Independent origins of a novel atympanic middle ear system within Chamaeleonidae.

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.

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.

Active learning narrows achievement gaps for underrepresented students in undergraduate science, technology, engineering, and math.

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.