SPECIAL PUBLICATION OF THE PALAEONTOLOGICAL SOCIETY OF INDIA No. 5; February, 2014; ISBN: 978-81-926033-2-2; pp. 205-213
PALAEOBIOGEOGRAPHIC CONSTRAINTS ON DRILLING GASTROPOD PREDATION: A CASE STUDY FROM THE MIOCENE KHARI NADI FORMATION IN KUTCH, GUJARAT SUBHENDU BARDHAN1*, SUMANTA MALLICK1 and SHILADRI S. DAS2 1
2
DEPARTMENT OF GEOLOGICAL SCIENCES, JADAVPUR UNIVERSITY. KOLKATA – 700 032, GEOLOGICAL STUDIES UNIT, INDIAN STATISTICAL INSTITUTE, 203 BARRACKPORE TRUNK ROAD, KOLKATA 700 035, INDIA * Corresponding author’s e-mail:
[email protected]
ABSTRACT Predator-prey interaction is an important aspect of biological system. Gastropod drilling predation can be traced in the fossil record and provide many reliable information about drilling activities e.g., drilling intensity, efficiency of predators through size and site stereotypy. Drilling frequency (DF) varies widely in space and time. Temporal changes, although complex, depicts a pattern. Drilling frequency was low during the Cretaceous and cyclically increased during the Eocene and Miocene. We, however have found low drilling frequencies on molluscs in the Early Miocene (Aquitanian) Khari Nadi Formation in Kutch, Gujarat. India experienced varying degree of isolation during the Oligocene – Miocene times and was completely cut off from the western Tethys during the Aquitanian. Escalated predators from Europe and other provinces were barred from invading the Indian waters which resulted in significant lowering of the drilling frequencies on molluscan assemblages. Keywords: Drilling predation, Kutch, Miocene, palaeobiogeographic constraints
INTRODUCTION Predator–prey interaction has a long geological history since the Neoproterozoic times (Bengston and Zhao, 1992; Hua et al., 2003). However, many such interactions, e.g., swallowing the prey whole or crushing of prey shells, hardly leave any readily identifiable features in the fossil record. Drilling predation is one such interaction, which has preservable fossil record and plays significant role in predator – prey system which resulted in evolutionary consequences like co-evolution which describes cases where two (or more) species reciprocally affect each other’s evolution and escalation which can be defined as changes occurring within any species due to the changes taking place within their enemies (Vermeij, 1987; Dietl and Alexander, 2000). Intensity of predation varies with time. Mesozoic Era is known as the time of major change in the nature of life on Earth. One of the major aspects of this change was the rise of many predatory groups. During the Middle to Late Mesozoic the predation pressure reached a peak, which is aptly called as Mesozoic marine revolution (Vermeij, 1977).
Palaeozoic drillholes were caused by many predatory/parasitic groups (e.g., see Fürsich and Jablonski, 1984; Baumiller, 1990, 1996; Leighton, 2001, 2003), while Mesozoic drillholes may have been made by some unknown gastropod predators (e.g., Newton, 1983; Smith et al., 1985; Newton et al., 1987; Harper et al., 1998, Harper, 2003; Heidelberger and Amler, 2002; Bardhan et al., 2012). Reports of unambiguous gastropod drilling predation came from the late Early Cretaceous, when two predatory gastropod families, the Muricidae and Naticidae, first appeared in the fossil record (Sohl, 1969; Taylor et al., 1983). Tertiary rock record is full of holes. Drillhole morphology, (e.g., shape and size of drillholes) provide many insights about the identity, behaviour, and size of the driller. Generally, naticids make tapered holes (‘truncated paraboloid’, see Carriker and Yochelson, 1968), whereas muricid drillholes are ‘straight – walled’ (but see Herbert and Dietl, 2002). Predatory drillholes provide many reliable information about various significant aspects of predation, including predation intensity, prey size, predator size, and
206 behaviour of predators (for reviews and references, see Kitchell et al., 1981; Vermeij, 1983, 1987; Kitchell, 1986; Kabat, 1990; Kowalewski, 2002; Kowalewski and Kelley, 2002; Leighton, 2002; Kelley et al., 2003). Naticid outer drillhole diameter is well correlated with predator size (Kitchell et al., 1981). Gastropod drilling predation shows spatiotemporal variation. In general, for any time plane, drilling intensity increases towards the equator (Vermeij, 1987). Temporally the pattern is complex and probably cyclic (Kelley and Hansen, 1993, 1996, 2006). All evidences indicate that the Miocene drilling frequencies on molluscan assemblages reached a new high. We here, have reported drilling frequencies on some bivalve and gastropod species systematically collected from the Khari Nadi Formation (Aquitanian) of Kutch, Gujarat. The DF values are significantly low in comparison to the global data. We have explored the reasons and considered the palaeobiogeographic constraints might have played a role.
SUBHENDU BARDHAN and OTHERS
Fossils are present in var ying mode of occurrences. In one section on the river bed of the Khari Nadi fossils are strongly enclosed in a coarse sandstone bed (Figure 3A) and were very hard to retrieve. We therefore, collected specimens following grid sampling protocol of Bardhan et al. (2012). We have made several grids of 4 square meter each. All the samples within these grids were photographed and if possible collected after detailed study. Besides, we have studied drilled samples outside the grid. All bivalve samples belonged predominantly to two species, Chlamys sp. and Ostrea sp. (Figure 3B, C). Most specimens are disarticulated valves and show little taphonomic influence. We have analysed both complete and broken shell separately. In another section where the fossils are overwhelmingly rich in gastropods especially turritelline species (Figure 4), the sediment is particularly friable and fossils are easy to retrieve. We therefor e employed bulk sampling protocol following Kowalewski (2002) and Mallick et al. (2013).
MATERIAL AND METHODS The present fossil specimens have been collected from the rocks of two localities (Figure 1), which belong to the Khari Nadi Formation of the Early Miocene (Biswas, 1992). This formation is dominantly arenaceous and overlies the rocks of the Maniyara Fort Formation (Figure 2). The thickness of the formation varies considerably and in the type section it attains a thickness of 65 meters. Biswas (1992) interpreted the depositional environment in littoral to shallow inner shelf areas.
Fig. 2. Stratigraphic position of the studied Khari Nadi Formation (modified after Biswas, 1992). Fig. 1. Map showing the fossil bearing localities (+) within the Khari Nadi Formation.
PALAEOBIOGEOGRAPHIC CONSTRAINTS ON DRILLING GASTROPOD PREDATION: A CASE STUDY FROM THE MIOCENE KHARI NADI FORMATION IN KUTCH, GUJARAT
We have studied drillhole morphology in detail and found that drill holes are different in different taxonomic groups. While the bivalves bears characteristic cylindrical drill holes (Oichnus simplex Bromley, 1981) allegedly made by muricids, majority of turritelline gastropods bear naticids drill holes ‘which are truncated spher ical paraboloid’ (Oichnus paraboloides Bromley, 1981; Carriker, 1981; Carriker and Yochelson, 1968). The different prey preference of muricids and naticids may be explained by the facts that
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the present bivalves are epifaunal (Chlamys sp. is epibyssated while Ostrea sp. is cemented in life mode). In other examples from modern as well as fossil case studies it is well known that muricids target epifaunal prey (Carriker, 1981). In contrast, the gastropods especially turritellines bear typical naticid drill holes. Naticids are known to target infaunal prey (Sawyer and Zuschin, 2010) and turritellines are dominantly infaunal (see Paul et al., 2013 and references therein).
Fig. 3. A. Coarse sandstone of the Khari Nadi Formation exposed along the Khari Nadi river near Lakshimpur, B-C. Drillholes on the shells of Chlamys sp. and Ostrea sp. respectively.
For bivalves frequency of drilling (DF) predation is calculated by dividing number of bored valves by total number of individuals in the collection (equation one of Bambach and Kowalewski, 2000).
where DV is the number of drilled valves. For gastropods, drilling frequency (DF) is expressed as the percentage of shells with complete drillholes divided by the total number of shells (Allmon et al., 1990).
i.e., N = [(RV + LV) / 2] + A So, the drilling frequency (DF) is: where LV, RV, A and N are number of left, right, articulated valves and total number of individuals respectively. So, the drilling frequency (DF) is: DF = DV/N
DF = DV/N where DV is the number of drilled individuals and N represents total number of samples.
208 Frequencies of both incomplete and multiple drillholes were measured. Unsuccessful drillholes are an indication of prey effectiveness (PE), which has been defined as a ratio between total incomplete drillholes and total number of attempted holes (see Vermeij, 1987 and Kelley et al., 2001). Multiple drillhole frequency is defined as the number of drillholes in multiply drilled specimens divided by the total number of attempted
SUBHENDU BARDHAN and OTHERS
holes (Vermeij, 1987 and Kelley et al., 2001). According to Kelley et al. (2001) both incomplete and multiple drillholes indicate relative efficiency of predator and prey. Incomplete drillholes indicate failure of the attack and multiple holes indicate repeated attacks. If prey are more vulnerable, then the value of incomplete and multiple drillhole frequencies should decrease.
Fig. 4. Three species of turritelline gastropod from the Khari Nadi Formation. A-B. Zaria angulata, abapertural and apertural views respectively, C-D. Turritella assimilis, apertural and abapertural views respectively, E-G. Haustator tauroperrites, abapertural and apertural views respectively, G. broken specimen. Note, complete gastropod drillholes in A, D and G (see arrows). RESULTS For Chlamys sp. the number of disarticulated valves is 202, which are mostly dominated by left valves. We have found only six articulated specimens of Chlamys sp. Therefore DF (following the above equation) is 7.48% (Drilled shell=8). Similarly in Ostrea sp. we found 168 disarticulated valves and DF is 5.95% (Drilled shell=5). In turritelline gastropods, the subfamily level
DF is 5.77% (N=1472; drilled samples=85). In species level, the data range from 3.24% in Haustator tauroperturrites (N=185) and 8.04% in Turritella assimilis (N=373). No incomplete or multiple drillholes were found in the bivalves, however, relatively high value of incomplete drilling frequency (PE=18.25%; N=126) and multiple drilling frequency (PE=14.29%; N=126) were recorded for the turritelline gastropods.
PALAEOBIOGEOGRAPHIC CONSTRAINTS ON DRILLING GASTROPOD PREDATION: A CASE STUDY FROM THE MIOCENE KHARI NADI FORMATION IN KUTCH, GUJARAT
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Table 1: Miocene drilling predation data on turritelline gastropods from all over the world (N=total number of shells examined; D=number of drilled shells; UD=number of undrilled shells; DF=drilling frequency). Formation/Place Age
Bulgaria Poland Maryland Venezuela Maryland Venezuela Maryland Florida Maryland Virginia Calvert Choptank St. Marys Eastover Panama Central Paratethys
Miocene Miocene Miocene Miocene Miocene Miocene Miocene Miocene Miocene Miocene Miocene Miocene Miocene Miocene Late Middle Miocene Lower and Middle Miocene
Turritellidae gastropod
Source
N
D
UD
DF%
2642 1461 101 35 416 73 63 239 4186 113 254 1581 2172 7 370 1757
1012 270 28 3 87 12 14 52 323 2 60 446 745 2 162 109
1630 1191 73 32 329 61 49 187 3863 111 194 1135 1427 5 208 1648
38.3 18.48 27.72 9 21 16.44 22.22 21.76 7.716 1.77 23.6 28.2 34.3 28.6 43.78 6.2
DISCUSSION Gastropod predation on molluscan assemblages has been now well studied and the temporal pattern has been established. For example, Kelley and Hansen (1993, 1996, 2006) described a cyclicity of drilling intensity for both bivalves and gastropods. For gastropods they reported low DF during the Cretaceous and rapid rise in the aftermath of K-T extinction which continued up to the late Eocene; then there was a decline during the Oligocene in the DF followed by rapid rise again during the Miocene. This pattern was valid for various taxonomic ranks ranging from assemblage to the level of species. For example, in turritelline assemblage the Miocene drilling frequencies recorded from other parts of the world were shown in Table 1. Most of the DFs are quite high in comparison to Kutch turritellines. Similar Miocene highs were also observed in bivalve assemblages (Table 2). Average DF on bivalves was again significantly higher than the Kutch bivalve species (chi-square test of independence, 2 = 39.109, df = 1, p
