The first possible choristoderan trackway from the Lower Cretaceous Daegu Formation of South Korea and its implications on choristoderan locomotion

Yuong-Nam Lee,Seung-Ho Jung,Dal-Yong Kong

doi:10.1038/s41598-020-71384-1

Yuong-Nam Lee, Seung-Ho Jung + Show 1 more

Open Access

https://doi.org/10.1038/s41598-020-71384-1

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Abstract

Here we report a new quadrupedal trackway found in the Lower Cretaceous Daegu Formation (Albian) in the vicinity of Ulsan Metropolitan City, South Korea, in 2018. A total of nine manus-pes imprints show a strong heteropodous quadrupedal trackway (length ratio is 1:3.36). Both manus and pes tracks are pentadactyl with claw marks. The manus prints rotate distinctly outward while the pes prints are nearly parallel to the direction of travel. The functional axis in manus and pes imprints suggests that the trackmaker moved along the medial side during the stroke progressions (entaxonic), indicating weight support on the inner side of the limbs. There is an indication of webbing between the pedal digits. These new tracks are assigned to Novapes ulsanensis, n. ichnogen., n. ichnosp., which are well-matched not only with foot skeletons and body size of Monjurosuchus but also the fossil record of choristoderes in East Asia, thereby N. ulsanensis could be made by a monjurosuchid-like choristoderan and represent the first possible choristoderan trackway from Asia. N. ulsanensis also suggests that semi-aquatic choristoderans were capable of walking semi-erect when moving on the ground with a similar locomotion pattern to that of crocodilians on land.

Highlights

South Korea has become globally famous for various tetrapod footprints from Cretaceous strata[1], among which some clades such as frogs2, birds[3] and mammals[4] have been proved for their existences only with ichnological evidence
Quadrupedal tracks with a pronounced heteropody; pentadactyl manus impression with claw marks and semi-symmetrical outline, wider than longer; divergence between digit I and V imprints ranges 180° to 210°; the digit IV imprint slightly longer than digit II; entaxonic; pentadactyl pes impression with claw marks and asymmetrical outline, longer than wide; webbing between the proximal portion of slender digits; the subequal digits III and IV imprints longer than others; the sole pad impression is elongate with a U-shaped “heel”; entaxonic
The well-preserved interdigital web traces of pes imprints clearly show that N. ulsanensis was left by a web-footed animal with five functional digits

Summary

Introduction

South Korea has become globally famous for various tetrapod footprints from Cretaceous strata[1], among which some clades such as frogs2, birds[3] and mammals[4] have been proved for their existences only with ichnological evidence. A new quadrupedal trackway with a pronounced heteropody (sensu stricto)[5] was discovered in the Daegu Formation (Albian, Lower Cretaceous), Ulsan City, which consists of nine manus-pes sets (Fig. 1). Both manus and pes are pentadactyl with sharp claw marks. They look different from any known quadrupedal dinosaur footprints because there is a clear indication of webbing between the pedal digits. New footprints differ from their tracks in morphology and appear to belong to that of other clade. The trackmaker’s locomotory posture on land was inferred from the trackway pattern

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