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Exoskeletal Structures and Ultrastructures in Lower Devonian Dalmanitid Trilobites of the Prague Basin (Czech Republic)

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Exoskeletal Structures and Ultrastructures in Lower Devonian Dalmanitid Trilobites of the Prague Basin (Czech Republic) Exoskeletal structures and ultrastructures in Lower Devonian dalmanitid trilobites of the Prague Basin (Czech Republic) PETR BUDIL & FRANTIEK HÖRBINGER Our current studies of the exoskeletal structures and ultrastructures in Lower Devonian dalmanitid trilobites of the Prague Basin are briefly described and discussed. The interior of the exoskeleton in most specimens from the Prague Ba- sin is recrystallised and largely filled with very fine homogeneous sparitic cement. The ultrastructures sensu stricto, e.g., the lamination, layers forming the exoskeleton, and the fine pores or “Osmólska” cavities, are mostly imperceptible even at higher magnifications. However, ultrastructural relics were observed in some polished thin sections and exoskeletal fragments using electron microscopy. Larger structures, especially the eyes, the megapores penetrating the exoskeleton, and the surface sculptures (prosopon sensu Gill 1949), are relatively well preserved and show very fine details. The bio- logical significance of megapores is briefly discussed. Modification of the inner parts of the exoskeletons by diagenetic processes, obscuring most of the fine internal structures, is evident. • Key words: Trilobita, Dalmanitidae, exoskeleton microstructure. BUDIL,P.&HÖRBINGER, F. 2007. Exoskeletal structures and ultrastructures in Lower Devonian dalmanitid trilobites of the Prague Basin (Czech Republic). Bulletin of Geosciences 82(1), 27–36 (4 figures, 1 table). Czech Geological Survey, Prague. ISSN 1214-1119. Manuscript received January 17, 2007; accepted in revised form March 7, 2007; issued March 30, 2007. • DOI 10.3140/bull.geosci.2007.01.27 Petr Budil, Czech Geological Survey, Klárov 3, 118 21, Praha 1, Czech Republic; [email protected] • František Hörbinger, Ke Zdravotnímu středisku 120, 155 00 Praha 5, Czech Republic; [email protected] The inner and outer fine structures and ultrastructures of 1993), only a few papers have discussed this topic using the trilobite exoskeleton, including visual organs, have the rich and apparently well preserved trilobite material been studied since the end of the nineteenth and the first from the Prague Basin (Barrandian area, Czech Republic). half of the twentieth century (Lindström 1901, Størmer Šnajdr (1980, 1985, 1987) and Chlupáč (1977) employed 1930). However, modern equipment such as the electron the surface exoskeletal sculpture as a useful systematic fe- microscope and X-ray analysis have proved to be very use- ature, and also defined some new terms (for example “me- ful in the investigation of these structures since 1960. This gapores” by Šnajdr 1985, 1987). Both authors discussed especially concerns the distinction of diagenetic structures many of the surface structures in detail, but without using from the original constitution of the exoskeleton and the fi- electron microscopy or thin sections for their study. Only nest ultrastructure of the exoskeletal fabric (see Dalingwa- one work, which is an unpublished thesis (Kasan 1997), ter 1973; Osmólska 1975; Teigler & Towe 1975; Miller deals in more detail with the sculpture of Bohemian Lo- 1976; Dalingwater & Miller 1977; Miller & Clarkson wer Devonian phacopid trilobites. In that thesis, electron 1980; Dalingwater et al. 1993, 1991; Størmer 1980; Mut- microscope images were used for the first time in the vei 1981; McAllister & Brand 1989; Wilmot & Fallick study of trilobites (Pl. V, figs 1–8 in Kasan 1997), and the 1989; Wilmot 1990a, b; Fortey & Wilmot 1991). These in- very poorly preserved, but probably present, lamination vestigations were reviewed and discussed in detail by of the exoskeleton in Reedops decorus (Hawle & Corda, Whittington & Wilmot in Kaesler et al. (1997) and by 1847) was briefly discussed. In the present paper, the re- Fortey & Owens (1999). Aside from the excellent studies sults of a test study of the presence of exoskeletal fine of eyes in Ananaspis Campbell, 1967, Reedops R.&E. structures and ultrastructures in Lower Devonian dalma- Richter, 1925 and Ormathops Delo, 1935 undertaken by nitid trilobites are presented. This preliminary study ac- Clarkson (1969, 1971), and some comparative studies of companies the systematic revision of this group (Budil et Dalmanitina Reed, 1905 (Clarkson 1968, Clarkson & al. in press), and therefore does not go into great detail. Levi-Setti 1975, Levi-Setti 1993, Horváth & Clarkson The present paper serves as an introduction and an asses- 27 Bulletin of Geosciences Vol. 82, 1, 2007 sment of the potential of the material for further study. Ne- Table 1. A review of studied samples. Abbreviations: NP – Number of vertheless, some of the observations discussed here pro- polished and covered thin sections, NS – Number of samples observed with electron microscope vide new information on dalmanitid morphology. Some exoskeletal structures, including eye structures of Silurian Species Formation NP NS and Devonian dalmanitid trilobites outside the Barrandian Odontochile hausmanni (Brongniart, 1822) Praha 24 1 area, have already been discussed by previous authors, Odontochile cristata Hawle & Corda, 1847 Praha 8 2 such as Campbell (1975, 1977) and Levi-Setti (1993). Reussiana reussi (Barrande, 1846) Praha 3 1 Zlichovaspis (Z.) rugosa rugosa (Hawle & Praha 7 0 Provenance of the material and methods Corda, 1847) Zlichovaspis (Z.) rugosa laura Šnajdr, 1985 Praha 11 1 A total of seventy-six thin sections and thirteen electron Zlichovaspis (Z.) auriculata (Dalman, 1826) Zlíchov 5 2 microscope samples of the fourten species from the Praha Zlichovaspis (Z.) cf. marieva (Šnajdr, 1985) Zlíchov 4 0 Zlichovaspis (Z.) spinifera spinifera and Zlíchov formations (Lower Devonian, Pragian and Praha 8 0 Emsian stages) have been studied (Tab. 1). (Barrande, 1846) Zlichovaspis (Z.) spinifera nomiona (Šnajdr, These species were selected as being representative of Praha 0 1 1987) the twenty-five dalmanitid species present in this strati- Zlichovaspis (Z.) vaneki nom. nud. (Budil et Zlíchov 0 1 graphic interval. Relatively simple methods were used in al., in press) this initial stage of investigation. The polished and cov- Zlichovaspis (Z.) tuberculata (Hawle & Zlíchov 2 0 ered thin sections were observed under a NIKON SMZ Corda, 1847) 1500 optical microscope, while broken exoskeletal frag- Zlichovaspis (Devonodontochile) maccoyi Zlíchov 4 3 ments (useful especially for the observation of fine sur- (Barrande, 1852) face details) were studied a with CamScan CS 3200 elec- Zlichovaspis (Devonodontochile) vigerle Zlíchov 0 1 tron microscope. The samples selected for electron (Šnajdr, 1987) microscope observation were coated with Au-Pd powder Zlichovaspis (Z.) sp. Zlíchov 1 0 in a vacuum chamber. The methodology developed by Dalingwater & Miller (1977) using etched polished thin sections or broken exoskeletal fragments with EDTA (di- Description and discussion sodium salt) was not used during this stage of the work. The use of such etching techniques and the testing of other Exoskeletal fine structures and ultrastructures methods is planned for a subsequent phase of the investi- gations, which will be focussed on inner exoskeletal ultra- The internal structures of the exoskeleton in most of the structures. A short description of all figured specimens samples have been almost entirely effaced by recrystallisa- is presented in the next section and in the figure captions. tion and by the homogeneous fine sparitic or microsparitic All figured and cited samples are housed in the palae- matrix that fills all spaces inside the former exoskeleton. ontological collections of the Czech Geological Survey So far, no absolutely certain remains of the prismatic outer (CGS). layer (see Dalingwater et al. 1991) have been observed. Figure 1. A–Odontochile hausmanni (Brongniart, 1822), Černá rokle near Kosoř, CGS PB 190. Vertical section through the pygidial axis, a detail of prominent interring processes (apodemes). × 5. • B – Odontochile hausmanni (Brongniart, 1822), Velká Chuchle, Přídolí, CGS PB 191. Vertical section through the slightly disarticulated thorax at the margin of axial part, showing imbricated segments with prominent apodemes. × 6.•C–Odontochile cristata Hawle & Corda, 1847, Praha-Konvářka, CGS PB 192. Vertical section through pygidium in axial part, the fine spiny granules possess a fine pore in the centre. × 36. • D – Odontochile hausmanni (Brongniart, 1822), Černá rokle near Kosoř, CGS PB 193. Vertical section through the pygidial axis, a detail of the interring process. × 21.•E–Zlichovaspis (Devonodontochile) maccoyi (Barrande, 1852), Lužce, CGS PB 194. Vertical section through the pygidial axis with perceptible interring processes and with distinctive perforation of the exoskeleton by megapores. × 26.•F–Odontochile hausmanni (Brongniart, 1822), Velká Chuchle, Přídolí, CGS PB 195. Detail of cross section of left pygidial margin with short fine spines and part of doublure. Note the “lamination” of the doublure (probably an artefact of polishing) in contrast with homogeneous structure of the dorsal exoskeleton. × 21.•G– Zlichovaspis (Z.) rugosa laura Šnajdr, 1985, Branžovy near Loděnice, CGS PB 196. Vertical section through the pygidial axis, detail of prominent inter- ring process. × 12. • H – Zlichovaspis (Z.) cf. marieva (Šnajdr, 1985), Švagerka, CGS PB 197. Vertical section through the pygidial axis with prominent interring processes. × 21. • I, K–N – Odontochile hausmanni (Brongniart, 1822), Černá rokle near Kosoř, CGS PB 198. Vertical sections through the eyes, showing lenses separated by interlensal sclera.I–×14,K–×36,L–×31,M–×11,N–×11.•J–Odontochile
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