Researchers often interpret the presence of tortoises in Pleistocene assemblages as evidence of an interglacial age, based on an assumption that these fossils indicate thermic climates, as modern giant tortoises require. Since the Paleocene, tortoises have been common components of terrestrial fossil assemblages and have repeatedly evolved species of giant size. Whereas extant giant tortoises are found only on islands off the coasts of South America and Africa, at least two species persisted in North America until the terminal Pleistocene. These tortoises, Hesperotestudo crassiscutata and Gopherus “hexagonatus,” both of which reached carapace lengths of >1 m, were distributed across the southern United States. This study provides new metrics to derive quantitative weight estimates from measurements of the tortoise shell. The linear measurements of 69 anatomical features of the shells of 108 live tortoises indicate that the regression between straight carapace length and weight is most significant, with a maximum r2 > 0.99. This regression is useful for tortoises that weigh between 1.8 and 339 kg. This mass estimate, coupled with a heat dissipation rate derived from thermoregulation modeling, provides estimates of how long tortoises can maintain a viable body temperature at low ambient temperatures. Depending on size, a tortoise can survive a maximum of 2.3 to 33 hours of freezing temperatures, which corresponds to a mean annual temperature ≥22°C and a mean winter low temperature ≥7.5°C. This analysis infers warmer temperatures at Pleistocene sites with fossil tortoise occurrences than previous qualitative estimates.
An increasing number of organizations use untrained volunteers to gather scientific data. This citizen science movement builds enthusiasm for science by engaging the public, as well as providing a way to gather large amounts of data at little or no expense. The challenge of citizen science is obtaining accurate information from participants. Many citizen science programs encourage participants to use visual identification guides to ensure they provide correct data. Identifying an image style that increases correct identifications helps not only the citizen science movement but also scientific instruction in general. This study tests three image-based identification guides for identifying late Hemphillian (5-4.5 m.y.a.) fossils from Polk County, Florida. Each guide has identical layout and text, differing only in image style: color photos, grayscale photos, or illustrations. Untrained participants each use one guide to identify fossils. Geology and paleontology professionals also identify fossils for comparison. Comparing results reveals that color photographic images produce results most similar to data from professionals. In addition, participants provide data on their years of education, previous experience finding fossils, and enthusiasm about finding fossils. Analysis of this information reveals that participants with higher education and/or previous experience finding fossils produce data most similar to that from professionals. Paradoxically, participants with higher enthusiasm produce data less similar to that from professionals, while moderate interest levels correlated with greater similarity.
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