth century. Since their initial discovery, uintatheres have been regarded as a classic example of dramatic sexual dimorphism in the fossil record, with males purported to be larger and possess more prominent horns and canines than females. However, the hypothesis that uintatheres were highly sexually dimorphic has never been formally tested. Here, I use traditional, linear morphometrics on a collection including most known skulls of Uintatherium anceps to quantify patterns of cranial variation within this taxon. Despite using a variety of traditional and novel statistical methods, I fail to detect any evidence of strong sexual dimorphism in Uintatherium. To verify my approach, I assembled a similarly sized dataset from Bison bison as an extant analog, and found strong, consistent evidence of sexual dimorphism. In light of these findings, as well as the current understanding of uintathere systematics and paleoecology, I argue that strong sexual dimorphism should not be treated as the null hypothesis for this clade.

The diversity of body shapes is one of the most prominent features of phenotypic variation in mammals. Yet, mammalian body shapes are poorly quantified and the underlying components contributing to its diversity as well as its relationship to other components of the skeleton are rarely tested. Here, we use lagomorphs (hares, rabbits and pikas) as a model system to (1) investigate which components of the skeleton contributed the most to body shape diversity, (2) examine the relationships between body shape and relative limb lengths, and (3) test how body size, ecotype, burrowing behavior, and locomotor mode influenced variation in lagomorph body shape and appendicular morphology. We quantified the body shape and functional proxies of the appendicular skeleton in 40 lagomorph species from osteological specimens held at museum collections. Using phylogenetic comparative methods, we found the relative length of the ribs and elongation or shortening of the thoracic and lumbar regions contributed the most to body shape evolution across lagomorphs. Second, we found that only leporids (hares and rabbits) exhibited a significant relationship between limb length and body shape, where more elongate species exhibit relatively shorter forelimbs and hindlimbs. Lastly, we found that models incorporating body size were the best predictors of lagomorph body shape and the majority of the appendicular traits, whereas models incorporating burrowing behavior and locomotor mode were largely poor fits. Broadly, these results indicate that larger lagomorphs tend to exhibit more robust body shapes with longer, more gracile forelimbs, whereas smaller lagomorphs tend to exhibit more elongate body shapes with shorter, more robust forelimbs. Overall, this work contributes to the growing understanding of mammalian body shape evolution and demonstrates the importance of not omitting body size in ecomorphological analyses.

The genus Trichiurus is the most economically valuable fish in the family Trichiuridae, currently recognized to include 10 valid species. However, historically numerous morphologically similar congeners have been erroneously assigned as synonyms or subspecies of T. lepturus. In this study, we examined 16 hairtail specimens collected from the southern waters of Java Island, Indonesia. Integrated morphological and mitochondrial phylogenetic analyses (COX1 and 16S rRNA), compared against global Trichiurus sequences, revealed that these specimens form an independent lineage that diverged early from other congeners. Consequently, we describe this lineage as a previously undescribed cryptic species. Diagnostic characters include: first anal-fin spine below 36th-37th dorsal-fin rays; anus below 35th-36th dorsal-fin rays; anteriormost tip of supraoccipital well posterior to posterior distal margin of eye; anterior margin of the pectoral-fin spine non-serrated; fangs on both jaws with barb-like processes; upper jaw long, mean 16.6% (15.5-17.6%) of preanal length; snout short, 12.0% (10.9-13.1%) of preanal length; eye small, diameter 5.3% (4.3-5.7%) of preanal length; and absence of hyperostosis on dorsal cranium. We herein propose the name Trichiurus javaensis sp. nov., and provide a formal morphological description and diagnostic characterization of this species.

The temperate rainforests of the Pacific Northwest of North America harbor many endemic taxa whose evolutionary histories have been shaped by major climatic and geologic events. The enigmatic taildropper slugs (genus Prophysaon) are one example, notable for their ability to autonomize their tails to escape predators. Despite extensive work uncovering the evolutionary history of individual lineages, relationships among the nine recognized species of Prophysaon remain poorly understood due to insufficient molecular data. To address this, we collected transcriptomes for six of the nine currently accepted species of Prophysaon. Using these data, we were able to resolve species relationships, calling into question the existing subgeneric classification based on morphology. We also detected undescribed phenotypic diversity within the P. andersonii--P. foliolatum species complex, with molecular data supporting the distinctness of two phenotypically distinct populations from Washington. Finally, our transcriptomic data suggest a moderate role of introgression in shaping the evolutionary history of Prophysaon. Here, we synonymize the subgenus Mimetarion with nominotypical Prophysaon. Future work should further investigate whether the undescribed diversity detected here represents species level differentiation.

The early evolutionary history of modern domestic horses (Equus caballus/E. ferus caballus), known as the DOM2 lineage, is well documented due to numerous archaeological and ancient DNA (aDNA) studies. Although many uncertainties remain in the domestication timeline, current evidence suggests that the domestication of modern horses began in the Pontic-Caspian steppe at least [~]2700 BCE (before common era), or even earlier. However, it is not known how long remnant wild horse populations survived or when domestic horses were introduced into Northern Europe. In this study, we review the current knowledge of horse domestication, focusing on Northern Europe. We analysed prehistoric horses from western Russia to assess the body sizes of wild horses from the Ivanovskaya site (5900-3800 BCE) in the Pontic-Caspian steppe, and the body weight of one Lithuanian wild horse (4000-3800 BCE). Additionally, we analysed body sizes of Late Bronze Age-Early Roman Age horses (1100 BCE-300 CE; common era) and re-analysed body sizes and estimated rider weights of historic domestic horses from Lithuania (100-1400 CE). We searched for pathological changes and signs of bit wear indicative of bridling. Furthermore, we investigated maternal genetic diversity by sequencing ancient mitochondrial DNA. We found that wild horses from Ivanovskaya were intermediate in body size between earlier and more recent horses of the Eurasian Steppe, and that the Lithuanian wild horse weighed only [~]270 kg and Late Bronze Age-Early Roman Age horses 200-300 kg. Lithuanian domestic horses were pony-sized (< 130 cm on average). Bit wear was confirmed on one tooth, the oldest domestic horse in Lithuania (799-570 cal BCE). Another tooth showed signs of the Equine Odontoclastic Tooth Resorption and Hypercementosis (EOTRH) condition. Mitochondrial DNA was successfully amplified from one Ivanovskaya wild horse along with 25 other ancient samples, including Lithuanias oldest domestic horse. mtDNA diversity was high, revealing several maternal lineages.

The Santa Catalina Mountains are an iconic member of the Madrean Sky Islands, rising above Tucson, Arizona, USA, where the Catalina Highway connects Sonoran desertscrub to stands of conifer forest nearly 2,800 meters in elevation. As one of the [~]54 forested mountain areas in this system, the Santa Catalinas host unique biotic communities relative to the surrounding lowlands. However, most of these sky islands lack the surveys of resident small mammals (either historical or recent) needed for studying biodiversity in the context of changing climate and habitat use. From 2021 to 2023, we surveyed 10 localities on the north and south slopes of the Santa Catalina Mountains using holistic sampling methods to document terrestrial small mammal diversity and preserve multiple tissue types. Here we summarize these new collections relative to previous voucher specimens and human observations, identifying gaps for future work to address. Our survey recorded the presence of 15 species, preserved 150 voucher specimens paired with a suite of flash-frozen tissues, and non-lethally sampled another 219 individuals (ear tissue, feces, ectoparasites, and measurements) to provide populational data from sites where vouchering occurred. Despite the road accessibility and long history of sampling in the Santa Catalina Mountains, our surveys extended the known elevational range for 8 species, including the first known specimen of Reithrodontomys fulvescens from the area. Our use of a transect-based survey design, which maximizes species diversity across biotic communities, paired with holistic specimen preservation techniques, provides a model for surveying patterns of population genetic and parasite sharing relationships across other Madrean Sky Islands, bridging a [~]40 year lull in specimen preservation while adding new data dimensions that promote integrative studies of small mammal biodiversity. With more complete sampling, other mountains will offer promising replicates for studying eco-evolutionary impacts of the regions episodic habitat connectivity. Teaser textSurveying the terrestrial small mammals of the Santa Catalina Mountains, part of the Madrean Sky Islands, we analyze modern occurrences relative to previous records and demonstrate the potential value of holistically surveying sky island small mammals.

The deepest phylogenetic divergence within crown birds (Neornithes) is that between the reciprocally monophyletic Palaeognathae and Neognathae. Extant palaeognath diversity comprises the iconic flightless "ratites" (ostriches, rhea, kiwi, cassowaries, and emu), as well as 46 species of volant tinamous in Central and South America (Billerman et al., 2020). Although the earliest stages of palaeognath evolution remain shrouded in mystery due to a sparse fossil record, a group of apparently volant extinct palaeognaths from the Paleogene of Europe and North America, the lithornithids, can help to clarify palaeognath origins. Here, we use high resolution microCT scanning to characterize the morphology of two lithornithid specimens from the early Eocene (Ypresian) London Clay Formation: the neotype of Lithornis vulturinus (NHMUK A5204), from the Isle of Sheppey, Kent, England, and a newly discovered clay nodule containing lithornithid postcranial remains from the nearby locality of Seasalter. This three-dimensional dataset reveals bones from the L. vulturinus neotype that are partially or completely covered by matrix, allowing us to redescribe this critical specimen in new detail and present a revised differential diagnosis of L. vulturinus. We refer the new specimen from Seasalter to L. vulturinus on the basis of apomorphies such as a proximally directed lateral process of the coracoid, caudally divergent lateral margins of the sternum, an arcuate deltopectoral crest, as well as its provenance from a nearby penecontemporaneous locality. The Seasalter specimen contains abundant postcranial material that provides new insight into bones damaged or missing in the neotype, including two undamaged scapulae bearing the hooked acromion that is a diagnostic feature of lithornithids, two complete coracoids, and a nearly complete three-dimensionally preserved sternum. Its estimated body mass is one third larger than that of the neotype, indicating intraspecific variation within L. vulturinus that may reflect sexual dimorphism. Molecular divergence dates and Cretaceous neognath fossils indicate the presence of total-clade palaeognaths before the K-Pg mass extinction event; detailed anatomical descriptions of Paleogene palaeognaths will assist in the identification of the first total-clade palaeognaths from the Cretaceous, and provide insight into how and when flight was independently lost among Cenozoic crown palaeognaths.

The delineation of closely related species remains a persistent challenge in Zoantharia, where morphological plasticity and limited genetic differentiation complicate taxonomy. In this study, we investigated the phylogenetic relationship between the widely distributed sibling taxa Palythoa tuberculosa (Indo-Pacific) and Palythoa caribaeorum (Atlantic) using ultraconserved elements (UCEs) recovered from genome skimming. A dataset comprising 116 loci (35,699 bp) across 37 specimens from Brazil, the Red Sea, Okinawa, and New Caledonia was analysed using both concatenated maximum-likelihood and coalescent-based approaches. Phylogenetic reconstructions did not recover monophyletic relationships corresponding to either species or geographic origin, instead revealing intermixed lineages across the Indo-Pacific and Atlantic regions. Concordance factor analyses indicated low gene concordance and moderate site concordance, suggesting pervasive gene tree discordance rather than a lack of phylogenetic signal. These patterns are consistent with previous studies based on mitochondrial, nuclear, and reduced-representation datasets, indicating that increased marker resolution does not resolve species boundaries within this complex. The observed lack of differentiation may reflect ongoing or recent connectivity among populations, potentially facilitated by long-distance dispersal promoted by anthropogenic rafting or historical range expansion, biological invasion, or biological processes such as incomplete lineage sorting. The results support the hypothesis that P. tuberculosa and P. caribaeorum represent a species complex or a case of incipient speciation rather than fully distinct evolutionary lineages. These findings indicate that genome-scale data alone may be insufficient to resolve very recent divergences, supporting the need for integrative approaches to resolve complicated species boundaries in zoantharians.

AO_SCPLOWBSTRACTC_SCPLOWSpecies represent a fundamental unit of biodiversity in evolutionary biology, but the nature of the speciation continuum and inadequate sampling of organisms with broad distributions provide substantial challenges to species delimitation. The Pacific Treefrog complex (Pseudacris regilla sensu lato) is an iconic but systematically poorly understood group of chorus frogs inhabiting a vast portion of western North America. Current studies tentatively recognize three species in this complex (P. hypochondriaca, P. regilla, P. sierra), but disagreement remains among morphological, mitochondrial, and nuclear genetic data. In this study, we used thorough geographic sampling and thousands of nuclear loci to clarify the phylogenetic relationships and divergence history of P. regilla s.l. lineages and recommend a new taxonomic arrangement. We inferred recent divergence with gene flow between P. regilla and P. sierra, topological inconsistencies, and genealogical divergence indices that place P. regilla and P. sierra firmly in the "gray zone" of speciation. Pseudacris hypochondriaca diverged over 0.5 Ma without gene flow until recent secondary contact with the "north" (P. regilla + P. sierra) lineage. Based on inferences from our genomic data and recently published acoustic signal differentiation, we propose a two species taxonomy for this complex, recognizing the "north" lineage as P. regilla. Our study shows how extensive geographic sampling, high-throughput sequencing, and multiple analytical approaches can resolve systematic uncertainties in challenging species complexes.

Silk glands have been found in two groups of amphipods: the Corophiida and the Ampeliscidae. The silk glands in Ampeliscidae, however, have yet to be examined in detail. Here we report, for the first time, the morphology and distribution of pereopodal glands in the Ampeliscidae, in non-thread producing Synopiidae, and in the Paragammaropsidae. In the Ampeliscidae we found two gland types distributed throughout all pereopods which have the ability to create threads. Pereopods three and four have additional silk extrusion morphology at the tip of the dactylus in which silk is transformed into semi-cylindrical threads used for building domiciles. Synopiid outgroup species have one of the gland types but lack silk extrusion morphology. Using ancestral state reconstruction analysis, we find that glands in the Synopiidae are likely ancestral and hypothesize that silk glands in Ampeliscidae are derived from these ancestral glands. Silk-spinning pereopods in the Paragammaropsidae had similarities with both Corophiida and Ampeliscidae but had distinctions. Ampeliscidae silk-spinning systems bear surprising resemblance to the Corophiida which presents one to reconsider the taxonomic placement of Ampeliscidae and the origins of silk-spinning in amphipods. This is the first comprehensive study on the glandular systems of Ampeliscidae, Synopiidae, and Paragammaropsidae using advanced microscopy, providing pertinent morphological data to the study of arthropod silk gland evolution and complex traits.

Life history strategies such as rapid growth and high population turnover rates observed in vertebrates have been thought to have emerged relatively late in evolution. However, very little direct evidence exists at the species level for early vertebrates. In this study, a large fossil collection of over 450 specimens of Protaspis spp, heterostracan agnathans from the Cottonwood Canyon Formation at Beartooth Butte, Wyoming, from the Early Devonian, was analyzed. Morphological observations, analysis of bone plate completeness, and length-frequency analyses using ELEFAN--commonly used in recent fish studies--were applied to reconstruct growth rates, cohort structure, and ontogenetic processes. Protaspis specimens exhibited a continuous growth series from juvenile to adult stages, and a clear cohort structure was identified from the length-frequency distributions. The ELEFAN analysis suggested a life-history characterized by rapid growth and a short life span, and these features remained consistent in subset analyses restricted by species or locality, confirming the robustness of the estimates. Furthermore, the integration of the dermal bone plates progressed during the late stages of ontogeny, revealing that the rapid growth during the juvenile stage preceded the completion of this defensive structure. Comparisons of their growth parameters with those of extant fishes show that Protaspis does not align with slow-growing, long-lived "living fossil" taxa, but instead clusters with small-bodied, fast-growing species. These findings suggest that life-history strategies involving rapid growth and high population turnover were already established in early jawless vertebrates, much earlier than previously assumed.

Natural history collections underpin our understanding of species distributions, yet some historical records remain embedded in modern avifaunal checklists despite limited documentation and no independent verification. One such case concerns the Dusky Parrot Pionus fuscus in Colombia: although reported from specimens collected by Melbourne A. Carriker Jr. in 1942 in the Serrania de Perija, the species has not been observed in the country for nearly eight decades yet continues to be included in national checklists and conservation assessments. We reassessed the validity of this record by applying a multi-evidence framework integrating historic archival reconstruction, specimen-based morphological comparisons, climatic niche analyses, biogeographic limit assessment and contemporary survey-effort data. Historical documentation and morphological evidence based on high-resolution specimen images and associated curatorial records demonstrate that the Carriker specimens correspond to Pionus chalcopterus, not P. fuscus. Climatic niche analyses reveal minimal environmental overlap between P. chalcopterus and P. fuscus, and place the Perija locality within the climatic niche of P. chalcopterus, while regional biogeography and extensive modern birdwatching coverage provide no support for the occurrence of P. fuscus in Perija. Together, these concordant lines of evidence demonstrate that P. fuscus does not occur in Colombia. Our findings support its removal from national bird lists and conservation assessments and highlight how integrated, multi-evidence reassessments of historical records strengthen ornithological baselines, improve biogeographic inference and ensure that conservation priorities rest on verifiable evidence.

The Dinaric karst of Croatia encompasses a network of over 10,000 caves and represents one of the worlds most important subterranean biodiversity hotspots. It is inhabited by remarkably diverse and often endemic species, including planarian flatworms, which are among the rarest macroinvertebrates encountered in cave habitats. Although the presence of cave planarians has long been known, no integrative research on this group has been conducted to date, and the evolutionary relationships between these animals and their surface water counterparts are currently unresolved. To address these gaps, we combined field sampling, phylogenetic analysis based on COI and 18S genes, and phenotypic characterization. Our results show that cave planariids in Croatia belong to at least three genera and are more widespread and diverse across both Croatia, and the broader Dinaric karst, than previously assumed. We increased the number of cave records in the Dinaric karst from 26 to 37 and documented cf. Atrioplanaria and Phagocata in Croatian caves for the first time. Phylogenetic reconstructions suggest numerous independent cave colonization events, including multiple instances within the genera Crenobia and cf. Atrioplanaria. Variation in pigmentation and eye reduction, both within and between populations, further reveal heterogeneous evolutionary trajectories of cave-associated phenotypes. The biogeographical patterns and high genetic diversity we report here point to a complex evolutionary history of planariids in the Dinarides. Our newly generated molecular phylogenies and systematic documentation of trait variability establish Planariidae as a valuable model for studying mechanisms underlying convergent evolution of pigment loss and eye reduction in cave environments.

Paleobiologists commonly use genera as a proxy for species in biodiversity studies. However, a lingering concern is that patterns among genera might not always faithfully reflect patterns among species. To date, the concern has focused chiefly on measured patterns of richness over time and on implied origination and extinction rates. However, similar issues might arise for studies of morphological disparity. Moreover, there potentially are additional implications of disparity patterns among species versus those among genera concerning the range of observable anatomical characters and whether disparity within genera is comparable to disparity among genera. If clades have some relatively slowly changing characters that workers have used to denote different genera, then we would expect to see congeneric species to cluster in morphospace; however, if such characters are rare, then within-genus disparity might approach among-genus disparity. Here, we use genus-level and species-level disparity patterns among acanthoceratid ammonoids from the Late Cretaceous. In particular, we examine whether these different level imply different evolutionary dynamics over a major ecological event (Ocean Anoxic Event 2) and how disparity within genera (i.e., among congeneric species) compares to disparity among genera. We find genus-level disparity somewhat inflates early acanthoceratid disparity but implies similar patterns over the OAE2. We also find that within-genus disparity is slightly lower than among-genus, but not hugely so. The combined results suggest that acanthoceratoid shell anatomy does not really show "genus" level characters, even if congeneric species do tend to be more similar to each other than to species in other genera. Thus, this might provide more of a warning for other types of studies using anatomical data (e.g., phylogenetic studies) than for disparity studies. Non-technical SummaryMany paleobiologists use genera to examine scientific questions. This leads to questions over whether this broader approach misses important species-level patterns. This study uses acanthoceratid ammonoids from the Late Cretaceous to examine disparity patterns at both the genus-level and the species-level. We specifically examine the disparity at both levels of this group over a time of high stress for this group, Ocean Anoxic Event 2 (OAE2). Our results show that genus-level disparity slightly exaggerates early acanthoceratid disparity but lowers to a similar pattern to the species-level disparity during OAE2. Within-genus disparity is shown to be slightly lower than among-genus, but not enough to be startling. Together, these results indicate that while some species within the same genus tend to be more alike to each other than those in other genera, there isnt a set of true "genus" level characters. This outcome leads to a warning against using anatomical data in phylogenetic studies, but less so for disparity studies.

Dental morphology and wear patterns provide insight into the dietary adaptations and ecological niches of living and extinct herbivores. Traditional classification statistics such as Linear Discriminant Analysis (LDA) are limited by assumptions of linearity, normality, and homoscedasticity. This study quantifies mesowear, the shape of molar cusps resulting from occlusal wear, and evaluates the performance of non-linear machine learning models in predicting herbivore diets based on geometric morphometric (GMM) data from adult mandibular second molars (M2) in bovids. We applied Generalized Procrustes Analysis and Principal Component Analysis (PCA) to digitized occlusal shape coordinates from 132 M2 specimens across 64 species. Using the resulting principal component scores, we compared the classification accuracy of LDA with three non-linear models: Random Forest, K-Nearest Neighbors, and Gradient Boosting. While LDA achieved a cross-validated accuracy of just 31%, all non-linear models achieved 99% cross-validation accuracy and 90% test accuracy, demonstrating substantially improved performance. Misclassification analyses revealed that non-linear models more effectively captured complex shape differences, particularly among species with overlapping wear patterns. Our findings support the integration of machine learning with geometric morphometrics to quantify mesowear and improve dietary classification, providing a framework for robust paleoecological inference.

The Socotra Cormorant (Phalacrocorax nigrogularis) is a threatened seabird endemic to the coastal areas of the Arabian Gulf and the Arabian Sea, two regions separated by the Strait of Hormuz. Conserving threatened species requires clear delineation of population boundaries and the evaluation of genetic diversity. However, information on population structure and genetic variation, necessary for such an assessment, is lacking for the Socotra Cormorants. In this study, we assessed population structure and genetic diversity of Socotra Cormorants using two contrasting genetic markers: (1) maternally inherited mtDNA cytochrome oxidase 1 (COI) and (2) a nuclear non-coding region, {beta}-fibrinogen intron 7 (FIB7). A total of 279 individuals were sampled from four colonies in the Arabian Gulf and one colony on Hasikiyah Island in the Arabian Sea. Findings based on COI-variation suggest that the Arabian Gulf colonies represent one large population with extensive gene flow between Gulf colonies--except for the most distant pair of colonies--but isolated from Hasikiyah in the Arabian Sea. COI-variation indicated significant differentiation between the colonies inside the Gulf and the Hasikiyah colony. This is consistent with the reported distribution patterns, and may reflect phylogeographic processes of the region. The Gulf population showed substantially lower COI-diversity, with significantly lower nucleotide and haplotype diversity compared to Hasikiyah. In contrast, FIB7 results indicated extensive connectivity among colonies, with no detectable population structure or significant differences between the Gulf population and Hasikiyah. This study presents the first characterization of population structure and genetic diversity of Socotra Cormorants. The low genetic diversity coupled with relative isolation of the Gulf Socotra Cormorants raises conservation concerns regarding their long-term viability by potentially reducing fitness and eroding their evolutionary capacity to adapt to environmental change. LAY SUMMARYO_LIThe Socotra Cormorant is a threatened seabird found in the Arabian Gulf and Arabian Sea, but little was previously known about its population structure and genetic diversity. C_LIO_LIWe analyzed 279 birds from five nesting colonies (4 in the Gulf and 1 in the Arabian Sea), using two genetic markers to assess population connectivity and variation. C_LIO_LIWe found that the Socotra cormorants inside the Gulf appear to form a large, genetically isolated population with relatively low genetic diversity. C_LIO_LIThis is the first study that evaluates population structure and genetic diversity of this endangered seabird. C_LIO_LIThis is important information for the conservation of the Gulf Socotra cormorants because low genetic diversity, coupled with relative isolation, is associated with reduced fitness, and suggests that they may have a lower chance to adapt to environmental changes. C_LI