Rostriamynodon: ancestor to elephants + manatees, not a perissodactyl

Holbrook 1999
added Rostriamynodon (AMNH 107635, Fig. 1) to his study on perissodactyls (Fig. 3) following work by Wall and Manning 1986 who thought Rostriamynodon was a basal rhino close to Amynodon, which nests basal to horses in the large reptile tree (LRT, 1763 taxa; subset Fig. 2).

Figure 1. Rostriamynodon skull in three views, colors added.

Figure 1. Rostriamynodon skull in three views, colors added.

So, a bit of a taxonomic mess here.
Taxon exclusion is once again the problem. In the LRT (subset Fig. 2) Rostriamynodon nests between the traditional ‘notoungulate’ Notostylops and the elephant (Fig. 5) + manatee (Fig. 6) clade.

Figure 2. Subset of the LRT focusing on ungulates sans artiodactyls.

Figure 2. Subset of the LRT focusing on ungulates sans artiodactyls.

Figure 3. Cladogram from Holbrook 1999 with LRT colors added. Taxon exclusion mars this cladogram.

Figure 3. Cladogram from Holbrook 1999 with LRT colors added. Taxon exclusion mars this cladogram.

Isectolophus was also added to the LRT,
(subset Fig. 2) and it nested uncontroversially basal to Protapirus in the tapir clade in both competing studies.

Taxa in this blogpost:
Amynodon advenus (Marsh 1877; 1m in length; Oligocene-Eocene, 40-23 mya) was originally considered an aquatic rhino. Here it nests with Mesohippus. The long neck and other traits are more horse-like than rhino-like. Manual digit 5 was retained. The skull was deeper as in basal forms like Hyracotherium.

Isectolophus scotti (Scott and Osborn 1887; Early Oligocene to Early Miocene) nests basal to Protapirus in the large reptile tree.

Figure 1. Notostylops skull colorized in three views.

Figure 4. Notostylops skull colorized in three views.

Notostylops murinis (Ameghino 1897, Riggs and Patterson 1935; 75cm in esitmated length; Eocene; FMNH-P13319; Fig. 4) is widely considered a ‘notoungulate’ a clade that has been split into several parts in the large reptile tree. Here it nests with the above specimen of Ectocion in the clade of elephants, rock hyraxes and sea cows. The jaws narrowed anteriorly. The anterior incisors were enlarged, like those of rodents. The mandible was more robust. No canines were present. The premolars were molarized

Rostriamynodon grangeri (Wall and Manning 1986; AMNH 107635; Eocene) was originally considered amynodontid rhino, but here nests between Notostylops and the elephant + siren clade. Note the splitting of the nasals and the anterior extension of the frontals along with the wide molars and the molarized premolars.

 

Figure 2. Skull of Elephas maximus with color overlays. Most of the bones are fused to one another, so this tracing is provisional, pending confirmation and/or better data. Compare to the skull of Procavis (Fig. 3).

Figure 5. Skull of Elephas maximus with color overlays. Note the separation of the nasals.

Figure 2. Dusisiren, a manatee sister has a robust tail and presumably, flukes.

Figure 6. Dusisiren, a manatee sister has a robust tail and presumably, flukes. Note the separation of the nasals, first seen in Rostriamynodon.

References
Hollbrook LT 1999. The phylogeny and classification of Tapiromorph perissodactyls (Mammalia). Cladistics 15:331–350.
Holbrook LT, Lucas SG and Emry RJ 2004. Skulls of the Eocene perissodactyls (Mammalia) Homolgalax and Isectolophus. Journal of Vertebrate Paleontology 24(4):951–956.
Scott WB and Osborn HF 1887. Preliminary Report on the Vertebrate Fossils of the Uinta Formation, Collected by the Princeton Expedition of 1886. Proceedings of the American Philosophical Society 24(126):255-264.
Wall WP and Manning E 1986. Rostriamynodon grangeri n. gen., n. sp. of amynodontid (Perissodactyla, Rhinocerotoidea) with comments on the phylogenetic history of Eocene Amynodontidae. Journal of Paleontology 60(4):911-919.

wiki/Notostylops
wiki/Rostriamynodon not yet posted
wiki/Protapirus
wiki/Isectolophus not yet posted

 

Eritherium: ‘most primitive and smallest known proboscidian ancestor’

Gheerbrant 2009
announced the discovery of Eritherium azzouzorum (late Paleocene; Morocco; Fig. 1) as the incomplete remains of the ‘most primitive and smallest known proboscidian’ and as the ‘oldest modern ungulate related to the elephant order.’

Figure 1. Taxa in the lineage of Notostylops in the LRT with Eritherium added appropriately with ghosted image of Notostylops applied and narrowed in dorsal and ventral views.

Figure 1. Taxa in the lineage of Notostylops in the LRT with Eritherium added appropriately with ghosted image of Notostylops applied and narrowed in dorsal and ventral views.

2014 brought us an older, but overlooked, proboscidian ancestor.
Radinskya yupingae (McKenna et al. 1989, Holbrook 2014; IVPP V-5255; Middle Paleocene; China; Fig. 1) was originally considered a perissodactyl-like herbivore, but never with confidence. Here Radinskya nests between Ectocion and Procavia, at the base of the elephant clade. Note the tiny procumbent second incisor. That’s the germ of what will become a giant tusk in elephants, mammoths and mastodons… and hyraxes (see Fig. 1). As in Procavia the tabulars contact one another medially, posterior to the central postparietal. The premolar is almost molar-like in appearance.

Gheerbrant’s cladograms
(Fig. 2) suffer from taxon exclusion and inappropriate taxon inclusion, as noted therein. The large reptile tree (LRT, 1346 taxa) nests elephants apart from each of the ungulate orders, which nest apart from each other. Artiodactyla (Owen 1848) is the basal clade, so all are artiodactyls in an expanded cladistic sense. Ungulata was coined earlier (Linneaus 1766), so there is that to consider. Hippos nest with Mesonyx outside this clade, so Mesonychidae is basal to all these clades. Phenacodontidae (Phenacodus is the last common ancestor in the LRT) is more basal still.

Figure 2. Cladograms from Gheerbrant 2009 nesting Eritherium with sirenians and proboscideans.

Figure 2. Cladograms from Gheerbrant 2009 nesting Eritherium with sirenians and proboscideans.

There is an old tradition
embraced by Gheerbrant and not confirmed by the LRT that nests embrithopods (like Arsinoitherium), anthracobunids and desmostylians (both mesonychids) with hyraxes, manatees and elephants (Fig. 2), but see the large reptile tree (LRT, 1346 taxa, subset Fig. 3). This tree topology continues unchanged even though more taxa are added every week. This is a measure of its strength.

FIgure 3. Subset of the LRT focusing on the hyrax, elephant and manatee clade.

FIgure 3. Subset of the LRT focusing on the hyrax, elephant and manatee clade. Other traditionally related taxa nest elsewhere after testing with a larger taxon list in the LRT.

Unfortunately,
there is not enough material to add Eritherium to the LRT, but placing Notostylops (not mentioned by Gheerbrant) over what little remains of Eritherium is a pretty good match (Fig. 1), except for the narrowness of the skull and much smaller teeth, as also seen in Radinskya, a taxon that is a little older and just as small as Eritherium.

Traditionally
Notostylops has been considered a notoungulate, which is why it is almost never included in elephant studies, as we learned earlier here.

References
Gheerbrant E 2009. Paleocene emergence of elephant relatives and the rapid radiation of African ungulates. DOI: 10.1073/pnas.0900251106 http://www.pnas.org/content/106/26/10717. PDF
Holbrook LT 2014. On the Skull of Radinskya (Mammalia) and Its Phylogenetic Position. Journal of Vertebrate Paleontology34(5):1203–1215.
McKenna MC, Chow M, Ting S and Luo Z 1989. Radinskya yupingae, a perissodactyl-like mammal from the late Paleocene of China. In Prothero DR, Schoch RM The evolution of perissodactyls. Oxford monographs on geology and geophysics. 15. New York: Oxford University Press. pp. 24–36.

wiki/Radinskya
wiki/Eritherium

NatGeo PR
Science Daily PR

 

Gomphotherium enters the LRT

Gomphotherium
(Burmeister 1837, Figs. 1-3) is an extinct elephant with a long tooth-tipped chin known worldwide from the Early Miocene to the Early Pleistocene.

No surprise here…
Gomphotherium nests with Paleomastodon and Elephas in the large reptile tree (LRT, 1345 taxa).

Figure 1. Long-legged Gomphotherium.

Figure 1. Long-legged Gomphotherium. The skull is unknown, made of plaster, so is blurred here.

Some gomphotheres
have long, elephantine legs (Fig. 1).

Figure 2. Short-legged Gomphotherium from the Norman, OK, USA museum.

Figure 2. Short-legged Gomphotherium from the Norman, OK, USA museum.

Others
have rather short legs (Fig. 2). This is a derived taxon, by the way (Fig. 3).

Figure 1. Gomphotherium jaws.

Figure 3. Gomphotherium jaws. OMNH mount is the Norman, OK short-legged specimen.

But they all have a really long chin.
Which they get from their father’s side of the family.  :  )

References
Gheerbrant E 2009. “Paleocene emergence of elephant relatives and the rapid radiation of African ungulates”Proceedings of the National Academy of Sciences of the United States of America. 106 (26): 10717–10721.

Notostylops: another former notoungulate

This used to be big news,
when a taxon no longer nested in a traditional clade and moved to another. But with the breakup of the Notoungulata, this has become commonplace for former members of this clade and I expect the trend to continue.

Figure 1. Notostylops skull colorized in three views.

Figure 1. Notostylops skull colorized in three views.

Now
in the large reptile tree (LRT) Notostylops murinis  (Ameghino 1897, Riggs and Patterson 1935; 75cm in esitmated length; Eocene; FMNH-P13319) nests with the Ectocion specimen that nests with elephants, not the one that nests with carnivores (Fig. 2).

FIgure 3. Subset of the LRT focusing on the hyrax, elephant and manatee clade.

FIgure 3. Subset of the LRT focusing on the hyrax, elephant and manatee clade.

In Notostylops, the anterior incisors were enlarged as in other elephant and sea cow ancestors, but the anterior jaws narrowed, so the incisors became close together, like those of rodents. The mandible itself was more robust. No canines were present. The premolars were molarized.

Of course all this is
based in the literature, not firsthand observation of the pertinent specimens. I encourage others to test these taxa to confirm these hypothetical interrelationships.

I became aware of this taxon
after reading Billet (2010), who wrote: “Intriguing similarities are also detected in the anterior dentition of Pyrotherium and the Casamayoran notoungulate Notostylops. These resemblances suggest a unique relationship between Pyrotheria and Notoungulata, specifically between Pyrotheria and Notostylops.” The large reptile tree does not confirm that relationship. Rather the former (Fig. 3) is a derived marsupial while the latter is a derived placental.

Figure 3. Pyrotherium is a marsupial, not a relative to Notostylops, contra Billet 2010.

Figure 3. Pyrotherium is a marsupial, not a relative to Notostylops, contra Billet 2010.

References
Ameghino F 1897. Mamiferos Cretaceos de la Argentina – Boletin Instituto Geografico Argentino 18:406-521.
Billet G. 2010. New Observations on the Skull of Pyrotherium (Pyrotheria, Mammalia) and New Phylogenetic Hypotheses on South American Ungulates. Journal of Mammal Evolution. 17:21-59.
Riggs ES and Patterson B 1935.
 Description of some notoungulates from the Casamayor (“Notostylops) beds of Patagonia. Proceedings of the American Philosophical Socity 75(2):163-215.

wiki/Notostylops

Two Ectocion specimens: neither is a phenacodontid

After reexamination
of the E. cedrus drawing, I determined that both taxa nest together with Procavia, the hyrax, at the base of the elephant/manatee clade.

Traditional paleontology considers
Ectocion osbornianus [osbornianum] (Cope 1882a, Granger 1915, Thewissen 1990; Fig. 1; Paleocene 55 mya)  a member of the Condylarthra or Phenacodontidae, alongside Phenacodus. Cope 1882a originally named the type, Oligotomus osbornianus from maxillary and dentary fragments with lophodont teeth. The specimen was renamed by Cope 1882e when he realized he had already given a fossil horse than generic name. The genus Ectocion is known from more than 500 jaws and hundreds of loose teeth. Skulls, evidently, are rare.

Figure 1. Ectocion nests with the rock hyrax, Procavia, giving rise to elephants + manatees.

Figure 1. Ectocion nests with the rock hyrax, Procavia, giving rise to elephants + manatees.

While searching online I found
two distinct skulls referred to Ectocion (Fig. 1). Neither is the holotype which was described from teeth and fragments. The Ectocion on the left is from Thewissen 1990. The one on the right is from Wikipedia. See the difference?

Neither nests with Phenacodus
or any other tested phenacodontid in the LRT. Instead the LRT nests Ectocion with Procavia, the rock hyrax, giving rise to Elephas and Dusisiren all with incisors transforming into proto-tusks and completely lacking a large canine or a dipping transverse premaxilla.

When shifted to phenacodontids
these taxa add 11 steps.

References
Cope ED 1882a. Contributions to the history of the Vertebrata of the lower Eocene of Wyoming and New Mexico, made during 1881. Proceedings of the American Philosophical Society: 139-197.
Cope ED 1882e. Note on Eocene Mammalia. American Naturalist 16:522.
Granger W 1915. A revision of the lower Wasatch and Wind River faunas, Part III: Order Condylarthra, families Phenacodontidae and Meniscotheriidae. Bulletin of the American Museum of Natural History 34:329-361.
Mac Intyre GT 1962. Simpsonictis, a new genus of viverravine miacid (Mammalia, Carnivora). American Museum Novitates 2118: 1-4.
Mac Intyre GT 1966. The Miacidae (Mammalia, Carnivora) Part 1. The systematics of Ictidopappus and Protictis. Bulletin of the American Museum of Natural History 131(2):115-210.
Matthew WD 1937. Paleocene faunas of the San Juan basin, New Mexico. Transactions of the American Philosophical Society, new series 30: 1-510.
Simpson GG 1935. New Paleocene mammals from the Fort Union of Montana. Proceedings of the U. S. National Musem 83: 221-244.
Thewissen JGM 1990. Evolution of Paleocene and Eocene phenacodontidae (Mammalia, Condylarthra). University of Michigan Papers on Paleontology 29:1-107.

wiki/Ectocion