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1. Intrageneric taxonomic distinction based on morphological variation in the macaque ( Macaca ) skeleton

   https://doi.org/10.1002/ar.25283  

   Kenyon‐Flatt, Brittany; von_Cramon‐Taubadel, Noreen (July 2023, The Anatomical Record)

   Abstract Taxonomic classification is important for understanding the natural world, yet current methods for species assessment often focus on craniodental morphology rather than the entire skeleton. Moreover, it is currently unknown how much variation could, or should, exist intragenerically. Here, we tested whether taxonomy can be accurately predicted based on patterns of morphological variation in macaques (H₁) and whether postcranial bones reflect subgeneric macaque taxonomy similarly, or better, than the cranium (H₂). Data included 3D scans of cranial and postcranial bones for eight macaque species (Macaca arctoides,Macaca fascicularis,Macaca fuscata,Macaca mulatta,Macaca nemestrina,Macaca nigra,Macaca radiata, andMacaca sylvanus). Fixed anatomical and semilandmarks were applied to scans of eight skeletal elements (crania = 45; mandible = 31; scapula = 66; humerus = 38; radius = 33; os coxa = 28; femur = 40; tibia = 40). For each skeletal element, regression analyses were performed to minimize the effects of sexual dimorphism. Between‐groups principal components analysis was used to visualize the major patterns of among‐species morphological variation, while the strength of correct taxon classification was measured with discriminant function analysis. Results suggested accepting the alternate hypothesis that different macaque species can be distinguished morphologically. Both cranial and many postcranial elements appeared to possess a taxonomic signal, and the limb bones—especially the upper limb—are reported to be more useful for taxonomic assessment than previously realized. Theoretically, certain behaviors and/or ecogeographical factors, as well as phylogeny, influenced skeletal morphology in macaques, likely contributing to taxonomic distinctions among different species. 

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2. A hypothesis-based approach to species identification in the fossil record: a papionin case study

   https://doi.org/10.3389/fevo.2024.1481903  

   Brasil, Marianne F; Monson, Tesla A; Stratford, Dominic J; Hlusko, Leslea J (January 2025, Frontiers in Ecology and Evolution)

   Modern papionin monkeys are a diverse group that encompasses a broad range of morphologies, behaviors, and ecologies. A fossil genus known from African Plio-Pleistocene deposits, Parapapio, is widely regarded as a candidate ancestor to later African papionins. However, despite general agreement that this genus sits at or near the base of the African papionin clade, the taxonomy within Parapapio remains highly contentious. This project evaluates the species-level taxonomy of Parapapio with an explicit hypothesis-based approach to interpreting morphological variation in this sample of fossils. We tested two hypotheses: (H₁) the craniodental variation within Parapapio does not cluster into three groups that reflect the three known species, and (H₂) all the Parapapio fossils can be accommodated within the craniodental shape and size variation observed for a single extant species of papionin. To test the first hypothesis, we assessed a subset of relatively complete and well-preserved Parapapio crania (n=16), intentionally without reference to previous taxonomic identifications. Specimens were sorted by similarity in cranial features and results were then compared with published taxonomic classifications. Our results demonstrate that morphological traits do not cluster consistently according to the current species categories within Parapapio, failing to reject our first hypothesis. To test our second hypothesis, we examined variation in cranial and dental metrics within Parapapio (n=64) relative to three extant papionin samples (n=310). Our results fail to reject the hypothesis that all Parapapio specimens could belong to a single species and suggest that the three-species paradigm does not reflect the anatomical variation of this genus. We recommend subsuming all Parapapio specimens within Parapapio broomi, the species name with taxonomic priority. The results of this hypothesis-testing approach to taxonomy carry substantial implications for the taxonomy of Parapapio, as well as for biochronological and paleoecological studies more generally, including the taxonomy and paleobiology of hominids recovered from these same deposits. 

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3. Pterion variation in the skulls of rhesus macaques from Cayo Santiago: Inheritance, development, and pathology

   https://doi.org/10.1002/ar.25417  

   Francis, George; Wang, Qian (February 2024, The Anatomical Record)

   Abstract The pterion is the sutural juncture of the frontal, parietal, sphenoidal, temporal, and zygomatic bones on the lateral aspect of the cranium. As a craniometric landmark, the pterion has a taxonomic valence, in addition to a common neurosurgical entry point in medicine. Variation in the articulation patterns at the pterion have been documented between primate species yet have a high degree of uniformity within species, suggesting a genetic control for this complex region of the skull. In this study, pterion pattern variation was investigated in 1627 Rhesus macaque crania of the Cayo Santiago colony. The colony's associated skeletal collections accompany known age, sex, and maternal lineages. Pterion pattern prevalence rates were tested against matrilines, as well as cranial shape, and cranial sutural fusion ages (including individuals with prematurely fused sutures). Five patterns were identified, the most prominent being the prevailing Old World Monkey frontotemporal (FT) articulation (83.4%). The relative frequency of those not exhibiting the FT pattern was found to vary considerably between matrilineal families (p = 0.037), ranging from 5.3% to 34.2%. Mothers with the non‐FT pterion pattern were three times as likely to bear non‐FT offspring. Cranial shape additionally varied with pterion type. Males exhibiting zygomaticotemporal (ZT) and sphenoparietal (SP) articulations possessed a relatively longer and narrower cranium than those with the default FT type (p = < 0.001). Cranial sutural fusion ages were not found to differ between pterion types, though all individuals with craniosynostosis (6; 0.38%) exhibited the FT type. The study provided strong evidence for a genetic source for pterion pattern as well as outlining a relatively novel relationship with cranial shape and sutural fusion ages. A unifying explanation may lie in those genes involved in both sutural and craniofacial development, or in the variation of brain growth processes channeling sutural articulation at the pterion. Both may be heritable and responsible for producing observed matrilineal differences in the pterion. 

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4. An integrative genomic and phenomic analysis to investigate the nature of plant species in Escallonia (Escalloniaceae)

   https://doi.org/10.1038/s41598-021-03419-0  

   Jacobs, Sarah J.; Grundler, Michael C.; Henriquez, Claudia L.; Zapata, Felipe (December 2021, Scientific Reports)

   Abstract What we mean by species and whether they have any biological reality has been debated since the early days of evolutionary biology. Some biologists even suggest that plant species are created by taxonomists as a subjective, artificial division of nature. However, the nature of plant species has been rarely tested critically with data while ignoring taxonomy. We integrate phenomic and genomic data collected across hundreds of individuals at a continental scale to investigate this question inEscallonia(Escalloniaceae), a group of plants which includes 40 taxonomic species (the species proposed by taxonomists). We first show that taxonomic species may be questionable as they match poorly to patterns of phenotypic and genetic variation displayed by individuals collected in nature. We then use explicit statistical methods for species delimitation designed for phenotypic and genomic data, and show that plant species do exist inEscalloniaas an objective, discrete property of nature independent of taxonomy. We show that such species correspond poorly to current taxonomic species ($$< 20\%$$ $<20\%$) and that phenomic and genomic data seldom delimit congruent entities ($$< 20\%$$ $<20\%$). These discrepancies suggest that evolutionary forces additional to gene flow can maintain the cohesion of species. We propose that phenomic and genomic data analyzed on an equal footing build a broader perspective on the nature of plant species by helping delineate different ‘types of species’. Our results caution studies which take the accuracy of taxonomic species for granted and challenge the notion of plant species without empirical evidence. Note: A version of the complete manuscript in Spanish is available in the Supplemental Materials. 

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5. Effect of topographic complexity on species richness in the Galápagos Islands

   https://doi.org/10.1111/jbi.14230  

   Roell, Yannik E.; Phillips, John G.; Parent, Christine E. (August 2021, Journal of Biogeography)

   Abstract AimThe accumulation of species through time has been proposed to have a hump‐shaped relationship on volcanic islands (highest species richness during intermediate stages of an island's lifespan). Change in topographic complexity (TC) of islands over time is assumed to follow the same relationship. However, TC can be measured in different ways and may not have the same impact across taxonomic groups. Here, we quantify TC across the Galápagos Islands and test the assumption that TC follows a predictable trajectory with island age. Subsequently, we ask whether including TC improves statistical models seeking to explain variation in species richness across islands. LocationGalápagos Archipelago, Ecuador. TaxonNative and endemic terrestrial animals and plants. MethodsFor each island, we generated eight TC indices from a 30‐m resolution digital elevation model. We tested for a relationship between each index and island age, and whether it significantly contributes to observed variation in species richness, using 11 different models for 12 taxonomic groups across the Galápagos Islands. ResultsFour TC indices were significantly negatively correlated with either island age or ontogenetic age and only one index followed the hump‐shaped relationship with age. No index consistently contributed to the variation in species richness for all taxonomic groups. However, for all 12 taxonomic groups, incorporating at least one TC index in modelling species richness improved one or more models. The most common TC index improving models was standard deviation of slope, although each index improved at least five models across all taxa. Different factors predicted taxon‐specific richness, and habitat diversity was significant for all taxa. Main conclusionsTopographic complexity is an important component influencing species richness, but its impact likely differs among taxonomic groups and different scales. Therefore, future studies should incorporate broad, multi‐dimensional measures of TC to understand the biological importance of TC. 

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