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The seemingly aberrant coiling of heteromorphic ammonoids suggests that they underwent more significant changes in hydrostatic properties throughout ontogeny than their planispiral counterparts. Such changes may have been responses to different selective pressures at different life stages. The hydrostatic properties of three species of Didymoceras (D. stevensoni, D. nebrascense, and D. cheyennense) were investigated by creating virtual 3D models at several stages during growth. These models were used to compute the conditions for neutral buoyancy, hydrostatic stability, orientation during life, and thrust angles (efficiency of directional movement). These properties suggest that Didymoceras and similar heteromorphs lived low-energy lifestyles with the ability to hover above the seafloor. The resultant static orientations yielded a downward-facing aperture in the hatchling and a horizontally facing aperture throughout most of the juvenile stage, before terminating in an upward direction at maturity. Relatively high hydrostatic stabilities would not have permitted the orientation of Didymoceras to be considerably modified with active locomotion. During the helical phase, Didymoceras would have been poorly suited for horizontal movement, yet equipped to pirouette about the vertical axis. Two stages throughout growth, however, would have enhanced lateral mobility: a juvenile stage just after the formation of the first bend in the shell and the terminal stage after completion of the U-shaped hook. These two more mobile phases in ontogeny may have improved juvenile dispersal potential and mate acquisition during adulthood, respectively. In general, life orientation and hydrostatic stability change more wildly for these aberrantly coiled ammonoids than their planispiral counterparts.
People hold a variety of prior conceptions that impact their learning. Prior conceptions that include erroneous or incomplete understandings represent a significant barrier to durable learning, as they are often difficult to change. While researchers have documented students' prior conceptions in many areas of geoscience, little is known about prior conceptions involving paleontology. In this Element, data on student prior conceptions from two introductory undergraduate paleontology courses are presented. In addition to more general misunderstandings about the nature of science, many students hold incorrect ideas about methods of historical geology, Earth history, ancient life, and evolution. Of special note are student perceptions of the limits of paleontology as scientific inquiry. By intentionally eliciting students' prior conceptions and implementing the pedagogical strategies described in other Elements in this series, lecturers can shape instruction to challenge this negative view of paleontology and improve student learning.
Two end-member models are proposed to explain marine biotic responses to greenhouse conditions. Global warming and increasing sea level may: (1) promote dispersal of marine species, leading to larger geographic ranges and decreased speciation and biodiversity; or (2) result in formation of isolated epicontinental basins that host endemic radiations, leading to smaller geographic ranges and increased speciation and biodiversity. The Cenomanian–Turonian (C–T) interval, marked by greenhouse warming, sea-level rise, ocean anoxia, and biotic turnover, presents an opportunity to test these two end-member models. In particular, how cephalopods responded to these global changes has not been clear. A global database of 7262 cephalopod occurrences was used to evaluate biodiversity changes through the C–T interval. Both species- and genus-level diversity peaked in the late Cenomanian. The global diversity drop across the C/T boundary was modest; rather, diversity was low during the middle Cenomanian and middle Turonian, times of brief cooling. Regional variations in diversity responses may reflect the degree and timing of environmental perturbations within different oceanographic settings. Surprisingly, cephalopod faunas in the European Platform, Western Interior, and South Atlantic all shifted equatorward across the C/T boundary, whereas other regions saw no change in latitudinal distributions. Global generic geographic ranges did not change through the C–T interval, but the percentage of cosmopolitan genera did increase significantly across the C/T, both globally and within the Western Interior and Europe, whereas cosmopolitans dropped in the Pacific and South Atlantic. Neither end-member model for biodiversity change in a greenhouse world is supported for C–T cephalopods, as diversity increased without an associated increase in geographic range. It may be that sea-level rise and global warming led to both endemic radiations in epicontinental basins and an increase in cosmopolitan taxa in some regions, demonstrating the importance of combining global and regional-scale analyses.
In the most effective learning environments, undergraduates go beyond memorization to become more deeply engaged with the material. Active learning approaches, in which students participate in activities that result in improved learning, promote this sort of deep experience. Educational theories such as constructivism and recent research in cognitive and learning sciences demonstrate the importance of allowing students opportunities to confront misconceptions, reason out solutions, work collaboratively, and construct their own understandings of key concepts. Numerous studies have documented improved learning in classes using active learning approaches when compared to traditional class formats. Various obstacles to implementing active learning strategies exist, such as student and faculty resistance to such practices and the academic reward structure, which penalizes faculty who invest time in innovative teaching. These obstacles, however, are not insurmountable—effective communication of the benefits of active learning for improving student learning outcomes and the recruitment and retention of STEM majors can help. Paleontology instructors have a wide variety of active learning techniques to choose from, including some that make use of our field's uniquely visual and temporal characteristics (e.g., concept sketches, timelines), current research areas (e.g., textual analysis, case studies, guided inquiry), and classic controversies (e.g., role-playing, debates, and panel discussions). New technologies, such as classroom response devices and Web 2.0 tools, can facilitate many of these activities both in and out of the classroom. Incorporating active learning approaches into paleontology courses can help instructors clarify their course goals and learning outcomes while empowering students to succeed.
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