Paleobiota of the Posidonia Shale

Biological interactions

• The "Monotis"-Dactylioceras bed shows an accumulation of the bivalves Meleagrinella substriata and the ammonite Dactylioceras, that were the most abundant representatives of its group on the Altdorf region, and were probably washed to near epicontinental waters by a rapid event, or as result of a large succession of events. This assemblage has been compared with modern Brazilian coastal mangroves and also linked to tsunami events.

• Several empty ammonite shells from Holzmaden have been found with associated decapods inside. This includes a possible member of the genus Paleastacus inside a chamber of a Harpoceras. This decapod is related to the family Erymidae, which are considered to be possible bottom-dweller carnivores or carrion feeders. The associated fossil has several spherical structures that had been interpreted as decapod coprolites, implying that the animal lived for a long period within the shell. More recent studies had recovered new data about the inquilinism of decapods inside ammonites, this time, however, recovering three eryonoids together within a body chamber. The eryonoids most likely used the ammonoid as some kind of shelter, possibly due to the shell being an ideal location to molt, protection against predators, a source of food or that the shell was used as a long-term shelter. One key aspect found was that the muddy bottom was not suitable for burrowing, implying that the decapods inhabited a different shelter due to being unable to make their own. Other biota are found related to the decayed ammonite shells, such as serpulid annelids and bivalves, creating what was denominated as "benthic islands".
• Beyond trace fossils, several vertebrate specimens show associations with crustacean exoskeletal remains such as GPIT-PV-31586 and SMNS 58389 (Pachycormus macropterus) with necrophagous interaction as well SMNS 55934 (Stenopterygius quadriscissus) or SMNS 95401 (Metopacanthus sp.).

• The genus Clarkeiteuthis and its predatory behaviour, found associated with fishes of the genus Leptolepis. Based on the position of prey and predator, it was suggested that the cephalopods caught and killed the fishes while the schools were still in well-oxygenated waters and then descended into oxygen-depleted water layers where the cephalopod suffocated and died attached to its prey. The cephalopods' arms were contracted over the fish, likely killing it quickly by cutting its spine.
• Several Geotheutis have been reported with eumelanin preserved along with their ink sacs.
• A specimen of Jeletzkyteuthis found in Ohmden has appeared predating a Parabelopeltis. The association of these 2 genera shows the predatory behaviour of this group when its members lived in epicontinental seas, which is rather different than extant Vampyromorphs.
• A pabulite (fossilized meal which never entered the digestive tract) was recovered from Holzmaden, being composed of an associated Passaloteuthis laevigata with its arms embracing an exuvia of a crustacean. The belemnnite itself can be seen as the remnant of a failed predation attempt from a Hybodus, corroborating a possible tropic chain.

• One of the most complex organism interactions on the Posidonia Shale were the crinoid megarafts that grouped a wide variety of animals, creating large floating ecosystems. The largest megaraft found measured 18 metres (59 ft), and is based on an Agathoxylon trunk, where different animals were attached. The first attached animals would have been the growing community of oysters, bivalves and crinoids, that would add a small weight to the raft (about 800 kilograms (1,800 lb)). The presence of these megarafts were in part possible due to the absence of marine wood worms which destroy tree logs in less than 3 years along with the absence of modern raft wood predators (that appeared on the Bathonian). These rafts could last up to 5 years, which is the main reason the crinoids attached were able to reach huge sizes. These rafts were likely also essential to distribute animals along sea basins. Seirocrinus & Pentacrinites were some of the main crinoid colonizers of the floating rafts. Seirocrinus is the main representative of the pelagic crinoids, being among the longest animals known, reaching 26 m long in the largest documented specimen. The ecology of the genus is widely known, with it being known that the smallest stems were among the first animals to colonize the rafts, with at least 2 generations of crinoids found per raft, where the hydrodynamic changes of the log influenced the settlement of the crinoids. It is believed that Seirocrinus underwent seasonal reproduction linked to monsoonal conditions that sent new logs to the sea. The large crinoids would have feed on pelagic micronutrients, and after the log fell to the bottom, all of the colony would have died.
• Thoracic barnacles of the genus Toarcolepas became the oldest epiplanktonic barnacle known in the fossil record, probably motivated by the appearance of the giant crinoid rafts. It has been found in situ associated with fossil wood.

• The shark Hybodus includes specimens with gastric contents full of belemnnite fragments. This implies active predatory behaviour by the genus towards several kinds of belemnnites, such as Youngibelus.
• A speiballen (a regurgitated mass composed of indigestible stomach contents) had been found in the Holzmaden quarry. The speiballen measures 285 mm in length with a diameter of 160 mm, and consists of 4 members of the genus Dapedium (Dapediidae) and a jaw identified as Lepidotes (Semionotidae). The maker of this speiballen has been suggested to be a shark like Hybodus, an actinopterygian or a marine reptile.
• A specimen of Pachycormus has been found with stomach contents that include hooks similar to the ones found on genera like Clarkeiteuthis.
• Another specimen of Pachycormus macropterus preserves an ammonite inside its gut, likely swallowed by accident and directly responsible for the fish's death.
• SMNS 51144 (Saurostomus esocinus) was found with Chondrites sp. burrows in the abdominal cavity, what indicates a possible opportunistic scavenger. Other Chondrites sp. includes SMNS 17500 and MHH 1981/25 (Stenopterygius uniter) that either suggest the ichthyosaurs were preserved immediately below one such bioturbation horizon or scavenger association.
• The known specimens of Toarcocephalus are evidence of successful predation events, as the head of one was isolated, likely as product of a decapitation, with another preserved within a regurgitated mass.
• One of the most emblematic finds of the formation is that of a mother Stenopterygius giving birth to live young. While specimens have been found with embryos, the bones of these embryos are scattered partly beyond the body limits of the mother. There have been various theories about this scenario: either the bones of embryos had been deposited before the body of the adult went to the sea floor, or in the ichthyosaurs' last moments where it sank to the bottom and may have given untimely birth to some of the foetuses, and finally another option follows post mortem hydrostatic pressure being too high to be prevented by the body, exploding or expelling its embryos.
• The specimen SMNS 53363 (Eurhinosaurus?) from Aichelberg was found with two encrusted large oysters (Liostrea) on the right pterygoid, considered to be part of a reef stage over bones.
• SMNS 80234 (Stenopterygius quadriscissus) represents another female with embryos, yet also shows ribs broken perimortem that may represent either intraspecific aggression or a predation attempt. This specimen has several taxa associated: ammonite aptychi, two ophiuroids (Sinosura brodiei) and an articulated echinoid (Diademopsis crinifera) indicate a short-lived deadfall community.
• SMNS 81841 (Stenopterygius quadriscissus) represents one of the clearest examples of deadfall communities described in the formation: the skeleton is associated with serpulids surrounded by a mass of disarticulated ophiuroid remains, indeterminate echinoid tests, an isolated crinoid ossicle, the byssate bivalve Oxytoma inaequivalvis, the pectinid Propeamussium pumilus, Eopecten strionatis, Plagiostoma sp., Meleagrinella sp., "Cucullaea" muensteri, with the genera Parainoceramya dubia and Liostrea associated with the carcass. As many of these bivalves show overgrowth the community likely persisted for some time. Fossil traces of Gastrochaenolites isp. attributed to mechanical bivalve borers are abundant implicating prolonged exposure of the skeleton on the seafloor.
• SMNS 81719 (Stenopterygius uniter) includes Liostrea, Propeamussium pumilus, Plagiostoma sp. and Parainoceramya dubia, with other invertebrates found (?) not being part of the deadfall community, such as several ammonites and Parainoceramya valves, being stratigraphically below the specimen. This specimen includes also traces of scavenging activity, possibly by crustaceans.
• SMNS 80113, (Stenopterygius triscissus) was found populated by Parainoceramya, a specimen of Eopecten strionatis and an unexpected specimen of the small infaunal lucinid Mesomiltha pumila, equivocal evidence for the sulfophilic stage.
• Local ichthyosaur soft tissues include skin enough well preserved to infer coloration and appearance on the living animal, as well evidence for homeothermy and crypsis.
• Gut contents of the local pterosaurs are known: Campylognathoides preserves hooks of the coleoid Clarkeiteuthis (therefore being one of the few teuthophagous pterosaurs), while Dorygnathus preserves remains of Leptolepis.