No abstract

The teeth of two megatooth macro-predatory shark species (Carcharocles chubutensis and Carcharocles megalodon; Otodontidae, Chondrichthyes) occur within the Miocene Chesapeake Group of Maryland, U.S.A. Definitive separation between all the teeth of Carcharocles chubutensis and Carcharocles megalodon is impossible because a complex mosaic evolutionary continuum characterizes this transformation, particularly in the loss of lateral cusplets. The cuspleted and uncuspleted teeth of Carcharocles spp. are designated as chronomorphs because there is wide overlap between them both morphologically and chronologically. In the lower Miocene Beds (Shattuck Zones) 2-9 of the Calvert Formation (representing approximately 3.2 million years, 20.2-17 Ma, Burdigalian) both cuspleted and uncuspleted teeth are present, but cuspleted teeth predominate, constituting approximately 87% of the Carcharocles spp. teeth represented in our sample. However, in the middle Miocene Beds 10-16A of the Calvert Formation (representing approximately 2.4 million years, 16.4-14 Ma, Langhian), there is a steady increase in the proportion of uncuspleted Carcharocles teeth. In the upper Miocene Beds 21-24 of the St. Marys Formation (representing approximately 2.8 million years, 10.4-7.6 Ma, Tortonian), lateral cusplets are nearly absent in Carcharocles teeth from our study area, with only a single specimen bearing lateral cusplets. The dental transition between Carcharocles chubutensis and Carcharocles megalodon occurs within the Miocene Chesapeake Group. Although this study helps to elucidate the timing of lateral cusplet loss in Carcharocles locally, the rationale for this prolonged evolutionary transition remains unclear.

No abstract

Organismal biology (OrgBio) comprises the diversity, structures, and functions of all organisms from bacteria to humans. Arguably, OrgBio is often the most poorly taught and least conceptually rigorous section of the introductory biology sequence offered at most U.S. institutions of higher education. This article reports on the successful implementation of conceptual and pedagogical reforms in an introductory OrgBio course offered at a large public university. Conceptual reforms were based on a theoretical framework consisting of universal physical and chemical laws, deep molecular homologies, and diverse structure–function relationships. Pedagogical reforms involved the development of group active engagements (GAEs) that were designed to encourage students to develop their abilities to engage in principles-based reasoning. A new model for characterizing different approaches toward principles-based reasoning in biology was developed to analyze these GAEs. Two surveys indicated that OrgBio students developed more favorable perceptions about the effectiveness of GAE-based course offerings, as compared to similar lecture-based versions.