When archaeocetes became odontocetes they made two first-draft dolphins

According to Wikipedia – Archaeoceti
“they include the initial amphibious stages in cetacean evolution, thus are the ancestors of both modern cetacean suborders, Mysticeti and Odontoceti.”

This is wrong according to the large reptile tree, (LRT, 2330 taxa) which nests archaeocetes (Fig 1) basal to Odontoceti only.

By contrast, mysticetes arose from hippos and desmostylians.

According to Wikipedia – Mammalodon
“is an extinct genus of archaic baleen whale.”

This is also wrong. In the LRT Mammalodon (Fig 1) nests between archaeocetes and odontocetes.

“Mammalodon was, at first, considered to be a member of Archaeoceti,”

This is correct according to the LRT.

According to Wikipedia – Janjucetus
“is an extinct genus of cetacean, and a basal baleen whale.”

This is also wrong. In the LRT Janjucetus (Fig 1) nests between archaeocetes and odontocetes with Mammalodon.

“Unlike modern mysticetes, it possessed large teeth for gripping and shredding prey, and lacked baleen, and so was likely to have been a predator that captured large single prey animals rather than filter feeding.”

This is correct.

Phylogenetic miniaturization.
In the LRT this series of taxa (Fig 1) not only produces smaller taxa with a shorter rostrum (due to neotony) it also produced two odd dolphin-sized taxa, Mammalodon and Janjucetus (Fig 1) – that took an evolutionary detour. They had teeth unlike their relatives and unlike each other.

Between Coronodon and Aetiocetus
the tooth shape simplified to conical shapes in Aetiocetus and Chonecetus (a reversal) from the primitive multi-cusped teeth of Coronodon. Simple cones were successful. They are also found in dolphins and sperm whales.

In this regard, Mammalodon and Janjucetus are exceptions from this pattern.
Those experiments failed.

Mammalodon colliveri
(Pritchard 1939; Late Oligocene, est 3 m in length) was previously considered a basal mysticete with teeth, closely resembling Janjucetus. Here it nests with Janjucetus and archaeocetes leading to odontocetes. The snout is shorter than the cranium.

Janjucetus hunderi
(Fitzgerald 2006; late Oligocene; est. 3.5m in length) was originally considered the basalmost Mysticeti (baleen whale), but it had large serration teeth, the whale-like post-crania imnagined by Fitzgerald is supported by phylogenetic bracketing, but this is a relative of Aetiocetus, basal to Odontoceti (toothed whale). The skull was more than twice as wide as tall. The orbit was at mid skull, not in the posterior half, as in related taxa. This is a result of phylogenetic miniaturization and neotony.

References
Fitzgerald EMG 2006. A bizarre new toothed mysticete (Cetacea) from Australia and the early evolution of baleen whales. Proceedings of the Royal Society B 273:2955-2963.
Pritchard G B 1939. On the discovery of a fossil whale in the older tertiaries of Torquay, Victoria. The Victorian Naturalist 55:151-159.

wiki/Archaeoceti
wiki/Aetiocetus
wiki/Coronodon
wiki/Janjucetus
wiki/Mammalodon

Mammalodon and Janjucetus move to the odontocete clade

Source: https://pterosaurheresies.wordpress.com/2024/12/05/when-archaeocetes-became-odontocetes-they-made-two-first-draft-dolphins/