Multituberculates and rodents: cousins? or not?

The big question is: what are they?
The LRT nests multituberculates with rodents, but currently that’s a minority view of one.

Kielan-Jaworowska Z and Hurum 2001 wrote:
“Traditionally palaeontologists believed that multituberculates might have originated from cynodonts independently from all other mammals, or diverged from other mammals at a very early stage of mammalian evolution.” Unfortunately these authors do not say which taxa attract multis to the the pre-eutherian grades and clades.

Simpson (1945, p. 168) stated:
“The multituberculate structure was so radically distinctive throughout their history that it seems hardly possible that they are related to other mammals except by a common origin at, or even before, the class as such”

Hahn et al. (1989) and Miao (1993)
reported that multituberculates might be a sister taxon of all other mammals. On the other hand, Kielan-Jaworowska et al. 1986; Miao 1988; Wible 1991; Rougier et al. 1992; Wible and Hopson 1993, 1995; Hurum 1994, 1998a, b) demonstrated the homogeneity of the internal structure of the skull and vascular system of all mammals, including multituberculates.

Hurum et al. 1996; Rougier et al. 1996a report
Multituberculate ear ossicles display the same pattern as those of all other mammals.

The notion
that multituberculates might form a sister taxon of all other mammals is related to the idea that they are close relatives to the Haramiyidae, a family represented until recently only by isolated teeth, with numerous cusps arranged in longitudinal rows, known from the Late Triassic and Early Jurassic mostly in Europe. Key to these thoughts are the idea that most fossil material comes from teeth.

Jenkins et al. (1997)
described from the Upper Triassic of Greenland Haramiyavia clemmenseni, assigned to the Haramiyidae, represented by dentaries and partial maxillae with teeth and fragments of the postcranial skeleton. Haramiyavia has been interpreted as having orthal jaw movement (standard up-down rotation on a glenoid axis). On this basis Jenkins et al. excluded the Haramiyida from the Allotheria, which have propalinal (fore-and-aft) movement of the dentary and backward (palinal) power stroke. In turn Butler (2000) revised all known allotherians and argued that dental resemblance supports the hypothesis that the Multituberculata originated from the Haramiyida.

Kielan-Jaworowska Z and Hurum 2001 wrote:
“Finally, the most recent analyses of mammalian relationships, including analysis of the skeleton of a symmetrodont Zhangheotherium (Hu et al. 1997; here recovered as a pangolin ancestor), and the skeleton of the eutriconodont Jeholodens (Ji et al. 1999; here recovered as a tritylodontid), did not support multituberculate-therian sister-group relationship. In both of these papers the Multituberculata were placed between Monotremata (Ornithorhynchus) and Symmetrodonta (Zhangheotherium), being a sister taxon of all the Holotheria” (last common ancestor of Kuehneotherium and Theria). In other words, close to monotremes.

Kielan-Jaworowska Z and Hurum 2001 wrote about the multi brain:
“The multituberculate brain, designated cryptomesencephalic (characterised by an expanded vermis, no cerebellar hemispheres, and lack of the dorsal midbrain exposure) is very different from that in Theria, which originally had eumesencephalic brains (characterised by a wide cerebellum with extensive cerebellar hemispheres and large dorsal midbrain exposure).”

This appears to assume only one direction for brain development, with no evolutionary backsliding. Unfortunately Kielan-Jaworowska and Hurum employed a hypothetical ancestor for their multituberculate cladogram.

We’ve already seen teeth in whales reverse from the typical W and Y molar cusp patterns, to linear molar cusps to simple pegs.

Figure 1. Rodent and multituberculate right pedes dorsal view. Note the derived pes of Kryptobaatar based on the primitive pedes of Shenshou and Paramys. Multis have a reduced astragalus (orange) for a looser ankle joint for an arboreal niche.

Figure 1. Rodent and multituberculate right pedes dorsal view. Note the derived pes of Kryptobaatar based on the primitive pedes of Shenshou and Paramys. Multis have a reduced astragalus (orange) for a looser ankle joint for an arboreal niche.

Kielan-Jaworowska Z and Hurum 2001 wrote about the multituberculate foot:
“Another character neglected until recently in phylogenetic analyses of early mammals involves the foot structure. In the multituberculate foot the middle metatarsal (M3) is abducted from the longitudinal axis of the tuber calcanei, while the calcaneus contacts distally the 5th metatarsal (Kielan-Jaworowska and Gambaryan 1994). This type of foot appeared at that time to be unique among mammals, but Ji et al. (1999) described a similar type of foot in the eutriconodont Jeholodens. It follows that there are two groups of characters related to brain and foot structure, which ally multituberculates with eutriconodonts.”

Figure 2. Squirrel pes.

Figure 2. Squirrel pes, not similar to a multi ankle yet still able to clamber and roared on tree trunks.

The trouble is
a large gamut analysis of mammalian relationships does not find a better nesting for those highly-derived, but primitive-brained, rodent-like mutituberculates than with rodents. They have similar teeth, similar extremities, similar skulls. And that twisted heel-bone (calcaneum) is a derived trait. So why are multis supposed to nest with mammals earlier than placentals?

If anyone can produce a pre-therian that attracts multis, please bring it to my attention. So far, I have failed to find out, and so multis continue to nest with rodents and plesiadapids.

References
Kielan-Jaworowska Z and Hurum JH 2001. Phylogeny and Systematics of multituberculate mammals. Paleontology 44, 389–429.
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Yanoconodon: Proximal sister to the Mammalia

Updated September 22, 2018
with the addition of pertinent taxa.

This post was composed several weeks ago.
After all the intervening excitement I’m glad to bring Yanoconodon to your attention.

Yanoconodon alllini (Luo, Chen, Li and Chen 2007; Early Cretaceous, 122 mya; 13 cm in length; Figs. 1, 2) is known from a nearly complete and articulated crushed fossil. It is traditionally considered a eutriconodont, a clade that traditionally includes Spinoletes, Repenomamus, GobiconodonLiaoconodon and Jeholodens. Unfortunately that clade is paraphyletic in the large reptile tree (LRT) because other traditional members nest outside this clade in the LRT. Here Yanoconodon nests with Maotherium in that clade (Fig. 3).

Yanoconodon had a semi-sprawling posture
and a a long, robust torso with an unusually thick lumbar vertebrae provided with very short ribs. The limbs were short. The canines were quite narrow. The posterior jaw bones were still attached to the jaw. They had not yet become completely reduced to middle ear bones and completely separated from the jaw bones. So, by definition and cladogram (Fig. 3), Yanoconodon was not a true mammal. Wikipedia disagrees as that author reports, “Despite this feature Yanoconodon is a true mammal.”

FIgure 1. Yanaconodon nests as the proximal outgroup to the Mammalia in the LRT.

FIgure 1. Yanoconodon nests as the proximal outgroup to the Mammalia in the LRT. Even so it has several autapomorphies (differences from the actual  hypothetical ancestor.)

from the Luo, Chen and Chen abstract
“Detachment of the three tiny middle ear bones from the reptilian mandible is an important innovation of modern mammals. Here we describe a Mesozoic eutriconodont nested within crown mammals (1) that clearly illustrates this transition: the middle ear bones are connected to the mandible via an ossified Meckel’s cartilage. The connected ear and jaw structure is similar to the embryonic pattern in modern monotremes (egg-laying mammals) and placental mammals, but is a paedomorphic feature retained in the adult, unlike in monotreme and placental adults. This suggests that reversal to (or retention of) this premammalian ancestral condition is correlated with different developmental timing (heterochrony) in eutriconodonts. (2) This new eutriconodont adds to the evidence of homoplasy of vertebral characters in the thoraco-lumbar transition and unfused lumbar ribs among early mammals. (3) This is similar to the effect of homeobox gene patterning of vertebrae in modern mammals, making it plausible to extrapolate the effects of Hox gene patterning to account for homoplastic evolution of vertebral characters in early mammals.” (4)

Notes

  1. The LRT nests Yanoconodon just outside the crown mammals. Not sure why the authors say this, given what they report about the posterior jaw bones as posterior jaw bones.
  2. Curious that the retention of “this pre-mammalian ancestral condition” does not indicate to the authors that Yanoconodon is indeed a pre-mammal.
  3. Yanoconodon does not nest as an early mammal in the LRT.
  4. …or…not, if Yanoconodon is indeed a non-mammalian trithelodont. Other non-mammalian cynodonts lived alongside Jurassic mammals. Only one purported eutriconodont listed above is a mammal, Volaticotherium. It nests as a basal placental. Triconodon is a mammal, too, a monotreme known from just a dentary and teeth.
Figure 2. From Luo et al. the posterior jaw bones of Yanoconodon. These are not middle ear bones, so Yanoconodon is not a mammal.

Figure 2. From Luo et al. the posterior jaw bones of Yanoconodon. These are not middle ear bones, so Yanoconodon is not a mammal. The malleus is the articular. The incus is quadrate.

Yanoconodon is a great transitional fossil.
You can’t call it a mammal, because it nests outside the last common ancestor of all mammals.

Figure 3. Basal mammals begin with Ornithorynchus, the most primitive living mammal. Yanoconodon nests just outside this clade.

Figure 3. Basal mammals begin with Ornithorynchus, the most primitive living mammal. Yanoconodon nests just outside this clade.

References
Luo Z, Chen P, Li G, and Chen M 2007. A new eutriconodont mammal and evolutionary development in early mammals. Nature 446:15. online Nature

wiki/Yanoconodon

Romer’s ‘gap’ gets filled by Clack et al. 2016

According to Clack et al. 2016
“The term ‘Romer’s Gap’ was coined for a hiatus of approximately 25 million years (Myr) in the fossil record of tetrapods, from the end-Devonian to the mid-Mississippian (Viséan).”

This paper starts to fill Romer’s gap
with five new, incomplete taxa. three stem tetrapods and two stem amphibians, suggesting a deep split among crown tetrapods. That conclusion confirms an earlier one first reported here based on: (1) tetrapod footprints in the Middle Devonian, (2) the first appearance of reptiles in the Viséan and (3) the earlier split of microsaurs + amphibians, evidently before the end of the Devonian or at the very origin of the Carboniferouus following the post-Devonian extinction event.

Figure 1. Above, two trees recovered by Clack et al. 2016 compared to the one tree recovered by the LRT below.

Figure 1. Above, two trees recovered by Clack et al. 2016 compared to the one tree recovered by the LRT below. Left tree: Strict consensus of four equally parsimonious trees obtained from implied weights search with K = 4. Right tree:Bayesian analysis tree. Note the widely varying nesting sites of certain taxa.

Unfortunately the phylogenetic analyses
of Clack et al, (Fig. 1) fail to separate basal reptiles from microsaurs, fail to nest Gephyrostegus and Silvanerpeton as basalmost reptiles and fail to split basal reptiles into Archosauromorpha and Lepidosauromorpha in or before the Viséan. These problems are in addition to their inability to find accord in their own two published topologies (Fig. 1).

Figure 2. A new Romer's Gap taxon, Koilops, nests with basalmost tetrapods. The skull is similar to that of Acanthostega.

Figure 2. A new Romer’s Gap taxon, Koilops, nests with basalmost tetrapods. The skull is similar to that of Acanthostega. Note the interpretive changes between the the color version, which helps one understand the anatomy and the line art Clack et al. 2016 tracing, which still includes some guesswork and perhaps some misinterpretation. Large parts of the squamosal and postorbital are missing here. I’m not saying the colored tracing is 100% correct. This is a difficult fossil. I am saying it is so much easier to understand than the line drawing.

Koilops (Fig. 2) was a basal tetrapod, smaller than most.

Figure 2. Aytonerpeton is a tiny taxon with an inch-long skull. Here CT scans have helped delineate the bones colored for identification.

Figure 3. Aytonerpeton is a tiny taxon with an inch-long skull. Here CT scans have helped delineate the bones colored for identification. The orbit appears to have on odd bean shape, relatively large, but this is a tiny taxon.  CT scan from Clack et al. 2016.

Based on chronological and phylogenetic bracketing
we should expect to find amphibian-like reptiles (with amniote eggs) prior to the Viséan in Romer’s Gap, but they are likely to be a minority component. Utegenia, or similar sister, should be found there, along with other basal seymouriamorphs and reptilomorphs.

Figure 1. Which came first? The tracks or the trackmakers? In this case the tracks came first, strong indications that the variety of Devonian trackmakers we have found were all commonplace in the Late Devonian. The variety of basal reptiles and microsaurs found in the Visean must also reflect a wide radiation of derived taxa, pointing to an earlier origin.

Figure 4. From August 22, 2016, this graph shows what taxa are likely to be found in the late Devonian and Tournaisian (earliest Carboniferous = Romer’s Gap).

References
Clack JA and 14 other authors 2016. Phylogenetic and environmental context of a Tournaisian tetrapod fauna. Nature ecology & evolution 1, 0002 (2016) | DOI: 10.1038/s41559-016-0002

 

Fleshing out Andrewsarchus, the giant tenrec

All we know of Andrewsarchus
is its skull — without a mandible. A few days ago the dentary of a sister taxon, Sinonyx, was added to the skull of Andrewsarchus ((Osborn 1924; middle Eocene, 45 mya; AMNH 20135; 83cm skull length; also see Fig. 1) just to see if it would fit.

Before that…
everyone forever has always fleshed out Andrewsarchus like a giant bear/dog, moving the eyeballs to the top and giving it a bear/dog nose. Image googling Andrewsarchus will give you an idea what a widespread and accepted tradition that has been. I even followed that tradition back in 1989 in the book Giants, which you can see here as subset 1 of a larger pdf of the entire book.

Unfortunately,
Andrewsarchus does not nest with bears, dogs or mesonychids. It nests with tenrecs and Rhynchocyon (Fig. 2.), one type of elephant shrew. (The other type of elephant shrew is unrelated, as we learned here, Fig. 2). Tenrecs have a long flexible nose.

So, here, without further adieu
is a first shot at adding tenrec soft tissue to the skull of Andrewsarchus (Fig. 1). Is it close to being correct? I hope so, given the present evidence.

Figure 1. Andrewsarchus restored as giant tenrec alongside, Canis, the wolf to scale. Note the small and low-set eyes on Andrewsarchus. The mandible comes from Sinonyx. Note the natural tilt of the canid skull permitting binocular vision. Andrewsarchus had low-set eyes, rather un-canid-like. We have to give up the bear-dog restoration of Andrewsarchus.

Figure 1. Andrewsarchus restored as giant tenrec alongside, Canis, the wolf to scale. Note the small and low-set eyes on Andrewsarchus. The mandible comes from Sinonyx. Note the natural tilt of the canid skull permitting binocular vision. Andrewsarchus had low-set eyes, rather un-canid-like. We have to give up the bear-dog restoration of Andrewsarchus.

Now, just imagine the post-crania…
and the best clue we have is the living tenrec, Rhynchocyon (Fig. 2) with long legs, robust torso and short tail, only ten times bigger.

Figure 6. Rhynchocyon (above) and Macroscelides (below) compared. Though both are considered elephant shrews, they nest in separate major mammal clades in the LRT.

Figure 3. Rhynchocyon (above) and Macroscelides (below) the other type of elephant shrew compared. Though both are considered elephant shrews, they nest in separate major mammal clades in the LRT.

Maybe it’s time to 
give up the bear-dog restoration for Andrewsarchus and give it the giant  tenrec restoration it deserves based on phylogenetic bracketing and phylogenetic analysis.

Figure 3. The skull of Andrewsarchus mated to the body of Leptictis to make a chimaera.

Figure 3. The skull of Andrewsarchus mated to the body of Leptictis to make a chimaera.

References
Osborn HF 1924. Andrewsarchus, giant mesonychid of Mongolia. American Museum Noviattes 146: 1-5.

Pleuraspidotherium and Orthaspidotherium

These two taxa don’t make very many lists.
That may be because Pleuraspidotherium amonieri  (Paleocene; Lemoine 1882; Fig. 1) and Orthaspidotherium edwardsi (Ladevèze, Missiaen and Smith 2010; ) are not directly related to any ‘big name’ clades and they have a very basal condylarth (herbivorous mammal) look. Instead these two nest with rather plesiomorphic Meniscotherium and highly derived Astrapotherium in the large reptile tree (LRT, 898 taxa). Both Pleuraspidotherium and Orthaspidotherium were originally recognized as phenacodontids related to Meniscotherium, so we’re tracking traditional nestings here.

Figure 1. Orthaspidotherium from x et al. 2009 is a plesiomorphic mammalian herbivore, basal to all later forms, from elephants to baleen whales to giraffes.

Figure 1. Orthaspidotherium from Ladevèze, Missiaen and Smith 2010 is a plesiomorphic mammalian herbivore, basal to all later forms, from elephants to baleen whales to giraffes.

However in the LRT,
both taxa nest together and apart from Phenacodus.

Figure 1. Pleurospidotherium a

Figure 1. Pleuraspidotherium a

These two were among the very first
slightly larger mammalian herbivores that first appeared in the Cenozoic. We see the origin of the notched diastema here separating the anterior premolars from the poster premolars and molars.

Figure 2. Subset of the LRT showing the nestings of Pleurospidotherium and Orthaspidotherium at the base of the herbivorous mammals.

Figure 2. Subset of the LRT showing the nestings of Pleurospidotherium and Orthaspidotherium at the base of the herbivorous mammals.

Halliday 2015 reports
“Ladevéze et al. (2010) hypothesised that Pleuraspidotheriidae are closest relatives to arctocyonids such as Chriacus, in a group also including the basal artiodactyls, but their taxonomic sampling was very low, and only very few representatives of each supposed group were present.” 

In the LRT
Chriacus nests with bats and Arctocyon nests with Didelphis in the Metatheria, both far from the Pleuraspidotheriidae. None of these relationships is found in Halliday et al. 2015.

Halliday 2015 reports, 
“With the exception of Primates (Russell, 1964), Rodentia (Jepsen, 1937), and Carnivora (Fox, Scott & Rankin, 2010), no extant order of placental mammal has an unambiguous representative during the Paleocene.” Pleuraspidotherium and Orthaspidotherium are also in the Paleocene, so they are early representatives of the herbivorous placental clades.

“Despite numerous suggestions of Cretaceous placentals, no Cretaceous eutherian mammal has been unambiguously resolved within the placental crown.” In the LRT multituberculates and Shenshou from the Jurassic are rodent sisters, Volaticotherium is a basal pre-placental from the earliest Cretaceous. Docofossor is a basal Oxfordian (early Late Jurassic) marsupial.  Maotherium a pre-mammal from the early Cretaceous, Zhangheotherium, a basal pangolin is from the earliest Cretaceous, and Maelestes, a basal tenrec is from the late Cretaceous, so the Halliday claim is not validated by the LRT and a Cretaceous origin would therefore NOT require the existence of long ghost lineages, contra Halliday et al. 2015.

Halliday et al. 2015 illustrates
the ‘current consensus” of mammalian relationships with the first split at Xenarthra + Tenrecoidea and kin splitting from Glires + the rest of the placentals in something of a mishmash of tree branches. The LRT, by contrast, recovers complete resolution at all branches and does not replicate the “consensus” topology.

Halliday et al. then reports on their own phylogenetic analysis based on 680 traits and 177 taxa. The resulting topology bears little similarity to the the LRT with the first split separating (primates + plesiadapids) + (rodents + rabbits) + xenarthra  from the rest of the placentals, then Phenacodus + Meniscotherium and kin splitting next from the remaining placentals in one test.

Another result split Xenarthra and Procavia + Potamogale and kin from the rest of the mammals. Among their seven conclusions, they report, “No definitive crown-placental mammal has yet been found from the Cretaceous, as Protungulatum is resolved as a stem eutherian, and therefore the Cretaceous occurrence of Protungulatum cannot be considered definitive proof of a Cretaceous origin for placental mammals.”

This is contradicted by the LRT results.

References
Halliday T et al. 2015. Resolving the relationships of Paleocene placental mammals. Biologoical Reviews. doi: 10.1111/brv.12242
Ladevèze S, Missiaen P and Smith T 2010. First Skull Of Orthaspidotherium edwardsi (Mammalia, “Condylarthra”) From The Late Paleocene Of Berru (France) And Phylogenetic Affinities Of The Enigmatic European Family Pleuraspidotheriidae”. Journal of Vertebrate Paleontology. 30 (5): 1559–1578.
Lemoine V 1882. Sure l’encephale de l’Artocyon et du Pleurospidotherium aumonieri. Bulletin de la Societe Géologie de France 3 series t. X. Also. Comptes Rendus.

wiki/Orthaspidotherium
wiki/Pleuraspidotherium 

An imaginary mandible for Andrewsarchus

All I did
was take the mandible from sister Sinonyx and scale it to Andrewsarchus (Fig. 1; Osborn 1924). I also added a patch to extend the apparently broken and missing posterior nasals over the fontanelle between the frontals because that’s how far the nasal extends in Sinonyx.

See how sometimes
you don’t ‘see’ something until after you see it in a sister?

Figure 1. Andrewsarchus with Sinonyx mandible. The lower canine helps constrain the shape of the missing upper canine. 

Figure 1. Andrewsarchus with Sinonyx mandible. The lower canine helps constrain the shape of the missing upper canine. Note the transparent extension of the posterior nasals to cover up the fontanelle between the frontals, as in Sinonyx.

BTW
it bothered me that Sinonyx and Andrewsarchus were so much larger than their sisters, especially their closest sister, a type of elephant shrew, Rhynchocyon. Moreover, several traits appear to be homologous. So I retested the relationship of Sinonyx and Andrewsarchus with mesonychids and I retested them with prejudice. Any traits that could relate Sinonyx and Andrewsarchus with mesonychids I scored that way.

In the end,
I was not able to nest Sinonyx and Andrewsarchus with mesonychids.

Furthermore
when I removed all tenrec and odontocete sisters from the tenrec clade (see Fig. 2), leaving only Sinonyx and Andrewsarchus alone they still did not nest with mesonychids, but kept their node unchanged between the Ptilocercus clade and Onychodectes.

Figure 3. Tenrec-Odontocete clade with Leptictis now nesting with the elephant shrew Rhynchcyon and the long-tailed tenrecs nesting with the short tailed tenrecs, basal to Pakicetus.

Figure 2. Tenrec-Odontocete clade with Leptictis now nesting with the elephant shrew Rhynchcyon and the long-tailed tenrecs nesting with the short tailed tenrecs, basal to Pakicetus. This tree moves Sinonyx closer to Pakicetus. Indohyus has already been associated with pakicetids.

Testing like this
brought certain problems to the surface. The current tree has been improved over earlier versions.

Here’s how the tenrec clade now stands:
(Fig. 2) Leptictis and the elephant shrew Rhynchocyon now nest together. They are both similar in size and build.

Giant Andrewsarchus and smaller Sinonyx still nest together. Would still like to see some post-crania for  these two.

The two living short-tailed terrestrial tenrecs, Hemicentetes and Tenrec now nest with two extinct long-tailed aquatic tenrecs, Lepticitidium and Indohyus. The latter has already been associated with pakicetids in the literature  (Rao 1971, Thewissen et al. 2007.)

Likewise Sinonyx and Andrewsarchus have already been associated with the origin of whales in the literature. The new tree topology brings them closer to Pakicetus.

Early members of the tenrec clade
were insectivore speedsters with long slender legs, based on the habits of Rhynchocyon. More derived tenrecs like Tenrec, are not speedy and Hemicentetes is protected with spinesLeptictidium had much longer hind limbs than fore limbs and was likely bipedal. Indohyus had subequal limbs so likely remained a quadruped. Tradtionally Indohyus has been considered an artiodactyl, but given the opportunity to nest with artiodactyls in the LRT, it does not do so.

Perhaps the most convergent clade
By all the present evidence, some tenrecs converged with rabbits and elephant shrews, some with mesonychids, others with artiodactyls and still others with mysticete whales. It’s a pretty amazing and woefully under appreciated clade.

It is interesting to consider the possibility
that since both elephant shrews and tenrecs have a proboscis that extends beyond the jaw line, it is possible that early land whales, Andrewsarchus and Sinonyx, might have had a similar long nose. Some of these taxa might have used such a snorkel to breathe while underwater, just below the surface — or — the long nose was the first soft tissue to disappear during the transition, because whales have no such nose.

References
Osborn HF 1924. Andrewsarchus, giant mesonychid of Mongolia. American Museum Noviattes 146: 1-5.
Rao AR 1971. 
New mammals from Murree (Kalakot Zone) of the Himalayan foot hills near Kalakot, Jammu and Kashmir state, India. Journal of the Geological Society of India. 12 (2): 124–34.
Thewissen JGM, Cooper LN, Clementz MT, Bajpai S and Tiwari BN 2007. Whales originated from aquatic artiodactyls in the Eocene epoch of India. Nature 450:1190-1195.

wiki/Leptictidium
wiki/Indohyus

 

 

Pigs and whales? No.

Sometimes when you add a common extant taxon
to the LRT, there can be more here than meets the eye. That was the case with Sus, the extant pig (Fig. 1).

Figure 1. Skeleton of Sus, the pig, a taxon commonly used as an outgroup for whales. In the LRT it is a sister to other even-toed ungulates, like Giraffa, not Odontoceti nor Mysticeti.

Figure 1. Skeleton of Sus, the pig, a taxon commonly used as an outgroup for whales. In the LRT it is a sister to other even-toed ungulates, like Giraffa, not Odontoceti nor Mysticeti.

Backstory
I was looking at a list of outgroup taxa for whales in Bianucci and Gingerich 2011 and comparing to to the outgroup taxa for whales in Geisler et al. 2011 and other workers:

  1. Gingerich 2011 listed: Elomeryx and illustrated a cow (Bos).
  2. Bianucci and Gingerich 2011 listed: Sinonyx, Mesonyx, Hippopotamus and Sus in that order toward Cetacea.
  3. Geisler et al. listed: Sus, Bos and Hippopotamidae in that order toward Cetacea.
  4. O’Leary and Gatesy 2008 listed: Eoconodon, Sinonyx and Hapalodectes [all considered Mesonychia by them]
  5. O’Leary et al. 2013 listed: Sus, Bos and Hippopotamus in that order toward Cetacea.

Note that
Sus, the pig; Bos, the cow; and Hippopotamus, the obvious, somehow makes it to three lists as outgroup taxa for whales in general. Believe it or not, these three earned their status after testing by traditional paleontologists. Despite having very few traits in common with whales, creating a great leap of phylogenetic faith to connect them all. If you’re bothered by that, I join you!

Figure 1. Ancodus nests as a more derived sister to Sus and it retains digit 1 on the manus and pes.

Figure 2. Ancodus nests as a more derived sister to Sus and it retains digit 1 on the manus and pes. Is this the same taxon as Elomeryx? If not, they appear to be quite close.

Sidenote:
Elomeryx (see above) is said to be widespread and common, but apparently has been confused online with Ancodus (Fig. 1). Are they the same? If different, how different? I’m confused and could use some clarity.

When we add Sus to the LRT
Sus nests much more reasonably between Tapirus and Ancodus (Fig. 2), two pig-like taxa with hooves. Notably extant Sus (Fig. 2) loses digit 1 on both the manus and pes while extinct Ancodus retains those digits indicating a convergent loss of these digits in the ancestors of pigs and in the ancestors of deer + giraffes.

By contrast O’Leary and Gatesy 2008 report, 
“Cetacea was the extant sister taxon of Hippopotamidae, followed successively by Ruminantia, Suina and Camelidae. The wholly extinct Mesonychia was more closely related to Cetacea than was any ‘‘artiodactylan. The osteological–dental data alone, however, did not support inclusion of cetaceans within crown ‘‘Artiodactyla.’ Recently discovered ankle bones from fossil whales reinforced the monophyly of Cetartiodactyla but provided no particular evidence of derived similarities between hippopotamids and fossil cetaceans that were not shared with other ‘‘artiodactylans’’. Can you sense their lack of resolution? Based on present evidence, O’Leary and Gatesy were suffering from taxon exclusion.

No such problem
with the LRT where whales are not related to pigs, cows or camels. Odontocete whales arise from tenrecs. Mysticete whales arise from desmostylians, as we learned earlier here.

References
Bianucci G and Gingerich PD 2011. Aegyptocetus tarfa, n. gen. et sp. (Mammalia, Cetacea), from the middle Eocene of Egypt: clinorhynchy, olfaction, and hearing in a protocetid whale. Journal of Vertebrate Paleontology. 31 (6): 1173–88.
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\
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