Date Thesis Awarded
Bachelors of Science (BS)
Recent studies have suggested that sexual dimorphism in modern birds may be tied to increased extinction risk at the species level. If this is the case, it may represent a clear example of species-level selection, i.e., selection occurring at or above the species level. The fossil record provides an ideal opportunity to test this possibility over longer timescales. The goal of this study is to investigate the relationship between sexual dimorphism and extinction and diversification in ammonoid cephalopods. To do this, I compiled global data on the presence and absence of sexual dimorphism in Mesozoic ammonoids at the genus level from a recent literature compilation. To quantify survivorship across background intervals, I compiled first and last global occurrence data from the Paleobiology Database and the biostratigraphic literature to calculate genus-level durations. With which I found that monomorphic genera had shorter durations than dimorphic genera in the fossil record. This was the same trend seen in a number of other superfamilies. Meaning in at least ammonoids, dimorphism may actually extend one's stratigraphic duration. To explore this possibility in more detail, I selected a single superfamily on which to focus our diameter measurements, (Acanthocerataceae) to assess the extent to which the magnitude of sexual dimorphism is correlated with survivorship. I found that there was actually a positive correlation between magnitude and duration. I also assessed survivorship across the Cenomanian-Turonian extinction. I found no significant results regarding their extinction or diversification after this extinction. The general trend among our results could be due to a dietary niche separation between males and females. This would reduce intraspecific competition for resources and could extend their duration.
Still, Claire E. L., "The effects of sexual dimorphism on survivorship in fossil ammonoids: A role for sexual selection in extinction" (2010). Undergraduate Honors Theses. Paper 452.
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