Cambaytherium 2020: Still not a primitive perissodactyl

We looked at this genus earlier
when Rose et al. 2014 first described Cambaytherium from some bits and pieces of this sheep-sized mammal from the Early Eocene (Fig. 1). Back in 2017 the large reptile tree (LRT; subset Fig. 5) nested Cambaytherium within the oreodont + mesonychid + hippo (Fig. 6) + anthracobunid (Fig. 2) + desmostylian (Figs. 3, 6) + mysticete (Fig. 3) clade. In the LRT that clade is far from Perissodactyla (= tapirs + horses + rhinos). 

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

Figure 1. Cambaytherium with a an alternate rostrum reversing taphonomic shifts.

Rose et al. 2020 update their discoveries
with new data (= more bones from more specimens) of Cambaytherium, which they still insist is a perissodactyl (rhino + horse) ancestor) ancestor.

Unfortunately,
taxon exclusion was the problem then and remains the problem now. The authors do not include  enough taxa that nest closer to Cambaytherium in LRT (subset Fig. 5), other than adding Anthracobune (Fig. 2) and Behemotops (Fig. 3).

Figure 3. Anthracobune reconstructed with a larger skull to match the teeth on the mandible.

Figure 2. Anthracobune reconstructed with a larger skull to match the teeth on the mandible.

Rose et al. 2020 employed 72 taxa.
That is twenty more than in Rose et al. 2014. Their more recent strict consensus resulted in 408 shortest trees. If that many shortest trees happened in the LRT using only 72 taxa, I would dive back in and fix what was wrong. In this case, taxon exclusion is still the problem with Rose et al. 2020.

Figure 1. Rorqual evolution from desmostylians, Neoparadoxia, the RBCM specimen of Behemotops, Miocaperea, Eschrichtius and Cetotherium, not to scale.

Figure 3. Rorqual evolution from desmostylians, Neoparadoxia, the RBCM specimen of Behemotops, Miocaperea, Eschrichtius and Cetotherium, not to scale.

Rose et al. 2020 explain their 20 taxon additions:
“The Eocene desmostylian Behemotops proteus was included for two reasons. First, there are interesting similarities between the teeth of this taxon and those of cambaytheres and anthracobunids (Ray et al., 1994). Second, the analysis of Cooper et al. (2014) placed Desmostylia in a polytomy that included most perissodactyls and anthracobunids (but not cambaytheres). Historically, paleontologists have considered Desmostylia (like anthracobunids) to be closely related to tethytheres (Domning et al., 1986; Ray et al., 1994).”

Rose et al. 2020 cherry-picked some of the right taxa, but not enough of the right taxa, according to the LRT. They are “Pulling a Larry Martin” (= putting too much attention on a few ‘key’ traits). These mammal experts still have no idea what the actual outgroups and relatives of Cambaytherium are because they don’t include enough pertinent taxa (see Fig. 5).

In the LRT, force-shifting Cambaytherium
to the base of the Perissodactylia added 18 steps to the LRT. That’s not a large number considering the phylogenetic distance, so convergence is an issue here. Convergence is something the LRT handles pretty well due to its wide gamut of taxa.

Another fault:
Rose et al. 2014 put their faith in genomic results with unclear and mixed results. Never put your faith in genomic results in deep time studies (especially fossil taxa). Also, don’t trust the work of others. Don’t borrow cladograms. Do your own phenomic analysis with a wide gamut of taxa, as in the LRT. Then you’ll have a good model for actual evolutionary events.

From the Rose et al. 2020 abstract:
“The anatomy of Cambaytherium, a primitive, perissodactyl-like mammal from the lower Eocene Cambay Shale Formation of Gujarat, India, is described in detail on the basis of more than 350 specimens that represent almost the entire dentition and the skeleton.”

Many of the specimens are small disarticulated and broken pieces of bone. At least one skull is pretty well fossilized in 3D (Fig. 1).

“Cambaytherium combines plesiomorphic traits typical of archaic ungulates such as phenacodontids with derived traits characteristic of early perissodactyls.”

The authors cannot be more specific due to taxon exclusion.

“Cambaytherium was a subcursorial animal better adapted for running than phenacodontids but less specialized than early perissodactyls. The cheek teeth are bunodont with large upper molar conules, not lophodont as in early perissodactyls; like perissodactyls, however, the lower molars have twinned metaconids and m3 has an extended hypoconulid lobe. A steep wear gradient with heavy wear in the middle of the tooth row suggests an abrasive herbivorous diet.

Homologous desmostylian and hippo teeth also show heavy wear.

“Three species of Cambaytherium are recognized: C. thewissi (∼23 kg), C. gracilis (∼10 kg), and C. marinus (∼99 kg). Body masses were estimated from tooth size and long bone dimensions. Biostratigraphic and isotopic evidence indicates an age of ca. 54.5 Ma for the Cambay Shale vertebrate fauna, the oldest Cenozoic continental vertebrate assemblage from India, near or prior to the initial collision with Asia.

“Cambaytheriidae (also including Nakusia and Perissobune (Fig. 4) and Anthracobunidae are sister taxa, constituting the clade Anthracobunia, which is sister to Perissodactyla.

You heard it here first: The LRT nested Cambaytherium with Anthracobune (Fig. 3), but far from Perissodactyla due to taxon exclusion.

Perissobune (Fig. 4) has not been tested in the LRT, but closely resembles the basal perissodactyl, Protapirus (Fig. 4), with a taller coronoid process and only two lower molars. Compare to the distinctly different mandible of Cambaytherium (Fig. 1).

“We unite them in a new higher taxon, Perissodactylamorpha.

This is invalid, inappropriate, premature and based on cherry-picked taxa.

Figure 3. Perissobune mandible compared to diagram of a primitive perissodactyl, Protapirus. Compare to figure 1.

Figure 4. Perissobune mandible compared to diagram of a primitive perissodactyl, Protapirus. Compare to figure 1.

Continuing from the Rose et al. 2020 abstract:
“The antiquity and occurrence of Cambaytherium—the most primitive known perissodactylamorph—in India near or before its collision with Asia suggest that Perissodactyla evolved during the Paleocene on the Indian Plate or in peripheral areas of southern or southwestern Asia.”

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

Figure 5. The oreodont-mesonychid-hippo-desmoystlian-mysticete clade subset of the LRT

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

Figure 6. Merycopotamus, Hippopotamus, and Paleoparadoxia compared to scale.

Back in 2017 readers learned the following
from Rose et al. 2014, “Cambaytherium was found on the marine coastline of island India.”

Then I added, “close to where odontocete whales were also evolving from Tenrec relatives like Pakicetus. Based on its relationships and geography, Cambaytherium was likely much more aquatic than is typical for perissodactyls.”

Figure 1. Simbakubwa from Broths and Stevens 2019, colors added, and compared to a lion mandible. Note the two medial views of the mandible with different shapes. Dorsal view of indented mandible and palate is similar to hippos.

Figure 7. Simbakubwa from Broths and Stevens 2019, colors added, and compared to a lion mandible. Note the two medial views of the mandible with different shapes. Dorsal view of indented mandible and palate is similar to hippos.

For some reason no one wants to test enigma taxa with hippos 
and mesonychids. We looked at this same problem earlier with the putative carnivore, Simbakumba, which also turned out to be a hippo relative.


References
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.
Rose KD et al, 2020. Anatomy, Relationships, and Paleobiology of Cambaytherium (Mammalia, Perissodactylamorpha, Anthracobunia) from the lower Eocene of western India, Journal of Vertebrate Paleontology (2020). DOI: 10.1080/02724634.2020.1761370

wiki/Cambaytherium
phys.org/news/2020-11-indian-fossils-hypothesis-hoofed-mammals.

From Phys.org
“New research published today in the Journal of Vertebrate Paleontology describes a fossil family that illuminates the origin of perissodactyls—the group of mammals that includes horses, rhinos and tapirs. It provides insights on the controversial question of where these hoofed animals evolved, concluding that they arose in or near present day India.”

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.

 

New Pappaceras chewing data from Wang et al. 2017

At the base of the giant indricotheres
we find Pappaceras (Fig. 1). To that everyone agrees. Where the disagreements start is what came before Pappaceras? In the large reptile tree (LRT, 1012 taxa) it’s Miohippus (Fig.1 1) and Equus the extant horse.

Figure 1. Miohippus, Pappaceras and a freehand sketch of Pappaceraus, the latter two from Wang et al. 2017, but colorized here.

Figure 1. Miohippus, Pappaceras and a freehand sketch of Pappaceraus, the latter two from Wang et al. 2017, but colorized here. Note the freehand sketch differs from the CT scan in several subtle and not so subtle ways.

Wang et al. 2017
bring new insight into the chewing mechanism in Pappaceras. They write: “The paraceratheriid Pappaceras is the earliest unequivocal rhinocerotoid genus to date, for which the osteological morphology is relatively unique compared to other perissodactyls. The reconstruction of the masticatory muscles suggests that Pappaceras meiomenus is strictly herbivorous, probably folivorous, with a primary component of vertical biting.”

Distinct from the LRT
The Wang et al. cladogram nests horses at the base of the Perissodactyla. Chalicotheres and brontotheres nest together without resolution. Indricotheres nest with rhinos as sisters to tapirs. The LRT does not support that tree topology at all. The Wang et al. cladogram also nests a perissodactyl outgroup taxon I had never heard of before: Cambaytherium. which I just added to the LRT and we’ll talk about tomorrow. It is not related to perissodactyls in the LRT.

The freehand drawing of Pappaceras
by Wang et al. (Fig. 1`) is distinct in certain subtle aspects from their CT scan (Fig. 1). It’s better to trace directly from photos. Or just use the CT scans. Freehand drawing, by its nature, emphasizes things that catch the eye and deemphasizes things that don’t catch the eye, but perhaps should.

References
Wang H-B, Bai B, Gong Y-X, Meng J and Wang Y-Q 2017. Reconstruction of the cranial musculature of the paraceratheriid rhinocerotoid Pappaceras meiomenus and inferences of its feeding and chewing habits. Acta Palaeontologica Polonica 62 (2): 259–271.

Maybe horses are just tall, skinny, hornless rhinos…

Short one today,
With yesterday’s addition of two more basal rhinos to the large reptile tree (LRT 1010 taxa) maybe it’s time to change our thinking from ‘either horse or rhino’ to ‘horses are a type of rhino’. We know they are related. Maybe they are more intimately related than we first thought. That would make indricotheres like Paraceratherium giant hornless rhinos again, if you prefer it that way.

Figure 3. Subset of the LRT with the addition of Metamynodon and Amynodon, two former rhinos.

Figure 1. Subset of the LRT with the addition of Metamynodon and Amynodon, two former rhinos.

Even though,
in the LRT (subset Fig. 1) fewer taxa intervene at present between indricotheres and horses than indricotheres and extant rhinos, like Ceratotherium. Sort of like, you know, birds are a type of dinosaur. It just takes some getting used to – creating a new mental paradigm following the present data without excluding pertinent taxa.

 

Two more odd ‘hornless rhinos’ nest slightly elsewhere in the LRT

First a little backstory
Earlier, Paracerathierium and Juxiatwo traditional hornless rhinos, nested with three-toed horses in the large reptile tree (LRT, 1009 taxa, Fig. 3).

Figure 1. Metamynodon nests with Eotitanops. It had large fangs and a bulky body like a hippo.

Figure 1. Metamynodon nests with Eotitanops. It had large fangs and a bulky body like a hippo.

Today
the giant hippo-like traditional rhino, Metamynodon planifroms (Scott and Osborn 1867; Early Eocene; 4m long), nests with Eotitanops, the basal brontothere, though not far from Ceratotherium, the white rhino.

Figure 2. Amynodon was formerly linked to Metamynodon as a basal rhino, but here nests with Mesohippus.

Figure 2. Amynodon was formerly linked to Metamynodon as a basal rhino, but here nests with Mesohippus.

And
the smaller long-necked traditional rhino, Amynodon, nests with Mesohippus, the basal horse. Both were derived from a sister to Hyracotherium, basal to both rhinos and horses.

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.

Figure 3. Subset of the LRT with the addition of Metamynodon and Amynodon, two former rhinos.

Figure 3. Subset of the LRT with the addition of Metamynodon and Amynodon, two former rhinos.

Traditional cladograms
nest horses separate from tapirs + rhinos. The LRT nests horses with rhinos both derived from a sister to Hyracotherium and a sister to tapirs + chalicotheres. Traditional cladograms also avoid mixing brontotheres, horses and rhinos, like we do here.

References
Marsh OC 1877. Notice of some new vertebrate fossils. American Journal of Arts and Sciences 14:249-256
Scott WB and Osborn HF 1887. Preliminary account of the fossil mammals from the White River formation contained in the Museum of Comparative Zoology. Bulletin of the Museum of Comparative Zoölogy at Harvard College 13(5):151-171.

wiki/Mesohippus
wiki/Amynodontidae
wiki/Metamynodon

Lambdotherium: not a basal brontothere — it’s another pig relative!

Earlier a putative stem brontothere, Danjiangia, was re-nested with basal artiodactyls in the large reptile tree (LRT, 1005 taxa).

Here another putative stem brontothere,
Lambdotherium (Cope 1880, Mader 1998; Eocene, 50mya; Fig. 1) likewise moves away from the basal brontothere, Eotitanops. In the LRT  Lambdotherium nests with Ancodus (Fig. 2), another basal artiodactyl close to extant pigs.

Figure 1. Lambdotherium traditionally nests with the basal brontothere, Eotitanops, but here nests with Ancodus, a basal artiodactyl.

Figure 1. Lambdotherium traditionally nests with the basal brontothere, Eotitanops (ghosted here), but here nests with Ancodus, a basal artiodactyl. Brontotheres have a very tall naris. Pigs do not. 

I don’t know of any post-crania
for Lambdotherium. Note that Ancodus (Fig. 2), like Eotitanops, has a pentadatyl manus. Lambdotherium was traditionally considered a brontothere based on its teeth. The LRT employs relatively few dental traits. And maybe some specimens need to be reexamined. The very high arch of the Lambdotherium squamosal, among many other traits, is more similar to pig-like taxa, than to basal brontotheres, which here nest closer to rhinos, than to horses, contra the Wikipedia report on brontotheres.

Distinct from both rhinos and horses,
brontotheres have four toes on the forefeet. All are derived from a sister to Hyrachyus, which likewise has four toes.

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.

References
Cope ED 1880. The bad lands of the Wind River and their fauna. The American Naturalist 14(10):745-748.
Mader BJ 1998. Brontotheriidae. In Janis CM, Scott KM, and Jacobs LL (eds.), Evolution of Tertiary Mammals of North America 1:525-536.
Mihlbachler MC 2004. Phylogenetic Systematics of the Brontotheriidae (Mammalia, Perissodactyla). PhD dissertation. Columbia University. p. 757.
Mihlbachler MC 2008. Species taxonomy, phylogeny and biogeography of teh Brontotheriidae (Mammalia: Perissodactyla). Bulletin of the American Museum of Natural History 311:475pp.

wiki/Eotitanops
wiki/Lambdotherium

Splitting up the Ungulates

Get ready for a good dose of heresy
brought to you by the large reptile tree (LRT 1003 taxa) a fully resolved online morphological study.

A little backstory
According to Wikipedia: Ungulates are any members of a diverse group of primarily large mammals that includes odd-toed ungulates such as horses and rhinoceroses, and even-toed ungulates such as cattlepigsgiraffescamelsdeer, and hippopotami.”

“However, in 2009 morphological and molecular[ work has found that aardvarks, hyraxes, sea cows, and elephants are more closely related to sengistenrecs, and golden moles than to the perissodactyls and artiodactyls, and form Afrotheria. Elephants, sea cows, and hyraxes are grouped together in the clade Paenungulata, while the aardvark has been considered as either a close relative to them or a close relative to sengis in the clade Afroinsectiphilia. This is a striking example of convergent evolution.

“There is now some dispute as to whether this smaller Ungulata is a cladistic (evolution-based) group, or merely a pheneticgroup (form taxon) or folk taxon (similar, but not necessarily related). Some studies have indeed found the mesaxonianungulates and paraxonian ungulates to form a monophyletic lineage, closely related to either the Ferae (the carnivorans and the pangolins) in the clade Fereuungulata or to the bats. Other studies found the two orders not that closely related, as some place the perissodactyls as close relatives to bats and Ferae in Pegasoferae and others place the artiodactyls as close relatives to bats.” 

About that last hypothesis ~
If I had recovered that relationship I would expect pitchforks and torches.

Today
the LRT presents a hypothesis of mammal relationships in which hippos nest apart from other artiodactyls and perissodactyls nest apart from those two, separated by the elephant/hyrax/manatee clade with the hyrax-like Ectocion at it base (Fig. 1).

Figure 1. Subset of the LRT focusing on ungulates, which split into three clades here.

Figure 1. Subset of the LRT focusing on ungulates, which split into three clades here.

Note:
Hippos do indeed nest with whales, but only the mysticete whales. And desmostylians separate hippos from mysticetes. Odontocetes, like Orcinus, had a separate ancestry as we learned earlier here. The even-toed artiodactyls nest together with pig-types toward the base and deer-types a little later. The odd-toed perissodactyls nest together.

There are no
tenrecs, aardvarks or golden moles in this sector of the LRT.

Ungulata is not a monophyletic cladistic group,
unless it also includes the elephants and whales with Mesonyx as a basal member, (a taxon close to the last common ancestor). I’m not the first one to come to this conclusion. Probably best just to drop this name from usage and realize that hooves appeared several times in mammal evolution.

A little extra study
cleared up the earlier Pappaceras issue. Now the nesting is more in accord with consensus with regard to the indricotheres, but they’re still closer to 3-toed horses than to 3-toed rhinos.

Also note:
the <50 Bootstrap scores surrounding Hyracotherum, a basal horse/rhino. I could only separate sister taxa by 2 steps. It takes at least 3 steps to bounce the Boostrap score over 50. Small steps. Small steps.

 

Macrauchenia: a South American perissodactyl

Figure 1. Macrauchenia museum mount.

Figure 1. Macrauchenia museum mount.

Figure x. Macrauchenia cladogtam. Tapir and Chalicotherium are perissodactyls.

Figure x. Macrauchenia cladogtam. Tapir and Chalicotherium are perissodactyls.

Famous for its assumed
elephant-like proboscis, arising from a dorsal narial opening (Fig 2), Macrauchenia was a long-legged grazing ungulate with three toes on each manus and pes. In the large reptile tree it nests with Chalicotherium, which, in turn, nests with Tapirus, (the tapir) an extant perissodactyl with a short flexible trunk. A recent analysis of collagen sequences (Welker et al. 2015) found the same relationship. Not sure why this needed resolution… tapirs also have a trunk, dorsal narial opening, three hooves per foot AND some still live in South America. I guess that used to be considered ‘convergence.’ Here the LRT calls it ‘homology.’

Discovered by Charles Darwin in 1834,
and published by Richard Owen in 1836, Macrauchenia patachonica (Pliocene 7mya to Pleistocene .02mya; 3m length) was otherwise similar to a camel in proportions with a horse-like skull. Macrauchenia was an herbivore with a full arcade of short teeth in its jaws (Fig. 2). The last premolar looks like a molar, but, like other premolars, it is slightly larger than the other teeth and all sister taxa have 3 molars per side.

Figure 2. Macrauchenia skull in several view (from Owen 1836?) with bones colorized here. Note the dorsal extension of the premaxilla.

Figure 2. Macrauchenia skull in several view (from Owen 1836?) with bones colorized here. Note the dorsal extension of the premaxilla. The fossa posterior to the naris could anchor large proboscis muscles. 6 premolars and 3 molars appear to have been present. Not sure about the palatine here.

Wikpedia reports, “Macrauchenia was a long-necked and long-limbed, three-toed South American ungulate mammal, typifying the order Litopterna.  Early forms are near the condylarths, to such an extent that the litopterns might be considered merely as surviving and diversely specialized condylarths.” The LRT did not nest Macrauchenia with the basal Condylartha, but that is still a monophyletic clade that now includes all hoofed and edentate mammals — along with all the original basal condylarths.

Thanks to reader SBJ
for suggesting a number of South American mammals to add to the LRT. This is number one of several to come.

References
Owen R 1838. Description of Parts of the Skeleton of Macrauchenia patachonica. In Darwin, C. R. Fossil Mammalia Part 1 No. 1. The zoology of the voyage of H.M.S. Beagle. London: Smith Elder and Co.
Welker F et al. 2015. Ancient proteins resolve the evolutionary history of Darwin’s South American ungulates. Nature. doi:10.1038/nature14249. ISSN 0028-0836.
wiki/Macrauchenia