Overlooked reversals in vertebrate evolution

Some of the following reversals were covered in earlier posts. 
Others premiere here. Still others remain overlooked or forgotten for the moment. Come back over time to see additions as they spring to mind.

Reversals are distinct from convergent traits
in that reversals also appear in ancestral taxa (in the LRT) while convergent traits do not.

  1. Platypus electrosensory bill — sturgeon, paddlefish, shark electrosensory rostrum
  2. Odontocete simple cone teeth — basal bony fish through pelycosaur simple cone teeth
  3. Multituberculate reappearance of post-dentary bones — cynodont jaw joint
  4. Prohalecites gill cover (operculum) — sturgeon, paddlefish, ratfish gill cover
  5. Minjinia, a disc-head, jawless placoderm — drepanaspid jawless anapsid
  6. Echinosorex, the moonrat and member of Glires lacks gnawing incisors — tree shrews that are not members of Glires also lack gnawing incisors
  7. Fins (dorsal, pectoral, pelvic, caudal) in ichthyosaurs, odontocetes, mysticetes, and other tetrapods — Similar fins in basal tetrapods (= fish)
  8. Loss of hind limbs in snakes, whales, amphisbaenids — lampreys, Birkenia
  9. Acanthostega radius twice as long as the ulna — as in pre-tetrapod lobefin fish
  10. Ossified skin (bony plates) in ankylosaurs, glyptodonts, etc. — Ossified scales in basal vertebrates (= fish)
  11. Flightless birds — flightless pre-bird theropods
  12. Loss of a flexible neck in mysticetes — basal vertebrates and tetrapods
  13. Heterodont dentition in Longisquama + pterosaurs and, by convergence in cynodonts —as in Hybodus, a shark basal to bony fish
  14. New world vulture overall morphology (pigeon sisters) — Old world vultures (hawk sisters)
  15. Long-legged shore birds (stilts, Himantopus, derived from short-legged Eocypselus) — long-legged basal birds like seriemas (Cariama).
  16. Atavistic tails in humans — monkeys, lemurs
  17. Extensible ventral mouth parts in skates — as in pre-gnathostome sturgeons
  18. Gill openings ventral to pectoral fins in skates and rays — as in osteostracans
  19. Separation of the gill basket from the neurocranium in sturgeons — as in Birkenia
  20. Fusion of the gill basket with the neurocranium in osteostracoderms — as in Arandaspis.
  21. Extended rostrum in pachycormiforms — as in Chondrosteus and sharks.
Figure 1. Skulls of pterosaur ancestors from Huehuecuetzpalli through Macrocnemus, Cosesaurus, Longisquama and the pterosaur Bergamodactylus.

Figure 1. Skulls of pterosaur ancestors from Huehuecuetzpalli through Macrocnemus, Cosesaurus, Longisquama and the pterosaur Bergamodactylus. Note the heterodont dentition (#13). These taxa were omitted from the recent pterosaur precursor paper by Ezcurra et al. 2020, by Hone and Benton 2007, 2008 and every other cladogram (Kellner 2003, Unwin 2003) over the last twenty years.

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