BULLETIN OF THE GEOLOGICAL SOCIETY OF DENMARK · VOL. 68 · 2020 Small ornithopod dinosaur tracks and crocodilian remains from the Middle Jurassic Bagå Formation, Bornholm, Denmark: Important additions to the rare Middle Jurassic vertebrate faunas of Northern Europe JESPER MILÀN, PETER L. FALKINGHAM & INKEN JULIANE MUELLER-TÖWE Milàn, J., Falkingham, P.L. & Mueller-Töwe, I. J. 2020. Small ornithopod dinosaur tracks and crocodilian remains from the Middle Jurassic Bagå Formation, Born- holm, Denmark: Important additions to the rare Middle Jurassic vertebrate faunas of Northern Europe. Bulletin of the Geological Society of Denmark, Vol. 68, pp. 245–253. ISSN 2245-7070. https://doi.org/10.37570/bgsd-2020-68-11 Geological Society of Denmark Two new small tridactyl dinosaur tracks are found in the Middle Jurassic Bagå https://2dgf.dk Formation of Bornholm and are interpreted as ornithopodian in origin. A skeletal fragment is identified as a crocodilian skull fragment. Previous finds of dinosaur Received 15 May 2020 tracks from the locality consist of two sizes of sauropods, a medium sized theropod Accepted in revised form and thyreophorans. The addition of tracks from ornithopod dinosaurs and skeletal 26 October 2020 Published online evidence of crocodilians now give a broader picture of a diverse Middle Jurassic 17 November 2020 vertebrate fauna. This is an important addition to the understanding of the terres- trial Mesozoic ecosystem of Denmark, and a valuable addition to the scarce Middle © 2020 the authors. Re-use of material is Jurassic vertebrate record of Europe. permitted, provided this work is cited. Creative Commons License CC BY: Keywords: Dinosaur, ornithopod, crocodile, ichnology, Middle Jurassic, Bathonian, https://creativecommons.org/licenses/by/4.0/ Bajocian. Jesper Milàn [[email protected]], Geomuseum Faxe, Østsjællands Museum, Østervej 2, DK-4640 Faxe, Denmark. Peter L. Falkingham [[email protected]], School of Biological and Environmental Sciences, Liverpool John Moores University, L3 3AF, UK. Inken Juliane Mueller-Töwe [[email protected]], Geological Survey of Denmark and Greenland, Øster Voldgade 10, DK-1350 Copenhagen K, Denmark. Mesozoic terrestrial vertebrates are rare in Denmark, An extensive vertebrate fauna including crocodiles, as terrestrial outcrops are limited to a few geographi- dinosaurs, birds, turtles, amphibians, sharks, other cally restricted exposures on the west and southwest fish and a single mammal tooth has been retrieved coast of the Baltic island of Bornholm (Kear et al. 2016) by screen washing of samples from the lowermost (Fig. 1). The oldest evidence of terrestrial vertebrates Cretaceous Rabekke Formation in the coastal cliff consists of cross-sections through footprints in the east of Arnager (Lindgren et al. 2004, 2008; Rees et al. Lower Jurassic (Hettangian) Sose Bugt Member of 2005; Schwarz-Wings et al. 2009), and large dinosaur the Rønne Formation (Clemmensen et al. 2014), and tracks up to 70 cm in length associated with lungfish a diminutive theropod footprint known from the aestivation burrows are exposed in cross-section Pliensbachian Hasle Formation (Milàn & Surlyk 2015), (Surlyk et al. 2008). Inland quarries in the overly- together with a small fragment of a femur from a juve- ing Jydegaard Formation have produced remains nile sauropodomorph (Milàn & Cuny 2019). The Mid- of dinosaurs, turtles, crocodiles, fish scales, shark dle Jurassic (Bajocian – Bathonian) Bagå Formation has teeth and coprolites (Noe-Nygaard et al. 1987; Noe- hitherto yielded tracks from theropod, thyreophoran Nygaard & Surlyk 1988; Bonde & Christiansen 2003; and sauropod dinosaurs, preserved as natural casts of Christiansen & Bonde 2003; Bonde 2004, 2012; Milàn sandstone (Milàn & Bromley 2005; Milàn 2011). et al. 2012). After the initial report of dinosaur tracks Dinosaur tracks and crocodilian remains from the Bagå Formation, Bornholm · 245 from the Middle Jurassic Bagå Formation (Milàn & including ferns, cycads and conifers (Bartholin 1892; Bromley 2005), which included tracks attributed to Florin 1958; Gry 1969; Hoelstad 1985), and vertebrate large sauropods and thyreophorans, new tracks from trace fossils are known from tracks of sauropod, theropods, thyreophorans and small sauropods were theropod, and thyrophorean dinosaurs (Milan 2011; described by Milàn (2011). This paper describes new Milàn & Bromley 2005). tracks from ornithopod dinosaurs as well as the first skeletal evidence of a crocodilian skull fragment from the Bagå Formation. Material and Methods Two tracks are described here. The first specimen is a Geological setting small track preserved as track and naturally formed cast (Track 1) found in a sandstone boulder in the Bagå The Bagå Formation is located on the west coast of clay pit. (Fig. 2A). The boulder was split along a thin the Danish Island of Bornholm situated in the Baltic clay seam, revealing the impression and naturally Sea, and the type section is the Bagå Graven clay pit formed cast of a small tridactyl track. To enhance the of the now closed Hasle Klinkefabrik at the small features of the track, the infilling clay was mechani- town of Sorthat (Gravesen et al. 1982; Michelsen et al. cally removed in some parts of the track. The speci- 2003; Nielsen et al. 2010) (Fig. 1). Today quarrying has men was found by amateur geologist Christian Bach ceased, and the clay pit is water-filled and known as Hansen in the summer of 2018. The specimen was Pyritsøen (pyrite lake). The Bagå Formation comprises declared Danekræ (National treasure) (DK-1007) and thick grey clay, dark to black coaly clays with rootlets, stored in the collection of the Natural History Museum coal beds, and medium- to fine-grained, cross-bedded of Denmark (NHMD 625523). or laminated sandstone. In the upper part, poorly A second track (Track 2) is larger and was brought sorted, muddy and pebbly sandstone beds locally con- to our attention by Rene Vilsholm from the exhibition tain boulders of weathered granite, and deposition is centre NaturBornholm. The cast is preserved in coarse interpreted to have taken place in lakes and swamps, sandstone (Fig. 2B). The specimen is stored in the col- small crevasse channels, lacustrine deltas and fluvial lection of the Natural History Museum of Denmark channels (Gravesen et al. 1982; Koppelhus & Nielsen (NHMD 676864). 1994; Michelsen et al. 2003; Nielsen et al. 2010). The Bagå Both tracks were digitized via photogrammetry, Formation is palynologically dated to Middle Jurassic, using photos taken with a 16mp FujiFilm FinePix Bajocian – Bathonian (Gry 1969; Koppelhus & Nielsen XP80, and processed using AliceVision Meshroom 1994). The formation contains abundant plant fossils 2019.1.0 (https://alicevision.github.io) (Moulon et al. NORWAY 15°E N SWEDEN 56°N DENMARK Hasle GERMANY 14°E Fig. 1. Map of Bornholm with Meso- Bornholm zoic and Palaeozoic outcrops indi- Kultippen Sorthat Pyritsøen cated. The type locality of the Bagå Formation is the water-filled clayp- it, Pyritsøen, between Hasle and Rønne Rønne towns, located at 55.150816°N, 14.704770°E. Kultippen is situat- Cretaceous Arnager ed further north along the coast Jurassic just south of Hasle at 55.170088°N, Palaeozoic 14.705822°E. Bagå Graven and Kul- Precambrian 0 10 km 55°N Fault tippen are indicated by red stars. Modified from Graversen (2009). 246 · Bulletin of the Geological Society of Denmark 2012; Jancosek & Pajdla, 2011). Models of track 1, its wide, however, part of one of the outer digits is miss- natural cast, and track 2 were constructed using 21, ing and we estimate that the total width would have 18, and 20 photos respectively. Digital models are pre- been around 18 cm. The cast is 2.9–4.1 cm deep. Each sented as textured and false colour images (Fig. 3), and digit cast shows the presence of one large, rounded all photos and models are made available at h t t p s :// pad encapsulating the whole digit (Fig. 2B). The two doi.org/10.6084/m9.figshare.7994216.v1 following the complete digit casts terminate in casts of short blunt protocol set out by Falkingham et al. (2018). claws. The casts of the digits are separated from the The hip height of the track makers was estimated cast of the metatarsal-phalangeal pad by a shallower using the relations between foot length and hip height. area (Fig. 3B). The metatarsal-phalangeal pad is broad Alexander (1976) proposed that hip-height could be with a wide proximal part. The divarication angle approximated as 4 × foot length, while Thulborn (1990) between the outer digits is estimated to be about 75°. expanded upon this by suggesting that hip-height could be more accurately predicted from 4.5, 4.8 or 4.6 Bone fragment × foot length for respectively theropods, ornithopods Description. Small, elongated bone fragment measur- and bipeds in general with foot length < 25 cm. ing 53 mm in length and 31 mm in the widest end A small bone fragment (Fig. 4) was found at the and 22 mm in the thinnest end (Fig. 4). The bone is locality Kultippen north of Bagå Graven in the sum- roughly oval to D-shaped in cross section. The thin- mer of 2016, by amateur geologist Christian Rasmus- nest end is broken but the broad end has preserved the sen. Kultippen is the locality where excess excavated suture for the adjacent bone. The flatter surface of the material from Bagå Graven was dumped near the bone is strongly ornamented by closely spaced, oval beach. The specimen is declared Danekræ (DK-869) to rounded pits, 3-6 mm wide and up to 2 mm deep, and is stored in the collection of the Natural History Museum of Denmark (NHMD 625420). New finds Track 1 Description. Tridactyl track measuring 8.4 cm in length and with a maximum width across the impressions of the outer digits of 8.9 cm. The impression of the track is 1.1 cm deep at the deepest part (Fig. 2A). The track is preserved as track and naturally formed cast in a 5 cm block of coarse sandstone.