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Figure 1 in Air sac attachments or tendon scars: the distinction between soft tissue traces in archosaur bone
Figure 1. Lamellar bone fibres in an anhanguerid pterosaur ulna (DGEO-CTG-UFPE 7516; A-F) and in a spinosaurine theropod tibia (LPP-PV-0042; G-L). Note that these fibres are only visible at high magnifications (100×; arrowheads). Silhouettes in A and G indicate sampled elements (not to scale; art by Felipe A. Elias). All polarized light. Crossed nicols in A-E and G-L. Parallel nicols in F. Compensator in A-D, G-I and L. The relative angle to the cortical surface is approximately 80° in A, B; 340° in C; 290° in D-F; 120° in G-L. Scale bar in A, H = 250 µm; in B, I = 50 µm; G = 500 µm; in C-F, J-L = 10 µm.
Figure 4 in Air sac attachments or tendon scars: the distinction between soft tissue traces in archosaur bone
Figure 4. Side-by-side comparison between lamellar bone fibres A, pneumosteum B and Sharpey's fibres C, all indicated by arrowheads. A, an anhanguerid pterosaur ulna (DGEO-CTG-UFPE 7516). B, a megaraptoran theropod caudal vertebra (MPMA 08-003-94). C, a dorsal vertebra of Arrudatitan (MPMA 12-0001-97-1024). Magnifier indicates microscope magnification. All polarized light and crossed nicols. Compensator in B. The relative angle to the bone surface is approximately 290° in A; 320° in B; 150° in C. Scale bar in A = 10 µm; in B = 50 µm; in C = 300 µm.
Figure 3 in Air sac attachments or tendon scars: the distinction between soft tissue traces in archosaur bone
Figure 3. Pneumosteum in saurischian dinosaurs. A-C, a megaraptoran theropod caudal vertebra (MPMA 08-003-94). D-F, a cervical vertebra of the lithostrotian titanosaur Uberabatitan (CPPLIP-1024). G-I, a dorsal vertebra of the saltasaurid titanosaur Ibirania (LPP-PV-0200). Pneumosteum is distinguished from regular lamellar bone due to the presence of an array of tiny asbestiform densely packed fibres (usually shorter than 60 µm; arrowheads). These feature low optical relief and undulose extinction. Silhouettes in A, D and G indicate sampled elements (not to scale; art by Felipe A. Elias). All polarized light. Crossed nicols in A-E and G-I. Parallel nicols in F. Compensator in A-D, G-I, and L. The relative angle to the bone surface is approximately 320° in A-B; 220° in C-D; 105° in E-F; 290° in G; 80° in H-I. Scale bar in A, D = 250 μm; in C, E = 100 μm; in B, F, H, I = 50 μm; in G = 200 μm.
Figure 2 in Air sac attachments or tendon scars: the distinction between soft tissue traces in archosaur bone
Figure 2. Sharpey's fibres in a dorsal vertebra of Arrudatitan (MPMA 12-0001-97-1024; A-F) and in a spinosaurine theropod tibia (LPP-PV-0042; G-I). Note that these fibres are visible at low magnifications (5×; arrowheads). G, H show a cross pattern of Sharpey's fibres. Silhouettes in A and G indicate sampled elements (not to scale; art by Felipe A. Elias). All polarized light. Crossed nicols in A-F. Parallel nicols in. Compensator in G, H. The relative angle to the bone surface is approximately 150° in A-C; 90° in D; 70° in E; 120° in F; 90° in G-I. Scale bar in A = 300 µm; in D, I = 250 µm; in B, C, E, F = 100 µm; in G, H = 500 µm.
Osteology of the late Triassic bipedal archosaur Poposaurus gracilis (Archosauria: Pseudosuchia) from Western North America
<p><i>Poposaurus gracilis</i> is a bipedal pseudosuchian archosaur that has been poorly understood since the discovery of the holotype fragmentary partial postcranial skeleton in 1915. <i>Poposaurus</i>. <i>gracilis</i> is a member of Poposauroidea, an unusually morphologically divergent clade of pseudosuchians containing taxa that are bipedal, quadrupedal, toothed, edentulous, and some individuals with elongated thoracic neural spines (i.e., sails). In 2003, a well preserved, fully articulated, and nearly complete postcranial skeleton of <i>P</i>. <i>gracilis</i> was discovered with some fragmentary cranial elements from the Upper Triassic Chinle Formation of Grand Staircase‐Escalante National Monument of southern Utah, USA. The aim of this work is to describe the osteology of this specimen in detail and compare <i>P</i>. <i>gracilis</i> to other closely related pseudosuchian archosaurs. The open neurocentral sutures throughout the majority of the vertebral column, the small size of this individual, and the presence of seven evenly spaced cyclic growth marks in the histologically sectioned femur indicate that this specimen was a skeletally immature juvenile, or subadult when it died. The pes of <i>P</i>. <i>gracilis</i> contains multiple skeletal adaptations and osteological correlates for soft tissue structures that support a hypothesis of digitigrady for this taxon. When coupled with the numerous postcranial characters associated with cursoriality, and the many anatomical traits convergent with theropod dinosaurs, this animal likely occupied a similar ecological niche with contemporaneous theropods during the Late Triassic Period.</p>
Data from: Assessing bite force estimates in extinct mammals and archosaurs using phylogenetic predictions
Bite force is an ecologically important biomechanical performance measure is informative in inferring the ecology of extinct taxa. However, biomechanical modelling to estimate bite force is associated with some level of uncertainty. Here, I assess the accuracy of bite force estimates in extinct taxa using a Bayesian phylogenetic prediction model. I first fitted a phylogenetic regression model on a training set comprising extant data. The model predicts bite force from body mass and skull width while accounting for differences owning to biting position. The posterior predictive model has a 93% prediction accuracy as evaluated through leave-one-out cross-validation. I then predicted bite force in 37 species of extinct mammals and archosaurs from the posterior distribution of predictive models. Biomechanically estimated bite forces fall within the posterior predictive distributions for all except four species of extinct taxa and are thus as accurate as that predicted from body size and skull width, given the variation inherent in extant taxa and the amount of time available for variance to accrue. Biomechanical modelling remains a valuable means to estimate bite force in extinct taxa and should be reliably informative of functional performances and serve to provide insights into past ecologies.
Figure 8 in Osteological comparison of casque ontogeny in palaeognathous and neognathous birds: insights for selecting modern analogues in the study of cranial ornaments from extinct archosaurs
Figure 8. Examples of modern casque analogues suitable for specific non-avian dinosaur ornamentation comparisons in the context of (top row) development, (middle row) structural composition, and (boưom row) homologous structures. Each skull shown in right lateral view. Grey regions depict non-ornamental elements, and orange-highlighted regions depict ornamental elements for each represented species (see main text for relevant osteology); neognathous birds surveyed from the literature collectively represented by hornbill illustration (lowest less).
Figure 7 in Osteological comparison of casque ontogeny in palaeognathous and neognathous birds: insights for selecting modern analogues in the study of cranial ornaments from extinct archosaurs
Figure 7. Illustrations of bony cranial anatomy among exemplar dinosaurs with skull ornamentation, i.e. Saurolophus osborni (paired nasals, prefrontals, and frontals; Bell 2011), Protoceratops andrewsi (paired parietals and squamosals; Dodson 1976), Stegoceras validum (paired frontals and parietals; Schoư et al. 2011), Citipati osmolskae (paired premaxillae, nasals, and frontals; Clark et al. 2002), Carnotaurus sastrei (paired frontals; Paulina Carabajal 2011), Monolophosaurus jiangi (paired premaxillae, nasals, lacrimals, prefrontals, and frontals; Brusaưe et al. 2010), Numida meleagris (paired frontals), Macrocephalon maleo (paired frontals and parietals); Casuarius casuarius (mesethmoid, median casque element, paired nasals, paired lacrimals, and paired frontals; Green and Gignac 2021). Each skull shown in right lateral (top) and dorsal (boưom) views. Grey regions depict non-ornamental elements and orange-highlighted regions depict ornamental elements for each represented species.
Figure 6 in Osteological comparison of casque ontogeny in palaeognathous and neognathous birds: insights for selecting modern analogues in the study of cranial ornaments from extinct archosaurs
Figure 6. Three-dimensional renderings from micro-computed tomography data of a developmental series of Casuarius casuarius: A, TLG C025; B, TLG C037; C, TLG C031; D, AMNH SKEL 963; E, AMNH SKEL 962 (see Table 1). Skulls are shown in (top) less lateral and (boưom) dorsal views. Casque elements specific to Casuarius casuarius are indicated by colored cells [dark red (X) = element not participating at specified age; dark green (✓) = element participating at specified age] in the table, and grey cells indicate bones that do not contribute to bones in the species represented in this figure, but do contribute to others in the study. Dashed line divides specimens without (less) and with (right) casques developmentally present.
Figure 5 in Osteological comparison of casque ontogeny in palaeognathous and neognathous birds: insights for selecting modern analogues in the study of cranial ornaments from extinct archosaurs
Figure 5. Three-dimensional renderings from micro-computed tomography data of a developmental series of Macrocephalon maleo: A, UAZ MM005; B, UAZ MM003; C, UAZ MM004; D, UAZ MM002; E, UAZ MM006 (see Table 1). Skulls are shown in (top) less lateral and (boưom) dorsal views. Casque elements specific to Ma. maleo are indicated by colored cells [dark red (X) = element not participating at specified age; dark green (✓) = element participating at specified age] in the table, and grey cells indicate bones that do not contribute to bones in the species represented in this figure, but do contribute to others in the study. Dashed line divides specimens without (less) and with (right) casques developmentally present.
Figure 3 in Osteological comparison of casque ontogeny in palaeognathous and neognathous birds: insights for selecting modern analogues in the study of cranial ornaments from extinct archosaurs
Figure 3. Three-dimensional renderings from micro-computed tomography data of immature (A) Numida meleagris (TLG NM002), (B) Macrocephalon maleo (UAZ MM003), and (C) Casuarius casuarius (TLG C004). (Immature specimens are figured to emphasize clearer suture lines.) Broad cranial casque paưerns divided into geminal (sampled neognaths; N. meleagris and Ma. maleo) and disunited (sampled palaeognath; Casuarius casuarius). Skulls are shown in (top) lateral and (boưom) dorsal views with elements that will contribute to the fully matured adult casque false coloured (maroon = nasals; green = median casque element; blue = mesethmoid; orange = lacrimals; purple = frontals; yellow = parietals).
Figure 2 in Osteological comparison of casque ontogeny in palaeognathous and neognathous birds: insights for selecting modern analogues in the study of cranial ornaments from extinct archosaurs
Figure 2. Three-dimensional renderings from micro-computed tomography data of adult neognaths: A, Gallus gallus (PMG GG001); B, Numida meleagris (TLG NM007); C, Macrocephalon maleo (UAZ MM006); along with palaeognaths: D, Dromaius novaehollandiae (TLG E167); E, Casuarius casuarius (AMNH SKEL 962). In order to determine the cranial bones contributing to casques of ornamented taxa, the cranial osteology of non-casqued neognathous and palaeognathous relatives was used for comparison; (A) G. gallus and (D) D. novaehollandiae, respectively. Micro-computed tomography image data of the two non-casqued taxa were collected via a 2010 GE phoenix v|tome|x s240 high-resolution microfocus computed tomography system (μ-CT) housed in the Microscopy and Imaging Facility of the AMNH and a 2018 Nikon XT H 225 ST μ-CT system housed at the Micro-CT Imaging Consortium for Research and Outreach. Scanning parameters were 110–121 kV, 130–457 μA, ranging from 84.52–101.94 μm, 200–267 ms exposures with isometric voxel size at resolutions, W target, and none or a 0.125 mm filter.
Figure 1 in Osteological comparison of casque ontogeny in palaeognathous and neognathous birds: insights for selecting modern analogues in the study of cranial ornaments from extinct archosaurs
Figure 1. Photographs of adult: A, helmeted guinea fowl (Numida meleagris); B, maleo (Macrocephalon maleo); C, southern cassowary (Casuarius casuarius). All three species possess osseous casques dorsal to their orbits and neurocranium. Photos by T.L.G.
Osteology of the late Triassic bipedal archosaur Poposaurus gracilis (Archosauria: Pseudosuchia) from Western North America
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Data from: Assessing bite force estimates in extinct mammals and archosaurs using phylogenetic predictions
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Data from: Joint histology in Alligator mississippiensis challenges the identification of synovial joints in fossil archosaurs and inferences of cranial kinesis
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Supplementary data for "The craniomandibular anatomy of the early archosauriform Euparkeria capensis and the dawn of the archosaur skull"
<p>Supplementary material for "The craniomandibular anatomy of the early archosauriform<br> Euparkeria capensis and the dawn of the archosaur skull"</p> <p>Contains:</p> <p>-3D surface model of skull of SAM-PK-5867</p> <p>-3D surface renderings of CT scans of SAM-PK-5867, SAM-PK-6047A, UMZC T.692a</p> <p>-CT data for UMZC T.692a</p> <p>-Photograph bank</p>
Data from: Paleohistological estimation of bone growth rate in extinct archosaurs
The clade Archosauria contains two very different sister groups in terms of diversity (number of species) and disparity (phenotypic variation): Crurotarsi (taxa more closely related to crocodiles than to birds) and Ornithodira (pterosaurs and dinosaurs including birds). The extant species of Crurotarsi may constitute a biased sample of past biodiversity regarding growth patterns and metabolic rates. Bone histological characters can be conserved over hundreds of millions of years in the fossil record and potentially contain information about individual age at death, age at sexual maturity, bone growth rates, and basal metabolic rates of extinct vertebrates. Using a sample of extant amniotes, we have constructed a paleobiological model to estimate bone growth rate from bone histological traits. Cross-validation tests show that this model is reliable. We then used it to estimate bone growth rates in a sample of extinct archosaurs including Crurotarsi and Ornithodira. After testing for phylogenetic signal, optimization of femoral growth rates through squared change parsimony onto a time-calibrated tree of amniotes shows two divergent evolutionary trends: whereas bone growth rates increase from the last common ancestor of Ornithodira to extant birds, they decrease from the last common ancestor of Crurotarsi to extant crocodiles. However, we conclude, on the basis of recent evidence for unidirectional airflow in the lungs of alligators, that crocodiles may have retained the capacity of growing at high rates.
Data from: Associated evolution of bipedality and cursoriality among Triassic archosaurs: a phylogenetically controlled evaluation.
Bipedalism evolved more than twice among archosaurs, and it is a characteristic of basal dinosaurs and a prerequisite for avian flight. Nevertheless, the reasons for the evolution of bipedalism among archosaurs have barely been investigated. Comparative analysis using phylogenetically independent contrasts showed a significant correlation between bipedality (relative length of forelimb) and cursoriality (relative length of metatarsal III) among Triassic archosaurs. This result indicates that, among Triassic archosaurs, bipeds could run faster than quadrupeds. Bipedalism is probably an adaptation for cursoriality among archosaurs, which may explain why bipedalism evolved convergently in the crocodilian and bird lineages. This result also indicates that the means of acquiring cursoriality may differ between archosaurs and mammals.
Data from: Morphological and biomechanical disparity of crocodile-line archosaurs following the end-Triassic extinction
Mesozoic crurotarsans exhibited diverse morphologies and feeding modes, representing considerable ecological diversity, yet macroevolutionary patterns remain unexplored. Here we employ a unique combination of morphological and biomechanical disparity metrics to quantify the ecological diversity and trophic radiations of Mesozoic crurotarsans, using the mandible as a morpho-functional proxy. We recover three major trends. First, the diverse assemblage of Late Triassic crurotarsans was morphologically and biomechanically disparate, implying high levels of ecological variation; but, following the end-Triassic extinction, disparity declined. Second, the Jurassic radiation of marine thalattosuchians resulted in very low morphological disparity but moderate variation in jaw biomechanics, highlighting a hydrodynamic constraint on mandibular form. Third, during the Cretaceous terrestrial radiations of neosuchians and notosuchians, mandibular morphological variation increased considerably. By the Late Cretaceous, crocodylomorphs evolved a range of morphologies equaling Late Triassic crurotarsans. In contrast, biomechanical disparity in the Cretaceous did not increase, essentially decoupling from morphology. This enigmatic result could be attributed to biomechanical evolution in other anatomical regions (e.g. cranium, dentition or postcranium), possibly releasing the mandible from selective pressures. Overall, our analyses reveal a complex relationship between morphological and biomechanical disparity in Mesozoic crurotarsans that culminated in specialized feeding ecologies and associated lifestyles.
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