This section summarises current PhD projects that are not funded by the Austrian Science Fund (FWF) but by other sources:

- Drivers of elasmobranch diversity in deep time

- Palaeoparasitology of archosaurs (Crurotarsi, Avemetatrsalia, Testudinata)

Drivers of elasmobranch diversity in deep time

Team

• Manuel A. Staggle, MSc (PhD student, University Assistant Praedoc)

• Univ.-Prof. Dr. Jürgen Kriwet (Supervisor)

• Prof. Dr. Michael J. Benton (Technical Advisory Committee Member)

The current biodiversity on our planet is experiencing an anthropogenically driven extinction event, very similar to past mass extinctions, with global extinction rates being elevated up to a thousand times higher than in former extinction events as documented by the fossil record. Despite being well-adapted predators, this new mass extinction event doesn’t spare sharks, rays, and skates, which face many threats today, with an estimated one third of all species being threatened according to the IUCN Red List criteria. However, it is mandatory to study biodiversity dynamics of elasmobranchs (sharks, rays, skates) in deep time to better understand the current effects of environmental changes on and the future for these fishes.
Isolated teeth predominantly characterize the fossil record of elasmobranchs, which renders recognizing the timing of their origin difficult. The morphological variety of teeth and other elasmobranch remains from the Triassic and Early Jurassic implies that elasmobranchs including both stem and crown members were already very diverse and might have been far more diverse than currently known. In the Late Triassic, a major radiation and diversification of elasmobranchs, which probably all represent stem members, is supposed to have occurred in relation to the Rhaetian transgression, which created an extensive shallow epicontinental sea over most of western Europe providing suitable environments for elasmobranchs. The status of all pre-Jurassic elasmobranchs including synechodontiforms, however, needs to be re-evaluated. After the Late Triassic mass extinction, a rapid diversification and expansion of crown elasmobranchs can be observed in the Early Jurassic, with the first substantial divergence into the two major shark clades Galeomorphii and Squalomorphii, as well as the first fossil appearance of batoids in the Toarcian. So far, crown elasmobranchs thus only are known to extend back into the earliest Jurassic.
In the Late Jurassic, batoids became more diverse and abundant and, except for squaliforms and pristiophoriforms, all major clades of elasmobranchs already occurred in marine habitats, due to a great radiation and by the Cretaceous, also freshwater habitats were inhabited. After a further diversification event during the latest Jurassic and the earliest Cretaceous, the first shark faunas with truly modern appearance are supposed to have been emerged during the Early Cretaceous. The earliest squaliforms as well as various basal lamniforms are known from this time, while pristiophoriform sharks were the last modern sharks that probably evolved around the Early/Late Cretaceous boundary. Although the beginning of the Cretaceous thus seems to be an important time interval in the evolution of modern elasmobranchs, assemblages from this time nevertheless are scarce and insufficiently described.
At the end of the Mesozoic, elasmobranch fishes were already very abundant and diverse, with more than 200 known fossil species. During the K/Pg-boundary extinction event, elasmobranchs suffered significant losses at all systematic levels, while new taxa replaced those going extinct in the Palaeogene. The severity of this mass extinction is also reflected by the ecological impact to the ecosystem structure, which led to a faunal turnover in lamniform sharks from big oceanic apex predators (pre-extinction event) to small fish eaters (post extinction event; Lilliput effect). The Neogene, finally witnessed the major diversification events and the appearance of modern taxa contributing to the modern elasmobranch diversity.
The ultimate goals is to analyse possible biotic and abiotic drivers and environmental perturbations of major transitions in crown elasmobranch evolution to better understand their diversity and diversification patterns in deep time. Relationships between morphology, biological behaviour and environmental context in the fossil record will be established and the observed adaptations in the past will be compared to today's conditions for better understanding possible responses to external influences. Also of importance will be the resilience of individual groups in terms of diversity.

The following hypotheses form the basis of this project:

• Climate change is significantly influencing the diversity of elasmobranch fishes during the Phanerozoic on local, regional, and global scales.

• Biotic factors (e.g., reproduction, competition) were mayor drivers, but also sustainers of elasmobranch evolution and diversity through time.

• Specific environmental characteristics lead to particular community structures, biological interactions within them, and characteristic metabolic demands and extinction dynamics.

Palaeoparasitology of archosaurs (Crurotarsi, Avemetatrsalia, Testudinata)

Team

• Patrick Etzler, MSc (PhD student)

• Univ.-Prof. Dr. Jürgen Kriwet (Supervisor)

• N.N. (Technical Advisory Committee Member)

Coprolites have been known since the 1820s at the latest and were initially identified as stomach stones by the British fossil collector Mary Anning and described as fossil excrements in 1829 by the palaeontologist William Buckland, who subsequently defined the term coprolite. Despite this long history, coprolites received little scientific attention for almost 200 years and were regarded as curiosities or displayed as collection items. Due to the often difficult assignment to th eir producer, the direct informative value is sometimes limited, whereby the morphology of the finds must also be carefully considered. As trace fossils, they provide an indication of the behavior of extinct vertebrates and offer information about their diet, digestion and excretion. The preservation of food components, such as undigested beetles, can provide insights into the palaeoenvironment and its interactions as well as palaeodiversity. In addition to the use of coprolites in Quaternary science and archaeology, there has also been an increase in interest within palaeontology for around 30 years. The study of palaeoparasites in particular has received increasing attention over the last 10 years. Under special taphonomic circumstances, coprolites offer good opportunities for the preservation of endoparasites, which can be found in vertebrates through the natural course of the food chain. Among these, parasitic representatives of the phyla Nematoda, Platyhelminthes and Rotifera are particularly well known, which have been passed down in coprolites through Ascaridida, Oxyurida, Cestoda and Acanthocephala. Recent turtles, crocodiles and birds are also predominantly infested by these parasites, both in the wild and in captivity. A significant role in the preservation of parasite eggs in coprolites is played by feeding habits, predator prey relationships and the associated ingestion and spread of parasites in the intestine, as well as the individual digestion of the animals in the form of the gastric acid environment, among other things. In the fossil excrement of the Triassic Silesaurus opolensis, incom pletely decomposed remains of beetles, as well as presumably algae, fungi and wood fibers, were identified. For example, round or cylindrical shapes of coprolites, as well as the absence of bone remains, are a distinctive feature of Crocodylomorpha. The Ascaridida of Cretaceous crocodyliforms found in coprolites show morphological and morphometric similarities to their recent forms, which occur in modern crocodilians and indicate ingestion by fish or amphibians. Such palaeoparasitological findings contain important information about the relationship between parasite and host in the geological past and thus provide information about the palaeoenvironment, palaeoclimate, food webs and evolutionary background. Coprolites show a wide variety of forms and are therefore classified according to morphotypes based on characteristic properties. The helminth eggs found in them can with stand strong environmental influences due to very resistant structur es such as thick chitin and lipid layers and thus remain preserved for palaeontology under favorable deposition conditions. Due to the different dietary habits and physiology of the various animal classes, there are formative diffe rences in excretions. Even within birds, there are differences in the characteristics of excretions, which, among other things, clearly differentiate the pellets of owls from other birds of prey, despite the adaptations to similar ecological niches. Fossil turtles provided information about their diet via coprolites and traces of ectoparasites were also found on shells, whereas research on endoparasites is still limited. Traces of parasites are also known from herbivorous dinosaur coprolites and stomach contents.
The ultimate goal is to gain deeper insights into endoparasites infesting Archosauria in deep time based on coprolite analyses and to establish possible similarities of parasite infections between extinct and extant members of this group. This will enable to better understand host-parasite relationships during crucial times of reptile evolution and whether changing environmental conditions result in changing host-parasite relationships, but also to recover and trace the origin and evolution of infectious diseases typical for archosaurs. For this, a combination of geological and biological approaches will be employed and the strenghts and weaknesses of the methods will be tested and, if necessary, adjusted.

Turtle coprolite from the Miocene of Madgascar.