Zoology • Using evolution as the foundation, we rely on numerous “tools” to understand relationships among animals • • • • Comparative anatomy Genetics Paleontology Geology Theme of this course • Common ancestry accounts for most similarities, and adaptive modifications account for most differences • Primarily a comparative anatomy approach, nested within best available information on genetics, paleontology, and geology Viewing animal relatedness… • We use models Viewing animal relatedness… • Various models have been used in the past… Viewing animal relatedness… • Currently, cladograms are used: • A model of animal relatedness • Branches “should” represent a monophyletic lineage of organisms • Monophyletic: all the descendants can be traced back to a common and unique ancestor • Includes synapomorphies: shared morphological traits • With some uncertainty Eucarya Opisthokonta Metazoa Protostomia Deuterostomia Protista notochord and post anal tail deuterostomes, pharyngeal slits and dorsal nerve cord ? segmentation? multiple germ layers, bilateral symmetry, coelom multicellular ? opisthokont membrane-bound nucleus Primarily a comparative anatomy approach… • But anatomy (and evolution) can be a little tricky… • Homologous structures. analogous structures • Rudimentary structures, vestigial structures Key Terms • homologous structures: structures found among species because of common ancestry • structures might be rudimentary (e.g., in early stages of development) But… • Some homologous structures might be vestigial (remnant structures that had greater function in ancestry) And even more tricky… • Analogous structures: structures found among species but not because of ancestry • Our ideas on homologous vs. analogous structures, rudimentary vs. vestigial structures… • …subject to change; I’m good with the 51% rule. • Our ideas on phylogeny (animal relatedness)?
