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Table 1 Examples of historical holdovers, phylogenetic and ontogenetic, revealing traces of prior conditions

From: Vestiges of the natural history of development: historical holdovers reveal the dynamic interaction between ontogeny and phylogeny

  Evolutionary Developmental
Original function altered or absent (=non-functional) Vestiges: Cormorant wing-drying & dog circling behaviors; mammalian dive reflex; dewclaw; cave animal eyes; coccyx; vermiform appendix; piloerection Circulatory shunts including fossa ovalis & ligamentum arteriosum; male nipples; inguinal canal & looped vas deferens from descent of testes
Function, if any, continues, yet reveal past states of evolution (via phyletic analysis) or development Primate fingernails & stereoscopic vision as synapomorphies (shared, derived characters); cephalization with terminal rather than central head Cranial sutures & epiphyseal joints; umbilicus (navel) & other scars
Function lost or shifted, yet compound clues reveal joint evo-devo history within lineage Atavisms: Sudden reversion to retention of tail in humans or of limbs in snakes or cetaceans; bird teeth; Exaptations: fish lungs before swim bladders; feathers for insulation before flight Homologies: Pharyngeal glands (e.g., tonsils) & chordate gill arches; male & female genitalia
May be altered or non-functional; development in divergent lineages reveals clues to history/homology (in common origins & developmental processes) Phylogenetic (not merely phyletic) processes: mammalian ear ossicles as derived reptilian jaw bones; mammary glands as derivative sweat glands; perhaps sexual dimorphism in size and structures as conserved features