2022 | 75/2 | 189–198 | 4 Figs. | 1 Tab. | www.geologia-croatica.hr Journal of the Croatian Geological Survey and the Croatian Geological Society 1. INTRODUCTION Abnormalities and malformations provide a unique insight into the palaeobiology and regenerative abilities of animals, including trilobites (BABCOCK, 2003). The fossil record of trilobites in par­ ticular contains numerous examples of morphological abnormali­ ties that have been variously interpreted. OWEN (1985) reviewed all earlier documented trilobitic abnormalities and suggested three types: injuries, pathologies, and teratologies. OWEN (1985), Healed injury in a nektobenthic trilobite: “Octopus-like” predatory style in Middle Ordovician? Oldřich Fatka1, Petr Budil2 and Radek Mikuláš3 1 Charles University, Institute of Geology and Palaeontology, Albertov 6, CZ–128 43, Prague 2, Czech Republic; (fatka@natur.cuni.cz) 2 Czech Geological Survey, Klárov 3, 118 21 Prague 1, Czech Republic; (petr.budil@geology.cz) 3 Academy of Sciences of the Czech Republic, Institute of Geology, v.v.i., Rozvojová 269, CZ–165 02 Praha 6 – Lysolaje, Czech Republic; (mikulas@gli.cas.cz) doi: 10.4154/gc.2022.17 Abstract The Lower Paleozoic sediments of the Barrandian area are globally renowned as a classical ex- ample of well-preserved skeletal marine fauna, including abundant remains of trilobites. Seve ral tens of morphologically anomalous exoskeletons of trilobites have been collected and docu- mented from Cambrian to Devonian clastic sediments and carbonates. One of them, an excep- tionally well preserved, articulated and partly enrolled exoskeleton of the Ordovician nektoben- thic trilobite Parabarrandia bohemica (NOVÁK, 1884) exhibits a prominent palaeopathological anomaly in its pygidium. We interpret this anomaly as a healed traumatic injury and attribute this damage to a failed predatory attack. The subsequently healed injury is classified as the ichno- genus Oichnus BROMLEY, 1981. The structure on the pygidium is strongly reminiscent of inju- ries caused by octopods and a large cephalopod is proposed as a potential durophagous pred- ator responsible for the herein described trilobite injury. However, an attack from an unknown arthropod while the trilobite was in a soft-shelled stage cannot be excluded. BABCOCK (1993, 2003, 2007), FATKA et al. (2015), BICKNELL & PATERSON (2018), BICKNELL & PATES (2020) concluded that the majority of trilobite abnormalities represent healed injury. The general rarity of repaired injuries in trilobites suggests that predatory attacks (particularly on soft­shelled individuals) were often successfully executed (BICKNELL & PATERSON, 2018). In the Barrandian area, the study of anomalous trilobite exo­ skeletons has a long tradition. BARRANDE (1852, pl. 9, FIG. 19) 1. Fatka 2. Šimunek 3. Kurtanjek 4. Marković 5. Ratković 6. Schnaider 7. Borojević-Šostarić Article history: Manuscript received December 07, 2020 Revised manuscript accepted March 16, 2022 Available online June 23, 2022 Keywords: Trace fossils, Palaeopathology, Praedichnia, Barrandian area, Prague Basin, Czech Republic Figure 1. Location of the Prague Basin. A. Map of Europe showing the Czech Republic, B. Map of the Czech Republic with the location of the Prague Basin. The studied specimen comes from the Šárka locality, C. Detailed geographical position of the named localities within the Prague Basin. Localities: 1 – Osek, 2 – Čilina, 3 – Svatá Dobrotivá, 4 – Králův Dvůr, 5 – Drabov, 6 – Brdatka, 7 – Veselá, 8 – Malé Přílepy, 9 – Libuš, 10 – Hodkovičky, 11 – Michle, 12 – Spořilov, 13 – Jinonice, 14 – Šárka, 15 – Hloubětín and Štěrboholy. G eo lo gi a C ro at ic a Geologia Croatica 75/2190 Ta bl e 1. S um m ar y of tr ilo bi te s w ith a bn or m al iti es d oc um en te d fro m th e O rd ov ic ia n of th e Ba rr an di an a re a Sp ec ie s A no m al y / c ul pr it of th e at ta ck Co nt rib ut io n St ra tig ra ph y / l oc al ity (F ig s 1 a nd 2 ) Pr ic yc lo py ge b in od os a bi no do sa (S A LT ER , 1 85 9) la rg e an om al ou s e ye / cu lp rit u nk no w n M A RE K (1 96 1, p l. 2, fi g. 8 ), KR A FT (1 97 2, p l. 3, fi g. 6 ), BR U TH A N SO VÁ (2 00 4, Te xt -fi g. 8 G ) m id dl e- la te D ar riw ili an (Š ár ka F or m at io n) / O se k or Pr ah a – Li bu š l oc al ity As ap he llu s d es id er at us (B A RR A N D E, 1 87 2) ex te ns iv e in ju ry o f p yg id iu m / su pp os ed ly n au til oi d ce ph al op od ŠN A JD R (1 98 0) m id dl e- la te D ar riw ili an (Š ár ka F or m at io n) / un kn ow n Ar ei as pi s b ar ra nd ei (N O VÁ K in P ER N ER , 1 91 8) sh or te ne d an d he al ed le ft p le ur a of th e 9t h th or ac ic se gm en t / c ul pr it un kn ow n BU D IL e t a l. (2 01 0, p . 1 00 -1 02 , fi g. 3 A -C ) m id dl e- la te D ar riw ili an (Š ár ka F or m at io n) / O se k lo ca lit y Pa ra ba rr an di a bo he m ic a (N O VÁ K, 1 88 4) py gi di um b ea rin g tw o pu nc tu re s s ur ro un de d by sw el lin g / l ar ge c ep ha lo po d or u nk no w n ar th ro po d Th is st ud y m id dl e- la te D ar riw ili an (Š ár ka F or m at io n) / Pr ah a – Šá rk a lo ca lit y Eo ha rp es b en ig ne ns is (B A RR A N D E, 1 87 2) te ra to lo gi ca l r ig ht m ar gi n of b rim / cu lp rit u nk no w n PR A N TL & P ŘI BY L (1 95 4, p l. 10 , fi g. 3 ) la te D ar riw ili an – e ar ly S an db ia n (D ob ro tiv á Fo rm at io n) / Sv at á D ob ro tiv á lo ca lit y Pl ac op ar ia zi pp ei (B O EC K, 1 82 7) an om al ou s t hi rd to fi ft h rig ht p le ur ae o f t ho ra x / c ul pr it un kn ow n ŠN A JD R (1 97 9b , fi g. 1 ) la te D ar riw ili an – e ar ly S an db ia n (D ob ro tiv á Fo rm at io n) / M al é Př íle py lo ca lit y Pl ac op ar ia zi pp ei (B O EC K, 1 82 7) an om al ou s g la be lla r l ob e L2 / cu lp rit u nk no w n ŠN A JD R (1 97 9b , fi gs 2 , 3 ) la te D ar riw ili an – e ar ly S an db ia n (D ob ro tiv á Fo rm at io n) / M al é Př íle py lo ca lit y Pl ac op ar ia zi pp ei (B O EC K, 1 82 7) an om al ou s g la be lla r l ob e / c ul pr it un kn ow n ŠN A JD R (1 97 9b , fi g. 4 ) la te D ar riw ili an – e ar ly S an db ia n (D ob ro tiv á Fo rm at io n) / Pr ah a – H od ko vi čk y lo ca lit y D al m an iti na so ci al is (B A RR A N D E, 1 84 6) fir st to th ird p le ur ae a t t he ri gh t s id e of p yg id iu m / cu lp rit u nk no w n ŠN A JD R (1 95 6, p l. 4, fi g. 2 ) m id dl e Sa nd bi an (L et ná F or m at io n) / Či lin a at Ro ky ca ny lo ca lit y D al m an iti na so ci al is (B A RR A N D E, 1 84 6) an om al ou s r ig ht fi xi ge na / du ro ph ag ou s p re da to r ŠN A JD R (1 99 0, p . 5 8- 59 ) m id dl e Sa nd bi an (L et ná F or m at io n) / Be ro un , e xa ct lo ca lit y un kn ow n D al m an iti na so ci al is (B A RR A N D E, 1 84 6) an om al ou s p yg id ia l a xi s a nd o f b ot h rig ht a nd le ft p le ur ae / du ro ph ag ou s p re da to r ŠN A JD R (1 99 0, p . 6 0- 61 ) m id dl e Sa nd bi an (L et ná F or m at io n) / Be ro un , e xa ct lo ca lit y un kn ow n D al m an iti na so ci al is (B A RR A N D E, 1 84 6) an om al ou s t hr ee a nt er io r p le ur ae a t t he ri gh t s id e of p yg id iu m / cu lp rit u nk no w n VO KÁ Č (1 99 6, p . 2 0, fi g. 5 ) m id dl e Sa nd bi an (L et ná F or m at io n) / D ra bo v ne ar Be ro un lo ca lit y D al m an iti na so ci al is (B A RR A N D E, 1 84 6) an om al ou s t hr ee a nt er io r p le ur ae a t t he le ft si de o f p yg id iu m / cu lp rit u nk no w n VO KÁ Č (1 99 6, p . 2 0, fi g. 6 ) m id dl e Sa nd bi an (L et ná F or m at io n) / Ve se lá n ea r Be ro un lo ca lit y D al m an iti na so ci al is (B A RR A N D E, 1 84 6) de fo rm ed ri gh t fi xi ge na a nd li br ig en a of c ep ha lo n / c ul pr it un kn ow n VO KÁ Č (1 99 6, p . 2 0, fi g. 7 ) m id dl e Sa nd bi an (L et ná F or m at io n) / Ve se lá n ea r Be ro un lo ca lit y D al m an iti na so ci al is (B A RR A N D E, 1 84 6) re ge ne ra te d vi su al su rf ac e of th e le ft ey e, th e pa lp eb ra l l ob e, th e lib rig en a an d th e fix ig en a / s up po se dl y la rg e ar th ro po d or n au til oi d ce ph al op od FA TK A e t a l. (2 02 1, fi gs 4 -7 ) m id dl e Sa nd bi an (L et ná F or m at io n) / Ve se lá n ea r Be ro un lo ca lit y Ec co pt oc hi le cl av ig er a (B EY RI CH , 1 84 5) an om al ou s m or ph ol og y of th e se co nd a nd th ird p le ur al lo be o f p yg id iu m / su pp os ed ly la rg e ar th ro po d or n au til oi d ce ph al op od ŠN A JD R (1 98 0, p l. 1, fi g. 2 ), m id dl e Sa nd bi an (L et ná F or m at io n) / D ra bo v ne ar Be ro un Ec co pt oc hi le cl av ig er a (B EY RI CH , 1 84 5) an om al ou s m or ph ol og y of th e se co nd a nd th ird p le ur al lo be s / su pp os ed ly la rg e ar th ro po d or n au til oi d ce ph al op od M O RA VE C (2 00 6, fi gs 1 -3 ) m id dl e Sa nd bi an (L et ná F or m at io n) / Ve se lá lo ca lit y D ea na sp is go ld fu ss i ( BA RR A N D E, 1 84 6) tr au m at ic d am ag e of th e rig ht a nt er ol at er al m ar gi n of c ep ha lic fr in ge , c al lu se d di st al e nd o f t he fi ft h an d si xt h rig ht th or ac ic p le ur a an d rig ht p os te ro la te ra l m ar gi n of p yg id iu m / un kn ow n ŠN A JD R (1 97 9a , p . 4 9, p l. 1, fi g. 1 ) m id dl e Sa nd bi an (L et ná F or m at io n) / Pr ah a – Le tn á lo ca lit y D ea na sp is go ld fu ss i ( BA RR A N D E, 1 84 6) irr eg ul ar d is tr ib ut io n of fr in ge p its / un kn ow n ŠN A JD R (1 97 9a , p . 4 9, p l. 1, fi g. 2 ) m id dl e Sa nd bi an (L et ná F or m at io n) / Pr ah a – Le tn á lo ca lit y D ea na sp is se nf te nb er gi (H AW LE & C O RD A , 18 47 ) a s M ar ro lit hu s s en fte nb er gi ca llu se d ro un de d in de nt at io n at th e le ft p os te ro -la te ra l m ar gi n of p yg id iu m / un kn ow n ŠN A JD R (1 97 9a , p . 4 9, p l. 1, fi g. 4 ) la te S an db ia n to e ar ly K at ia n (V in ic e Fo rm at io n) / Pr ah a G eologia C roatica Fatka et al.: Healed injury in a nektobenthic trilobite: “Octopus-like” predatory style in Middle Ordovician? 191 figured a pathological cephalon of the Devonian Lioharpes venu- losus (HAWLE & CORDA, 1847). Other pathological specimens were studied by PRANTL (1948, 1954). In the last sixty years, numerous trilobite exoskeletons showing healed traumatic inju­ ries and other kinds of anomalies have been documented from Cambrian to Devonian deposits (e.g., PRANTL & PŘIBYL, 1954; ŠNAJDR, 1978a, b, 1981, 1985, 1990a, b; BUDIL et al., 2010; FATKA et al., 2009, 2015; BICKNELL et al. 2021). Here we describe an internal mould of the nileid trilobite Parabarrandia bohemica (NOVÁK, 1884) housed in collections of the National Museum Prague. This partly enrolled specimen shows the below described palaeopathological anomaly on its py­ gidium. 2. GEOLOGICAL SETTING Ordovician skeletal fossils, including trilobites, have been known for more than 200 years in the Barrandian area (e.g., SCHLOTHEIM, 1823; BARRANDE, 1846; for summary see BRUTHANSOVÁ et al., 2007). The late Middle­early Upper Ordovician Šárka and Do­ brotivá formations of the Prague Basin (Fig. 1) are a classical source of diverse and well­preserved skeletal fauna (e.g., HAVLÍČEK & VANĚK, 1966), including abundant trilobites (BUDIL et al., 2007). A rich association of disarticulated and ar­ ticulated trilobites, agnostids, echinoderms, brachiopods, hyo­ liths, organic­walled microfossils, and graptolites associated with remains of phyllocarid crustaceans, bivalves, cephalopods, ostra­ cods, and trace fossils have been thoroughly examined from these two formations for nearly two hundred years (CHLUPÁČ, 1970; KRAFT, 1972; BUDIL et al., 2007; MANDA, 2008; POLECHOVÁ, 2013; LAJBLOVÁ & KRAFT, 2014; AUBRECHTOVÁ & TUREK, 2018; KRAFT et al., 2020). Since the 19th century studi es, several tens of thousands articulated trilobite exoskeletons have been collected at several tens of outcrops of Middle Ordovician rocks (e.g., MAREK, 1961; BUDIL et al., 2007; MERGL et al., 2008). Such extensive material occasionally includes anomalous specimens. 2.1. Previously described cases of anomalous trilobites From the Barrandian area, twenty anomalous trilobites showing healed traumatic injuries have been reported from late the Mid­ dle to early Late Ordovician strata; data about these earlier re­ ports are summarized in Table 1 and Figures 1 and 2. 3. MATERIAL AND METHODS The studied specimen of Parabarrandia is preserved as an inter­ nal mould in a siliceous nodule and is housed in the National Mu­ seum, Prague (inventory number NM L59869). The external mould is unknown. The specimen was collected by V. Schüs from an unknown locality within the Praha­Šárka area in 1943. Con­ sidering the lithology, it is likely to have been from the “U trian­ glu” site, which is within the higher levels of the Šárka Formation (see PERŠÍN & BUDIL, 2009). The specimen was coated with ammonium chloride to enhance contrast and photographed with a digital Canon EOS 70 D camera. 4. DESCRIPTION OF THE INJURED PARABARRANDIA (FIG. 3) The dorsoventrally flattened, slightly damaged and partly en­ rolled exoskeleton is 42 mm wide and 90 mm long. The smooth Figure 2. Stratigraphic ranges of injured trilobites and molluscs from the Ordovician of the Prague Basin (Barrandian area, Czech Republic). Correlation modified from FATKA et al. (2013), GUTIÉRREZ-MARCO et al. (2017) and COLMENAR et al. (2017). G eo lo gi a C ro at ic a Geologia Croatica 75/2192 surface of the internal mould has slender unbranched to irregu­ larly branched burrows assigned herein, following KRAFT et al. (2020), to the ichnogenera Palaeophycus HALL, 1847, Arach- nostega BERTLING, 1992 and Pilichnus UCHMAN, 1999. Un­ branched cylindrical tunnels in the cephalon and the thoracic axis (reaching ~ 2 mm in diameter) are classified as Palaeophycus isp. (Pal in Fig. 3A). Narrow straight to slightly curved tunnels are common at the axial surface of the thorax and are observed in the axial and pleural pygidial surface; several intricate tunnels are noted in thoracic pleurae. Such fine homogeneously distributed tunnels along the internal surface of the exoskeleton are classi­ fied as Pilichnus isp. A wide pygidial doublure with fine terrace lines is exposed due to breaks of pleurae and lateral, posteriolateral and posterior pygidial margin. Several minute Pilichnus isp. are also seen in the doublure (Pil in Fig. 3B). Fine, ramified burrows on the sur­ face of internal moulds with an oval cross-section are classified as Arachnostega isp. (Ar in Fig. 3B). Pilichnus has primarily been described from fine-grained soft substrates (UCHMAN, 1999). In accordance with the limited acceptance of the substrate as an ichnotaxobase (BERTLING et al., 2006), we can also classify as Pilichnus thin branched tunnels made in direct contact with the trilobite shell. Pilichnus built in this way can be transferred to more complex systems corresponding to Arachnostega. We sug­ gest that transitional forms between Pilichnus isp. (= thin branch tunnels in contact with the shell) and Arachnostega isp. (= open or almost closed networks in contact with the shell) can exist and are observed on the studied specimen. Two prominent punctures are observed on the left anterior surface of the pygidial pleural field (arrows in Figs. 3B, D). The larger puncture is elliptical with its longer axis oriented parallel with the pleural furrow (a in Fig. 3D). The longer axis of this puncture reaches ~ 1.8 mm. The smaller puncture is rounded and measures 0.9 mm in diameter (b in Fig. 3D). Both punctures rep­ resent small craters surrounded by an elliptical swelling, which is ~ 9.5 mm wide and 4 mm long (dotted line in Fig. 3D). Remarks. Morphologically comparable pit developed on up­ per and lower lamellae of the bilaminar cephalic fringe of the Si­ lurian trilobite Bohemoharpes ungula was described and figured by ŠNAJDR (1978b, pl. 1, figs. 1-5; 1990, p. 62-63), who inter­ preted this anomaly as resulting from an activity of an endopara­ sitic organism. Recently, this interpretation was also accepted by DE BAETS et al. (2022, Table 1). Figure 3. Parabarrandia bohemica (NOVÁK, 1884), Šárka Formation (Middle Ordovician, middle-late Darriwilian), Prague Basin, Praha-Šárka locality. Internal mould of the partly enrolled exoskeleton housed in the National Museum Prague under the inventory number NM L59869. A. View of the cephalon with four anterior thoracic segments, B. View of the pygidium with exposed doublure and the three posterior-most thoracic segments, C. Reconstruction of the unrolled exoskeleton (adopted after FORTEY, 1985, fig. 5C), D. Detail of the left side of the pygidium showing the position of the two punctures (a and b) and the surrounding swelling (marked by dotted line). Ara - Arachnostega isp., Pal - Palaeophycus isp., Pil - Pilichnus isp. A, B, D – coated with ammonium chloride. G eologia C roatica Fatka et al.: Healed injury in a nektobenthic trilobite: “Octopus-like” predatory style in Middle Ordovician? 193 5. DISCUSSION The Ordovician record of injured skeletal invertebrates in the Barrandian area includes gastropods, cephalopods, and trilobites. Up to now, only two injured brachiopods are known (BUDIL & FATKA, unpublished observation). 5.1. Injured gastropods Failed predation and shell repair in Ordovician bellerophontoide­ an gastropods were studied by HORNÝ (1996, 1997a, b, c) who reported examples of repaired shell breakage in Sinuitops ne- glecta BARRANDE in PERNER, 1903, Bucanopsina calypso (PERNER, 1903), Grandostoma bohemicum (PERNER, 1903), and Lophospira infausta (BARRANDE in PERNER, 1903) from the Zahořany, Bohdalec and Králův Dvůr formations (Fig. 3). These specimens were collected from different districts of Prague, for example Spořilov, Michle, Hloubětín, Štěrboholy, Jinonice, and the Králův Dvůr locality (Fig. 1C). HORNÝ (1997a, p. 168­169) distinguished three types of shell injuries in bel­ lerophontoidean gastropods: (1) scaloped U­shaped marginal breakages, (2) a scalloped crescentic marginal breakage, and (3) a deep local injury without a shell breakage and not representing the Oichnus-trace fossil. The first type was interpreted as injuries caused by predatory molluscs, likely small cephalopods; the sec­ ond type was ascribed to non­biological causes or attacks by a small chelicerate arthropod or predatory echinoderms (e.g., ophi­ uroids). The third type of injury was explained as an injury made possibly by an ophiuroid or trilobite by HORNÝ (1997a, p. 167). 5.2. Injured cephalopods AUBRECHTOVÁ (2015, p. 196, fig. 9C, J) described and figured two specimens of Bactroceras sandbergeri BARRANDE, 1867 with sub­lethally damaged shells from the middle­late Darriwili an Šárka Formation from the Osek and Šárka localities. Recently, AUBRECHTOVÁ & TUREK (2018, p. 408, figs. 5D, E, G) figu- red and briefly described Trilacinoceras cf. discors (HOLM, 1891) with sublethal shell damage associated with anomalous growth (Figs. 1C, 2) from the Dobrotivá Formation from the Šárka locality. 5.3. Injured trilobites OWEN (1985), BABCOCK (1993, 2003, 2007), BICKNELL & PATERSON (2018), BICKNELL & SMITH (2021) and BICK­ NELL et al. (2022) published comprehensive reviews of trilobite abnormalities and discussed their possible causes. Injuries ob­ served in diverse parts of the exoskeleton were ascribed to dam­ age due to predation or during ecdysis (BABCOCK, 1993, p. 220). RUDKIN (1979, 1984), BICKNELL & PATERSON (2018, p. 5) and PATES & BICKNELL (2019) considered sub­lethal in­ juries of trilobites during a moulting event showing signs of re­ generation including an over­thickened (calloused) cuticle along the scar. Conversely, injuries without callouses are attributed to attacks on fully calcified individuals (JAGO & HAINES, 2002). In the Barrandian area, injured trilobites have been classified to nine genera (Table 1). The oldest recorded are the few trilobites from the Šárka Formation; similarly, there are rare specimens showing healed injuries in the overlying Dobrotivá Formation (Table 1, Fig. 2). The most abundant injured trilobite specimens are observed in the late Sandbian Letná Formation, and the youngest malformed specimen was described from the late Sand­ bian ­ early Katian Vinice Formation (Table 1, Fig. 2). In following sections 5.3.1 – 5.3.3, the current knowledge on the supposed lifestyle of trilobite specimens is summarised. This summary reviews the potential predators. Some trilobites were able to eliminate the predation pressure by cryptic behaviour (see FATKA & BUDIL, 2014), while other heavily skeletonised species or good swimmers effectively used passive defensive strategies. 5.3.1. Benthic trilobites In the Barrandian area, most Ordovician trilobites with healed traumatic injury after failed predatory attacks have been classi­ fied as benthic and nektobenthic forms. Placoparia zippei Placoparia is one of the most common Ordovician trilobites in the Barrandian area (BRUTHANSOVÁ & BUDIL, 2003). Be­ cause of the thick exoskeleton and the unattached (natant) hypos­ tome condition, this blind pliomerid genus has been usually con­ sidered as a benthic, partly buried, particle feeder by PŘIBYL & VANĚK (1976, p. 11), HAVLÍČEK & VANĚK (1990, p. 228; 1996, p. 227, 228, 236, 237), VOKÁČ & GRIGAR (2010, p. 162), BRUTHANSOVÁ & BUDIL (2003, p. 217), BUDIL et al. (2007, p. 68), and RÁBANO et al. (2010). FORTEY (1985, p. 228) clas­ sified this genus tentatively as an atheloptic trilobite. Also, HENRY (1989, p. 148) included Placoparia to taxa typical for the atheloptic assemblage of FORTEY & OWENS (1987). Because of the wide palaeogeographical distribution of the Darriwillian species Placoparia cambriensis, OWENS & SER­ VAIS (2007, p. 282) expressed the opinion, that this species might have been epipelagic. However, they did not definitely exclude the possibility that Placoparia belongs to atheloptic taxa. Eoharpes and Deanaspis Deanaspis belongs to the most common trilobites in the Letná Formation (PŘIBYL & VANĚK, 1969). In comparison, remains of Eoharpes are always rare in the Šárka and Dobrotivá forma­ tions (FATKA & BUDIL, 2014). Species of both Eoharpes and Deanaspis have been interpreted as benthic filter feeders (e.g., HAVLÍČEK & VANĚK 1990, p. 230; 1996, p. 228, 236; MERGL et al., 2008, p. 277). MIKULÁŠ & BUDIL (2013) supposed that in Deanaspis, the thorax was held above the water­sediment in­ terface, while the flat cephalic rim and long spines surrounded the filter-chamber beneath the cephalon and thorax, similarly as in Cryptolithus tesselatus (see FORTEY & OWENS, 1999, p. 449, Fig. 16). A comparable strategy is also supposed in the morpho­ logically similar harpetids (see FORTEY & OWENS, 1999, p. 448, Fig. 14), including Eoharpes. HENRY (1989, p. 148) listed Eoharpes as a typical member of the atheloptic assemblage of FORTEY & OWENS (1987). A cluster of six articulated specimens of E. benignensis en­ tombed under a large asaphid pygidium described by FATKA & BUDIL (2014) documents the cryptic behaviour of these benthic trilobites. This gregarious cluster of small trilobites, incapable of a group defence, was explained by the ‘‘guide effect’’ reducing their risk of predation through attack abatement, both through dilution and avoidance effects (see CHILDRESS & HERRN­ KIND, 1997). Eccoptochile Articulated exoskeletons of this large cheirurid trilobite are very rare, while disarticulated remains are quite abundant. HAVLÍČEK & VANĚK (1996, p. 236, 237), MERGL et al. (2008, p. 277) and VOKÁČ & GRIGAR (2010, p. 162) classified Eccoptochile as a benthic trilobite. G eo lo gi a C ro at ic a Geologia Croatica 75/2194 Dalmanitina Both disarticulated parts and articulated exoskeletons and Dal- manitina are very common in the Letná Formation (FATKA et al., 2021). PŘIBYL & VANĚK (1976, p. 9) classified Dalmanitina as a good swimmer occasionally burrowing in the top layer of a shallow water bottom. Asaphellus BUDIL et al. (2007, p. 68) and MERGL et al. (2008, p. 277) as­ signed this genus to large benthic predators. GIBB et al. (2010), and more recently also NETO DE CARVALHO & BAUCON (2016) documented co­occurrence of the trace fossil genera Ru- sophycus and Cruziana and articulated exoskeletons of the asaphid trilobite Asaphellus. Such close association of the puta­ tive tracemarker and its trace documents a benthic life of these large and heavily skeletonised trilobites. 5.3.2. Nektobenthic trilobites Most pelagic trilobites were poorly streamlined (see FORTEY 1985), and it is supposed that they swam quite slowly. Some larger trilobites like Parabarrandia show a hydrofoil shape, with the head end prolonged into an elongate “nose,” comparable to extant sharks (FORTEY, 1985) and are hypothesized to have swum much faster. Areiaspis BUDIL et al. (2007, p. 68) and MERGL et al. (2008, p. 277) clas­ sified rare specimens of this genus as deeper-water nektonic or benthic trilobites. The narrow axis and shape of its exoskeleton precluded good swimming ability. Parabarrandia Remains of this large nileid trilobite occur infrequently in the north-eastern part of the Prague Basin. FORTEY (1985, p. 223- 224; 2004, p. 450) assigned the large, nileid genus Parabarrandia with its very streamlined exoskeleton and long anterior snout (or ‘nose’) to actively swimming pelagic inhabitants of the mesope­ lagic cyclopygid biofacies (Fig. 4). In agreement with FORTEY (1985), HENRY (1989, p. 148) reported the occurrence of Para- barrandia classified as a mesopelagic predator. In comparison, HAVLÍČEK & VANĚK (1990, p. 228; 1996, p. 228, 236) pre­ ferred a benthic life, while BUDIL et al. (2007, p. 68), MERGL et al. (2008, p. 277), PERŠÍN & BUDIL (2009, p. 34), RABANO et al. (2010, p. 420) and DAVID & BUDIL (2015, p. 4) classified it as a nektobenthic trilobite. 5.3.3. Nektonic trilobites Pricyclopyge binodosa binodosa This is the most common cyclopygid trilobite in the Šárka For­ mation (MAREK, 1961; BRUTHANSOVÁ, 2004, p. 304). FORTEY (1985, p. 223) as well as BUDIL et al. (2007, p. 68) and MERGL et al. (2008, fig. 277) classified the poorly streamlined cyclopygid Pricyclopyge as a sluggish mesopelagic trilobite. 5.4. Potential predators In the Ordovician of the Barrandian area, injured gastropods are ascribed to cephalopods, echinoderms and arthropods (HORNÝ, 1996, 1997a, b, c). Injuries to cephalopods were likely interpreted to be made by other cephalopods (AUBRECHTOVÁ, 2015; AU­ BRECHTOVÁ & TUREK, 2018). The malformed Parabarrandia bohemica described and considered here also requires an expla­ Figure 4. Middle-late Darriwilian Šárka Formation. Sketch representing the distribution of major biofacies associated with the Šárka Formation. The shallowest part of the basin was inhabited by the poor orthid brachiopod association, further basinward, the Placoparia Association with rich trilobites, brachiopods and other skeletal fauna prevails; in the offshore slope settings it continuously passed into the poor atheloptic trilobite association which also included the poor benthic den- droid ‘gardens’. The water column was inhabited by sparse? planktonic graptolites and taxa of the poorly diverse caryocarids and Cyclopygid Biofacies. Poorly oxy- genated black shales in the central parts of the basin were dominated by the Paterula Association. Modified after FATKA & MERGL (2009) with data published by LEFEBVRE (2007) and FATKA & VODIČKA (in press). G eologia C roatica Fatka et al.: Healed injury in a nektobenthic trilobite: “Octopus-like” predatory style in Middle Ordovician? 195 nation. ALPERT & MOORE (1975), WHITTINGTON & BRIGGS (1985), ŠNAJDR (1980, 1981) and RÁBANO & AR­ BIZU (1999) proposed that sea anemones, anomalocarids and cephalopods caused the injuries of Cambrian and Ordovician tri­ lobites. BICKNELL et al. (2018, 2021 and 2022) suppose that tri­ lobites could damage other trilobites. BRETT & WALKER (2002, p. 94) suggested that priapulids, nautiloid cephalopods, phyllo­ carid crustaceans and other arthropods (e.g., eurypterids) were likely Ordovician durophagous predators. The recently described specimen of Dalmanitina with a malformed and regenerated eye is interpreted as an unsuccessful attack by a cephalopod or a large arthropod (FATKA et al., 2021). From the morphology of the mal­ formed Parabarrandia, combined with the large size of the taxon, we exclude predators including sea anemones, anomalocarids, echinoderms, and priapulids as the injury makers. Consequently, cephalopods and arthropods are the potential culprits. 5.4.1. Cephalopods Recent cephalopods are commonly active carnivorous predators (FERNÁNDEZ­ÁLVAREZ et al., 2018). Similarly, fossil cepha­ lopods are considered carnivorous (NIXON, 1988 but see MI­ RONENKO, 2020). Large cephalopods were abundant in marine assemblages from the Early Ordovician (e.g., BRETT & WALKER, 2002; KRÖGER, 2011), including the Barrandian area (MANDA, 2008; AUBRECHTOVÁ, 2015 and AUBRECH­ TOVÁ & TUREK, 2018). 5.4.2. Arthropods The length of the carapace of planktic phyllocarids does not ex­ ceed 50 mm in the Ordovician (RACHEBOEUF & CRASQUIN, 2010). Consequently, phyllocarids are excluded as a potential cul­ prit of the herein studied trilobite. Presuming a benthonic mode of life for Paleozoic marine chelicerates (for eurypterids see BRADY, 2001), sublethal predator−prey interactions between chelicerates and nektobenthic trilobites like Parabarrandia might be possible. 5.5. Ichnological aspect 5.5.1. Feeding post-mortem After KRAFT et al. (2020) and other authors, producers of Pal- aeophycus apparently preferred an easily accessible and nourish­ ing food that was easily consumed, e.g., their trace makers selec­ tively oriented on decaying soft tissues. The Arachnostega and Pilichnus traces are oriented in a manner suggesting systematic feeding. These trace makers spent more time in a carcass. The occurrence of Palaeophycus, Arachnostega and Pilichnus in the internal mould of the Parabarrandia attests to a post-mortem feeding activity on the trilobite carcass. Also, the perfect articu­ lation of the trilobite exoskeleton suggests a carcass, not an exu­ vium (see VALLON et al., 2015). 5.5.2. Attack on living specimen of Parabarrandia Two prominent punctures penetrate the trilobite exoskeleton and are surrounded by swelling. The morphology in NM L59868 il­ lustrates, that this exoskeletal anomaly occurred in life of the Parabarrandia, likely during the “paper­shelled” stage of HEN­ NINGSMOEN (1975) or “soft-shelled” stage of SPEYER & BRETT (1985). The other possibility is in vivo attack by a culprit capable of boring. Trace fossils representing morphologically recurring, lethal, sub­lethal (not completely successful) or “mistaken” (to empty shell) attacks are called praedichnia (see EKDALE, 1985; VAL­ LON et al., 2016). Most documentation of these trace fossils as­ cribe the record to holes drilled in mollusc and brachiopods. MIKULÁŠ et al. (2006) and JACOBSEN & BROMLEY (2009) introduced ichnotaxonomical names for biting traces, subse­ quently attributed to praedichnia (compare PIRRONE et al., 2014 and VALLON et al., 2016). Confirmed living marine perpetrators drilling their prey are mainly gastropods and octopod cephalopods (VERMEIJ, 2002, p. 385). Most drill holes are interpreted to be caused by predatory gastropods such as naticids and muricids. BROMLEY (1981) pro­ posed that the ichnofossils that are made by naticid drilling were Oichnus paraboloides BROMLEY, 1981 and muricids made Oichnus simplex BROMLEY, 1981. The holes in the pygidium of Parabarrandia are morpho­ logically comparable to drill holes found in modern molluscs and crustaceans (e.g., ARNOLD & ARNOLD, 1969; BOYLE & KNOBLOCH, 1981; NIXON & MACONNACHIE, 1988; HARPER, 2002). The elliptical outline and dimensions of our drill holes are in accordance with the morphology of the ichno­ species Oichnus ovalis BROMLEY, 1993, an ichnofossil inter­ preted to be the result of boring by octopod cephalopods (see BROMLEY, 1993; WISSHAK et al., 2015). Further, the drilling of two or even three holes in one shell is a strategy known to be deployed in some species of recent octopods (NIXON & MA­ CONNACHIE, 1988). NIXON (1979, 1980) reported that in recent Octopus vul- garis, the drilling activities are carried out by a salivary papilla lying just below the radula. The role of saliva produced by sali­ vary glands was later shown to be important for a successful at­ tack, as it contains a wide spectrum of paralysing and proteolytic substances (NIXON, 1988, p. 709). Some of them are responsible for the breakdown of the musculo­skeletal attachment mecha­ nism in crabs within 20 min of capture (NIXON, 1984). Similar breakdown of the musculo­skeletal attachment mechanism would probably mean the same for trilobites. The key ichnogenus Oichnus BROMLEY, 1981 and other morphologically similar ichnotaxa have been recently revised (WISSHAK et al., 2015). For the creation of our trace, drilling behaviour seems to be the most plausible because of the absence of sharp edges typical for biting, combined with the diminutive, protected space. In terms of systematic ichnology, the herein described struc­ tures from Parabarrandia are attributable to the ichnospecies Oichnus ovalis BROMLEY, 1993. Ancient, fossilised structures were interpreted as octopus borings, based on observations from studies of the recent octopods (BROMLEY, 1993; NIXON, 1979, 1980; NIXON & MACONNAICHE 1988). Based on these obser­ vations, we interpret the structures observed in the specimen of Parabarrandia studied here as resulting from an “Octopus­like” predatory attack. Origination of the swelling on the internal mould. We sup­ pose that the trilobite was attacked during the “soft­shelled” stage. The thin exoskeleton was probably drilled (= “Octopus­ like” predatory style). Consequently, in the injured area, the soft tissue under the unbiomineralised exoskeleton overdeveloped. This swelling would have been recorded during exoskeletal hard­ ening with swelling expressed both on the external and internal surfaces of the exoskeleton. 6. CONCLUSION (1) The exoskeletal anomaly seen at the left pygidial side of Para- barrandia represents a partly healed injury after a failed preda­ tory attack during life. G eo lo gi a C ro at ic a Geologia Croatica 75/2196 (2) Two scenarios explain this anomaly: a – The healed injury classified as the ichnospecies Oichnus ovalis BROMLEY, 1993 can be interpreted as an exoskeletal anomaly which originated after a failed “octopus­like” strategy of the predatory attack. This preferred interpretation reflects the nektobenthic lifestyle of Parabarrandia and the nektonic life­ style of the suspected predator. b – The morphology and the extent of the swelling surround­ ing both punctures combined with the noticeable absence of any crack of the surrounding exoskeleton indicates the high flexibility of the cuticle during the attack. The attack resulted in two re­ stricted perforations (punctures) followed by plastic deformation of the exoskeleton copying the swelling. In such cases, the injury could result from attack of an unknown predatory arthropod. FINANCIAL SUPPORT: This research was supported by the Czech Science Foundation (GACR) project no. 18­14575S and by Cooperatio GEOL (OF). COMPETING INTERESTS: The authors declare that they have no conflict of interest. ACKNOWLEDGEMENT We acknowledge both reviewers Lothar H. VALLON (Østsjæl­ lands Museum, Faxe, Denmark) and Russell D.C. 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