Argyrolagus: a South American kangaroo!

Earlier we looked at giant South American wombats, like Toxodon and Pyrotherium. And, of course, the basal stem marsupial, Didelphis, still lives in North America. So don’t be too surprised to find kangaroos (Figs. 1-4)  and other unrecognized derived marsupials in South America. They were there!

First you find them in the ground,
then you find them in a large gamut cladogram where taxa nest themselves with a miniimum of traditional bias.

Simpson 1970 reported, “Argyrolagids are marsupials, but show no clear affinity with any others known. They probably arose from didelphids independently of other known families and are distinct at the superfamily level, at least.” Well, all marsupials and placentals arose from didelphids in the large reptile tree, but let’s save that cladogram (Fig. 4) for later.

Sanchez-Villagra and Kay 1997 reported, “The Argyrolagidae are one of the most enigmatic extinct groups of South American mammals.” Several workers have even questioned the marsupial affinities of this clade. What they needed was the LRT.

Argyrolagids look like little kangaroos.
They probably hopped like little kangaroos. So what set them apart from kangaroos? Turns out, not much…

Argyrolagus palmeri and Proargyrolagus bolivianus (Fig. 1; Ameghino 1904; Simpson 1970, Sanchez-Villagra and Kay 1997; Late Oligocene, Plio-Pleistocene)) was just added to the large reptile tree (LRT, 1031 taxa), and it nested with a big kangaroo, Macropus (Fig. 2).

So why was Argyrolagus
EVER considered an enigma? Is it because kangaroos don’t live in South America? Or is this yet another case of taxon exclusion?

Figure 1. The skull of Proargyrolagus and an illustration of Argyrolagus. The traits shown here align very closely with Macropus, the kangaroo, to no one's surprise... so why was this considered an enigma taxon?

Figure 1. The skull of Proargyrolagus and an illustration of Argyrolagus. The differences are subtle yet notable. In either case, the traits shown here align very closely with Macropus, the kangaroo (see figure 2). So why were these considered enigma taxa?

Perhaps so.
Online I don’t see many cladograms that include both taxa. In the large gamut  reptile tree Argyrolagus shares nearly all of its tested traits with Macropus, the kangaroo (Fig. 2) and it’s easy to see why. The small list of differences incude: smaller size, four premaxillary teeth, naris open ventrally, caudals 3x longer than tall, lack of a maxillary diastema.

Figure 2. The extant kangaroo, Macropus, nests as a sister to Proargyrolagus in the LRT.

Figure 2. The extant kangaroo, Macropus, nests as a sister to Proargyrolagus in the LRT. Even the pelvis in lateral view looks like the one n Argyrolagus.

Based on their similar small size
Argyrolagus has been compared to extant ricocheting rodents, like kangaroo rats. Surprisingly and apparently argyrolagids haven’t yet been compared to real kangaroos in a phylogenetic analyses.

Argyrolagids and toxodontids are found in South America.
Kangaroos and wombats come from Australia. 180–140 million years ago, during the Jurassic, Gondwana split these related taxa apart. So their genesis and radiation must have been earlier, perhaps in the early Jurassic.

If you know of a paper
that includes both Argyrolagus and Macropus as taxa, and they nest far from each other, let me know. I’d like to learn the details. This could be a grand case of homoplasy. But at present, we’re looking at overlooked homology and both giant wombats and tiny kangaroos in Bolivia.

On a similar note
Smithsonian online mentioned the roots of kangaroos and wombats in South America. The article referenced Nilsson et al. (Fig. 3) who studied the genomics of Australian and South American marsupials. They report, “The evolutionary relationships among the seven marsupial orders have, however, so far eluded resolution.  In particular, the relationships between the four Australasian and three South American marsupial orders have been intensively debated since the South American order Microbiotheria was taxonomically moved into the group Australidelphia.The four Australasian orders share a single origin with Microbiotheria as their closest sister group, supporting a clear divergence between South American and Australasian marsupials. Placing the retroposon insertion pattern in a paleobiogeographic context indicates a single marsupial migration from South America to Australia.” (Marsupials are resolved in the LRT).

Figure 3. Phylogenetic tree of marsupials derived from retroposon data from Nilsson et al. No extinct taxa are shown here.

Figure 3. Phylogenetic tree of marsupials derived from retroposon data from Nilsson et al. No extinct taxa are shown here.

Nilsson et al. 2010 further report,
Dromiciops is clearly only distantly related to Australian marsupials, supporting a single Gondwanan migration of marsupials from South America to Australia.” In the LRT Dromiciops, a South American opossum, is closely related to tested marsupials (Fig. 4) from Australia and South America.

Figure 4. Geographic distribution of basal Theria, focusing on marsupials.

Figure 4. Geographic distribution of basal Theria, focusing on marsupials. Patterns are just beginning to emerge with this number of taxa all radiating before the mid-Jurassic splitting of Gondwana.

The geographical radiation of basal therians
(Fig, 4) indicates a world-wide distribution with both marsupials and placentals (metatherians and eutherians) arising out of Asia before being restricted to North America (Didelphis), South America, Madagascar and Australia. At least that’s how it looks with this admittedly small sample set.

References
Ameghnino F 1904. Nuevas especies de mamíferos, cretáceos y terciarios de la República Argentina [New species of mammals, Cretaceous and Tertiary, from the Argentine Republic]. Anales de la Sociedad Cientifica Argentina 56–58:1-142.
Nilsson MA et al. (6 co-authors) 2010. Tracking marsupial evolution using archaic genomic retroposon insertions. https://doi.org/10.1371/journal.pbio.1000436
Sanchez-Villagra MR and Kay RF 1997. A skull of Proargyrolagus, the oldest argyrolagid (Late Oligocene Salla Beds, Bolivia), with brief comments concerning its paleobiology. Journal of Vertebrate Paleontology 17(4):717-724.
Simpson GG 1970. The Argyrolagidae, extinct South American marsupials. Bulletin of the Museum of Comparative Zoology 139, 1–86.

wiki/Argyrolagus

Oops! What’s wrong with this picture?

So far you’ve learned so much about the skeletons of vertebrates. Now, can you tell what is wrong with the published image below? It will be obvious once you know what to look for. Scroll down for the solution.

Figure 1. Can you tell what is wrong with this picture of a museum mount of Ernanodon published in Vickers-Rich and Rich 1993?

Figure 1. Can you tell what is wrong with this picture of a museum mount of Ernanodon published in Vickers-Rich and Rich 1993?

Earlier we looked at and nested the basal marsupial, Ernanodon (Figs. 1, 2). The museum mount published in Vickers-Rich and Rich 1993, has one glaring error. Can you spot it?

Ernanodon anteilos (Ting [Ding] 1979; Paleocene; 50 cm in length) was originally considered placental mammal, perhaps a primitive anteater, then regarded as a primitive pangolin, like Manis. Here Ernanodon nests with Hyaenodon and Deltatheridum as a creodont marsupial, sharing large canines with both.

The skull was robust with a jaw joint nearly as far back as the occiput. The claws were broad and long, ideal for digging. The tail was long, but very slender.

Figure 2. Here is the same museum mount repaired in Photoshop. The pelvis was originally installed backwards. Here the pelvis is correctly mounted.

Figure 2. Here is the same museum mount repaired in Photoshop. The pelvis was originally installed backwards. Here the pelvis is correctly mounted.

Answer
The pelvis of the museum mount was installed backwards. Here (Fig. 2) the pelvis has been flipped in Photoshop to its correct position.

References
Ding SY 1979. A new edentate from the Paleocene of Guangdong. Vertebrata PalAsiatica 17:57–64. [Chinese 57–61; English 62–64].
Vickers-Rich P and Rich TH 1993. Wildlife of Gondwana. REED, Chatswood, Australia. 276 pp.

wiki/Ernanodon

Vintana and the vain search for the clades Allotheria and Gondwanatheria

Figure 1. 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.

Figure 1. 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.

Earlier we looked at Vintana (Fig. 1, Krause et al. 2014a, b). To Krause et al. Vintana represented the first specimen in the clades Allotheria and Gondwanatheria to be known from more than teeth and minimal skull material.

To Krause et al. 
Allotheria included Multituberculata and nested between the clade Eutriconodonta (including Repenomamus and Jeholodens) and the clade Trechnotheria (including the spalacotheres Maotherium and Akidolestes) and Cronopio, Henkelotherium, Juramaia, Eomaia, Eutheria and Metatheria.

Taxon exclusion issues
The large reptile tree (LRT, 1005 taxa) did not recover the above clades or relationships. Alotheria does not appear in the LRT.

  1. Multituberculata, Henkelotherium and Maotherium nest within Glires (rats and rabbits and kin) in the LRT.
  2. Repenomamus and Jeholodens nest within the pre-mammalian trityllodontid cynodonts in the LRT.
  3. Akidolestes nests within basal Mammalia, close to Ornithorhynchus in the LRT.
  4. Cronopio and Juramaia nest within basal Mammalia between Megazostrodon and Didelphis in the LRT.
  5. Eomaia nests at the base of the Metatheria in the LRT.
  6. Vintana nests with Interatherium among the derived Metatheria (marsupials), with wombats, like Vombatus and Toxodon in the LRT.

Despite a paper in Nature
and a memoir of 222 pages in the Journal of Vertebrate Paleontology; despite CT scans and firsthand examination with electron microscopes; despite being examined and described by many of the biggest name and heavy hitters in paleontology… Krause et al. never understood that Vintana was just a derived wombat, evidently due to taxon exclusion problems.

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.

Figure 2. Interatherium does not nest with notoungulates or other purported interotheres. Rather cat-sized Interatherium nests with wombats,with Vintana,  between Vombatus and the giant Toxodon

The large reptile tree now includes
1005 taxa, all candidates for sisterhood with every added taxon. Despite the large gamut of 74 taxa employed by Krause et al. they did not include the best candidates for Vintana sisterhood. Perhaps the fault lies in the reliance of prior studies and paradigms. Perhaps the fault lies in the over reliance by Krause et al. and other mammal workers, on dental traits. Perhaps the fault lies in the absence of pertinent sisters to the above-named taxa, including Interatheriium for Vintana.

In any case
Vintana does not stand alone as the only taxon in its clade represented by skull material. Based on its sisterhood with Interatherium, we have  pretty good idea what its mandibles and post-crania looked like. Yes, Vintana is weird. But Interatherium is also weird in the same way, just not as weird.

The LRT has dismantled and invalidated
several other clades, too, Ornithodira and Parareptilia among them.

References
Krause DW, Hoffmann S, Wible JR, Kirk EC, and several other authors 2014a. First cranial remains of a gondwanatherian mammal reveal remarkable mosaicism. Nature. online. doi:10.1038/nature13922. ISSN 1476-4687.
Krause DW et al. 2014b. Vintana sertichi (Mammalia, Gondwanatheria) from the Late Cretaceous of Madagascar. Journal of Vertebrate Paleontology Memoir 14. 222pp.

wiki/Vintana
pterosaur heresies – Vintana

Necrolestes: 125 year-old assessment beats recent analysis.

As usual
I had second hand (academic papers and figures) rather than firsthand access to the specimens. It doesn’t matter how good your players are if you don’t show up on the right field at the proper hour. Here you’ll see, once again, how excluding the actual sister to an enigma taxon is the major problem, solvable by second-hand phylogenetic analysis in a large gamut study, the large reptile tree (LRT) that minimizes the problem of taxon exclusion.

Figure 1. Necrolestes skull. Note the scale bar problems. DGS colors the bones here.

Figure 1. Necrolestes skull. Note the scale bar problems. DGS colors the bones here. The lacrimal and infraorbital are enlarged here, providing a large opening for large facial nerves. Note the larger lower incisors as compared to the drawing above.

Necrolestes patagonensis  (Ameghino 1891; early Miocene, 16mya; Fig. 1; YPM PU 15065, 15384, and 15699) has been argued about for over a hundred years. Originally (Ameghino 1891) it was described as the only known extinct placental “insectivore” from South America and allied to Chrysochloris (Fig. 2), the extant golden mole.

Well done Ameghino!

Unfortunately, as time went on…
Saban 1954 considered Necrolestes a palaeanodont (Ernanodon was previously considered one). Patterson 1958 considered it a borhyaenoid metatherian. Asher et al. 2007 looked at several candidates and could not make a firm conclusion. Ladevèze et al. 2008 supported metatherian affinities. Goin et al. 2008 also could not be specific with regard to a closest known sister taxon.

The latest paper on the subject
Rougier et al. 2012 reported, “earlier studies leaned toward placental affinities and more recent ones endorsed either therian or specifically metatherian relationships.” Ultimately they nested Necrolestes with Cronopio (Fig. 4) which they considered a non-therian mammal. That is correct. They considered an earlier Van Valen 1988 statement  inspired, “…the enigmatic Miocene genus Necrolestes, usually thought to be a marsupial, is [conceivably] a late surviving Gondwantherian pantothere.” That is incorrect.

Figure 2. Chrysochloris skull lateral view. Note the many similarities to Necrolestes, including a ventral naris, expanded bulla, and similar shapes for the other bones.

Figure 2. Chrysochloris skull lateral view. Note the many similarities to Necrolestes, including a ventral naris, dorsally expanded bulla, and similar shapes for the other bones. Note the orbit is very tiny in this burrowing taxon. I don’t see an infraorbital foramen. here, distinct from Necrolestes.

Asher et al. 2007 report,
“Characters that support [Necrolestes] status as a therian mammal include a coiled cochlear housing of the inner ear. Necrolestes shows similarities to eutherian mammals, such as small incisive foramina and possibly three molars. Consistent with its status as a metatherian is the presence of five upper incisors, transverse canal foramina, and a broad proximal fibula. However, we cannot confirm other characters claimed by previous researchers as evidence for affinity with marsupial or nonplacental mammals, such as the presence of an inflected mandibular angle and epipubic bones.”

Asher et al. report,
“The external digital flexor in Chrysochloris ossifies along nearly the entire forearm, from the humeral medial epicondyle to the carpus. Necrolestes shows a similarly elongate element stretching proximally from the carpus.”

Asher et al. report,
“The idea that [Necrolestes] is related to golden moles was favored in the first two publications describing its anatomy (Ameghino, 1891; Scott, 1905). We do not believe Patterson’s contention that the status of Necrolestes as a marsupial is ‘‘virtually assured’’. We admit that the list of possible taxonomic affiliations for this animal still remains long.”

Figure 1. The Golden Mole (Chrysocloris asiaticus) nests with the tree shrew and elephant shrew in the large reptile tree, not the common mole. Image copyright Digimorph.org and used with permission.

Figure 3. The Golden Mole (Chrysochloris asiaticus) nests with the tree shrew and elephant shrew in the large reptile tree, not the common mole. Image copyright Digimorph.org and used with permission.

 

 

The large reptile tree
(920 taxa) tested Necrolestes against a wide gamut of mammal candidates and nested it securely with the golden mole, Chrysochloris. To shift Necrolestes next to Cronopio adds 22 steps.

Distinct from sister taxa
Necrolestes had five upper incisors and four lowers. That is closer to the primitive numbers for mammals and two more than in Chrysochloris. The molars are also primitive in having fewer cusps, but that also happens in whales and armadillos… and golden moles… with their simplified zalambdodont teeth… so let’s focus on other traits. Dental traits are plastic and can lead analysis astray.

Rougier et al. report,
“the first upper and lower premolars are double rooted and the following five molariform elements are single rooted, a condition shared only with the recently described meridiolestidan mammal Cronopio.” Convergent dental traits might be leading these workers so far afield the neglected to add Chrysochloris to their analysis, which seems odd and dangerous based on the long list of shared traits and overall similarity, not by convergence.

Figure 4. Cronopio nests between Juramaia and Didelphis + Ukhaatherium in the LRT. Rogier et al. nest this taxon with Necrolestes, contra the LRT. This taxon has an anterior naris, not a ventral one.

Figure 4. Cronopio nests between Juramaia and Didelphis + Ukhaatherium in the LRT. Rogier et al. nest this taxon with Necrolestes, contra the LRT. This taxon has an anterior naris, not a ventral one.

Rougier et al. gave us straw dogs
when they compared the basicrania of several sister candidates, but NOT that of Chrysochloris, to that of Necrolestes. Here I add a basicranium Rougier et al. chose to not show. Chrysochloris more closely matches the morphology of Necrolestes than any of the other three candidates. I don’t see Chrysochloris listed in the Supplemental Information for Rougier et al. which appears to test non-placental mammals only. So this is what I mean by another case of taxon exclusion. Ameghino (1891) got it right originally. Rougier Wible, Beck and Apesteguía 2012, for some reason, dropped the ball.

Figure 3. Necrolestes basicrania compared to three candidates by Rougier 2012. Here I add the basicranium for Chrysochloris for comparison and it's a better match.

Figure 3. Necrolestes basicrania compared to three candidates by Rougier 2012. Here I add the basicranium for Chrysochloris for comparison and it’s a better match. The blue element is the posterior mandible, which is not shown on the Rougier et al. drawings. Not how the lower (posterior) element curls over the basicranial element in only two candidates here. This is a placental trait. The LRT uses no petrosal traits, but image speaks for itself. Excluding the actual sister taxon was done for reasons unknown in this flawed study.

 

Deleting Chrysochloris from the LRT
nests Necrolestes with the remaining basal Glires, but resolution is lost. Not sure why, but Necrolestes has a history (see above) of being a confusing taxon when not nested with Chrysochloris.

Deleting all placentals from the LRT,
except Necrolestes, nests it between Didelphis and Asioryctes a node apart from Cronopio. So taxon exclusion doesn’t recover what Rougier et al. recovered.

Now that we have golden moles in Africa and South America
this is evidence that golden moles first appeared before those continents split apart 118 to 115 mya, long before the end of the Cretaceous. Video link here. Naish reports, “Golden moles and tenrecs appear to be close relatives, forming a clade usually termed Afrosoricida Stanhope et al., 1998 (though this is essentially synonymous with Tenrecoidea McDowell, 1958, see Asher (2001)“. That relationship is not supported by the LRT. Golden moles probably first appeared in the Early Jurassic, given that other Glires, multituberculates, split from rodents about the same time and are found as early as Middle Jurassic strata.

Rougier et al. tested earlier studies and found them flawed
Similarly, I tested Rougier et al. and found it flawed. Perhaps someday someone will likewise test this test and present additional insight into this former enigma taxon.

References
Ameghino F 1891. Nuevos restos de mamíferos fósiles descubiertos por Carlos Ameghino en el Eoceno inferior de la Patagonia austral. Especies nuevas, adiciones y correciones [New remains of fossil mammals discovered by Carlos Ameghino in the lower Eocene of southern Patagonia. New species, additions and corrections]. Rev Arg Hist Nat 1:289–328. Spanish.
Asher RJ, Horovitz I, Martin T and Sanchez-Villagra MR 2007. Neither a Rodent nor a Platypus: a Reexamination of Necrolestes patagonensis Ameghino. American Museum Novitates 3546:1-40.
Ladevèze S, Asher RJ, Sánchez-Villagra MR 2008. Petrosal anatomy in the fossil mammal Necrolestes: evidence for metatherian affinities and comparisons with the extant marsupial mole. J Anat 213(6):686–697.
Patterson B 1958. Affinities of the Patagonian fossil mammal Necrolestes. Breviora Mus Comp Zool 94:1–14.
Rougier GW, Wible JR,  Beck RMD and Apesteguía S 2012. The Miocene mammal Necrolestes demonstrates the survival of a Mesozoic nontherian lineage into the late Cenozoic of South America.
Saban R 1954. Phylogénie des insectivores [Phylogeny of the insectivores]. Bull Mus Natl d’Hist Nat. Ser 2 26:419–432. in French
Van Valen L 1988. Faunas of a southern world. Nature 333(6152):113.

Tetrapod Zoology on golden moles

Notoryctes the marsupial mole

Wikipedia reports, “Marsupial moles are a family (Notoryctidae) of cladotherian mammals of the order Notoryctemorphia. They are rare and poorly understood. Once classified as monotremes, they are now thought to be marsupials. Their precise classification was for long a matter for argument.”

Earlier we looked at other mammal moles.

  1. Eastern mole – Talpa  (Carnivora, Placentalia)
  2. Docofossor (basal Placentalia)
  3. Golden mole – Chrysochloris (Glires, Placentalia)

And some reptilian ‘moles’.

  1. Mexican mole lizard – Bipes (Scincomorpha, Squamata)
  2. Mermaid skink – Sirenoscincus mobydick (Scincomorpha, Squamata)
  3. Texas blind snake – Leptotyphlops dulcis (Serpentes, Squamata)

Today we’ll round out this topic
with the extant marsupial mole (Notoryctes; Stirling 1888, 1891;  Figs. 1-3; 12-16 cm long) which nests with Anebodon at the base of the Marsupialia in the large reptile tree. The two-teat pouch opens backwards to keep dirt out.

Figure 2. Notoryctes skeleton. The hind limbs were not included so the femur and tibia are added here.

Figure 1. Notoryctes skeleton. The hind limbs were not included so the femur and tibia are added here.

We see burrowing synapsids
all the way back to Thrinaxodon, but moles spend all their time underground.

FIgure 3. Notoryctes in vivo.

FIgure 2. Notoryctes in vivo.

Notoryctes typhlops (Stirling 1891; extant; up to 16 cm in length) is the marsupial mole.  This taxon is blind with eyes reduced to vestigial lenses and without external ears. Three molars are present. Several neck vertebrae are fused, as are the sacrals. The tail verts are quite robust, especially for a mole. Tiny epipubes are present. A cloaca is present, a trait otherwise seen in monotremes and tenrecs. The forelimb has transformed to support the two large digging claws.

Figure 1. Notoryctes skull from copyright Digimorph.org, used with permission.

Figure 3. Notoryctes skull from copyright Digimorph.org, used with permission. Colors added. Although the orbit portion of the confluent lateral temporal fenestra, the eyeball is small and blind.

The claws of the third and fourth digits
are enormous. The canine (orange, Fig. 1) is considered by some as a 4th upper and 3rd lower incisor.

Figure 2. Anebodon partial skull. This is the only known and tested sister to Notoryctes.

Figure 4. Anebodon partial skull. This is the only known and tested sister to Notoryctes.

 

 

References
Bi S-D, heng X-T, Meng J, Wang X-L, Robinson N and Davis B 2016. A new symmetrodont mammal (Trechnotheria: Zhangheotheriidae) from the Early Cretaceous of China and trechnotherian character evolution. Nature Scientific Reports 6:26668 DOI: 10.1038/srep26668
Gadow H 1892. On the systematic position of Notoryctes typhlops. Proc. Zool. Soc. London 1892, 361–370.
Stirling EC 1888. Transactions of the Royal Society, South Australia 1888:21
Stirling EC 1891. Transactions of the Royal Society, South Australia 1891:154

wiki/Notoryctes

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.

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

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

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

 

The Tasmanian wolf has a new sister: Hyaenodon

Here’s an enigmatic mammal
that has been aching to be nested in a recognized clade for over 150 years. It should not have been this difficult to nest Hyaenodon (Fig. 1).

Figure 1. Hyaenodon horrid us was the size of a large dog. This carnivorous marsupial was formerly considered a creodont.

Figure 1. Hyaenodon horrid us was the size of a large dog. This carnivorous marsupial was formerly considered a creodont.

It’s interesting to see how
Wikipedia plays down the affinities of Hyaenodon (Laizer and Parieu, 1838; Eocene-Miocene, Figs. 1-3): “a group of extinct carnivorous fossil mammals from Eurasia, North America and Africa…Some species of this genus were among the largest terrestrial carnivorous mammals of their time; others were only of the size of a marten.” The Wiki authors do not place Hyaenodon into the Eutheria nor the Metatheria. They don’t create a family tree for Hyaenodon. Most authors consider Hyaenodon a member of the Creodonta, a clade considered a ‘wastebasket’ by Wikipedia. That clade may have to be revised or deleted in the future, but at present only one creodont has been tested and it has dropped out.

About Creodonts and Carnivorans
Wikipedia reports, “creodonts and carnivorans were once thought to have shared a common ancestor, but given that different teeth are involved in making up the carnassials (both between creodonts and carnivorans and between the main groups of creodonts), this appears to be a case of evolutionary convergence. 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), OxyaenidaeAmbloctonidaeand 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.[13]Hyaenodontidae was not included among the creodonts until 1909.[14] Over time, various groups were removed, and by 1969 it contained, as it does today, only the oxyaenids and the hyaenodontids.”

Figure 1. Hyaenodon skull cast showing in orange the lacrimal - septomaxilla common to most, if not all, metatherians.

Figure 2. Hyaenodon skull cast showing in orange the lacrimal – septomaxilla common to most, if not all, metatherians.

When added to the large reptile tree (now 796 taxa)
Hyaenodon (chimaera taxon, based on several specimens and authors) nested with another carnivorous mammal, Thylacinus, the Tasmanian wolf, a basal marsupial. They scored nearly identically.

Unique for marsupials,
Thylacinus had largely cartilaginous epipubic bones with a highly reduced osseous elements. Perhaps that’s why epipubes were never found with Hyaenodon.

Figure 4. Thylacinus, the Tasmanian wolf, recently extinct, was a sister to Hyaenodon.

Figure 3. Thylacinus, the Tasmanian wolf, recently extinct, was a sister to Hyaenodon. Note the three molars and lack of epipubes.

In both taxa
only three molars were present. That’s one less than in most marsupials and the number typical, but not universal, in placentals. In both taxa the jugal extends nearly to the back of the skull where the jaw joint is. That’s a typical marsupial trait. Likewise, the septomaxilla appears on the snout (Fig. 2), as in the marsupials Vombatus and Vintana. The occiput (Fig. 4) is also very metatherian.

Figure 2. Hyaenodon occiput. Note the strong resemblance to the occiput of Vintana, with the post parietal above the supraoccipital and framed by tabulars and tall squamosals.

Figure 4. Hyaenodon occiput. Note the strong resemblance to the occiput of Vintana, with the post parietal above the supraoccipital and framed by tabulars and tall squamosals.

This link to Scott (1895, p183)
discusses “M. Gaudrey’s (1878) view as to the marsupial  character of the genus [Hyaenodon] is definitely disproved by the abundant material now at command.” Good job, Gaudrey! You’ve been vindicated! (…about 150 years too late, unfortunately).

Figure 6. Subset of the large reptile tree: the marsupials featuring the newest taxon, Hyaenodon.

Figure 6. Subset of the large reptile tree: the marsupials featuring the newest taxon, Hyaenodon.

Hyaenodon species
According to Wikipedia, H. gigas was the size of a bear (est. 1,100 lbs, 500 kgs, 3 m). H. horridus was the size of a large dog (est. 88 lbs, 40 kgs). H. microdon and H. mustelinus were much smaller, about the size of Eomaia, another basal marsupial. There were several mid-sized taxa, too. Hyaenodon leptorhynchus was the type species.

Once again,
this discovery was made without ever having seen the fossil first hand. The LRT and a computer monitor are all the tools one needs in many cases, such as this one.

References
Gaudrey A 1878. Les enchaînements du monde animal dans les temps géologiques  mammifères tertiaires. F. Savy. (ed.) Paris 28pp.  online here.
Laizier L and de Parieu J 1838. Description et determination d’une machoire fossile appartenant a un mammifere jusqu’a pressent inconnu, Hyaenodon leptorhynchus. Comptes-rendus hebdomadaires des séances de l’Académie des Sciences, Paris 7:442.
Scott WM 1895. The osteology of Hyaenodon. Academy Natural Sciences Philadelphia Journal 9:499-536. online here.

wiki/Hyaenodon