Mystery solved: Thylacoleo is a giant sugar glider…

no doubt, a little too big to glide…
and Thylacoleo (Fig. 2) is looking even less carnivorous in phylogenetic bracketing.

Sugar gliders
(Fig. 1) are phalangers (Fig. 6), a marsupial clade nesting between kangaroos and wombats (Fig. 5).

Figure 1. Sugar glider, Petaurus breviceps, skeleton in two views, plus a skull with mandible, lacking in the skeleton.

Adding the marsupial sugar glider,
Petaurus (Figs. 1, 3), and the cuscus, Phalanger (Fig. 6), to the large reptile tree (LRT, 1231 taxa) resolves a decades-old phylogenetic problem because Petaurus, the sugar glider, nests as a sister to Thylacoleo, the marsupial lion (Figs. 2, 4). Phalanger, the cuscus, nests as their last common ancestor, which has been suggested earlier.

According to the AustraliaMuseum website
“Most palaeontologists think that the ancestors of thylacoleonids were herbivores, an unusual occurrence since most carnivores evolved from other carnivorous lineages. One proposal suggests that thylacoleonids evolved from a possum ancestor (Phalangeroidea) based on dental formula, the skull of the cuscus Phalanger, and on a phalangerid-like musculature. Alternatively, evidence from certain skull features may show that thylacoleonids branched off the vombatiform line, the lineage that includes wombats and koalas.”

In the LRT,
wombats and koalas are now sister taxa to the cuscus clade. Without the sugar glider and the cuscus, the marsupial lion earlier nested with the wombat, Vombatus.

Just to be clear,
Phalanger is not an ancestor to Didelphis, the Virginia opossum, in the LRT, even though the Australian Museum called it a ‘possum ancestor.’

Figure 2. Thylacoleo skeleton compared to Petaurus skeleton to scale.

Long thought to be a super predator, 
in the midst of a clade of gentle wombat-like herbivores, Thylacoleo had, for its size, the strongest bite of any mammal, living or extinct, despite having tiny upper canines. This linking with sugar gliders further erodes the carnivorous hypothesis. 

Figure 3. Skulls of the genus Petaurus with many more teeth than in Thylacoleo, but in the same general pattern. Note the lower third premolar and its similarity to the same tooth in Thylacoleo. The big organe tooth at the tip of the dentary is the canine. The lower incisors are absent.

Arboreal or not?
Wikipedia reports, “The claws [of Thylacoleo] were well-suited to securing prey and for climbing trees.” And now we know how that came to be. Petaurus, despite its arboreal abilities, does not have a divergent thumb, like the one found in Thylacoleo.

Dentary canines
traditionally considered large, rodent-like incisors due to their placement, the anterior-most (medial-most) dentary teeth are actually canines. The incisors and their alveoli have disappeared. This can only be traced via phylogeny (see Arctocyon and Didelphis). The ancestrally small lower incisors are gone, replaced with ancestrally large large lower canines that meet medially like typical incisors. Notably, the lower canines maintain their traditional placement relationship to the upper canines (Fig. 6).

Even more interesting,
some marsupial taxa that experience a phylogenetic miniaturization, like Eurygenium (basal to Toxodon) the incisors reappear and the canines are not much larger than the incisors. That’s called a reversal or an atavism.

Figure 4. Thylacoleo skull. Many times larger than Petaurus, with fewer larger teeth, this is a giant sugar glider. The large orange tooth is the lower canine. The upper canine is a vestige. 

Size
Thylacoleo was 71 cm tall at the shoulder, about 114-150cm long from head to tail tip, about the size of a jaguar.

Petaurus is 40cm long to the tail tip, about the size of a ‘flying’ squirrel. Loose folds of skin spanning the fore and hind limbs to the wrists and ankles are used to extend glides from tree to tree, or up to 140m. The diet includes sweet fruits and vegetables.

Figure 5. The sugar glider, Petaurus, in vivo. Note the wrinkled fur between the fore and hind limb. That’s the gliding membrane.

Petaurus species
According to Wikipedia, “There are six species, sugar glider, squirrel glider, mahogany glider, northern glider, yellow-bellied glider and Biak glider, and are native to Australia or New Guinea.” Whichever one is closest to Thylacoleo has not been tested or determined.

Figure 5. Subset of the LRT focusing on Marsupialia, Metatheria and then nesting of Thylacoleo.

Petaurus breviceps (Waterhouse 1839; Early Miocene to present; up to 30cm) is the extant sugar glider, a nocturnal squirrel-like marsupial able to climb trees and glide with furry membranes between the fore and hind limbs. An opposable toe is present on each hind foot. Sharp claws tip every digit.

Phalanger orientalis (Pallas 1766; 34 cm in length) is a nocturnal arboreal folivore marsupial known as thte Northern common cuscus. Commonly considered a ‘possum’ the cuscus nests between wombats and kangaroos, basal to sugar gliders and marsupial lions.

Figure 6. The cuscus (genus: Phalanger orientalis) nests with Petaurus and Thylacoleo in the LRT. Those anterior dentary teeth look like incisors, but phylogenetically are actually canines.

Thylacoleo carnifex (Owen 1859; Pliocene-Pleistocene; 1.14 m long) was a giant sugar glider like Petaurus. Thylacoleo had the strongest bite of any mammal with the largest, sharpest molars of any mammal. It had fewer but larger teeth than Petaurus. The manus included retractable claws. The pes had a very large heel bone (calcaneum). This supposedly carnivorous ‘marsupial lion’ nests with herbivores. Pedal digit 1 likely had a phalanx and claw, but it has not been shown.

References
Goldingay RL 1989. The behavioral ecology of the gliding marsupial, Petaurus australis. Research Online. University of Wollongong Thesis Collection. PDF
Owen R 1859. On the fossil mammals of Australia. Part II. Description of a mutilated skull of the large marsupial carnivore (Thylacoleo carnifex Owen), from a calcareous conglomerate stratum, eighty miles S. W. of Melbourne, Victoria. Philosophical Transactions of the Royal Society 149, 309-322. 
Waterhouse GR 1838. Observations on certain modifications observed in the dentition of the Flying Opossums (the genus Petaurus of authors). Proceedings of the Zoological Society of London. 4: 149–153.

wiki/Petaurus
wiki/Thylacoleo
https://australianmuseum.net.au/thylacoleo-carnifex

The koala (genus: Phascolarctos) joins the LRT

Something cute and fuzzy today.
As the koala (genus: Phascolarctos) is added to the large reptile tree (LRT, 1187 taxa, subset Fig. 1). And, based on phylogenetic bracketing, the case for carnivory in Thylacoleo (Fig. 4) fades.

Figure 1. The koala, Phascolarctos cinereus, nests between Thylacoleo + Vombatus and the interatheres and toxondontids in the herbivorous clade of the Marsupialia. Thylacoleo is the exceptional carnivore.

Everyone loves the koala.
It’s a cute climbing wombat.

Figure 2. Skeleton of the koala (genus: Phascolarctos)

Two ‘thumbs’
one big toe and two skinny central toes distinguish the auto podia of Phasolarctos.

Figure 3. Koala (Phascolarctos) skull. Note the differences between the photo and drawing.

The Thylacoleo problem
Smack dab in the middle of a long list of marsupial herbivores nests the marsupial lion, Thylacoleo (Figs. 4, 5) nesting here (Fig. 1) as a sister to the wombat, Vombatus. Said to be carnivorous due to its shearing post-canine teeth, it would be the exception in this clade of plant-eaters. Wait! Doesn’t Triceratops also have scissor-like shearing teeth? Maybe it’s the cat-like retractable claws found on Thylacoleo? Another tree-climber, Phasolarctos doesn’t have claw sheaths like Thylacoleo. This problem has surrounded Thylacoleo for decades and it won’t be solved here. More data below.

BTW,
the Arctocyon to Vincelestes clade (Fig. 1) are all carnivores, except Ernanodon, a likely ant/termite eater with blunt post-canine teeth.

Figure 4. Thylacoleo skeleton. This is another wombat with unusual hands and and feet… and teeth. Said to be carnivorous, it would be the exception in this clade of herbivores. The bony manus claws resemble those of cats, with a small bony core and large keratinous claws.  Look at the size of that calcaneum. This was not a speedy predator, if it was a predator at all.

This YouTube video
describes the finding of a complete and unburied Thylacoleo skeleton. About 45 minutes long, as I recall…

References

wiki/Thylacoleo
wiki/Koala

Eurygenium: another wombat close to Toxodon

This was a odd-looking cover taxon
in the Journal of Vertebrate Paleontology back in 1997 (Fig. 1).

Figure 1. Eurygenium is a smaller, less robust, longer legged version of Toxodon. The original reconstruction appears to be trying to feed itself with its right hand, but this appears to be unlikely based on phylogenetic bracketing and that antebrachium does not appear to be able to pronate.

Eurygenium latirostris (Ameghino 1894. E. pacegnum Shokey 1997; late Oligocene, 25 mya; 76 cm in length) was described by Shockey as close to the origins of Toxodontidae. That is confirmed here in the large reptile tree (LRT (1028 taxa), but no prior authors nested these taxa with wombats and marsupials as they do here. Most authors considered both taxa notoungulates, a taxon that has been dispersed and essentially invalidated here in the LRT.

Figure 2. Toxodon WAS a notoungulate placental. Now it’s a wombat marsupial. Now, just imagine tiny little toxodons or maybe just one tiny little toxodon in the marsupium of this beast. Wombats wear their pouches backwards, by the way. So if the baby wants to look outside the pouch, it sees a short thick tail wagging back and forth. Quite a sight, I’m sure, for baby and all outside observers.

Eurygenium is also close to Pyrotherium, and is from the same beds.

By the way…
Wombats wear their pouches backwards, so if the baby wants to look outside the pouch, it sees a short thick tail wagging back and forth. Quite a sight, I’m sure, for baby and all outside observers.

Figure 3. Toxodon and the much smaller Eurygenium to scale.

References
Shockey BJ 1997. Two new notoungulates (Family Notohippidae) from the Sall Beds of Bolivia (Deseadan: late Oligocene) : systematics and functional morphology. Journal of Vertebrate Paleontology 17(3):584-599.

Groeberia: no longer an enigma taxon and no longer an allothere

Wiikipedia reports,
“Groeberiidae is a family of strange non-placental mammals from the Eocene and Oligocene epochs of South America. Chimento et al. 2013 determined that Groeberia was a member of the Allotheria, a mammal clade not recovered in the large reptile tree (LRT, 1013 taxa). Simpson & Wyss 1999, considered Groberia relatives to be diprotodontians (wombats), By contrast McKenna 1980 claiming that considering them metatherians was “an act of faith”. The LRT supports that nesting as Groeberia nests with Vintana, another former enigma, both within the Metatheria (marsupials).

Groeberia minoprioi (Patterson 1952,  MMP 738) and G. pattersoni (Simpson 1970) are best known from a tall and narrow anterior skull and mandibles (Fig. 1) with an unusual set of teeth.

Figure 1. Groeberia drawing, photo and color-coded bones and teeth. This taxon nests with Vintana in the LRT and that canine-ish tooth must be a premolar because canines are unknown in this clade going back several nodes. As in related taxa, the jugal contacts the premaxilla. The descending process on the jugal is just appearing here.

The large reptile tree (LRT, 1012 taxa) nests Groeberia with Vintana (Fig. 2) among the wombats.

Note the large gnawing incisors backed up by an long upper premolar in the place usually occuupied by a canine. The tooth is not a canine because no more primitive relatives have a canine. Not also the small bump below the jugal. This becomes much longer in relatives like Vintana.

Figure 2. Vintana as originally illustrated. I added colors to certain bones. Note the high angle of the ventral maxilla and the deep premaxilla. Lateral view reduced to scale with other views.

References
Chimento NR, Agnolin  FL and Novas FE 2015. The bizarre ‘metatherians’ Groeberia and Patagonia, late surviving members of gondwanatherian mammals. Historical Biology: An International Journal of Paleobiology. 27 (5): 603–623. doi:10.1080/08912963.2014.903945]
McKenna MC 1980. Early history and biogeography of South America’s extinct land mammals.
Patterson B 1952. Un nuevo y extraordinario marsupial deseadiano. Rev Mus Mun Cienc Nat Mar del Plata. 1:39–44.

wiki/Groeberiidae

More notoungulates leave this extinct clade.

Some of the taxa I met this weekend, and you’ll meet shortly,
I’ve never heard of before. Even so, here’s another paleo story waiting to be told.

When I added
Protypotherium (Fig. 1) and Miocochilius (Fig. 2) to the large reptile tree (now 828 taxa, but not yet updated), I learned that they were both considered members of the Interatheridae, which Wikipedia considers,  “an extinct family of notoungulate mammals from South America.”

Figure 1. Protypotherium nests with Miocochilius and Homalodotherium in the LRT between mesonychids and paenungulates.

Earlier we learned
that all tested members of the Notoungulata do nest not with each other, but with a variety of established clades within the Theria. Some members of the invalid Notoungulata nested with wombats, others with various placentals. And today this issue keeps dragging on…

Figure 2. Miocochilius has reduced it imprint to just two functional fingers and toes. Look at those long horse-like teeth exposed by erosion of the bone.

So where there’s an Interatheridae…
there should be an Interatherium. And there is one (Fig. 3). Trouble is, the Interatherium skull with that crooked diastema did not look like the straight jawed full set of teeth found in Protypotherium and Miocochilius. So I added Interatherium to the LRT to find out.

Turns out, like many notoungulates before, 
that Interatherium nests with wombats, between Vombatus and Toxodon even though Interatherium is much smaller, longer, and leaner than its sisters. It also lacks digit 1 on all four extremities. Apparently there is a wide range of wombat/marsupial morphologies that we’re just now beginning to appreciate and identify. For instance, that notch and descending maxillary palate in Interatherium (Fig. 3) resemble those of the bizarre marsupial beaver-mimic wombat, Vintana, which also nests nearby.

Figure 3. Interatherium does not nest with notoungulates or other purported interotheres. Rather cat-sized Interatherium nests with wombats, between Vombatus and the giant Toxodon.

If Interatherium is a marsupial, 
the two placentals, Protypotherium and Miocochilius, cannot be interatheres. Or if they were defined as interatheres, that definition should be modified. Best to just call Protypotherium and Miocochilius typotheres — unless Typotherium turns out to be unrelated to these two, too.

Now,
as I look up “Typotherium,” I see it is better known by its senior synonym, Mesotherium, originally named, according to Wikipedia, in the belief that it was a transitional taxon between rodents and pachyderms. I have not tested Mesotherium (Fig. 4) yet, but with that diastema, it looks more like Interatherium, the wombat, than Protypotherium and Miocochilius, the condylarths. Only testing will tell, though…

Figure 4. Mesotherium. What is it, if not the long lost link between rodents and elephants?  Just kidding! I don’t see scale bars for this taxon, but Wiki reports it was the size of a small sheep at 55 kilograms (121 pounds. So it probably had a skull the size of a small sheep.

But wait, there’s more…
There was, indeed, a larger member of the Protypotherium and Miocochilius clade. Seems that the  clawed browser, Homalodotherium (Fig. 5), which I earlier nested with the clawed ungulate, Chalicotherium, now nests with Protypotherium and Miocochilius given the opportunity to do so (taxon exclusion rises again!). These three form a clade nesting between mesonychids (including hippos and Paleoparadoxia) and paenungulates (elephants, hyraxes and sea cows) where big front teeth rule, but tusks are not yet present in these three (yet-to-be-named clade) taxa. Maybe we should call this clade of three (so far) the new ‘Notoungulata’. Does that work for you? If someone can send me the reference for the origin of this term, we’ll see if that will fit or not.

Figure 6. Bear-sized Homalodotherium nests with cat-sized Protypotherium and Miocochilius. They all have a full arcade (11×4) of relatively flat teeth. Note the resemblance to Chalicotherium here, by convergence.

I’m catching up
but still behind in updating the pertinent web page at ReptileEvolution.com. It’s not easy, but I’m getting there.

References
Ameghino F 1882. Ungulata, Typotheria, Interatheridae. Catalog de la Prov. de Buenos Aires en la Expedicion Cont. Sud-America. March 1882. Boletino Instituto Geologia Argentino, June 1882. Cont. Conocimenient Mamif. Fosil. Repub. Argentina, in Accd. Nac. Cien., Cordoba 6:474-480. 1889.
Croft DA 2007. The Middle Miocene (Laventan) Quebrada Honda wildlife, southern Bolivia and a description of ITS Notoungulates. Palaeontology 50(1):277-303.
Huxley TH 1870. Anniversary address of the President of the Geological Society. Quarterly Journal of the Geological Society of London 26:42-64.
Stirton RA 1953. A new genus of interatheres from the Miocene of Colombia. University of California Publications in Geological Sciences 29: 265-348

wiki/Homalodotherium
wiki/Protypotherium
wiki/Miocochilius

 

 

Former ‘notoungulate’ Periphrangis is really a wombat

Periphrangis harmeri (Roth 1899; Fig. 1; Oligocene, 48-28 mya) has long been considered a notoungulate. Earlier the LRT nested two former notoungulates as wombats. Periphranigis also shares several wombat traits, including a jugal that contacts the jaw glenoid, procumbent incisors and a septomaxilla.

Figure 1. Periphrangis was considered a notoungulate, but it is clearly a wombat with four molars and a jugal that contacts the jaw glenoid, among several other identifying traits.

When we first looked at Haramiyavia
(Jenkins et al. 1997, Luo et al. 2005) here, this small Late Triassic mammal was considered a basal multituberculate. Now that several wombats have been added to the LRT Haramiyava could be another wombat. Wombats share procumbent incisors and a convex ventral mandible. Hard to tell with present data. In either case, both wombats and multituberculates are rather derived taxa for the Late Triassic.

Figure 2. Haramiyavia reconstructed and restored. Missing parts are ghosted. Three slightly different originals are used for the base here.

Arctocyon
(Fig. 3; Blainville 1841, Gould and Rose 2014; YPM VP 021233; 60 mya) was long and widely considered (see Wikipedia page) a primitive plantigrade ungulate condylarth procreodi placental.  In the LRT Arctocyon nests with basal carnivorous/omnivorous marsupials. Essentially it is a giant opossum, like Didelphis, but with a few derived traits, more like Thylacinus, a taxon that reduces the epipubes and molar count, hence the earlier traditional confusion. Just look at these taxa side-by-side. It’s obvious, but it’s also in the matrix scores.

Figure 3. Arctocyon mumak is no longer an ungulate placental, but a carnivorous marsupial, close to Thylacinus.

Small brains and long jugals extending to the jaw glenoid
also give them away as metatherians. Not sure why even recent authors (Gould and Rose 2014) are not seeing this. They must be counting molars.

References
Blainville HM 1841. Osteographie et description iconographique des Mammiferes récentes et fossiles (Carnivores) 1, 2 Paris.
Gould FDH and Rose KD 2014. Gnathic and postcranial skeleton of the largest known arctocyonid ‘condylarth’ Arctocyon mumak (Mammalia, Procreodi) and ecomorphological diversity in Procreodi. Journal of Vertebrate Paleontology 34(5):1180-1202.
Jenkins FA, Jr, Gatesy SM, Shubin NH and Amaral WW 1997. Haramiyids and Triassic mammalian evolution. Nature 385(6618):715–718.
Luo Z-X, Gatesy SM, Jenkins FA, Jr, Amaralc WW and Shubin NH 2015. Mandibular and dental characteristics of Late Triassic mammaliaform Haramiyavia and their ramifications for basal mammal evolution. PNAS 112 (51) E7101–E7109.
Roth S 1899. Aviso preliminar sobre mamíferos mesozóicos encontrados en Patagonia [Preliminary notice on Mesozoic mammals found in Patagonia]. Revista del Museo de La Plata 9:381-388