Siwalik Fossil Park, Himachal Pradesh State, India: Part 1
Khursheed Dinshaw (India)
The Siwalik Fossil Park is located amidst the scenic Siwalik Hills in the district of Sirmaur in the state of Himachal Pradesh, India. On 23 March 1974, the park was established by the Geological Survey of India in collaboration with the Himachal Pradesh Government. It contains many life-size, fibreglass models. These models are outside in the park and are based on the study of the fossils that have been found here and a field museum. The models are of prehistoric animals, which thrived in the area from to 1 to 2.5mya. The museum displays Siwalik vertebrates collected from the area. A catalogue of all the fossils and specimens displayed in the museum has now been documented providing their photographs, taxonomic status and locality, along with collectors’ names and the field season during which they were collected.
The Siwalik rocks are famous the world over for the remains of various vertebrate animals and plants. There are varied geological formations of the park, like the Jarasi, Spiti and Giumal Formations. The Jarasi consists of red purple shale with gypsum bands and are Neo-proterozoic to Ediacaran in age.
The Spiti Formation is one which has fossiliferous shale containing ammonites, belemnites, bivalves and brachiopods. Its broad age is Oxfordian to early Valanginian. The Guimal Formation has fossiliferous sandstone with shells and it belongs to the Lower Cretaceous.
A large number of lakes interspersed with swamps and dense forests occupied the Siwalik area during the time when these animals were alive. In particular, the ecological setting gave considerable scope for the abundant development of turtles, fossils of which (shells and dermal scutes) have been found. This animal gradually dwindled in number during the last two million years and leaving just the present day form of land tortoises of smaller size.
Fossils in the museum include a complete carapace, whose surface is without ornamentation while its mouth opening is a clear arc-shaped. There is also another complete carapace, which is partly damaged at the posterior end. The carapace is the back convex part of the shell of the turtle consisting of animal’s rib cage, combined with dermal plates beneath the skin, which interlock to form a hard shell exterior to the skin. The shell is covered by scutes, which are horny plates made of keratin that protect the shell from scrapes and bruises. Another exhibit is a complete carapace, which was collected from a thick clay bed. This indicates that this form preferred a lake/swamp habitat.
Another partial carapace, which is a fairly large size, has distinct ornamentation and was recovered from a fragile, poorly graded siltstone bed indicating that it lived in a dry habitat. Completing the collection of fossil turtles, there are fused vertebras, which probably belonged to a large turtle, and a carapace that is highly domed and is characterised by completely fused dermal plates and an absence of surface ornamentation.
Fossils of hippopotamus are found in profusion in the 2 to 3myr rocks of this region. All fossils belong to the same species, Hexaprotodon sivalensis, whose jaw had six incisors and two large canines. The species became extinct about 1.5mya from this area. The fossils include skulls, jaws and teeth.
PS Gill, Director of the Geological Survey of India in Chandigarh, says:
The skull and mandible of crocodile recovered from the rocks in Siwalik and skull fossil of gharial from Mansol near Chandigarh in the state of Punjab are about 2.5mya. The gharial had a long, slender snout that was at least three times as long as it is broad at the base. It had 25 to 30 slightly curved and pointed teeth of nearly uniform size on each side of the jaw. The Siwalik form, Gavialis browni, resembles in shape and size the living form, namely Gavialis gangeticus”.
From the pre-Siwalik rocks there are leaf impressions, completely fossilised specimens of the Glossopteris, Vertebraria indica, and well-silicified rounded fragment of stem, petrified wood fossil fragments and more complete fossil wood. Plants and animals devoid of hard parts get preserved in the form of imprints within rock beds. Distinct impressions of leaves of plants occurring in some of the rocks are pertinent examples of this mode of preservation. These form no internal part of the plants or animals represented by them.
Fossil fish, amphibians and reptiles from pre-Siwalik rocks include an extinct genus of ray-finned fish from the Jurassic showing rows of rectangular scales. Other displays include fin fragments, fin rays originating from the base, a cast of a plastron, which is the ventral surface of a shell of turtle, and cast of a rock showing impression of a small, fully-preserved juvenile frog.
Early discoveries in the park included Tragulids (small, hornless ungulates looking much like large rodents or rabbits) and consist of three genera, namely Dorcabune, Dorcatherium and Siamotragulus. In the Early and Middle Miocene, they were common, but their numbers dwindled making them unusual by the Late Miocene and Pliocene.
The second part of this article is entitled Siwalik Fossil Park, Himachal Pradesh State, India: Part 2.
All photographs are by Khursheed Dinshaw.