Paleontologists have identified a new species of tuatara-like sphenodontian reptile from dozens of fossilized specimens found in Arizona, the United States.
Holotype of Navajosphenodon sani. Image credit: Simões et al., doi: 10.1038/s42003-022-03144-y.
Sphenodontians are one of the longest living lineages of reptiles, with a fossil record of at least 230 million years and with recent morphological and molecular clock estimates suggesting their split from their closest relatives — squamates (lizards and snakes) — during the Late Permian epoch, about 259 million years ago.
Importantly, sphenodontians achieved a widespread geographic distribution between the Middle and early Late Triassic, with fossils recovered from various localities in the United Kingdom, the United States, Germany, Brazil, Argentina, and Zimbabwe, indicating they quickly occupied northern and southern portions of the supercontinent Pangaea.
Interestingly, these creatures sustained a higher diversity compared to squamates during the Triassic and Jurassic, being surpassed by the latter as the most species-rich group of lepidosaurs only in the Cretaceous period.
This discrepancy in species richness between squamates and sphenodontians only increased during the Late Cretaceous and Cenozoic, culminating in the current 11,000+ species of squamates and only one surviving sphenodontian species, the tuatara (Sphenodon punctatus).
“The discovery of the nearly complete sphenodontid fossil from North America is a ‘WOW’ moment in paleontology,” said Dr. Nic Rawlence, director of the Otago Palaeogenetics Laboratory and a researcher in the Department of Zoology at the University of Otago.
The newly-identified sphenodontian species lived in North America during the Early Jurassic epoch, some 190 million years ago.
Dubbed Navajosphenodon sani, it is represented by 15 specimens, consisting mostly of dentary and maxillary elements. Among those, the most complete specimen was designated as the holotype.
The fossils were recovered from the Kayenta Formation in Coconino County, Arizona, the United States.
“Using some amazing analytical methods, we’ve shown that Navajosphenodon sani is the oldest member of the lineage that led to tuatara,” the paleontologists said.
“By comparing the new fossil to tuatara, we’ve shown that the body form of tuatara has been conserved for at least 190 million years — a great example of if it ain’t broke, don’t fix it.”
“This is remarkable and fits with what we know of slow rates of genome evolution in tuatara.”
The discovery of Navajosphenodon sani is reported in a paper in the journal Communications Biology.
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T.R. Simões et al. 2022. An exceptionally preserved Sphenodon-like sphenodontian reveals deep time conservation of the tuatara skeleton and ontogeny. Commun Biol 5, 195; doi: 10.1038/s42003-022-03144-y
