[Palaeontology, Vol. 54, Part 2, 2011, pp. 397–415] THE CAPSULE: AN ORGANIC SKELETAL STRUCTURE IN THE LATE CRETACEOUS BELEMNITE GONIOTEUTHIS FROM NORTH-WEST GERMANY by LARISA A. DOGUZHAEVA and STEFAN BENGTSON Department of Palaeozoology, Swedish Museum of Natural History, PO Box 50007, SE-104 05 Stockholm, Sweden; e-mails [email protected]; [email protected] Typescript received 7 February 2009; accepted in revised form 1 June 2010 Abstract: An unusual, bilaterally symmetrical black struc- A flare along the periphery of the alveolus marks a region ture that embraces the protoconch and the phragmocone where the rostrum was not yet formed, suggesting that the and is overlain by a rostrum has been studied in the Santo- capsule extended beyond the rostrum. Modification of the nian–early Campanian (Late Cretaceous) belemnite genus skeleton in Gonioteuthis comprises a set of supposedly inter- Gonioteuthis from Braunschweig, north-west Germany. The related changes, such as innovation of the organic capsule, structure is here named the capsule. Energy dispersed spec- partial elimination of the calcareous rostrum and a diminish- trometry analyses of the capsule show a co-occurrence of sul- ing of the pro-ostracum, resulting in the appearance of a phur with zinc, barium, iron, lead and titanium, suggesting new type of pro-ostracum that became narrower and shorter their chemical association. The capsule was originally made and lost the spatula-like shape and gently curved growth of organic material that was diagenetically transformed into lines of a median field that are typical for the majority of sulphur-containing matter. The material of the capsule dif- Jurassic and Cretaceous belemnites. The partial replacement fers from the chitin of the connecting rings in the same spec- of a calcareous rostrum with an organic capsule in belemni- imens. The capsule has a complex morphology: (1) ventral tellids may have been an adaptive reaction to an unfavour- and dorsal wing-like projections that are repeated in a brevi- able environmental condition, perhaps related to difficulties conic shape of the alveolus, (2) an aperture with lateral lobes in calcium carbonate secretion during the Late Cretaceous and ventral and dorsal sinuses copied by growth lines and that forced animals to reduce carbonate production and to (3) a ventral ridge that fits with the position of the fissure in secret an organic capsule around the protoconch and the the rostrum. The alveolus in the most anterior part of the phragmocone. rostrum is crater-like. It is lined with thin, pyritized, lami- nated material, which appears to be the outermost portion Key words: Germany, Late Cretaceous, cephalopods, cole- of the capsule attached to the inner surface of the rostrum. oids, belemnites, shell ultrastructure, organic skeleton. T he pioneering Early Carboniferous members of the belemnites, the rostra lack their anterior part (see Chris- Belemnoidea can be recognized by the presence of a tensen 1975, 1997a; Christensen and Schulz 1997; Kosˇtˇa´k rostrum (Flower 1945; Flower and Gordon 1959), an ink 2005; Kosˇtˇa´k and Wiese 2008). These belemnites represent sac and arm hooks (Mapes et al. 2007, 2010). From that fewer than ten genera of the family Belemnitellidae time until the Jurassic, the rostrum went through signifi- Pavlow, 1914, which was the only existing family in the cant morphological and ultrastructural transformations, northern hemisphere from the Late Cenomanian to the but without attaining the characteristics of the rostrum in latest Maastrichtian (see Christensen 1997b). Two more Jurassic to Cretaceous belemnoids. The rare Hettangian peculiar features of the rostrum in the belemnitellids are (earliest Jurassic) small-sized rostra supposedly mark the the ventral fissure and the vascular imprints on the sur- rising of the order Belemnitida (Schwegler 1939; Weis face (see Jeletzky 1950, fig. 1; Christensen 1975, fig. 22, and Delsate 2005; Weis and Mariotti 2008). Through the pl. 12, figs 1–4; Christensen and Schulz 1997, fig. 69A–D, Early Jurassic, the rostra became larger, more diverse in pls 1–3). The selective postmortem destruction of the shape and more widely distributed geographically. Most alveolar part of the rostrum in belemnitellids points out Jurassic to Cretaceous belemnites retained the radial-con- an unknown structural peculiarity that made this part of centric structure of the rostra. In some Late Cretaceous the rostrum less resistant to fossilization than the rest of ª The Palaeontological Association doi: 10.1111/j.1475-4983.2010.01027.x 397 398 PALAEONTOLOGY, VOLUME 54 the rostrum. The missing part of the rostrum was trum. This study was aided using scanning electron believed to be originally built up either of some unstable, microscopy and energy dispersive spectrometry. presumably organic material, which was lost during fossil- The genus Gonioteuthis populated the Central European ization (Saemann 1861–1862; Schlu¨ter 1876; Moberg Subprovince in the late middle Coniacian–early Campa- 1885; Crick 1904; Naidin 1964; Christensen 1975) or of nian and rarely reached also the northernmost part of the aragonite that was not preserved (Bandel and Spath 1988; Tethyan Realm (Jeletzky 1950; Christensen 1997a, b). The Barskov et al. 1997; Christensen 1997a; Kosˇtˇa´k and Wiese presence of the capsule indicates the partial substitution 2008). Since then, the hypothesis of an organic composi- of calcareous material of the rostrum with an organic tion of the alveolus part of the rostrum has remained substance. This change in skeletal material may have been untested and no observations supporting it have been an adaptive reaction to an environment in the Central reported. The idea of an aragonitic composition of the European Subprovince during the Late Cretaceous that alveolar part of the rostrum is based on stable-isotope was possibly unfavourable to calcium carbonate secretion data from the Turonian in northern Siberia showing con- (see Worsley 1971). sistently high d18O values in the belemnite rostra and lower values in the co-occurring calcitic shells of gastro- pods and inoceramids, as well as different 13C contents in MATERIAL AND METHODS the alveolus and postalveolar parts, respectively (Naidin et al. 1987; Barskov et al. 1997; Dauphin et al. 2007). The belemnites under examination, purchased in Ger- A perishable substance of unknown composition lining many in the beginning of the twentieth century, are now a pseudoalveolus (an unusually shortened alveolus typical housed at the Department of Palaeozoology of the for belemnitellid genera Praeactinocamax Naidin, Actinoc- Swedish Museum of Natural History. Their original labels amax Miller, Goniocamax Naidin, Gonioteuthis Bayle, contain the following information: ‘Actinocamax granula- Belemnellocamax Naidin) and continuing a calcareous tus Blainv., Upper Cretaceous, Braunschweig; Collegium rostrum was discovered in the belemnitellid belemnite Coralinum, Braunschweig’. Judging from the distribution Gonioteuthis granulata (de Blainville) and briefly of Gonioteuthis granulata in northern Germany, the speci- described by Ernst (Ernst 1964, pp. 156–157). Based on mens must have come from Santonian to lower Campa- his observations, Ernst concluded that the perishable sub- nian strata (Christensen 1976). stance was associated with the pseudoalveolus, and the Twenty fragmentary rostra are available for study; their latter was an original shell character rather than a post- maximum diameter is 12 mm, and the maximum pre- mortem broadening of the alveolus. Since then, this idea served length is 68 mm; seven rostra preserve the alveolus has attracted little attention. with a fragmentary phragmocone inside. Initially, the cap- Shells of Gonioteuthis preserving what could be referred sule was noticed in the alveolus because of its black col- to as ‘a perishable substance of unknown composition our, which contrasts with the brown hue of the rostrum. lining a pseudoalveolus’ (Ernst 1964, pp. 156–157) have The specimens were split longitudinally to expose the been recovered in collections of the Department of Palae- alveolus and to access the site of the potentially preserved ozoology, Swedish Museum of Natural History. They structure. Because of the ventral fissure of the rostrum, come from Braunschweig, north-west Germany. The pres- the longitudinal fracture usually runs in the sagittal plane. ent article reports our recent study on this enigmatic, In four of the split specimens, a protoconch was exposed rarely observed skeleton structure. This originally organic as well. The portions of rostra that revealed morphologi- skeletal element – here named a capsule – embraces the cal features of the structure under study, such as a black protoconch and phragmocone and is overlain by the ros- material and curved growth lines, were examined in a EXPLANATION OF PLATE 1 Figs 1–7. Gonioteuthis granulata, Santonian–early Campanian, Late Cretaceous; Braunschweig, north-west Germany; NRM-PZ Mo. 8183, a ventro-dorsally split specimen. 1, general view of the phragmocone surrounded by the capsule showing ventral (left) and dorsal (right) wing-like projections on the longitudinal fracture of the rostrum; scale bar represents 5 mm. 2, view of orad end of the capsule and surrounding alveolus of the rostrum; scale bar represents 5 mm. 3, enlarged detail of 1 to show the ventral portion of the capsule-bearing longitudinal ridges and adjoined part of the fissure; scale bar represents 500 lm. 4, enlarged detail of 3 to show that material of the capsule continues into the material lining the fissure; scale bar represents 250 lm. 5, enlarged detail of 3 showing a cross section of the capsule and its granular ultrastructure; scale bar represents 25 lm. 6, a fragment of the thin conotheca with a mural ring of a septum; scale bar represents 100 lm. 7, enlarged detail of 1, a granular ultrastructure of the dorsal wing-like projection of the capsule; scale bar represents 100 lm. PLATE 1 1 2 3 4 5 6 7 DOGUZHAEVA and BENGTSON, Gonioteuthis granulata 400 PALAEONTOLOGY, VOLUME 54 scanning electron microscope (Hitachi S-4300) equipped ues along the chamber length and forms the phragmo- with an energy dispersive spectrometer (EDS).