Pseudictops: what little we know is unique

There are not many mammals with crenulated/serrated teeth.
Pseudictops lophiodon (Matthews, Granger and Simpson 1929, Sulimski 1968, Late Paleocene, 57 mya; Fig. 1; AMNH 21727) is one such mammal. From the start Pseudictops was compared to anagalids like Leptictis (Fig. 2), a basal elephant shrew and ancestor to tenrecs, pakicetids and odontocete whales.

Figure 1. Pseudictops lophiodon compared to the slightly larger Siamotherium.

Figure 1. Pseudictops lophiodon compared to the slightly larger Siamotherium. The mandible is extremely robust and appears to nearly lack a coronoid process, distinct from most mammals.Note the crenulations and and/or robust serrations on the anterior teeth.

Figure 1a. Pseudictops anterior teeth.

Figure 1a. Pseudictops anterior teeth.

The dentary incisors
are deeply rooted in a deep dentary. Not sure why the two dentaries (Fig. 1) have distinct shapes. Perhaps they are not actually related to one another or perhaps some parts are missing from the smaller one and plasterered over.

Figure 2. Leptictis, an early Oligocene elephant shrew.

Figure 2. Leptictis, an early Oligocene elephant shrew.

Now that you’ve met Pseudictops, a quick look at Ictops
reveals a cranium with a double parasagittal crest, as in sister taxon, Leptictis

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) compared. Though both are considered elephant shrews, they nest in separate major mammal clades in the LRT.


References
Matthew WD, Granger W and Simpson GG 1929. Additiions to the fauna of the Gashato Formatin of Mongolia. American Museum Novitates 376:1–12.
Sulimski A 1968. Paleocene genus Pseudictops Matthew, Granger and Simpson 1929 (Mammalia) and its revision. www.palaeontologia.pan.pl/Archive/1968-19–1011-129–10-14.pdf

 

Siamotherium: neither helohyid, cetartiodactyl, hippo nor anthracothere

Taxon exclusion again.
I know you’re getting tired of this, but Siamotherium (Fig. 1) is an anagalid, a sister to Anagale (Fig. 1) in the large reptile tree (LRT, 1378 taxa), basal to the leptictid-tenrec-odontocete clade. These are taxa ignored in prior studies.

There is no guesswork here.
The LRT considers a wider gamut of mammal candidates and lets the taxa nest wherever they want to without restriction. Sometimes taxa nest in places that paleontologists had not yet imagined.

For those wondering what a helohyid is…
… and count me among that curious group, Helohyus (sorry, no Wikipedia entry), is the namesake for this primitive pig-like artiodactyl clade. More on this taxon in later posts.

The resemblance of Siamotherium to Anagale is strong.
(Fig. 1) One wonders why this similarity went unnoticed before.

Figure 1. Siamotherium to scale with Anagale. Both nest basal to the tenrec-odontocete clade.

Figure 1. Siamotherium to scale with Anagale. Both nest basal to the tenrec-odontocete clade. The mandible of Anagale fits well on the maxilla of Siamotherium when enlarged.

Anagale gobiensis (Simpson 1931; early Oligocene; 30cm in length; AMNH 26079) was originally considered an insectivore, close to the tree shrew Tupaia and tending to link to lemurs like Notharctus. Thirty years later McKenna 1963 argued against tupaioid affinities, but could not provide a more suitable nesting.

Here rabbit-sized Anagale nests with Siamotherium and the IVPP V2385 specimen of Hapalodectes. The closest living relative to these taxa is Rhynchcyon, the golden rumped elephant shrew (Fig. 3).

The teeth of Anagale were typically worn and the claws were shovel-shaped, suggesting a diet of subterranean worms and beetles. The peculiar combination of large fissured claws of the manus and distally spatulate unguals of the pes is uncommon in mammals. The ectotympanic bulla protecting the middle ear bones is quite large, and so is the eardrum that it framed.

Siamotherium pondaungensis (Suteethorn et al. 1988; Soe et al. 2017; Eocene) was originally considered a small anthracothere close to Hippopotamus, but here nests with Anagale. Siamotherium is larger, has a straight jugal and only three molars.

Sisters of these taxa
had a Mesozoic genesis. Distinct from other clades is the posterior rise of the post-parietal creating a nuchal crest. This crest is still present in the giant elephant shrew, Andrewsarchus, and odontocete whales (Fig. 2). Also of interest, the digitigrade hands and feet with fewer digits converge on those of basal artiodactyls (Fig. 3). No wonder these get confused and ignored in traditional paleontology.

Figure 2. Odontoceti (toothed whale) origin and evolution. Here Anagale, Andrewsarchus, Sinonyx, Hemicentetes, Tenrec Indohyus and Leptictidium precede Pakicetus. Maiacetus and Orcinus are aquatic odontocetes.

Figure 2. Odontoceti (toothed whale) origin and evolution. Here Anagale, Andrewsarchus, Sinonyx, Hemicentetes, Tenrec Indohyus and Leptictidium precede Pakicetus. Maiacetus and Orcinus are aquatic odontocetes.

Like basal artiodactyls,
elephant shrews, like Rhynchocyon (Fig. 3), also have digitrade hands and feet. This has led to all sorts of confusion with regard to whales and their putative, but invalidated ancestors among the artiodactyls.

Figure 4. Skeleton of the elephant shrew, Rhynchocyon. Note the digitigrade manus and pes, like those of basal artiodactyls.

Figure 3. Skeleton of the elephant shrew, Rhynchocyon. Note the digitigrade manus and pes, like those of basal artiodactyls.

References
Simpson GG 1931. A new insectivore from the Oligocene, Ulan Gochu horizon, of Mongolia. American Museum Novitates 505:1-22.
Soe AN t al. (6 co-authors) 2017. New remains of Siamotherium pondaungensis (Cetartiodactyla, Hippopotamoidea) from the Eocene of Pondaung, Myanmar: Paleoecologic and phylogenetic implications. Journal of Vertebrate Paleontology 37(1):e1270290https://doi.org/10.1080/02724634.2017.1270290
Suteethorn V, Buffetaut E Helmcke-Ingava Rt JaegerJ-J and Jongkanjanasoontorn Y 1988. Oldest known Tertiary mammals from South-East Asia: Middle Eocene primate and anthracotheres from Thailand. Neues Jahrbuch f€ur Geologie und Pal€aontologie, Monatshefte 9:563–570.

wiki/Siamotherium (no Wikipedia entry yet)

SVP 2018: Where to nest and what is the Anagalidae?

López-Torres and Fostowicz-Frelik seek to understand
the phylogenetic position of the Anagalidae, “an enigmatic and poorly studied group of primitive members of Euarchontoglires known from the Palaeogene of China.” 

On the other hand
this clade is well understood in the large reptile tree (LRT, 1311 taxa, subset Fig. 3). The genus Anagale (Fig. 1) is basal to Andrewsarchus, tenrecs and odontocetes, taxa notably missing from traditional lists (see below). Taxon inclusion is the key to understanding this and all other tetrapod clades.

First of all, some traditional clade members:

  1. Traditional Euarchontoglires = rodents, lagomorphs (rabbits) treeshrews, colugos and primates.
  2. Traditional Anagalidae = elephant shrews, rodents and lagomorphs.
  3. Traditional Anagaloidea = also includes Zalambdalestes (a Solenodon (clade = Glires) sister in the LRT).

None of these groupings
are recovered in the LRT (which is genus to specimen-based).

Figure 1. Anagale nests at the base of the tenrec - odontocete clade, not with rabbits, in the LRT.

Figure 1. Anagale nests at the base of the tenrec – odontocete clade, not with rabbits, in the LRT.

All prior clade memberships suffer from taxon exclusion.
Anagale (Figs, 1, 2) itself nests at the base of the tenrec – odontocete clade (Fig. 2) a hypothesis first recovered in the LRT.

Where Anagale and kin nest in the LRT:

  1. Anagalidae = Anagale (Fig. 2), some but not all elephant shrews, tenrecs, pakicetids, toothed whales and their kin. In other words, this is the tenrec-odontocete clade.
Figure 1. Odontoceti (toothed whale) origin and evolution. Here Anagale, Andrewsarchus, Sinonyx, Hemicentetes, Tenrec Indohyus and Leptictidium precede Pakicetus. Maiacetus and Orcinus are aquatic odontocetes.

Figure 2. Odontoceti (toothed whale) origin and evolution. Here Anagale, Andrewsarchus, Sinonyx, Hemicentetes, Tenrec Indohyus and Leptictidium precede Pakicetus. Maiacetus and Orcinus are aquatic odontocetes.

López-Torres and Fostowicz-Frelik 2018 report:
“Anagalids were originally suggested to be closely related to modern treeshrews, lagomorphs, some primitive eutherian groups such as zalambdalestids and pseudictopids, and Macroscelidae (within the broader concept of ‘Anagalida’), but that idea was later rejected, especially with growing evidence of molecular relationships among major mammalian clades and the generally accepted monophyly of Glires. Our study presents a new, more comprehensive phylogenetic analysis based on 190 dental characters.”

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

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

Dental characters only???
Yikes. The authors continue: “The resulting strict consensus tree (based on 76 equally-parsimonious trees) disagrees with the previous conception of anagalid monophyly. Instead, anagalids are heavily paraphyletic, appearing as several offshoots at the base of Glires, which suggests that anagalids could be considered stem Glires.” 

The LRT is nearly fully resolved and anagalids are not stem Glires.
They are the sisters to Glires. Add these relevant taxa (Fig. 2) and let us know if your tree recovers the same tree topology.

These authors need to expand their taxon and character lists.
Contra tradition, Anagale and kin have little to do with rodents or rabbits. Add taxa. Let the taxa nest where they want to. Don’t limit the taxon list. Soon this clade will be well understood, no longer an enigma.

References
López-Torres S and Fostowicz-Frelik L 2018. The phylogenetic position of the Anagalidae within Euarchontoglires and its implication for the evolution of Glires and Euarchonta. SVP abstract.

wiki/Euarchontoglires
wiki/Anagaloidea

Elephant shrews are diphyletic

I never thought it would get this far
and so deep when I started ReptileEvolution.com. I keep thinking I”m coming to the end. But there’s more to be found in the metaphorical and literal leaf litter here than I ever imagined five or so years ago when this all began…

Earlier we nested the extant short-eared elephant shrew, Macroscelides (Fig. 1), with the tree shrew, Tupaia and the golden mole, Chrysochloris. Today we nest the gold-rumped elephant shrew, Rhynchocyon (Fig. 2) with the mesonychid-like tenrec, Sinonyx.

How can that be?
They’re both elephant shrews!!

Once you see them together,
(Figs. 1, 2) you’ll see the many differences that separate them. And that’s the way they also test in the large reptile tree. These two putative elephant shrews are not closely related because several non-elephant shrews phylogenetically separate them. And that’s why these two are diphyletic. Macroscelides arises from within Glires, the rodent and rabbit clade. Rhynchocyon arises from within Tenreccetacea, or tenrecs + whales.

Not sure how the others will line up. We’ll save those for later…

Figure 3. Macroscelides proboscideus skull. Note the several basic differences between the this skull and that of Ryhncocyon and you'll be as surprised as I was that these were not noticed in prior studies. If so, please bring them to my attention.

Figure 1. Macroscelides proboscideus skull. Note the several basic differences between the this skull and that of Ryhncocyon and you’ll be as surprised as I was that these were not noticed in prior studies. If so, please bring them to my attention. Imarge from Digimorph.org and used with permission.

The canines on Rhynchocyon
(Fig. 2) were the first clue that not all elephant shrews were sisters. Few skull traits unite Rhynchocyon and Macroscelides, but both do have an elongate flexible nose and long slender legs poking out from fur ball bodies.

Perhaps you’ll be as surprised as I was
that these differences were not noticed in prior studies. If so, please bring them to my attention. A Google search reveals relatively little literature on this/these clade(s) and none (so far) pertinent to the present discussion.

Figure 2. Rhynchocyon skull with select bones colored. Note the large canines, angled rostrum and just the genesis of the high cranial crest seen in the much larger Sinonyx.

Figure 2. Rhynchocyon skull with select bones colored. Note the large canines, angled rostrum and just the genesis of the high cranial crest seen in the much larger Sinonyx.

Unfortunately
there are no skeletons of Rhynchocyon on the net or in published literature that comes up in a Google search.

Figure 4. Skeleton of Macroscelides proboscides from Digimorph.org and used with permission. Note the high sacral spines and elongate metatarsals here.

Figure 3. Skeleton of Macroscelides proboscides from Digimorph.org and used with permission. Note the high sacral spines and elongate metatarsals here.

In life
(Fig. 4) you can see how earlier workers could have allied these two taxa. And you can see how traits they have in common could be plesiomorphic and/or could be homoplastic (a result of convergence).

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 4. Rhynchocyon (above) and Macroscelides (below) compared. Though both are considered elephant shrews, they nest in separate major mammal clades in the LRT. Note how the lips cover the fangs in Rhynchocyon.

On a lighter note…
This little movie character has not gone unnoticed in this discussion. This is Scrat, the sabertooth ?squirrel from the Ice Age movie franchise. Perhaps a close cousin to Rhynchocyon ~ after the nose job and lip tuck.

Figure 7. Scrat, the sabertooth squirrel, from the Ice Age movie franchise, has fangs, a long rostrum and short cranium like Rhynchocyon -- by convergence, no doubt.

Figure 5. Scrat, the sabertooth squirrel, from the Ice Age movie franchise, has fangs, a long rostrum and short cranium are like Rhynchocyon — by convergence, no doubt. Different nose.

Digimorph.org