Resurrecting extinct taxa: Creodonta, Mesonychidae, Desmostylia and Gephyrostegidae

Taxonomy
“the branch of science concerned with classification, especially of organisms; systematics.”  Taxon: a taxonomic group of any rank, such as a species, family, or class.

The large reptile tree
(LRT, 1366 taxa) has resurrected several taxa (in this case, clades) long thought to be extinct.

Figure 1. Adding Sinopa to the LRT nests it here, between the extant quoll (Dasyurus) and the extant Tasmanian devil (Sarcophilus).

Figure 1. Members of the traditionally extinct Creodonta include the extant quoll (Dasyurus) and the extant Tasmanian devil (Sarcophilus).

Creodonta
According to Wikipedia: “Creodonta” was coined by Edward Drinker Cope in 1875. Cope included the oxyaenids and the viverravid Didymictis but omitted the hyaenodontids. In 1880. he expanded the term to include MiacidaeArctocyonidaeLeptictidae (now Pseudorhyncocyonidae), OxyaenidaeAmbloctonidae and Mesonychidae. Cope originally placed creodonts within the Insectivora. In 1884, however, he regarded them as a basal group from which both carnivorans and insectivorans arose. Hyaenodontidae was not included among the creodonts until 1909. Over time, various groups were removed, and by 1969 it contained, as it does today, only the oxyaenids and the hyaenodontids.

In the LRT, Oxyaena and Hyaenodon are members of an extinct clade. However, Sinopa is considered a hyaenodontid, and it nests between the extant quoll (genus: Dasyurus) and the extant Tasmanian devil (genus: Sarcophilus). Sarkastodon is considered an oxyaenid and it nests as a sister to Sarcophilus. So… either the quoll and Tasmanian devil are living members of the Creodonta, or we’ll have to redefine the Creodonta.

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.

Desmostylia
According to Wikipedia: “Desmostylians are the only known extinct order of marine mammals. The Desmostylia, together with Sirenia and Proboscidea (and possibly Embrithopoda), have traditionally been assigned to the afrotherian clade Tethytheria, a group named after the paleoocean Tethys around which they originally evolved. The assignment of Desmostylia to Afrotheria has always been problematic from a biogeographic standpoint, given that Africa was the locus of the early evolution of the Afrotheria while the Desmostylia have only been found along the Pacific Rim. That assignment has been seriously undermined by a 2014 cladistic analysis that places anthracobunids and desmostylians, two major groups of putative non-African afrotheres, close to each other within the laurasiatherian order Perissodactyla.”

In the LRT, desmostylians are indeed derived from anthracobunids, which, in turn, are derived from hippos and mesonychids. Mysticeti, the clade of baleen whales are derived from desmostylians. So… baleen whales are extant desmostylians.

Figure 3. Four mesonychids to scale. Here Mesonyx, Anthracobune, Paleoparadoxia and Hippopotamus are compared.

Figure 3. Four mesonychids to scale. Here Mesonyx, Anthracobune, Paleoparadoxia and Hippopotamus are compared.

Mesonychidae
According to Wikipedia, “Mesonychidae is an extinct family of small to large-sized omnivorouscarnivorous mammals closely related to cetartiodactyls (even-toed ungulates & cetaceans) which were endemic to North America and Eurasia during the Early Paleocene to the Early Oligocene. The mesonychids were an unusual group of condylarths with a specialized dentition featuring tri-cuspid upper molars and high-crowned lower molars with shearing surfaces. They were once viewed as primitive carnivores, like the Paleocene family Arctocyonidae, and their diet probably included meat and fish. In contrast to this other family of early mammals, the mesonychids had only four digits furnished with hooves supported by narrow fissured end phalanges.”

In the LRT, mesonychids include hippos and baleen whales. So, they are extant mesonychids. On the other hand, Arctocyonidae includes Arctocyon, which nests in the unrelated marsupial clade, Creodonta (see above). Certain other traditional mesonychids, like Sinonyx and Andrewsarchus, are not mesonyhids, but nest with the elephant shrew, Rhychocyon, close to tenrecs.

Figure 1. Silvanerpeton and Gephyrostegus to the same scale. Each of the two frames takes five seconds. Novel traits are listed. This transition occurred in the early Viséan, over 340 mya. Gephyrostgeus is more robust and athletic with a larger capacity to carry and lay eggs.

Figure 1. Silvanerpeton and Gephyrostegus to the same scale. Each of the two frames takes five seconds. Novel traits are listed. This transition occurred in the early Viséan, over 340 mya. Gephyrostgeus is more robust and athletic with a larger capacity to carry and lay eggs.

Gephyrostegidae
According to Wikipedia, “Gephyrostegidae is an extinct family of reptiliomorph tetrapods from the Late Carboniferous including the genera GephyrostegusBruktererpeton, and Eusauropleura.”

In the LRT, Gephyrostegus is the last common ancestor of the Amniota (= Reptilia). So… gephyrostegids include all living mammals, archosaurs (crocs + birds) and lepidosaurs.

References

wiki/Gephyrostegidae
wiki/Mesonychidae
wiki/Desmostylia

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Cornwallius: not a desmostylian, an ancestor to desmostylians

These taxa
are part of the a recent review of mysticete (baleen whale) ancestors you can read about here, here and here.

Cornwallius sookensis (originally Desmostylus sookensis, Hay 1923, Cornwall 1922; Beatty 2006a, b; Early Oligocene, 25 mya; Fig. 1) was originally and traditionally considered a desmostylian (Fig. 3). Here it nests with Cambaytherium (Fig. 2), both basal to anthracobunids like Janjucetus. These taxa have a narrow skull and a deep jugal beneath the squamosal. The nares are anterior, rather than dorsal in location.

Figure 1. Adult Cornwallius look more like desmostylians. Juveniles look more like anthracobunids. Both are descendant taxa.

Figure 1. Adult Cornwallius look more like desmostylians. Juveniles look more like anthracobunids. Both are descendant taxa.

Note the resemblance
(lack of a downturned snout) on the juvenile to Cambaytherium (above). Apparently, neotony produces a straights-snout anthracobunid. Otherwise it evolves to the tusky, droop-snout, desmostylian grade.

Figure 2. Cambaytherium with a an alternate rostrum reversing taphonomic shifts.

Figure 2. Cambaytherium with a an alternate rostrum reversing apparent taphonomic shifts.

Beatty 2006
produced the following cladogram (Fig. 3) in which desmostylians are derived from the Moeritherium/Elephas clade. In the large reptile tree (LRT, 1163 taxa) cambaytheres and desmostylians arise from mesonychids and hippos.

Figure 2. From Beatty 2006b, a phylogeny of desmostylians derived from moeritherium, an aquatic relative of elephants and sirenians (manatees). Actually desmostylians arise from cambaytheres and anthracobunids, arising from hippos and mesonychids. 

Figure 3. From Beatty 2006b, a phylogeny of desmostylians derived from moeritherium, an aquatic relative of elephants and sirenians (manatees). Actually desmostylians arise from cambaytheres and anthracobunids, arising from hippos and mesonychids.

References
Beatty, BL 2006a. Rediscovered specimens of Cornwallius (Mammalia, Desmostylia) from Vancouver Island, British Columbia, Canada. Vertebrate Palaeontology. 1(1):1–6.
Beatty, BL 2006b. Specimens of Cornwallius sookensis (Desmostylia, Mammalia) from Unalaska Island, Alaska. Journal of Vertebrate Paleontology. 26(3):785–87.
Cooper LN, Seiffert ER, Clementz M, Madar SI, Bajpai S, Hussain ST, Thewissen JGM 2014. Anthracobunids from the Middle Eocene of India and Pakistan Are Stem Perissodactyls. PLoS ONE. 9 (10): e109232. doi:10.1371/journal.pone.0109232. PMID 25295875.
Cornwall IE 1922. Notes on the Sooke Formation, Vancouver Island, B.C. Canadian Field Naturalist. 36:121–23.
Hay OP 1923. Characteristics of sundry fossil vertebrates. Pan-American Geologist. 39:101–120.
Kumar K 1991. Anthracobune aijiensis nov. sp. (Mammalia: Proboscidea) from the Subathu Formation, Eocene from NW Himalaya, India”. Geobios. 24 (2): 221–39. doi:10.1016/s0016-6995(91)80010-w. OCLC 4656806310.
Rose, KD et al. (8 other authors) 2014. Early Eocene fossils suggest that the mammalian order Perissodactyla originated in India. Nature Communications. 5 (5570). doi:10.1038/ncomms6570.

wiki/Cambaytherium
wiki/Cornwallius

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

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

Neoparadoxia swimming animation

The origin of the Mysticeti
Earlier we nested baleen whales with desmostylians like Neoparadoxia (Fig. 1; Barnes 2013). 

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 1. GIF animation of the Neoparadoxia (original image from Barnes 2013). It seems unlikely 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.

Recovered by phylogenetic analysis
The large reptile tree (LRT 1040 taxa) nests desmostylians as proximal outgroups to the mysticetes. Mysticeti, like the gray whale Eschrichtius robustus (Fig. 2)have a large robust tail and no visible hind limbs. That’s just the opposite of what you find in what little we know of known desmostylians (Fig. 1). Noteworthy: we don’t know the tail length in several of the long-jawed desmostylians, the ones most like mysticetes. This is when you have to put away traditional biases and let the cladogram truly be your guide.

Figure 6. Eschrichtius-robustus, the gray whale is the most basal mysticete tested in the LRT with a skull similar to Desmotylus and Beheomotops.

Figure 2. Eschrichtius-robustus, the gray whale is the most basal mysticete tested in the LRT with a skull similar to Desmotylus and Beheomotops. The sacrals here are orange and the robust tail follows to the right. 

In similar fashion
pterosaur workers have been looking in vain for a long manus reptile as the proximal ancestor to the Pterosauria, overlooking taxa with small forelimbs like Cosesaurus, Sharovipteryx and LongisquamaAll this time, they did not realize the elongation of the forelimb elements to various degrees was the LAST transformation that occurred in the known outgroups to the Pterosauria (Peters 2002). You, too, will make discoveries like this when you put away traditional biases, expand your taxon list and let the cladogram be your guide.

As you might remember
the origin of the Odontoceti (toothed whales) started with swimming tenrecs like Leptictidium (Fig. 3) and its close relative Pakicetus, both with a very long tail and large feet.

Figure 1. Leptictidium is known as a hopper. Here it nests with whales. Combine the two and when Lepticitidium jumps in the water, it continues hopping. That long, long tail is homologous to the long, long tail in Zeuglodon.

Figure 1. Leptictidium is known as a hopper. Here it nests with whales. Combine the two and when Lepticitidium jumps in the water, it continues hopping. That long, long tail is homologous to the long, long tail in Zeuglodon.

References
Barnes LG 2013. A new genus and species of Late Miocene Paleoparadoxiid (Mammalia, Desmostylia) from California. Contributions in Science 521:51-114.
Peters D 2002. A New Model for the Evolution of the Pterosaur Wing – with a twist. – Historical Biology 15: 277–301.

Weirdest skull of all: Eubalaena australis (Southern right whale)

There are few mammal skulls
that depart from the basic placental pattern (bauplan) like that of Eubalaena australis (Desmoulins 1822; 15-18 m in length; extant), the Southern right whale (Fig. 1). All the parts are there. They just have weird shapes and are shifted around a bit.

The giant mouth
is much deeper than in Caperea (Bisconti 2012, Fordyce and Marx 2013 ) or Balaenoptera (Fig. 2; Linneaus 1758), with much longer baleen. The skull is relatively larger and the postcrania shorter and deeper with relatively larger forelimbs than Balaeonoptera. The mandible moves relatively little. The coronoid process is absent. The lower lip rises to meet the upper jaw, as in Caperea (Fig. 2), but much more so due to the great height of the giant skull.

Note the hammerhead cranium in dorsal view
creating a T-shape with the addition of that long triangular rostrum (Fig. 1). The mandible is much wider than the rostrum. That resulting space between them is where the water exits after entering from the front and after being filtered by the tall baleen strips.

Surprisingly,
five digits are present on the manus following a long lineage of thumb-less ancestors. So the reappearance of the thumb here is a minor atavism.

Figure 1. Eubalaena australis skeleton with several bones colorized and eyeball added. Note the reappearance of the thumb here (if valid) after a long run of four-fingered ancestors.

Figure 1. Eubalaena australis skeleton with several bones colorized and eyeball added. Note the reappearance of an atavistic thumb after a long run of four-fingered ancestors.

The cervical series
is tightly interwoven, like a stack of bent playing cards. The caudal transverse processes have broad tips. The chevrons are longer than deep.

Figure 2. Caperea, the pygmy right whale, is a much smaller sister to Eubalaena. Only the skeleton with the ribs angled back fits the stranded in vivo specimen and the skull is a better fit when it is slightly larger.

Figure 2. Caperea, the pygmy right whale, is a much smaller sister to Eubalaena. Only the skeleton with the ribs angled back fits the stranded in vivo specimen and the skull is a better fit when it is slightly larger.

The pygmy right whale (Caperea marginata)
(Fig. 2; Gray 1846; 6m; extant) looks like a small, slender right whale with tiny flippers. While it nests with Eubalaena in the LRT (Fig. 9), it retains something of a gray whale (Eschrichtius, Fig. 4) appearance. Caperea is the smallest of all baleen whales, by far.

The cervicals are all fused to one another. The dorsals have paddle-shaped ribs, but don’t be fooled by the museum mounts (Fig. 2, above). Such ribs cannot fit into a living Caperea without rotating posteriorly about 45º (Fig. 2, below). The lumbars are reduced to one. The chevrons are shorter than long, as in right whales and cetotheres.

The dorsal fin is above the sacral vertebrae, distinct from odontocetes, in which the dorsal fin is above the dorsal ribs.

By comparison
Balaenoptera (Fig. 2) the blue whale, is longer, with a relatively smaller, shallower skull. It feeds by expanding a giant throat sack with water inflow then expelling it with the tongue and by throat constrictions.

Figure 3. Blue whale (Balaenoptera musculus) skull and skeleton. Note the lack of a thumb goes back to Mesonyx.

Figure 3. Blue whale (Balaenoptera musculus) skull and skeleton. Note the lack of a thumb goes back to Mesonyx.

The California Gray Whale
(Eschrichtius robustus; 15m; extant; Gray 1864; Fig. 7) nests at the base of all tested mysticetes (Fig. 9) and provides the best clues to envision the post-crania of Behemotops, and other derived desmostylians.

Figure 6. Eschrichtius-robustus, the gray whale is the most basal mysticete tested in the LRT with a skull similar to Desmotylus and Beheomotops.

Figure 6. Eschrichtius-robustus, the gray whale is the most basal mysticete tested in the LRT with a skull similar to Desmotylus and Beheomotops.

The maxilla of the gray whale retains a tooth alveolus
for the canine which is aligned along the jawline in Desmostylus (Fig. 8), a trait not found elsewhere among mammals. The dentary tip also retains a tooth alveolus, similar to that found in Desmostylus.

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 7. 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. See figure 8. I wonder if we’ll someday find teeth in a dissection of the Gray Whale. Someone should look for them.

Note the maxilla of this Desmostylus
(Fig. 8) shares many traits with basal mysticetes, including a general toothlessness (molars still are present below the orbit), a concave maxilla ventral margin, and a dorsal naris. The dentary has anteriorly oriented, tusk-like incisors, growing from alveoli similar to those in the gray whale (Fig. 7).  I wonder if we’ll someday find teeth in a dissection of the Gray Whale. Someone should look for them. I wonder if someday someone will find teeth in a dissection of the Gray Whale. Someone should look for them.

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

The evidence keeps mounting
that mysticetes and odontocetes had separate origins among desmostylians and tenrecs, respectively.

Figure 4. Subset of the LRT showing mesonychids including hippos, anthracobunids, desmostylians and mysticete 'whale.'

Figure 9. Subset of the LRT showing mesonychids including hippos, anthracobunids, desmostylians and mysticete ‘whale.’

References
Desmoulins C 1822. Baleine. Dictionnaire Classique d’Histoire Naturelle 155-165
Gray JE 1864. “Eschrichtius“. Annals of the Magaztine Natural History. 3 (14): 350.
Linnaeus C 1758. Systema naturæ per regna tria naturæ, secundum classes, ordines, genera, species, cum characteribus, differentiis, synonymis, locis. Tomus I. Editio decima, reformata.

wiki/Balaenoptera
wiki/Eubalaena
wiki/Caperea
wiki/Eschrichtius

 

 

All toothless whales are baleen whales

Updated November 20, 2016 based on input from Dr. RW Boessenecker who corrected a mistake I made reconstructing Tokarahia by noting the mandible was axially rotated in situ 180º. Correcting that error produces the bowed out Gothic arch set of mandibles, typical of mysticetes. 

Preamble
Several of the mistakes discussed below are based on the long-standing tradition that whales are monophyletic. That is, odontocetes (toothed whales) and mysticetes (baleen whales) were long thought to have a common ancestor with flukes and fins. That paradigm  was overturned by the large reptile tree (LRT) earlier here. Workers thought that common ancestor would be an archaeocete, but, so far, all tested archaeocetes nest basal to extant odontocetes and were derived from tenrecs in the LRT.

Almost fifty years ago whale monophyly was questioned
by Van Valen (1968), who listed a number of traits that distinguish Odontoceti from Mysticeti. Unfortunately this was before computer-assisted phylogenetic analysis and neither desmostylians nor tenrecs were offered as basal taxa with legs. This was also long before any whales with legs had been discovered. Gotta give Van Valen credit for his insight way back then.

Yesterday we looked at the desmostylian ancestors of today’s mysticete (baleen) whales. Less than 24 hours ago I encountered for the first time Aetiocetus (Emlong 1966; Figs. 1, 2). I learned it has long been considered a toothed basal mysticete. Evidently some of the back teeth are leaf-shaped and all of the teeth are small and widely spaced. Most whale workers are happy with this hypothesis or relationships, but the LRT finds otherwise based on an expanded taxon list.

Figure 1. Aetiocetus skull in several views.

Figure 1. Aetiocetus skull in several views. Most whale workers today consider this taxon close to the origin  of baleen whales. The transversely crested cranium is a trait found in living odontocetes, not mysticetes.

I added Aetiocetus
to the large reptile tree and, while given the opportunity to nest with mysticetes, Aetiocetus nested instead between Zygorhiza and Orcinus + Physeter, all members of the Odontoceti. As recently as 2015, Ekdale et al. (Fig. 2) were trying to use Aetiocetus to explain the origin of baleen in modern whales.

Figure 2. Palate and teeth of the odontocete Aetiocetus alongside palates of juvenile gray whale and embryo fin whale, members of the Mysticeti. Aetiocetus was long thought to be a basal mysticete.

Figure 2. Palate and teeth of the odontocete Aetiocetus alongside palates of juvenile gray whale and embryo fin whale, members of the Mysticeti. Aetiocetus was long thought to be a basal mysticete.

18 hours ago I encountered another mysticete,
Tokarahia kauaeroa (Boessenecker and Fordyce 2015; Late Oligocene; OU 2235), which has no teeth. Their reconstruction (Fig. 2) is

Figure 2. Tokarahia, a toothless odontocete long thought to be a basal mysticete. Original interpretation of materials is presented alongside a new interpretation, closer to the bones in situ. See figure 4.

Figure 3. Tokarahia, a toothless odontocete long thought to be a basal mysticete. Original interpretation of materials is presented alongside a new interpretation, closer to the bones in situ. See figure 4. The humerus is rotated so the ball joint fits into the ventral socket of the scapula.

Unfortunately
I thought Boessenecker and Fordyce changed the curve of the mandible in their reconstruction and did not follow the very narrow mandibles in restoring the largely missing or buried rostrum. They also moved the orbit anteriorly. I attempted a mistaken correction (Fig. 3) that was based on a narrow mandible interpretation. Dr Boessenecker reported the mandible was axially rotated in situ (Fig. 4). Those corrections was applied shortly thereafter. A good lesson in keeping an open mind.

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

Figure 4. Tokarahia in situ and as originally reconstructed (on right). Flipping the right mandible and reconstructing the skull anew (at left).

12 hours ago
I also learned about Isanacetus laticephalus (Kimura and Ozawa 2002; early Miocene, 18 mya; MFM 28501; Fig. 5, 6). This fossil whale is indeed a mysticete. In the LRT it nests between the desmostylian Behemotops (presumably with at least front legs) and extant baleen whales.

Figure 5. Isanacetus skull in several views. I also present skull tracings in DGS that differ in some respects from the published drawings.

Figure 5. Isanacetus skull in several views. I also present skull tracings in DGS that differ in some respects from the published drawings. Isanacetus is a basal mysticete, derived from a sister to Behemotops.

Like all mysticetes and derived desmostylians
Isanacetus has a ventrally concave rostrum, a wide flat skull and other traits that distinguish mysticetes from odontocetes + tenrecs. Isanacetus is also one of the smallest known mysticetes, about twice the size of its current desmostylian sister, Behemotops (Fig. 6) and half again longer in the skull than the more completely known Desmostylus.

Figure 6. Isanacetus compared to sisters recovered in the LRT. Balaeonoptera is much reduced.

Figure 6. Isanacetus compared to sisters recovered in the LRT. Balaeonoptera is much reduced. The loss of teeth actually occurred when mysticetes had legs!

More backstory for those keenly interested
Below are some earlier and traditional reports on Aetiocetus and aetiocetids, which was considered by these authors to be related to mysticetes and cetotheres (extinct mysticetes).

Whitmore and Sanders 1976 report,
“The cheek teeth [of Aetiocetus] are leaf shaped, similar to those of Patriocetus, but smaller and with the roots coalesced. The triangular rostrum, reduced dentition, and the conformation of the posterior ends of the maxillae, premaxillae, and nasals (Ernlong, 1966:s) are characters that would be expected in the ancestor of the mysticetes. Thenius (1969:489) stated: “Even if Aetiocetus, because of its geologic age (upper Oligocene) cannot be a direct stem form of the cetotheres, yet this genus documents that a specific family (Aetiocetidae) must be classified as ancestor, the link between ancient and baleen whales.

“Among the few Cetacea known from deposits of middle Oligocene age are two occurrences of unmistakable Mysticeti. One of these, Mauicetus Benham, 1939, from New Zealafid, has long nasals embraced by premaxillae and maxillae which extend posteriorly to the level of the supraorbital process of the frontal, together with an anteriorly thrusting triangular supraoccipital. The Oligocene Mysticeti, had already evolved the elongated, edentulous rostrum, constituting 3/4 to 4/5 of total skull length, that typifies the modern baleen whales. The mandible of Oligocene Mysticeti was also edentulous and, like those of modem baleen whales, was long and slim.”

Berta and Demere 2005 reported,
“Aetiocetids are the most taxonomically and morphologically diverse clade of toothed mysticetes known from the late Oligocene of the eastern and western North Pacific. Aetiocetids can be distinguished from other toothed mysticetes by the following unequivocal synapomorphies: lobate or triangular parietal-frontal suture; zygomatic process of squamosal expanded near anterior end; “window” in the palate exposing vomer; short, broad extension of the palatine that overlaps the pterygoid; and exoccipital developed ventrally as an anteriorly directed posterior sinus.

The presence of palatal nutrient foramina associated with the upper teeth in all aetiocetids suggests that these toothed mysticetes had already evolved some type of baleen. The form and function of this rudimentary baleen is currently unknown, but the fact that these archaic mysticetes also possessed procumbent anterior teeth, broad diastemata, and posterior teeth with sharply pointed cusps, accessory denticles, and longitudinal enamel ridges suggests development of a specialized type of filter feeding differing from that of other toothed and edentulous mysticetes.”

Unfortunately
these authors had not expanded their taxon set to include desmostylians, which pull mysticetes away from odontocetes + tenrecs.

Eckland et al. 2015 report
“The origin of baleen in mysticetes heralded a major transition during cetacean evolution. Extant mysticetes are edentulous in adulthood, but rudimentary teeth develop in utero within open maxillary and mandibular alveolar grooves. The teeth are resorbed prenatally and the alveolar grooves close as baleen germ develops.”

That’s all well and good, but you really need a wide gamut taxon inclusion set that includes whales, tenrecs and desmostylians to find the diphyletic origins of extant whales and in desmostylians one should look for the origin of baleen, as discussed earlier here.

References
Berta A and Demere TA 2005. Phylogenetic relationships among the diverse toothed mysticete clade the aetiocetidae and reconsideration of the filter feeding niche. Evolution of  aquatic tetrapods. Fourth triennial convention abstracts May 16-20 2005, Akron, OH, USA.
Boessenecker RW and Fordyce RE 2015. A new genus and species of eomysticetid (Cetacea: Mysticeti) and a reinterpretation of ‘Mauicetus’ lophocephalus Marples, 1956: Transitional baleen whales from the upper Oligocene of New Zealand. Zoological Journal of the Linnean Society. in press. doi:10.1111/zoj.12297.
Demere TA 2005. Palate vascularization in an Oligocene toothed mysticete (Cetacea: Mysticeti): Aetiocetidae); implications for the evolution of baleen. Evolution of  aquatic tetrapods. Fourth triennial convention abstracts May 16-20 2005, Akron, OH, USA.
Ekdale EG, Demere TA and Berta A 2015. Vacularization of the gray whale palate (Cetacea, Mysticeti, Eschrichtius robustus): soft tissue evidence for an alveolar source of blood to baleen. The Anatomical Record Advances in Integrative Anatomy and Evolutionary Biology 298(4) · February 2015.
Whitmore FC Jr and Sanders AE 1976. Review of the Oligocene Cetacea. US Geological Survey Staff — Published Research. Paper 237.
Van Valen L 1968. Monophyly or diphyly in the origin of whales”. Evolution. 22 (1):37–41.

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