(a) Elucidate an evolutionary trend of Equidae with Indian occurrence. (20 marks) (b) Discuss the pre-cambrian/cambrian boundary…

(a) Evolutionary trend of Equidae and their Indian occurrence

Equidae, the horse family, are a standard example of evolution in response to a change from forest to grassland. The lineage is bushy, not a single straight line, but the main trends are clear.

(i) Size. It increased from a fox-sized Hyracotherium (Eohippus) of the Early Eocene, about 55 Ma, to the large Equus.

(ii) Limbs and digits. Limbs lengthened for speed, and the digits were reduced. Hyracotherium had four toes on the forefoot and three on the hind foot; Mesohippus of the Oligocene had three; Merychippus and Hipparion had three toes with only the middle one bearing weight; and Pliohippus and Equus have one.

(iii) Teeth. Low-crowned (brachydont) browsing teeth gave way to high-crowned (hypsodont) grazing teeth with cement and complex enamel folds, suited to abrasive grass.

(iv) Skull and brain. The face lengthened and the brain enlarged.

Indian occurrence. Equids are not found in India before the late Miocene. They are known from the Siwalik Group of the Himalayan foreland. Hipparion (and related forms) enters the Middle Siwalik, at Nagri and Dhok Pathan, from about 10.7 Ma, and is abundant in the Dhok Pathan Formation. Equus sivalensis occurs in the Upper Siwalik (Tatrot and Pinjor, Early Pleistocene), and Equus namadicus in Pleistocene Narmada alluvium.

The sequence from Hipparion to Equus matches the expansion of grassland and the aridity that followed the uplift of the Himalaya.

(b) The Precambrian–Cambrian boundary with Indian examples

The boundary separates the Ediacaran from the Cambrian at about 538.8 Ma. Its GSSP is at Fortune Head, Newfoundland, defined by the first appearance of the trace fossil Treptichnus pedum. It marks the rise of complex burrowing and of skeletonised animals, the small shelly fossils.

In India it is recognised by fossils, carbon-isotope shifts and lithological change, because no single lithology marks it.

(i) Lesser Himalaya (Krol Belt). The Krol Formation (Ediacaran, stromatolitic carbonates) is overlain by the Tal Formation, whose lower parts hold trace fossils and small shelly fossils of the earliest Cambrian. The Tal also contains phosphorite, as at Mussoorie.

(ii) Spiti and Zanskar. The Parahio Formation of Spiti has Lower Cambrian trace fossils and trilobites.

(iii) Rajasthan. The Marwar Supergroup of Rajasthan shows late Ediacaran to Early Cambrian strata, with Cambrian trace fossils in its upper part.

(iv) Vindhyan Supergroup. The age of its upper part is debated, and it is used with caution.

Carbon-isotope excursions and ash-bed ages help correlate these sections with the global boundary.

(c) Rainwater harvesting and its techniques

Rainwater harvesting is the collection of rain from roofs or land and its storage or recharge into the ground, to raise the water table and reduce runoff. It is widely needed because of falling groundwater levels and urban flooding.

(i) Rooftop harvesting. Roof water runs through gutters and pipes, and a filter, into a storage tank, or into a recharge pit, trench or recharge well to the aquifer. Suitable for urban areas.

(ii) Surface spreading and storage. Check dams and nala bunds across streams, percolation tanks on permeable ground, gully plugs, contour bunds and farm ponds slow runoff and let it infiltrate.

(iii) Subsurface dykes hold groundwater in a stream bed.

(iv) Injection (recharge) wells send filtered water into deeper confined aquifers.

The sketches should show a roof, pipe, filter, tank and recharge pit, and the section of a percolation tank or check dam with the water table.

Indian examples. Traditional tankas and kunds in Rajasthan, and johads. Tamil Nadu made rooftop harvesting mandatory for buildings in 2001–03. The Jal Shakti Abhiyan's "Catch the Rain" campaign promotes it. Suitable sites depend on rainfall, soil permeability and the depth to the water table.