A 104-Ma record of deep-sea Atelostomata (Holasterioda, Spatangoida, irregular echinoids) - a story of persistence, food availability and a big bang.

Deep-sea macrobenthic body fossils are scarce due to the lack of deep-sea sedimentary archives in onshore settings. Therefore, hypothesized migrations of shallow shelf taxa into the deep-sea after phases of mass extinction (onshore-offshore pattern in the literature) due to anoxic events is not constrained by the fossil record. To resolve this conundrum, we investigated 1,475 deep-sea sediment samples from the Atlantic, Pacific and Southern oceans (water depth ranging from 200 to 4,700 m), providing 41,460 spine fragments of the crown group Atelostomata (Holasteroida, Spatangoida). We show that the scarce fossil record of deep-sea echinoids is in fact a methodological artefact because it is limited by the almost exclusive use of onshore fossil archives. Our data advocate for a continuous record of deep-sea Atelostomata back to at least 104 Ma (late early Cretaceous), and literature records suggest even an older age (115 Ma). A gradual increase of different spine tip morphologies from the Albian to the Maastrichtian is observed. A subsequent, abrupt reduction in spine size and the loss of morphological inventory in the lowermost Paleogene is interpreted to be an expression of the "Lilliput Effect", related to nourishment depletion on the sea floor in the course of the Cretaceous-Paleogene (K-Pg) Boundary Event. The recovery from this event lasted at least 5 Ma, and post-K-Pg Boundary Event assemblages progress-without any further morphological breaks-towards the assemblages observed in modern deep-sea environments. Because atelostomate spine morphology is often species-specific, the variations in spine tip morphology trough time would indicate species changes taking place in the deep-sea. This observation is, therefore, interpreted to result from in-situ evolution in the deep-sea and not from onshore-offshore migrations. The calculation of the "atelostomate spine accumulation rate" (ASAR) reveals low values in pre-Campanian times, possibly related to high remineralization rates of organic matter in the water column in the course of the mid-Cretaceous Thermal Maximum and its aftermath. A Maastrichtian cooling pulse marks the irreversible onset of fluctuating but generally higher atelostomate biomass that continues throughout the Cenozoic.

Geometric morphometric analysis of morphologic disparity, intraspecific variation and ontogenetic allometry of beyrichitine ammonoids.

Beyrichitine ammonoids of NV Nevada reveal a high taxonomic diversity of Anisian (Middle Triassic). This diversity is, however, in contrast to their relatively low morphologic disparity. Depending on the exact definition, morphologic disparity of a data set is a direct consequence of the sum of all ontogenetic changes. In the past, however, the interplay of both morphological processes has only rarely been addressed. Using geometric morphometric methods, this study aims at a quantification of allometric processes and the morphologic disparity of beyrichitine ammonoids. The multivariate statistical analysis revealed that morphologic disparity, intraspecific variation respectively, within and between the studied species seems to be the result of deviations in the ontogenetic allometric growth pattern (i.e. heterochrony). During deposition of the studied stratigraphic sequence, a general progressive pedomorphism (juvenilization) was observed. The intraspecific variability pattern coincides with the total morphologic disparity of the analyzed species, which suggests that intraspecific variability facilitated morphologic disparity. The comparison of ontogenetic allometric patterns and changes in intraspecific variation and morphologic disparity are likely to refine our understanding of the intrinsic factors influencing the speciation of this group.

Ontogeny of highly variable ceratitid ammonoids from the Anisian (Middle Triassic).

Ammonoids reached their greatest diversity during the Triassic period. In the early Middle Triassic (Anisian) stage, ammonoid diversity was dominated by representatives of the family Ceratitidae. High taxonomic diversity can, however, be decoupled from their morphologic disparity. Due to its high phenotypic variability, the high diversity of ceratitids of the Anisian of Nevada was initially assumed to be caused by artificial over-splitting. This study aims to contribute data to settle this issue by applying geometric morphometrics methods, using landmarks and semi-landmarks, in the study of ontogenetic cross-sections of ammonoids for the first time. The results reveal that alterations in ontogenetic trajectories, linked to heterochronic processes, lead to the morphologic diversification of the species studied herein. Our knowledge, based on these ontogenetic changes, challenge the traditional treatment of species using solely adult characters for their distinction. This study furthermore demonstrates that the high diversity of the Anisian ammonoid assemblages of Nevada based on the traditional nomenclatoric approach is regarded to be reasonably accurate.

Two echinoid species from the early Aptian (Early Cretaceous) of the Kopet-Dagh Basin, NE Iran.

Two echinoid species from the Sarcheshmeh Formation, early Aptian, Lower Cretaceous, of the Kopet-Dagh Basin, NE Iran, are described: a phymosomatoid specimen of Tetragramma sp., and the spatangoid echinoid Miotoxaster collegnii (Sismonda, 1844). This is the first report of echinoids from the Sarcheshmeh Formation from northeastern Iran.

Ecophenotypic Variation and Developmental Instability in the Late Cretaceous Echinoid Micraster brevis (Irregularia; Spatangoida).

The Late Cretaceous echinoid genus Micraster (irregular echinoids, Spatangoida) is one of the most famous examples of a continuous evolutionary lineage in invertebrate palaeontology. The influence of the environment on the phenotype, however, was not tested so far. This study analyses differences in phenotypical variations within three populations of Micraster (Gibbaster) brevis from the early Coniacian, two from the Münsterland Cretaceous Basin (Germany) and one from the North Cantabrian Basin (Spain). The environments of the Spanish and the German sites differed by their sedimentary characteristics, which are generally a crucial factor for morphological adaptations in echinoids. Most of the major phenotypical variations (position of the ambitus, periproct and development of the subanal fasciole) among the populations can be linked to differences in their host sediments. These phenotypic variations are presumed to be an expression of phenotpic plasticiy, which has not been considered in Micraster in previous studies. Two populations (Erwitte area, Germany; Liencres area, Spain) were tested for stochastic variation (fluctuating asymmetry) due to developmental instability, which was present in all studied traits. However, differences in the amount of fluctuating asymmetry between both populations were recognised only in one trait (amount of pore pairs in the anterior paired petals). The results strengthen previous assumptions on ecophenotypic variations in Micraster.