THREE-DIMENSIONAL SOFT TISSUE PRESERVATION REVEALED IN THE SKIN OF A NON-AVIAN DINOSAUR by MATTEO FABBRI 1 , JASMINA WIEMANN 1 , FABIO MANUCCI 2 and DEREK E. G. BRIGGS 1 1 Department of Geology & Geophysics, Yale University, PO Box 208109, New Haven, CT 06520, USA; matteo.fabbri@yale.edu, jasmina.wiemann@yale.edu, derek.briggs@yale.edu 2 Geo-Model, via Abbate Tommaso 78, Altino (VE), 30020, Italy; fabiomanucci@gmail.com Typescript received 2 October 2018; accepted in revised form 19 November 2019 Abstract: The most commonly preserved soft tissues asso- ciated with ornithischian dinosaurs are skin remains. The apparent resistance of hadrosaur skin to decay, and its abun- dance in the fossil record relative to that of other tetrapods, has been attributed to factors such as thickness and compo- sition. Here we report additional intrinsic factors within hadrosaur skin: 3D-preserved eumelanin-bearing bodies, dermal cells and blood vessel fragments in an organic matrix composed of protein fossilization products. The skin is much thinner than that of living mammals of similar size. It is likely that the preservation of hadrosaur skin is related to the arrangement of the layers composing it. Key words: skin, taphonomy, hadrosaur, melanin, soft tissue. T HE skin is the largest organ in the body of any verte- brate and carries out important functions such as home- ostasis, sensory reception and visual signaling (Landmann 1986). The skin is composed of three layers: the epidermis (outer), dermis and the subcutis (innermost). The epider- mis is composed of stratified layers of keratinized cells (the stratum corneum, stratum intermedium and stratum basale) whereas the dermis is characterized by a stratum spongiosum of loose collagen fibres and a lower stratum compactum of tightly packed, orthogonal arrays of colla- gen fibres (Landmann 1986; Cooper & Greenberg 1992). Colouration of the skin is generally determined by mela- nophores and chromatophores and the structural layering of the integument (McNamara et al. 2016; Shawkey & D’Alba 2017). Chromatophores and melanophores are usually stored at the interface between the epidermis and dermis in vertebrates (Prum & Torres 2003, 2004; Chang et al. 2009; McNamara et al. 2016; Shawkey & D’Alba 2017). The innermost layer of the skin, the subcutaneous layer, separates the integument from the rest of the body. Integument is probably the most abundant type of soft tissue in the vertebrate fossil record (Schweitzer 2011; Davis 2014) and it is providing increasingly important evidence of reptile evolution and ecological diversity in the past (e.g. Martill 1995; Briggs et al. 1997; Martill et al. 2000; Bell 2012; Lindgren et al. 2013, 2014, 2018; Davis 2014; McNamara et al. 2016, 2018; Yang et al. 2019). Fossilized skin is preserved in three main ways: as impressions, compressions or permineralized, three- dimensional skin (Schweitzer 2011). Impressions are occa- sionally found in association with bones or footprints (e.g. Lockley et al. 2004; Paik et al. 2017). Compressions are preserved as a carbon-rich layer surrounding bones (e.g. Briggs et al. 1997; Qiang et al. 1998; Wang et al. 2019). Permineralized skin is the rarest of the three modes of preservation (Schweitzer 2011; Bell 2012; Davis 2014) and usually occurs in association with three dimen- sionally preserved skeletons. Permineralized skin was pre- viously thought to be a high-fidelity mineralized replication of the original organic tissue (Schweitzer 2011). However, recent investigations of a few exception- ally preserved examples have challenged this view by recovering original organic molecules. Dinosaurian integument preserved as a result of early mineralization is known in Ornithischia, Sauropoda and Theropoda (Briggs et al. 1997; Martill et al. 2000; Bell 2012; Davis 2014; McNamara et al. 2018). The preservation of integu- ment is most prevalent in hadrosaurs (Bell 2012; Davis 2014). However, the taphonomic processes that favour the fossilization of skin and associated molecular preser- vation are still poorly understood (Lyson & Longrich 2011; Bell 2012; Davis 2014). Previous investigations of dinosaur skin were performed on the basal ceratopsian Psittacosaurus (Lingham-Soliar 2008), a nodosaur (Brown © The Palaeontological Association doi: 10.1111/pala.12470 1 [Palaeontology, 2019, pp. 1–9]