PBS Eons video on Paraceratherium, the giant horse

Finally the PBS Eons narrator spilled the beans
on why mammal workers traditionally considered Paraceratherium (Fig. 1) to be a giant hornless rhino. It was (as I suspected, but never learned from emails to rhino experts) the shape of the molar cusps. That issue is addressed below.

Figure 1. Equus the horse shares many traits with Paraceratherium, the giant rhino/horse.

Figure 1. Equus the horse shares many traits with Paraceratherium, the giant rhino?/horse?

The following are my two comments yesterday
in the YouTube comments section:

Not a rhino! A giant three-toed horse. Molars are convergent between closely related horses and rhinos. Details here: https://pterosaurheresies.wordpress.com/2016/12/30/maybe-paraceratherium-is-really-a-giant-horse/ and here: https://pterosaurheresies.wordpress.com/2017/01/03/more-taxa-for-the-paraceratheriumgiant-horse-hypothesis/ and here: https://pterosaurheresies.wordpress.com/2018/11/11/aceratherium-vs-paraceratherium/

PS. Hyrachyus IS basal to rhinos. Pappaceras nests between two 3-toed horses (Mesohippus and Miohippus) and Juxia is the size and shape of a horse because it nests between Equus (the modern horse) and Paraceratherium. If you exclude horses from the analysis, sure Paraceratherium will nest with rhinos. When horses are added to the analysis Paraceratherium and Juxia nest with Equus. Don’t trust just one character like molar shape. Look at all the traits from nose to tail and then do your analysis. More details here: https://pterosaurheresies.wordpress.com/2017/04/27/indricotheres-horse-like-rhinos-or-rhino-like-horses/

wiki/Juxia
wiki/Paraceratherium
wki/Indricotheriinae

Aceratherium vs. Paraceratherium

Aceratherium is a hornless rhino (Figs 2-4).
Paraceratherium is a GIANT hornless horse (Fig. 1). Even so, the two are similar enough that that latter was named for the former. Thereafter Paraceratherium became known as a rhino.

Figure 1. Equus the horse shares many traits with Paraceratherium, the giant rhino/horse.

Figure 1. Equus the horse shares many traits with Paraceratherium, the giant three-toed horse.

However,
and as we learned earlier by testing prior assumptions in the large reptile tree (LRT, 1318 taxa, subset Fig. 5), Aceratherium nested between rhinos and brontotheres. Paraceratherium nested with other large three-toed horses.

Fig. 1. Aceratherium skeletal mount. This hornless rhino is transitional to brontotheres, not indricotheres (= paraceratheres).

Fig. 2 Aceratherium skeletal mount. This hornless rhino is transitional to brontotheres, not indricotheres (= paraceratheres) in the LRT.

Even so,
the convergence is impressive! No wonder earlier workers named the one for the other.

Figure 2. Aceratherium acutum skull drawing and fossil.

Figure 3. Aceratherium acutum skull drawing and fossil.

Convergence is rampant within the LRT.
For example, we’ve seen mysticetes and odontocetes converge so much we call them all ‘whales’ or ‘cetaceans‘, two terms that need to be dumped in favor of something more in keeping with their phylogenetic nestings. The same has happened with Aceratherium and Paraceratherium. The details of their skeletal traits distinguish them. You can examine those traits in a MacClade file by request.

Figure 1. Indricothere skulls to scale along with horse and rhino skulls.

Figure 4. Indricothere skulls to scale along with horse and rhino skulls.

Perhaps this is just one more instance of paleontology
turning a blind eye toward testing a wider gamut of taxa to validate prior hypotheses… or invalidate them. That’s why the LRT is here: to test prior hypotheses.

Figure 5. Various ungulates and kin subset of the LRT. Here Aceratherium, a hornless rhino, does not nest with Paraceratherium, a giant three-toed horse.

Figure 5. Various ungulates and kin subset of the LRT. Here Aceratherium, a hornless rhino, does not nest with Paraceratherium, a giant three-toed horse.

Shifting all the paraceratheres
over to the aceratheres adds 21 steps to the LRT.

Aceratherium incisivum (Kaup 1832; originally Rhinoceros incisivum, Cuvier 1822; Miocene; 2.3m long) nests with short-legged Metamynodon and shares with it long anterior dentary teeth, a straight jugal and a short nasal. Aceratherium lacks an upper canine.

Figure 2. GIF movie (3 frames) showing what is known of the skeletons of Baluchitherium and Indricotherium. Note the more horse-like morphology.

Figure 6. GIF movie (3 frames) showing what is known of the skeletons of Baluchitherium and Indricotherium. Note the more horse-like morphology.

Paraceratherium transouralicum  (P. bugtiense holotype, Pilgrim 1908; Baluchitherium, Osborn 1923; late Oligocene, 34-23mya; 4.8m shoulder height, 7.4m long) was long considered a giant hornless rhinoceros, but here nests with the horse, Equus. They share a long neck, straight ventral dentary and the retention of premaxillary teeth, among other traits. Paraceratherium retains three toes, as in ancestral horse/rhinos like Heptodon and Hyracotherium.

Figure 3. In the LRT Mesohippus nests basal to horses and indricotheres.

Figure 7. Mesohippus, the last common ancestor in the LRT to horses and indricotheres.

References
Chow M and Chiu C-S 1964. An Eocene giant rhinoceros. Vertebrata Palasiatica, 1964 (8): 264–268.
Cuvier G 1822a. Recherches sur les ossements fossiles. Tome second, G. Doufor et d’Ocagne éd., Paris, – (1822b). Tome troisième, – (1824). Tome cinquième.
Forster-Cooper C 1911. LXXVIII.—Paraceratherium bugtiense, a new genus of Rhinocerotidae from the Bugti Hills of Baluchistan.—Preliminary notice. Annals and Magazine of Natural History Series 8. 8 (48): 711–716. doi
Forster-Cooper C 1924. On the skull and dentition of Paraceratherium bugtiense: A genus of aberrant rhinoceroses from the Lower Miocene Deposits of Dera Bugti. Philosophical Transactions of the Royal Society B: Biological Sciences. 212 (391–401): 369–394.
Granger W and Gregory WK 1935. A revised restoration of the skeleton of Baluchitherium, gigantic fossil rhinoceros of Central Asia. American Museum Novitates. 787: 1–3.
Kaup J 1832. Über Rhinoceros incisivus Cuv., und eine neue Art, Rhinoceros schleier-macheri, Isis von Oken, Jahrgang1832 (8: 898-904.
Lucas SG and Sobus JC 1989. The Systematics of Indricotheres”. In Prothero DR and Schoch RM eds. The Evolution of Perissodactyls. New York, New York & Oxford, England: Oxford University Press: 358–378. ISBN 978-0-19-506039-3.
Osborn HF 1923. Baluchitherium grangeri, a giant hornless rhinoceros from Mongolia. American Museum Novitates. 78: 1–15. PDF
Pilgrim GE 1910. Notices of new mammalian genera and species from the Tertiaries of India. Records of the Geological Survey of India. 40 (1): 63–71.
Wood HE 1963. A primitive rhinoceros from the Late Eocene of Mongolia. American Museum Novitates 2146:1-11.

wiki/Juxia
wiki/Paraceratherium
wki/Indricotheriinae
wiki/Metamynodon
wiki/Aceratherium

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

More taxa for the ‘Paraceratherium=giant horse’ hypothesis

Figure 1. Adding a basal horse, Mesohippus, and a basal indricothere, Juxia, to the large reptile tree keeps indricotheres in the horse clade.

Figure 1. Adding a basal horse, Mesohippus, and a basal indricothere, Juxia, to the large reptile tree keeps indricotheres in the horse clade.

When you create a heresy
by breaking with decades of tradition, it’s always a good idea to test your hypothesis of interrelationships by adding pertinent taxa.

A few days ago Paraceratherium, a derived and gigantic indricothere, was nested in the large reptile tree (LRT, Fig. 1) with Equus, the extant horse. Tradition dictated that it should have nested with Ceratotherium, the extant white rhino – IF Paraceratherium was indeed a giant hornless rhino. But it wasn’t then and it isn’t now, based on current data. (One must always be willing to accept better data that busts up your favorite discoveries).

Today
Juxia (Chow and Chiu, 1964), a horse-sized indricothere with more premaxillary teeth and Mesohippus (Marsh 1875) a primitive three-toed horse, are added to the LRT (subset Fig. 1) to test the prior nesting. Mesohippus is known from a dozen species. Juxia is known form a nearly complete skeleton and a less-complete referred specimen. It is one of the smaller and more primitive indricotheres.\

Figure 2. A selection of horse and indricothere skulls to scale. No other taxa are more closely related to these than each is to each other.

Figure 2. A selection of horse and indricothere skulls to scale. No other taxa are more closely related to these than each is to each other.

Everyone knows indricotheres are supposed to be
giant hornless rhinos. But in the LRT they continue to nest with horses. The Bootstrap numbers (Fig. 1) are strongly supportive. And its pretty obvious when you get them together (Fig. 2). Both Juxia and Paraceratherium (Figs. 1, 4) look like giant three-toed horses, because that’s what they are. Not sure why this was never noticed before. Let me know if you know of any prior literature on this hypothesis of relationships.

Figure 3. In the LRT Mesohippus nests basal to horses and indricotheres.

Figure 3. In the LRT Mesohippus nests basal to horses and indricotheres (see figure 4).

Figure 1. Equus and Paraceratherium nest together on the LRT.

Figure 4. Equus and Paraceratherium nest together on the LRT.

References
Chow M and Chiu C-S 1964. An Eocene giant rhinoceros. Vertebrata Palasiatica, 1964 (8): 264–268.
Marsh OC 1875. Notice of new Tertiary mammals, IV. American Journal of Science 9(51):239-250.

wiki/Paraceratherium
wiki/Juxia
wiki/Mesohippus