#24: Quantitative Osteological Ontogeny of Alligatoroids — Presentation Detail — Celebration of Scholars

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#24: Quantitative Osteological Ontogeny of Alligatoroids

Name: Brett Jackson
Major: Biology
Hometown: Estherville, IA
Faculty Sponsor:
Other Sponsors:
Type of research: Independent research

Abstract

Although sister group relationships of many clades are well supported, the developmental causes of evolutionary novelties are not obvious. This limitation might be overcome by comparison of growth series. Alligatoroidea is a model clade for this work, given a phylogeny that spans tens of millions of years, numerous extinct taxa with growth series, and two living species.

The primary goal here was to recover growth series, using cladistic analysis, of fossil and living alligatoroids: Leidyosuchus canadensis, Diplocynodon hantoniensis, and Alligator mississippiensis. Secondary goals were to compare the growth series and identify ancestral growth patterns. Data for L. canadensis (14 specimens, 27 characters) and D. hantoniensis (24 specimens, 19 characters) was from the primary literature; data for A. mississippiensis (four specimens, 43 characters) was from skeletons.

One tree was retained for the D. hantoniensis mandible (CI: 1.0, RC of 1.0, 6 steps); four growth stages were recovered. Five trees were retained for the D. hantoniensis skull (CI: 0.83, RC: 0.0, 12 steps); one growth stage was recovered. Eighteen trees for L. canadensis were retained (CI: 0.77, RC: 0.46, 36 steps); four growth stages were recovered. One tree for A. mississippiensis was retained (CI: 0.94, RC: 0.63, 19 steps); three growth stages were recovered.

There are two shared growth changes (presumably inherited from their common ancestor) between A. mississippiensis and D. hantonensis: a straight to concave side of the skull table, and a distinct ridge on angular. Future work will include additional extinct alligatoroids.

Poster file