As stated above, you seem to suggest that the relatively recent date (1500-1200 BP) ascribed to the submerged structures by the NIO has been arrived at based primarily on "what is claimed to a sculpture of a lion at location 4". In my own reading of the NIO statement, though, this doesn't seem to be as clearcut as you imply (I appreciate that you were there, of course, and I wasn't, so were presumably privy to other conversations not apparent in the NIO press release).
Just to quote some of the relevant parts of the press statement:
<i>A team of underwater archaeologists from National institute of Oceanography NIO have successfully 'unearthed' evidence of submerged structures off Mahabalipuram and <b>established first-ever proof of the popular belief that the Shore temple of Mahabalipuram is the remnant of series of total seven of such temples built that have been submerged in succession.</b> The discovery was made during a joint underwater exploration with Scientific Exploration Society, U.K.</i>
<i>The team of archaeologists from NIO, trained in diving, carried out underwater exploration between April 1 – 4, 2002 and have successfully recorded evidence of presence of ruins underwater off Mahabalipuram. The salient features of the findings are as follows:</i>
<i><b>· Underwater investigations were carried out at 5 locations in the 5 – 8 m water depths, 500 to 700 m off Shore temple.</b></i>
<i>· Investigations at each location have shown presence of the construction of stone masonry, remains of walls, a big square rock cut remains, scattered square and rectangular stone blocks, big platform leading the steps to it amidst of the geological formations of the rocks that occur locally.</i>
<i>· Most of the structures are badly damaged and scattered in a vast area, having biological growth of Barnacles, Mussels and other organisms.</i>
<i><b>· The construction pattern and area, about 100m X 50m, appears to be same at each location.</b> The actual area covered by ruins may extend well beyond the explored locations.</i>
<i><b>· Based on what appears to be a Lion figure, of location 4, ruins are inferred to be parts of temple complex.</b></i>
<i><b>· The possible date of the ruins may be 1500-1200 years BP. Pallava dynasty, ruling the area during the period, has constructed many such rock cut and structural temples in Mahabalipuram and Kanchipuram.</b></i>
From the NIO press statement itself, it seems to me that the discovery of the apparent lion sculpture has been used <i>only</i> to suggest that these ruins were part of a temple complex. The NIO's reasons for arriving at a preliminary date of 1500 BP-1200 BP for the submerged structures seems to have been based on a combination of factors, including the relatively shallow depth at which the ruins were discovered (5-8 m), the relatively close proximity of the ruins to the shore (500-700 m), the fact that all five locations displayed similar construction patterns, and the fact that local Tamil tradition has long maintained that the Shore Temple was the last surviving of seven original temples (the belief that parts of Mamallapuram were submerged in the past seems to be relatively common knowledge among Tamils themselves - something Prema has alluded to in an earlier post on this MB, and referred to by Kat above).
In an earlier thread (over at Ma'at, but possibly here as well), I posted some information about Mamallapuram that it might be useful to repeat here:
(1) <i><b>Mamallapuram, the city of Mamalla, is after the title of great Pallava ruler Narasimhavarman-I (AD 630-68).</b> It was a sea-port during the time of Periplus (Ist century AD) and Ptolemy (AD 140) and many Indian colonists sailed to South-East Asia through this port town. While there is some evidence of architectural activity going back to the period of Mahendravarman-I (AD 600-30), the father of Mamalla, most of the monuments like rock-cut rathas, sculptured scenes on open rocks like Arjuna's penance, the caves of Govardhanadhari and ahishasuramardini,the Jala-Sayana Perumal temple (the sleeping Mahavishnu or Chakrin at the rear part of the Shore temple complex) are attributed to the period of Narasimhavarman-I Mamalla.</i> From <a href="[asi.nic.in];
(2) <i><b>The Shore Temple was commissioned by Narasimhavarman’s son, Rajasimhavarman.</b> Its proper name is, in fact, the Rajasimheswara. <b>Before it was designated a UNESCO World Heritage Site, and surrounded by a protective barrier ("like anti-tank fortifications" in the words of one critic) the 8th century temple was on the beach, exposed to the breaking waves.</b></i> From <a href="[www3.bc.sympatico.ca] SHORE">here</a>
(3) <i>In the south-east of India, after the collapse of the Andhra dynasty as early as the first century BC, the Pallavas came to power. The Pallavas were Buddhists to start with, but in the fifth century they converted to Brahmanism. Also, they were great sea-faring traders and their chief seaport at Mamallapuram (now Mahabalipuram) later also blossomed into a great artistic centre during the reign of Narsimha Varman I ...</i>
<i><b>After the death of Narsimha Varman I ... some construction was carried out at Mamallapuram and famous amongst these is the Shore Temple dedicated to Lord Shiva ... Local legend claims that there were once four other temples alongside of this, but they were washed away by the sea. In fact this existing temple also gives signs of melting away, from the constant onslaught of the sun and water erosion.</b></i> From <a href="[www.indianartcircle.com];
(4) <i><b>They say there were seven pagodas or temples on the shores of Mahabalipuram. All but one were pillaged by the rapacious sea, though there is little underwater evidence to substantiate
their existence.</b></i> From <a href="[www.indianvisit.com];
(5) <i><b>Though now deserted, Mamallapuram was a substantial city, created as a port for overseas trade by the Pallava ruler, Narasimhavarman І- called ‘Mamalla,’ the ‘great fighter’ – who reigned from c. 630 to 668.</b> Today, a beach of white sand remains facing the deep blue of the bay of Bengal, and separated from the mainland by salt water inlets; it is covered with carved and excavated rock. Nothing of the secular architecture of this once thriving seaport and important pilgrim center has survived, because much of it was constructed of perishable materials. The foundations of the citadel can, however, still be traced. Inside were the palaces and administrative buildings, the wooden framework of which was filled in with brick and plaster.</i> From <a href="[www.indiablessings.com];
Just curious, but isn't this <i>historical</i> context relevant to any discussion about the possible dating of these submerged structures?
P.S. - Apologies for being such a 'stickler' for detail ...