(a) Discuss the evolutionary trends in the lineage of equidae and give any two examples of their Indian occurrences. (20…

(a) Evolutionary trends in the lineage of Equidae

The Equidae (horse family) are a classic example of evolution recorded in fossils. The lineage runs: Hyracotherium (Eohippus, Early Eocene), Mesohippus (Oligocene), Merychippus (Miocene), Pliohippus (Pliocene) and Equus (Pleistocene to recent). The family branched like a bush with many side lines, not a straight line.

Trends:

• Size increased from a fox-sized animal about 25–50 cm high to a horse about 150 cm.
• Limbs and feet lengthened, fitting fast running on open ground.
• Toes reduced: four toes in front and three behind in Hyracotherium; three in Mesohippus and Merychippus, with the middle toe bearing the weight; one toe (hoof) in Pliohippus and Equus, with side toes reduced to splints.
• Teeth changed from low-crowned (brachydont), browsing, with simple cusps, to high-crowned (hypsodont) grazing teeth with cement and complex enamel ridges, resisting the wear of grass.
• The skull and face lengthened, the jaw deepened to hold tall teeth, and the brain enlarged and became more complex.
• These changes followed the spread of grasslands in the Miocene, so the trends are adaptive responses to a shift from forest browsing to grassland grazing and running.

Indian occurrences: Hipparion (a three-toed grazing horse of the Miocene–Pliocene) is known from the Middle and Upper Siwaliks of the Himalayan foothills, such as Hipparion antelopinum and H. theobaldi; Equus sivalensis is found in the Pleistocene Upper Siwaliks, and Equus namadicus in Pleistocene Narmada valley deposits.

(b) Cenozoic stratigraphy of the Kuchh basin

The Cenozoic rocks of Kuchh lie on the Deccan Trap and are largely marine, in a basin open to the Arabian Sea.

Succession (older to younger):

• Matanomadh Formation (Palaeocene): shale, mudstone and limestone with volcanic material, fluvial to shallow marine.
• Naredi Formation (Early Eocene): shale, limestone and sandstone with glauconite; shallow marine.
• Harudi and Fulra formations (Middle Eocene): shale with lignite and gypsum (Harudi), and foraminiferal limestone (Fulra), mainly lagoonal to shallow open-marine.
• Maniyara Fort Formation (Oligocene): limestone, claystone and sandstone, shallow marine, with reefs.
• Khari Nadi and Chhasra formations (Early Miocene): siltstone, claystone and sandstone, nearshore and estuarine.
• Sandhan Formation (Mid–Late Miocene): sandstone and limestone.
• Pleistocene to Recent: miliolite limestone, alluvium and Rann sediments.

Fossil content: larger foraminifera such as Nummulites, Assilina and Discocyclina in the Eocene, and Lepidocyclina (Nephrolepidina), Eulepidina and corals in the Oligocene; Miogypsina, gastropods (Turritella), oysters, echinoids and molluscs in the Miocene; also crabs, fish and sirenian remains.

Environment: repeated transgression and regression in a warm, shallow tropical shelf, with lagoons and evaporitic conditions at times; the sequence shows rising sea level in the Eocene and Oligocene and a shift to nearshore deposits in the Miocene.

(c) Artificial recharge of confined aquifers; roof-top injection well

A confined aquifer has natural recharge only at a distant outcrop, and the overlying aquitard stops infiltration from the local surface. Heavy pumping therefore lowers the piezometric head, and the aquifer is depleted faster than it is refilled. Consequences are falling wells, land subsidence due to compaction, saline-water intrusion in coastal areas and loss of artesian flow. Artificial recharge is essential because water must be put directly into the aquifer through wells.

Roof-top rainwater injection well: rain falling on the roof is led through gutters and a down-pipe, with a first-flush diverter to discard the initial dirty water, into a desilting or settling chamber and then a filter bed of gravel, coarse and fine sand. The clean water flows by gravity into a recharge (injection) well. The well is a bore of about 100–300 mm diameter, with blank casing through the clay layers, a slotted screen opposite the confined aquifer, a gravel pack around the screen, and a clay or cement seal in the annular space above to stop surface water leaking in. Water must be filtered so that the screen does not clog, and the well should be cleaned or back-washed periodically.