Two pre-hippo, pre-desmostylian, pre-mysticete taxa join the LRT

Figure 1. Agriochoerus is a late-surviving oreodont with a diastema and a sister to Merycoidodon.

Figure 1. Agriochoerus is a late-surviving oreodont with a diastema. It is a sister to Merycoidodon. A postorbital bar appears in the other tested oreodont, Merycoidodon, but is reconstructed here based on what appears to be broken bone.

An oreodont with a diastema
Agriochoerus antiquus (Leidy 1850; Late Eocene to Oligocene; 38–16mya) was similar to Merycoidodon, but had a diastema with the loss of the anterior premolars and the addition of one molar. The dentary canines were larger. Oreodonts nest at the base of the hippo-mysticete clade in the large reptile tree (LRT, 1381 taxa) and between the Phenacodus clade and the Homalodotherium + artiodactyl clades.

Figure 1. Merycopotamus, Hippopotamus, and Paleoparadoxia compared to scale.

Figure 2. Merycopotamus, Hippopotamus, and the desmostylian, Paleoparadoxia, compared to scale. The resemblance between taxa here are coming into clearer focus in the LRT, but overlooked elsewhere.

Not an anthracothere. Not even an artiodactyl.
Merycopotamus dissimilis (Falconer & Cautley 1847; Middle Miocene to Late Pliocene; Fig. 2) was considered an Asian anthracothere (pig-like artiodactyl), but here nests between Ocepeia and Hippopotamus (Fig. 2) apart from the artiodactyls, closer to oreodonts and mesonychids. Note the migration of the orbit posteriorly, the re-appearance of the postfrontal and prefrontal, the massive dentary with massive retroarticular process and the larger dentary canine, as in hippos.

Figure 3. The oreodont-mesonychid-hippo-desmoystlian-mysticete clade subset of the LRT

Figure 3. The oreodont-mesonychid-hippo-desmoystlian-mysticete clade subset of the LRT. These taxa were not nested together  in smaller studies that omitted various taxa.

Few mammals
enlarge the dentary to a size that competes with the skull. Hippos do that. Few mammals enlarge the retro process of the dentary to such a large size. Hippos do that. The retro process anchors the jaw-closing masseter muscle complex.

Figure 4. Merycopotamus skull and mandible with colors identifying the reappearances of the prefrontal and postfrontal.

Figure 4. Merycopotamus skull and mandible with colors identifying the reappearances of the prefrontal and postfrontal.

I looked at none of these taxa firsthand.
Rather, the data came from photos and these taxa were added to the LRT. For doing this and continuing to do this for the last seven years I have incurred the disdain of paleontologists and would-be paleontologists world-wide. Judge for yourself whether or not the LRT has provided scientific value or pseudoscientific propaganda, as others assert without testing.

References
Falconer H and Cautley PT 1847. Fauna antiqua sivalensis, Atlas. Smith, Elder and Co., London, 136 pp.
Leidy J 1850. [Abstract of remarks made before a meeting of the Academy of Natural Sciences of Philadelphia, December 17th, 1850]. Proceedings of the Academy of Natural Sciences of Philadelphia 5(1):121-122.
Thorpe MR 1921. Two new forms of Agriochoerus. American Journal of Science (8): 111–126.

wiki/Agriochoerus

 

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Enigmatic oreodont, Merycoidodon, joins the LRT

Something of an enigma.
Wikipedia reports, “Merycoidodon is an extinct genus of terrestrial herbivore.” That’s rather vague for a common sheep-sized fossil from the USA.

Figure 1. Merycoidodon reconstruction traced by an unknown artist from an AMNH mount photo.

Figure 1. Merycoidodon reconstruction traced by an unknown artist from an AMNH mount photo.

In Late Eocene
to Late Oligocene (38–16mya) deposits, Merycoidodon (Leidy 1848) lived in large herds, principally in South Dakota. but also found from Alberta to Florida, typically preferring well-watered areas. Leidy considered it a member of the ruminantoid Pachydermata‘.

Figure 2. Merycoidodon skull. Colors added.

Figure 2. Merycoidodon skull. Colors added.

Merycoidodontoidea
Wikipedia reports, “Merycoidodontoidea, sometimes called “oreodonts,” or “ruminating hogs”, is an extinct superfamily of prehistoric cud-chewing artiodactyls with short faces and fang-like canine teeth. As their name implies, some of the better known forms were generally hog-like, and the group has traditionally been placed within the Suina (pigs, peccaries and their ancestors), though some recent work suggests they may have been more closely related to camels.” Evidently the phylogenetic nesting of Merycoidodon is not clear to the Wikipedia writers. That may be due to its generalize appearance.

Spaulding et al. 2009
nested Merycoidodon ancestral to Camelus + Lama, derived from Hyracotherium and Cainotherium, among tested taxa. The Spaulding et al. cladogram separated hippos from mesonychids, nesting hippos with Diacodexis (largely incomplete) and Indohyus, an omitted tenrec in the LRT.

Figure 3. the Merycoidodon cladogram includes hippos, whales and a number of extinct taxa.

Figure 3. the Merycoidodon cladogram includes hippos, whales and a number of extinct taxa.

In the large reptile tree
(LRT, 1376 taxa) Merycoidodon nests firmly as the proximal outgroup at the base of the Mesonyx to mysticete (baleen whale) clade (subset Fig. 3). Merycoidodon also nests between the Phenacodus clade and the Homalodotherium clade + artiodactyl clades.

It is worth noting again
that hippos do not nest with artiodactyls in the LRT, breaking a traditional paradigm.

Figure 1. Mesonyx, the first known mesonychid was a sister to Hippopotamus in the large reptile tree. So maybe it was a plant eater.

Figure 5 Mesonyx nests between oredonts, like Merycoidodon, and hippos, like Hippopotamus.

I’ve been curious about oreodonts for decades.
What were they? Happy to finally test it and nest it where it belongs, basal to hippos, and transitional to modern hoofed ruminants. The generalized appearance of Merycoidodon is appropriate to its basal and transitional nesting. Based on its nesting basal to Ocepeia (middle Paleocene), the genesis of Merycoidodon must extend to the early Paleocene, if not before.

Figure 3. Hippopotamus. This stout, wide-faced, fanged mammal does not nest with deer.

Figure 6. Hippopotamus. This stout, wide-faced, fanged mammal does not nest with deer,but with Mesonyx.

References
Leidy 1848. On a new fossil genus and species of ruminantoid Pachydermata: Merycoidodon culbertsonii. Proceedings of the Academy of Natural Sciences of Philedelphia Vol IV, 47-51.

Merycoidodontidae (Thorpe 1923)
Mesonychidae (Cope 1880)

wiki/Merycoidodontoidea
wiki/Merycoidodon

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

SVP 2018: New Mammalodon relative with marine worm bores

Shipps, Peredo and Pyenson 2018 report
on a Late Oligocene mammalodontid, the first from the Northern Hemisphere. “The skull and teeth of this specimen bear boreholes from bone-eating Osedax worms, providing valuable information on the taphonomy of the specimen. Critically, this specimen preserves intact ear bones and several teeth.”

Osedax is marine worm.
According to Wikipedia, “The worms bore into the bones of whale carcasses to reach enclosed lipids, on which they rely for sustenance.”

Figue 1. Mammalodon nests within the clade Anthracobune basal to desmostylians and mysticetes.

Figue 1. Mammalodon nests within the clade Anthracobune basal to desmostylians and mysticetes.

Mammalodon (Fig. 1) is indeed in the lineage of mysticete whales, but several nodes distant (Fig. 2) in the large reptile tree. It is related to Janjucetus and Anthracobune, basal to desmostylians, not far from hippos. Desmostylians are also found along the Pacific rim, so this appearance of an ancestor in Washington state is expected. All are mesonychids, not ungulates.

Figure 2. Subset of the LRT focusing on mysticetes, including Sitsqwayk, and their predecessors.

Figure 2. Subset of the LRT focusing on mysticetes, including Sitsqwayk, and their predecessors.

References
Shipps BK, Peredo CM and Pyenson ND 2018. An unexpected Northerner with burrowed bones: a new mammalodontid (Mysticeti) from the Pacific Northwest with Osedax bores provides insight into Oligocene marine taphonomy and mysticete evolution. SVP abstracts.

wiki/Osedax
wiki/Janjucetus
wiki/Mammalodon
wiki/Anthracobune

 

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

Harpagolestes uintensis is a mesonychid. Harpagolestes macrocephalus is not.

Welcome to the wonderful world of convergence!
Harpagolestes uintensis (Fig. 2) and H. macrocephalus (Fig. 1) look similar enough to be considered similar, but they are not congeneric in the LRT. One of them needs a new generic name.

Of the several heresies
recovered by the large reptile tree (LRT, 1120 taxa) the latest is the separation of some former mesonychids (Fig. 1, Andrewsarchus, Sinonyx, Hapalodectes) from current and traditional mesonychids (Fig. 2, Mesonyx and Harpagolestes uintensis). The clade of former mesonychids now nests as giant tenrecs. This clade produced odontocete whales and transitional taxa. The latter group of true mesonychids gave rise to mysticete (baleen) whales and the following transitional taxa: hippos, anthrobunids and desmostylians.

Figure 1. Harpagolestes macrocephalus compared to sisters Sinonyx and Andrewsarchus to scale.

Figure 1. Harpagolestes macrocephalus compared to sisters Sinonyx and Andrewsarchus to scale.

Today the addition of Harpagolestes macrocephalus
(Fig. 1) to the LRT nests it not congenerically with Harpagolestes uintensis (Fig. 2), but between Andrewsarchus and Sinonyx. So the two are not congeneric.

Figure 1. Andrewsarchus, Sinonyx, Mesonyx and Harpagolestes to scale for direct comparison of these two tenrecs with these two mesonychids.

Figure 1. Andrewsarchus, Sinonyx, Mesonyx and Harpagolestes to scale for direct comparison of these two tenrecs with these two mesonychids.

We’ve seen convergence many times
in the LRT. This is just one more example of convergence that has been traditionally overlooked.

Deleting nine tenrecs
on either side of Sinonyx + Andrewsarchus + H. macrocephalus changes nothing in the LRT. The above taxa still nest with odontocetes far from mesonychids through mysticetes, though some loss of resolution occurs in the mammal subset of the LRT.

Deleting hippos and anthracobunids
from the mesonychid clade changes nothing.

References
O’Leary MA and Rose KD 1995. Postcranial skeleton of the early Eocene mesonychid Pachyaena (Mammalia: Mesonychia). Journal of Vertebrate Paleontology 15(2):401-430.

Related mammals that nest at the bases of several hoofed clades

The value
of the large reptile tree (LRT, 1013 taxa) and the reconstructions gathered together at ReptileEvolution.com lie in their ability to put faces on names (Figs, 1) sometimes to scale (Fig. 2) to help one recognize patterns that may have gone unrecognized while just looking at names and scores.

These are the mammals that nest with one another
as sisters after deletion of more derived taxa in each of their several clades (listed at right, Fig. 1). Thus they, more or less, represent the basal radiation of hoofed mammals prior to each clade radiation. And to no one’s surprise, they look like each other, despite wide variations in size.

Frankly,
I’m reexamining the traits of these taxa because the LRT had trouble resolving them. There were mistakes in there. Now, after some score corrections, the resolution is complete again, but some Bootstrap scores have risen to just above 50. Not great, but better than below 50. Remember, I don’t have access to these specimens and sometimes work from published drawings.

Figure 1. Skulls of taxa nesting at the bases of several mammal clades starting with mesonychids.

Figure 1. Skulls of taxa nesting at the bases of several mammal clades starting with mesonychids. The differences are harder to see than in derived taxa in each clade (column at right). See figure 2 for skeletons to scale.

Some of these basal taxa
gave rise to baleen whales. Others were ancestral to giraffes, elephants, horses and everything in between. None of these taxa are nearly so famous or interesting to the general public, but it is from these generalized (plesiomorphic) taxa that the few and subtle evolutionary changes that are key to each clade first make an appearance.

Figure 2. Skeletons of taxa basal to various clades derived from basal mesonychids, all to scale.

Figure 2. Skeletons of taxa basal to various clades derived from basal mesonychids, all to scale. Note the presence of phylogenetic miniaturization at the base of the Artiodactyla. Consider this scenario: mesonychids radiated widely, including to create larger and smaller taxa. The larger homalotheres did not radiate greatly, as far as we know. On the other hand, the smaller taxa radiated to become a long list of extinct and exact hoofed taxa. And, of course, the mesonychid clade radiated to include today’s hippos and baleen whales. 

Sometimes a ‘show and tell’ drives a point home
better than just a ‘tell’. Even so, these are not the precise individuals in the direct lineage of known derived taxa, but the close relatives of those perhaps eternally unknown and hypothetical individuals. The suite of traits that lump and separate these taxa can be gleaned from the present MacClade file, continually added to and updated, and available here., which is where you can also see the cladogram from which the above taxa were pulled.