A similar character also appears in the Soleidae, but is never covered by lower lip in that family; soleids do not occur in the Neotropics.
dcterms:bibliographicCitation
2003, Roberto E. Reis, Sven O. Kullander, Carl J. Ferraris, Check List of the Freshwater Fishes of South and Central America, page 666:
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Larvae of the flatfish family Soleidae most closely resemble tonguefish larvae but the smaller jaws and more attenuated body shape in cynoglossids serves to distinguish them from larval soleids.
dcterms:bibliographicCitation
2005, T. W. Farooqi, R. F. Shaw, J. G. Ditty, J. Lyczkowski-Shultz, “Chapter 207: Cynoglossidae: Tongue fishes”, in William J. Richards, editor, Early Stages of Atlantic Fishes, page 2368:
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The oldest soleids, Eobuglossus eocenicus and Turahbuglossus cuvillieri, both known from single specimens from the Upper Lutetian of Egypt (Chabanaud 1937; Chanet 1994, 1997), are also among the first known flatfish fossils and they are identical to skeletons of recent soleids.
dcterms:bibliographicCitation
2008, Thomas A. Monroe, “Chapter 2: Systematic diversity of the Pleuronectiformes”, in Robin N. Gibson, editor, Flatfishes: Biology and Exploitation, page 14: