Initially thought to represent a species of Platyosphys (now Pachycetus), Antaecetus was described in 2015 based on fossils from the Aridal Formation of the Gueran depression, southwestern Morocco.

The fossil material, consisting of a partial skull (later thought to have been that of Eocetus[1]), a tympanic bulla and various vertebrae was recovered in 2014 along with remains of various other basal whales, leading to the recognition of the Gueran depression as an important assemblage for research on early cetaceans.

[2] Several years after this initial paper was published a second publication was released, dealing in part with the taxonomy of Platyosphys in an attempt to clarify its status.

At the same time, following the discovery of an additional, much better preserved specimen from El Brije, P. aithai was reexamined and found to be sufficiently distinct to warrant it being placed in its own genus, which the authors dubbed Antaecetus.

In the myths Antaeus was the son of Gaia and the sea god Poseidon and was said to reside in western North Africa with his tomb being found in Morocco.

The species name derives from Amer Ait Ha, an experienced fossil collector who was responsible for guiding researchers to the Gueran locality.

[2] The skull of Antaecetus is noticeably smaller than that of Pachycetus relative to its body, measuring a total of 69.5 cm (27.4 in) from the tip of the premaxillae to the occipital condyles.

Philip Gingerich and colleagues note that canine size may be sexually dimorphic in archaeocetes, meaning that the El Brije specimen could be a female.

The diapophysis is eventually lost by the posterior vertebrae of the thorax and the rib articulation is altered even further, with the capitular facets becoming even more pit-like and now being situated atop the elevated surface of the parapophysis.

[2][1] A phylogenetic analysis conducted in 2023 confirmed the hypothesis that Antaecetus was a close relative of Pachycetus, the relationship between them being strongly supported by the results and validating the clade Pachycetinae that was erected to contain the two taxa.

For instance, the corresponding increase in ballast and lung volume would have been useful for a slow-moving animal, possibly one feeding in shallow waters close to the ocean floor.

[1] From this Gingerich, Ayoub Amane and Zhouri hypothesize that Antaecetus, like Pachycetus, was a slow-moving animal inhabiting shallow coastal waters.

However, its precise ecology proved to be more elusive, with its small, gracile teeth unfit to deal with either vegetation or hard-shelled prey (ruling out lifestyles akin to those of manatees and sea otters).

Antaecetus was one of the larger whales of this assemblage, together with the large protocetid Pappocetus and the basilosaurid Eocetus schweinfurthii, which was the largest cetacean of the locality.