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Cretaceous Research 42 (2013) 85e92

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Cretaceous Research

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Food resources and habitat selection of a diverse vertebrate fauna from the upperlower Campanian of the Kristianstad Basin, southern Sweden

Anne Mehlin Sørensen a,*, Finn Surlyk a, Johan Lindgren b

aDepartment of Geosciences and Natural Resource Management, University of Copenhagen, Øster Voldgade 10, DK-1350 Copenhagen K, DenmarkbDepartment of Geology, Lund University, Sölvegatan 12, SE-223 62 Lund, Sweden

a r t i c l e i n f o

Article history:Received 26 November 2012Accepted in revised form 1 February 2013Available online 28 February 2013

Keywords:Marine vertebratesTrophic structureLate CretaceousKristianstad BasinSweden

* Corresponding author. Tel.: þ45 35322448.E-mail address: anne@geo.ku.dk (A.M. Sørensen).

0195-6671/$ e see front matter � 2013 Elsevier Ltd.http://dx.doi.org/10.1016/j.cretres.2013.02.002

a b s t r a c t

During the latest early Campanian, a diverse vertebrate assemblage inhabited the shallow coastal watersof the Kristianstad Basin, southernmost Sweden. The taxon-rich fauna includes numerous species ofsharks, rays, chimaeroids, bony fish, mosasaurs, plesiosaurs, aquatic birds, crocodiles, and turtles.Vertebrate fossils have been found at several localities within the basin, representing at least threedifferent environments: near-shore waters around a rocky island, presumably murky, shallow watersadjacent to a river mouth, and more open coastal waters. Many vertebrates in the marine faunal com-munity were high-level predators, others were piscivorous, bottom-dwellers that fed primarily onbenthic invertebrates and fish, or omnivores that fed on algae and invertebrates. The fauna thus exploiteda wide range of food sources and habitats. Six trophic levels, ranging from primary producers to fifth-level consumers, are recognised, indicating a high loss of energy and reflecting a mixture of shallowcoastal and more open water ecosystems. The trophic structure suggests that the basin was a richpalaeoenvironment with high faunal diversity and productivity.

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1. Introduction

Southern Sweden was transgressed several times during theLate Cretaceous, resulting in a shallow-marine archipelago withnumerous low islands and peninsulas (Surlyk and Christensen,1974; Surlyk and Sørensen, 2010). The sea offered a wide range ofhabitats for marine vertebrates, including rocky shores, deepercoastal waters, and protected shallow-water settings. The upperlower Campanian deposits of the Kristianstad Basin, northeastSkåne (Fig. 1), have yielded a rich vertebrate fauna, comprisingabout 40 species of sharks, six species of rays, six species of mo-sasaurs, six species of plesiosaurs, three species of aquatic birds,one species of crocodile, one taxon of ornithischian dinosaur, andan unknown number of turtle, bony fish and chimaeroid taxa(Tables 1 and 2). Furthermore, the basin has produced one of thefinest fossil invertebrate rocky shore faunas known to date (e.g.,Sørensen and Surlyk, 2010, 2011; Sørensen et al., 2011, 2012).

Studies of the Cretaceous vertebrate fauna from southernSweden commenced in 1827 when Nilsson described a few iso-lated reptilian teeth; he continued his work in 1836 and 1857with descriptions of an incomplete mosasaur skull erroneously

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referred to as a plesiosaur (see Persson, 1959; Lindgren, 2004)and some isolated mosasaur tooth crowns. The material exam-ined by Nilsson (1836) was redescribed by Hisinger (1837).Angelin (1877) and Schröder (1885) described mosasaur remainsfrom the basin. Subsequently, Moberg (1884), Lundgren (1888a,b,1889), Nathorst (1894), Hennig (1910), and Kuhn (1939)mentioned, listed or redescribed the mosasaur material. Davis(1890) described selachian teeth, chimaeroid teeth and finspines, plus teeth, vertebrae and scales of bony fishes.Törnebohm and Hennig (1904) noted additional mosasaur fossilsfrom the basin, while a few finds of vertebrates were reported byVoigt (1929) and Lundegren (1934). Studies on the vertebratefauna continued with Persson’s (1954, 1959, 1960, 1962, 1963,1967, 1990, 1996) papers on skeletal remains of plesiosaurs,mosasaurs, marine turtles, dinosaurs and crocodiles (note thatthe material described by Persson (1996) is a partial lower jaw ofa marine turtle and not a plesiosaur jugal). The mosasaur faunawas listed once again by Russell (1967). More recently, sharkteeth have been either listed or described by Bergström andSundquist (1978), Bergström (1983), Siverson (1992a,b, 1993,1995) and Rees (1999), while teeth and bones of mosasaurs weredescribed by Lindgren and Siverson (2002, 2004, 2005) andLindgren (2004, 2005a,b), mosasaur bite marks on a plesiosaurpropodial by Einarsson et al. (2010), bones of aquatic birds byRees and Lindgren (2005), a carapace fragment of a soft-shelled

ÅsenIvö Klack

Ignaberga

10 km

N

Balsberg

Maltesholm

Kristianstad

Häsleholm

Hanö Bay

Linderödåsen

Nävlingeåsen

Ivö50 km

Skåne

KristianstadBasin

Faults

UpperCretaceous

Town

Locality

Ullstorp

AxeltorpOppmannaUgnsmunnarna

IvetoftaKjuge

Fig. 1. Simplified geological map of northeast Skåne (southern Sweden), showing the Kristianstad Basin and the location of the Cretaceous localities mentioned in the text. Modifiedfrom Norling and Bergström (1987) and Lindgren and Siverson (2002).

A.M. Sørensen et al. / Cretaceous Research 42 (2013) 85e9286

turtle by Scheyer et al. (2012), dental and vertebral elements ofdinosaurs by Lindgren et al. (2007), and vertebrate coprolites byEriksson et al. (2011).

The aim of the present contribution is to provide an overview ofthe vertebrate fauna based on the scattered literature items listedabove, and to present a palaeoecological synthesis based on thoseanimals that once inhabited the shallow coastal waters thatcovered southern Sweden. This work complements recent studiesof important invertebrate groups (see Sørensen and Surlyk, 2010,2011; Sørensen et al., 2011, 2012) and aids in a reconstruction ofthe higher levels of the trophic structure of this marine Cretaceousecosystem.

2. Geological setting

TheUpper Cretaceousmarine succession of theKristianstadBasinwasdepositedduringanumberof transgressive events,when the sealevel periodically rose up to about 100 m higher than it is today(Sahagian et al.,1996; Kominz et al., 2008). The relatively small-sizedbasin was situated at the northeastern margin of the epeiric Chalk

Table 1Recorded number of vertebrate species per group from ten localities in the Kristianstad

Vertebrategroups/sites

Ivö KlackRocky shore

UgnsmunnarnaShoreface

IgnabergaShoreface

MaltesholmShoreface

ÅsenProtectedenvironme

Sharks 23 24 28 12 34Rays 1 1 2 e 5Mosasaurs 6 3 3 1 6Plesiosaurs 4 e 2 1 1Crocodiles 1 e e e e

Turtles 1 Remains Remains 1 RemainsAquatic birds 3 e e e e

Dinosaurs e e e e 1Total number

of species39 28 35 15 47

Sea, which covered most of northwest Europe during this time in-terval. The basinwas open towards the southeast butmay have beenclosed towards the west, based on present-day topography of Skåne(Surlyk and Sørensen, 2010). The palaeolatitude was about 50�N(Smith et al., 1994) and the climate was warm temperate to sub-tropical (Surlyk and Christensen, 1974; Surlyk and Sørensen, 2010).The marine Upper Cretaceous succession in the basin is less than200 m thick, thins towards the north where it onlaps low-reliefbasement rocks, and consists mainly of skeletal carbonate gravel,sand and silt (Surlyk and Sørensen, 2010). Most outcrops exposestrata from the uppermost lower Campanian e lower upper Cam-panian interval (Christensen, 1975).

3. Localities

3.1. Ivö Klack (Blaksudden in older literature)

This locality is an abandoned and partly overgrown kaolin andlimestone quarry located on the northern slope of the Island of Ivö(Fig. 1). The uppermost lower Campanian succession comprises

Basin.

nt

AxeltorpShoreface

BalsbergShoreface

Oppmanna IvetoftaShoreface

KjugeShoreface

Total numberof species

e e e e e 38e e e e e 62 1 Remains Remains e 61 e e Remains 1 6e e e e e 1e e e e e 1e e e e e 3e e e e e 13 1 1 62

Table 2Distribution of vertebrate species in the Kristianstad Basin, their inferred diet and position in the water column. C ¼ Carnivore, P ¼ Piscivore, O ¼ Omnivore, H ¼ Herbivore,N ¼ Nektonic, NB ¼ Nektobenthic, A ¼ Aquatic, T ¼ Terrestrial.

Ivö Klack Ugnsmunnarna Ignaberga Maltesholm Åsen Axeltorp Balsberg Kjuge Diet Position

SharksAnomotodon hermani, Siverson, 1992a,b X X X X C NArchaeolamna kopingensis (Davis, 1890) X X X X C NGaleorhinus sp. X X X C NCarcharias aasenensis Siverson, 1992a,b X X X C NCarcharias latus (Davis, 1890) X X X X X C NCarcharias tenuis (Davis, 1890) X X X X C NCederstroemia nilsi Siverson, 1995 X C NBChiloscyllium gaemersi, Müller, 1989 X C NBChiloscyllium sp. X X X X X C NBCretodus borodini, Cappetta and Case, 1975 X X C NCretalamna appendiculata (Agassiz, 1843) X X X X X C NCretorectolobus sp. X X C NBCretoxyrhina mantelli (Agassiz, 1843) X X C NHemiscyllidae sp. X C NHemiscyllium hermani, Müller, 1989 X X X C NHeterodontus sp. 1 X X X X X C NBHeterodontus sp. 2 X X X C NBHybodus sp. X X X C NPalaeogaleus sp. X X C NParanomotodon sp. X X X X C NParaorthacodus andersoni (Case, 1978) X X X C NParaorthacodus conicus (Davis, 1890) X X X X C NPararhincodon spp. X X X X C NBParatriakis? sp. X X X X X C NPolyacrodus siversoni, Rees, 1999 X C NPolyacrodus sp. X C NPseudocorax laevis (Leriche, 1906) X X C NScapanorhynchus perssoni Siverson, 1992a,b X X X C NScyliorhinidae sp. 1 X C NScyliorhinidae sp. 2 X C N‘Scyliorhinus’germanicus (Herman, 1982) X X X X X C NBSerratolamna sp. X C NSqualicorax kaupi (Agassiz, 1843) X X X X X C NSqualidae spp. X X X X X C NSquatina spp. X X X X C NBSquatirhina sp. X X X X X C NBSynechodus sp. 1 X X X X C NSynechodus sp. 2 X X X X X C NRaysRhinobatoidea sp.1 X C NBRhinobatoidea sp. 2 X X C NBRhinobatos casieri, Herman, 1977 X C NBRhinobatos sp. 1 X C NBRhinobatos sp. 2 X C NBRhinobatos sp. 3 X X X C NBMosasaursClidastes propython, Cope, 1869 X X X X X C NDollosaurus sp. X X C NHainosaurus sp. X X X X C NEonatator sternbergi (Wiman, 1920) X X X C NPlatecarpus? sp. X X C NTylosaurus ivoensis (Persson, 1963) X X X X X X C NPlesiosaursElasmosaurus? cf. gigas (Schröder, 1885) X P NElasmosaurus? cf. helmersenii (Kiprijanoff, 1882) X P NScanisaurus cf. nazarowi (Bogolubov, 1911) X X X X X P NScanisaurus sp. X X P NPolycotylidae sp. X C NPolycotylidae? sp. X C NCrocodilesAigialosuchus villandensis, Persson, 1960 X C ATurtlesOsteopygis? sp. X O MTrionychidae indet. X O MTurtle remains X X X X O MDinosaursLeptoceratopsidae sp. X H TAquatic birdsBaptornis sp. X P AHesperornis rossicus, Nessov and Yarkov, 1993 X P AHesperornis sp. X P A

A.M. Sørensen et al. / Cretaceous Research 42 (2013) 85e92 87

A.M. Sørensen et al. / Cretaceous Research 42 (2013) 85e9288

22e24 m of coarse-grained skeletal carbonates composed of frag-ments of mainly bivalves, bryozoans, brachiopods, and echinoids,deposited along a steep, irregular rocky shore with abundantencrusted basement boulders and hummocks (Surlyk andChristensen, 1974). In the carbonates occurs a predominance ofoysters which formed banks along the shoreline (Surlyk andSørensen, 2010; Sørensen et al., 2012). Important fossil materialwas collected during quarrying activities which started in 1888 andcontinued until the late 1960s. Together with Åsen (see below), IvöKlack is the most extensively collected locality in the area. A total of23 shark, one ray, six mosasaur, four plesiosaur, one crocodile, andthree aquatic bird species, together with one taxon and numerousremains of turtles have been recorded from Ivö Klack (Table 1).

3.2. Ugnsmunnarna

This locality is a partly overgrown cliff section, about 4 m inheight, situated on the western shore of Ivö Island, about 3 kmsouth of Ivö Klack (Fig. 1). The uppermost lower Campanian suc-cession consists of skeletal sandstones interbedded with fourapproximately 20 cm thick shell beds (Persson, 1960). The succes-sion was deposited in a more distal and deeper-water part of thesea around the Ivö palaeo-island (M. Yamininia and F. Surlyk, un-published data 2009). Material was collected by surface picking andsieving one of the shell beds. A total of 24 shark, one ray, and threemosasaur species, together with fragmentary remains of turtleshave been recorded from the locality (Table 1).

3.3. Ignaberga

This locality currently comprises two limestone quarries situ-ated along the faulted southern basin margin formed by the Näv-lingeåsen horst (Fig. 1; Surlyk, 1973, 1980; Christensen, 1975;Erlström and Gabrielson, 1992). The uppermost lower Campaniansuccession consists of skeletal sandstones composed of fragmentsof bivalves, bryozoans, echinoids, and calcareous algae. A total of28 shark, two ray, three mosasaur, and two plesiosaur species,together with remains of turtles have been recorded from thelocality (Table 1).

3.4. Maltesholm

This limestone quarry, now disused, is situated adjacent to thenorthern margin of the Linderödsåsen horst (Fig. 1; Christensen,1975; Sandström, 2001). The uppermost lower Campanian suc-cession consists of skeletal sandstones with abundant fragments ofrudistid bivalves, calcareous algae and belemnites, but few otherfossil remains. A total of 12 shark, onemosasaur, one plesiosaur andone turtle taxon have been recorded (Table 1).

3.5. Åsen

This locality is an abandoned clay pit, presently used as arubbish tip. The uppermost lower Campanian marine successionconsists of unconsolidated quartz sand. The succession wasdeposited in a protected coastal, presumably murky environ-ment. The presence of floodplain sediments, hybodont sharkteeth and the topography of the basement rock (i.e., the Höljeånvalley), suggest that a fluvial system was located nearby (Rees,1999). Material was collected by sieving of the sediments. Atotal of 34 shark, five ray, six mosasaur, and one dinosaur spe-cies, together with remains of plesiosaurs, turtles and aquaticbirds (J. Lindgren, unpublished data) have been found at the site(Table 1).

3.6. Axeltorp

This locality isanabandonedandovergrownlimestonequarry. Theuppermost lower Campanian marine succession consists of 3e5 mof skeletal sandstone (Christensen, 1975). Two mosasaur and oneplesiosaur species have been recorded from the locality (Table 1).

3.7. Balsberg

This is a natural cave located on the southwestern slope of theBalsberget hill (Fig. 1). The uppermost lower Campanian successionconsists of skeletal sandstones with abundant pebbles of crystallinebasement rocks (Christensen, 1975). A single mosasaur tooth hasbeen recorded from the locality (Table 1).

3.8. Ivetofta

This is a drill core situated in the town of Bromölla. The sedi-ments penetrated are of latest early Campanian age. Remains ofmosasaurs have been recorded from the core (Persson, 1967).

3.9. Kjuge

This locality is a natural cliff section located near Lake Ivösjön.The uppermost lower Campanian marine succession consists ofcalcarenites with interbedded conglomerates composed of largeshell fragments and crystalline basement pebbles (Christensen,1975). One species of plesiosaur has been recorded from the locality.

3.10. Oppmanna

The marine succession is of late early Campanian age (Nilsson,1836; Moberg, 1884; Schröder, 1885). Remains of mosasaurs havebeen recorded from the locality.

4. Material

A substantial portion of the material from the Kristianstad Basinwas collected at Ivö Klack during quarrying activities in the period1915e1925. This collection is largely biased towards large-sizedspecimens since the quarry workers were paid for their findings.The bulk of the skeletal material from Ivö Klack comprises isolatedvertebral centra together with fragmentary propodials and teeth.Bulk samples fromÅsen have been extensively sieved for vertebrateremains, resulting in large collections of isolated teeth and bones(e.g., Rees, 1999; Lindgren and Siverson, 2002, 2004, 2005;Lindgren, 2004, 2005a,b). The material from other localities in thebasin has been more-or-less randomly collected over the last 200years and should thus be treated with caution. Importantly, anumber of sharks, most species of rays and turtles, and all bony fishand chimaeroids remain undescribed and are thus not included inTable 2. The bulk of the material referred to herein is housed at theDepartment of Geology, Lund University, Lund, Sweden, theWestern Australian Museum, Perth, Australia, and at the SwedishMuseum of Natural History, Stockholm, Sweden.

5. The vertebrate fauna

5.1. Sharks

A total of 38 species of sharks have been identified from theupper lower Campanian of the Kristianstad Basin (Siverson,1992a,b, 1993, 1995; Rees, 1999) and all were active predators.Some species were capable of handling almost everything that theyencountered, whereas others fed predominantly on smaller food

A.M. Sørensen et al. / Cretaceous Research 42 (2013) 85e92 89

items, such as bony fish, rays, cephalopods, and other invertebrates(Siverson, 1992a). Large nektonic species such as Squalicorax kaupi(Agassiz, 1843) and Cretoxyrhina mantelli (Agassiz, 1843) presum-ably occupied the top of the food web and thus played importantroles in many marine ecosystems (Shimada and Cicimurri, 2005;Shimada, 2008). Teeth of large nektonic sharks have been foundembedded in partially digested mosasaur bones from the WesternInterior Seaway of North America, suggesting that theywere able tofeed or scavenge on these large reptiles (Everhart et al., 1995;Shimada, 1997). Bite marks and scratches inflicted by sharks arealso relatively common on reptile bones from the Kristianstad Basin(Einarsson et al., 2010).

5.2. Rays

Six species of rays have been identified from the upper lowerCampanian of the Kristianstad Basin (Table 2; Siverson, 1993), all ofthem belonging to the Rhinobatoidae, although most of themremain undescribed. Modern rays are carnivores, feeding primarilyon invertebrates and small-sized fish at or close to the sea floor(Last and Stevens, 2009). Five species of rays have been found atÅsen, whereas they are rare at other localities, suggesting that theymay have preferred murky and estuarine waters, comparable withsome of their modern relatives (Last and Stevens, 2009).

5.3. Mosasaurs

Six species of mosasaurs are found in the upper lower Campa-nian of the Kristianstad Basin (Lindgren and Siverson, 2002, 2004,2005; Lindgren, 2004, 2005a,b). Mosasaurs were carnivorous

Fig. 2. Reconstruction of marine vertebrates in the Kristianstad Basin during the late early Cjust to the bottom left of it, the latter chasing belemnites and pachydiscid ammonites. In the uis the plesiosaur Scanisaurus. Two sharks and a marine turtle occupy the right of the pictu

reptiles at the top of the marine food chain. Most taxa fed pre-dominantly on fish and cephalopods (Russell, 1967; Lindgren et al.,2010), although teeth and/or bones of smaller mosasaurs, poly-cotylid plesiosaurs, aquatic birds, sharks, and turtles have beenfound as preserved stomach contents (Massare, 1987; Konishi et al.,2011 and references therein). All mosasaur taxa are found at morethan one locality, suggesting that they lived in the entire basin.

Isolated teeth and bones of Clidastes propython Cope, 1869 andEonatator sternbergi (Wiman, 1920) are fairly common in the basin.These mosasaurs are both relatively small-sized, with adult bodylengthsof less thanabout6m.Numerous teethandvertebraeof small-sized, presumably juvenile individuals of C. propython have beenfound at Åsen, suggesting that the area probably offered some pro-tection from predation by larger mosasaurs (Lindgren and Siverson,2002, 2004). Tylosaurus ivoensis (Persson, 1963) was the largestmosasaur living in the basin with an estimated lower jaw length inexcessof1.5m(Fig. 2; Lindgren,2004).Toothcrownsof this speciesarecommonly broken at the apex and heavily worn, suggesting that thismosasaurcommonly fedonfleshyanimalswith largebones (Lindgren,2004). The relatively high diversity of mosasaurs in the basin isprobably due to the dissimilarity in body size and/or dentitions be-tween different species, reflecting disparity in exploited food sourcesand thus avoidance in the competition for food (Lindgren, 2005b).

5.4. Plesiosaurs

Six species of plesiosaurs were identified by Persson (1954,1959, 1962, 1963, 1967, 1990), although Bardet and Godefroit (1995)considered the material from the Kristianstad Basin to be indeter-minate. Nevertheless, in view of the fact that the last

ampanian. In the centre is the mosasaur Tylosaurus with a small polycotylid plesiosaurpper left corner is the aquatic bird Hesperornis diving for bony fish, and to the right of itre (illustration by Stefan Sølberg).

Fig. 3. Species richness amongst different life forms of the Late Cretaceous vertebratefauna of the Kristianstad Basin. In the present work aquatic refer to species that areable to crawl on land; i.e., turtles and crocodiles.

A.M. Sørensen et al. / Cretaceous Research 42 (2013) 85e9290

comprehensive review of the plesiosaur fauna from the basin wasprovided by Persson (1959, 1963), his taxonomy is used in thepresent note (albeit with caution), pending a much needed reviewof the fauna.

The extremely long-necked elasmosaurs were highly adapted tothe marine realm. They were presumably primarily piscivorous andhad small heads. Their teeth were adapted for catching small prey,such as fish and cephalopods (Massare, 1987). Preserved stomachcontents of elasmosaurs from theWestern Interior Seaway indicatethat they also fed on invertebrates (McHenry et al., 2005). Some ofthemmight thus have been benthic ‘grazers’ using lateral sweeps ofthe neck to gather benthic invertebrates and gastrolites over awidearc of the sea floor (Taylor, 1987; McHenry et al., 2005). Moreover,they could reach lengths of up to 14 m, weigh several tonnes, andwere probably slow swimmers due to their unusual body form(Massare, 1988). Scanisaurus is an elasmosaurid with a proportion-ally short neck and a large head (Fig. 2; Persson, 1959). The smallerpolycotylids had a short neck and a large, elongate head (Fig. 2;Everhart, 2005). Plesiosaurs are found in all three environmentsrecognised, suggesting that they inhabited the entire basin.

5.5. Aquatic birds

Three species of aquatic birds have been reported from the basin,and they all belong to the Hesperornithiformes (Fig. 2; Rees andLindgren, 2005). Hesperornithiforms were toothed, aquatic birds, upto2mlong.Theywerepiscivoresandtheir teethhadthesamefunctionas the serrated beaks of modern goosanders and mergansers, whichhold and turn their prey so that it can be swallowed, head first (Reesand Lindgren, 2005). Even though hesperornithiforms were flight-less, they were well adapted to a marine life and may have migratedover long distances for breeding and they probably nested onshore(Feduccia,1996). Their remains havebeen found at IvöKlack andÅsen.

5.6. Turtles

Turtle remains are abundant in the Kristianstad Basin, eventhough only two taxa have been identified so far (Fig. 2; Persson,1959, 1963; Scheyer et al., 2012). The diet of Cretaceous marineturtles is poorly known but bivalve remains have been found inbody cavities of small protostegid turtles from the Lower Creta-ceous of Australia (Kear, 2006). Cretaceous turtles probablyexhibited a broad range of feeding habits similar to their modernrelatives which utilise a variety of feeding strategies rangingfrom herbivory to omnivory (Kear, 2006). The abundance of turtleremains suggests that they thrived in the shallow sea.

5.7. Crocodiles

Only remains of a single skull from Ivö Klack can be positivelyidentified as being from a crocodile (Persson, 1959, 1963), and theskull has been assigned to as Aigialosuchus villandensis Persson,1959. The shape of the skull is highly elongate and similar to thatof modern gavials, which are fish-eating, although the teeth ofAigialosuchus indicate that these may have been adapted to adifferent mode of feeding (Persson, 1959).

5.8. Dinosaurs

One species of a possible leptoceratopsid dinosaur has beencollected at Åsen (Lindgren et al., 2007). The Leptoceratopsidae is afamily of relatively small-sized, horned dinosaurs which presum-ably fed on ferns, cycads, and conifers (You and Dodson, 2004).Teeth similar to those from Åsen have also been recovered fromlowermost Campanian sediments at Ullstorp (Fig. 1), suggesting

that leptoceratopsids frequented the area during large parts of theearly Campanian.

6. Discussion and summary

6.1. Preferred habitats

The marine vertebrate fauna is subdivided into six life forms onthe basis of diet and preferred position in the water column (Fig. 3).Most species were nektonic carnivores and their remains are foundthroughout the basin. This indicates that they cruised the area withno preferred habitat, even though they may have chosen differentfood sources and/or preferred different water depths.

The high diversity of mosasaurs and sharks at Ivö Klack reflects,at least to some extent, a collection bias, but it also shows that therocky shoreline was a place to live for the larger predators. Theirpresence along the rocky shore suggests that this environmentmust have housed a productive ecosystem, where the rich inver-tebrate fauna and its larvae attracted small nektonic predators,such as fish and cephalopods, which were then prey for the largerpredators. The richness of this environment probably also made it afeeding and nursery ground for migratory species similar to mod-ern rocky shores (compare Levinton, 2001). The remains of acrocodile at Ivö Klack could be indicative of the fact that thesereptiles preferred coastal waters to be able to rest, heat up, and laytheir eggs on adjacent land, in analogy with their modern relatives(Thorbjarnarson, 1992).

At Åsen numerous remains of vertebrates (Table 1) have beencollected and the environment is interpreted to have offered someprotection for juvenile animals from larger predators, presumablydue to murky waters produced by a nearby fluvial system (Rees,1999; Lindgren and Siverson, 2002, 2004). Many benthic speciesof sharks and rays have been recorded at this site, indicating thatthey also may have preferred such a setting. These species areassumed to have fed on benthic invertebrates and fish, althoughonly few invertebrate taxa have been recorded at Åsen, albeit ingreat numbers (Sørensen and Surlyk, 2008). The low diversity ofinvertebrates and high number of bottom-dwelling sharks and rays

A.M. Sørensen et al. / Cretaceous Research 42 (2013) 85e92 91

could indicate that they primarily ate soft-bodied or aragonite-shelled invertebrates. This opens a taphonomic window to thepalaeoecology of this protected environment, indicating that awiderange of invertebrates must have lived there to produce sufficientfood supplies for the vertebrates.

A highly diverse shark fauna has been found at most localities inthe basin, indicating an overall high diversity. Remains of aquaticbirds have only been found at Ivö Klack and Åsen, suggesting thatthese birds preferred coastal environments for fishing and nesting,or it may refer to collecting biases since these two sites are themostintensively sampled. Most species probably cruised around theentire basin, but the diversity suggests that they occupied differentniches and thus exploited different food sources, pursued a range oflife strategies, and may have occupied different parts of the watercolumn.

6.2. Reconstruction of the trophic structure

Most vertebrate species found in the basin were nektonicpredators, high in the trophic system, preying on cephalopods, fishand smaller vertebrates (Fig. 4). Large nektonic sharks and mosa-saurs were top-level predators, due to their ability to hunt large-sized prey items (Fig. 4). Elasmosaurs, nektonic sharks, poly-cotylid plesiosaurs, smaller mosasaurs, aquatic birds, and croco-diles were all primarily piscivores, belonging to the next level in thetrophic structure, the quaternary consumers. Bones of aquatic birdsand shark teeth have been found elsewhere as preserved stomachcontents of mosasaurs (Martin and Bjorg, 1987), and teeth of largesharks have been found embedded in mosasaur bones (Everhart,2004), suggesting that at least birds, sharks, and mosasaurs wereprey of the larger predators at the top of the food web (Massare,1987 and references therein). Carnivorous nektobenthic sharksand rays, and larger fish were presumably tertiary consumerspreying primarily on smaller fish (Fig. 4). The omnivorous marineturtles and small fish at the secondary consumer level presumably

Fig. 4. Reconstruction of the late early Campanian food web in the Kristianstad Basin,showing the six inferred trophic levels of the vertebrate fauna.

lived on invertebrates and zooplankton of the primary consumersand the primary producers (Fig. 4).

The six trophic levels recognised among the vertebrates in thebasin indicate a high loss of energy (Levinton, 2001). Normally 10e45% of the production at one trophic level is used for production bythe fauna at the next higher level, resulting in a high loss of energywhen going from one level to the next. Six trophic levels are notnormal in a single ecosystem, but could reflect a mixture of eco-systems, such as the pelagic and benthic systems (Levinton, 2001).The size and high diversity of the large marine predators indicatethat there must have been a high density of potential prey items atthe lower trophic levels, such as fish, cephalopods and benthic in-vertebrates. This is in agreement with the huge amounts of benthicinvertebrates and belemnites found throughout the basin. Thevertebrate fauna thus shows that the basin was a rich palaeo-environment with high species richness, density and productivityat all levels within the food web.

Acknowledgements

This study was funded by the Danish National Research Council,the Carlsberg Foundation and the Swedish Research Council. JesperMilàn is thanked for constructive comments on an earlymanuscriptversion and Stefan Sølberg for drafting Fig. 2. We thank journalreviewers Gilles Cuny and John Jagt for constructive comments.

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