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Rummel AD, Sheehy ET, Schachner ER, Hedrick BP. Sample Size and Geometric Morphometrics Methodology Impact the Evaluation of Morphological Variation. Integr Org Biol 2024; 6:obae002. [PMID: 38313409 PMCID: PMC10833145 DOI: 10.1093/iob/obae002] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/07/2023] [Revised: 11/03/2023] [Accepted: 01/19/2024] [Indexed: 02/06/2024] Open
Abstract
Geometric morphometrics has had a profound impact on our understanding of morphological evolution. However, factors such as sample size and the views and elements selected for two-dimensional geometric morphometric (2DGM) analyses, which are often dictated by specimen availability and time rather than study design, may affect the outcomes of those analyses. Leveraging large intraspecific sample sizes (n > 70) for two bat species, Lasiurus borealis and Nycticeius humeralis, we evaluate the impact of sample size on calculations of mean shape, shape variance, and centroid size. Additionally, we assessed the concordance of multiple skull 2D views with one another and characterized morphological variation in skull shape in L. borealis and N. humeralis, as well as a closely related species, Lasiurus seminolus. Given that L. seminolus is a morphologically cryptic species with L. borealis, we assessed whether differences in skull shape and in 2DGM approach would allow species discrimination. We found that reducing sample size impacted mean shape and increased shape variance, that shape differences were not consistent across views or skull elements, and that trends shown by the views and elements were not all strongly associated with one another. Further, we found that L. borealis and L. seminolus were statistically different in shape using 2DGM in all views and elements. These results underscore the importance of selecting appropriate sample sizes, 2D views, and elements based on the hypothesis being tested. While there is likely not a generalizable sample size or 2D view that can be employed given the wide variety of research questions and systems evaluated using 2DGM, a generalizable solution to issues with 2DGM presented here is to run preliminary analyses using multiple views, elements, and sample sizes, thus ensuring robust conclusions.
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Affiliation(s)
- A D Rummel
- Department of BioSciences, Rice University, Houston, TX 77005, USA
| | - E T Sheehy
- Department of Ecology and Evolutionary Biology, Tulane University, New Orleans, LA 70118, USA
| | - E R Schachner
- Department of Physiological Sciences, College of Veterinary Medicine, University of Florida, Gainesville, FL 32603, USA
| | - B P Hedrick
- Department of Biomedical Sciences, College of Veterinary Medicine, Cornell University, Ithaca, NY 14853, USA
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Grand Pré CA, Thielicke W, Diaz Jr RE, Hedrick BP, Elsey RM, Schachner ER. Validating osteological correlates for the hepatic piston in the American alligator ( Alligator mississippiensis). PeerJ 2023; 11:e16542. [PMID: 38144194 PMCID: PMC10749092 DOI: 10.7717/peerj.16542] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/07/2023] [Accepted: 11/08/2023] [Indexed: 12/26/2023] Open
Abstract
Unlike the majority of sauropsids, which breathe primarily through costal and abdominal muscle contractions, extant crocodilians have evolved the hepatic piston pump, a unique additional ventilatory mechanism powered by the diaphragmaticus muscle. This muscle originates from the bony pelvis, wrapping around the abdominal viscera, extending cranially to the liver. The liver then attaches to the caudal margin of the lungs, resulting in a sub-fusiform morphology for the entire "pulmo-hepatic-diaphragmatic" structure. When the diaphragmaticus muscle contracts during inspiration, the liver is pulled caudally, lowering pressure in the thoracolumbar cavity, and inflating the lungs. It has been established that the hepatic piston pump requires the liver to be displaced to ventilate the lungs, but it has not been determined if the lungs are freely mobile or if the pleural tissues stretch ventrally. It has been hypothesized that the lungs are able to slide craniocaudally with the liver due to the smooth internal ceiling of the thoracolumbar cavity. We assess this through ultrasound video and demonstrate quantitatively and qualitatively that the pulmonary tissues are sliding craniocaudally across the interior thoracolumbar ceiling in actively ventilating live juvenile, sub-adult, and adult individuals (n = 7) of the American alligator (Alligator mississippiensis) during both natural and induced ventilation. The hepatic piston is a novel ventilatory mechanism with a relatively unknown evolutionary history. Questions related to when and under what conditions the hepatic piston first evolved have previously been left unanswered due to a lack fossilized evidence for its presence or absence. By functionally correlating specific characters in the axial skeleton to the hepatic piston, these osteological correlates can be applied to fossil taxa to reconstruct the evolution of the hepatic piston in extinct crocodylomorph archosaurs.
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Affiliation(s)
- Clinton A. Grand Pré
- Cell Biology and Anatomy, Louisiana State University Health Sciences Center, New Orleans, LA, USA
| | | | - Raul E. Diaz Jr
- Department of Biological Sciences, California State University Los Angeles, Los Angeles, CA, USA
| | - Brandon P. Hedrick
- Department of Biomedical Sciences, Cornell University, Ithaca, NY, United States of America
| | - Ruth M. Elsey
- Louisiana Department of Wildlife and Fisheries, Grand Chenier, LA, USA
- Murfreesboro, TN, USA
| | - Emma R. Schachner
- Department of Physiological Sciences, College of Veterinary Medicine, University of Florida, Gainesville, FL, USA
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Pintore R, Cornette R, Houssaye A, Allain R. Femora from an exceptionally large population of coeval ornithomimosaurs yield evidence of sexual dimorphism in extinct theropod dinosaurs. eLife 2023; 12:83413. [PMID: 37309177 DOI: 10.7554/elife.83413] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/12/2022] [Accepted: 04/24/2023] [Indexed: 06/14/2023] Open
Abstract
Sexual dimorphism is challenging to detect among fossils due to a lack of statistical representativeness. The Angeac-Charente Lagerstätte (France) represents a remarkable 'snapshot' from a Berriasian (Early Cretaceous) ecosystem and offers a unique opportunity to study intraspecific variation among a herd of at least 61 coeval ornithomimosaurs. Herein, we investigated the hindlimb variation across the best-preserved specimens from the herd through 3D Geometric Morphometrics and Gaussian Mixture Modeling. Our results based on complete and fragmented femora evidenced a dimorphism characterized by variations in the shaft curvature and the distal epiphysis width. Since the same features vary between sexes among modern avian dinosaurs, crocodilians, and more distant amniotes, we attributed this bimodal variation to sexual dimorphism based on the extant phylogenetic bracketing approach. Documenting sexual dimorphism in fossil dinosaurs allows a better characterization and accounting of intraspecific variations, which is particularly relevant to address ongoing taxonomical and ecological questions relative to dinosaur evolution.
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Affiliation(s)
- Romain Pintore
- UMR 7179, Mécanismes Adaptatifs et Évolution (MECADEV), Muséum National d'Histoire Naturelle, CNRS, Paris, France
- Structure and Motion Laboratory, Department of Comparative Biomedical Sciences, Royal Veterinary College, Hatfield, United Kingdom
| | - Raphaël Cornette
- UMR 7205, Institut de Systématique, Évolution, Biodiversité (ISYEB), Muséum National d'Histoire Naturelle, CNRS, Sorbonne Université, EPHE, UA, Paris, France, Paris, France
| | - Alexandra Houssaye
- UMR 7179, Mécanismes Adaptatifs et Évolution (MECADEV), Muséum National d'Histoire Naturelle, CNRS, Paris, France
| | - Ronan Allain
- UMR 7207, Centre de Recherche en Paléontologie - Paris (CR2P), Muséum National d'Histoire Naturelle, CNRS, Sorbonne Université, Paris, France
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Laitman JT, Smith HF. Dinosaurs of all ilks bow and pay tribute to Peter Dodson, their intrepid chronicler, in an Anatomical Record Special Issue in his honor. Anat Rec (Hoboken) 2023. [PMID: 37151192 DOI: 10.1002/ar.25233] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/18/2023] [Accepted: 04/18/2023] [Indexed: 05/09/2023]
Affiliation(s)
- Jeffrey T Laitman
- The Anatomical Record, Center for Anatomy and Functional Morphology, Icahn School of Medicine at Mount Sinai, New York, New York, USA
| | - Heather F Smith
- The Anatomical Record, Center for Anatomy and Functional Morphology, Icahn School of Medicine at Mount Sinai, New York, New York, USA
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Schachner ER, Diaz RE, Coke R, Echols S, Osborn ML, Hedrick BP. Architecture of the bronchial tree in Cuvier's dwarf caiman (Paleosuchus palpebrosus). Anat Rec (Hoboken) 2022; 305:3037-3054. [PMID: 35377558 DOI: 10.1002/ar.24919] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/22/2021] [Revised: 02/25/2022] [Accepted: 03/09/2022] [Indexed: 01/16/2023]
Abstract
We imaged the lungs of five Cuvier's dwarf caiman (Paleosuchus palpebrosus) via computed tomography (CT) and micro-computed tomography (μCT) and compared these data to the lungs of the American alligator (Alligator mississippiensis). These data demonstrate anatomical commonalities between the lungs of P. palpebrosus and A. mississippiensis, and a few notable differences. The structural similarities are (a) a proximally narrow, distally widened, hook-shaped primary bronchus; (b) a cervical ventral bronchus that branches of the primary bronchus and immediately makes a hairpin turn toward the apex of the lung; (c) a sequential series of dorsobronchi arising from the primary bronchus caudal to the cervical ventral bronchus; (d) intraspecifically highly variable medial sequence of secondary airways; (e) sac-like laterobronchi; and (f) grossly dead-ended caudal group bronchi in the caudal and ventral aspects of the lung. The primary differences between the two taxa are in the overall number of large bronchi (fewer in P. palpebrosus), and the number of branches that contribute to the cardiac regions. Imaging data of both a live and deceased specimen under varying states (postprandial, fasting, total lung capacity, open to atmosphere) indicate that the caudal margin and position of the lungs shift craniocaudally relative to the vertebral column. These imaging data suggest that the smooth thoracic ceiling may be correlated to visceral movement during ventilation, but this hypothesis warrants validation. These results provide the scaffolding for future comparisons between crocodilians, for generating preliminary reconstructions of the ancestral crocodilian bronchial tree, and establishing new hypotheses of bronchial homology across Archosauria.
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Affiliation(s)
- Emma R Schachner
- Department of Cell Biology and Anatomy, School of Medicine, Louisiana State University Health Sciences Center, New Orleans, Louisiana, USA
| | - Raul E Diaz
- Department of Biological Sciences, California State University Los Angeles, Los Angeles, California, USA
| | - Rob Coke
- San Antonio Zoo, San Antonio, Texas, USA
| | - Scott Echols
- The Medical Center for Birds, Oakley, California, USA
| | - Michelle L Osborn
- Department of Comparative Biomedical Sciences, School of Veterinary Medicine, Louisiana State University, Baton Rouge, Louisiana, USA
| | - Brandon P Hedrick
- Department of Cell Biology and Anatomy, School of Medicine, Louisiana State University Health Sciences Center, New Orleans, Louisiana, USA
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Morphometrics of the Spinal Cord and Surrounding Structures in Alligator mississippiensis. BIOLOGY 2022; 11:biology11040514. [PMID: 35453713 PMCID: PMC9024830 DOI: 10.3390/biology11040514] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 02/09/2022] [Revised: 03/22/2022] [Accepted: 03/24/2022] [Indexed: 02/04/2023]
Abstract
Simple Summary Morphometric analysis of the spinal cord and surrounding tissue of the American alligator (Alligator mississippiensis) reveals that there are four significantly discrete regions; cervical, thoracic, lumbar, and caudal. Crocodylians, unlike mammals, have a caudal spinal cord that extends throughout the length of their tail (which accounts for roughly 50% of their total body length). Alligator mississippiensis has one of the largest ranges of body sizes among terrestrial vertebrates, this study documents how the different spinal structures change with increasing body size. Though most of the structures exhibit slightly positive allometry, a few exhibit slightly negative allometry; these differences mean that there are significant relational changes as hatchlings grow into large adults. This study provides the first documentation that A. mississippiensis has an expansive subdural space, a lumbar cistern, at the pelvis. Abstract Understanding the fluid dynamics of the cerebrospinal fluid requires a quantitative description of the spaces in which it flows, including the spinal cord and surrounding meninges. The morphometrics of the spinal cord and surrounding tissues were studied in specimens of the American alligator (Alligator mississippiensis) ranging from hatchlings through adults. Within any size class of alligators (i.e., hatchlings), along the axial length there are significant differences in the size of the spinal cord, meninges, and vertebral canal; these differences can be used to define discrete cervical, thoracic, lumbar and caudal regions. When compared across the range of body sizes in Alligator, every structure in each spinal region had a distinctive growth rate; thus, the physical arrangements between the structures changed as the alligator grew. The combination of regional differentiation and differential growth rates was particularly apparent in the lumbar meninges where a unique form of lumbar cistern could be identified and shown to decrease in relative size as the alligator ages. This analysis of the spinal cord and surrounding tissues was undertaken to develop a data set that could be used for computational flow dynamics of the crocodilian cerebrospinal fluid, and also to assist in the analysis of fossil archosaurs.
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