| SUNY-Oswego | 1969-1970 | Instructor | Geology |
| McMaster University | 1970-1973 | Post-Doct. Fellow | Geology |
| Brooklyn College | 1973-1977 | Asst. Prof. | Geology |
| Brooklyn College | 1977-1981 | Assoc. Prof. | Geology |
| Field Museum of Nat. Hist. | 1980-1981 | Visiting Scientist | Geology |
| John G. Shedd Aquarium | 1980-1981 | Research Assoc. | Fishes |
| Brooklyn College | 1981-present | Professor | Geology |
| New York Aquarium | 1981-1990 | Research Assoc. | Osborn Labs |
| City Univ. NY | 1984-present | Professor | Earth & Env Sci |
| Brooklyn College | 1989-1998 | Chairman | Geology |
| American Museum of Nat. Hist. | 1992-1996 | Research Assoc. | Invertebrates |