Kristianstad Basin

Geological background The Kristianstad Basin is located in northeastern Skåne, the southernmost province of Sweden, extending from Hanöbukten, a bay in the Baltic Sea, in the east to the town of Hässleholm in the west. The basement of the basin is crystalline and deeply weathered bedrock from the Precambrian. Most of this weathering, and the uneven topography of the basement, is due to the warm and moist climate experienced during the Jurassic or Early Cretaceous. The sediments within the basin are dominated by fine- to coarse-grained sandy biocalcarenites (calcarenites that contain fossils) and more or less consolidated sandstones. Conglomeratic beds are also common, typically consisting of belemnite rostra or bivalve shells and coarse terrigenous clastic rocks. There are also several flint beds in the upper parts of the strata, dating to the early Late Campanian through the earliest Maastrichtian. This strata, the "Belemnellocamax mammillatus"-strata, is exceptionally rich in vertebrate fossils and diversity. The biozones of the Kristianstad Basin, based on the local belemnite fossils, are: } 83.5 Prominent fossil sites Most of the sites within the Kristianstad Basin are the result of commercial kaolin clay/limestone exploitation. Ivö Klack was once the shores of a small and rocky Cretaceous island and is one of the most extensively excavated sites in the basin, having been excavated since quarrying activities started in 1888. Though quarrying stopped in the late 1960s, the site continues to be excavated by paleontologists and amateurs. == History of research ==

Local paleontological and geological research , who first discovered fossils in the Kristianstad Basin in 1725. The Kristianstad Basin is one of the most prolific and historically famous Mesozoic fossil sites in Scandinavia. The earliest known fossil discoveries within the basin were made by the physician and paleontologist Magnus Bromelius at Ivö Klack and Ignaberga in 1725. Most of the early fossil finds were belemnite fossils, descriptions of which were published by physician and naturalist Kilian Stobæus in 1752 (whose work Opuscula included the first illustrations of the common Belemnellocamax mammillatus belemnites), naturalist Göran Wahlenberg in 1821 and zoologist and archaeologist Sven Nilsson in 1826, 1827, 1835 and 1857. Early sedimentological studies were also conducted throughout the 19th and early 20th centuries, prominently by paleontologist and geologist Bernhard Lundgren in 1888 and geologist Alf Lundegren in 1931 and 1934. The only other site of known dinosaur fossils in Sweden is the Höganäs Formation, where they were first announced to be present by researchers in 2022. Though theropod teeth were reported from Ivö Klack by Per-Ove Persson in the 1950s, these have since been identified as fish teeth, probably from the genus Protosphyraena. Fossil material conclusively identified as dinosaurian was recovered only relatively recently, with the earliest discovery being two teeth from a small Ornithopod, similar to those of Hypsilophodon, being found at Ivö Klack in 2001. More comprehensive material referred to a leptoceratopsid ceratopsian ("Kristianasaura") was described in 2007 After comparisons with the same bone in the Australian megaraptoran Australovenator, the bone, an incomplete right tibia, could confidently be identified as coming from a small non-avian theropod dinosaur. The dinosaur fossils recovered represent the remains of specimens transported out into the sea during floods or storms. Despite being fragmentary and few in number, they are scientifically important as they represent some of the few remains of the poorly known dinosaur fauna of the Baltic Shield, which was an isolated landmass during the Late Cretaceous. It is also possible that the recovered dinosaurs were not from the landmass itself, but from the rocky islands of the adjacent archipelago in the Kristianstad Basin itself. The recovered dinosaurs all represent animals with lengths less than three meters (9 ft), but this does not necessarily mean that larger dinosaurs were absent; it is equally likely that only small animals were transported out into the sea where they could be fossilized and preserved. When large dinosaurs are excluded, the dinosaur fauna preserved in the Kristianstad Basin resembles that of Campanian–Maastrichtian dinosaur-bearing formations in Canada, which also include small ornithopods (such as Parksosaurus) and leptoceratopsids (such as Unescoceratops). == Fossil content ==

Marine reptiles The warm shallow seas of the Kristianstad Basin were inhabited by a variety of marine reptiles, with several mosasaurs and plesiosaurs present. In addition to these extinct groups, turtle remains are abundant in the Kristianstad Basin, though only two taxa have been identified so far; an indeterminate trionychid (a freshwater softshell turtle) and a sea turtle. Elasmosaurids recognized as being present in the basin, per Persson's taxonomy, include two species of the large Elasmosaurus as well as one or two species of the local genus Scanisaurus, Groups represented include cephalopods, bivalves, gastropods, brachiopods, echinoderms, corals, crustaceans, bryozoans and polychaetes. Genera identified include, among others, Campanile, Nerita and Patella. Brachiopods, superficially similar to bivalves, are represented by numerous genera, the most prominent being Crania, Magas, Rhynchonella and Terebratula. The local echinoderm fauna, which also included starfish and crinoids, was dominated by sea urchins, which occur in many different genera, the most common of which are Cidaris, Echinocorys, Echinogalerus, Holaster, Micraster, Phymosoma and Salenia. Cephalopods are represented by the abundant belemnites and the less common ammonites. Five genera of belemnites are recorded; Actinocamax, Belemnella, Belemnellocamax, Belemnitella and Gonioteuthis. Belemnites were a basic part of the food web and likely served as prey for many of the vertebrates in the basin, such as fish, plesiosaurs and the smaller mosasaurs. Crustaceans include both barnacles and decapods (the group that contains modern lobsters and crabs), represented by the genera Callianassa and Protocallianassa. Decapod fossils are primarily just the claws, as they are more easily preserved than other portions of the crustacean exoskeleton. Corals are primarily represented by the genera Leptophyllia, Micrabacia and Parasmilia. Polychate fossils are typically trace fossils; fossilized burrows and nests. Terrestrial and amphibious life Aigialosuchus found in the Kristianstad Basin Fossil plants that grew in the coastal areas surrounding the basin and on the islands dotted throughout include conifers, deciduous trees, ferns and low-growing flowering plants. Fossil wood has been recovered from late Middle Santonian to earliest Campanian-age deposits at Åsen, representing the tree genera Pinus, Platanus, Scandianthus, Silvianthemum and Actinocalyx. In addition to the aforementioned dinosaurs and the freshwater turtle, further land-dwelling and amphibious animals have also been discovered in the basin. The basin preserves the fossils of the crocodylomorph Aigialosuchus, which lived alongside the coastlines of the mainland and the small islands. The jaws of Aigialosuchus are long and thin, suggesting a diet mostly composed of fish, but its teeth are unusually robust, meaning that it might also have fed on shelled invertebrates or larger animals. Fossils of small scincomorph lizards, similar to Araeosaurus, have also been discovered. Fossils of amphibious birds, hesperornithiforms, have also been found, representing the two genera Baptornis and Hesperornis. == Depositional environment ==

During the transgressions experienced during the Late Cretaceous, the inland sea within the Kristianstad Basin remained very shallow, and its northern parts formed an archipelago with several low islands and a number of small peninsulas. Remnants of these islands and peninsulas remain today in the form of rocky hills and mounts throughout northeastern Skåne, such as the Ivö Klack site, Fjälkinge backe, Kjugekull, Oppmannaberget, Vångaberget, Västanåberget and Ryssberget. The climate was subtropical to temperate and local plant life included low-growing flowering plants, ferns, conifers and deciduous trees. Most of the area preserved in the Kristianstad Basin was a shallow marine inner shelf environment, as indicated by the present invertebrate fauna (which has been compared to modern faunas). Most of the water was probably less than 40 meters (131 ft) deep, but there were a wide range of environments present. These environments included rocky and sandy beach areas, drowned river valleys and neritic and deeper offshore environments. There were also shallow and protected coastal bays as well as coastal waters that were significantly deeper. Some structures within the rocks of the Basin, combined with the often fragmented and broken condition of the fossils recovered, indicate that the Cretaceous environment was a high-energy environment, where the water was fast-moving and agitated, created by waves and currents. Paleoecology of Ivö Klack and Åsen Ivö Klack was a small island during the Campanian. Teeth from large lamniform sharks, such as Cretoxyrhina and Cretalamna, are significantly more common at Ivö Klack than they are in other sites, such as Ignaberga. The prominence of large sharks in the area probably derives from large sharks requiring large prey, and large marine reptiles being common at Ivö Klack as well. There are plesiosaur fossils from Ivö Klack with shark bite marks. Modern great white sharks are known to patrol around small islands inhabited by seals, possibly a behavior also present in the similar Cretoxyrhina. Fossil remains of large marine reptiles are also especially common at Ivö Klack. The high diversity of sharks and mosasaurs recovered at Ivö Klack shows that large predators frequented the rocky coastline. There must have been a productive ecosystem, with a diverse invertebrate fauna attracting small nektonic predators (such as cephalopods and fish), which then in turn attracted larger predators. It is probable that the richness of the environment also made Ivö Klack a nursery and feeding ground for migratory species, similar to rocky shores today. The discovery of the basin's only crocodylomorph at Ivö Klack might indicate that Aigialosuchus preferred to live in coastal waters, where it could lay its egg on adjacent land, rest and heat up, similar to modern crocodilians. The Åsen site is believed to have been a murky river mouth during the Campanian. Teeth and vertebrae of small-sized (probably juvenile) Clidastes mosasaurs have been found at Åsen, which suggests that the area offered some protection against predation by larger mosasaurs and other predators, possibly due to the murky waters produced by some nearby river system. This murky setting also seems to have been preferred by the many species of benthic sharks and rays recovered at Åsen. Particularly, rays are significantly more common at Åsen than elsewhere. It is probable that they preferred the murky and estuarine environment there, similar to the environments preferred by their modern relatives. The sharks and rays at Åsen probably fed on fish and invertebrates, which occur with less diversity (though still large numbers) at Åsen than elsewhere. They might have primarily fed on soft-bodied invertebrates, less likely to be preserved in the fossil record. == See also ==