Multiple drill holes

Twelve per cent (44 out of 353) of drilled echinoid tests bear two, three or sometimes four drill holes (Table 1 and Fig. 15A-G). Drill holes situated on a single test usually differ in size and the distances between them are relatively long (Fig. 15A, C, D, G). This suggests that multiple perforations were produced by several cassid predators which attacked different parts of a single urchin. This is consistent with laboratory observations of Recent cassids (Hughes and Hughes 1971), which...

Summary and conclusions

Test-drilling predation by cassid gastropods on minute clypeasteroid echinoids has been studied in the fossil assemblage of the Heterostegina Sands (middle Miocene, Holy Cross Mountains, Poland). The analysed prey, collected from two sublithofacies of the Heterostegina Sands (coarse- and fine-grained sands), represent three species of Echinocyamus, E. linearis, E. pusillus, and E. pseudopusil-lus. The drill holes were presumably produced by one cassid species, Semicassis miolaevigata. The...

Materials and methods

The material for this study comes from the Heterostegina Sands, deposited within the Korytnica Basin, a terminal part of a shallow bay which developed during the middle Mio- Acta Palaeontol. Pol. 50 (3) 409-428, 2005 Fig. 1. Palaeoenvironmental sketch of the Korytnica Basin with sample localities (adapted from Zlotnik 2003). Fig. 1. Palaeoenvironmental sketch of the Korytnica Basin with sample localities (adapted from Zlotnik 2003). cene transgression of the Parathetys Sea on the southern...

Size selectivity

Relative abundances of drilled tests of E. linearis and drilled tests of E. pusillus bearing small and large drill holes A and relative abundances of single and multiple drilled tests of the same species B . All specimens collected from the coarse-grained Heterostegina Sands. Size-selective drilling has been recognised in two analysed prey, E. linearis and E. pusillus from the coarse-grained sands. The investigation showed that the larger tests of both Fig. 11. Drilling pr dation...

Intraspecific siteselectivity

The drill holes observed on tests of E. linearis were not positioned randomly. The investigation shows that the aboral side of tests of this species was drilled preferentially. The preference displayed by cassids was evident, as 85 of the drill holes were situated on the aboral side of test only 52 were expected there in the case of random drilling . Detailed numerical data shows that the dorsal preference displayed by cassids was mainly a result of a great concentration of drill holes on the...

The origin of drill holes

The origin of drill holes observed in tests of E. linearis from the Heterostegina Sands was discussed in detail in our previous paper see Ceranka and Zlotnik 2003 and references cited therein . The results presented there can be briefly summarised as follows 1 The penetrations observed in tests of E. linearis are typical for drillings produced by predators Carriker and Yochelson 1968 Carriker 1981 Kitchell et al. 1981 Rohr 1991 Kowalewski and Flessa 1994 and cassids are the only well-documented...

Drilling predation intensities

The frequency of drilled tests varies notably both among the prey species and across the facies Fig. 9B Table 3 . Within a given environment, the drilling predation rates recognised for particular prey do not seem to change in any substantial matter Fig. 9A Table 3 . The only possible exceptions variations in drilling predation intensities recognised for E. pusillus and E. linearis within the fine-grained sands are most probably statistical artifacts caused by the small size of samples Fig. 9A...

Size morphology and structure of the preys test

Internal Irregular Echinoid

The analysed prey species are represented by small specimens test length 1.4-6.0 mm . E. linearis is slightly smaller mean test length 2.4 mm than E. pusillus and E. pseudpusillus mean test length 2.6 and 2.7 mm respectively and the difference is statistically significant Table 1 . In all species studied, the uppermost part of the aboral side of the test is almost completely dominated by an apical disc and a large petalodium see Fig. 4O and schemes of echinoid tests on Fig 3 . Both the peristom...

Morphology and size of drill holes

The drill holes are relatively small. The maximum drill hole diameter ranges from 0.04 mm to 1.8 mm, with a mean of 0.26 mm Table 1 . The size frequency distributions of drill holes recognised for all prey species are highly right-skewed and generally unimodal, with small drill holes below 0.4 mm in diameter dominating Fig. 7 . The analysed drill holes are ca. three times smaller than those recognised by Nebelsick and Kowalewski 1999 for a Recent representative of Echinocyamus E. crispus from...

Possible taphonomic biases

Echinocyamus Pusillus Fossil

Drilling predation makes the prey skeleton more prone to mechanical destruction and dissolution Roy et al. 1994 and results of this study below, but see also Zushin and Stanton 2001 . This can generate serious taphonomic biases because the intensity of drilling predation may be underestimated due to preferential destruction of the drilled skeletons. Specifically, the relative frequency of multiple drilled skeletons Fig. 15. Tests of representatives of Echinocyamus bearing multiple drill holes....