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1. Safe Casting and Reliable Cusp Reconstruction Assisted by Micro‐Computed Tomographic Scans of Fossil Teeth

   https://doi.org/10.1002/ar.24047  

   O'Hara, Mackie C. ; Le Cabec, Adeline ; Xing, Song ; Skinner, Mark F. ; Guatelli‐Steinberg, Debbie ( January 2019 , The Anatomical Record)

   Dental replicas are frequently utilized in paleoanthropological studies of perikymata and enamel hypoplasia. However, fossil teeth are often fragile and worn, causing two problems: (1) the risk of damage by removing enamel fragments when impression‐making material is separated from the fossil tooth surface, and (2) the need to reconstruct worn portions of the crown to assess perikymata number, distribution, and hypoplasia timing. This study presents the advantages of μCT data of canines and lateral incisors for (1) detecting cracks along the enamel‐dentine junction (EDJ) which could cause damage when casting, and (2) reliably and non‐destructively reconstructing worn or broken cusps. Fragile teeth ofHomo naledi, Miocene, and Pleistocene specimens were μCT‐scanned: 2D virtual sections and 3D models allowed for inspecting crack pattern beyond the external surface and 2D virtual sections were used to digitally reconstruct cusp tips (onlyHomo naledi). Micro‐CT scans allowed cracks running along the EDJ and communicating with radial cracks in the enamel to be identified prior to casting. Cusp reconstructions using μCT data were conducted as precisely as when using thin‐sections or photographs, and with high intra‐ and inter‐observer agreement, while preserving the original specimen and affording numerous planes of virtual section. When available, μCT data should be inspected prior to tooth casting to exclude teeth that show a pattern of cracks that could lead to damage. Virtual sections allow for accessible, reliable, and non‐destructive cusp reconstructions that may be used for developmental (e.g., perikymata and enamel hypoplasia) or enamel thickness studies. Anat Rec, 302:1516–1535, 2019. © 2018 American Association for Anatomy

    

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2. Quantification of enamel decussation in gracile and robust capuchins ( Cebus, Sapajus , Cebidae, Platyrrhini)

   https://doi.org/10.1002/ajp.23246  

   Hogg, Russell T. ; Elokda, Abdallah ( February 2021 , American Journal of Primatology)

   Multiple behavioral and biomechanical analyses have demonstrated that capuchin monkeys (CebusandSapajus) are specialized for breaking down hard‐object foods as compared to other cebid monkeys. In addition to a complex suite of craniodental adaptations, it has specifically been demonstrated that capuchins possess highly complex dental enamel, with extensive Hunter–Schreger banding and other decussation, that likely serve as an adaptation to resist crack propagation during hard‐object feeding. Furthermore, it has been demonstrated that robust capuchins (Sapajusspp., formerlyCebus apella) demonstrate further adaptation for hard‐object feeding than other capuchins, routinely breaking down extremely mechanically challenging foods. However, there has been no comparison of dental enamel complexity in robust versus gracile capuchins, to assess whether the dental enamel inSapajusfollows this same pattern of further specialization. Therefore, this study compares dental enamel complexity in images of dental thin sections from a sample of robust versus gracile capuchins using image compression ratio (ICR) analysis. ICR is a variable that correlates with enamel complexity, such that higher ICR values are indicative of increased complexity in the form of enamel decussation. We found no significant difference between robust and gracile capuchins when assessing all teeth in our sample together, however, we did find that robust capuchins have significantly higher ICR values than gracile capuchins for canine teeth, specifically. Our results support prior studies suggesting that robust capuchins are specialized to generate increased masticatory loads with their anterior dentition, specifically, as compared to gracile species.

    

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3. Stable isotope fingerprinting traces essential amino acid assimilation and multichannel feeding in a vertebrate consumer

   https://doi.org/10.1111/2041-210X.13903  

   Manlick, Philip J. ; Newsome, Seth D. ( June 2022 , Methods in Ecology and Evolution)

   Animals often consume resources from multiple energy channels, thereby connecting food webs and driving trophic structure. Such ‘multichannel feeding’ can dictate ecosystem function and stability, but tools to quantify this process are lacking. Stable isotope ‘fingerprints’ are unique patterns in essential amino acid (EAA) δ¹³C values that vary consistently between energy channels like primary production and detritus, and they have emerged as a tool to trace energy flow in wild systems. Because animals cannot synthesize EAAs de novo and must acquire them from dietary proteins, ecologists often assume δ¹³C fingerprints travel through food webs unaltered. Numerous studies have used this approach to quantify energy flow and multichannel feeding in animals, but δ¹³C fingerprinting has never been experimentally tested in a vertebrate consumer.

   We tested the efficacy of δ¹³C fingerprinting using captive deer micePeromyscus maniculatusraised on diets containing bacterial, fungal and plant protein, as well as a combination of all three sources. We measured the transfer of δ¹³C fingerprints from diet to consumer liver, muscle and bone collagen, and we used linear discriminant analysis (LDA) and isotopic mixing models to estimate dietary proportions compared to known contributions. Lastly, we tested the use of published δ¹³C source fingerprints previously used to estimate energy flow and multichannel feeding by consumers.

   We found that EAA δ¹³C values exhibit significant isotopic (i.e. trophic) fractionation between consumer tissues and diets. Nevertheless, LDA revealed that δ¹³C fingerprints are consistently routed and assimilated into consumer tissues, regardless of isotopic incorporation rate. Isotopic mixing models accurately estimated the proportional diets of consumers, but all models overestimated plant‐based protein contributions, likely due to the digestive efficiencies of protein sources. Lastly, we found that δ¹³C source fingerprints from published literature can lead to erroneous diet reconstruction.

   We show that δ¹³C fingerprints accurately measure energy flow to vertebrate consumers across tissues with different isotopic incorporation rates, thereby enabling the estimation of multichannel feeding at various temporal scales. Our findings illustrate the power of δ¹³C fingerprinting for quantifying food web dynamics, but also reveal that careful selection of dietary source data is critical to the accuracy of this emerging technique.

    

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4. Fissures, folds, and scrolls: The ontogenetic basis for complexity of the nasal cavity in a fruit bat ( Rousettus leschenaultii )

   https://doi.org/10.1002/ar.24488  

   Smith, Timothy D. ; Curtis, Abigail ; Bhatnagar, Kunwar P. ; Santana, Sharlene E. ( July 2020 , The Anatomical Record)

   Mammalian nasal capsule development has been described in only a few cross‐sectional age series, rendering it difficult to infer developmental mechanisms that influence adult morphology. Here we examined a sample of Leschenault's rousette fruit bats (Rousettus leschenaultii) ranging in age from embryonic to adult (n= 13). We examined serially sectioned coronal histological specimens and used micro‐computed tomography scans to visualize morphology in two older specimens. We found that the development of the nasal capsule inRousettusproceeds similarly to many previously described mammals, following a general theme in which the central (i.e., septal) region matures into capsular cartilage before peripheral regions, and rostral parts of the septum and paries nasi mature before caudal parts. The ossification of turbinals also generally follows a rostral to the caudal pattern. Our results suggest discrete mechanisms for increasing complexity of the nasal capsule, some of which are restricted to the late embryonic and early fetal timeframe, including fissuration and mesenchymal proliferation. During fetal and early postnatal ontogeny, appositional and interstitial chondral growth of cartilage modifies the capsular template. Postnatally, appositional bone growth and pneumatization render greater complexity to individual structures and spaces. Future studies that focus on the relative contribution of each mechanism during development may draw critical inferences how nasal morphology is reflective of, or deviates from the original fetal template. A comparison of other chiropterans to nasal development inRousettuscould reveal phylogenetic patterns (whether ancestral or derived) or the developmental basis for specializations relating to respiration, olfaction, or laryngeal echolocation.

    

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5. A distinguishing feature of Pongo upper molars and its implications for the taxonomic identification of isolated hominid teeth from the Pleistocene of Asia

   https://doi.org/10.1002/ajpa.23928  

   Ortiz, Alejandra ; Bailey, Shara E. ; Delgado, Miguel ; Zanolli, Clément ; Demeter, Fabrice ; Bacon, Anne‐Marie ; Nguyen, Thi M. H. ; Nguyen, Anh T. ; Zhang, Yingqi ; Harrison, Terry ; et al ( October 2019 , American Journal of Physical Anthropology)

   The taxonomic status of isolated hominoid teeth from the Asian Pleistocene has long been controversial due to difficulties distinguishing between pongine and hominin molars given their high degree of morphometrical variation and overlap. Here, we combine nonmetric and geometric morphometric data to document a dental pattern that appears to be taxonomically diagnostic amongPongo. We focus on the protoconule, a cuspule of well‐documented evolutionary history, as well as on shape differences of the mesial fovea of the upper molars.

   We examined 469 upper molars of eight hominid genera (Australopithecus,Paranthropus,Homo,Meganthropus,Sivapithecus,Pan,Gorilla, andPongo), including representatives ofHomo erectusand extinct and recentPongo. Analyses were conducted at the enamel‐dentine junction to overcome the limitations introduced by dental wear.

   We found that a moderate or large protoconule is present in ~80% of Pleistocene and extantPongo. Conversely, a moderate to pronounced protoconule in hominins,Meganthropus, and African great apes occurs in low frequencies (~0–20%). Canonical variate analyses for the mesial fovea show that Pleistocene and extantPongocluster together and are clearly differentiated from all other groups, except forSivapithecus.

   This study suggests that the protoconule and the shape of the mesial fovea in upper molars are useful features for the taxonomic identification of isolated hominid teeth. By identifying these new features, our results can contribute to the better understanding of hominoid evolutionary history and biogeography during the Asian Pleistocene. However, we emphasize that the reported features should be used in combination with other diagnostic variables for the most accurate taxonomic assessments.

    

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