[Neal Robbins]

Ichthyolestes was an ancestor of today's whales. This creature was about the size of a fox. It lived in what is now Pakistan about 50 million years ago, which was during the Eocene period.
Ichthyolestes was a Pakicetid. The Pakicetids were land dwelling mammals that lived close to the Tethys Sea. Ichthyolestes and other pakicetids are discussed in an article titled Skeletons of terrestrial cetaceans and the relationship of whales to artiodactyls. It was published in Nature 413, 227-281 on September 20, 2001. The authors are J.G.M. Thewissen, E.M. Williams, L.J. Roe, and S.T. Hussain. This excerpt says:

Aquatic postcranial adaptations are pronounced in late Eocene basilosaurids and dorudontids, the oldest obligage aquatic cetaceans for which the entire skeleton is known, and therefore can be used to evaluate pakicetid morphology. Aquatic adaptations of basilosaurids and dorudontids include: presence of short neck vertebrae, thoraic and lumbar vertebrae that are similar in length; infused sacral vertebrae, lack of a sacro-iliac joint; presence of a short tail with a ball-vertebra (a vertebra at the base of the fluke), with anterior acromion and small supraspinous fossa; an ulna with a large and transversely flat olecranon; a wrist and distal forearm flattened in the plane of the hand; and tiny hind limbs.
Pakicetids display none of these features. Pakicetid neck vertebrae are longer than late Eocene whales (Fig. 1a and b), and the trunk vertebrae increase in size from anterior to posterior (Fig. 1c-f) as in land animals. Lumbar and caudal veretebrae are long compared to those of modern cetaceans, but not as long as in extinct cetaceans that swam by undulating their spine (for example, the remingtonocetid Kutchicetus).

The authors make another important point of comparison in this statement:

The pakicetid sacrum consists of four solidly fused vertebrae and there is a strong sacro-iliac joint, as in land mammals and in amphibious whales, such as Ambulocetus and Kutchicetus, but unlike other cetaceans.

The author also mention that Pakicetus was the largest in size of the known pakicetid genera. They point out that Kutchicetus was 5% smaller and that Ichthyolestes was 29% smaller.

Neal Robbins

P.S. The taxonomy of Ichthyolestes is:

Kingdom: Animalia
Phylum: Chordata
Class: Animalia
Order: Cetacea
Family: Protocetidae
Subfamily: Pakicetinae
Genus: Ichthyolestes
Species: Ichthyolestes pinfoldi