The archaeocetes (archaeo = ancient, cetes = cetaceans) are a group of mammals lived from 50 to 35 million years ago that gave origin to dolphins and whales. They are a very important group for the history of life because, leaving from the mainland, they accomplished the exceptional task of adapting to a completely different environment: water. This drastic change that occurred in the relatively short time of about 10 million years is accompanied and made possible by the deep physical changes we can observe in this hall, described step by step, on its three different levels.
At the first level of this evolutionary scale and in continuity with the previous exhibition we still find the artiodactyls, the mammal group archaeocetes originated from, represented by the skeleton of a fossil hippo (about 800,000 years ago, Rome) and by the life-size model of the small Indohyus. Hippopotamus is indicated by molecular biology as the living animal most closely related to dolphins and whales, but it is precisely the Indohyus, lived 50 million years ago in India to be the closest to the origin of cetaceans. In fact, although Indohyus is still an artiodactyl, and rather similar to the Mouse-deer, some peculiarities of its inner ear and the heaviness of its bones divide it from all other artiodactyls and is an evidence that it spent a lot of time in water.
At the beginning of the second level, we find the first true archaeocete, the oldest one: Pakicetus, lived in Pakistan about 48 million years ago. In fact it is in southern Asia, on the coast of the ancient Tethys, a wide tropical sea once located between Spain and Indonesia, which originated and evolved the first archaeocetes. On this same level are described in detail the many changes that made possible the complete adaptation of archaeocetes to aquatic life as the transformation of the legs into fins and the displacement of the nostrils on the top of the head.
On the third level we find the skeleton and the life-size model of Ambulocetus, lived 48 million years ago in Pakistan, to witness that intermediate stage of adaptation in which the archaeocetes appearance reminded that of large otters whose lifestyle they share. Also similar to Ambulocetus was Aegyptocetus whose original fossil is visible inside the glass case. It is a very rare specimen, one of the very few fossils of archaeocetes in Italy and the most complete one. Actually, this animal lived about 40 million years ago in Egypt and arrived in Italy within a block of nummulitic limestone purchased by a marble company.
The last phase of the transformation is represented by the big skull of Cinthyacetus: more than 9 meters long and with the hind legs reduced to rudiments. This archaeocete, lived between 38 and 35 million years ago in South America, was not able to get out of the water and its tail ended with the big fan fin so typical of today’s cetaceans, whose story is told on the upper floor.