Lepidosauromorphs are distinguishable fromarchosauromorphs (reptiles closer to archosaurs) by their primitive sprawling gait (allowing for the same sinusoidal trunk and tail movement seen in fish), the sliding "joint" between the coracoids and the sternum (for a longer stride), and theirpleurodont dentition. In contrast, Archosauromorphs possess aparasagittal gait, a reduction in their dermal girdle, a reduction and/or loss of the sternum, and a more thecodont dentition. Living lepidosauromorphs have retained an ectothermic ("cold blooded") metabolism, unlike the ancestral condition in archosauromorphs.
While some putative stem-lepidosauromorphs likePalaeagama are known from the LatePermian, the oldest definitive lepidosauromorphs,Sophineta andPaliguana, are known from the EarlyTriassic.[4][5]Taytalura from the early LateTriassic of Argentina is the most complete fossil of an early lepidosauromorph and is one of the few fossils robustly inferred as an early evolving lepidosauromorph.[6] TheKuehneosauridae, a family of reptiles with elongated ribs which allowed them to glide akin to livinggliding lizards have been historically typically considered early lepidosauromorphs. However, several recent studies have been found them in other positions withinSauria, including Archosauromorpha.[7] Almost all non-lepidosaurian lepidosauromorphs became extinct by the end of the Triassic, the with the latest non lepidosaur-lepidosauromorphs beingMarmoretta from the Middle Jurassic of Britain and an indeterminate form from the Middle JurassicMoskvoretskaya Formation of Russia, which appear to be closely related toFraxinisaura from the Middle Triassic of Germany.[5][8][9] Other studies have recoveredMarmoretta as a stem-squamate.[10]
^de Queiroz, K.; Cantino, P. D.; Gauthier, J. A., eds. (2020). "Pan-Lepidosauria J. A. Gauthier and K. de Queiroz, new clade name".Phylonyms: A Companion to the PhyloCode. Boca Raton: CRC Press. pp. 1075–1078.ISBN978-1-138-33293-5.
^Simōes, Tiago R.; Caldwell, Michael W.; Talanda, Mateusz; Bernardi, Massimo; Palci, Alessandro; Vernygora, Oksana; Bernardini, Federico; Mancini, Lucia; Nydam, Randall L. (30 May 2018). "The origin of squamates revealed by a Middle Triassic lizard from the Italian Alps".Nature.557 (7707):706–709.Bibcode:2018Natur.557..706S.doi:10.1038/s41586-018-0093-3.PMID29849156.S2CID44108416.
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