Dinosaur tracks in Lower coastal plain sediments (Sose Bugt Member, Rønne Formation) on Bornholm, Denmark

LARS B. CLEMMENSEN, JESPER MILAN, GUNVER K. PEDERSEN, ANNE B. JOHANNESEN AND CONNIE LARSEN

Clemmensen, L.B., Milan, J., Pedersen, G.K., Johannesen, A.B. & Larsen, C. 2014: tracks in Lower Jurassic coastal plain sediments (Sose Bugt Member, Rønne Formation) on Bornholm, Denmark. Lethaia,Vol. 47, pp. 485–493.

Fluvial palaeochannels of coastal plain sediments of the Lower Jurassic Sose Bugt Member of the Rønne Formation exposed in the coastal cliffs at Sose Bugt, Bornholm, contain abundant dinosaur or other large tracks in the form of deformation structures exposed in vertical section. The tracks are represented by steep-walled, flat- to-concave-bottomed depressions, with a raised ridge at each side. The tracks are filled with laminated sediments, draping the contours of the bottom of the depression. Un- derprints, stacked concave deformations beneath the prints, are present beneath each track. Contemporary Upper – Lower Jurassic strata from southern and Poland contain a diverse track fauna, supporting our interpretation. This is the earliest evidence of dinosaur activity in Denmark. □ Bornholm, coastal plain, dinosaur tracks, lake sediments, Lower Jurassic.

Lars B. Clemmensen [[email protected]], Jesper Milan [[email protected]], Anne B. Joh- annesen [[email protected]], and Connie Larsen [[email protected]], Depart- ment for Geosciences and Natural Resource Managements, University of Copenhagen, Øster Voldgade 10, DK-1350 Copenhagen K, Denmark; Jesper Milan [[email protected]], Geomuseum Faxe/Østsjællands Museum, Østervej 2, DK-4640 Faxe, Denmark; Gunver K. Pedersen [[email protected]], GEUS Geological Survey of Denmark and Greenland, Øster Voldgade 10, DK-1350 Copenhagen K, Denmark; manuscript received on 12/04/2013; manuscript accepted on 04/12/2013.

Outcrops of terrestrial sediments in Den- and jawbone fragments of actinopterygians, post- mark are restricted to a few scattered exposures cranial remains of and primitive , along the southwest coast of the Baltic Island of small dromaeosaurid and perhaps Bornholm (Fig. 1). Despite the very limited extent teeth, and a single of a multi-tuberculate mam- of the exposures, an increased interest and intensive mal (Lindgren et al. 2004, 2008; Rees et al. 2005; field studies during the last decade have yielded evi- Schwarz-Wings et al. 2009). In contrast to the dimin- dence of a relatively diverse fauna of terrestrial verte- utive body , a trample ground with abundant brates, from and Early cross-sections through large dinosaur tracks (up to deposits (Fig. 2). 70 cm in length), and possible lungfish aestivation To date, the earliest evidence of dinosaur activity burrows have been described from an adjacent expo- comes from the Middle Jurassic Baga Formation sure in the coastal cliff (Surlyk et al. 2008). (Gravesen et al. 1982) (Fig. 2), exposed in the aban- The overlying Jydegaard Formation (Fig. 2), doned Hasle Klinker Factory clay pit at Baga, at the known from inland quarries, has yielded dromaeo- coast between Hasle and Rønne. This pit has yielded saurian teeth, Dromaeosaurides bornholmensis and a a diverse dinosaur ichnofauna comprising large and possible tooth crown from a juvenile sauropod small tracks of sauropods, thyreophoreans and (Bonde & Christiansen 2003; Christiansen & Bonde theropods but no body fossils (Milan & Bromley 2003), as well as fragments from carapaces of , 2005; Milan 2011). teeth of the crocodile Pholidosaurus, and abundant The lowermost Cretaceous Rabekke Formation, teeth and scales of the holostean fish Lepidotes and exposed in a coastal cliff east of Arnager (Gravesen the freshwater Hybodus and some pycnodont et al. 1982) (Fig. 2), has recently yielded remains of a jaws, small stem-teleosteans and coprolites (Noe- rich fauna of micro- including abundant Nygaard et al. 1987; Noe-Nygaard & Surlyk 1988; crocodile teeth ( sp., Theriosuchessp.,and Rees 2001; Bonde 2004; Milan et al. 2012). For a sp.), fragments of carapaces, scales complete review of the Mesozoic vertebrate faunas,

DOI 10.1111/let.12073 © 2014 Lethaia Foundation. Published by John Wiley & Sons Ltd 486 Clemmensen et al. LETHAIA 47 (2014)

A

B C

Fig. 1. A, geological map of Bornholm (map modified from Graversen 2009). Localities with dinosaur tracks are indicated with dots; the locality at Sose Bugt with newly recognized dinosaur tracks is described in the article. B, detailed geological map of the Sose Bugt area. C, location of Bornholm in a broader geographical context. including the marine fauna of Bornholm, see Bonde found in the Asen locality in the (2012). Basin (Lindgren et al. 2007) (Fig. 2). In environments similar to those on addition to the ichnofauna, a few dinosaurian verte- Bornholm are known to have supported a rich dino- brae have been found in the same level as the tracks saur fauna in nearby , southern Sweden, from Billesholm coal mine (Bolau€ 1954). which was connected to Bornholm during most of During a recent field course, deformation struc- the Mesozoic (Surlyk et al.1995; Michelsen et al. tures were observed in the Lower Jurassic Sose Bugt 2003). The – Early Jurassic Hogan€ €as Member of the Rønne Formation (Gravesen et al. Formation has yielded tracks and trackways of the- 1982; Surlyk et al. 1995) at the type section in Sose ropod and possible thyreophorean dinosaurs as well Bugt on the south coast of Bornholm (Fig. 1). The as a few indeterminate skeletal remains (Bolau€ 1952, deformation structures showed many of the charac- 1954; Pleijel 1975; Ahlberg & Siverson 1991; Gierlin- teristics known from vertebrate tracks emplaced in ski & Ahlberg 1994; Milan & Gierlinski 2004), and soft sediment and exposed in cross-section (e.g. remains of neoceratopsian dinosaurs have been Loope 1986; Allen 1997; Milan & Bromley 2006, LETHAIA 47 (2014) Dinosaur tracks in Denmark 487

System Fennoscandian Border Zone Material and methods Stage Series NWSkåne SE Bornholm U Jydegård Formation Six detailed sedimentological sections were mea- Valanginian L sured along a c. 50-m-long coastal cliff at Sose Vita- Robbe-

Lower U bäck dale Formation Bugt. Within these sections, we recognize eight sed- Ryazanian

Cretaceous Clay L Rabekke Formation imentary units and correlate them across the profile U Annero (Fig. 3). Continued coastal erosion ensures the Volgian M Fm Nytorp availability of good exposures, and the deformation Sand

L structures described here were seen after a with r

e U p Kimmeridgian p particularly severe erosion. However, landslides may Annero Fm Annero

U L Fyle- dalen frequently cover large parts of the formation, mak- U Clay Oxfordian M ing it difficult to measure complete sedimentologi- L cal logs. The deformation structures occur in four U main levels; we here focus on deformation struc- Callovian Fortuna M Marl – L tures 1 8 in the uppermost two levels (Fig. 3). ? ? U Glass These structures were cleaned with hand-held

m

Bathonian M F Sand l scrapers and photographed. Based on photographs Vilhelmsfält a Mb L d

e

Fm i r and field notes, simplified, interpretive sketches of

a Middle Jurassic U Bagå Formation Bajocian M the deformation structures were produced. A few of L Fug- lunda the structures were dug out to reveal the plan- Mb Aalenian U surface geometry. L ?? U Toarcian M Ryde- bäck Sorthat Formation Geological setting L Mb U Pliensbachian In the Early Jurassic, Bornholm and Scania in south-

L Fm Rya Katslösa Hasle Formation – Mb ern Sweden formed part of the NW SE trending Galge- – Lower U Pankarp Mb Sorgenfrei Tornquist Zone, which separates the Sinemurian løkke Mb L Döshult Danish Basin from the (Michelsen et al. Mb Sose Bugt Mb Helsingborg 2003). The uppermost Triassic and lowermost Juras- Hettangian ? Mb Munkerup Mb sic in Bornholm and Scania (Fig. 3) include non- Rønne Formation Bjuv Mb marine, coastal and shallow marine deposits referred

Rhaetian Höganäs Fm

Sst. € € Vallåkra Mb Höör to the Rønne, Hoganas and Rya Formations (Surlyk et al. 1995; Nielsen 2003; Lindstrom€ & Erlstrom€ Upper Triassic Norian Kågeröd Risebæk Mb Fm Fm 2006). On Bornholm, the Lower Jurassic Rønne For- Kågeröd mation comprises lacustrine, floodplain or coastal Marine mudstones and siltstones Unconformity plain, tidal and marine shoreface deposits of Hettan- Shallow marine and Dinosaur skeleton remains gian to Sinemurian age (Gravesen et al. 1982; Surlyk siltstones Paralic and non-marine sandstones, Dinosaur tracks et al. 1995). These paralic deposits contain organic- siltstones, mudstones and coals rich beds and plant material testifying to a warm Hiatus and humid climate (Petersen et al. 2003). € € Fig. 2. Stratigraphical scheme of Mesozoic units on Bornholm The sediments of the Hoganas Formation are and southern Scania (Skane), with indications of vertebrate ich- interpreted to have been deposited in lagoons, no and body fossils. Stratigraphical scheme modified from swamps, lakes and floodplains. The formation con- Michelsen et al. 2003. tains two extensive coal beds, and numerous hori- 2008; Milan et al. 2006). This is the first record of zons enriched in comminuted plant debris. The dinosaurs from the Lower Jurassic in Denmark. The spore–pollen flora in Scania includes bryophytes and aim of this study is to describe the newly observed Equisetites, which usually thrive under wet and deformation structures from the Lower Jurassic Sose humid conditions, and Taxodiacean, pollen Bugt Member of the Rønne Formation, to discuss the and spores are abundant. A majority of the possibility that they are dinosaur tracks and to put grew under moist and preferably rather warm condi- them into context with the other Scandinavian finds tions (Lindstrom€ & Erlstrom€ 2006). of Lower Jurassic dinosaur tracks. We also describe The Lower Jurassic Sose Bugt Member of the related sediments and interpret the depositional envi- Rønne Formation (Gravesen et al. 1982) is exposed ronment in which the presumed dinosaurs lived. in the coastal cliff at Sose Bugt on the south coast of 488 Clemmensen et al. LETHAIA 47 (2014)

m A CDEF 3.0 m m 3.0 8 4.0 m

2.0 7 t7

t1 t2 2.0 2.0 6 3.0 t3 t4 t5 t6 t8 1.0 B 5 m 2.0 3 4

1.0 1.0 2.0 t 2 0 Clay Silt Sand

1.0 t 0 Clay Silt Sand 1 0 1.0 Clay Silt Sand

0 Clay Silt Sand

0 Legend Clay Silt Sand

Coal Water escape structure Coal clasts Burrows

Structureless Lenticular bedding Tracks t Plant debris Bioturbation

Parallel lamination Faint parallel lamination Slump folds Roots Twigs Erosive surface

Fig. 3. Sedimentological logs (A–F) from the studied section of the Lower Jurassic Sose Bugt Member in the south-facing coastal cliff at Sose Bugt on Bornholm. The logs show the lateral facies variations of lacustrine and fluvial deposits over a distance of c. 50 metres. Eight sedimentary units (1–8) are distinguished. Sediment deformation structures, interpreted as dinosaur tracks, are located in unit 1, unit 2, at the boundary between unit 6 and 7, and in the middle part of unit 7.

Bornholm (Fig. 1). The exposure comprises lacus- sequence 1 are divided into eight depositional units trine, marine shoreface, coastal plain and incised (Fig. 3), which comprise the deformation structures valley deposits. The repeated shifts between non- described here and interpreted as dinosaur tracks. marine and marine depositional environments sug- Parasequences PS1–PS3 were interpreted as lacus- gest that the palaeogeographical position of locality trine based on the abundance of roots and stems, the was relatively close to the regional coastline. The very low content of pyrite in the coal bed and the sequence stratigraphic interpretation indicates that absence of marine palynomorphs (Surlyk et al. the Hettangian–Sinemurian mainly consists of 1995). deposits belonging to transgressive systems tracts. During periods with increasing rate of sea-level rise, Unit 1. – This lowermost unit is seen in logs A–D the newly formed accommodation space was filled (Fig. 3) and shows considerable variation in sedi- by coastal lake and lagoonal deposits. Only close to mentary characteristics. It is dominated by silt- the time of maximum flooding was the paralic envi- streaked mud with very thin laminae or lenses of ronment flooded by marine water (Surlyk et al. pale silt interbedded in dark grey clay. The original 1995). lamination is disturbed by pervasive penecontempo- raneous deformation structures including folds, c. Sedimentary units 5 cm high, and water escape structures. The base of the unit is not exposed, and the top is locally trun- The 24-m-thick succession of the Sose Bugt Member cated by an erosion surface overlain by silt and fine- was divided into three sequences and 18 parase- grained sand of unit 2 (log C) or by a shallow, chan- quences by Surlyk et al. (1995). In the present study, nelized sand bed (log A). Log D shows that unit 1 parasequences PS1, PS2 and basal part of PS3 of also includes 10- to 30-cm-thick layers of sand, some LETHAIA 47 (2014) Dinosaur tracks in Denmark 489 of them with soft sediment deformation structures by Arndorff (1992). The erosive surface separating and water escape structures. Unit 1 is sharply or ero- units 2 and 3 is interpreted as a lacustrine transgres- sively overlain by unit 2 and constitutes the lower sive surface. part of PS1 of Surlyk et al. (1995). The silt-streaked mudstone is interpreted as Unit 3. – This unit is seen at logs A–E. It is 10– deposited at low energy in a body of standing water 40 cm thick and composed of horizontally lami- (a lake) by settling from suspension (clay) and from nated, brown heterolithic sediment with a fairly high dilute gravity currents (the planar to lensoid silt proportion of comminuted plant debris. The strata streaks). The small folds suggest that the sedimen- are not penetrated by rootlets. The basal surface, tary pile was subject to slumping, which may have which is erosive, is locally overlain by pockets of generated the water escape structures. We suggest sand or intraformational clasts of coaly mudstone. that the deformation structures below the channeli- Unit 3 is overlain by shallow lake deposits of unit 5 zed sand (log A) can be attributed to dinosaur tram- (logs A and B) and by channel deposits of unit 4 pling at the lake floor. The majority of the remaining (logs C–E). soft sediment deformation structures are not suffi- Unit 3 is interpreted as recording episodic depo- ciently distinct to be interpreted with certainty. The sitional events, possibly as overbank flooding. The upper erosion surface is interpreted as a forced absence of rootlets suggests that the sediment was regression due to a fall in lake level. deposited in a lake, and the scarcity of wave rip- ples indicates that the water was deeper than wave Unit 2. – This unit is present in logs A–E and base. If the lake was small, water depth may not forms the upper part of PS1 of Surlyk et al. (1995). have been more than a few metres. Deposition Unit 2 is dominantly silty with a small proportion from overbank flooding suggests the proximity of of very fine-grained sand deposited as thin streaks a river. or small lenses. Root traces increase in number upwards in the unit, and comminuted plant debris Unit 4. – This unit is seen at logs C–E. It consists of is common in the upper 5–10 cm. At log C, the fine- to medium-grained, low-angle cross-bedded unit is a c. 1-m-thick, upward-coarsening succes- sand, which locally contains intraformational clasts sion overlying two thin, normally graded sand beds of coaly mudstone. The lower boundary of unit 4 is at the base of the unit. In log E, only the upper part erosive and locally truncates the upper part of unit 3 of unit 2 is exposed as a structureless, silty to very (Fig. 3). Unit 4 is interpreted as deposited in a fine-grained sediment with numerous rootlets. The minor river channel. unit is erosively truncated and overlain by unit 3 (Fig. 3). Unit 5. – This unit is seen at log A and C–E. It is Unit 2 is thinner and more complex in log A, a 20- to 30-cm-thick unit of interbedded sand and where it comprises a 20-cm-thick bed of structure- mud, in which the sand layers become thinner and less silt with lenses of pale, fine-grained sand. It is more fine-grained upwards. The sand locally con- cut by a small, channelized sand body with rare tains comminuted plant debris. The lower bound- burrows and trough cross-bedding. This sand body ary is locally erosional, as seen where it truncates outlines large deformation structures and is over- unit 4 in log E. The upper boundary is transitional lain by structureless silt and a small channelized to unit 6. sand body. Coal-rich lithologies form intraforma- Unit 5 is interpreted to record episodic deposition tional clasts, and locally organic-rich sediment is of sand from sediment gravity flows in a lake in preserved above a horizon of rootlets, which are which water depth increased with time. The bound- seen in the top of unit 2 throughout the outcrop ary between units 5 and 6 thus reflects relatively deep (Fig. 3). water and low-energy conditions. Unit 5 corre- The coarsening upward succession of very fine- sponds to the lower part of PS2 of Surlyk et al. grained silt and sand is interpreted as lake-fill depos- (1995). its. The large deformation structures are interpreted as dinosaur tracks, but as the sediment was fine- Unit 6. – This unit is seen in logs A, C, D and E grained and water-logged, these footprints are much where it overlies unit 5 with a transitional boundary. deformed. The extensive root horizon at top of unit Unit 6 forms an upward-coarsening succession rang- 2 suggests that the former lake deposits were subaer- ing from silt to very fine-grained sand, with a maxi- ially exposed and overgrown. This is supported by mum thickness of c. 120 cm (log A). The sediment palaeosol development in unit 2, where a sandy loam is structureless to weakly laminated with few thin with illuviated iron sesquioxides has been described streaks of silt or very fine-grained sand. Upwards, 490 Clemmensen et al. LETHAIA 47 (2014) the content of sand increases gradually. Locally, a Description of dinosaur tracks large number of coalified wood (twigs and stems) are found parallel to bedding planes (logs C, D and The exposed section at Sose Bugt contains four levels E). A well-developed horizon of vertical roots, none with deformation structures interpreted as dinosaur of which resemble tree roots, is seen in the upper c. tracks: unit 1 (log A), unit 2 (log A), the boundary 80 cm of unit 6 (log A). The density of roots between unit 6 and 7 (logs C, E and F) and unit 7 increases upwards. In contrast, the roots generally (log F) (Fig. 3). The best preserved dinosaur tracks are lacking in unit 6 where this is truncated by unit 7 at the boundary between unit 6 and 7 are steep- (logs C–F) and unit 6 is overlain by a thin coal bed, walled, concave-to-flat-bottomed depressions, with unit 8, or truncated by channel deposits, unit 7. Unit a raised ridge at each side of the walls. Where visible, 6 corresponds to the upper part of PS2 of Surlyk the infillings are laminated, draping the contours of et al. (1995). A series of conspicuous deformation the bottom of the depression. The seven track struc- structures interpreted as dinosaur tracks are seen at tures in the main level between units 6 and 7 are clo- the top of unit 6 (Fig. 3). These structures are sely spaced. Below each structure, a series of bowl- described below in more detail. shaped deformation structures are present in the Unit 6 is interpreted to record fairly steady pro- subjacent layers. These structures become succes- gradation of the lake shoreline. Thin homogeneous sively shallower downwards. In the following, the sand beds are interpreted as episodic infill probably three most informative structures will be described from fluvial currents. The extensive root horizon at in detail. top of unit 6 suggests that the former lake deposits were subaerially exposed and overgrown and the Dinosaur track 4. – This structure from the main roots indicate a fairly dense vegetation devoid of level at the boundary between unit 6 and unit 7 con- trees. The subaerial exposure is supported by palaeo- sists of two adjacent flat-bottomed depressions, each sol development in unit 6, where a silty to sandy about 20 cm wide, separated by a raised ridge. The loam shows strong iron staining due to illuviation of shaft of the depressions is subvertical, and each side sesquioxides (Arndorff 1992). of the depressions is bordered against the sediment surface by a raised ridge. One of the depressions has Unit 7. – This unit is seen in logs C–F and com- a steep-walled deep structure protruding 15 cm prises trough cross-bedded sand, horizontally lami- down below the bottom of the depression (Fig. 4A, nated sand and structureless sand bounded by B). Subsediment deformations are present below erosional surfaces. The lowest of these separates hor- both main depressions. The structures are infilled izontally bedded sand (unit 7, log E) from hetero- with layered sand containing scattered coal clasts; lithic silt (unit 6). This facies is erosionally overlain the sand drapes and moulds the contours of the by structureless or cross-bedded sand (logs C–F), depressions (Fig. 4A, B). The structure is overlain by locally with a high content of coalified wood (log F). channel sand of unit 7. The common occurrence of erosional surfaces, the well-sorted and relatively coarse-grained sediment as Dinosaur track 7. – This structure from the upper- well as the current generated structures indicate that most level in unit 7 is impressed into a layer of finely unit 7 is the fill of a small fluvial stream. laminated mud, which drapes a cross-bedded chan- nel deposit (Fig. 4C, D). The structure is 17 cm wide Unit 8. – Unit 8 is a 10- to 15-cm-thick coal-rich and consists of a concave-bottomed depression in a bed characterized by a high amount of inertinite mud layer, which has been compressed below the (coal bed D in Surlyk et al. 1995). It is seen in all structure and displaced upwards in sharply defined logs and is continuous through the outcrop. The raised ridges on each side. The shaft of the structure coal petrography indicates that the bed formed has steep walls, and the whole structure is infilled either from oxidation of a fragile herbaceous-like with structureless sand containing abundant rootlets vegetation or as redeposition of a dessicated peat (Fig. 4C, D). surface. The top 4 cm of the bed is almost entirely allochtonous, and the bed represents a limnotelmatic Dinosaur track 3. – This structure from the main facies (Surlyk et al. 1995). The organic material level at the boundary between unit 6 and unit 7 is accumulated in fresh water in a relatively high- almost 40 cm wide and shows a remarkable set of energy zone at low water depth (limnotelmatic deformation structures. The main structure is a flat- facies). Units 7 and 8 form the basal part of PS3 in bottomed depression with sharply defined walls, Surlyk et al. (1995). The formation of peat is inter- with a sharp ridge towards the surface it originates preted as reflecting a rise in lake level. from (Fig. 4E, F). The upper part of the structure LETHAIA 47 (2014) Dinosaur tracks in Denmark 491

A B

C D

E F

Fig. 4. Cross-sections through deformation structures representing dinosaur tracks. A, dinosaur track 4 (log F). Double track structure consisting of two flat-bottomed depressions. B, interpretative drawing of A with descriptive structures highlighted. C, dinosaur track 7 (log F). Track emplaced in a thin layer of laminated mud. D, interpretative drawing of C, illustrating the compaction of the clay layers and the sideways displacement of the sediment into raised ridges. E, dinosaur track 3 (log E–F). Track with a prominent zone of deformed and rotated sediment. F, interpretative drawing of E. contains two tracks filled with structureless sand (Fig. 3). This is in agreement with Surlyk et al. containing numerous coal clasts. Below these tracks (1995), who referred parasequences 1, 2 and the is a mixed zone of subvertically rotated sediments basal part of parasequence 3 (our units 1–8) to a similar to what can be found below vertebrate tracks lacustrine environment, because freshwater green (Brown 1999; Graversen et al. 2007). The whole algae such as Botryococcus spp. are particularly abun- structure is covered by channel sand of unit 7 dant in the coal bed (unit 8). No marine pal- (Fig. 4E, F). ynomorphs have been recovered from these sediments. The lacustrine successions are thin and show lateral facies variations within the 50 m Discussion distance from log A to log F. These observations suggest that the lakes were small and shallow. The Palaeoenvironment channel deposits observed in units 1, 2, 4 and 7 are interpreted as small streams or creeks. The small The sedimentological logs are divided into eight freshwater lakes and small streams may have formed units, which are interpreted as mainly lacustrine 492 Clemmensen et al. LETHAIA 47 (2014) on a large coastal plain or a large delta plain. Overly- (Bolau€ 1952; Pleijel 1975; Ahlberg & Siverson 1991; ing sediments in the Sose Bugt succession include a Gierlinski & Ahlberg 1994) and a single track of pre- large channel and two levels of marine shoreface sumed thyreophorean affinity (Milan & Gierlinski deposits separated by non-marine deposits (Surlyk 2004). The Upper Triassic and Lower Jurassic strata et al. 1995). It is probable, that the freshwater lakes of the Holy Cross Mountains in Poland have a were located fairly close to the shoreline as the lake diverse tetrapod ichnofauna with tracks of early level changes are related to changes in relative sea mammals, small- to large-sized theropods, ornithis- level (Surlyk et al. 1995). chians and sauropods (Gierlinski 1997, 1999; Gier- linski et al. 2001, 2004). Dinosaur tracks The Swedish and Polish finds demonstrate that an abundant and diverse dinosaur fauna was present in The morphology of the deformation structures here the region during the Late Triassic and Early Jurassic interpreted as dinosaur tracks displays a remarkable times. This supports the dinosaurian interpretation difference in degree of preservation and architecture, of the tracks from the Lower Jurassic at Sose Bugt. from sharply defined to chaotic mingling of the sedi- The tracks from Sose Bugt thus fills a biogeographi- ments, but most of them share a common morphol- cal gap between the Swedish and Polish track faunas. ogy, with raised ridges around steep walls, concave to flat bottoms and layered infilling. This morphol- ogy is consistent with the morphology of vertebrate Conclusions tracks exposed in cross-section (Loope 1986; Allen 1997; Milan et al. 2006). The presence of deforma- The lowermost part of the Lower Jurassic Sose Bugt tions in the layers below the structures is consistent Member of the Rønne Formation is interpreted as with the interpretation of the structures as vertebrate lacustrine and fluvial. At the exposure in Sose Bugt tracks, as they are consistent with the morphology of on Bornholm, newly recognized deformation struc- undertracks and other subsediment deformations tures exposed in cross-section at the base of small formed below vertebrate tracks (Brown 1999; Man- fluvial palaeochannels are interpreted as dinosaur ning 2004; Milan & Bromley 2006, 2008; Graversen tracks. This is consistent with abundant finds of con- et al. 2007). Further, the structures are consistent temporary dinosaur tracks from both Sweden and with dinosaur tracks exposed in cross-section, Poland, which were part of the same landmass dur- described from the nearby Lower Cretaceous Rabe- ing the Lower Jurassic. This is the geologically earli- kke Formation (Surlyk et al. 2008). One of the struc- est record of dinosaurs in Denmark. tures was excavated by exposing the original bedding Acknowledgements. – The fieldwork on Bornholm was sup- plane in order to examine the three-dimensional ported by the Department for Geosciences and Natural Resource morphology of the structure. It turned out to be Management, University of Copenhagen. Spencer G. Lucas and subcircular in shape, which excludes the possibility an anonymous reviewer provided critical reviews that helped to that the structures are cut through small channels shape the focus of the paper. and supports our interpretation that they are tracks from vertebrates. Dinosaur tracks 1–6 and 8 are located at the floor References of a small shallow stream (unit 7) connected to the Ahlberg, A. & Siverson, M. 1991: Lower Jurassic dinosaur foot- freshwater lake. Also dinosaur track 7 seen in the prints in Helsingborg, southern Sweden. Geologiska F€orenin- gens i Stockholms F€orhandlingar 113, 339–340. middle part of unit 7 is located at the base of a shal- Allen, J.R.L. 1997: Subfossil mammalian tracks (Flandrian) in the low stream deposit. This suggests that the dinosaurs Severn , S.W. Britain: mechanics of formation, preser- preferred to use shallow channels as paths, possibly vation and distribution. Philosophical Transactions of the Royal Society of London, B 352, 481–518. because they had a fairly stable sandy substrate and a Arndorff, L. 1992: Lateral relations of deltaic palaeosols from the shallow water depth. It may be speculated that the Lower Jurassic Rønne Formation on the island of Bornholm, channels also provided an easy path through dense Denmark. Palaeogeograhy, Palaeoclimatology, Palaeoecology 100, 235–250. vegetation at the lake shorelines. It is also possible Bolau,€ E. 1952: Neue Fossilfunde€ aus dem Rh€at Schonens und that the sandy substrate in the streams preserved the ihre pal€aogeographisch-okologische€ Auswertung. Geologiska footprints better than the surrounding silty to F€oreningens i Stockholm F€orhandlingar 74,44–50. Bolau,€ E. 1954: The first finds of dinosaurian skeletal remains in muddy sediments. the Rhaetic-Liassic of N. W. Scania. Geologiska F€oreningens i Coal-bearing strata in the Upper Triassic – Lower Stockholm F€orhandlingar 76, 501–502. Jurassic Hogan€ €as Formation in southern Sweden has Bonde, N. 2004. An (Ryazanian) fauna of ‘Pur- beck-Wealden’ type at Robbedale, Bornholm, Denmark. In yielded abundant well-preserved tracks from thero- Arratia, G. & Tintori, A. (eds): Mesozoic 3 – Systematics, pod dinosaurs with a track lengths from 15 to 35 cm LETHAIA 47 (2014) Dinosaur tracks in Denmark 493

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