Journal: Anatomical record (Hoboken, N.J. : 2007)
Working on the hypothesis that an important function of the lamellate antennae of adult male beetles belonging to the genus Rhipicera is to detect scent associated with female conspecifics, and using field observations, anatomical models derived from X-ray microcomputed tomography, and scanning electron microscopy, we have investigated the behavioural, morphological, and morphometric factors that may influence molecule capture by these antennae. We found that male beetles fly upwind in a zigzag manner, or face upwind when perching, behaviour consistent with an animal that is tracking scent. Furthermore, the ultrastructure of the male and female antennae, like their gross morphology, is sexually dimorphic, with male antennae possessing many more of a particular type of receptor - the sensillum placodeum - than their female counterparts (approximately 30,000 v. 100 per antenna, respectively). Based on this disparity, we assume that the sensilla placodea on the male antennae are responsible for detecting scent associated with female Rhipicera beetles. Molecule capture by male antennae in their alert, fanned states is likely to be favoured by: a) male beetles adopting prominent, upright positions on high points when searching for scent; b) the partitioning of antennae into many small segments; c) antennal morphometry (height, width, outline area, total surface area, leakiness, and narrow channels); d) the location of the sensilla placodea where they are most likely to encounter odorant molecules; and e) well dispersed sensilla placodea. The molecule-capturing ability of male Rhipicera antennae may be similar to that of the pectinate antennae of certain male moths. This article is protected by copyright. All rights reserved.
The axolotl Ambystoma mexicanum is one of the most commonly used model organisms in developmental and regenerative studies because it can reconstitute what is believed to be a completely normal anatomical and functional forelimb/hindlimb after amputation. However, to date it has not been confirmed whether each regenerated forelimb muscle is really a “perfect” copy of the original muscle. This study describes the regeneration of the arm, forearm, hand, and some pectoral muscles (e.g., coracoradialis) in transgenic axolotls that express green fluorescent protein (GFP) in muscle fibers. The observations found that: (1) there were muscle anomalies in 43% of the regenerated forelimbs; (2) however, on average in each regenerated forelimb there are anomalies in only 2.5% of the total number of muscles examined, and there were no significant differences observed in the specific insertion and origin of the other muscles analyzed; (3) one of the most notable and common anomalies (seen in 35% of the regenerated forelimbs) was the presence of a fleshy coracoradialis at the level of the arm; this is a particularly outstanding configuration because in axolotls and in urodeles in general this muscle only has a thin tendon at the level of the arm, and the additional fleshy belly in the regenerated arms is strikingly similar to the fleshy biceps brachii of amniotes, suggesting a remarkable parallel between a regeneration defect and a major phenotypic change that occurred during tetrapod limb evolution; (4) during forelimb muscle regeneration there was a clear proximo-distal and radio-ulnar morphogenetic gradient, as seen in normal development, but also a ventro-dorsal gradient in the order of regeneration, which was not previously described in the literature. These results have broader implications for regenerative, evolutionary, developmental and morphogenetic studies. Anat Rec, 2014. © 2014 Wiley Periodicals, Inc.
Palaeobatrachidae are extinct frogs from Europe closely related to the Gondwanan Pipidae, which includes Xenopus. Their frontoparietal is a distinctive skeletal element which has served as a basis for establishing the genus Albionbatrachus. Because little was known about developmental and individual variation of the frontoparietal, and its usefulness in delimiting genera and species has sometimes been doubted, we investigate its structure in Palaeobatrachus and Albionbatrachus by means of X-ray high resolution computer tomography (micro-CT). To infer the scope of variation present in the fossil specimens, we also examined developmental and interspecific variation in extant Xenopus. In adults of extinct taxa, the internal structure of the frontoparietal bone consists of a superficial and a basal layer of compact bone, with a middle layer of cancellous bone between them, much as in early amphibians. In Albionbatrachus, the layer of cancellous bone, consisting of small and large cavities, was connected with the dorsal, sculptured surface of the bone by a system of narrow canals; in Palaeobatrachus, the layer of cancellous bone and the canals connecting this layer with the dorsal surface of the frontoparietal were reduced. The situation in Palaeobatrachus robustus from the lower Miocene of France is intermediate - while external features support assignment to Palaeobatrachus, the inner structure is similar to that in Albionbatrachus. It may be hypothesized that sculptured frontoparietals with a well-developed layer of cancellous (i.e., vascularized) bone may indicate adaptation to a more terrestrial way of life, whereas a reduced cancellous layer might indicate a permanent water dweller. This article is protected by copyright. All rights reserved.
Psittacosaurus is one of the most abundant dinosaurs known, which allows for extensive study of its growth and form. Previous studies have evaluated growth trajectories of Psittacosaurus using bone histology. However, we present the first study of Psittacosaurus comparative juvenile histology and describe the histology of Psittacosaurus within its first year of life based on multiple sections taken from an exquisite monospecific assemblage of juveniles from the Yixian Formation in Liaoning, China. Specimens studied had femur lengths ranging from 30-36 mm. The five juveniles examined all have similar histologic patterns in the midshaft and epiphyseal regions showing that there is limited plasticity in bone development in juvenile Psittacosaurus and that all of the specimens in the assemblage were likely the same age. The microstructure patterns are compatible with the hypothesis that Psittacosaurus was precocial and that these juveniles were neonates. Based on comparisons with other juvenile ornithischians, juvenile Psittacosaurus had a growth rate similar to Orodromeus, slower than that of Maiasaura, Dysalotosaurus, or hadrosaurs consistent with small body size. Our results support previous studies that demonstrated that the orientation of vascular canals is likely not solely reflective of growth rate, but is also affected by underlying biomechanical, structural processes. The number of studies done on theropod and sauropodomorph histology dwarfs those of ornithischians. More studies of ornithischian histology are necessary in order to better establish phylogenetic trends in microstructure and to learn more about growth in this important clade. This article is protected by copyright. All rights reserved.
To identify cells and analyze proliferative activity of hematopoietic tissue, black scorpionfish head kidney and spleen cells were characterized by light microscopy and flow cytometry. Hematopoiesis of black scorpionfish head kidney was formed by the following series: erythropoietic, granulopoietic, lymphopoietic and thrombopoietic. Flow cytometric analysis allowed dividing blood cells in hematopoitetic organs into subpopulations differing by size, granularity and proliferative activity. Three distinct subpopulations were observed during the wintering period. The number of small low-granulated cells, identified as lymphocytes and thrombocytes, was 41 ± 4% in both wintering and spawning fish. Proliferating subpopulation of blast (high-granulated) cells amounted to about 36% of the total cell count with 50 ± 5% of proliferating cells; the largest low-granulated cells (10% of total cells) comprised maturing white blood cells, monocytes, and macrophages. The spawning period was accompanied with an increase of maturing neutrophils and enhancement of blast cell proliferation. In the spleen three distinct subpopulations were observed. The subpopulation of small low-granulated cells comprised lymphocytes and thrombocytes similar to the head kidney and amounted 33 ± 4%. Other cells with larger diameter were identified as red blood cells. No proliferation was observed during the wintering period in the spleen, however, spawning induced cell proliferation of erythroblasts (small granulated cells) with the number of dividing cells 84 ± 1%. This article is protected by copyright. All rights reserved.
The attachments of jaw muscles are typically implicated in the evolution and shape of the dorsotemporal fenestra on the skull roof of amniotes. However, the dorsotemporal fenestrae of many archosaurian reptiles possess smooth excavations rostral and dorsal to the dorsotemporal fossa which closely neighbors the dorsotemporal fenestra and jaw muscle attachments. Previous research has typically identified this region, here termed the frontoparietal fossa, to also have been attachment surfaces for jaw-closing muscles. However, numerous observations of extant and extinct archosaurs described here suggest that other tissues are instead responsible for the size and shape of the frontoparietal fossa. This study reviewed the anatomical evidence that support soft-tissue hypotheses of the frontoparietal fossa and its phylogenetic distribution among sauropsids. Soft-tissue hypotheses (i.e., muscle, pneumatic sinus, vascular tissues) were analyzed using anatomical, imaging and in vivo thermography techniques within a phylogenetic framework using extant and extinct taxa to determine the inferential power underlying the reconstruction of the soft tissues in the skull roofs of dinosaurs, pseudosuchians and other reptiles. Relevant anatomical features argue for rejection of the default hypothesis-that the fossa was muscular-due to a complete lack of osteological correlates reflective of muscle attachment. The most-supported inference of soft tissues is that the frontoparietal fossa contained a large vascular structure and adipose tissue. Despite the large sizes and diverse morphologies of these fossae found among dinosaur taxa, these data suggest that non-avian dinosaurs had the anatomical foundation to support physiologically-significant vascular devices and/or vascular integumentary structures on their skull roofs. This article is protected by copyright. All rights reserved.
The unusual clubbed tails of glyptodonts among mammals and ankylosaurines among dinosaurs most likely functioned as weapons of intraspecific combat or interspecific defense and are characterized by stiffening of the distal tail and, in some taxa, expansion of the distal tail tip. Although similarities in tail weaponry have been noted as a potential example of convergent evolution, this hypothesis has not been tested quantitatively, particularly with metrics that can distinguish convergence from long-term stasis, assess the relative strength of convergence, and identify potential constraints in the appearance of traits during the stepwise, independent evolution of these structures. Using recently developed metrics of convergence within a phylomorphospace framework, we document that convergence accounts for over 80% of the morphological evolution in traits associated with tail weaponry in ankylosaurs and glyptodonts. In addition, we find that ankylosaurs and glyptodonts shared an independently derived, yet constrained progression of traits correlated with the presence of a tail club, including stiffening of the distal tail as a precedent to expansion of the tail tip in both clades. Despite differences in the anatomical construction of the tail club linked to lineage-specific historical contingency, these lineages experienced pronounced, quantifiable convergent evolution, supporting hypotheses of functional constraints and shared selective pressures on the evolution of these distinctive weapons. Anat Rec, 2019. © 2019 Wiley Periodicals, Inc.
Body size has thermal repercussions that impact physiology. Large-bodied dinosaurs potentially retained heat to the point of reaching dangerous levels, whereas small dinosaurs shed heat relatively easily. Elevated body temperatures are known to have an adverse influence on neurosensory tissues and require physiological mechanisms for selective brain and eye temperature regulation. Vascular osteological correlates in fossil dinosaur skulls from multiple clades representing different body-size classes were identified and compared. Neurovascular canals were identified that differentiate thermoregulatory strategies involving three sites of evaporative cooling that are known in extant diapsids to function in selective brain temperature regulation. Small dinosaurs showed similarly sized canals, reflecting a plesiomorphic balanced pattern of blood supply and a distributed thermoregulatory strategy with little evidence of enhancement of any sites of thermal exchange. Large dinosaurs, however, showed a more unbalanced vascular pattern whereby certain sites of thermal exchange were emphasized for enhanced blood flow, reflecting a more focused thermal strategy. A quantitative, statistical analysis of canal cross-sectional area was conducted to test these anatomical results, confirming that large-bodied, and often large-headed, species showed focused thermal strategies with enhanced collateral blood flow to certain sites of heat exchange. Large theropods showed evidence for a plesiomorphic balanced blood flow pattern, yet evidence for vascularization of the large antorbital paranasal air sinus indicates theropods may have had a fourth site of heat exchange as part of a novel focused thermoregulatory strategy. Evidence presented here for differing thermoregulatory strategies based on size and phylogeny helps refine our knowledge of dinosaur physiology. Anat Rec, 2019. © 2019 American Association for Anatomy.
The extinct non-avian dinosaur Tyrannosaurus rex, considered one of the hardest biting animals ever, is often hypothesized to have exhibited cranial kinesis, or, mobility of cranial joints relative to the braincase. Cranial kinesis in T. rex is a biomechanical paradox in that forcefully-biting tetrapods usually possess rigid skulls instead of skulls with movable joints. We tested the biomechanical performance of a tyrannosaur skull using a series of static positions mimicking possible excursions of the palate to evaluate Postural Kinetic Competency in Tyrannosaurus. A functional extant phylogenetic bracket was employed using taxa which exhibit measurable palatal excursions: Psittacus erithacus (fore-aft movement) and Gekko gecko (mediolateral movement). Static finite element models of Psittacus, Gekko, and Tyrannosaurus were constructed and tested with different palatal postures using anatomically-informed material properties, loaded with muscle forces derived from dissection, phylogenetic bracketing, and a sensitivity analysis of muscle architecture and tested in orthal biting simulations using element strain as a proxy for model performance. Extant species models showed lower strains in naturally-occurring postures compared to alternatives. We found that fore-aft and neutral models of Tyrannosaurus experienced lower overall strains than mediolaterally-shifted models. Protractor muscles dampened palatal strains, while occipital constraints increased strains about palatocranial joints compared to jaw-joint constraints. These loading behaviors suggest that even small excursions can strain elements beyond structural failure. Thus, these postural tests of kinesis, along with the robusticity of other cranial features, suggest that the skull of Tyrannosaurus was functionally akinetic. This article is protected by copyright. All rights reserved.
Osteoderms constitute a morphological system that plays an important role in squamate systematics. However, their study and visualization have always been difficult due to their isolated occurrence in the skin, among the first organs to be removed during the skeletonization process. High-resolution X-ray computed tomography (HRXCT) offers a nondestructive means of visualizing osteoderms both in their natural relationship to each other and to the underlying cranial bones. Although it is often stated that Varanus komodoensis has a ‘chain mail’ of osteoderms, this morphological system was never described in this taxon. Further, given its size, it might be expected that V. komodoensis would present the extreme of osteoderm development in extant varanids, a group that tends to have weakly-developed osteoderms or none at all. Indeed, our HRXCT scan of a 19-year-old captive individual reveals an elaborate mesh of cephalic osteoderms that are incredibly numerous and morphologically diverse. We describe this skeletal system and compare it to the cephalic osteoderms in other varanoids. This article is protected by copyright. All rights reserved.