How to Render Species Comparable Taxonomic Units Through Deep Time: A Case Study on Intraspecific Osteological Variability in Extant and Extinct Lacertid Lizards.

Generally, the species is considered to be the only naturally occurring taxon. However, species recognized and defined using different species delimitation criteria cannot readily be compared, impacting studies of biodiversity through Deep Time. This comparability issue is particularly marked when comparing extant with extinct species because the only available data for species delimitation in fossils are derived from their preserved morphology, which is generally restricted to osteology in vertebrates. Here, we quantify intraspecific, intrageneric, and intergeneric osteological variability in extant species of lacertid lizards using pairwise dissimilarity scores based on a data set of 253 discrete osteological characters for 99 specimens referred to 24 species. Variability is always significantly lower intraspecifically than between individuals belonging to distinct species of a single genus, which is in turn significantly lower than intergeneric variability. Average values of intraspecific variability and associated standard deviations are consistent (with few exceptions), with an overall average within a species of 0.208 changes per character scored. Application of the same methods to six extinct lacertid species (represented by 40 fossil specimens) revealed that intraspecific osteological variability is inconsistent, which can at least in part be attributed to different researchers having unequal expectations of the skeletal dissimilarity within species units. Such a divergent interpretation of intraspecific and interspecific variability among extant and extinct species reinforces the incomparability of the species unit. Lacertidae is an example where extant species recognized and defined based on a number of delimitation criteria show comparable and consistent intraspecific osteological variability. Here, as well as in equivalent cases, application of those skeletal dissimilarity values to paleontological species delimitation potentially provides a way to ameliorate inconsistencies created by the use of morphology to define species. [Intraspecific variation; Lacertidae; morphological disparity; osteology; species delimitation; taxonomic bias.].

Orbital Foraminal Morphometrics in Nonsyndromic Unilateral Coronal Craniosynostosis.

ABSTRACT: Nonsyndromic unilateral coronal craniosynostosis (UCS) is a rare congenital disorder that results from premature fusion of either coronal suture. The result is growth restriction across the suture, between the ipsilateral frontal and parietal bones, leading to bony dysmorphogenesis affecting the calvarium, orbit, and skull base. Prior studies have reported associations between UCS and visual abnormalities. The present study utilizes a novel geometric morphometric analysis to compare dimensions of orbital foramina on synostotic versus nonsynostotic sides in patients with UCS. Computed tomography head scans of pediatric UCS patients were converted into 3-dimensional mesh models. Anatomical borders of left and right orbital structures were plotted by a single trained team member. Dimensions between synostotic and nonsynostotic sides were measured and compared. Medical records were examined to determine prevalence of visual abnormalities in this patient cohort. Visual abnormalities were reported in 22 of the 27 UCS patients (77.8%). Astigmatism (66.7%), anisometropic amblyopia (44.4%), and motor nerve palsies (33.3%) represented the 3 most prevalent ophthalmologic abnormalities. Orbits on synostotic sides were 11.3% narrower ( P < 0.001) with 21.2% less volume ( P = 0.028) than orbits on nonsynostotic sides. However, average widths, circumferences, and areas were similar between synostotic and nonsynostotic sides upon comparison of supraorbital foramina, infraorbital foramina, optic foramina, and foramina ovalia. Therefore, previously proposed compression or distortion of vital neurovascular structures within bony orbital foramina does not seem to be a likely etiology of visual abnormalities in UCS patients. Future studies will examine the role of ocular and/or neuro-ophthalmologic pathology in this disease process.

Craniofacial Dysmorphology in Infants With Non-Syndromic Unilateral Coronal Craniosynostosis.

BACKGROUND: Unilateral coronal craniosynostosis (UCS) is a congenital disorder resulting from the premature suture fusion, leading to complex primary and compensatory morphologic changes in the shape of not only the calvarium and but also into the skull base. This deformity typically requires surgery to correct the shape of the skull and prevent neurologic sequelae, including increased intracranial pressure, sensory deficits, and cognitive impairment. METHODS: The present multicenter study sought to reverse-engineer the bone dysmorphogenesis seen in non-syndromic UCS using a geometric morphometric approach. Computed tomography scans for 26 non-syndromic UCS patients were converted to three-dimensional mesh models. Two hundred thirty-six unique anatomical landmarks and semi-landmarked curves were then plotted on each model, creating wireframe representations of the Patients' skulls. RESULTS: Generalized Procrustes superimposition, Principal Component Analysis, and heatmaps identified significant superior displacement of the ipsilateral orbit ("harlequin" eye deformity), anterior displacement of the ear ipsilateral to the fused coronal suture, acute deviation of midline skull base structures ipsilateral to the fused coronal suture and flattening of the parietal bone and associated failure to expand superiorly. CONCLUSIONS: The described technique illustrates the impact of premature coronal suture fusion on the development of the entire skull and proposes how bone dysmorphology contributes to the Patients' neurologic sequelae. By bridging novel basic science methodologies with clinical research, the present study quantitatively describes craniofacial development and bone dysmorphogenesis.

The Expanding Role of Geometric Morphometrics in Craniofacial Surgery.

INTRODUCTION: Geometric morphometrics (GM) is an advanced landmark-based quantitative method used to study biological shape and form. Historically, GM has been limited to non-biomedical fields such as comparative biology; however, this technique confers advantages over traditional cephalometric methods, warranting a review of current applications of GM to human craniofacial disorders. METHODS: The RISmed package was used to extract metadata associated with PubMed publications referencing GM analysis techniques in craniofacial and reconstructive surgery. PubMed search terms included "geometric AND morphometric AND craniofacial;" and "geometric AND morphometric AND reconstructive surgery." Duplicate search results were eliminated. RESULTS: Search yielded 139 studies between 2005 and 2020, of which 27 met inclusion criteria. Human craniofacial studies constituted 2% of all queried GM studies. Among these, cleft lip and palate were the most commonly studied craniofacial conditions (7 studies, 26%), followed by sagittal craniosynostosis (4 studies, 15%). Seventeen studies (63%) used GM to assess skeletal structures, seven studies (26%) examined both skeletal and soft tissues, and three studies (11%) analyzed soft tissues only. Eleven studies (40.1%) employed a GM approach to evaluate postoperative changes in craniofacial morphology. Two studies (7%) systematically compared GM analysis with conventional shape measurements. CONCLUSION: The ability to study shape while controlling for variability in structure size and imaging technique make GM a promising tool for understanding growth patterns in complex craniofacial diseases. Furthermore, GM overcomes many limitations of traditional cephalometric techniques, and hence may claim an expanded role in the study of human craniofacial disorders in clinical and research settings.

Sphenotemporal and Fronto-Orbital Dysmorphology in Unilateral Coronal Synostosis Using Geometric Morphometric Curve-Based Analysis.

BACKGROUND: Geometric morphometric analysis with Procrustes superimposition is a commonly used method to characterize and study complex dysmorphology. The present study employs an advanced Procrustes-based approach to studying craniofacial dysmorphology in unilateral coronal synostosis and quantitatively describe bony patterns in this disorder, in order to better understand the associated fronto-orbital and sphenotemporal deformities. METHODS: Forty-one unilateral coronal synostosis (UCS) patients and 41 age- and sex-matched controls underwent high-resolution computed tomography imaging. Thirty-one anatomical landmarks were labeled on each imaging set. Landmarks were used to calculate angle, lengths, and define fronto-orbital and sphenotemporal anatomical curves. A validated geometric morphometric workflow was used to perform a Procrustes superimposition to register landmarks into a common space and perform a principal components analysis. RESULTS: Supraorbital bar curvature was significantly increased ipsilateral to the fused suture and decreased contralateral, P < 0.0001 for both sides. The sagittal sphenotemporal curve also showed ipsilateral increase in curvature (P < 0.0001) but there was no effect on the contralateral side (P > 0.05). CONCLUSIONS: Geometric morphometric analysis revealed significant dysmorphology between UCS patients and controls. These results suggest bilateral changes in fronto-orbital curvature and ipsilateral changes in sagittal sphenotemporal curvature, which may be useful in further characterizing the dynamic craniofacial changes in UCS.

Craniofacial Dysmorphology in Unilateral Coronal Synostosis Using Three-Dimensional Landmark-Based Analysis With Generalized Procrustes Superimposition.

BACKGROUND: Geometric morphometric analysis with Procrustes superimposition is an advanced computational tool that can be used to quantify dynamic changes in complex three-dimensional structures. The present study couples high resolution CT imaging with a Geometric Morphometric approach in order to further understand the complex dysmorphology that occurs in unilateral coronal synostosis (UCS). METHODS: Forty-one UCS patients and 41 age- and sex-matched controls received high-resolution CT imaging. Thirty-one anatomical landmarks were identified on each imaging set. A geometric morphometric workflow was used to perform a Procrustes superimposition to register landmarks into a common space. Procrustes-aligned landmarks were used to derive angle calculations, lengths, and other anatomical measurements. Three-dimensional coordinates were also used to perform a principal components analysis (PCA). RESULTS: Unilateral coronal synostosis patients exhibited significant angular deviation at the levels of the inferior skull base, mid-posterior fossa, and vertex. Both left- and right-sided UCS patients showed increased lengthening in the transverse (left-right) dimension, exhibiting increased length between the left and right EAC (P = 0.047). Conversely, UCS patients revealed shortening in the midline AP dimension as evidenced by the decreased Nasal root-Lambda (P < 0.0001) and Nasal root-superior dorsum sellae (P = 0.01) distances compared with controls. PCA revealed that 25.26% of variation in shape among the patients sampled to be driven by flattening of the skull and that18.93% of variation was driven by right-sided deformity and mediolateral expansion. CONCLUSIONS: Significant dysmorphology between UCS patients and controls was quantified using Geometric Morphometric approach, which may be useful in further characterizing the dynamic craniofacial changes in UCS.

Cranial anatomy and phylogenetic affinities of Bolosaurus major, with new information on the unique bolosaurid feeding apparatus and evolution of the impedance-matching ear.

Resolving the phylogenetic relationships of early amniotes, in particular stem reptiles, remains a difficult problem. Three-dimensional morphological analysis of well-preserved stem-reptile specimens can reveal important anatomical data and clarify regions of phylogeny. Here, we present the first thorough description of the unusual early Permian stem reptile Bolosaurus major, including the first comprehensive description of a bolosaurid braincase. We describe previously obscured details of the palate, allowing for insight into bolosaurid feeding mechanics. Aspects of the rostrum, palate, mandible, and neurocranium suggest that B. major had a particularly strong bite. We additionally found B. major has a surprisingly slender stapes, similar to that of the middle Permian stem reptile Macroleter poezicus, which may suggest enhanced hearing abilities compared to other Paleozoic amniotes (e.g., captorhinids). We incorporated our new anatomical information into a large phylogenetic matrix (150 OTUs, 590 characters) to explore the relationship of Bolosauridae among stem reptiles. Our analyses generally recovered a paraphyletic "Parareptilia," and found Bolosauridae to diverge after Captorhinidae + Araeoscelidia. We also included B. major within a smaller matrix (10 OTUs, 27 characters) designed to explore the interrelationships of Bolosauridae and found all species of Bolosaurus to be monophyletic. While reptile relationships still require further investigation, our phylogeny suggests repeated evolution of impedance-matching ears in Paleozoic stem reptiles.

Palaeophysiology of pH regulation in tetrapods.

The involvement of mineralized tissues in acid-base homeostasis was likely important in the evolution of terrestrial vertebrates. Extant reptiles encounter hypercapnia when submerged in water, but early tetrapods may have experienced hypercapnia on land due to their inefficient mode of lung ventilation (likely buccal pumping, as in extant amphibians). Extant amphibians rely on cutaneous carbon dioxide elimination on land, but early tetrapods were considerably larger forms, with an unfavourable surface area to volume ratio for such activity, and evidence of a thick integument. Consequently, they would have been at risk of acidosis on land, while many of them retained internal gills and would not have had a problem eliminating carbon dioxide in water. In extant tetrapods, dermal bone can function to buffer the blood during acidosis by releasing calcium and magnesium carbonates. This review explores the possible mechanisms of acid-base regulation in tetrapod evolution, focusing on heavily armoured, basal tetrapods of the Permo-Carboniferous, especially the physiological challenges associated with the transition to air-breathing, body size and the adoption of active lifestyles. We also consider the possible functions of dermal armour in later tetrapods, such as Triassic archosaurs, inferring palaeophysiology from both fossil record evidence and phylogenetic patterns, and propose a new hypothesis relating the archosaurian origins of the four-chambered heart and high systemic blood pressures to the perfusion of the osteoderms. This article is part of the theme issue 'Vertebrate palaeophysiology'.

A Digital Endocranial Cast of the Early Paleocene (Puercan) 'Archaic' Mammal Onychodectes tisonensis (Eutheria: Taeniodonta).

Eutherian mammals-placentals and their closest extinct relatives-underwent a major radiation following the end-Cretaceous extinction, during which they evolved disparate anatomy and established new terrestrial ecosystems. Much about the timing, pace, and causes of this radiation remain unclear, in large part because we still know very little about the anatomy, phylogenetic relationships, and biology of the so-called 'archaic' eutherians that prospered during the ~10 million years after the extinction. We describe the first digital endocranial cast of a taeniodont, a bizarre group of eutherians that flourished in the early Paleogene, reconstructed from a computed tomography (CT) scan of a late Puercan (65.4 million year old) specimen of Onychodectes tisonensis that recovered most of the forebrain and midbrain and portions of the inner ear. Notable features of the endocast include long, broad olfactory bulbs, dorsally-positioned rhinal fissures, and a lissencephalic cerebrum. Comparison with other taxa shows that Onychodectes possessed some of the largest olfactory bulbs (relative to cerebral size) of any known mammal. Statistical analysis of modern mammals shows that relative olfactory bulb dimensions are not strongly correlated with body size or fossorial digging for shelter, but relative bulb width is significantly greater in taxa that habitually dig to forage for food. The anatomical description and statistical results allow us to present an ecological model for Onychodectes and similar taeniodonts, in which they are animals of simple behavior that rely on a strong sense of smell to locate buried food before extracting and processing it with their specialized skeletal anatomy.