Villaseñor-Amador, Suarez and Cruz 2021
identified bipedalism in the protosquamate, Huehuecuetzpalli (Albian, Early Creteaceous, Fig. 1), as they discuss locomotion types in various Cretaceous lizards. They did not have matching trackways.
Highlights from Villaseñor-Amador, Suarez and Cruz 2021:
The extinct lizard Huehuecuetzpalli mixtecus had a bipedal gait.
The ancestral condition in lizards is inferred to be terrestrial.
The ancestral condition in lizards is inferred with hindlimbs longer than forelimbs.
The bipedal gait was common in lizards since the Lower Cretaceous.
From the abstract:
“Here, we use quantitative methods to infer the type of locomotion of two Albian Mexican lizards (Lower Cretaceous) and three Cretaceous lizards from Brazil, North America and Spain, assessing the similarities of the hindlimb-forelimb length ratio amongst extinct and extant species.“
“The species Huehuecuetzpalli mixtecus was bipedal while Tijubina pontei was facultative bipedal, Hoyalacerta sanzi, Tepexisaurus tepexii and Polyglyphanodon sternbergi cannot be differentiated amongst terrestrial or arboreal with the approach used in this work. The ancestral character state reconstruction analysis showed a terrestrial ancestral locomotion type, with a basal character state of hindlimbs longer than forelimbs. Equal length between hind and forelimbs appear to be a derivate state that evolved multiple times in lizard evolutionary history.”
“Huehuecuetzpalli could have been an arboreal insectivore considering the extended lengths of its tendril-like toes, the brevity of its torso and the weight reduction in its attenuated palate. The robust hind limb and three sacral vertebrae might suggest a facultative bipedal capability in the manner of similar living lizards and Lacertulus, but the lack of an anterior ilial process argues against that possibility.”
Shine and Lambeck 1989
reported on an extant lizard that spends much of its day bipedally, and the rest of its day in the trees: Chlamydosaurus knigii (Fig. 2). Unfortunately, Villaseñor-Amador did not cite this important work. From the Shine and Lambeck abstract: “Chlamydosaurus are apparently unique among reptiles in using bipedal locomotion during routine foraging.”https://pterosaurheresies.wordpress.com/2013/10/13/the-unexpected-bipedalmarine-connection/
BTW, twenty years ago
there were manuscript referees for Peters 2000 who refused to believe the first-hand observations of Shine and Lambeck 1989 (above). Sadly, that’s a peek at reality, denial of published field observations by a third party. I’m sharing this old anecdote with you budding young paleontologists so you won’t be shocked when it happens to you.
Matching tracks would have been better evidence.
Earlier we talked about bipedalism in Middle Triassic Cosesaurus (Fig. 3), a lepidosaur taxon close to pterosaurs (Peters 2000a, b) that left quadrupedal and bipedal Rotodactylus tracks (Fig. 3 gray tone) left in Early and Middle Triassic strata. Note the anterior process of the ilium + prepubis + 4 sacrals + long neck + long attenuated tail, all traits that enable a bipedal configuration, even while standing still. Note the elongate, locked down coracoids. Those indicate flapping, as in birds and pterosaurs. So Cosesaurus was rarely, if ever, quadrupedal, but often flapping.
Peters D 2000a. Description and Interpretation of Interphalangeal Lines in Tetrapods. Ichnos 7:11-41.
Peters D 2000b. A Redescription of Four Prolacertiform Genera and Implications for Pterosaur Phylogenesis. Rivista Italiana di Paleontologia e Stratigrafia 106 (3): 293–336.
Reynoso V-H 1998. Huehuecuetzpalli mixtecus gen. et sp. nov: a basal squamate (Reptilia) from the Early Cretaceous of Tepexi de Rodríguez, Central México. Philosophical Transactions of the Royal Society, London B 353:477-500.
Shine R and Lambeck R 1989. Ecology of Frillneck liizards, Chlamydosaurus kingii (Agamidae), in tropical Australia. Australian Wildlife Research 16(5):491–500.
Villaseñor-Amador D, SuÃrez NX and Cruz J 2021. Bipedalism in Mexican Albian lizard (squamata) and the locomotion type in other Cretaceous lizards. Journal of South American Earth Sciences 103299 doi: https://doi.org/10.1016/j.jsames.2021.103299
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