A surprising ancestor for kangaroos: Interatherium

Traditionally the short-faced kangaroo,
(genus: Procoptodon; Owen 1870; Pleistocene; Figs. 1, 3) was considered an aberrant taxon with a weirdly shortened face, so unlike that of traditional kangaroos, like Macropus (Fig. 1). However, by adding taxa, like Procoptodon and Dendrolagus (Fig. 1), to the large reptile tree (LRT, 1248 taxa, subset Fig. 4) Interatherium (Figs. 1,2) shifts over to become an ancestral kangaroo, despite lacking hopping legs and diprotodont teeth. The skulls of Interatherium and Procoptodon are incredibly similar, even if the post-crania and dental formula of Procoptodon has evolved.

Figure 1. Skulls of kangaroo ancestors and sisters, including Procoptodon (short-faced kangaroo) alongside Interatherium (ancestral kangaroo) and Dendrolagus (basal kangaroo). Interatherium does not have diprotodont dentition.

Figure 1. Skulls of kangaroo ancestors and sisters, including Procoptodon (short-faced kangaroo) alongside Interatherium (ancestral kangaroo) and Dendrolagus (basal kangaroo). Interatherium does not have diprotodont dentition. Nambaroo nests within Glires, not Metatheria.

Interatherium (Mid-Miocene)
has not been linked to Procoptodon (Pleistocene) before.

And why should it?

  1. Balbaroo (Flannery, Archer and Plane, 1983; Black et al. 2014, Middle Miocene) was hailed as a kangaroo ancestor, but in the LRT it nests with the phalanger, Phalanger
  2. Cookeroo bulwidarri (Butler et al. 2016; Late Oligocene, Early Miocene, 23-18mya)was hailed as a non-hopping kangaroo ancestor. The LRT has not tested it yet, but it looks like Macropus (Fig. 1).
  3. Palaeopotorous priscus (den Boer and Kear 2018; middle Miocene) was hailed as a non-hopping kangaroo ancestor, based on teeth.
  4. Tradition considers Interatheriidae “an extinct family of notoungulate (placental) mammals from South America, known from the Eocene through the Miocene. These animals were principally small-sized, occupying a habitat like hares and marmots.The majority were very small, like rodents.”
  5. Interatherium has four fingers (Fig. 2), lacking a thumb (convergent, it turns out, with Protypotherium, a placental herbivore traditionally considered related). Kangaroos retain five fingers (but I’d like to see a good X-ray or something similar).
Figure 2. Interatherium is the surprising ancestor of kangaroos, with a special affinity to the short-face kangaroo.

Figure 2. Interatherium is the surprising ancestor of kangaroos, with a special affinity to the short-face kangaroo.

Current DNA studies
place a small wallaby, Lagostrophus, at the base of their kangaroo cladogram, but Lagostrophus already has diprodontid teeth. That’s too easy. We’re looking for an earlier, more primitive taxon, without obvious kangaroo traits.

Figure 4. Procoptodon is a basal kangaroo, close to Interatherium (Fig. 3).

Figure 3. Procoptodon is a basal kangaroo, close to Interatherium (Fig. 3). Here longer legs and longer feet differentiate this taxon from Interatherium.

Interatherium (Miocene) represents a late-surviving member
of a much earlier (Late Jurassic) kangaroo radiation, in which the interathere clade lost its thumb. Alternate scenario: perhaps the thumb was never collected in the matrix. The epipubes were likewise somehow overlooked, though I think I see them is an online image of an in situ fossil. More data needed here.

This Late Jurassic kangaroo genesis
is based on the Early Cretaceous appearance of Anebodon, a kangaroo cousin more closely related to the extant marsupial mole, Notoryctes. These burrowers, in turn, have more kangaroo-like sister taxa, today represented by the bandicoot Perameles and the biliby, Macrotis, which combine long hind limbs and digging front limbs.

Note, the front dentary teeth of Interatherium
(Fig. 1). The change to diprotodonty (two anterior fangs) has not happened yet in Interatherium, but the canines are on the way out and the squamosals are very tall.

Figure 4. Subset of the LRT focusing on the Metatheria (=Marsupials). Here the diprotodont dentition evolved twice.

Figure 4. Subset of the LRT focusing on the Metatheria (=Marsupials). Here the diprotodont dentition evolved twice.

Interatherium rodens (Ameghino 1887, 1894; Middle Miocene; 50cm in length) the Interatheridae and Interatherium were long considered members of the Notoungulata, a clade that has broken up in the LRT. Here (Fig. 4) Interatherium nests at the base of the kangaroos, derived from the more basal marsupials like Eomaia. Interatherium retains several small incisors, but apparently has lost its thumb, unlike kangaroos.

Note
that Interatherium, nesting at the base of the kangaroo clade (Fig. 4), is also the sister to the Toxodon + the wombat (genus: Vombatus) clade. There the diprotodont dental pattern appears by convergence because, like Interatherium, basal taxa (genus: Eurygenium, late Oligocene, and Toxodon) lack a diprotodont dental pattern.

Goodbye, Diprotodontia.
The clade Diprotodontia is no longer monophyletic (Fig. 4) and can no longer be exclusively defined by the diprotodont dental pattern, which now appears twice within the Metatheria. Please test this heresy and let me know what you get. Taxon exclusion is once again the problem here.

References
Ameghino F 1887. Observaciones generales sobre el orden de mamíferos estinguidos sud-americanos llamados toxodontes (Toxodontia) y sinopsis de los géneros y especies hasta ahora conocidos. Anales del Museo de La Plata 1:1-66.
Ameghino F 1894. Enumeration synoptique des especes de mammifères fossiles des formations éocènes de Patagonie. Boletin de la Academia Nacional de Ciencias en Cordoba (Republica Argentina) 13:259-452.
Black KH et al. 2014. A New Species of the Basal “Kangaroo” Balbaroo and a Re-Evaluation of Stem Macropodiform Interrelationships. PloseOne https://doi.org/10.1371/journal.pone.0112705
den Boer W and Kear BP 2018. Is the fossil rat-kangaroo Palaeopotorous priscus the most basally branching stem macropodiform? Journal of Vertebrate Paleontology; e1428196 DOI: 10.1080/02724634.2017.1428196
Butler K, Travouillon KJ,Price GJ, Archer M and Hand SJ 2016. Cookeroo, a new genus of fossil kangaroo (Marsupialia, Macropodidae) from the Oligo-Miocene of Riversleigh, northwestern Queensland, Australia. Journal of Vertebrate Paleontology. doi:10.1080/02724634.2016.1083029.
Cooke BN 2000. Cranial remains of a new species of balbarine kangaroo (Marsupalia: Macropodoidea) from the Oligo-Miocene freshwater limestone deposits of Riversleigh World Heritage Area, Northern Australia. Journal of Paleontology 74(2) 317-26.
Flannery TF, Archer M and Plane MD 1983. Middle Miocene kangaroos (Macropodoidea: Marsupialia) from three localities in northern Australia, with a description of two new subfamilies. Bureau of Mineral Resources, Journal of Australian Geology and Geophysics 7: 287–302.
Owen R 1873. Procoptodon goliah, Owen. Proceedings of the Royal Society of London 21, 387.

wiki/Interatherium
wiki/Lagostrophus
wiki/Procoptodon
http://www.abc.net.au/news/2016-02-19/extinct-non-hopping-species-may-be-ancestors-of-kangaroo/7185650
Palaeopotorous PR: https://www.sciencedaily.com/releases/2018/04/180411111019.htm

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Metathere (aka: marsupial) issues

Metatherians
(aka marsupials) can be a difficult clade to understand phylogenetically. Taxon exclusion, as usual, causes problems, here and elsewhere. Case in point: recently adding taxa to the large reptile tree (LRT, 1247 taxa) shifted and clarified some prior interrelationships in which certain untenable dental patterns appeared. This was cause for concern and re-study. I’m pleased to report that the herbivorous metathere subset of the tree topology did change to a more logical and gradual pattern after adding several taxa. Now the dental atavisms no longer appear. But this new topology comes at the cost of recovering a dual and parallel origin for the diprotodont form of dentition (Fig. 1) in which the anteriormost dentary teeth are larger than typical canines and jut out anteriorly.

Figure 1. Marsupial mandibles. Traditional diprodonts have two large anterior dentary teeth. These arose twice in the LRT.

Figure 1. Marsupial mandibles. Traditional diprodonts have two large anterior dentary teeth. These arose twice in the LRT with the present list of taxa, once with kangaroos, and again with wombats. See figure 3.

First and second,
let’s take a look at two previously published metatherian tree topologies: Horovitz and Sánchez-Villagra 2003 (which covers many living and some extinct taxa) and Williamson, Brusatte and Wilson 2014 (in which taxa are all Cretaceous or earlier and most are known from isolated teeth). The LRT includes no tooth-only taxa… and that’s a good thing.

Horovitz and Sánchez-Villagra 2003 (Fig. 2) employed bones and soft tissue.
From their abstract: “We… assembl[ed] a morphological data matrix consisting of a new suite of 149 postcranial characters and incorporated a series of previously published data on the craniodental (76 characters) and soft tissue (5 characters) anatomy. Twenty-one marsupial terminal taxa representing all the major radiations of marsupials and 10 outgroups… were investigated. All currently accepted marsupial orders were recovered by the analysis.”

Figure 1. A cladogram of metatherian mammals based on skeletal and soft traits by Horovitz and Sánchez-Villagra 2003.

Figure 2. A cladogram of metatherian mammals based on skeletal and soft traits by Horovitz and Sánchez-Villagra 2003. This cladogram lacks a large number of carnivorous metatherians, a large number of basal prototheres and a large number of basal eutherians. On the other hand, the LRT is missing the uncolored taxa. Colors correspond to the metathere subset of the LRT (Fig. 3). Horovitz and Sánchez-Villagra 2003 recovered a monophyletic Diprotodontia in contrast to the LRT.

More recently,
Williams et al. 2014 reported, “Our understanding of this group has increased greatly over the past 20 years, with the discovery of new specimens and the application of new analytical tools. Here we provide a review of the phylogenetic relationships of metatherians with respect to other mammals, discuss the taxonomic definition and diagnosis of Metatheria, outline the Cretaceous history of major metatherian clades, describe the paleobiology, biogeography, and macroevolution of Cretaceous metatherians, and provide a physical and climatic background of Cretaceous metatherian faunas.” They built their study on Williams 2012, which focused on teeth. They report, “As in the previous analysis of Williamson et al. (2012), homoplasy is rampant.” Hmm. That’s a phrase I used to describe character distribution in the LRT!

Williams et al. 2014 reported, 
“The oldest confidently identified therian fossil is the eutherian Juramaia from the early Late Jurassic (ca. 160 million years old) of China (Luo et al. 2011).” The LRT nests Juramaia as a basalmost prototherian. They considered Sinodelphys (Early Cretaceous, 120 mya) to be the oldest known marsupial. In 2015 (a year after Williams et al.) Agilodocodon (Middle Jurassic, 170 mya) was announced as a docodont (but nests with Eomaia, Early Cretaceous, 125 mya) in the LRT.

Williams et al. 2014 reported, 
“Deltatheroidans were long regarded as eutherians (Gregory and Simpson 1926; Van Valen 1966) or stem boreosphenidan species (Fox 1974; Kielan-Jaworowska et al. 1979), but are now generally accepted as basal metatherians (Butler and Kielan-Jaworowska 1973; Kielan-Jaworowska and Nessov 1990; Rougier et al. 1998).” The LRT confirms a nesting within the Metatheria for Deltatheridium, not as a sister.

Williams et al. 2014 reported,
“The interrelationships of most major metatherian subclades are unresolved.” This is due to taxon exclusion and using too many tooth-only taxa. On the other hand, the metatherian taxa and clades within the LRT are fully resolved. The two studies share only 4 taxa in common so the Wiliams et al. cladogram will not be shown. Despite the availability of museum specimens, no extant taxa were used in Williams et al. 2014 study, which concentrated on Cretaceous taxa to the detriment of the study.

Maybe it would have been better
for Williams et al. 2014 to first establish relationships using extinct and extant skeletons of a wide gamut of mammals, as the LRT does, and then see where the tooth-only taxa fit in.

Figure 1. Subset of the LRT focusing on the Metatheria (=Marsupials). Here the diprotodont dentition evolved twice.

Figure 3. Subset of the LRT focusing on the Metatheria (= Marsupials). Here the diprotodont dentition evolved twice.

 

 

More on metatherians soon…

References
Horovitz I and Sánchez-Villagra MR 2003. A morphological analysis of marsupial mammal higher-level relationships. Cladistics 19(3):181 – 212.
DOI: 10.1111/j.1096-0031.2003.tb00363.x
Myers P, Espinosa R, Parr CS, Jones T, Hammond GS and Dewey TA 2018. The Animal Diversity Web (online). Accessed at https://animaldiversity.org.
info@tree-kangaroo.net
Williamson TE, Brusatte SL and Wilson GP 2014. The origin and early evolution of metatherian mammals: the Cretaceous record. ZooKeys 465:1–76.

doi: 10.3897/zookeys.465.8178
http://zookeys.pensoft.net

Let’s look at bandicoots!

Although bandicoots
(genus: Perameles, Fig. 1) are omnivores, they are basal taxa in the herbivorous metatherian clade in the large reptile tree (LRT, 1242 taxa, Fig. 4). They are closest to digging and burrowing marsupials, like the golden mole, Notoryctes, yet still close to the ancestry of the fast, leaping kangaroos, like Macropus. And they are derived from a sister to Arctocyon, the large carnivore.

Figure 1. Perameles nasuta, the long-nosed bandicoot, nests as basal member of the herbivorous marsupials.

Figure 1. Perameles nasuta, the long-nosed bandicoot, nests as basal member of the herbivorous marsupials. Look at those huge lumbar vertebrae! Scale bar = 1cm.

Perameles nasuta (Geoffroy 1804, extant, 40 cm long) is the long nosed bandicoot. This basal marsupial is a nocturnal omnivore, like its ancestor Didelphis (Fig. 2). It has a rear-facing pouch, three long digging fingers, two short ones and a pes dominated by pedal digit 4. Digits 2 and 3 were reduced to grooming claws, as in kangaroos. Gestation lasts a mere 12.5 days, then the young spend another 8 weeks in the marsupium. The long nose of bandicoots is a basal trait retained by Ukhaatherium and prototheres like Cronopio and Juramaia.

YouTube videos
of bandicoots show they have a high metabolism and can scoot away rapidly, like rats or rabbits, distinct from their slower moving opossum ancestors. Of course, Perameles was ancestral to kangaroos, like Macropus (Fig. 3), so their leaping ability is nascent here and their odd feet are nearly identical. Kangaroo hands are still primitive with five sub-equal fingers, not evolved for digging, like odd hand of Perameles (Fig. 1).

According to Wikipedia
“The position of the Peramelemorphia within the marsupial family tree has long been puzzling and controversial. There are two morphological features in the order that appear to show a clear evolutionary link with another marsupial group: the type of foot, and the teeth. Unfortunately, these clear signposts point in opposite directions.” The LRT solves this problem by nesting omnivorous Perameles at the base of the herbivores and allowing for convergence between the large kangaroo and wombat anterior dentaries.

Adding taxa
is helping to clarify phylogenetic relationships among the marsupials. We’ll look at these soon.

References
Geoffroy E. 1804. Mémoire sur un nouveau genre de mammifères á bourse, nommé Perameles. Annales de la Musee National d’ Histoire Naturelle de Paris 4: 56–64.

Ukhaatherium: a late-surviving Morganucodon in the LRT

Ukhaatherium nessovi (Late Cretaceous, Novacek et al. 1997) has traditionally been nested with the proto-placental, Asioryctes. Here in the large reptile tree (LRT, 1243 taxa), Ukhaatherium nests as a basal therian in the large reptile tree. Morganucodon (Latest Triassic/Earliest Jurassic, Küehne 1949) nests with Ukhaatherium, with virtually identical scores and are similar in size.

Figure 1. Morganucodon skull in several views. Compare to Ukhaatherium in figure 2.

Figure 1. Morganucodon skull in several views. Compare to Ukhaatherium in figure 2.

When you see them together,
(Figs. 1,2) the similarities between Morganucodon and Ukhaatherium are strikingly obvious.

Figure 2. Skull and dentition of Ukhaatherium. Compare to Morganucodon in figure 1.

Figure 2. Skull and dentition of Ukhaatherium. Compare to Morganucodon in figure 1.

The long snout of prototheres
is retained in basal therians like Morganucodon and Ukhaatherium. The epipubic bones found in Ukhaatherium are no surprise in the LRT, where it nests in the middle of other taxa that share this trait.

Figure 3. Ukhaatherium in situ.

Figure 3. Ukhaatherium in situ.

Rowe 1988 defined Mammaliaformes
as Morganucondontidae + Mammalia. Here Morganucodontidae nest within the Mammalia, so Mammaliaformes is a junior synonym of Mammalia.

Figure 3. Subset of the LRT with the addition of Perameles and Morganucodon.

Figure 4. Subset of the LRT with the addition of Perameles and Morganucodon. Sharp-eyed readers with good memories will not subtle changes in this tree near protorotheres.

And, by the way,
Ukhaatherium + Morganucodon is still close to Asioryctes in the LRT. If we let a little time go by from the Latest Triassic to the Latest Cretaceous, then that’s enough time for the tiny posterior jaw bones in Morganucodon to evolve into the tiny ear bones of Ukhaatherium, convergent and parallel to those of other therian and prototherian mammals (which already show distinct patterns in this regard).

References
Kuehne WG 1949. On a triconodont tooth of a new pattern from a fissure-filling in South Glamorgan. Proceedings of the Zoological Society of London 119:345-350
Novacek MJ, Rogier GW, Wible JR, McKenna MC, Dashzev g D and Horovitz I 1997. Epipubic bones in eutherian mammals from the Late Cretaceous of Mongolia Nature 389: 483-486.
Rowe TS 1988. Definition, diagnosis and origin of Mammalia. Journal of Vertebrate Paleontology 8(3):241–264.

wiki/Ukhaatherium
wiki/Morganucodon

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. Petaurus breviceps skeleton in two views, plus a skull with mandible, lacking in the skeleton.

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.

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.

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.

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.

The sugar glider in vivo.

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 glidersquirrel glidermahogany glidernorthern glideryellow-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 2. Thylacoleo skeleton compared to Petaurus skeleton to scale.

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.

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.

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)

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

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.

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

Masrasector: not a placental… a killer marsupial

Of course, by that I mean,
skunk-sized Masrasector nananubis (Fig. 1; Simons and Gingerich 1974; Borths and Seiffert 2017), like other hyaenodonts in the LRT (Fig. 2), is also a marsupial… a descendant of a sister to the quiet little, nocturnal Virginia opossum (Didelphis, Fig. 2), but closer to Borhyaena.

[Note: everyone agrees that hyaenodonts are NOT related to hyaenas.]

Taxon exclusion,
based on tradition, evidently keeps marsupials out of current phylogenetic analyses of hyaenodonts. Hopefully that will be corrected, or at least tested, in the future.

Hyaenodonts,
like Masrasector, are traditionally considered placental (eutherian) carnivorous creodonts. They have not one, but three carnassial teeth.

According to the LRT,
that was by convergence. Certain bats also have carnassial teeth. So it can happen.

By contrast
the large reptile tree (LRT, 1066) nests Masrasector and all other hyaenodonts as marsupial carnivores. Borths and Seiffert (2017) did not expand their taxon list to include marsupials and thus, taxon exclusion implanted a deadly flaw in their otherwise brilliant and technical paper.

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

Figure 2. Arctocyon is no longer an ungulate placental, but a carnivorous marsupial.

Borths and Seiffert note:
“Body mass in hyaenodonts is difficult to estimate because there are no living taxa analogous to these large-headed placental carnivores with multiple carnassials.”

“The most surprising part of this study was that Masrasector and its kin are part of a massive radiation of hyaenodonts that originated in Africa.” 

“Hyaenodonts have been a little neglected as a group.”

Wikipedia reports on the history of the Creodonta:
“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.[12] 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.”

Figure 2. Masrasector nests with Borhyaena in the marsupial clade.

Figure 3. Masrasector nests with Borhyaena in the marsupial clade.

Earlier we looked at members at the base of this clade, like Amphicyon and Arctocyon (Fig. 2), giant closer descendants of Didelphis. Hyaenodonts and other creodonts are different from members of the Carnivora because they’re not placentals, something that has escaped the notice of paleontologists. Creodonts / hyaenodonts appear earlier in the fossil record because marsupials appear before placentals.

References
Borths MR, Seiffert ER 2017. Craniodental and humeral morphology of a new species of Masrasector (Teratodontinae, Hyaenodonta, Placentalia) from the late Eocene of Egypt and locomotor diversity in hyaenodonts. PLoS ONE 12(4): e0173527.
Simons EL, Gingerich PD 1974. New carnivorous mammals from the Oligocene of Egypt. Annals of the Geological Survey of Egypt. 1974; 4: 157–166.
Author interview online here.
Pasttime.org podcast interview here.