plesiomorphousadj.
/ˌpliːzɪəˈmɔːfəs/, U.S. /ˈˌplisiəˈmɔrfəs/ΘΚΠ
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plesiomorphous1832
plesiomorphic1849
1832 W. Whewell in Rep. Brit. Assoc. 2 364 50. To determine whether the angles of plesiomorphous crystals are separated by definite or indefinite steps.
1845 N. Brit. Rev. 2 314 The term plesiomorphous (nearly of the same shape) is generally substituted.
1857 Philos. Trans. (Royal Soc.) 147 41 Hematite may be associated with Quartz..and with Calcite..forming a small plesiomorphous group.
2. Taxonomy. = plesiomorphic adj. 2.
ΚΠ
1966 D. D. Davis & R. Zangerl tr. W. Hennig Phylogenetic Systematics ii. 89 We will call the characters or character conditions from which transformation started..in a monophyletic group plesiomorphous, and the derived conditions..apomorphous.
1983 Systematic Zool. 32 34 Synapomorphies cannot be distinguished from parallelisms when the taxa maintaining the plesiomorphous character alternative are undescribed or extinct.
2000 Jrnl. Morphol. 243 219 The selachian, chimaeroid, and actinopterygian conditions are all derivable from this plesiomorphous state.
This entry has been updated (OED Third Edition, September 2006; most recently modified version published online March 2022).
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adj.1832