The middle Smithian (Early Triassic) ammonoid Arctoceras blomstrandi

The ammonoid genus Arctoceras (Hyatt) occurs across all palaeolatitudes, and is a key genus for middle Smithian biostratigraphical correlations globally. In this study, intraspecific variations in conch morphology, ornamentation and allometry are examined in relation to stratigraphic position. Arctoceras is the most abundant ammonoid genus in the middle Smithian of Svalbard. Originally, seven Arctoceras species were described from Svalbard. Later, as the importance of intraspecific variation was recognized, six of the Arctoceras species from Svalbard were treated as junior synonyms of Arctoceras blomstrandi (Lindström). Yet, the variations in A. blomstrandi conch morphology remain poorly quantified and the dependence on stratigraphic position, unknown. We quantify the intraspecific variation in conch morphology, ornamentation and allometry in relation to stratigraphy of the Svalbard Arctoceras. The results support the assignment of all Arctoceras morphotypes from Svalbard to a single species A. blomstrandi. The new data allow for an updated species description and open the way for the use in biostratigraphy of the endmember morphology A. blomstrandi var. costatus. We document consistent changes in conch morphology and ornamentation in the studied stratigraphic interval, with a distinct shift towards more evolute and ornate conchs in the top of the interval. The trends in the strength of ornamentation are partly explained by covariation with conch morphology (Buckman's law). The most marked shift in the conch morphology and allometric development of A. blomstrandi coincides with the onset of the positive carbon isotope excursion at the end of the middle Smithian, but pre‐dates the mid–late Smithian cooling of the sea surface

Triploporella remesi (Steinmann, 1903), dasycladalean green alga from the Tithonian-Lower Berriasian of tramberk (Czech Republic) revisited

The dasycladalean green alga Triploporella remesi (Steinmann) is redescribed based on material collected from the Kotouč quarry near Štramberk (Moravia, Czech Republic), probably corresponding to the type locality. The alga is Tithonian–early Berriasian in age according to the age assigned to the Štramberk Limestone. The new material, in addition to the detailed description of Steinmann, indicates that the short club-shaped calcareous skeleton probably represents the fertile upper part of a far longer club-shaped thallus. The well-developed phloiophorous primary laterals are similar to those of other species of Triploporella in having a proximal cylindrical sterile part followed by a stronger distal cylindrical fertile part. Secondary phloiophorous laterals probably combined to create a cortex at their distal ends. The simple undivided spores inferred by previous authors are shown to be recrystallized cyst containers.Web of Science52339439