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 5. Subset of the LRT focusing on the tenrec/odontocete clade with several whales added.

Figure 1. Subset of the LRT focusing on the tenrec/odontocete clade with several whales added.

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

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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 5. Subset of the LRT focusing on the tenrec/odontocete clade with several whales added.

Figure 2. Subset of the LRT focusing on the tenrec/odontocete clade. Mysticetes have another lineage. Coronodon nests at the base of the Odontoceti, but clearly more transitional taxa are waiting to be discovered.

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

Monodon: THE weirdest skull of all mammals

Today two blogposts are published
because they relate strongly to one another. Here is the post on torsioned tenrec/odontocete skulls.

Figure 1. Distinct from most narwhals, this skull also has right tusk emerging from the canine position. And yes, that's the maxilla covering most of the skull, even above the orbit! I added an eyeball here to help locate the orbit. The mesethmoid is the red bone that divides the naris (blow hole).

Figure 1. Distinct from most narwhals, this skull also has right tusk emerging from the canine position. And yes, that’s the maxilla covering most of the skull, even above the orbit! I added an eyeball here to help locate the orbit. The mesethmoid is the red bone that divides the naris (blow hole).

The narwhal (genus Monodon, Fig. 1)
is famous for having one giant spiral tooth sticking out ahead of its skull. Monodon also has one of the most bizarre skulls of all mammals and departs from that of all tetrapods, partly due to the root of the tooth and partly due to the migration of the nares to the back of the skull. Except for its tips, the jugal is missing. The maxilla, lacks teeth (if you don’t count the tusk) and rather than extending below the orbit, extends over the forehead, following the naris on its migration to the back of the skull. The bulbous portion of the skull, the cranium is made of parietals in most mammals, but the parietals are greatly reduced, nearly absent in Monodon.

Figure 2. The beluga, Delphinapterus, is closely related to, though less derived than the narwhal, Monodon. More teeth of a regular shape were present in the jaws. Those two yellow arrows indicate a misalignment of the centerline of the top of the occiput vs. the bottom. Compare to figure 3.

Figure 2. The beluga, Delphinapterus, is closely related to, though less derived than the narwhal, Monodon. More teeth of a regular shape were present in the jaws. Those two yellow arrows indicate a misalignment of the centerline of the top of the occiput vs. the bottom. Compare to figure 3. The mesethmoid is the red bone in the blow hole. This skull is also bent left, as in the narwhal.

The sister taxon of the narwhal
is the beluga (genus: Delphinapterus). It helps one understand the narwhal a bit better. At least the beluga has a few traditional teeth. These two taxa nest together in the large reptile tree (LRT, 1087 taxa, Fig. 4).

Figure 3. Chonecetus has a more primitive skull with nares closer to the snout tip and no maxilla above the orbit.

Figure 3. Chonecetus has a more primitive skull with nares closer to the snout tip and no maxilla above the orbit. Not a transitional taxon to baleen whales, which have another separate origin. This drawing lacks any indication of torsion, perhaps because the back half was separated from the front half and the artist ‘repaired’ the twist.

Less derived and more primitive
is Chonecetus (Fig. 3), which has nares closer to the snout tip, and more teeth, and more cranium. This taxon and its sister, Aetiocetus, have been traditionally considered transitional from toothed whales to baleen whales, like Balaenoptera, but baleen whales have an entirely separate ancestry derived from desmostylians, like Desmostylus.

Figure 5. Subset of the LRT focusing on the tenrec/odontocete clade with several whales added.

Figure 4. Subset of the LRT focusing on the tenrec/odontocete clade with several whales added.

A recent paper on Monodon tusks (Nweeia et al. 2012)
found “the narwhal tusks are the expression of canine teeth and that vestigial teeth have no apparent functional characteristics and are following a pattern consistent with evolutionary obsolescence.” (See Figs. 5, 6).

Figure 4. Image from Nweeia et al. 2012 showing the unerupted right tusk and the root of the left tusk in the male narwhal along with two unerupted tusks in the female.

Figure 5. Image from Nweeia et al. 2012 showing the unerupted right tusk and the root of the left tusk in the male narwhal along with two unerupted tusks in the female. Note the angle of the posterior skull relative to the anterior midline.

In dorsal or ventral view
it is clear that the the tusk (left) side of the skull is longer than the right side due to angling the posterior skull relative to the rostrum.

Figure 6. CT scans of a female narwhal (Monodon) showing soft tissues and unerupted teeth. Note the angle of the posterior skull relative to the anterior.

Figure 6. CT scans of a female narwhal (Monodon) showing soft tissues and unerupted teeth. Note the angle of the posterior skull relative to the anterior. The left side, the tusk side, is shorter than the right side in figure 5, so the label ‘ventral’ is an error here. This is a dorsal view of the female skull in figure 5. Always test scale bars and labels.

I wonder about the bending of the skull
toward the left in these two whales. Could asymmetry have anything to do with stereo auditory senses? Asymmetry is also found in owl skulls, another taxon that depends strongly on acute hearing for locating prey.

Figure 7. Fetal narwhal skull, here colorized from Nweenia et al. 2012. The jugal disappears in adults.

Figure 7. Fetal narwhal skull, here colorized from Nweenia et al. 2012. The jugal disappears in adults. The asymmetry is already apparent here.

Figure 8. Common bottle nose dolphin skull (genus: Tursiops) also displays a bit of asymmetry in dorsal view.

Figure 8. Common bottle nose dolphin skull (genus: Tursiops) also displays a bit of asymmetry in dorsal view. Note the yellow arrows on the parietal showing the wee bit of torsion here. 

Update:
With 1187 taxa and 231 traits full resolution was recovered in the LRT after running PAUP FOR 16 minutes and 15 seconds. The single best tree has 16,329 steps.

References
Linnaeus C 1758. Systema naturæ per regna tria naturæ, secundum classes, ordines, genera, species, cum characteribus, differentiis, synonymis, locis. Tomus I. Editio decima, reformata.’
Nweeia MT et al. (9 co-authors) 2012. Vestigial tooth anatomy and tusk nomenclature for Monodon monoceros. The Anatomical Record 295:1006–1016.
Pallas PS 1766. Miscellanea Zoologica.

wiki/Narwhal
wiki/Beluga_whale

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.

 

Aetiocetus: it’s supposed to be a baleen whale ancestor

This is going to be another paleo story about taxon exclusion.
Earlier we looked at paleoworkers trying to nest turtles among diapsids and pterosaurs among archosaurs… but this only happens when more closely related taxa are overlooked or omitted. In the case of the toothed archaic whale, Aetiocetus (Fig. 1), it sure looks like a good candidate for baleen ancestry. The palate was wide, triangular and flat. Unfortunately there are better candidates that were overlooked. Details below.

Figure 1. Three species attributed to Aetiocetus. Other workers considere these basal to baleen whales, but they don't include tenrecs and desmostylians in their analyses.

Figure 1. Three species attributed to Aetiocetus. Other workers considere these basal to baleen whales, but they don’t include tenrecs and desmostylians in their analyses. The teeth of A. polydentatus are simple cones, as in modern toothed whales.

Wikipedia reports:
Aetiocetus is a genus of extinct basal mysticete (baleen whale (late Oligocene, 30 mya). The large reptile tree (LRT, 1161 taxa) nests it with other toothed whales, far from mysticetes. Some traits that distinguish Aetiocetus from other toothed whales include:

  1. the nostrils of the whale had migrated further back on the skull than seen in archaeocetes, but not so far as in modern whales.
  2. no more than three small denticles on the anterior and posterior margins of the posterior upper teeth.
  3. postcanine teeth heterodont.
  4. The base of the rostrum, or snout, of the whale, is greater than 170% of the width of the occipital condyles where the skull meets the neck.
  5. notch by the internal nostrils formed of the palatine, pterygoid, and vomer bones
  6. coronoid process of the dentary well developed
  7. zygomatic arch is expanded anteriorly and posteriorly but is narrow at the middle.
  8. mandibular symphysis not fused.
  9. descending process of the maxilla becomes a toothless plate below the orbit.
  10. wide rostrum

According to Wikipedia,
all these features are functionally related to filter-feeding with baleen and are hallmarks of the Mysticeti. The presence of teeth seems ‘paradoxical’ to these workers. Unfortunately, this hypothetical relationship is recovered only in the absence of desmostylians. 

According to the National Library of Medicine
“All bones possess larger or smaller foramina (openings) for the entrance of the nourishing blood-vessels.”

According to Marx et al. 2016:
“Aetiocetids have previously been proposed as the most basal mysticetes to possess baleen, the key adaptation of modern whales. More specifically, the widespread occurrence of palatal nutrient foramina (in Aetiocetus, Fucaia and Morawanocetus), which in extant mysticetes supply the baleen rack, has been used to infer the existence of an incipient baleen structure between or just lingual to the teeth (Deméré and Berta, 2008; Deméré et al., 2008). While such an interpretation is possible, it also remains untested: just as the origin of feathers in non-avian dinosaurs does not mark the beginnings of flight, so the appearance of palatal foramina in mysticetes need not indicate the presence of baleen. Instead, the foramina of aetiocetids could, for example, have supplied its immediate predecessor – namely, well-developed gums, the presence of which is indicated both by the strongly emergent teeth of early mysticetes (Deméré and Berta, 2008; Fitzgerald, 2010) and, possibly, the largely unworn incisor of NMV P252567.”

Baleen was not found in any specimen of Aetiocetus. 
The presence of baleen is inferred from the presence of nutrient foramina. If so, then baleen had two convergent origins and Aetiocetus represents a dead end, leaving no modern descendants. If nutrient foramina only fed the skin and other tissues that lined the jaws, then no baleen was present.

Baleen WAS found
in the basal mysticete, Miocaperea (Bisconti 2012, skull 1 meter long; Miocene). Traditionally whale workers consider taxa like Caperea and Miocaperea highly derived because desmostylians are not included in their analyses. By contrast, the LRT finds these to be basal mysticetes, Caperea for right whales and Miocaperea for all other mysticetes. Most studies nest Caperea with right whales (clade: Balaenoidea; Demere et al. 2005, Churchill et al. 2012, Ekdale et al. 2011. Marx 2010, did not. All wrongly assume Odontoceti as the outgroup.

Figure 4. The caption for this photo is: "Brian Beatty measuring the jaws of one of our toothed mysticetes. Photo by R. Boessenecker."

Figure 2. The caption for this photo is: “Brian Beatty measuring the jaws of one of our toothed mysticetes. Photo by R. Boessenecker.” This was the traditional view of mysticete origins prior to the addition of desmostylians to the LRT.

The image above
is from  the CCNHM blogsite and the caption for the photo is: “Brian Beatty measuring the jaws of one of our toothed mysticetes. Photo by R. Boessenecker.” Perhaps unknown to Professor Beatty, this is true only in the absence of desmostylians from phylogenetic analysis, an easy mistake to make prior to the entry of desmostylians to the LRT. Various authors have been bending over backwards trying to discover the origin of mysticetes among toothed whales. But they cannot be discovered there. Mysticetes arise from desmostylians, taxa studied by Professor Beatty, but the mysticete connection was not realized.

And that, again demonstrates the value of the LRT,
which permits taxa that have never been tested together to nest together. Taxon inclusion solves every problem in paleontology.

Chronology
This is always a problem due to the rarity of fossils, typically (but not always) recovered as late survivors long after initial radiations. These are taxa recovered by the LRT in the lineage of mysticetes.

  1. Mesonyx: Paleocene or earlier
  2. Ocepeia: Paleocene
  3. Cambaytherium: Eocene
  4. Anthracobune: Eocene
  5. Desmostylus: Oligocene
  6. Cetotherium: Oligocene
  7. Miocaperea: Late Miocene
  8. Caperea and others: Recent

Characters that separate aetiocetids from cetotheres:

  1. Skull shorter than half the presacral length
  2. Snout not constricted
  3. Premaxilla/maxilla notch less than 25º
  4. Naris angle 30-90º but dorsal
  5. Nasals subequal to frontals
  6. Orbit shape in lateral view at least half longer than tall
  7. Frontals without posterior processes
  8. Postparietals angled from the dorsal plane
  9. Tabulars absent
  10. Squamosal descending process at right angle
  11. Frontals and parietals both fused
  12. Occiput far posterior to quadrate articulation
  13. Opisthotics descend
  14. Vomernasal (or other anterior palatal opening) separate from choanae (internal narial opening) by maxilla
  15. Premaxilla teeth present and robust
  16. Last maxillary tooth present and anterior to orbit
  17. Some cervical neural spines taller than centra
  18. 10th caudal length not > chevron depth
  19. Interclavicle/sternal elements present
  20. Scapula not robust
  21. Manual digit 1 present

Interesting tidbits
The coronoid process becomes larger in two tested cetotheres, but not the basal Cetotherium. You wouldn’t think baleen whales would need a tall coronoid process (used for biting), and most don’t have one, but Tokharia and Yamatocetus do.

It only takes the deletion of a few desmostylians to nest baleen whales with toothed whales, due to the large number of similar traits (which is why we call them all ‘whales’. Conversely it only takes the deletion of a few archaic whales to nest odontocetes with baleen whales, as I discovered through testing these options.

For more heretical desmostylian information,
click here.

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.
Buchholtz E 2010. Vertebral and rib anatomy in Caperea marginata: Implications for evolutionary patterning of the mammalian vertebral column. Marine Mammal Science 27: 382-397.
Churchill M, Berta A, Deméré TA 2012. The systematics of right whales (Mysticeti: Balaenidae). Marine Mammal Science 28: 497-521.
Deméré TA, Berta A and McGowen MR 2005. The taxonomic and evolutionary history of modern balaenopteroid mysticetes. Journal of Mammalian Evolution 12: 99-143.
Ekdale E G, Berta A and Deméré TA 2011. The comparative osteology of the petrotympanic complex (ear region) of extant baleen whales (Cetacea: Mysticeti). PLoS ONE 6:1-42.
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.
Fitzgerald EMG 2012. Possible neobalaenid from the Miocene of Australia implies a long evolutionary history for the pygmy right whale Caperea marginata (Cetacea, Mysticeti). Journal of Vertebrate Paleontology 32:976-980.
Marx FG 2011. The more the merrier? A large cladistic analysis of mysticetes, and comments on the transition from teeth to baleen. Journal of Mammalian Evolution 18:77-100.
Marx et al. 2016. Suction feeding preceded filtering in baleen whale evolution. Memoirs of Museum Victoria 75: 71–82.
Van Valen L 1968. Monophyly or diphyly in the origin of whales. Evolution. 22 (1):37–41.

wiki/Aetiocetus

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.

New taxa in the lineage of right whales

Tubby right whales
like Eubalaena (Fig. 1) are different from sleek rorquals, like the blue whale (Balaenoptera). Right whales don’t have the huge throat sack that rorquals expand with sea water + krill. Instead longer baleen fringes and huge lower lips filter right whale meals and usually in a horizontal, rather than a vertical, attack formation.

Figure 1. Taxa in the lineage of right whales include Desmostylus, Caperea and Eubalaena. The tiny bit of jugal posterior to the orbit (in cyan) is found in all baleen whales tested so far. The frontals over the eyes are just roofing the eyeballs in Desmostylus, much wider in Caperea and much, much longer in Eubalaena.

Figure 1. Taxa in the lineage of right whales include Desmostylus, Caperea and Eubalaena. The tiny bit of jugal posterior to the orbit (in cyan) is found in all baleen whales tested so far. The frontals over the eyes are just roofing the eyeballs in Desmostylus, much wider in Caperea and much, much longer in Eubalaena.

According to Wikipedia:
“The pygmy right whale (Caperea marginata), a much smaller whale of the Southern Hemisphere, was until recently considered a member of the Family Balaenidae. However, they are not right whales at all, and their taxonomy is presently in doubt. Most recent authors place this species into the monotypic Family Neobalaenidae, but a 2012 study suggests that it is instead the last living member of the Family Cetotheriidae, a family previously considered extinct.”

That 2012 study was by Marx and Fordyce. The large reptile tree (LRT, 1060 taxa) does not support that assignment, perhaps because Marx and Fordyce omitted tenrecs and desmostylians from their whale analysis. At present all cetiotheres in the LRT have straight rostra and mandibles, a far cry from the dipped snout of these taxa. Note the deep baleen in Caperea (Fig. 1). That’s a right whale trait.

Figue 2. Caperea is a transitional taxon between tubby Desmostylus and tubby Eubalaena. Note the tiny manus (flipper). It is neotenous. See text for details. Note the short tail, not much longer than the tail found in Desmostylus.

Figue 2. Caperea is a transitional taxon between tubby Desmostylus and tubby Eubalaena. Note the tiny manus (flipper). It is neotenous. See text for details. Note the short tail, not much longer than the tail found in Desmostylus.

Caperea marginata (The pygmy right whale; Bisconti 2012, Fordyce and Marx 2013) looks like a small blue whale, but has long, inclned ribs, only one lumbar vertbra, and a short tail. The mandible is deep and concave ventrally. Like Eubalaena the lacrimal is deeper than the maxilla. Note the tiny forelimb. The manus has a few extra bones that, when put back together, create a digit 1. Mid-phalanges (3.2, 4.2, 4.3) lost in basal therapsids reappear in this taxon with a netonous tiny manus.

Figure 2. Limusaurus also has four fingers and a scapula with a robust ventral area, like Majungasaurus, but those four fingers are not the same four fingers found in Majungasaurus.

Figure 3. Limusaurus also has an extra digit medial to the other three common to most therapies. We call that digit zero, otherwise found in certain very basal tetrapods only.

We’ve seen this before.
Remember Limusaurus? (If not, check out Fig. 3) That’s the oviraptorid-like theropod with an equally tiny manus provided with an extra medial digit (digit zero). Same thing here provides the reappearance of digit 1, reduced or absent in all ancestors beginning with Mesonyx. And THAT explains the reappearance of manual digit 1 (the thumb) in the right whale, Eubalaena (Fig. 1), the only exception in this clade of thumbless taxa.

Figure x. Desmostylus skull in several views. Note the nasals have a different shape (upper left) than originally traced (lower right). Arrows point to wider mandibles than rostrum.

Figure x. Desmostylus skull in several views. Note the nasals have a different shape (upper left) than originally traced (lower right). Arrows point to wider mandibles than rostrum.

Little things to look for in desmostylians retained by baleen whales

  1. The mandible is wider than the rostrum (Fig. x). That’s where the giant lower lips arise.
  2. A bit of jugal is attached to the front of the squamosal, even when the portion below the orbit is missing.
  3. The reduction of teeth is completed in baleen whales
  4. The ventral portion of the rostrum is visible in lateral view
  5. The anterior tips of the mandibles either have tusks or the alveoli  from which tusks once emerged. Here (Fig. x) the tusks are tiny.
  6. Same with the anterior maxillae, but smaller because those tusks disappear earlier.  Here (Fig. x) the tusks are tiny. Blame it on neotony.
  7. The tail series of Caperea is really quite short (Fig. 2)—and shorter still IF you imagine a former pelvis the size of the one in Desmostylus, now greatly reduced (Fig. 1). And that is a big part of the solution to the lack of a large tail in desmostylians: don’t lengthen the tail…shrink that giant pelvis!!! And blame it on neotony.
Figure 7. Desmostylus jaws with green and blue arrows pointing to buried canine and anterior dentary tusks. Compare to gray whale rostrum in figure 6.

Figure 4. Desmostylus jaws with green and blue arrows pointing to buried canine and anterior dentary tusks. Compare to gray whale rostrum in figure 6.

Figure 8. Gray whale (Eschirctius) anterior rostrum. Green arrow points to the canine alveolus lacking a tooth. Missing mandible teeth would have appeared along anterior rims of the mandibles (blue arrow), as in desmostylians.

Figure 5. Gray whale (Eschirctius) anterior rostrum. Green arrow points to the canine alveolus lacking a tooth. Missing mandible teeth would have appeared along anterior rims of the mandibles (blue arrow), as in desmostylians.

We’ll look at
cetiotheres and rorquals in the next few days.

References
Domning DP, Ray, CE and McKenna, MC 1986. Two new Oligocene desmostylians and a discussion of Tethytherian systematics. Smithsonian Contributions to Paleobiology. 59. pp. 1–56.
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.
Marsh OC 1888. Notice of a new fossil sirenian, from California. American Journal of Science 25(8):94–96.
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
Tsai C-Hi and Fordyce RE 2015. Ancestor–descendant relationships in evolution: origin of the extant pygmy right whale, Caperea marginata. Biol Lett. 2015 Jan; 11(1): 20140875.

wiki/Caperea
wiki/Desmostylus