Abstract
Small theropod tracks, ichnogenus Minisauripus, from the Jinju Formation (Cretaceous) of Korea reveal exquisitely preserved skin texture impressions. This is the first report for any dinosaur of skin traces that cover entire footprints, and every footprint in a trackway. Special sedimentological conditions allowed footprint registration without smearing of skin texture patterns which consist of densely-packed, reticulate arrays of small (<0.5 mm) polygons, preserved as both impressions and casts, the latter essentially foot replicas. The skin texture resembles that reported for two Lower Cretaceous avian theropods (birds) from China which had quite different foot morphologies. This is also the oldest report of Minisauripus from Korea predating five reports from the Haman Formation of inferred Albian age. Minisauripus is now known from six Korean and three Chinese localities, all from the Lower Cretaceous. This gives a total sample of ~95 tracks representing ~54 trackways. With >80% of tracks <3.0 cm long, Minisauripus is pivotal in debates over whether small tracks represent small species, as the database suggests, or juveniles of large species.
Highlights
Small theropod tracks, ichnogenus Minisauripus, from the Jinju Formation (Cretaceous) of Korea reveal exquisitely preserved skin texture impressions
Defined phalangeal pad traces were not observed on digit IV. Due to these diagnostic morphological features the new ichnospecies M. zhenshounani was erected on the basis of the Shandong material[4], which included tracks somewhat longer than those reported from other sites: i.e., with footprint length (FL) up to 6.1 cm, including distinctive fine claw traces, whereas >80% of the global sample was in the FL range of 1.1–2.9 cm
The most significant results of the present study pertain to: (1) the evidence that Minisauripus is not confined to the Haman Formation in Korea and has a longer stratigraphic range than previously inferred; (2) the sample gives us the first detailed insight into the skin texture of a diminutive theropod, essentially replicating the soft tissue ornamentation; (3) the role of skin in revealing locomotor dynamics during registration of footprints, and; (4) the significance of the Jinju and other Minisauripus samples, in paleobiological debates over the implications of footprint evidence for diminutive size in theropod trackmakers
Summary
Ichnogenus Minisauripus, from the Jinju Formation (Cretaceous) of Korea reveal exquisitely preserved skin texture impressions. The skin texture resembles that reported for two Lower Cretaceous avian theropods (birds) from China which had quite different foot morphologies This is the oldest report of Minisauripus from Korea predating five reports from the Haman Formation of inferred Albian age. The addition of the new Chinese site increased the database so that “a total of ~92 Minisauripus tracks, representing at least 55 trackways, are recorded from a total of eight localities”[6] exclusive of sites in very close proximity which fall geographically within single key site locations This constitutes a large multi-site sample of diminutive tracks, which bear only slight resemblance to larger theropod tracks assigned to quite different ichnotaxa In addition diminutive tracks of purported microraptorine affinity have been described[9]
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