Tetrapod body plan; vertebrate skeleton evolution; homology vs analogy; vestigial organs; cladistics; comparative embryology; deuterostome / protostome split; segmentation; fin-to-limb transition; eye convergent evolution; vertebrate brain…
Comparative Anatomy
Tetrapod body plan
Four-limbed vertebrate Bauplan emerged in late-Devonian; Acanthostega and Ichthyostega ~365 Ma show pre-aquatic-to-terrestrial…
Vertebrate skeleton evolution
Notochord -> cartilaginous endoskeleton (lampreys / sharks) -> mineralized bone (Ostracoderms 480 Ma); jaw evolution from gill-arch…
Homology vs analogy
Owen 1843 distinction: homology = same structure different function (bird wing / bat wing / human arm); analogy = same function different…
Vestigial organs
Wiedersheim 1893 catalogue: human appendix / coccyx / wisdom-teeth / ear-muscles / plica-semilunaris; whale pelvic bones; snake hindlimb…
Cladistics replaces scala naturae
Hennig 1950 cladistic method replaces Aristotelian scala-naturae chain-of-being with branching phylogeny; synapomorphies (shared-derived)…
Comparative embryology (Haeckel / von Baer)
Haeckel 1866 biogenetic law (ontogeny recapitulates phylogeny) overstated; von Baer 1828 four laws (general -> specific) more accurate;…
Deuterostome / protostome split
Grobben 1908: bilaterian split based on blastopore fate; protostome (mouth-first: arthropod / mollusc / annelid) vs deuterostome…
Segmentation (arthropod vs vertebrate)
Both arthropods and vertebrates segmented body-plans but evolved independently per Hox-cluster studies; pair-rule + segment-polarity…
Fin-to-limb transition
Tiktaalik (Daeschler 2006) ~375 Ma intermediate; pelvic-fin to hindlimb skeletal homology; Hox-13 expression in autopod (digits);…
Eye evolution (convergent)
40+ independent eye originations across phyla (Salvini-Plawen-Mayr 1977); shared deep homology via Pax6 master-regulator (Quiring 1994);…
Vertebrate brain evolution
Conserved tripartite forebrain / midbrain / hindbrain; mammalian cortex expansion (mouse 1.4 cm^2 -> human 2400 cm^2 with gyrification);…
Blastopore fate (mouth or anus)
Embryonic blastopore = first opening of gastrulation; in protostomes becomes mouth, in deuterostomes becomes anus; oldest synapomorphy of…
Homology vs analogy (Owen 1843)
R Owen 1843 distinction: homology = same structure different function (vertebrate forelimb); analogy = different structure same function…
Vertebrate Bauplan / archetype
Geoffroy Saint-Hilaire 1822 + Owen 1848 vertebrate archetype; modular body-plan + cephalization + bilateral symmetry; modern evo-devo…
Convergent evolution (eye)
~40 independent eye-evolution events: vertebrate camera eye (RPE-cone-rod), cephalopod camera eye (no blind spot), arthropod compound,…
Tetrapod limb (Tiktaalik 2006)
Daeschler-Shubin 2006 Tiktaalik roseae fish-tetrapod transitional; Devonian 375 Mya; 1-2-3-4-5 digit pattern; humerus + radius/ulna +…
Geometric morphometrics (Bookstein 1991)
F Bookstein 1991 Procrustes-superposition + thin-plate-spline + landmark-coordinates; quantitative shape-comparison; modern 3D-microCT +…
Extant Phylogenetic Bracket (Witmer 1995)
L Witmer 1995 EPB: infer soft-tissue characters of extinct taxa from extant phylogenetic relatives sandwich; e.g. dinosaur-bird-crocodilian…