Martin Košťák

Lower Turonian record of belemnite Praeactinocamax from NW Siberia and its palaeogeographic significance

Specimens of the belemnitellid Praeactinocamax Naidin, 1964 are described from the Upper Cretaceous of NW Siberia (Taimyr Region, Lower Agapa River, Russia). The rostra determined as Praeactinocamax aff. plenus consist of an aragonitic anterior part and a calcitic posterior part with a sharp boundary in between. This boundary surface is referred to as the “alveolar fracture”, and it is a typical morphological feature of early belemnitellids and not a result of diagenetic processes. The occurrence of Praeactinocamax in Arctic areas shows a wider palaeobiogeographical distribution of the genus in the Late Cenomanian—Early Turonian interval than previously known. This finding suggests that migration of the late Cenomanian—early Turonian fauna occurred across Turgai channel. The geographic position of these new records may also explain the occurrence of Praeactinocamax in the Turonian of the US Western Interior Seaway, the origin of which has been hitherto unclear.

Extremely Rare Turonian Belemnites from the Bohemian Cretaceous Basin and Their Palaeogeographical Importance

New records of extremely rare late Turonian belemnites are described from the Úpohlavy working quarry in the Bohemian Cretaceous Basin. These specimens are referred to Praeactinocamax bohemicus (Stolley, 1916). An alveolar fragment possibly represents Praeactinocamax strehlensis (Fritsch, 1872) and would be the third find of this species ever recorded. All finds derive from a thin horizon in the uppermost part of the Hudcov limestone (Teplice Formation, uppermost Subprionocyclus neptuni Ammonite Zone). The small faunule most likely had its origin in a taxon from the Praeactinocamax manitobensis/walkeri/sternbergi group of the North American Province, and its occurrence in Europe can be seen in the context of a southward shift of Boreal taxa in the course of a late Turonian cooling event.

New Paleocene Sepiid Coleoids (Cephalopoda) from Egypt: Evolutionary Significance and Origin of the Sepiid ‘Rostrum’

New coleoid cephalopods, assignable to the order Sepiida, are recorded from the Selandian/Thanetian boundary interval (Middle to Upper Paleocene transition, c. 59.2 Ma) along the southeastern margin (Toshka Lakes) of the Western Desert in Egypt. The two genera recognised, Aegyptosaepia n. gen. and ?Anomalosaepia Weaver and Ciampaglio, are placed in the families Belosaepiidae and ?Anomalosaepiidae, respectively. They constitute the oldest record to date of sepiids with a ‘rostrum-like’ prong. In addition, a third, generically and specifically indeterminate coleoid is represented by a single rostrum-like find. The taxonomic assignment of the material is based on apical parts (as preserved), i.e., guard, apical prong (or ‘rostrum-like’ structure), phragmocone and (remains of) protoconch, plus shell mineralogy. We here confirm the shell of early sepiids to have been bimineralic, i.e., composed of both calcite and aragonite. Aegyptosaepia lugeri n. gen., n. sp. reveals some similarities to later species of Belosaepia, in particular the possession of a distinct prong. General features of the phragmocone and protoconch of the new form are similar to both Belocurta (Middle Danian [Lower Paleocene]) and Belosaepia (Eocene). However, breviconic coiling and the presence of a longer ventral conotheca indicate closer ties with late Maastrichtian–Middle Danian Ceratisepia. In this respect, Aegyptosaepia n. gen. constitutes a link between Ceratisepia and the Eocene Belosaepia. The occurrence of the new genus near the Selandian/Thanetian boundary suggests an earlier origin of belosaepiids, during the early to Middle Paleocene. These earliest known belosaepiids may have originated in the Tethyan Realm. From northeast Africa, they subsequently spread to western India, the Arabian Plate and, probably via the Mediterranean region, to Europe and North America.

Amphispirula gen. nov. from the Eocene of southern Moravia (Czech Republic): a new ancestor of the Recent deep-sea squid Spirula?

A single specimen of an enigmatic coleoid cephalopod from the Eocene of southern Moravia (Czech Republic) represents the oldest record of a spirulid with a markedly, endogastrically coiled phragmocone. Distinctly oblique septa in Amphispirula gen. nov. show similarities to sepiid coleoids, but a ventrally closed siphuncle refers this taxon to the order Spirulida. The existence of a coiled phragmocone-bearing coleoid in the Eocene significantly precedes Miocene records of Spirulirostra – a guard-bearing coleoid, which is suggested to be ancestral to Recent Spirula. A mosaic of morphological features in Amphispirula might point to an older and unknown ancestor of modern Spirula, but more likely represents a new evolutionary lineage within spirulid cehalopods. http://zoobank.org/urn:lsid:zoobank.org:pub:BF5D1CBB-4AD4-4B54-9B45-07E224B24CF3

Comprehensive analysis and reinterpretation of Cenozoic mesofossils reveals ancient origin of the snapping claw of alpheid shrimps

Alpheid snapping shrimps (Decapoda: Caridea: Alpheidae) constitute one of the model groups for inferences aimed at understanding the evolution of complex structural, behavioural, and ecological traits among benthic marine invertebrates. Despite being a super-diverse taxon with a broad geographical distribution, the alpheid fossil record is still poorly known. However, data presented herein show that the strongly calcified fingertips of alpheid snapping claws are not uncommon in the fossil record and should be considered a novel type of mesofossil. The Cenozoic remains analysed here represent a compelling structural match with extant species of Alpheus. Based on the presence of several distinct snapping claw-fingertip morphotypes, the major radiation of Alpheus lineages is estimated to have occurred as early as 18 mya. In addition, the oldest fossil record of alpheids in general can now be confirmed for the Late Oligocene (27–28 mya), thus providing a novel minimum age for the entire group as well as the first reliable calibration point for deep phylogenetic inferences.