The evolution of the vertebrate ear is a complicated story of convergence, co‐option, loss of function, and occasional regaining of said function. An incredible variety of structures has been adopted ...as sound receptors, but only chameleons are known to have a bony airborne sound receiver. In some chameleons, the pterygoid bone captures sound vibrations and relays them to the inner ear via a connection to the extracolumella. The distribution of this unique hearing system has not been examined across Chamaeleonidae. Here, I report on dissections on 12 species across four genera and describe their middle ear anatomy for the first time. Half of these species were found to have a link between their extracolumella and pterygoid, and ancestral state reconstruction supports four independent acquisitions of this novel sound‐conduction pathway. Species with this pathway tend to have a gular pouch, which seems to produce biotremors and possibly airborne sound, suggesting that this hearing system plays some role in intraspecific communication. Three species were also μ‐CT scanned using enhanced contrast to investigate differences in the musculature surrounding the middle ear cavity. In species with a middle ear connected to the pterygoid, the muscles directly lateral to the pterygoid insert farther anterior onto the mandible, which may serve to minimize dampening of vibrations on the pterygoid. Together, these data suggest that the ear plays a more significant role in the lives of some chameleons than has been recognized, and that parallelism is common in the evolution of the ear.
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.
Dicynodonts were one of the most diverse and abundant clades of tetrapods from the Lopingian (late Permian) to the Late Triassic. Despite their ecological and biostratigraphic importance, the early ...evolutionary history of dicynodonts is not well understood. Six skulls belonging to the poorly known dicynodont Abajudon kaayai were recently collected from the Guadalupian (middle Permian) lower Madumabisa Mudstone Formation of Zambia. The skulls exhibit characters of endothiodonts, emydopoids, and basal dicynodonts that are not preserved in the holotype from the Ruhuhu Formation of Tanzania. Here we describe the anatomy of the Zambian specimens and use this information in a revised phylogenetic analysis of Permian and Triassic dicynodonts. Abajudon kaayai is found to be the sister taxon of Endothiodon. Endothiodontia is reconstructed as the sister group of Therochelonia, with Emydopoidea placed at the base of Therochelonia. This phylogenetic arrangement helps to explain the mosaic of endothiodont and emydopoid features seen in A. kaayai and in taxa such as Niassodon and Cryptocynodon. The presence of A. kaayai in both the lower Madumabisa Mudstone and Ruhuhu formations allows for the first biostratigraphic correlation of the two strata. The absence of this species in contemporaneous South African Karoo deposits suggests that the early evolutionary history of endothiodont dicynodonts took place outside of the main Karoo Basin.
The Permian-Triassic mass extinction (PTME) was one of the transformative events of the Phanerozoic, marked by extinction, post-Permian transformation of surviving ecosystems, and the formation of ...new communities. The South African Karoo Basin has served as the primary source of data on the terrestrial component of these events, but its global applicability remains poorly known. Here, we compare Permian-Triassic communities of the Karoo Basin with those from the Luangwa and Ruhuhu basins of Zambia and Tanzania, respectively, analyzing their functional structures and simulating dynamic responses to environmental perturbation. Results show that compositional similarities of late Permian communities among the basins underlie similarities in their dynamics and resistance to secondary extinction. The Karoo Basin ecosystem also displays evidence of a transformation to increased resistance during the late Permian. Although the Karoo Basin ecosystem was reduced significantly by the PTME, structural features of that resistance persisted into the Early Triassic, facilitated by a greater susceptibility to extinction of small-body-sized amniotes and large carnivorous amniotes. It was undone by the initial stages of postextinction restructuring. Continued evolution of the Triassic ecosystem led to a recovery of resistance, but in a community compositionally dissimilar from its Permian antecedents. Likewise, the upper part of the Lifua Member of the Manda Beds (Middle Triassic) of Tanzania was structurally distinct from the Karoo Basin communities but displayed similar dynamics. The recurrence and convergence of communities with different histories toward similar dynamics suggest that there are taxon-independent norms of community assembly and function operating on geological timescales.
Until recently, the Guadalupian (middle Permian) tetrapod fossil record was known almost exclusively from the Karoo Basin of South Africa and the Cis-Urals region of Russia, limiting progress towards ...understanding global middle Permian tetrapod biogeography. Recent work has shed light on several new or under-explored Guadalupian tetrapod-bearing basins, and we review and synthesize these findings here. We also review changes to the international and Russian Guadalupian time scales and present updated biostratigraphic correlations for all of the basins discussed. In general, there are few tetrapod genera or species shared between mid-Permian basins, a pattern starkly different from the generic cosmopolitanism seen during Lopingian (late Permian) times. The Paraná Basin of Brazil has produced a unique fauna that combines typical South African and Russian clades, suggesting a pathway for faunal interchange between the northern and southern portions of Pangea. The Dashankou fauna of China yields basal therapsids that suggest a northern Pangean origin for this clade. The Sundyr Assemblage of Russia preserves a latest Guadalupian fauna that seems to illustrate patterns of faunal turnover across the Guadalupian-Lopingian boundary. Continued field work in the lesser-known mid-Permian strata will facilitate testing hypotheses about the transition between early and middle Permian faunas, the end-Guadalupian extinction event, Pangean tetrapod biogeography, and the origins of widespread late Permian clades.
The reflected lamina of the angular has long been portrayed as a key component in understanding the evolution of the mammalian mandible and middle ear, yet the function of this structure in ...non-mammalian therapsids remains uncertain. We undertake a broad scale survey of two aspects of the reflected lamina that have been poorly characterized: the ridges and fossae on its lateral surface and the extent of the underlying angular cleft. These two features were visualized in a wide range of therapsids using CT data from the literature and blue light surface scanning. Most species exhibit a clade-specific pattern of surface topography, although dicynodonts are highly variable. A striking similarity in the general number and orientation of fossae and ridges is seen between the otherwise disparate therapsid clades, and we propose homologies in these surface features across Therapsida. These features may serve as useful phylogenetic characters in analyses of the relationships among the major therapsid clades. The angular cleft does not underlie all of what is often referred to as the ‘reflected lamina’ in the literature, and an updated definition of this term is provided. Several therapsid groups independently expanded the angular cleft to further separate the reflected lamina from the angular body. We discuss some functional consequences of our findings and note inconsistency between proposed clade-specific muscle attachment sites and the presence of homologous fossae and ridges across much of Therapsida.
We tested the hypothesis that underrepresented students in active-learning classrooms experience narrower achievement gaps than underrepresented students in traditional lecturing classrooms, averaged ...across all science, technology, engineering, and mathematics (STEM) fields and courses. We conducted a comprehensive search for both published and unpublished studies that compared the performance of underrepresented students to their overrepresented classmates in active-learning and traditional-lecturing treatments. This search resulted in data on student examination scores from 15 studies (9,238 total students) and data on student failure rates from 26 studies (44,606 total students). Bayesian regression analyses showed that on average, active learning reduced achievement gaps in examination scores by 33% and narrowed gaps in passing rates by 45%. The reported proportion of time that students spend on in-class activities was important, as only classes that implemented high-intensity active learning narrowed achievement gaps. Sensitivity analyses showed that the conclusions are robust to sampling bias and other issues. To explain the extensive variation in efficacy observed among studies, we propose the heads-and-hearts hypothesis, which holds that meaningful reductions in achievement gaps only occur when course designs combine deliberate practice with inclusive teaching. Our results support calls to replace traditional lecturing with evidence-based, active-learning course designs across the STEM disciplines and suggest that innovations in instructional strategies can increase equity in higher education.
Dicynodonts were one of the most diverse and abundant clades of tetrapods from the Lopingian (late Permian) to the Late Triassic. Despite their ecological and biostratigraphic importance, the early ...evolutionary history of dicynodonts is not well understood. Six skulls belonging to the poorly known dicynodont Abajudon kaayai were recently collected from the Guadalupian (middle Permian) lower Madumabisa Mudstone Formation of Zambia. The skulls exhibit characters of endothiodonts, emydopoids, and basal dicynodonts that are not preserved in the holotype from the Ruhuhu Formation of Tanzania. Here we describe the anatomy of the Zambian specimens and use this information in a revised phylogenetic analysis of Permian and Triassic dicynodonts. Abajudon kaayai is found to be the sister taxon of Endothiodon. Endothiodontia is reconstructed as the sister group of Therochelonia, with Emydopoidea placed at the base of Therochelonia. This phylogenetic arrangement helps to explain the mosaic of endothiodont and emydopoid features seen in A. kaayai and in taxa such as Niassodon and Cryptocynodon. The presence of A. kaayai in both the lower Madumabisa Mudstone and Ruhuhu formations allows for the first biostratigraphic correlation of the two strata. The absence of this species in contemporaneous South African Karoo deposits suggests that the early evolutionary history of endothiodont dicynodonts took place outside of the main Karoo Basin.
The Permian-Triassic mass extinction (PTME) was one of the transformative events of the Phanerozoic, marked by extinction, post-Permian transformation of surviving ecosystems, and the formation of ...new communities. The South African Karoo Basin has served as the primary source of data on the terrestrial component of these events, but its global applicability remains poorly known. Here, we compare Permian-Triassic communities of the Karoo Basin with those from the Luangwa and Ruhuhu basins of Zambia and Tanzania, respectively, analyzing their functional structures and simulating dynamic responses to environmental perturbation. Results show that compositional similarities of late Permian communities among the basins underlie similarities in their dynamics and resistance to secondary extinction. The Karoo Basin ecosystem also displays evidence of a transformation to increased resistance during the late Permian. Although the Karoo Basin ecosystem was reduced significantly by the PTME, structural features of that resistance persisted into the Early Triassic, facilitated by a greater susceptibility to extinction of small-body-sized amniotes and large carnivorous amniotes. It was undone by the initial stages of postextinction restructuring. Continued evolution of the Triassic ecosystem led to a recovery of resistance, but in a community compositionally dissimilar from its Permian antecedents. Likewise, the upper part of the Lifua Member of the Manda Beds (Middle Triassic) of Tanzania was structurally distinct from the Karoo Basin communities but displayed similar dynamics. The recurrence and convergence of communities with different histories toward similar dynamics suggest that there are taxon-independent norms of community assembly and function operating on geological timescales.
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