Development and assessment of an educational intervention to improve the recognition of frailty on an acute care respiratory ward.

BACKGROUND: Frailty is a robust predictor of poor outcomes among patients with chronic obstructive pulmonary disease yet is not measured in routine practice. We determined barriers and facilitators to measuring frailty in a hospital setting, designed and implemented a frailty-focused education intervention, and measured accuracy of frailty screening before and after education. METHODS: We conducted a pilot cross-sectional mixed-methods study on an inpatient respiratory ward over 6 months. We recruited registered nurses (RNs) with experience using the Clinical Frailty Scale (CFS). RNs evaluated 10 clinical vignettes and assigned a frailty score using the CFS. A structured frailty-focused education intervention was delivered to small groups. RNs reassigned frailty scores to vignettes 1 week after education. Outcomes included barriers and facilitators to assessing frailty in hospital, and percent agreement of CFS scores between RNs and a gold standard (determined by geriatricians) before and after education. RESULTS: Among 26 RNs, the median (IQR) duration of experience using the CFS was 1.5 (1-4) months. Barriers to assessing frailty included the lack of clinical directives to measure frailty and large acute workloads. Having collateral history from family members was the strongest perceived facilitator for frailty assessment. The median (IQR) percent agreement with the gold-standard frailty score across all cases was 55.8% (47.2%-60.6%) prior to the educational intervention, and 57.2% (44.1%-70.2%) afterwards. The largest increase in agreement occurred in the 'mildly frail' category, 65.4%-81% agreement. CONCLUSIONS: Barriers to assessing frailty in the hospital setting are external to the measurement tool itself. Accuracy of frailty assessment among acute care RNs was low, and frailty-focused rater training may improve accuracy. Subsequent work should focus on health system approaches to empower health providers to assess frailty, and on testing the effectiveness of frailty-focused education in large real-world settings.

Plicidentine in the oral fangs of parrotfish (Scarinae, Labriformes).

Parrotfish play important ecological roles in coral reef and seagrass communities across the globe. Their dentition is a fascinating object of study from an anatomical, functional and evolutionary point of view. Several species maintained non-interlocked dentition and browse on fleshy algae, while others evolved a characteristic beak-like structure made of a mass of coalesced teeth that they use to scrape or excavate food off hard limestone substrates. While parrotfish use their highly specialized marginal teeth to procure their food, they can also develop a series of large fangs that protrude from the upper jaw, and more rarely from the lower jaw. These peculiar fangs do not participate in the marginal dentition and their function remains unclear. Here we describe the morphology of these fangs and their developmental relationship to the rest of the oral dentition in the marbled parrotfish (Leptoscarus vaigiensis), the star-eye parrotfish (Calotomus carolinus), and the palenose parrotfish (Scarus psittacus). Through microtomographic and histological analyses, we show that some of these fangs display loosely folded plicidentine along their bases, a feature that has never been reported in parrotfish. Plicidentine is absent from the marginal teeth and is therefore exclusive to the fangs. Parrotfish fangs develop a particular type of simplexodont plicidentine with a pulpal infilling of alveolar bone at later stages of dental ontogeny. The occurrence of plicidentine and evidence of extensive tooth wear, and even breakage, lead us to conclude that the fangs undergo frequent mechanical stress, despite not being used to acquire food. This strong mechanical stress undergone by fangs could be linked either to forced contact with congeners or with the limestone substrate during feeding. Finally, we hypothesize that the presence of plicidentine in parrotfish is not derived from a labrid ancestor, but is probably a recently evolved trait in some parrotfish taxa, which may even have evolved convergently within this subfamily.

Histological analysis of ankylothecodonty in Silesauridae (Archosauria: Dinosauriformes) and its implications for the evolution of dinosaur tooth attachment.

Dinosaurs possess a form of tooth attachment wherein an unmineralized periodontal ligament suspends each tooth within a socket, similar to the condition in mammals and crocodylians. However, little information is known about tooth attachment and implantation in their close relatives, the silesaurids. We conducted a histological survey of several silesaurid taxa to determine the nature of tooth attachment in this phylogenetically and paleoecologically important group of archosaurs. Our histological data demonstrate that these early dinosauriforms do not exhibit the crocodilian/dinosaur condition of a permanent gomphosis, nor the rapid ankylosis that is plesiomorphic for amniotes. Instead, all sampled silesaurids exhibit delayed ankylosis, a condition in which teeth pass through a prolonged stage where the teeth are suspended in sockets by a periodontal ligament, followed by eventual mineralization and fusion of the tooth to the jaws. This suggests that tooth attachment in crocodylians and dinosaurs represent the further retention of an early ontogenetic stage compared to silesaurids, a paedomorphic trend that is mirrored in the evolution of synapsid tooth attachment. It also suggests that the dinosaur and crocodylian gomphosis was convergently acquired via heterochrony or, less likely, that the silesaurid condition represents a reversal to a plesiomorphic state. Moreover, if Silesauridae is nested within Ornithischia, a permanent gomphosis could be convergent between the two main dinosaur lineages, Ornithischia and Saurischia. These results demonstrate that dental characters in early archosaur phylogenies must be chosen and defined carefully, taking into account the relative duration of the different phases of dental ontogeny.

Histology and µCT reveal the unique evolution and development of multiple tooth rows in the synapsid Endothiodon.

Several amniote lineages independently evolved multiple rows of marginal teeth in response to the challenge of processing high fiber plant matter. Multiple tooth rows develop via alterations to tooth replacement in captorhinid reptiles and ornithischian dinosaurs, but the specific changes that produce this morphology differ, reflecting differences in their modes of tooth attachment. To further understand the mechanisms by which multiple tooth rows can develop, we examined this feature in Endothiodon bathystoma, a member of the only synapsid clade (Anomodontia) to evolve a multi-rowed marginal dentition. We histologically sampled Endothiodon mandibles with and without multiple tooth rows as well as single-rowed maxillae. We also segmented functional and replacement teeth in µ-CT scanned mandibles and maxillae of Endothiodon and several other anomodonts with 'postcanine' teeth to characterize tooth replacement in the clade. All anomodonts in our sample displayed a space around the tooth roots for a soft tissue attachment between tooth and jaw in life. Trails of alveolar bone indicate varying degrees of labial migration of teeth through ontogeny, often altering the spatial relationships of functional and replacement teeth in the upper and lower jaws. We present a model of multiple tooth row development in E. bathystoma in which labial migration of functional teeth was extensive enough to prevent resorption and replacement by newer generations of teeth. This model represents another mechanism by which multiple tooth rows evolved in amniotes. The multiple tooth rows of E. bathystoma may have provided more extensive contact between the teeth and a triturating surface on the palatine during chewing.

Plicidentine and the repeated origins of snake venom fangs.

Snake fangs are an iconic exemplar of a complex adaptation, but despite striking developmental and morphological similarities, they probably evolved independently in several lineages of venomous snakes. How snakes could, uniquely among vertebrates, repeatedly evolve their complex venom delivery apparatus is an intriguing question. Here we shed light on the repeated evolution of snake venom fangs using histology, high-resolution computed tomography (microCT) and biomechanical modelling. Our examination of venomous and non-venomous species reveals that most snakes have dentine infoldings at the bases of their teeth, known as plicidentine, and that in venomous species, one of these infoldings was repurposed to form a longitudinal groove for venom delivery. Like plicidentine, venom grooves originate from infoldings of the developing dental epithelium prior to the formation of the tooth hard tissues. Derivation of the venom groove from a large plicidentine fold that develops early in tooth ontogeny reveals how snake venom fangs could originate repeatedly through the co-option of a pre-existing dental feature even without close association to a venom duct. We also show that, contrary to previous assumptions, dentine infoldings do not improve compression or bending resistance of snake teeth during biting; plicidentine may instead have a role in tooth attachment.

Tooth attachment and pleurodont implantation in lizards: Histology, development, and evolution.

Squamates present a unique challenge to the homology and evolution of tooth attachment tissues. Their stereotypically pleurodont teeth are fused in place by a single "bone of attachment", with seemingly dubious homology to the three-part tooth attachment system of mammals and crocodilians. Despite extensive debate over the interpretations of squamate pleurodonty, its phylogenetic significance, and the growing evidence from fossil amniotes for the homology of tooth attachment tissues, few studies have defined pleurodonty on histological grounds. Using a sample of extant squamate teeth that we organize into three broad categories of implantation, we investigate the histological and developmental properties of their dental tissues in multiple planes of section. We use these data to demonstrate the specific soft- and hard-tissue features of squamate teeth that produce their disparate tooth implantation modes. In addition, we describe cementum, periodontal ligaments, and alveolar bone in pleurodont squamates, dental tissues that were historically thought to be restricted to extant mammals and crocodilians. Moreover, we show how the differences between pleurodonty and thecodonty do not relate to the identity of the tooth attachment tissues, but rather the arrangements of homologous tissues around the teeth.

New insights into patterns and rates of tooth replacement in serrasalmid and characid fishes, with implications for the subsistence fishery of Peru's remote ribereños villages.

We explored patterns, rates and unexpected socio-ecological consequences of tooth replacement in serrasalmids and characids of the Peruvian Amazon using microcomputed tomography. Of 24 specimens collected in February 2019, representing a mix of red-bellied piranha Pygocentrus nattereri, redeye piranha Serrasalmus rhombeus, silver dollar fish Ctenobrycon hauxwellianus and mojara Astyanax abramis, six individuals possessed edentulous jaw quadrants. On average, 22.9% of fish collected per day from these species featured incomplete dentition, a value three to five times higher than anticipated based on replacement rates estimated from captive fish, differences that may be driven by ontogeny, seasonality or environmental quality.

Thecodont tooth attachment and replacement in bolosaurid parareptiles.

Permian bolosaurid parareptiles are well-known for having complex tooth crowns and complete tooth rows in the jaws, in contrast to the comparatively simple teeth and frequent replacement gaps in all other Paleozoic amniotes. Analysis of the specialized dentition of the bolosaurid parareptiles Bolosaurus from North America and Belebey from Russia, utilizing a combination of histological and tomographic data, reveals unusual patterns of tooth development and replacement. The data confirm that bolosaurid teeth have thecodont implantation with deep roots, the oldest known such example among amniotes, and independently evolved among much younger archosauromorphs (including dinosaurs and crocodilians) and among synapsids (including mammals). High-resolution CT scans were able to detect the density boundary between the alveolar bone and the jawbone, as confirmed by histology, and revealed the location and size of developing replacement teeth in the pulp cavity of functional teeth. Evidence provided by the paratype dentary of Belebey chengi indicates that replacement teeth are present along the whole tooth row at slightly different stages of development, with the ontogenetically more developed teeth anteriorly, suggesting that tooth replacement was highly synchronized. CT data also show tooth replacement is directly related to the presence of lingual pits in the jaw, and that migration of tooth buds occurs initially close to these resorption pits to a position immediately below the functional tooth within its pulp cavity. The size and complex shape of the replacement teeth in the holotype of Bolosaurus grandis indicate that the replacement teeth can develop within the pulp cavity to an advanced stage while the previous generation remains functional for an extended time, reminiscent of the condition seen in other amniotes with occluding dentitions, including mammals.

Early Jurassic dinosaur fetal dental development and its significance for the evolution of sauropod dentition.

Rare occurrences of dinosaurian embryos are punctuated by even rarer preservation of their development. Here we report on dental development in multiple embryos of the Early Jurassic Lufengosaurus from China, and compare these to patterns in a hatchling and adults. Histology and CT data show that dental formation and development occurred early in ontogeny, with several cycles of tooth development without root resorption occurring within a common crypt prior to hatching. This differs from the condition in hatchling and adult teeth of Lufengosaurus, and is reminiscent of the complex dentitions of some adult sauropods, suggesting that their derived dental systems likely evolved through paedomorphosis. Ontogenetic changes in successive generations of embryonic teeth of Lufengosaurus suggest that the pencil-like teeth in many sauropods also evolved via paedomorphosis, providing a mechanism for the convergent evolution of small, structurally simple teeth in giant diplodocoids and titanosaurids. Therefore, such developmental perturbations, more commonly associated with small vertebrates, were likely also essential events in sauropod evolution.

Lateralized Feeding Behavior in a Paleozoic Reptile.

Lateralized behaviors have been reported in a variety of extant vertebrates, including birds and reptiles [1-3] and non-human mammals [4-6]. However, evidence of lateralized behaviors in extinct vertebrates is rare, primarily because of the difficulty of identifying such behaviors with confidence in fossils. In rare instances, paleontologists can infer asymmetry in predatory or foraging behavior, including predation scars on trilobites [7], directionality of invertebrate traces [8], and even behavioral asymmetry in fossil non-human primates [9, 10]. Because lateralized behaviors have been linked to hemispheric (brain) lateralization in some vertebrates [11-15], evidence of lateralized behaviors in ancient vertebrates might yield clues about the evolutionary origins of vertebrate brain lateralization. Here, we show the earliest evidence of lateralized behavior in a fossil reptile based on repeatable observations of tooth wear in a large sample of intact jaws. The patterns of dental wear along the tooth rows of nearly one hundred jaws of the small, early Permian (289 million years ago) reptile Captorhinus aguti indicate that it exhibited lateralized behavior, preferring to feed using the right side of the jaw. Discovery of such a feeding behavior in this ancient, terrestrial, and omnivorous animal provides direct evidence of the deep history of directional behavior among amniotes and may indicate an early origin of brain lateralization.

Conflicting evidence for the use of caudal autotomy in mesosaurs.

The early Permian mesosaurs were the first amniotes to re-invade aquatic environments. One of their most controversial and puzzling features is their distinctive caudal anatomy, which has been suggested as a mechanism to facilitate caudal autotomy. Several researchers have described putative fracture planes in mesosaur caudal vertebrae - unossified regions in the middle of caudal vertebral centra - that in many extant squamates allow the tail to separate and the animal to escape predation. However, the reports of fracture planes in mesosaurs have never been closely investigated beyond preliminary descriptions, which has prompted scepticism. Here, using numerous vertebral series, histology, and X-ray computed tomography, we provide a detailed account of fracture planes in all three species of mesosaurs. Given the importance of the tail for propulsion in many other aquatic reptiles, the identification of fracture planes in mesosaurs has important implications for their aquatic locomotion. Despite mesosaurs apparently having the ability to autotomize their tail, it is unlikely that they actually made use of this behaviour due to a lack of predation pressure and no record of autotomized tails in articulated specimens. We suggest that the presence of fracture planes in mesosaurs is an evolutionary relic and could represent a synapomorphy for an as-yet undetermined terrestrial clade of Palaeozoic amniotes that includes the earliest radiation of secondarily aquatic tetrapods.

Unique Tooth Morphology and Prismatic Enamel in Late Cretaceous Sphenodontians from Argentina.

Mammals and reptiles have evolved divergent adaptations for processing abrasive foods. Mammals have occluding, diphyodont dentitions with taller teeth (hypsodonty), more complex occlusal surfaces, continuous tooth eruption, and forms of prismatic enamel that prolong the functional life of each tooth [1, 2]. The evolution of prismatic enamel in particular was a key innovation that made individual teeth more resilient to abrasion in early mammals [2-4]. In contrast, reptiles typically have thin, non-prismatic enamel, and shearing, polyphyodont dentitions with multi-cusped or serrated tooth crowns, multiple tooth rows, rapid tooth replacement rates, or batteries made of hundreds of teeth [5-9]. However, there are rare cases where reptiles have evolved alternative solutions to cope with abrasive diets. Here, we show that the combined effects of herbivory and an ancestral loss of tooth replacement in a lineage of extinct herbivorous sphenodontians, distant relatives of the modern tuatara (Sphenodon punctatus) [10], are associated with the evolution of wear-resistant and highly complex teeth. Priosphenodon avelasi, an extinct sphenodontian from the Cretaceous of Argentina, possesses a unique cone-in-cone dentition with overlapping generations of teeth forming a densely packed tooth file. Each tooth is anchored to its predecessor via a rearrangement of dental tissues that results in a novel enamel-to-bone tooth attachment. Furthermore, the compound occlusal surfaces, thickened enamel, and the first report of prismatic enamel in a sphenodontian are convergent strategies with those in some mammals, challenging the perceived simplicity of acrodont dentitions [11-15] and showcasing the reptilian capacity to produce complex and unusual dentitions.

The iliosacral joint in lizards: an osteological and histological analysis.

The development of the iliosacral joint (ISJ) in tetrapods represented a crucial step in the evolution of terrestrial locomotion. This structure is responsible for transferring forces between the vertebral column and appendicular skeleton, thus supporting the bodyweight on land. However, most research dealing with the water-to-land transition and biomechanical studies in general has focused exclusively on the articulation between the pelvic girdle and femur. Our knowledge about the contact between the pelvic girdle and vertebral column (i.e. the ISJ) at a tissue level is restricted so far to human anatomy, with little to no information available on other tetrapods. This lack of data limits our understanding of the development and evolution of such a key structure, and thus on the pattern and processes of the evolution of terrestrial locomotion. Therefore, we investigated the macro- and microanatomy of the ISJ in limb-bearing squamates that, similar to most non-mammalian, non-avian tetrapods, possess only two sacral ribs articulating with the posterior process of the ilium. Using a combination of osteology, micro-computed tomography and histology, we collected data on the ISJ apparatus of numerous specimens, sampling different taxa and different ontogenetic stages. Osteologically, we recorded consistent variability in all three processes of the ilium (preacetabular, supracetabular and posterior) and sacral ribs that correlate with posture and locomotion. The presence of a cavity between the ilium and sacral ribs, abundant articular cartilage and fibrocartilage, and a surrounding membrane of dense fibrous connective tissue allowed us to define this contact as a synovial joint. By comparison, the two sacral ribs are connected to each other mostly by dense fibrous tissue, with some cartilage found more distally along the margins of the two ribs, defining this joint as a combination of a syndesmosis and synchondrosis. Considering the intermediary position of the ISJ between the axial and appendicular skeletons, the shape of the articular surfaces of the sacral ribs and ilium, and the characteristics of the muscles associated with this structure, we argue that the mobility of the ISJ is primarily driven by the movements of the hindlimb during locomotion. We hypothesize that limited torsion of the ilium at the ISJ happens when the hip is abducted, and the joint is likely able to absorb the compressional and extensional forces related to the protraction and retraction of the femur. The mix of fibres and cartilage between the two sacral ribs instead serves primarily as a shock absorber, with the potential for limited vertical translation during locomotion.

Histology of Caenagnathid (Theropoda, Oviraptorosauria) Dentaries and Implications for Development, Ontogenetic Edentulism, and Taxonomy.

The fossil record of caenagnathid oviraptorosaurs consists mainly of their fused, complexly sculptured dentaries, but little is known about the growth and development of this diagnostic structure. Previous work has suggested that the ridges and grooves on the occlusal surface are either the vestiges of teeth and their alveoli or were adaptations to increase shearing action during mastication. In addition, the distinctiveness of the dentaries has led to their use for species-level taxonomy, without a complete understanding of their variation through ontogeny. Here, we describe additional caenagnathid mandibles from the Dinosaur Park Formation of Alberta, Canada, and perform histological analyses to assess relative ontogenetic stage and the nature of the occlusal elaborations. The results show that the mandibular symphysis is synostosed early in ontogeny and does not accurately reflect ontogenetic stage in caenagnathids. In contrast, the presence of cyclical growth marks in a large specimen shows that mandibles can be used for relative histological maturity estimation. Histological features of the ridges of bone surrounding the lingual groove indicate that they are not the vestiges of tooth-bearing tissues and that caenagnathids did not lose their teeth through ontogeny as suggested in previous work. Instead, increased secondary remodeling in these structures is consistent with their use for food processing. Unexpectedly advanced maturity in a small specimen suggests that at least three caenagnathid species of varying body sizes coexisted in the Dinosaur Park Formation. These results stress the necessity of histological analysis when assessing maturity or ontogenetic trends in fossil material. Anat Rec, 303:918-934, 2020. © 2019 Wiley Periodicals, Inc.

A severe pleural complication associated with granulomatosis with polyangiitis.

We describe the case of a previously healthy male patient who presented to a respiratory clinic with sinusitis, pulmonary cavities, and hemoptysis. Three weeks following a diagnosis of Granulomatosis with Polyangiitis (GPA) and initiation of immunosuppressive treatment, the patient suddenly developed a large pneumothorax that was complicated by empyema. In this report we discuss and highlight the rare pleural complications associated with GPA, and alert clinicians to monitor for these important complications even after disease-modifying treatment is initiated.

The Influence of Prior Performance Information on Ratings of Current Performance and Implications for Learner Handover: A Scoping Review.

PURPOSE: Learner handover (LH) is the sharing of information about trainees between faculty supervisors. This scoping review aimed to summarize key concepts across disciplines surrounding the influence of prior performance information (PPI) on current performance ratings and implications for LH in medical education. METHOD: The authors used the Arksey and O'Malley framework to systematically select and summarize the literature. Cross-disciplinary searches were conducted in six databases in 2017-2018 for articles published after 1969. To represent PPI relevant to LH in medical education, eligible studies included within-subject indirect PPI for work-type performance and rating of an individual current performance. Quantitative and thematic analyses were conducted. RESULTS: Of 24,442 records identified through database searches and 807 through other searches, 23 articles containing 24 studies were included. Twenty-two studies (92%) reported an assimilation effect (current ratings were biased toward the direction of the PPI). Factors modifying the effect of PPI were observed, with larger effects for highly polarized PPI, negative (vs positive) PPI, and early (vs subsequent) performances. Specific standards, rater motivation, and certain rater characteristics mitigated context effects, whereas increased rater processing demands heightened them. Mixed effects were seen with nature of the performance and with rater expertise and training. CONCLUSIONS: PPI appears likely to influence ratings of current performance, and an assimilation effect is seen with indirect PPI. Whether these findings generalize to medical education is unknown, but they should be considered by educators wanting to implement LH. Future studies should explore PPI in medical education contexts and real-world settings.

Current Perspectives on Tooth Implantation, Attachment, and Replacement in Amniota.

Teeth and dentitions contain many morphological characters which give them a particularly important weight in comparative anatomy, systematics, physiology and ecology. As teeth are organs that contain the hardest mineralized tissues vertebrates can produce, their fossil remains are abundant and the study of their anatomy in fossil specimens is of major importance in evolutionary biology. Comparative anatomy has long favored studies of dental characters rather than features associated with tooth attachment and implantation. Here we review a large part of the historical and modern work on the attachment, implantation and replacement of teeth in Amniota. We propose synthetic definitions or redefinitions of most commonly used terms, some of which have led to confusion and conflation of terminology. In particular, there has long been much conflation between dental implantation that strictly concerns the geometrical aspects of the tooth-bone interface, and the nature of the dental attachment, which mostly concerns the histological features occurring at this interface. A second aim of this work was to evaluate the diversity of tooth attachment, implantation and replacement in extant and extinct amniotes in order to derive hypothetical evolutionary trends in these different dental traits over time. Continuous dental replacement prevails within amniotes, replacement being drastically modified only in Mammalia and when dental implantation is acrodont. By comparison, dental implantation frequently and rapidly changes at various taxonomic scales and is often homoplastic. This contrasts with the conservatism in the identity of the tooth attachment tissues (cementum, periodontal ligament, and alveolar bone), which were already present in the earliest known amniotes. Because the study of dental attachment requires invasive histological investigations, this trait is least documented and therefore its evolutionary history is currently poorly understood. Finally, it is essential to go on collecting data from all groups of amniotes in order to better understand and consequently better define dental characters.

Dental ontogeny in extinct synapsids reveals a complex evolutionary history of the mammalian tooth attachment system.

The mammalian dentition is uniquely characterized by a combination of precise occlusion, permanent adult teeth and a unique tooth attachment system. Unlike the ankylosed teeth in most reptiles, mammal teeth are supported by a ligamentous tissue that suspends each tooth in its socket, providing flexible and compliant tooth attachment that prolongs the life of each tooth and maintains occlusal relationships. Here we investigate dental ontogeny through histological examination of a wide range of extinct synapsid lineages to assess whether the ligamentous tooth attachment system is unique to mammals and to determine how it evolved. This study shows for the first time that the ligamentous tooth attachment system is not unique to crown mammals within Synapsida, having arisen in several non-mammalian therapsid clades as a result of neoteny and progenesis in dental ontogeny. Mammalian tooth attachment is here re-interpreted as a paedomorphic condition relative to the ancestral synapsid form of tooth attachment.

Tooth development, histology, and enamel microstructure in Changchunsaurus parvus: Implications for dental evolution in ornithopod dinosaurs.

The great diversity of dinosaurian tooth shapes and sizes, and in particular, the amazing dental complexity in derived ornithischians has attracted a lot of attention. However, the evolution of dental batteries in hadrosaurids and ceratopsids is difficult to understand without a broader comparative framework. Here we describe tooth histology and development in the "middle" Cretaceous ornithischian dinosaur Changchunsaurus parvus, a small herbivore that has been characterized as an early ornithopod, or even as a more basal ornithischian. We use this taxon to show how a "typical" ornithischian dentition develops, copes with wear, and undergoes tooth replacement. Although in most respects the histological properties of their teeth are similar to those of other dinosaurs, we show that, as in other more derived ornithischians, in C. parvus the pulp chamber is not invaded fully by the newly developing replacement tooth until eruption is nearly complete. This allowed C. parvus to maintain an uninterrupted shearing surface along a single tooth row, while undergoing continuous tooth replacement. Our histological sections also show that the replacement foramina on the lingual surfaces of the jaws are likely the entry points for an externally placed dental lamina, a feature found in many other ornithischian dinosaurs. Surprisingly, our histological analysis also revealed the presence of wavy enamel, the phylogenetically earliest occurrence of this type of tissue. This contradicts previous interpretations that this peculiar type of enamel arose in association with more complex hadrosauroid dentitions. In view of its early appearance, we suggest that wavy enamel may have evolved in association with a shearing-type dentition in a roughly symmetrically-enameled crown, although its precise function still remains somewhat of a mystery.

Tooth germ initiation patterns in a developing dentition: An in vivo study of Xenopus laevis tadpoles.

The transparency of soft tissue in Xenopus laevis tadpoles and the anterior-posterior orientation of their developing tooth germs in the upper jaw offer a unique opportunity for the in vivo charting of the first 15-20 days of the developing dentition. Twenty-two X. laevis tadpoles were anesthetized daily and their mouths opened to record the first appearance, position, and development of tooth germs in the upper jaw. The initiation patterns revealed considerable variability between animals, and even between the jaw quadrants in the same animal. This variability appears within a structural boundary and the results are consistent with the presence of an odontogenic band. The final length of dental rows far exceeded the jaw growth for each quadrant during the recording period. This in vivo investigation underlines the limits of cross-sectional studies, and in particular the assumption that tooth germs initiate at the same position in the dental row. The tooth germ initiation patterns in this study did not align with the predictions of standard models for the development of the dentition-Zahnreihen, Clone, and New Progress Zone theories.