Petr Budil

The ontogeny of Ellipsocephalus (Trilobita) and systematic position of Ellipsocephalidae

Laibl, L., Fatka, O., Budil, P., Ahlberg, P., Szabad, M., Vokáč, V. & Kozák, V., 24.3.2015. The ontogeny of Ellipsocephalus (Trilobita) and systematic position of Ellipsocephalidae. Alcheringa 39, 477–487. ISSN 0311-5518. Well-preserved early holaspid stages of the Cambrian Series 3 trilobites Ellipsocephalus hoffi (Schlotheim, 1823) and Ellipsocephalus polytomus Linnarsson, 1877 have been discovered in the Příbram-Jince Basin (Czech Republic) and Jämtland (Sweden), respectively. Both species show remarkable morphological changes during late ontogeny. The earliest holaspides share long genal spines, and long macrospines on the second thoracic segment. Whereas macrospines disappear abruptly in later stages, genal spines are progressively shortened. Consequently, the ontogeny of trilobites of Ellipsocephalidae is revised. The morphology of early meraspid cranidia and ontogenetic patterns in the disappearance of macrospines suggest that this family is closely related to members of Redlichiida rather than Ptychopariida. Lukáš Laibl [lukaslaibl@gmail.com] and Oldřich Fatka [fatka@natur.cuni.cz], Charles University, Institute of Geology and Palaeontology, Albertov 6, 128 43, Prague 2, Czech Republic; Petr Budil [petr.budil@geology.cz], Czech Geological Survey, Klárov 3, Prague 1, 118 21, Czech Republic; Per Ahlberg [per.ahlberg@geol.lu.se], Department of Geology, Lund University, Sölvegatan 12, SE-223 62 Lund, Sweden; Michal Szabad [geosz.pb@seznam.cz], Obránců míru 75, 261 02 Příbram VII, Czech Republic; Václav Vokáč [lichas@seznam.cz], Ke Kukačce 21, 312 00 Pilsen, Czech Republic; Vladislav Kozák [vlada.kozak@tiscali.cz], K Moravině 11/1689, 190 00 Prague 9, Czech Republic.

Intraspecific bimodal variability in eye lenses of two Devonian trilobites

Abstract. Arthropods are known to display a variable number of eye lenses and this number mostly increases during their development. In trilobites, most species possessing schizochroal eyes exhibit a notable intraspecific variation in the number of dorso ventral files of eye lenses that can be age related (i.e., growth) or not (i.e., living environment). Several previous studies have shown that some trilobite groups (e.g. phacopids) tend to have fewer lenses/files in representatives from the deeper habitats than those from shallower habitats. In this study, we analyzed the pattern of variation in the number of dorso ventral files of eye lenses in two Devonian phacopid trilobites from the Prague Basin of the Czech Republic. We quantified their intraspecific variability. To better understand the patterning, we compared more than 120 individuals. Data first reveal evidence of a bimodal distribution of lens/file number without intermediate forms among each of two studied populations of Prokops prokopi (Chlupáč, 1971) and throughout the ontogeny of Pedinopariops insequens (Chlupáč, 1977). Our results indicate that caution must be taken for taxonomical affiliation and biodiversity analyses of taxa in which the intraspecific variability is unclear. Additionally, we investigated possible relations of these bimodalities to the stratigraphical position of studied populations and to the paleoenvironment. In Prokops prokopi, a slightly different age of both populations, together with supposed differences in the local environments can be responsible for observed variability. In Pedinopariops insequens, stress conditions possibly related to the approaching onset of the Basal Choteč Event can be responsible for surprising intrapopulation variability. We speculate that the stress conditions could cause a bimodal selection and possibly also the change of ontogenetic trajectory within this species. Pedinopariops insequens was the only phacopid in the Prague Basin that crosses the Lower/Middle Devonian boundary and survived also the onset of Basal Choteč Event.

Juvenile phacopid trilobites from the Prague Basin (Czech Republic)

Complete early ontogenetic stages of phacopid trilobites are very rare in the fossil record worldwide. Although phacopid trilobites were a common component of the Devonian communities inhabiting the Prague Basin, only two articulated juvenile individuals have been described so far. However, rich and diverse fauna, including common remains of meraspid and young holaspid specimens of the phacopid Pedinopariops superstes superstes, has been found in the late Emsian Daleje Shale (Daleje-Třebotov Formation) at the Čeřinka Quarry near Bubovice. The rather unusual association of skeletal fauna in the Daleje Shale collected from the Čeřinka Quarry probably reflects the specific position of the locality, which corresponds to the transition from shale facies to carbonate facies. This newly described association contains common molted young holaspids, one entire meraspid specimen, and one poorly preserved but entire late meraspid–early holaspid specimen. The young individuals of P. superstes superstes strongly resemble the ancestral Pedinopariops degener; with the exception of their smaller eyes, they are somewhat reminiscent of the coarsely tuberculated descendent Pedinopariops superstes superior. The principal differences between the early stages of P. superstes superstes and the adult specimens include the relatively coarse tuberculation of the dorsal exoskeleton, which is more strongly vaulted and shows a less advanced level of eye development in young specimens. However, co-occurring adult specimens appear to be typical P. superstes. Here, the newly collected material is supplemented with a description of two as yet unreported remains of juvenile Pedinopariops superstes from other localities, and one well preserved specimen of an entire meraspid of Reedops cf. bronni, as well as a detailed discussion of the two previously described specimens of Pedinopariops insequens and Prokops hoeninghausi. Possible causes of an obvious paucity of articulated meraspid and young holaspid specimens when compared with adult and subadult ontogenetic stages in phacopid trilobites are discussed.KurzfassungVollständige frühontogenetische Entwicklungsstadien der phacopiden Trilobiten hinterließen weltweit sehr wenige fossile Reste. Obwohl die phacopiden Trilobiten ein häufiger Bestandteil der devonischen Assoziationen des Prager Beckens sind, wurden bisher nur zwei artikulierte juveniele Exemplare beschrieben. Die reiche und vielfältige Fauna, einschließlich der häufig vorkommenden Überreste der meraspiden und frühholaspiden Individuuen des Phacopides Pedinopariops superstes, wurde im Daleje Schiefer (Daleje-Třebotov Formation) des spät Emsiums in dem Steinbruch Čeřinka in der Nähe von Bubovice gefunden. Die relativ spezifische Assoziazion der skeletalen Fauna die im Steinbruch Čeřinka gefunden wurde, wiederspiegelt höchstwahrscheinlich die spezifische Lage der Lokalität, welche dem Übergang von schiefer Facies in kalkstein Facies entspricht. Die neulich beschriebene Assoziazion enthält häufig vorkommende junge Holaspiden, einen vollständigen Meraspiden und einen schlecht erhaltenen aber vollständigen spät meraspid- jung holaspid Exemplar. Bis auf die kleinen Augen, ähneln die jungen Individuen des P. superstes superstes, dem ancestralen P. degener sehr, ausserdem ähneln sie teilweise durch die grob tuberculare Oberfläche dem descendent P. superstes superior. Die wichtigsten Unterschiede zwischen frühen Stadien des P. superstes superstes und erwachsenem Individuen besteht in relativ grobe Tuberkeln auf dem stärker gewölbten dorsalen Exoskeleton und kleinerem Augen in jungen Exemplaren. Die gemeinsam vorkommenden reifen Individuen stimmen der Diagnose den typischen P. superstes zu. Das neulich gesammeltes Material ist mit zwei, bis jetzt nicht publizierten Resten des Pedinopariops superstes ergänzt, die aus anderen Fundstellen kommen, einem gut erhaltenem vollständigen Meraspiden von Reedops cf. bronni, sowie durch detailierte Diskussion der zwei schon früher beschribenen stadien von Pedinopariops insequens und Prokops hoeninghausi. Die möglichen Gründe für das Nichtvorhandensein der artikulierten Individuen der Meraspiden und Frühholaspiden von phacopiden Trilobiten werden diskutiert und verglichen.

Preservation of the digestive structures in Harpides (Trilobita) from the Lower Ordovician of the Barrandian area (Czech Republic)

Remains of the digestive system are described in the holotype of the rare harpidid trilobite Harpides grimmi Barrande, 1852 collected from the Lower Ordovician Milina Formation of the Prague Basin. The intestine (post-stomach alimentary canal) starts just behind the glabellar poste- rior margin and extends through the narrow axial region in all nineteen thoracic segments of this exceptionally preserved specimen. The anterior-most part of the digestive system is masked by the in situ hypostome preserved under the missing glabella. Similarly, also the posterior-most part of the post-stomach alimentary canal is absent, as the pygidium is not preserved. This specimen constitutes the first example of preserved digestive structures in the family Harpididae. Earlier finds of digestive system in Ordovician trilobites are briefly assessed.