Search

An unusually high proportion of large-bodied carnivorous theropod dinosaurs has been reported from the Moroccan Late Cretaceous Kem Kem Formation, a well-known package of North Africa vertebrate fossil-bearing sediments. We investigate whether recorded proportions of predator and prey taxa in Kem Kem sediments are real, or an artifact generated by collecting biases, by comparing field data to counts of fossil vertebrates from Moroccan fossil shops. The application of common techniques for standardizing ecological survey data confirms that previous workers have been misled by the acquisition by museums of specimens from commercial collectors rather than from detailed field surveying. Claims that an unusual number of theropod dinosaurs were present in North Africa Late Cretaceous ecosystems are likely the result of biases due to both commercial activity and collectorship biases.

Taxonomic diversity is only one possible biodiversity metric. Studies of taxonomic and morphologic diversity indicate that the two need not be closely linked. Mass extinctions, and their associated recovery periods, can be viewed as natural experiments for testing the link. After the Permian--Triassic mass extinction (ca. 253 Ma), ammonoid taxonomic diversity rapidly recovered to preextinction levels. Morphologic diversity, measured as variance, was used to compare taxonomic and morphologic recovery patterns of ammonoids after the Permian--Triassic. Morphologic diversity decreased significantly between the first and second stages of the Triassic (Griesbachian and Dienerian, respectively), despite an increase in taxonomic diversity and a tripling of sample size. During the third stage (Smithian), morphologic diversity returned to Griesbachian levels. The loss of representatives from two morphologically distinctive lineages at the end of the Griesbachian, followed by the evolution of many morphologically convergent forms, explains this pattern. These findings strengthen the case that morphologic metrics are valuable complements to taxonomic metrics in characterizing evolutionary patterns. Keywords: Permian, Triassic, ammonoids, biotic recovery, morphologic evolution.

The Middle Triassic ammonoid genus Ceratites diversified spectacularly within the Germanic Muschelkalk Basin during the Anisian/Ladian (244-232 Mya). Previous studies have interpreted this diversification as a sequence of rapid, endemic radiations from a few immigrant taxa. Here we investigate the possibility that geological and sampling biases, rather than ecological and evolutionary processes, are responsible for this pattern. A new specimen-based dataset of Ceratites species-richness and abundance was assembled. This dataset was combined with 1:200 000 geological maps in a geodatabase to facilitate geospatial analyses. One set of analyses compared species richness per geological map with the number of occurrences and localities per map. Per-map change in the amount of rock available to sample for fossils was also included as a variable. Of these three variables, number of occurrences is the most strongly correlated with richness. Variation in the amount of rock is not a strong determinant of species-richness. However, rarefaction of basin-wide species/abundance data demonstrates that differences in species-richness through time are not attributable to sample size differences. The average percent similarity among sites remained close to 50%throughout the Upper Muschelkalk. The rank abundance distribution (RAD) of species from the first interval of the Upper Muschelkalk is consistent with colonization of a disturbed environment, while the other two intervals have RADs consistent with more stable ecosystems. These results indicate that genuine ecological and evolutionary events are partly responsible for the observed differences in richness and abundance. Although changes in the RADs through time support changes in the ammonoid assemblage structure, the processes underlying increasing richness and change in RADs cannot be explained by increasing geographic distinctiveness or isolation among the ammonoid assemblages present at different localities. [ABSTRACT FROM AUTHOR]

We investigated the relationship between wing element proportions and flight mode in a dataset of living avian species to provide a framework for making basic estimates of the range of flight styles evolved by Mesozoic birds. Our results show that feather length (fprim) and total arm length (ta) (sum of the humerus, ulna and manus length) ratios differ significantly between four flight style groups defined and widely used for living birds and as a result are predictive for fossils. This was confirmed using multivariate ordination analyses, with four wing elements (humerus, ulna/radius, manus, primary feathers), that discriminate the four broad flight styles within living birds. Among the variables tested, manus length is closely correlated with wing size, yet is the poorest predictor for flight style, suggesting that the shape of the bones in the hand wing is most important in determining flight style. Wing bone thickness (shape) must vary with wing beat strength, with weaker forces requiring less bone. Finally, we show that by incorporating data from Mesozoic birds, multivariate ordination analyses can be used to predict the flight styles of fossils. [ABSTRACT FROM AUTHOR]