Updated November 8. 2016 with a revision to the nesting of Janjucetus after the inclusion of the desmostylian and mysticete sister, Behemotops.
You might have suspected this all along
since the two orders of whales, Odontoceti and Mysticeti, are so different from one another. The present study indicates we will never find a last common ancestor with flippers and fins for all living whales because the two orders arose from two widely separated mammal orders with legs.
Baleen whales (Mysticeti) arise from Paleoparadoxia and Anthracobune in the large reptile tree. So there IS now evidence in the LRT for a hippo relationship, as these taxa are more or less related to hippos. But the hippo clade (Mesonychidae) is separated from the artiodactyls by several nodes, so even mysticete whales are not close to artiodactyls.
Toothed whales (Odontoceti) still arise from tenrecs as noted here earlier.
That makes living whales diphyletic
and the order name ‘Cetacea’ invalid and useless because it is not monophyletic. It will probably take a century to disappear because it is so ingrained.
DNA tests validated
at least for Mysticeti as they relate to hippos, the only living mesonychids. Not sure if Odontoceti has been tested against tenrecs in DNA testing.
Discovered during testing
When you include living odontocetes and mysticetes in the same cladogram these taxa will nest together with either tenrecs or mesonychids in two separate trees due to their massive convergence. However, when you enter them in separate tests (Fig. 1) the two orders of whales will nest separately based on the present taxon and character lists.
Figure 1. Subset of the LRT, higher placental mammals with a focus on whales (yellow) and their ancestral clades, the Tenrecidae and Mesonychidae. Both are a fair distance from artiodactyls. This cladogram updates an earlier one that nested Janjucetus with Balaenoptera.
This we learn
after adding Janjucetus hunderi (Fig. 2; Fitzgerald 2006; Late Oligocene; NMV P216929 (Museum Victoria Palaeontology Collection, Melbourne, Australia), Orcinus (killer whale; Fig. 5) and Balaenoptera musculus (blue whale; Fig. 4) to the large reptile tree (Fig. 1).
Figure 2. Janjucetus is known from a well-preserved skull, a scapula rib and not much else. Here it is as a whale compared to Paleoparadoxia to scale. Janjucetus had legs, not flippers and flukes based on phylogenetic bracketing.
That low wide skull
and procumbent premaxillary teeth of Janucetus (Fig. 3) are obvious early clues that we’re not dealing with giant carnivorous tenrecs here, but with herbivores at home underwater, like hippos and desmostylians (including Paleoparadoxus (Fig. 2). Baleen whales also lack echolocation skills, something toothed whales got from tiny tenrecs.
“Desmostylians are the only known extinct order of marine mammals.”
Not any more.
From the Fitzgerald abstract
“Unlike all other mysticetes, this new whale was small, had enormous eyes and lacked derived adaptations for bulk filter-feeding. Several morphological features suggest that this mysticete was a macrophagous predator, being convergent on some Mesozoic marine reptiles and the extant leopard seal (Hydrurga leptonyx).”
That’s because Janjucetus is not a whale, but a whale ancestor more closely related to Anthracobune (Fig. 1).
Figure 3. The skull of Janjucetus in 3 views. Images from Fitzgerald 2006. Colors added. This is an incredible find that I just yesterday became aware of.
From the Fitzgerald text
“The origins and early evolution of the two extant suborders of Cetacea (Odontoceti and Mysticeti) remain poorly understood. Among the latter two groups, the origins of the Mysticeti (baleen whales), and their unique feeding mechanism,have proved particularly baffling.In this study, I report a new Late Oligocene toothed mysticete from Australia that is more basal than any previously described.”
Hate to report this, but it’s anthracobune, not a whale. The desmostylian, Behemotops makes a better (more parsimonious) ancestor to baleen whales.
Figure 4. Blue whale (Balaenoptera musculus) skull and skeleton. Note the lack of a thumb goes back to Mesonyx and Paleoparadoxia
Fitzgerald did not test Janjucetus and other whales against any of the taxa in the tenrec clade. Hippopotamus was the outgroup taxon. Has the monophyly of the Cetacea ever been questioned or tested before?
Figure 5. The killer whale (Orcinus orca) skeleton and skull with parts colorized. Note the retention of five fingers and a sternal series. This, too, is a giant aquatic tenrec.
A few days ago
we looked at the double-pulley shape of the artiodactyl and whale astragalus (ankle bone). Today I added an image of the Leptictidium (tenrec) ankle, also sharing a double-pulley ankle joint. You can see it here.
Figure 7. Sperm whale (Physeter macrocephalus) with bones colorized for clarity. Note the five fingers and fewer dorsal ribs.
Whales and molars
In the very little time that I’ve looked at whales and their ancestors it appears that the molars shrink and disappear, losing cusps and size, making room for more canines and more canine-like premolars. The incisors are missing from the premaxilla of the killer whale. Teeth are morphologically plastic and change their shape, size and number often, not only in mammals, but in many other reptile clades. I’m not a whale dentist, so if one is out there, please send any data you may have on whale tooth identification and eruption patterns and I will share it.
as you probably know, dugongs are whale-like herbivores with fins and whale-like flukes. So the separation of odontocetes from mysticetes should come as less of a shock. If I’ve made any errors here, please let me know. I’m still a newbie at whale morphology.
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.