SVP 2018: Tooth loss in mysticete whales x5 abstracts

Five SVP abstracts
fumble with the issue of tooth loss preceding the origin of mysticete whales under the invalid assumption that the traditional clade Cetacea is monophyletic. It is not. Whales had two or three (right whales make it three) separate origins, as we learned earlier here.

ABSTRACT 1
Ekdale and Deméré 2018
continue beating a dead horse trying to figure out how Aetiocetus evolved into the clade Mysticeti (Figs. 1-4). In the large reptile tree (LRT, 1038 taxa) mysticetes evolved from desmostylians (Fig. 2-4) while being tested against all prior candidate taxa. Odontocetes evolved from tenrecs, pakicetids and archaeocetids (Fig. 1). Ekdale and Deméré 2018 mistakenly (through taxon exclusion) consider the toothed Aetiocetus a member of the traditional ‘toothed mysticetes’ that they mistakenly think “plays a central role in the debate.”

Figure 4. Subset of the LRT focusing on the odontocetes and their ancestors.
Figure 4. Subset of the LRT focusing on the odontocetes and their ancestors.

The authors conclude:
“These results provide critical evidence that the lateral palatal foramina in A. weltoni are
homologous with lateral nutrient foramina in extant mysticetes. As such, the lateral nutrient
foramina in A. weltoni provide strong support for the hypothesis that aetiocetids possessed both teeth and some form of baleen.”
 Unfortunately the authors saw what they wanted to see. They never tested tenrecs or desmostylians and so failed to recover the correct phylogenetic framework upon which their work could proceed. Maybe a similar CT scan will find similar nerve and blood vessel patterns in desmostyians. Only testing will reveal what the cladogram indicates.

Figure 1. Subset of the LRT focusing on the mesonyx/mysticete clade showing the split between right whales and all other mysticetes.
Figure 2. Subset of the LRT focusing on the mesonyx/mysticete clade showing the split between right whales and all other mysticetes.

ABSTRACT 2
Gatesy et al. 2018 reassess “phylogenetic studies presented over the past dozen years that have variously reconstructed this complex evolutionary sequence. Early work proposed a step-wise transformation in which toothed mysticetes transitioned via ‘intermediate’ forms with both teeth and baleen to toothless filter feeders. Later studies presented alternative scenarios featuring filtration with teeth instead of baleen, loss of a functional dentition before the evolution of baleen, pure suction feeding, and/or convergent evolution of several key mysticete features. We reanalyzed published cladistic matrices in the context of extensive new molecular data, assessed character support for alternative relationships, and mapped six features related to filter feeding in Mysticeti: presence/absence of 1) teeth, 2) baleen, 3) lateral nutrient foramina on the palate (possible osteological correlates of baleen), 4) a broad rostrum, 5) laterally bowed mandibles, and 6) an unsutured mandibular symphysis.”

All for naught.
They could have and should have run a wide gamut phylogenetic analysis like the LRT which separates the ancestors of odontocetes from the ancestors of mysticetes by a wide phylogenetic distance of intervening taxa (Figs. 1, 2). The ancestors of mysticetes are not to be found among the ancestors of odontocetes. This has been online for two years now.

ABSTRACT 3
Geisler, Beatty and Boessnecker 2018
discuss, to no avail, new specimens of Coronodon havensteini, which they say is the most basal mysticete (in the absence of desmostylians and kin) and the LRT nests at the base of the odontocetes and aetiocetes. Surprisingly, the authors report, these specimens support the hypothesis that Coronodon engaged in macrophagy and filter feeding, and underscores the challenges for reconstructing the behaviors of extinct species based on the limited sample provided by the fossil record.” No they have evidence for macrophagy and they have contrived a scenario for filter feeding. 

Figure 1. Taxa in the lineage of the right whale (Eubalaena) include the pygmy right whale (Caperea) and the desmostylian, Desmostylus.
Figure 3. Taxa in the lineage of the right whale (Eubalaena) include the pygmy right whale (Caperea) and the desmostylian, Desmostylus. You don’t have to look for tooth loss in desmostylians. They already have that trait and so many more.

ABSTRACT 4
Lanzetti, Berta and Ekdale 2018
looked at fetal mysticetes and reported, “We present new evidence on the ontogeny of the minke whale, which develops a dense tissue dorsal to the rostral canal where the tooth buds are either already absent or clearly undergoing resorption. The identity of this tissue should be confirmed by histological analysis, but it may be the first sign of baleen development, as posited by previous studies of these species. Overall, the GM analyses show that the fossils occupy a different morphospace than modern species, possibly indicating that they had specific feeding adaptations not shared by modern mysticetes.”
Clearly they are not looking at desmostylians, which loose most of their teeth in adults.

Figure 1. Rorqual evolution from desmostylians, Neoparadoxia, the RBCM specimen of Behemotops, Miocaperea, Eschrichtius and Cetotherium, not to scale.
Figure 41. Rorqual evolution from desmostylians, Neoparadoxia, the RBCM specimen of Behemotops, Miocaperea, Eschrichtius and Cetotherium, not to scale.

ABSTRACT 5
Peredo 2018
thinks tooth loss precedes the origin of baleen in mysticetes by considering an Early Oligocene specimen from Oregon. In his thinking Peredo, like the authors above, is barking up the wrong tree when he reports, “Although living baleen whales are born without teeth, paleontological and embryological evidence demonstrate that they evolved from toothed ancestors that lacked baleen entirely.” However his specimen might be a desmostylian in the lineage of mysticetes when he reports, “This new material includes a transitional fossil mysticete that lacks both teeth and baleen entirely, demonstrating that tooth loss precedes the origin of baleen in mysticetes.”

A toothy Oregon taxon, Salishicetus, was described by Peredo and Pyenson 2018, who nested it basal to other aetiocetids. They reported, “The description of Salishicetus resolves phylogenetic relationships among aetiocetids, which provides a basis for reconstructing ancestral feeding morphology along the stem leading to crown Mysticeti.”

References
Ekdale EG and Deméré TA 2018. Tooth-to-baleen transition in mysticetes: New CT evidence of vascular structures on the palate of Aetiocetus weltoni (Mysticeti, Cetacea). SVP abstract.
Gatesy et al. (4 co-authors) 2018. Contrasting interpretations of the teeth to baleen transition in mysticete cetaceans. SVP abstract.
Geisler J, Beatty BL and Boessenecker RW 2018. New specimens of Coronodon havensteini provide insights into the transition from raptorial to filter feeding in whales. SVP abstract.
Lanzetti A, Berta A and Ekdale EG 2018. Looking at fossils in a new light: teeth to baleen transition in relation to the ontogeny and phylogeny of baleen whales. SVP abstract.
Peredo CM 2018. From teeth to baleen: Tooth loss precedes the origin of baleen in whales. SVP abstracts.
Peredo CM and Pyenson ND 2018. Salishicetus meadi, a new aetiocetid from the late Oligocene of Washington State and implications for feeding transitions in early mysticete evolution. Royal Society Open Science 5: 172336. http://dx.doi.org/10.1098/rsos.172336

Coronodon: another wannabe mysticete ancestor

Geisler et al. 2017
presented Coronodon as a recent addition to the panoply of toothed whales said to be ancestral to mysticetes. Taxon exclusion is once again the problem. The real ancestors of mysticetes (Fig. 3) are mesonychids, hippos, anthracobunids and desmostylians, as we learned earlier. These taxa were not tested by Geisler et al. 2017.

Figure 1. Coronodon, was originally considered a toothed mysticete, but only in the absence of desmostylians, the real ancestors of mysticetes.

Figure 1. Coronodon, was originally considered a toothed mysticete, but only in the absence of desmostylians, the real ancestors of mysticetes. This taxon lies at the base of Odontoceti and Aetioceti in the LRT.

Coronodon havensteini (Geisler et al., 2017; early Oligocene, 30 mya) was originally and is traditionally considered a mysticete whale, basal to baleen whales like Balaenoptera. With more tested taxa here it nests basal to odontocete whales like Aetiocetus and Physeter. The archaeocete teeth were considered the first stage in filter-feeding. Here they are relics from an archaeocete ancestry. Descendants in both branches (aetiocetes, odontocetes) both have simple peg teeth.

Figure 2. The nesting of Eocene Andrewsiphius basal to extant tenrecs between leptictids and pakicetids.

Figure 2. The nesting of Eocene Andrewsiphius basal to extant tenrecs between leptictids and pakicetids.

The LRT ancestors to mysticetes
are shown below:

Figure 1. Rorqual evolution from desmostylians, Neoparadoxia, the RBCM specimen of Behemotops, Miocaperea, Eschrichtius and Cetotherium, not to scale.

Figure 3. Rorqual evolution from desmostylians, Neoparadoxia, the RBCM specimen of Behemotops, Miocaperea, Eschrichtius and Cetotherium, not to scale. Key post-crania is missing here, but the skulls tell the tale.

References
Geisler JH; Boessenecker RW; Brown M; Beatty BL 2017. The origin of filter feeding in whales. Current Biology. 27 (13): 2036–2042.e2. doi:10.1016/j.cub.2017.06.003

wiki/Aetiocetus
wiki/Coronodon

Sitsqwayk: Not a transitional (toothed/baleen) whale

Sitsqwik cornishorum (Peredo and Uhen 2016, Fig. 1) was originally considered a transitional whale linking toothy aetiotheres to toothless mysticetes (but only in the absence of desmostylians).

Figure 1. Sitsqwayk reconstruction over the ghosted image of Cetotherium. 456 cm represents the 'total body length' according to Peredo and Uhen 2016. The rostrum is restored shorter here to match the mandible.

Figure 1. Sitsqwayk reconstruction over the ghosted image of Cetotherium. 456 cm represents the ‘total body length’ according to Peredo and Uhen 2016. Seems too short. The largely restored rostrum is shorter here to match the mandible.

Taxon exclusion issues
Here testing a wider gamut of mysticete ancestor candidates, Sitsqwayk nests between Cetotherium and two other cetotheres,  Yamatocetus and TokarahiaSitsqwayk has a short rostrum, a convex posterior mandible and a relatively large scapula. The total length was reported as 456 cm, which would make it proportionately much shorter than Cetotherium (ghosted Fig. 1), based on a common scapula size.

Figure 2. Subset of the LRT focusing on mysticetes, including Sitsqwayk, and their predecessors.

Figure 2. Subset of the LRT focusing on mysticetes, including Sitsqwayk, and their mesonychid and desmostylian predecessors. Note that hippos are not artiodactyls, contra tradition.

The term chaeomysticeti (see citation below)
refers to the ‘toothless’ mysticetes. Such a clade is only possible if aetiocetes and Mammalodon are considered mysticetes, but they are not in the large reptile tree (LRT, 1201 taxa) where all mysticetes are toothless and they arise from desmostylians. Mammalodon has teeth, but it is basal to desmostylians, which progressively loose their teeth as they transition to baleen.

Going one step further…
current evidence (i.e. the LRT) indicates that mysticetes should be divided between right whales and all other mysticetes, both with desmostylian ancestors with legs.

It only takes the deletion of a few taxa
to nest odontocetes with mysticetes, or to nest mysticetes with odontocetes in the LRT, due to massive convergence in living whales… as you might expect. That’s why taxon exclusion can be such a problem in phylogenetic analysis. (Keyword: ‘taxon exclusion‘ for dozens of examples of this in this blog).

References
Peredo CM and Uhen MD 2016. A new basal chaeomysticete (Mammalia: Cetacea) from the Late Oligocene Pysht Formation of Washington, USA. Papers in Palaeontology. 2 (4): 533–554.

wiki/Cetotherium
wiki/Sitsqwayk

Mystacodon: See how far they’ll go to ‘find’ a mysticete ancestor

According to Wikipedia
Mystacodon (Lambert et al. 2017) is a genus of toothed mysticete from the Late Eocene Yumaque Formation of Peru. It is the earliest known member of the Mysticeti, and the second confirmed Eocene mysticete.” Here (Fig. 1) you can compare it to the smaller and more primitive (because it has a bigger pelvis) Maiacetus, to scale. Mystacodon is no mysticete. It’s what a tenrec/odontocete becomes when it gets good at swimming, but not as good as Zeuglodon, which has an even smaller pelvis. We looked at the origin of mysticetes among desmostylians earlier here, here and here. It was first reported here, last October, perhaps too late for the manuscript submission publishing schedule. Even so, whale experts have omitted, overlooked or ignored desmostylians in their quest for mysticete ancestors, and this is what happens.

This is what happens with taxon exclusion.
You get a ‘by default’ nesting, like nesting turtles and Vancleavea with archosaurs or Tetraceratops with therapsids. It also reminds me of when David Hone and Sterling Nesbitt bent over backward to find a mandibular fenestra and an antorbital fossa on pterosaurs in a desperate attempt to prove an invalid hypothesis.

FIgure 1. This toothy whale with a tiny pelvis is Mystcodon, originally promoted as the earliest known mysticete (baleen whale).

FIgure 1. My, what big teeth you have! This toothy whale with a tiny pelvis is Mystcodon, originally promoted as the earliest known mysticete (baleen whale). Note the size and placement of the teeth matching Maiacetus.

And the whale authors got all the publicity they wanted
in this Guardian article with illustrations. Here is a quote from the article:

“Fossil hunters say they have unearthed a missing link in the evolution of baleen whales after digging up the remains of a creature thought to have lived more than 36 million years ago.

The whales, known as mysticeti, sport a bristling collection of sieve-like plates known as baleen that they use to filter water for food. Species include the enormous blue whale, the gray whale and the humpback whale.

But while baleen whales are known to have shared a common ancestor with toothed whales, which are the other major group of modern whales, the path by which the creatures emerged has been somewhat hazily understood. Now researchers say they have discovered the oldest known cousin of modern baleen whales, offering unprecedented insights into their evolution.

“This [split in the family tree] has been dated to about 38 or 39m years ago,” said Olivier Lambert, co-author of the research from the Royal Belgian Institute of Natural Sciences. “The whale we discovered here has been dated to 36.4 [million years ago], so it is only two to three million years younger than this presumed origin.”

From Nature.com:
“This is the fossil that we’ve been waiting for,” says Nick Pyenson, a palaeontologist at the Smithsonian National Museum of Natural History in Washington DC. 

“To determine where M. selenensis fit in the whale family tree, the researchers compared characteristics such as the shape of its skull and pelvic bone to those of other fossil whales. The creature’s flat snout resembles that of modern baleen whales. But its pelvic bone fit more with ancestral whales, complete with areas where the leg bones would typically slot in, says Lambert. “So, we think that this animal still had tiny legs protruding from the body.”

“Lambert and his colleagues think that M. selenensis might have sucked up its prey from the ocean floor. This wasn’t unusual, however, because baleen-whale ancestors around that time sported a wide variety of dental and feeding mechanisms. “There’s big toothed things, there’s little toothed things and there’s toothless things, all at once,” says Uhen. But by around 23 million years ago, all the whales in this group had baleen, and “all these toothy things go away”, he says.”

Mystacodon has a wide flat triangular rostrum…
so does Physeter, the sperm whale (Fig. 3).

Figure 3. Physeter (sperm whale) skull. Note the low, flat, triangular toothless rostrum.

Figure 3. Physeter (sperm whale) skull. Note the low, flat, triangular toothless rostrum.

Workers:
Examine all possible candidates. Don’t exclude relevant taxa. Mystacodon sheds no light on the origin of baleen whales—but it does shed light on the origin of odontocetes.

References
Lambert, O. et al. (seven co-authors) 2017. Earliest Mysticete from the Late Eocene of Peru Sheds New Light on the Origin of Baleen Whales. Current Biology 27:1535–1541.e2 doi:10.1016/j.cub.2017.04.026.

 

Evolution of the other baleen whales according to the LRT

Earlier we looked at the evolution of right whales from desmostylians like Desmostylus.  Today we’ll look at the other baleen whales: the rorquals, gray whales and cetotheres (Fig. 1), as recovered by the large gamut analysis of the large reptile tree (LRT, 1161 taxa, see subset below Fig. 3).

Figure 1. Rorqual evolution from desmostylians, Neoparadoxia, the RBCM specimen of Behemotops, Miocaperea, Eschrichtius and Cetotherium, not to scale.

Figure 1. Rorqual evolution from desmostylians, Neoparadoxia, the RBCM specimen of Behemotops, Miocaperea, Eschrichtius and Cetotherium, not to scale. No thumb on these flippers.

Distinct from traditional studies
the LRT (subset, Fig. 2) nests Caperea (the pygmy right whale) with right whales, not cetotheres (Fig. 1) … and not with Miocaperea (Fig. 1)  the tiny Miocene baleen whale.

Caudal #15
In figure 1 caudal 15 is dotted (Fig. 1), highlighting the terminal caudal in the desmostylian Neoparadoxia and its ancestors, the mysticete whales. In cetotheres caudal 15 remains the terminal caudal. In other baleen whales more caudal vertebrae are added. By homology the terminal caudal #15 is just beyond the coccyx in these taxa. As reported yesterday, it’s not that the tail lengthened, although it did, its that the pelvis shrank and the coccyx became much more robust in these taxa.

Figure 1. GIF animation of the Neoparadoxia (original image from Barnes 2013). It seems illogical that the tiny tail of a desmostylian like this would ever become the giant tail of a mysticete, while the giant hind limbs disappear into the torso, but phylogenetic analysis recovers just such a scenario. Many long-jawed desmostylians are known from cranial material only and these are likely to be those that had large tails and smaller hind limbs.

Figure 2 GIF animation of the Neoparadoxia (original image from Barnes 2013). It seems illogical that the tiny tail of a desmostylian like this would ever become the giant tail of a mysticete, while the giant hind limbs disappear into the torso, but phylogenetic analysis recovers just such a scenario (see figure 1). Many long-jawed desmostylians are known from cranial material only and these are likely to be those that had large tails and smaller hind limbs. The longer lumbar region in non-right whales.

A longer lumbar region
is present in these whales compared to right whales and Desmostylus shown yesterday.

Figure 2. Subset of the LRT focusing on the mesonyx/mysticete clade showing the split between right whales and all other mysticetes.

Figure 3. Subset of the LRT focusing on the mesonyx/mysticete clade showing the split between right whales and all other mysticetes.

It’s worth noting again
that most workers and traditional studies nest baleen whales with the broad-billed toothed archaeocete Aetiocetus… but that’s only in the absence of tenrecs and desmostylians that separate odontocetes from mysticetes in the LRT.

Figure 5. Traditional cladogram that nests baleen whales with toothed whales in the absence of tenrecs and desmostylians.

Figure 4. Traditional cladogram that nests baleen whales with toothed whales in the absence of tenrecs and desmostylians.

Let’s see if paleontologists will follow this suggestion
to include these taxa in future analyses. The present record of avoiding key taxa in other controversial clades, like turtles and pterosaurs, does not bode well.

The Mysticeti is diphyletic (or expanded)

Earlier the large reptile tree (LRT, 1160 taxa) split Cetacea into separate clades arising from tenrecs (Odontoceti) and hippos (Mysticeti). Today the Mysticeti splits Balaenidae (right and pygmy right whales) from all other mysticetes (Fig. 1). Desmostylians are basal to both. So either the Mysticeti is diphyletic (like turtles) developing in parallel…or this clade is expanded to now include some members with legs, teeth and not much of a tail.

Figure 1. Subset of the LRT focusing on the mesonyx/mysticete clade showing the split between right whales and all other mysticetes.

Figure 1. Subset of the LRT focusing on the mesonyx/mysticete clade showing the split between right whales and all other mysticetes.

This confirms
by phylogenetic bracketing, that some desmostylians had baleen.

This was brought about by
adding the smallest baleen whale, Miocaperea (Miocene, Bisconti 2012) and reexamining previously included taxa. DNA could not have recovered this split, as it requires fossil taxa. To those who know whales pretty well, the right whales are distinct from the others in morphology and feeding strategy.

Caperea, the pygmy right whale, was considered a cetiothere, but here nests with right whales… and Desmostylus.

Images and more data next time. I have to revise some web pages now.

References
Bisconti M 2012. Comparative osteology and phylogenetic relationships of Miocaperea pulchra, the first fossil pygmy right whale genus and species (Cetacea, Mysticeti, Neobalaenidae). Zoological Journal of the Linnean Society 166: 876-911.

wiki/Miocaperea
wiki/Baleen_whale

Related mammals that nest at the bases of several hoofed clades

The value
of the large reptile tree (LRT, 1013 taxa) and the reconstructions gathered together at ReptileEvolution.com lie in their ability to put faces on names (Figs, 1) sometimes to scale (Fig. 2) to help one recognize patterns that may have gone unrecognized while just looking at names and scores.

These are the mammals that nest with one another
as sisters after deletion of more derived taxa in each of their several clades (listed at right, Fig. 1). Thus they, more or less, represent the basal radiation of hoofed mammals prior to each clade radiation. And to no one’s surprise, they look like each other, despite wide variations in size.

Frankly,
I’m reexamining the traits of these taxa because the LRT had trouble resolving them. There were mistakes in there. Now, after some score corrections, the resolution is complete again, but some Bootstrap scores have risen to just above 50. Not great, but better than below 50. Remember, I don’t have access to these specimens and sometimes work from published drawings.

Figure 1. Skulls of taxa nesting at the bases of several mammal clades starting with mesonychids.

Figure 1. Skulls of taxa nesting at the bases of several mammal clades starting with mesonychids. The differences are harder to see than in derived taxa in each clade (column at right). See figure 2 for skeletons to scale.

Some of these basal taxa
gave rise to baleen whales. Others were ancestral to giraffes, elephants, horses and everything in between. None of these taxa are nearly so famous or interesting to the general public, but it is from these generalized (plesiomorphic) taxa that the few and subtle evolutionary changes that are key to each clade first make an appearance.

Figure 2. Skeletons of taxa basal to various clades derived from basal mesonychids, all to scale.

Figure 2. Skeletons of taxa basal to various clades derived from basal mesonychids, all to scale. Note the presence of phylogenetic miniaturization at the base of the Artiodactyla. Consider this scenario: mesonychids radiated widely, including to create larger and smaller taxa. The larger homalotheres did not radiate greatly, as far as we know. On the other hand, the smaller taxa radiated to become a long list of extinct and exact hoofed taxa. And, of course, the mesonychid clade radiated to include today’s hippos and baleen whales. 

Sometimes a ‘show and tell’ drives a point home
better than just a ‘tell’. Even so, these are not the precise individuals in the direct lineage of known derived taxa, but the close relatives of those perhaps eternally unknown and hypothetical individuals. The suite of traits that lump and separate these taxa can be gleaned from the present MacClade file, continually added to and updated, and available here., which is where you can also see the cladogram from which the above taxa were pulled.

 

Aetiocetus, Desmostylus and the origin of baleen

Aetiocetus
(Emlong 1966; late Oligocene, 30 mya; Fig. 1) has been the poster-child for basal baleen whales for several decades, embraced by all whale workers. That needs to change.

When Aetiocetus was first published,
Emlong wrote:“If it were not for the presence of functional teeth on this mature specimen, this cetacean could easily be placed in the order Mysticeti.” (= baleen whales). Nevertheless, Emlong placed his discovery within the Archaeoceti, based on its primitive dentition. He also noted the nares had migrated further back on the skull than in typical archaeocetes, though still anterior to the orbits.

In the pre-cladistic era
Van Valen 1968 placed Aetiocetus as a basal mysticete despite the presence of teeth.

Of course, this assumes
that baleen whales were derived from toothed whales, which they are not, according to a wider gamut study, the large reptile tree (LRT, 1011 taxa).

Figure 1. Palates of two baleen whales, one toothed whale and Neoparadoxia, a desmostylian. See text for details.

Figure 1. Palates of two baleen whales, one toothed whale (Aetiocetus) and Neoparadoxia, a desmostylian. See text for details, but note the vomer splitting the maxilla in three related taxa and the pointed premaxilla in only one.

Aetiocetus is remarkable
for having both a full set of teeth and nutrient foramina. According to cetacean workers,t he presence of nutrient foramina (tiny holes and grooves in the palatal portion of the maxilla) indicates the presence of baleen in Aetiocetus. That’s because nutrient foramina are otherwise absent in archaeocetes and odontocetes (so far). In baleen whales some of the lateral foramina are located in the alveolar grooves, where the tooth roots used to be and where the teeth are in Aetiocetus. Other nutrient foramina radiate along the roof of the mouth (palatal portion of the maxilla). What Aetiocetus was growing there, we may never know. Based on the LRT, that soft palatal tissue in Aetiocetus was not homologous with baleen, though it would have been convergent.

According to Wikipedia
Aetiocetus shares several traits with all mysticetes. The mandibular symphysis is not fused. The descending process of the maxilla becomes a toothless plate below the orbit. A wide rostrum is present.” There is no doubt that among toothed whales, aetiocetes share more traits with baleen whales than any other toothed whales. However, distinct from prior studies, the LRT permits baleen whales to nest wherever they want to. And they don’t want to nest with toothed whales.

Re: Aetiocetus traits
It should be noted that even though the mandibular symphysis is not fused, it is narrow with parallel tips, unlike the anteriorly wide jaws of mysticetes and desmostylians. As in Aetiocetus, sperm whales likewise have a wide palate, at least posteriorly,  Aetiocetes were contemporaries of basal baleen whales like Cetotherium. In the LRT cetotheres are not basal mysticetes, but gray whales are.

We looked at other mysticete traits
and the desmostylian/mysticete connection earlier here, here and here.

The LRT nests Aetiocetus
with NMV P252567 (Marx et al. 2016) and these two nest between the archaeocete Zygorhiza and the extant odontocetes, Orcinus and Physeter. Archaeocetes have teeth of several shapes. Extant odontocetes have simple cones only. The genus Aetiocetus could be phylogenetically transitional in that the species A. weltoni has different tooth types, but A. polydentatus has simple cones only. I say ‘could be’ because those species have not yet been tested in the LRT.

Perhaps overlooked by whale workers 
the desmostylian Neoparadoxia (Fig. 1) also has nutrient foramina in a toothless groove between its anteriorly directed tiny canine and four posterior teeth (premolar #3 and three molars). I am hard pressed to see foramina elsewhere in the palate from available photos. Barnes 2013 wrote: “There are two small centrally placed nutrient foramina in each palatine bone. One is near the maxillary–palatine suture, and the other is located more medial to that one.” Note, Barnes did not report foramina in the maxilla.

Like baleen whales,
the palate is wide and the premaxilla is transversely oriented in Neoparadoxia. The palate already includes a long toothless groove. We don’t know what was growing in that groove. In the heretical LRT Neoparadoxia and other desmostylians are baleen whale outgroups, so that could be where a baleen precursor was growing. The rostrum is downturned slightly. The nares are telescoped to the back creating a blowhole.

Marx et al. nested NMV P252567
within the Aetiocetidae and thought they were shedding new light on the origin of baleen. From their abstract: “Baleen is thought to have appeared in archaic tooth-bearing mysticetes during a transitional phase that combined raptorial feeding with incipient bulk filtering. Here we show that tooth wear in a new Late Oligocene mysticete belonging to the putatively transitional family Aetiocetidae is inconsistent with the presence of baleen, and instead indicative of suction feeding. Our findings suggest that baleen arose much closer to the origin of toothless mysticete whales than previously thought. In addition, they suggest an entirely new evolutionary scenario in which the transition from raptorial to baleen-assisted filter feeding was mediated by suction, thereby avoiding the problem of functional interference between teeth and the baleen rack.” Desmostylians also suck, apparently (see below). And then you don’t have to explain away tooth wear!

Geisler and Sanders 2003
did not consider anthracobunids, desmostylians and tenrecs in their phylogenetic analysis of whales, but instead relied on Sus, the pig, as an outgroup. A larger gamut analysis finds Sus is not related to whales of any sort. When you don’t have the correct outgroups, you can’t place confidence in the order of appearance of derived traits and the order of derived taxa.

Figure 3. Old, toothless Desmostylus mandible with single downturned canine compared to the empty alveolus and mandibles of the gray whale (Eschrichtius).

Figure 2. Old, toothless Desmostylus mandible with single downturned canine compared to the empty alveolus and mandibles of the gray whale (Eschrichtius).

Santos, Parham and Beatty 2016
described an old toothless (save for one canine) Desmostylus mandible (Fig. 2). It bears comparison to the mandible of Eschrichtius, the gray whale, which has an anterior alveolus for an absent canine. Feeding strategies were probably similar. Wikipedia reports, “The (gray) whale feeds mainly on benthic (= sea floor) crustaceans, which it eats by turning on its side …and scooping up sediments from the sea floor.”  Desmostylians were also sea floor feeders, but with their shovel-like jaws, did not have to turn on their sides. Chiba et al 2015, suggests desmostylians used suction to pull in their food, and did not chew it.

Figure 4. Comparison of several desmostylian mandibles with that of Eschrichtius, the gray whale. As this lineage of desmostylians get larger, they more closely match the mandible of the gray whale.

Figure 3. Comparison of several desmostylian mandibles with that of Eschrichtius, the gray whale. As this lineage of desmostylians get larger, they more closely match the mandible of the gray whale. Notice the increasing extent of toothlessness and the gradual lengthening of the mandible. Drawings from Chiba et al. 2015.

Chiba et al. 2015
were kind enough to include a set of desmostylian mandibles to scale (Fig. 3) which, as they grew phyllogenetically larger, more closely approximated the much larger mandible of the gray whale, Eschrichtius, an extant basal baleen whale. That Sanjussen specimen, in particular, comes as a confirming relegation! (Unfortunately this was completely lost on Chiba et al.)

Hypothetical evolution of a feeding strategy
If desmostylians were not vegetarians, but fed by digging their anterior tusks into crustacean-laden sediments, then forcing out the excess water before swallowing, they were essentially doing the same sort of benthic feeding as the gray whale.

But what about those odd-looking desmostylian teeth that disappear in old age?
When individual desmostylians were younger and smaller, their benthic prey would have been relatively larger and teeth may have been necessary for crushing the hard shells before swallowing them. On the other hand, older and larger specimens did not need molars because they could swallow their tiny prey without chewing. In desmostylians even a little bit of baleen would have improved the filtering ability. That humble genesis would ultimately evolve to become the giant strips of baleen found in giant mysticetes as the teeth disappeared phylogenetlcally (Fig. 3), not side-by-side with sharp teeth, as imagined in Aetiocetus.

Figure 4. Baleen highlighted in this gray whale skull. Brighter green is below the gum line.

Figure 4. Baleen highlighted in this gray whale skull. Brighter green is below the gum line.

Next steps in this feeding strategy hypothesis:
Baleen whales, other than the gray whale, have left their benthic feeding grounds for the open seas where some fill their expandable throats with sea water and sieve for prey as that volume is forced out past their lips. Others. like the right whale, use their tongue to force out the sea water through deeper baleen filters. Still others probably perform a combination of the two, tongue and throat.

Time to clear out a few Wikipedia misconceptions

  1. Wikipedia reports, “Desmostylians are the only known extinct order of marine mammals.” — not supported by the LRT. Mysticeti are a clade within Desmostylia.
  2. Wikipedia reports, “The Desmostylia, together with Sirenia and Proboscidea (and possibly Embrithopoda), have traditionally been assigned to the afrotherian clade Tethytheria” — not supported by the LRT. Desmostylia are related to anthracobuinds, Hippopotamus and mesonychids in order of increasing distance. Not sure why this isn’t obvious.
  3. Wikipedia reports, “Aetiocetus is a genus of extinct basal mysticete, or baleen whale.” — not supported by the LRT. Aetiocetus nests between archaic toothed whales and extant toothed whales in the LRT.

Next time someone runs a cladistic analysis on whales,
please use the cetacean taxa and outgroups recovered by the LRT to check their validity. If they are again excluded from future studies the present LRT hypothesis of relationships will never have a chance to be verified or become the consensus. Let’s not let pigs stay the ancestors of whales when we already know better!

References
Barnes LG 2013. A new genus and species of Late Miocene Paleoparadoxiid (Mammalia, Desmostylia) from California. Contributions in Science 521:51-114.
Chiba K et al. 2015. A new desmostylian mammal from Unalaska (USA) and the robust Sanjussen jaw from Hokkaido (Japan), with comments on feeding in derived desmostylids. Historical Biology 28(1-2): 289 DOI: 10.1080/08912963.2015.1046718
Cope ED 1872. Descriptions of some new Vertebrata from the Bridger Group of the Eocene. Proceedings of the American Philosophical Society 12:460-465
Ekdale EG and Berta A 2015. Vascularization of the gray whale palate (Cetacea, Mysticeti, Eschrichtius robustus): Soft tssue evidence for an alveolar source of blood to baleen. The Anatomical Record Advances in Integrative Anatomy and Evolutionary Biology. February 2015; DOI: 10.1002/ar.23119
Emlong D 1966. A new archaic cetacean from the Oligocene of Northwest Oregon. Bulletin of the Museum of Natural History, University of Oregon. 3: 1–51.
Geisler JH and Sanders AE 2003. Morphological evidence for the phylogeny of Cetacea. Journal of Mammalian Evolution. 10: 23–129. doi:10.1023/A:1025552007291
Gray JE 1864. “Eschrichtius“. Annals of the Magaztine Natural History. 3 (14): 350.
Kimura T and Ozawa T 2002. A new cetothere (Cetacea: Mysticeti) from the early Miocene of Japan. Journal of Vertebrate Paleontology 22(3):684-702
Linnaeus C 1758. Systema naturæ per regna tria naturæ, secundum classes, ordines, genera, species, cum characteribus, differentiis, synonymis, locis. Tomus I. Editio decima, reformata.
Reinhart RH 1959. A review of the Sirenia and Desmostylia. University of California Publications in Geological Sciences 36(1):1–146.
Santos G, Parham J and Beatty B 2016. New data on the ontogeny and senescence of Desmostylus (Desmostylia, Mammalia). Journal of Vertebrate Paleontology. doi: 10.1080/02724634.2016.1078344
Van Valen L 1968. Monophyly or diphyly in the origin of whales. Evolution. 22 (1):37–41.

wiki/Balaenoptera
fossilworks/Isanacetus
wiki/Eschrichtius
wiki/Paleoparadoxia
wiki/Neoparadoxia

Baleen boom and bust

A year and a half ago
Marx and Fordyce 2015 entitled an academic paper on whale evolution, “Baleen boom and bust.” The authors report, “The phylogeny of 90 modern and dated fossil species suggests three major phases in baleen whale history: an early adaptive radiation (36–30 Ma), a shift towards bulk filter-feeding (30–23 Ma) and a climate-driven diversity loss around 3 Ma.”

As part of their introduction,
Marx and Fordyce report, “Past studies have fundamentally disagreed on the phylogenetic position, and even monophyly, of many extant and extinct taxa, with major implications for tree topology and molecular estimates of divergence times. Such problems probably reflect limited taxonomic sampling, which is known to compromise both phylogenetic accuracy  and macroevolutionary inferences. Another key problem is the presentation of morphological data as simple character-based scorings, which are usually unsupported by illustrations and hence difficult to comprehend or repeat.”

That’s what I keep saying,
although I’m new to mysticetes. To their credit Marx and Fordyce score 90 taxa for 37,000+ molecular and 272 morphological characters. The project is illustrated with 400 annotated specimens at morphobank.org: project 687. Their oldest taxon is Himalaycetus (Bajpai and Gingerich 1998) from the early Eocene (53.5mya), so this stacks up to be an excellent paper…

except for a few things…

First a little backstory on Himalayacetus
The specimen is the central portion of a left dentary with molar teeth. In vivo the dentqry would have been about 30 cm long, so in the range of Pakicetus. Baipai and Gingerich compared Himalayacetus to Sinonyx, which they considered a mesonychid, and a “representative middle Eocene archaeocete.” In the LRT, you might remember, Sinonyx nested with tenrecs, not mesonychids. Based on chemical analysis, Himalayacetus frequented fresh and salt water, but was found in marine strata.

And here’s where Marx and Fordyce made their mistake(s).
Rather than testing a wide gamut of mammals as potential whale ancestors, Bajpai and Gingerich settled on tradition as they wrote, “Following Van Valen (1966), archaeocetes are generally regarded as descendants of Mesonychia, with which they were long confused.”

As readers all know by now,
“generally regarded” doesn’t cut the mustard anymore, not when testing will tell you what is… and what is not. The LRT shows that mesonychids are distant relatives of mysticetes. Hippos and desmostylians, like Behemotops, are much closer. Desmostylians have been overlooked by whale workers. And Sinonyx is not a mesonychid. It nests with tenrecs, including some giant ones like Andrewsarchus, even when given the opportunity to nest with mesonychids and hippos, which likewise do not nest with artiodactyls in the LRT.

Bajpai and Gingerich report, “The time of divergence of extant Cetacea from extant Artiodactyla is unchanged and lies in the range of 62.5–66.4 Ma, at or near the beginning of the Cenozoic.” Then they report, “Some systematists using molecular genetic clocks suggest divergence of Cetacea from other orders of mammals in the Mesozoic as early as 100 Ma, but the quantified likelihood of such a hypothesis is vanishingly small from the point of view of known fossils and radiometric calibration of the geologic time scale.”

In other words,
they took data and verbally diminished its importance before scientific testing. They assumed that whales are monophyletic. It’s really not their fault. The hypothesis of a separation of odontocetes from mysticetes is only a few weeks old and they published about 70 weeks ago and were no doubt writing their manuscript months to years before that.

So to sum up, except for the invalidated relationship
between basal mysticetes and basal odontocetes, the interrelationships between most of the whale taxa in Marx and Fordyce are valid —

…with a second exception that
some toothed whales are, but should not be, in the lineage of mysticetes…

…with a third exception that
primitive gray whales (Eschritus robustus) nest as highly derived in Marx and Fordyce, while highly derived right whales (Eubalaena australis) nest closer to the origin of baleen whales. So the phylogenetic order of those mysticetes is reversed…

…with a fourth exception that
Janjucetus is considered a basal mysticete and it is not that closely related. It nests with Anthracobune in the LRT and, since that clade is more primitive than the Desmostylia, Janjucetus probably had legs.

That these workers 
accepted the “generally regarded” ancestors without testing is something that can be repaired. All they have to do is add the intervening taxa listed by the LRT to their analysis. When that happens, Janjucetus will nest with Anthracobune. Baleen whales will be derived from desmostylians. Gray whales will nest primitively. Odontocete whales will nest with a long line of extinct and extant tenrecs. And all the currently known fossil toothed whales with nest with odontocetes.

All of these arguments also apply to 
Geisler et al. 2011, who used Sus (pig), Bos (cattle) and Hippopotamus as outgroups with a basal split between mysticetes and odontocetes. Of course there is a HUGE morphological gap between hippos and whales that is conveniently overlooked everywhere but in the LRT.

Which brings up the Yamatocetus illustration problem.
Yamatocetus (Fig. 1, lower left) is a cetiothere mysticete, but Marx et al. 2016 illustrated their Yamatocetus with tiny teeth that don’t appear to be present in photos of the specimen. You can see those photos here: morphobank.org: project 687. Moreover, teeth or not, Yamatocetus nests in the LRT after several toothless taxa. Flat straight jaws in mysticetes is a derived trait, which I can see could be confusing if you are in the monophyletic whales camp. Moreover, considering the extreme flatness of the Yamatocetus rostrum with rather sharp edges, if even rudimentary teeth were present they should, like all marginal teeth, erupt from the jaw margins. If oriented toward the dentary there is little to no room for tooth roots. In short, I think the illustrated teeth are dubious. Send me datum to the contrary if you have it.

Also note
the rather substantial morphological leap from the unnamed NMV P2525677 suction feeding odotocete (Fig. 1, upper right) to passively filtering mysticete Yamatocetus, (Fig. 1, lower left). Odontocetes are active hunters, as were their tenrec ancestors. Mysticetes are passive grazers, as were their desmostylian ancestors.

The origin of baleen
still appears to belong to derived desmostylians (Fig. 3), with concave ventral rostral margins, as noted earlier here and preserved in basal mysticetes.

Figure 2. from Marx et al. 2016. presumes the monophyly of whales and the origin of mysticetes from odontocetes with small teeth. Both are not supported by the LRT. Upper left: Dorudon. Upper right: NMV P2525677. Lower left: Yamatocetus Lower right: Eschrichtius.

Figure 2. from Marx et al. 2016. presumes the monophyly of whales and the origin of mysticetes from odontocetes with small teeth. Both are not supported by the LRT. Upper left: Dorudon. Upper right: NMV P2525677. Lower left: Yamatocetus Lower right: Eschrichtius. When desmostylians are added, Eschrichtius becomes the basalmost mysticete and Yamatocetus is derived.  Were teeth present in Yamatocetus? I have yet to see evidence for teeth, which should be absent in such a derived taxon. I have not seen photos of the Yamatocetus mandible. Does it exist?

Before leaving this topic
the convergence of mysticetes with odontocetes is truly so remarkable that it has gone unnoticed for all this time by both professionals and amateurs alike. To those who dismiss the ability of the LRT to lump and separate such closely convergent taxa, this has been a test of that ability.

Figure 1. Paleoparadoxia. Note the gap left by the diastema between the anterior and posterior teeth. With the phylogenetic placement of desmostylians at the base of the Mysticeti, can this gap be where baleen (light blue) originated? Good question.. The loss of teeth and the elaboration of the baleen in transitional taxa would take us to the toothless, baleen endowed whales.

Figure 3. Paleoparadoxia. Note the gap left by the diastema between the anterior and posterior teeth. With the phylogenetic placement of desmostylians at the base of the Mysticeti, can this gap be where baleen (light blue) originated? Good question.. The loss of teeth and the elaboration of the baleen in transitional taxa would take us to the toothless, baleen endowed whales. Note the similarity of Eschrichtius (Fig. 1, lower right).

References
Demere TA, McGowen MR, Berta A & Gatesy J. 2008. Morphological and Molecular Evidence for a Stepwise Evolutionary Transition from Teeth to Baleen in Mysticete Whales, Systematic Biology, 57 (1) 15-37. DOI: 10.1080/10635150701884632\
Geisler JH, McGowen MR, Yang G and Gatesy J 2011. A supermatrix analysis of genomic, morphological, and paleontological data from crown Cetacea. Evolutionary Biology 11:112.
Gingerich PD 2005. Aquatic Adaptation and Swimming Mode Inferred from Skeletal Proportions in the Miocene Desmostylian Desmostylus. Journal of Mammalian Evolution, Vol. 12, Nos. 1/2, June 2005.
Marx FG and Fordyce RE 2015. Baleen boom and bust: a synthesis of mysticete phylogeny, diversity and disparity, Royal Society open Science 2:14034.
Marx FG, Hocking DP, Park T, Ziegler T, Evans AR and Fitzgerald EMG 2016. Suction feeding preceded filtering in baleen whale evolution. Memoirs of Museum Victoria 75:71-82.
Okazaki Y 2012. A new mysticete form the upper Oligocene Ashiya Group, Kyushu, Japan and its significance to mysticete evolution. Bulletin of the Kitakyushu Museum of Natural History and Human History Series A (Natural History) 10:129-152.
Shikama T 1966. Postcranial skeletons of Japanese Desmostylia. Palaeontol. Soc. Japan Spec. Pap. 12: 1–202.

 

 

Adding Cetotherium to the LRT

Since we’re still talking about whales today…
Dr. RW Boessenecker was kind enough to let me know that one of the mandibles in Tokahahira was rotated 180º and so the mandible I thought bowed in for a narrow tip actually bowed out for a Gothic arch shape (Fig. 1). That earlier error has been repaired.

Figure 1. Tokarahia in situ and as originally reconstructed (on right). Flipping the right mandible and reconstructing the skull anew (at left).

Figure 1. Tokarahia in situ and as originally reconstructed (on right). Flipping the right mandible, taking the bow out of the left mandible and reconstructing the skull anew (at left).

Figure 2. Subset of the large reptile tree, the mesonychids, desmostylians and mysticetes.

Figure 2. Subset of the large reptile tree, the mesonychids, desmostylians and mysticetes (in blue).

Then I added Tokarahia to the LRT and it nested within the mysticetes between Isanacetus and Cetiotherium (Fig. 2). It looks like cetotheres were basal to at least two clades of extant mysticetes.

The basal mysticete,
Cetotherium riabinini (Cope 1895, Hofstein 1948, Gol’din et al. 2014; Late Miocene; NMNH-P 668/1; 2m in lenth), is known from a fairly complete dolphin-sized skeleton (Fig. 2). It had a relatively huge skull, massive rib cage, large manus (but see below) and a relatively short tail. Cetotheres, according to Wikipedia, are “archaic mysticetes with a cranium that has ‘a long ascending process of the maxilla with anteriorly diverging lateral border that interdigitates with the frontal’ and some other characters”,

That short tail
complements what we learned earlier about stem mysticetes arising from short-tailed desmostylians, including one with a possible robust tail, Behemotops.

Figure 3. Cetotherium skeleton with color overlays to help identify bones.

Figure 3. Cetotherium skeleton with color overlays to help identify bones. Three hypotehtical fluke sizes are suggested.  According to Hofstein (1965), the carpals, metacarpals and most of phalanges have not been preserved.

In the LRT
Cetotherium nests with Eubalaena (Fig. 4) the Southern right whale, which has greatly deepened its maw. They share, among other obvious traits, short chevrons. Eubalaena has five fingers after a long run of four-fingered ancestors. So the ‘thumb’ is new!

Figure 5. Eubalaena australis, the Southern right whale nests with Cetotherium in the LRT.

Figure 4. Eubalaena australis, the Southern right whale nests with Cetotherium in the LRT. The down curved rostrum appears to be secondarily evolved based on more primitive taxa with straight rostra.

Here’s an interesting Wiki-factoid
listed under Cetotherium“Cetotheriidae were thought to have gone extinct during the Pliocene until 2012, when it was hypothesized that the Pygmy right whale was the sole surviving species of this family. (Fordyce and Marx 2013)”

Figure 5. Caperera, the pygmy right whale, has fewer lumbar vertebrae, smaller forelimbs and broad ribs resembling those of Cetotherium.

Figure 5. Caperea, the pygmy right whale, has fewer lumbar vertebrae, smaller forelimbs and broad ribs resembling those of Cetotherium.

The pygmy right whale (Caperea marginata; Bisconti 2012) looks like a small blue whale, but has an oversized rib cage and a short tail. We’ll look at it more closely in a future blog.

Figure 6. Blue whale (Balaenoptera musculus) skull and skeleton. This image is presented again to compare and contrast with the above taxa. 

Figure 6. Blue whale (Balaenoptera musculus) skull and skeleton. This image is presented again to compare and contrast with the above taxa.

Sorry about the earlier error with Takarahia
(see above). I hate making those, but they happen. In Science you own up to your mistakes. And then you fix them. I’ll emphasize again, nearly every added taxon here is new to me. I gain any and all expertise by study. And, after finding a mistake, or adding a new taxon, by reexamination. Several other errors were corrected during the course of this blog post writing. Thank you for alerting me to mistakes. They are corrected as soon as I understand the problem.

References
Bisconti M 2012. Comparative osteology and phylogenetic relationships of Miocaperea pulchra, the first fossil pygmy right whale genus and species (Cetacea, Mysticeti, Neobalaenidae). Zoological Journal of the Linnean Society 166(4) 876—911.
Fordyce RE and Marx FG 2013. The pygmy right whale Caperea marginata: the last of the cetotheres. Proceedings of the Royal Society B: Biological Sciences 280(1753):1–6.
Gol’din P, Startsev D and Krakhmalnaya T 2014. The anatomy of Cetotherium riabinini Hofstein, 1948, a baleen whale from the late Miocene of Ukraine. Acta Palaeontologica Polonica. In press. doi:10.4202/app.2012.0107

wiki/Cetotherium
wiki/Pygmy_right_whale