Teleoceras spp.

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Teleoceras spp.


© @ Eurwentala
An illustration of T. major next to H. amphibius for comparison.

Temporal range: Neogene; Miocene to Pliocene; late Hemingfordian to late Hemphillian (~17.5-4.9 Ma)[1]

Scientific classification:

Domain: Eukaryota
(unranked): Unikonta
(unranked): Opisthokonta
(unranked): Holozoa
(unranked): Filozoa
Kingdom: Animalia
Subkingdom: Eumetazoa
(unranked): Bilateria
Superphylum: Deuterostomia
Phylum: Chordata
Infraphylum: Gnathostomata
Clade: Eugnathostomata
Clade: Teleostomi
Superclass: Tetrapoda
Clade: Reptiliomorpha
Clade: Amniota
Clade: Synapsida
Clade: Eupelycosauria
Clade: Sphenacodontia
Clade: Sphenacodontoidea
Order: Therapsida
Suborder: Cynodontia
Clade: Prozostrodontia
Clade: Mammaliaformes
Class: Mammalia
Legion: Cladotheria
Sublegion: Zatheria
Infralegion: Tribosphenida
Subclass: Theria
Clade: Eutheria
Infraclass: Placentalia
Subcohort: Exafroplacentalia
Magnorder: Boreoeutheria
Superorder: Laurasiatheria
Clade: Ungulata
Order: Perissodactyla
Suborder: Ceratomorpha
Superfamily: Rhinocerotoidea
Family: Rhinocerotidae
Tribe: †Teleoceratini
Genus: †Teleoceras
Species: †T. aepysoma[2]
†T. aginense
†T. americanum
†T. brachyrhinum
†T. fossiger
†T. guymonense
†T. hicksi
†T. major
†T. medicornutum
†T. meridianum
†T. proterum

Teleoceras is an extinct genus of rhinoceros that lived in North America from the Miocene to Pliocene epochs (late Hemingfordian to late Hemphillian NALMAs). There were multiple species in this genus.

Evolution:
It has been proposed that Teleoceras evolved from Diaceratherium, as the latter genus spread to North America. According to Donald Prothero, the early species were themselves quite short-legged. The limb bones became stumpier and more compressed to an extreme degree as the genus evolved.[3] However, the discovery of T. aepysoma remains from the late Hemphillian[2] suggests that this evolutionary trend was not followed by all lineages in the genus Teleoceras.

Description:
Most Teleoceras species possessed a small nasal horn, fused nasal bones, and a hippopotamus-like body consisting of a barrel-shaped trunk and short, robust limbs.[2][3] There are many other synapomorphies of Teleoceras proposed by Donald Prothero, which T. aepysoma shares with its relatives. This has led to its inclusion in the genus. However, this particular species lacked the small terminal nasal horn, barrel-shaped trunk, and stumpy limbs of other Teleoceras species. The presence of a nasal incision retracted to the anterior third premolar, also thought to be a synapomorphy of the genus, was questionable in T. aepysoma. Accordingly, the synapomorphies of Teleoceras have been revised, with the specifically aforementioned ones being removed.[2]

Teleoceras possessed upper chisel-like incisors (unlike most aceratheriines).[3] Some specimens possess large, tusk-like second lower incisors, while in others they are smaller. Specimens with tusk-like i2s were male, while those with smaller incisors were female.[2] The skull was very large, with high-crowned molars that were almost certainly used to feed on abrasive grasses.[3]

Two male specimens of T. aepysoma were estimated to have weighed 1,544 kg and 2,268 kg, respectively. This is substantially heavier than mass estimates of 568-702 kg for T. proterum.[2]


Mounted skeleton of T. proterum at the Florida Museum of Natural History.


A mounted skeleton of Teleoceras at the Harvard Museum of Natural History (image source).


Mounted cast of T. aepysoma at the East Tennessee State University Museum of Natural History, Gray, Tennessee.[2] Note the proportionately longer limbs in comparison to other species.

Paleobiology:
Because of its hippo-like proportions, Teleoceras was once thought to have led a hippo-like semiaquatic lifestyle.[3] However, oxygen isotope analysis of Teleoceras tooth enamel is inconsistent with this interpretation. δ¹⁸O values of a semiaquatic hippo-ecomorph would be expected to be much lower than those of contemporaneous terrestrial animals. Those of Teleoceras are actually similar to other Ashfall mammals.[1][4]

δ₁₃C values show that for the majority of its history, Teleoceras was primarily consuming C₃ plants. These would likely have been browse and C₃ grasses. There is evidence that as C₄ vegetation expanded (along with cooling global temperatures), Teleoceras was able to incorporate a modest amount of C₄ plants in its diet[1][4], but it and other rhinoceroses were never as successful at doing so as contemporaneous horses.[4]

Fossil assemblages of Teleoceras are dominated by subadult and young adult male individuals that were between 15-40% of their potential lifespan. The age-specific mortality rates were virtually identical to those of modern black rhinoceros populations. Modern rhinos are characterized by a high rate of intraspecific fight-related mortality, strongly suggesting that this accounted for the high mortality rate seen in Teleoceras. This is in contrast to mortality rates in hippos (which, as noted above, Teleoceras has been compared to), which are not elevated.[5] Pronounced intermale aggression is also supported by the delayed eruption of i2 in male Teloceras, as well as the tusk facets that were continually sharpened by the upper incisors. However, body size dimorphism varies within each assemblage, suggesting that the intensity of intermale competition is unrelated to the degree of sexual dimorphism.[6]

In Nebraska, a fossil assemblage (now colloquially known as “Rhino Pompeii”) of hundreds of T. major individuals was uncovered. Out of more than 200 individuals collected in the first few years, only 7 were adult males; the rest were females with their calves (some of which even had their calves in a nursing position under their bellies, while others had fetuses in their pelvic cavities). This shows that Teleoceras lived in large, male-dominated herds composed mostly of females and their young, just like many large ungulates today. Likewise, these rhinos were buried under ash blown from the Rocky Mountains. In addition to those that slowly died or were suffocated after being buried alive, bone pathologies indicate that many died by inhaling razor-sharp volcanic ash shards (which would have lacerated their lungs). Lastly, some of the specimens had seeds of Berriochloa (a common grass from the time period) in close proximity with their throat bones, providing further evidence that Teleoceras grazed.[3]

Extinction:
Teleoceras went extinct during the late Hemphillian about 4.9 million years ago.[1] As the global climate cooled, C₄ plants expanded and primary productivity would have declined. Rhinoceros abundance rapidly declined about 6.5 million years ago, coinciding with this expansion. As noted, while Teleoceras was able to incorporate C₄ plants in its diet to a certain extent, rhinos were not as successful at doing this as contemporaneous horses. Therefore, Teleoceras likely went extinct as a result of declining food resources due to the expansion of C₄ vegetation.[1]

References:

[1] Wang, B., & Secord, R. (2020). Paleoecology of Aphelops and Teleoceras (Rhinocerotidae) through an interval of changing climate and vegetation in the Neogene of the Great Plains, central United States. Palaeogeography, Palaeoclimatology, Palaeoecology, 542, 109411.
[2] Short, R. A., Wallace, S. C., & Emmert, L. G. (2019). A new species of Teleoceras (Mammalia, Rhinocerotidae) from the late Hemphillian of Tennessee. Bull Florida Mus Nat Hist, 56, 183-260.
[3] Prothero, D. R., & Schoch, R. M. (2002). Horns, tusks, and flippers: the evolution of hoofed mammals. JHU Press.
[4] MacFadden, B. J. (1998). [url=https://www.jstor.org/stable/2401243?seq=1#metadata_info_tab_contentsTale of two rhinos: isotopic ecology, paleodiet, and niche differentiation of Aphelops and Teloceras from the Florida Neogene[/url]. Paleobiology, 274-286.
[5] Mihlbachler, M. C. (2003). Demography of late Miocene rhinoceroses (Teleoceras proterum and Aphelops malacorhinus) from Florida: linking mortality and sociality in fossil assemblages. Paleobiology, 29(3), 412-428.
[6] Mihlbachlerll, M. C. (2005). LINKING SEXUAL DIMORPHISMAND SOCIALITY IN RHINOCEROSES: INSIGHTS FROM TELEOCERAS PROTER UM AND APHELOPS AMLA CORHIN US FROM THE LATE MIOCENE OF FLORIDA. Bull. Fla. Mus. Nat. Hist, 45(4), 495-520.

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Revisiting a Fossil Friend
by Brian Switek

phenomena.nationalgeographic.com/2015/04/08/revisiting-a-fossil-friend/

Some fossils feel like old friends. As happy as I am to encounter petrified skeletons I’ve never seen before in museum halls, there’s something comforting about rounding a corner to find a cast of AMNH 5027 – the first Tyrannosaurus I ever met – or see Stenomylus, a little North American camel that I’ve encountered in exhibits from New Haven to Los Angeles.

The ancient rhino Teleoceras recently joined the club, too. Paleontologists have exhumed so many of these squat, tubby rhinos that almost every major museum in America seems to have one. And, because of its stubby-legged, barrel-shaped body, the 17-4.5 million year old herbivore has often been cast as “the rhino that lived like hippo”. A life ambling between lake and shore seemed to be the only sort that made sense for such an oddly-proportioned mammal, and I repeated the traditional story when I tweeted a photo of the beast during a visit to Harvard’s Museum of Natural History.

But looks can be deceiving. Paleontologist Bobby Boessenecker – expert on aquatic and semiaquatic fossil mammals – jumped in on Facebook to point out a 1998 study that cast Teleoceras in a different way. (This is the nice thing about being friends with paleontologists – they’ll catch your errors and will immediately proffer citations to get you back on track.) According to the Paleobiology paper by Bruce MacFadden, at least some of the rotund rhinos stayed high and dry.

Different species of Teleoceras used to range across the span of North America, from Oregon to Florida. In some places – like the 10 million year old Ashfall Beds of Nebraska – they’ve been found by the dozens. MacFadden chose to focus on specimens found in the 9.5 to 4.5 million year old rock of the sunshine state, as well as those of its neighbor Aphelops – a rhino with longer legs that has often been reconstructed as a relatively swift species that browsed for soft plants in open habitats. And to investigate this “tale of two rhinos”, MacFadden turned to geochemical traces locked inside the rhinos’ teeth.

You are what you eat. That’s the basis for a branch of fossil research that focuses on geochemical isotopes. In short, different pathways in plant photosynthesis leave distinct signatures of the isotope 13C. That trace ends up becoming incorporated in teeth as they grow, and, by comparing these signatures in fossil teeth to those of living animals with known diets, paleontologists can narrow down what prehistoric mammals were munching on. Similar logic applies to other geochemical indicators. The water prehistoric animals imbibed, for example, left geochemical signposts in the form of 18O, and this isotope can be used to determine whether an animal in question had a more or less aquatic lifestyle.

By analyzing these carbon and oxygen isotopes in the fossil rhinos, MacFadden was able to check what had often been assumed on the basis of skeletal shapes. What he found didn’t fit the traditional Teleoceras tale.

In the oldest part of the sample, in teeth 9.5 and 7 million years old, MacFadden didn’t find much difference in diet between Teleoceras and the leggier Aphelops. They had similar carbon isotope signatures, indicating a diet of what are called C3 plants that included trees, forbs, shrubs, and some grasses.

By 4.5 million years ago, though, the rhinos were definitely picking off different parts of the menu. Aphelops appears to have been a browser, nibbling on soft plants, while Teleoceras was a “mixed feeder” with a large proportion of C4 grasses – which had spread into the region by that time – in its diet. This seemed to be in accord with evidence from elsewhere. At Nebraska’s Ashfall site, for example, plant material found around the throats and stomachs of Teleoceras hinted that the rhino snarfed down bushels of grass.

From diet, Teleoceras seemed more at home out in the grasslands than in the water – an idea mooted decades before by paleontologist William Diller Matthew. And the oxygen isotope signatures seemed to cinch it. Teleoceras didn’t have an oxygen isotope profile like that of a hippo, but instead seemed to match mammals that spend most of their time in the terrestrial realm. “While the δ18O results cannot rule out the possibility that Florida Teleoceras spent a small percentage of its daily life cycle in water,” MacFadden wrote, “the data do not support the previous hypothesis that this species was principally aquatic.”

In place of the old model, MacFadden proposed that Florida’s ancient rhinos avoided competition for the salad bar by eating different plants – Aphelops being more of a browser, like today’s black rhino, and Teleoceras pioneering the grazing lifestyle embodied by the modern white rhino. The low-slung appearance of Teleoceras wasn’t because it lived like a hippo. Stumpy legs were an old, common trait amongst the rhinoceros lineage it belonged to, and it didn’t have to be particularly tall if – by MacFadden’s estimation – 60% of the herbivore’s diet was grass. Teleoceras was not so much a hippoceros as a living lawnmower.

References:

- MacFadden, B. 1998. "Tale of two rhinos: isotopic ecology, paleodiet, and niche differentiation of Aphelops and Teleoceras from the Florida Neogene". Paleobiology. 24 (2): 274-286.

- Prothero, D. 2005. The Evolution of North American Rhinoceroses. Cambridge: Cambridge University Press. pp. 94-124

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Description of T. aepysoma from the Gray Fossil Site. Although it is referable to this genus for having most characteristics of the genus, it also lacked a few of them, among them the typical teleoceratine body proportions consisting of a barrel-shaped trunk and short, stumpy limbs. It also does not have a small nasal horn like other species do.

Teleoceras is the only North American genus of Teleoceratini, and presence of most characters supports referring the GFS specimens to this genus (Table 3). The GFS fossils exhibit several distinct features (see diagnosis below) that not only warrant erection of the new species, but also call in to question some of the characters used to define the genus. Specifically, the new species justifies removing the following characters from the generic diagnosis of Prothero (2005:94): “a small terminal nasal horn and fused nasals…teleoceratin body proportions…and short, robust limbs.”

Both ETMNH 609 and ETMNH 601 are considered males because of their large, tusk-like i2s. This is in contrast to the smaller i2s found in female rhinoceroses (Osborn, 1898a, 1898b; Voorhies and Stover, 1978; Dinerstein, 1991). Both skeletons are also adults based on the degree of epiphyseal fusion and tooth wear. The upper tooth row of ETMNH 609 matches age class XI of Hitchins (1978) and the lower tooth row matches age class X. The larger ETMNH 601 matches age class XIII of Hitchins (1978) on the upper teeth and age class XII on the lower teeth. Using Mihlbachler’s (2003) life span percentages, ETMNH 609 was at the beginning of an age class marking 25–35% of its potential life span and ETMNH 601 was at the beginning of an age class marking 35–52% of its potential life span. In extant Diceros, these life span percentages refer to 8–12 years old and 11–18 years old, respectively (Hitchins, 1978).

Mass estimates suggest Teleoceras aepysoma is quite large. Using equations based on the circumferences of the humerus and femur (Anderson et al., 1985), the mass of ETMNH 609 is estimated to be 1488 kg and 1335 kg, respectively, and that of ETMNH 601 is estimated to be 2330 kg and 2147 kg. These same equations produced mass estimates of 702 kg and 568 kg for T. proterum from the Love Bone Bed (MacFadden and Hulbert, 1990). The substantially greater mass estimates for T. aepysoma are corroborated by calculations using the calcaneum and constants from two modern rhino taxa (Ceratotherium simum and Diceros bicornis) (Christiansen, 2002). Mass was estimated separately for each constant and then averaged. Using this method, the estimated masses of ETMNH 609 and ETMNH 601 are 1544 kg and 2268 kg, respectively.

www.researchgate.net/publication/332786799_A_New_Species_of_Teleoceras_Mammalia_Rhinocerotidae_from_the_Late_Hemphillian_of_Tennessee