Diversity dynamics of ammonoids during the latest Bajocian and Bathonian (Middle Jurassic) in the epicratonic Polish Basin

Results of the analysis of Middle Jurassic (latest Bajocian–Bathonian) ammonoid diversity patterns in the Polish Basin are reported. The data used in this study are based on a large number of ammonoid specimens, collected bed-by-bed, from the Polish Jura in south-central Poland, as well as on existing literature. The ammonoid diversities, both at the genus and species levels, have been calculated for particular ammonite zones and subzones and compared with the regional transgressive–regressive cycles for the Polish Lowlands and Hallam’s global sea-level curve. The patterns of ammonoid diversity dynamics seem to be well correlated with global sea-level fluctuations. Particular diversity peaks correspond with major transgressive episodes. Three main regional bio-events related to transgressions have been distinguished for the Polish Basin: (1) the Latest Bajocian (Bomfordi Subchron) bio-event is related to a short-lasting immigration of Tethyan ammonoids; (2) a late Early Bathonian (Tenuiplicatus Chron) bio-event corresponds to a proliferation of Asphinctites tenuiplicatus (Brauns), most probably as a result of transgression-driven eutrophication of a shallow-marine environment; during this time, the immigration (passive dispersion?) of some single Tethyan species is also observed; and (3) a Late Bathonian (Hodsoni and Orbis chrons) bio-event corresponds to the highest ammonoid species diversity peaks and most probably is related to the major transgression during the Bathonian, which allowed easy migration of several species via several newly opened sea-ways

Insight into tube-building behaviour and palaeoecology of some agglutinating worms from the Upper Devonian of Nevada, USA

Agglutinated worm tubes from the Upper Devonian of the Devils Gate section in Nevada, USA are reported for the first time, filling a major gap in their Palaeozoic fossil record. Two small (5 mm and 6.7 mm in length) tubes are composed entirely of tentaculitid shells, and one large tube (55 mm in length) is formed from particles including ostracode carapaces, echinoderm ossicles, tentaculitid shells and putative bryozoan fragments aligned perpendicularly to the tube’s long axis. The tubes, in particular the large one have a cylindrical, curved and tapering tube morphology that is very similar to that of modern agglutinating polychaetes of the families Terebellidae and Pectinariidae. The large tube is dominated by objects that fall within a certain size-range, and although built from different types of particles, echinoderm ossicles are prevalent in the posterior part, whereas ostracode carapaces dominate in the middle and anterior parts of the tube. Tentaculitid shells are relatively rare in the large tube, despite being abundant in the surrounding host deposit. The faunal assemblage composing the tube suggests that the worm animal was rather specific in its selection of particles with a certain morphology. This is common behaviour amongst many modern agglutinating terebellid and pectinariid polychaetes. The preservation of such fragile tubes was enhanced by rapid burial, likely caused by gravity flow of sediment in a deep-slope setting

First Record of Soft Tissue Preservation in the Upper Devonian of Poland

Soft tissue preservation is reported from Upper Devonian deposits of the Holy Cross Mountains, central Poland, for the first time. The preserved soft tissues are muscles associated with arthropod cuticle fragments. The muscles are phosphatized with variable states of preservation. Well-preserved specimens display the typical banding of striated muscles. Other muscle fragments are highly degraded and/or recrystallized such that their microstructure is barely visible. The phosphatized muscles and associated cuticle are fragmented, occur in patches and some are scattered on the bedding plane. Due to the state of preservation and the lack of diagnostic features, the cuticle identification is problematic; however, it may have belonged to a phyllocarid crustacean. Taphonomic features of the remains indicate that they do not represent fossilized fecal matter (coprolite) but may represent a regurgitate, but the hypothesis is difficult to test. Most probably they represent the leftover remains after arthropod or fish scavenging. The present study shows that soft tissues, which even earlier were manipulated by scavenger, may be preserved if only special microenvironmental conditions within and around the animal remains are established

Coincidence of photic zone euxinia and impoverishment of arthropods in the aftermath of the Frasnian-Famennian biotic crisis

The lowermost Famennian deposits of the Kowala quarry (Holy Cross Mountains, Poland) are becoming famous for their rich fossil content such as their abundant phosphatized arthropod remains (mostly thylacocephalans). Here, for the first time, palaeontological and geochemical data were integrated to document abundance and diversity patterns in the context of palaeoenvironmental changes. During deposition, the generally oxic to suboxic conditions were interrupted at least twice by the onset of photic zone euxinia (PZE). Previously, PZE was considered as essential in preserving phosphatised fossils from, e.g., the famous Gogo Formation, Australia. Here, we show, however, that during PZE, the abundance of arthropods drastically dropped. The phosphorous content during PZE was also very low in comparison to that from oxic-suboxic intervals where arthropods are the most abundant. As phosphorous is essential for phosphatisation but also tends to flux off the sediment during bottom water anoxia, we propose that the PZE in such a case does not promote the fossilisation of the arthropods but instead leads to their impoverishment and non-preservation. Thus, the PZE conditions with anoxic bottom waters cannot be presumed as universal for exceptional fossil preservation by phosphatisation, and caution must be paid when interpreting the fossil abundance on the background of redox conditions

Middle Jurassic cyclostome bryozoans from the Polish Jura

New collections of bryozoans from the Middle Jurassic (Late Bajocian and Bathonian) of Poland add significantly to our knowledge of the diversity and biogeography of the Cyclostomata at a time when they were the dominant bryozoan order in the fossil record. A total of 16 species and one form-genus ("Berenicea") are present. Most are encrusters, predominantly on hiatus concretions. A single erect species was found in deposits interpreted as regurgitates of a marine vertebrate. The following new species are described: Microeciella annae sp. nov., M. kuklinskii sp. nov., M. maleckii sp. nov., M. mokrskoensis sp. nov., M. magnopora sp. nov., Reptomultisparsa harae sp. nov., and Hyporosopora bugajensis sp. nov. The taxonomic importance of the morphology of both the gonozooids and pseudopores is underlined, especially for encrusting species of the "Berenicea" type that are otherwise difficult to distinguish from one another. The described bryozoan assemblage encrusting hiatus concretions from the Polish Middle Jurassic is the richest that has been documented globally from this kind of substrate

Microconchids of the species Microconchus valvatus (Munster in Goldfuss, 1831) from the Upper Muschelkalk (Middle Triassic) of Germany

In the present paper, the commonly mentioned but poorly recognised microconchid species Microconchus valvatus (Münster in Goldfuss, 1831) is redescribed on the basis of material from the Upper Muschelkalk of Germany. ESEM studies of the microconchid tubes with clear morphological and microstructural characters were compared to the existing known Triassic species. Microconchus valvatus is characterised by fine growth lines and transverse riblets. ESEM analysis shows that tubes which appear smooth under the binocular microscope are in fact abraded. Thus, taphonomy must be taken into account and scanning microscopy must be used during studies of microconchid tubes. Quantitative ecology shows that particular microconchid populations developed various size ranges punctuated by some gaps, have non-normal distributions as expected in time-averaged assemblages, and suggests that differences among populations may reflect distinct hydrologic settings. This study provides a multidimensional investigation of microconchids and offers compelling evidence that microconchids were an important faunal group during the post-recovery Middle Triassic interval

A new microconchid species from the Silurian of Baltica

The diversity of Silurian microconchids is still poorly understood. Here, a new microconchid tubeworm species, Palaeoconchus wilsoni, is described from the Silurian (Ludlow) encrusting rugose corals from Estonia (Saaremaa Island) and a brachiopod shell from Sweden (Gotland). In Estonia, the microconchids are a dominant constituent of the encrusting assemblages, associated with cornulitids, Anticalyptraea, auloporids, trepostome bryozoans, hederelloids and enigmatic ascodictyids. It is notable that these Silurian encrusting assemblages are clearly dominated by tentaculitoids (microconchids, cornulitids and Anticalyptraea) which very often co-exist on the same coral host. Morphologically similar microconchids and Anticalyptraea may have exploited a more similar ecological niche than the straight-shelled cornulitids. However, the clear predominance of microconchids over Anticalyptraea in the communities may indicate that this genus was a less effective competitor for food than microconchid tubeworms

Encrustation patterns on Late Cretaceous (Turonian) echinoids from southern Poland

This study focuses on sclerobionts from a large collection of epibenthic echinoids ([2,000 specimens) of the genera Conulus and Camerogalerus. Samples were collected from five localities in southern Poland (Polish Jura and Miecho´w Trough), where Turonian carbonates with terrigenous input are exposed. Low intensity (mean ca. 5 %, maximum ca. 10 %) and slight encrustation (‘‘loosening effect’’) exclusively by episkeletozoans probably resulted from low productivity of encrusters while the importance of other factors cannot be excluded unambiguously. Echinoids served as a main substratum and after death formed shellgrounds (‘echinoid carpet’) offering abundant benthic islands for encrusters in an otherwise soft-bottom environment. The moderate abundance but low-diversity assemblage is represented by bivalves, sedentary polychaetes, foraminifera, bryozoans, corals, and sponges. This assemblage is similar to a nearly contemporaneous assemblage from the Bohemian Basin. The presence of numerous spirorbins offers insights into their early evolution and may indicate that their first peak in abundance after origination was not prior to the earliest Turonian. This is regarded as one of the important ecological steps towards the rise of modern sclerobiont communities. Encruster diversities are independent of their abundance and, as shown in our novel planar projections, lateral parts of tests were preferentially encrusted. This pattern is explained by the combination of largest flat area and stable orientation. Encrusting bivalves and serpulids dominated hard substrate environments in the Turonian of Poland

Late Triassic charophytes around the bone-bearing bed at Krasiejów (SW Poland) – palaeoecological and environmental remarks

Thousands of Late Carnian (Late Triassic) charophyte gyrogonites belonging to four species [Stellatochara germanica KOZUR & REINHARDT, Stomochara starozhilovae (KISIELEVSKY), Stenochara kisielevskyi BILAN and Porochara triassica (SAIDAKOVSKY)] occur in the beds around the vertebrate-bearing level at Krasiejów, SW Poland. The abundant and wellpreserved gyrogonites generally attest to fossilization in situ. Information about the habitat of recent charophytes is useful for reconstruction of their past environments. The factors limiting the habitat of modern charophytes suggests that these algae, and other micro- and macrofauna sedimented within the bone-bearing bed, lived in a shallow, freshwater environment (probably lacustrine). Above the bone bed, there is a rapid drop in gyrogonite abundance. This could have been caused by changes in environmental conditions: increase in salinity, or increase in water energy. The preliminary mineralogical data suggest arid to semi-arid climate

Sexual dimorphism in the Bathonian morphoceratid ammonite Polysphinctites tenuiplicatus

Asphinctites tenuiplicatus [M] and Polysphinctites secundus [m] from the Asphinctites tenuiplicatus Zone (Early Bathonian), are usually considered as a sexual dimorphic pair, although authors describe them as separate species. We used statistical methods to test the sexual dimorphic correspondence between those morphospecies, based on a rather large sample of well-preserved macro- and microconchs derived from a single horizon of calcareous concretions in the Polish Jura. Our results indicate that both dimorphs or sexes have identical ontogeny up to a critical diameter, from which they diverge towards the characteristic morphology and sculpture of each dimorph. Thus, both dimorphs are described as a single species: Polysphinctites tenuiplicatus [M and m]. After review of the several nominal species usually assigned to the genera Asphinctites and Polysphinctites throughout their stratigraphic and biogeographic range in the Early Bathonian of the Tethys, it is concluded that they actually correspond to only two species of a single lineage. The corresponding name for the lineage should be Polysphinctites (= Asphinctites as a junior synonym)