Pycnodont fishes are an extinct group of neopterygian fishes that had a worldwide distribution during the Mesozoic. They have often been in the focus of taxonomic and phylogenetic research but less is known about their biology. Pycnodonts are often interpreted as reef or reef-associated fishes. Recent reef fishes show a habitat partitioning between juvenile and adult individuals. Habitats or retreat areas which juvenile and small fishes normally favour are characterized, inter alia, by a high density of small fishes and a habitat with niches which give protection against predators. In the Late Jurassic of Hanover (Lower Saxony), such a retreat area is detected for small pycnodont fishes. The locality Tonjesberg shows a high density of small fishes, a low number of possible predators, and no distinctive intergeneric competition in comparison with closely related localities.
Coral reefs are a complex environment with a large biodiversity. Much research has been done to understand the diversity and ecology of coral reefs. Especially ichthyologists examined the relationship and interaction between the large numbers of fish species. In the last years, some authors tried to define coral reef fishes by means of taxonomy or ecology, but until today, there is no consent about a general definition of fishes on coral reefs. Most researchers only worked with teleost fishes in their studies. However, the history of fishes on shallow-water reefs is much older than the “teleost era”. Some typical extinct Mesozoic shallow-water fishes (Pycnodontiformes) are compared with extant coral reef fishes. The main result of this short discussion is that it is impossible to give a general definition of coral reef fishes. Shallow-water reef fishes are heterogenic in their lifestyle and have no closer taxonomic relationship in the course time.
Pycnodontiform fishes are a well-known group, represented in many conservation Lagerstatten worldwide. They occur from the Late Triassic to the Eocene, and some genera were distributed worldwide. Much work has been done during the last centuries, but most scientists studied the taxonomy. The palaeobiology of the Pycnodontiformes has been rarely the central question in their publications. This paper presents a method to reconstruct the standard length by the means of the prearticular length. The main result is a positive correlation between the prearticular length and the standard length, that it is possible to reconstruct the standard length of Gyrodus and Proscinetes from Lower-Saxony (NW-Germany) and the Solnhofen area (S-Germany) for paleobiological studies.
Pycnodontiform fishes are mostly represented by disarticulated cranial elements such as the vomer or prearticulars. These elements with their characteristic molariform dentition play an important role in establishing taxonomic identity. During the last 150 years, several species of pycnodonts were described from Lower Saxony based on the dentition of the prearticular and/or vomer. This paper describes a prearticular from Hanover which differs from all known prearticulars of this area and was determined as Proscinetes minutus. It has just three large oval teeth in the principal tooth row. Four tooth rows are above these three large teeth, each of them is formed by six to seven small quadrangular or roundish teeth. The teeth anterior to these tooth rows have no special alignment. They have a roundish form and are as small as the row teeth. Two tooth series are beneath these irregular teeth. This special dentition demonstrates that this prearticular does not belong to the genus Proscinetes because it has more than four tooth rows. It shows similarities (number of tooth rows and form of the large teeth) with the genus Eomesodon, but up to now it is not possible to identity the genus (cf. Eomesodon) with certainty based on a single dental element.
Chondrichthyan egg capsules have been well known since the nineteenth century, although their systematic affinities have been controversial for much of this time. Currently, 10 chondrichthyan egg capsule morphotypes are distinguished but their phylogenetic signal and evolutionary traits have not yet been analysed. Here, we present an analysis of all extant and currently known fossil chondrichthyan egg capsule types, and use a purported placoderm egg capsule as an outgroup for character coding. The phylogenetic hypothesis based on discrete morphological characters indicates that the enigmatic Carboniferous egg capsule morphotypes Crookallia and Vetacapsula form a monophyletic group together with the egg capsule morphotype of chimaerid holocephalans. The elasmobranch egg capsule morphotypes are sister to the holocephalan types. Based on these results we conclude that the ancestral chondrichthyan egg capsule morphotype combined features of those found in callorhinchid holocephalans and placoderms. From this ancestral type, two lineages of chondrichthyan egg capsule morphotypes diverged leading towards the major modern egg capsule morphotypes.
ABSTRACT Recent pike-like predatory fishes attack prey animals by a quick strike out of rest or slow movement. This fast-start behaviour includes a preparatory, a propulsive and a final phase, and the latter is crucial for the success of the attack. To prevent prey from escape, predators tend to minimise the duration of the interaction and the disturbance caused to surrounding water in order to not be detected by the prey's lateral line sensory system. We compared the hydrodynamic properties of the earliest fossil representative of the pike-like morphotype, the Triassic actinopterygian Saurichthys, with several recent pike-like predators by means of computational fluid dynamics (CFD). Rainbow trout has been used as a control example of a fish with a generalist body shape. Our results show that flow disturbance produced by Saurichthys was low and similar to that of the recent forms Belone and Lepisosteus, thus indicative of an effective ambush predator. Drag coefficients are low for all these fishes, but also for trout, which is a good swimmer over longer distances but generates considerable disturbance of flow. Second-highest flow disturbance values are calculated for Esox, which compensates the large disturbance with its extremely high acceleration performance (i.e. attacks at high speeds) and the derived teleostean protrusible mouth that allows prey catching from longer distances compared to the other fishes. We show CFD modelling to be a useful tool for palaeobiological reconstruction of fossil fishes, as it allows quantification of impacts of body morphology on a hypothesised lifestyle.
Pycnodontiform fishes are mostly represented by disarticulated cranial
elements such as the vomer or prearticulars. These elements with their characteristic
molariform dentition play an important role in establishing taxonomic
identity. During the last 150 years, several species of pycnodonts were described
from Lower Saxony based on the dentition of the prearticular and/or vomer.
This paper describes a prearticular from Hanover which differs from all known
prearticulars of this area and was determined as Proscinetes minutus. It has just
three large oval teeth in the principal tooth row. Four tooth rows are above
these three large teeth, each of them is formed by six to seven small quadrangular
or roundish teeth. The teeth anterior to these tooth rows have no special
alignment. They have a roundish form and are as small as the row teeth. Two
tooth series are beneath these irregular teeth. This special dentition demonstrates
that this prearticular does not belong to the genus Proscinetes because it has
more than four tooth rows. It shows similarities (number of tooth rows and form
of the large teeth) with the genus Eomesodon, but up to now it is not possible
to identity the genus (cf. Eomesodon) with certainty based on a single dental
element.
Los arrecifes de coral son entornos complejos con gran biodiversidad. Se han realizado muchas investigaciones para entender su diversidad y ecologia. Especialmente, los ictiologos han examinado la relacion e interaccion entre su gran numero de especies. En los ultimos anos algunos autores han tratado de definir los peces arrecifales por medio de la taxonomia o la ecologia, pero, de momento, no existe un consenso acerca de una definicion general de dichos peces. La mayoria de los investigadores solo trabajan con peces teleosteos. Sin embargo, la historia de los peces arrecifales de aguas someras es mucho mas antigua que la �edad de los teleosteos�. En esta breve discusion se han comparado algunos peces de aguas someras del Mesozoico (Pycnodontiformes) con peces arrecifales actuales. Su principal resultado es que es imposible dar una definicion general de los peces arrecifales, dado que los peces arrecifales de aguas someras son heterogeneos en su estilo de vida y no guardan ninguna relacion taxonomica a lo largo del tiempo.
