Papers by Axel von Hillebrandt
The attempt was made to prove if the Oberhauserellidae (Robertinina) are the ancestors of the pla... more The attempt was made to prove if the Oberhauserellidae (Robertinina) are the ancestors of the planktonic foraminifera. The Robertinina described here (Oberhauserellidae and Reinholdeinae) are from strata of late Rhaetian to early Hettangian age of the Northern Calcareous Alps. Specimens are especially well preserved with their original aragonitic tests and these are compared here with similarly preserved Reinholdella and in all probability planktonic Conoglobigerina from the Bathonian of Poland. A detailed systematic description is given for different genera and species. The outer and inner characters could both be studied and compared in detail. Described and figured are types of chambering, chamber shape, sutures between chambers, wall structure and surfaces, primary and secondary built apertures. Secondary thickening of the multilayered wall is typical for the Oberhauserellidae and can be seen in SEM photographs of wall surfaces and broken specimens. Pore diameter is similar in t...
Neues Jahrbuch für Geologie und Paläontologie - Abhandlungen, 2009
The earliest ammonite species of Jurassic type, Psiloceras spelae GUEX, was unknown till 1998. Th... more The earliest ammonite species of Jurassic type, Psiloceras spelae GUEX, was unknown till 1998. This species bridges the long gap between the latest Triassic and the earliest Jurassic ammonoids. It was discovered in North America, then in South America and finally in Europe. The species is proposed as boundary marker for the base of the Jurassic system. It is known in two forms which are regarded as subspecies. The European subspecies is here introduced as P. spelae tirolicum n. ssp. This taxon occurs in the Northern Calcareous Alps of Tyrol as the oldest European Jurassic type ammonite. Both subspecies characterize the first Jurassic ammonite biohorizon and are closely related. Their slight differences may be due to biogeographic separation. The preservation admits a complete diagnosis of the new subspecies. Besides psiloceratid characters still phylloceratid characters are present indicating the origin of the psiloceratids. Additionally, slightly younger psiloceratids are described which were known only from South and North America thus far. They are older than the oldest psiloceratids hitherto known from Europe. All these forms are elements of the first biochronological ammonite unit of the Jurassic, the Tilmanni Chronozone which is situated below the Planorbis Chronozone. It is assumed that during the end-Triassic biotic crisis only those ammonites survived which lived in the open parts of the oceans. A re-population of neritic shelf areas took place from the oceanic realms in line with the gradual Hettangian transgression. This may explain the global similarity of the first Jurassic ammonites and their later biogeographic diversification. A time calculation based on the sedimentation rate of the P. spelae tirolicum n. ssp. bearing sections leads to the conclusion that the earlier Triassic-Jurassic ammonite gap of about 250 to 300 ka now can be reduced to approximately 100 ka.
The Oberhauserellidae (particularly the transitional form Praegubkinella racemosa) have been cons... more The Oberhauserellidae (particularly the transitional form Praegubkinella racemosa) have been considered as the benthic ancestor stock of Jurassic planktic Favusellacea (e.g., Conoglobigerina, Globuligerina). In 2003, Hart et al., questioned if such Oberhauserellidae from the early Toarcian of northwestern Europe were mero-planktonic forms, implying that it was a "first" experimentation of a planktic mode of life, linked to anoxic stressful conditions. The distribution and abundance of robertininid foraminifera (Oberhauserella spp. and Reinholdella sp.) at the Doniford section (southwestern England) during the major perturbations of the * Corresponding author: [email protected].
Neues Jahrbuch für Geologie und Paläontologie - Abhandlungen, 2012
Kontinentalverschiebung und die paläozoogeographischen Beziehungen des südamerikanischen Lias
Tectonics of the Southern Central Andes, 1994
Ammonite faunas from the singularis horizon (Zitteli Subzone) and sphaeroceroides horizon (Alteco... more Ammonite faunas from the singularis horizon (Zitteli Subzone) and sphaeroceroides horizon (Altecostata Subzone) of the Singularis Zone are described. The faunal horizons of the Singularis Zone of this area can be correlated with those of the Singularis Zone of the Paso del Espinacito section (Northern Argentina). The oldest occurrences of the ammonite Emileia buckMan in the Andean Province are described from the singularis horizon and the sphaeroceroides horizon. The rich and diverse fauna of the circum-Pacific Pseudotoites spatH includes familiar Ps. argentinus arkell and Ps. sphaeroceroides (tornquist) as well as Ps. aff. kialagvikensis WesterMann & riccardi and Ps. aff. corona (arkell), previsously unknown from the region. All "Andean" members of Pseudotoites are part of a chronocline trending to larger and broader morphs.
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Papers by Axel von Hillebrandt