Abstract
We describe a Mesozoic fish Paralycoptera sp. (Teleostei: Osteoglossoidei), on the basis of a postcranial skeleton collected from the volcaniclastic mudstones of the Lai Chi Chong Formation of Hong Kong, China. The new finding—representing the city’s first Mesozoic fish—extends the geographical distribution of Paralycoptera from eastern mainland China into Hong Kong, demonstrating a wider distribution than previously appreciated for this genus. A radiometric age for the Lai Chi Chong Formation of 146.6 ± 0.2 Ma implies a temporal range expansion for Paralycoptera of approximately 40 million years back from the Early Cretaceous (∼110 Ma). However, spores found in the Formation suggest an Early Cretaceous age that is consistent with the existing age assignment to Paralycoptera. We argue that the proposed temporal range extension is genuine because it is based on recent high precision radiometric age data, but given the discrepancies with the biostratigraphic ages further investigation is needed to confirm this. This study provides an important step towards revealing Hong Kong’s Mesozoic vertebrate fauna and understanding its relationship to well-studied mainland Chinese ones.
Highlights
This study focuses on the identification of Stephen Hui Geological Museum (SHGM) L275 and understanding its ecology in the context of the palaeoenvironment of the Lai Chi Chong Formation, that has been inferred from its geology and plant fauna (Lee et al.1997) (Fig. 2)
In the anterior part of the specimen, there are four circular features directly on the vertebral column (Fig. 3) - these are the anterior rims of the vertebrae. This feature is identified in the osteoglossoid osteoglossomorph Paralycoptera wui, Institute Vertebrate Paleontology and Paleoanthropology (IVPP) V2989.100 (Fig. 4), and in other studied osteoglossomorph specimens like Yanbiania wangqingica, IVPP V6767-1, and Tongxinichthys microdus, IVPP 2332.1
A Late Jurassic age is cautiously assigned to SHGM L275 pending the discovery of an in situ specimen - the formation and locality information of SHGM L275 are based on its specimen label only, as it was not possible to verify this with the fossil's discoverer because they are not known
Summary
The preserved part corresponds to the caudal portion of the fish, with the head and abdominal portion missing. Twenty vertebrae are identified in this portion (Fig. 3) between the anterior part of the dorsal and anal fins and the caudal fin, with the anteriormost preserved one being an abdominal vertebra, and the rest (19) – caudal vertebrae. In the anterior part of the specimen, there are four circular features directly on the vertebral column (Fig. 3) - these are the anterior rims of the vertebrae. This feature is identified in the osteoglossoid osteoglossomorph Paralycoptera wui, IVPP V2989.100 (Fig. 4), and in other studied osteoglossomorph specimens like Yanbiania wangqingica, IVPP V6767-1, and Tongxinichthys microdus, IVPP 2332.1
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