Paleoecology of Bivalves from Lower Miocene of Kutch, India
Shibajyoti Das5th Year BS-MS
DES, IISER Kolkata
Outline• Introduction
• Previous work• Theme• Bivalve• Miocene global climatic scenario• Kutch
• Objectives• Material Methods• Results
• Taxonomic diversity• Rarefaction• γ diversity
• Morphological diversity• Discussion and Conclusion• References• Acknowledgement
http://www.fossilmall.com/Pangaea/pfossils/pf115/pfo433bb.JPG
Previous work• Physical triggers affect the biodiversity of organisms.
• Climate change – major driving force (Matthew, 1915).
• Increase in temperature – Increase in biodiversity (Mayhew et al. 2012).
• Evolutionary trend of Cenozoic Mollusc as a result of climatic shifts –
• North American (Roy et al., 2001)
• Antarctic (Ivany et al., 2000, 2003, 2004, 2008)
• European assemblages (Lockwood, 2005 )
• Decrease in Bivalve body size with an increase in temperature (Belanger, 2012).
Theme
• Possible effect of the physical trigger (climatic fluctuation) on
• Bivalve diversity and community structure
• Bivalve morphology (body size) from the Miocene of Kutch
Bivalves
• Good fossilization potential
• Common in the fossil record
• Accretionary growth recording events happening
during life
• δ18O and δ13C isotopic signature preserved
• Accretion: Adding discrete growth layers to
skeletons as they get larger.
http://paleoecology.syr.edu/research-pages/growth.html
Geologic time scale
Khari Nadi formation
Chhasra formation
Stratigraphy of Kutch after Biswas (1992)
Climatic fluctuations over the Tertiary Period
• Through the Tertiary climate varied from colder to warmer in
regular cycles.
• Average global temperature was warmer during the Tertiary
Period so that continental glaciations did not take place.
• Geochemical data demonstrate that the Miocene represents a
time of rapid palaeoclimatic change (Zachos et al. 2001).
Fluctuations during Miocene
Sea level estimates derived from New Jersey (Miller et al., 2005; Kominz et al., 2008) that provide a testable record of global sea-level. Also shown is the oxygen isotopic synthesis of Cramer et al. (2009). NHIS = northern hemisphere ice sheets.
Kutch, India
• The Early Miocene succession of Kutch represents a mixed carbonate-siliciclastic
depositional system (Kumar et al., 2009).
• The carbonate succession had abundant shallow marine benthic fauna consisting of shelled
organisms in large concentration.
• The carbonate-siliciclastic depoitional environment helps in good preservation of the
mollusc shell because:
• Carbonate shell
• Contrasting depositional environment
• Difference in texture of fossil and surrounding rocks
Objectives
• Characterization of Bivalves from Early Miocene of Kutch.
• Characterizing the nature of taxonomic and morphological diversity and
community structure of the bivalve community.
• Evaluating the possible effect of climatic change on the bivalve community.
Field area
Bio-assemblage
Field protocol• Selection of locality (ridge or river bed section).
• Identification of lithological units.
• Making brief lithologs.
• Collection of bulk lithological samples and fossils.
Methods used
Methods used
Identification protocol
• Paleodb database•Treaties of Invertebrate Paleontology•Borkar et al. 2004
Bivalve TaxonomyOstreidae
Veneridae
TellinidaePectinidae
GlycymeridaeCardiidae
Plicatulidae
Results
• Total Specimen Identified: 1479
• Khari Nadi formation : 902
• Chhasra formation: 577
• Number of identified Families:9
Family Khari Nadi Chassra
Arcidae 9 6
Cardiidae 38 6
Glycymeridae 10 2
Lucinidae 8 2
Plicatulidae 0 5
Pectenidae 234 50
Ostreidae 439 482
Tellinidae 56 8
Veneroidae 108 16
902 577
1. Taxonomic diversity
Abundance distribution
Family Khari Nadi (%) Chassra (%)Ostreidae 48.6 83.5Pectinidae 25.9 8.6Veneridae 11.9 2.7Tellinidae 6.2 1.3Arcidae 0.9 1.0Glycymeridae 1.1 0.3Lucininidae 0.8 0.3Cardiidae 4.2 1.0Plicatulidae 0 0.8
Rarefaction
• This curve is a plot of the number of taxa as a
function of the number of samples.
• Estimates the number of taxa that would have
been found if a smaller number of individuals
had been sampled.
A
B
Number of Individuals
Num
ber o
f Tax
a
γ diversity• Total taxonomic diversity in a landscape (Formation).
Mann-Whitney Test: p<<0.05
Most abundant families• Ostreidae
• Pectinidae
• Veneridae
• Tellinidae
Abundance in each locality
Khari nadiDominance = 0.47
ChassraDominance = 0.8
p = 0.0018
Results
• Body size measurement
• Length
• Height
• Total specimen measured: 373
• Khari Nadi formation : 281
• Chhasra formation: 92
• Number of Families whose specimens were measured: 4
Family Khari Nadi Chassra
Pectenidae 54 18
Ostreidae 125 65
Veneridae 69 6
Tellinidae 33 3
281 92
2. Morphological diversity
Body-Size plots
Percentage decrease: 49.35p << 0.05
Percentage decrease: 73.17p << 0.05
Percentage decrease: 30.63p << 0.05
Comparison of percentage shrink
Paleoclimate• δ18O values for two cross sectional
samples of Ostrea angulata
• Paleotemperature reconstruction from the δ18O values.
Khari Nadi
Chhasra
Khari Nadi
Chhasra
Khari Nadi
Discussion and Conclusion
• A significant increase in temperature from the older to the younger formation.
• Difference in abundance of families between the two formations.
• Significant difference in the γ diversity in the two formations.
Climate change and biodiversity• Beyond small geographical scales, biodiversity consistently decreases with latitude (Willig et
al. 2003; Hillebrand, 2004; Krug et al., 2009).
• Strong causal association between warmer climates and standing richness in marine realms (Rombouts, 2009; Tittensor et al., 2010).
• Increase in temperature – Increase in biodiversity (Mayhew et al. 2012).
Temperature Diversity
Discussion and Conclusion
• A significant change in the body size with body shrinkage in the
younger formation.
• Shrinkage percentage varies within families.
• Highest for epifaunal mobile (free swimmers)
• Low for epifaunal stationary (bysally attached)
• Lowest for infaunal
Temperature and body size
Figure: Working hypothesis of the major processes of climate change effects on organism size.
(1) Increased metabolic rate is likely to reduce body size unless organisms can consume enough additional resources to meet their increased demands.
(2) Decreased amounts of dissolved oxygen in warmer waters will make it difficult to meet increased metabolic needs.
(Sheridan and Bickford, 2001, Nature climate)
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Acknowledgements• Dr. Devapriya Chattopadhyay
• Saurav Dutta, Debarati Chattopadhyay, Mansi Jain, Mrinmoy Pal, Rohini Das, Neeti Mandal, Ravi Kiran, Debanjan Chandra, Jayjit Das and Dipanjana Dalui.
• Paleo lab members
• All members of the Department of Earth Sciences, IISER Kolkata
• Friends and family
Thank you