Abstract
Preserved labile tissues (e.g., skin, muscle) in the fossil record of terrestrial vertebrates are increasingly becoming recognized as an important source of biological and taphonomic information. Here, we combine a variety of synchrotron radiation techniques with scanning electron and optical microscopy to elucidate the structure of 72 million-year-old squamous (scaly) skin from a hadrosaurid dinosaur from the Late Cretaceous of Alberta, Canada. Scanning electron and optical microscopy independently reveal that the three-dimensionally preserved scales are associated with a band of carbon-rich layers up to a total thickness of ∼75 microns, which is topographically and morphologically congruent with the stratum corneum in modern reptiles. Compositionally, this band deviates from that of the surrounding sedimentary matrix; Fourier-transform infrared spectroscopy and soft X-ray spectromicroscopy analyses indicate that carbon appears predominantly as carbonyl in the skin. The regions corresponding to the integumentary layers are distinctively enriched in iron compared to the sedimentary matrix and appear with kaolinite-rich laminae. These hosting carbonyl-rich layers are apparently composed of subcircular bodies resembling preserved cell structures. Each of these structures is encapsulated by calcite/vaterite, with iron predominantly concentrated at its center. The presence of iron, calcite/vaterite and kaolinite may, independently or collectively, have played important roles in the preservation of the layered structures.
Highlights
Fossilized dinosaur integument has been known for nearly 150 years, yet it is only recently that it has been considered more than a simple impression of the original skin surface (Sternberg, 1953; Martill, 1991; Kellner, 1996)
back-scattered electron (BSE) Scanning Electron Microscopy (SEM) shows an outermost layer of white material identified as barite that caps a region of numerous thin, dark bands up to a total thickness of ⇠35–75 μ m
The main outcome of this work is the structural and compositional description of layers compatible with epidermal cell layers in the skin of a hadrosaur. These layers are composed of chains of carbonrich subcircular bodies, predominantly in the form of carbonyl
Summary
Fossilized dinosaur integument has been known for nearly 150 years, yet it is only recently that it has been considered more than a simple impression (i.e. trace fossil) of the original skin surface (Sternberg, 1953; Martill, 1991; Kellner, 1996). Significant advances in our understanding of the preservation and structure of squamous skin have been achieved with the use of synchrotron radiation techniques (Barbi et al, 2014, and references therein). It is generally accepted that labile tissues, such as skin and muscle, can preserve and remain intact millions of years after the death of the organism (Schweitzer et al, 2005; Lingham-Soliar, 2008; Manning et al, 2009; Li et al, 2010; Zhang et al, 2010; Li et al, 2012; Lindgren et al, 2014; Bertazzo et al, 2015; Lindgren et al, 2018). Hadrosaur skin is relatively common in the fossil record (Davis, 2014; Bell, 2014), few studies have investigated either its composition or the possible determining factors behind its preservation (e.g. Manning et al, 2009). We present a qualitative study of three-dimensionally preserved squamous skin ( referred to as skin) from a hadrosaurid dinosaur from the Upper Cretaceous (Campanian)
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