Neosauroides

Neosauroides Temporal range: Albian–Calabrian PreꞒ Ꞓ O S D C P T J K Pg N
Holotype of Neosauroides innovatus
Trace fossil classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Class:	Reptilia
Order:	Squamata
Family:	Scincidae
Genus:	† Neosauroides Kim et al., 2017
Type ichnospecies
†Neosauroides koreaensis Kim et al., 2017
Other ichnospecies [1]
†N. innovatus Kim et al., 2019

Neosauroides is an ichnogenus of probable scincid lizard mainly known from the Early Cretaceous (Albian) of South Korea. The ichnogenus contains two named ichnospecies, N. koreanensis and N. innovatus, representing the first lizard trackway reported from the Cretaceous period.

Discovery and naming

The ichnogenus Neosauroides means "new reptile" due to its novelty for being the only known lizard trackway from the Cretaceous period at the time of its initial description, and the type ichnospecies N. koreanensis from the Haman Formation is named in reference to Korea. ^[2] The second ichnospecies N. innovatus from the Jinju Formation, representing the largest known Cretaceous lizard trackway, is named in reference to the Jinju Innovation City. ^[1] Trace fossils identified as an indeterminate ichnospecies of Neosauroides have been discovered from the Early Cretaceous Hekou Group of China, ^[3] and from the Early Pleistocene (Calabrian) Bacons Castle Formation of the United States. ^[4]

Classification

The trackmaker of Neosauroides is probably a lizard, but its taxonomic identity is uncertain. The original description of N. koreanensis did not assign this ichnotaxon to a specific clade, ^[2] while the describers of N. innovatus included Neosauroides within the infraclass Lepidosauromorpha which includes all reptiles closer to lizards than archosaurs such as crocodilians and birds. ^[1] The authors also considered the other lizard ichnotaxon from the Hasandong Formation (Aptian) of South Korea, Sauripes hadongensis, as a potential nomen dubium due to insufficient description and problematic holotype designation, which would make Neosauroides to be the only valid Cretaceous lizard ichnotaxon. ^[1]

In 2021, Weems suggested that Neosauroides represents skink tracks based on an isolated footprint identified as N. isp. from the Early Pleistocene of the United States, the only record of this ichnogenus outside Cretaceous East Asia. ^[4] As of 2024, the oldest known skink Electroscincus zedi is reported from the Late Cretaceous (Cenomanian) Burmese amber, ^[5] slightly younger than the Albian-aged Haman and Jinju Formation. ^[6]

References

1. Kim, Kyung Soo; Lim, Jong Deock; Lockley, Martin G.; Kim, Dong Hee; Pinuela, Laura; Yoo, Jae Sang (2019). "Largest Cretaceous lizard track assemblage, new morphotypes and longest trackways comprise diverse components of an exceptional Korean Konservat-Lagerstätten ichnofauna". Scientific Reports. 9 (1): 13278. Bibcode:2019NatSR...913278K. doi: 10.1038/s41598-019-49442-0 . PMC   6746761 . PMID   31527673.
2. Kim, Kyung Soo; Lockley, Martin G.; Lim, Jong Deock; Pinuela, Laura; Xing, Lida; Moon, Hae Won (2017). "First report of lacertiform (lizard) tracks from the Cretaceous of Asia". Cretaceous Research. 69: 62–70. Bibcode:2017CrRes..69...62K. doi:10.1016/j.cretres.2016.08.013.
3. Xing, L.D.; Li, D.; Lockley, M.G.; Persons, W.S.; Klein, H.; Yang, J.; Li, L.; Peng, C. (2021). "Saurischian-dominated tracksites and first Cretaceous lizard trackway from China from the Hekou Group (Lower Cretaceous) of Lanzhou-Minhe Basin, Gansu, Northwest China". Historical Biology. 33 (12): 3703–3713. Bibcode:2021HBio...33.3703X. doi:10.1080/08912963.2021.1887863.
4. Weems, R.E. (2021). "Additions to the Early Pleistocene (Early Irvingtonian) Stratford Hall Local Ichnofauna from the Bacons Castle Formation, Westmoreland County, Virginia (USA)". New Mexico Museum of Natural History and Science Bulletin. 82: 487–496.
5. Daza, J. D.; Stanley, E. L.; Heinicke, M. P.; Leah, C.; Doucet, D. S.; Fenner, K. L.; Arias, J. S.; Smith, R. D. A.; Peretti, A. M.; Aung, N. N.; Bauer, A. M. (2024). "Compound osteoderms preserved in amber reveal the oldest known skink". Scientific Reports. 14. 15662. doi: 10.1038/s41598-024-66451-w . PMC   11231356 .
6. Lee, Tae-Ho; Park, Kye-Hun; Yi, Keewook (October 2018). "Nature and evolution of the Cretaceous basins in the eastern margin of Eurasia: A case study of the Gyeongsang Basin, SE Korea". Journal of Asian Earth Sciences. 166: 19–31. Bibcode:2018JAESc.166...19L. doi:10.1016/j.jseaes.2018.07.004. S2CID   135061525.