Meeting Abstract

40.2  Tuesday, Jan. 5  Inference of diel activity pattern suggests complex temporal resource and habitat partitioning among Mesozoic archosaurs SCHMITZ, Lars*; MOTANI, Ryosuke; University of California, Davis; University of California, Davis lschmitz@ucdavis.edu

Diel activity pattern (DAP) is an important behavioral characteristic of vertebrates that influences niche partitioning and resource use. Despite the complexity observed in the extant biosphere, our knowledge of vertebrate DAPs in the Mesozoic has been sparse. We remedied this problem with a threefold approach that is based on physiologic optics and eyeball morphology. First, we established that osteological features are correlated with optically relevant eyeball soft-tissue structures. These structure-function relationships are evident in both avians and squamates. Second, we demonstrated that groups of different DAP among extant terrestrial amniotes can be delineated with discriminant analysis of both eyeball soft-tissue and osteological dimensions. Third, we used discriminant analysis to infer the diel activity pattern of 33 fossil archosaurs, including Euparkeria, Proterosuchus, nine pterosaur, and 22 dinosaur (including four avians) species. Our analysis revealed that a variety of DAPs existed among Mesozoic archosaurs, including diurnal, nocturnal, and cathemeral or crepuscular patterns. The previous assumption of a dichotomous split of temporal habitat and resource use among terrestrial amniotes in the Mesozoic, with archosaurs being diurnal and mammals being nocturnal, needs to be re-evaluated. While quantitative inferences of the DAP of Mesozoic mammals are not available yet, our results suggest that many Mesozoic archosaurs were active both day and night. The results provide the first concrete evidence that the complex partitioning of temporal habitat and resources already existed in the Mesozoic.