Enigma Yalkaparidon nests in the LRT with other marsupial enigmas

Popularly known asThingodonta‘,
the small partial skull of Yalkaparidon coheni (Archer, Hand and Godthelp 1988; Early Miocene; QM-F13008; Fig. 1) is a traditional enigma marsupial. According to the Australian Museum, “nobody knows what its closest relatives are.”

This sounds like a job for the LRT! Thirty-three years of enigma-hood is far too long.

Figure 1. Yalkaparidon skull (right view flipped, colors and animation added). Shown about 1.5x actual size on a 72dpi computer monitor.
Figure 1. Yalkaparidon skull (right view flipped, colors and animation added). Shown about 1.5x actual size on a 72dpi computer monitor. Note how the anterior jugal has a descending process, taken to an extreme in Vintana in figure 2.

Here
in the large reptile tree (LRT, 1974 taxa; subset Fig. 4), Yalkaparidon nests basal to two other traditional enigma marsupials, Vintana (Fig. 2) and Groberia. Academic workers consider Yalkaparidon a diprodontian. Here Yalkaparidon is a diprodontian-mimic, not related to Diprodonton. These three taxa are close to Paedotherium and another rather new enigma, Adalatherium.

The reasons for the traditional omission of these taxa from marsupial trees:
Paedotherium was traditionally considered a notoungulate, a placental. It is neither in the LRT. Paedotherium was nested with marsupials here in 2019. Worse yet, Notoungulata is no longer a monophyletic clade after testing in the LRT.

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 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.

Archer et al. 1988
erected a new order for Yalkaparidon (Fig. 1). Adalatherium, Groberia and Vintana were described later as unique taxa, so they might have nested in this order. Unfortunately papers describing each new ‘unique’ taxon did not mention Yalkaparidon or Archer.

Described in 1888, Paedotherium
has traditionally and mistakenly considered a member of the Notoungulata and the Eutheria. Neither are correct according to the LRT. According to the LRT, Notoungulata is a wastebasket clade and is not monophyletic. Eutheria include placental mammals. Papers describing each new ‘unique’ taxon (Yalkaparidon (Fig. 1). Adalatherium, Groberia and Vintana) did not mention Paedotherium (Fig. 3).

Figure 2. Miocene Paedotherium was excluded by Krause et al. It nests with Late Cretaceous Adalatherium in the LRT.
Figure 3. Miocene Paedotherium was excluded by Krause et al. It nests with Late Cretaceous Adalatherium in the LRT.

Beck et al. 2013 ran a cherry-picked analysis
that omitted pertinent taxa listed above. They reported, “characters are similarly poorly resolved and do not clarify the supraordinal relationships of Yalkaparidon beyond suggesting that it is probably a member of Marsupialia.” They concluded, “We have not been able to confidently resolve the phylogenetic relationships of this taxon.”

Convergence can be troublesome.
Let the software determine your inclusion set, outgroups and all interrelationships. Don’t short-change your study by cherry-picking taxa. The more taxa, the better. The LRT minimizes taxon exclusion by including so many taxa, more than in any other similar study.

Figure x. Subset of the LRT focusing on basal Theria = Marsupialia.
Figure 4. Subset of the LRT focusing on basal Theria = Marsupialia.

Whatever they teach you at the university level,
it is not necessary to personally examine a specimen like this firsthand in order to understand it better than those who examined it firsthand. It is also not necessary to add characters for tiny cranial foramina and other minutia. Beck et al. proved that. Instead, it is only necessary to include related and pertinent taxa in a single analysis. If you don’t know which taxa are related and pertinent, just keep adding taxa until your software tells you which taxa are related and pertinent. Don’t assume anything you learned under the tutelage of a professor. Sometimes they know. Sometimes they don’t. Test every taxon you can get your eyes on in one large study. Then, when you have your own large cladogram, like the LRT, you can use it with authority for the rest of your career.

Once again, this appears to be a novel hypothesis of interrelationships.
If not, please provide a citation for the earlier hypothesis so I can promote it here.

PS
This reminds me of the origin of pterosaurs problem from twenty years ago. Back then, adding taxa nested enigma pterosaurs with enigma Cosesaurus, with enigma Sharovipteryx and with enigma Longisquama.

Lesson for today (and twenty years ago):
Add taxa and your enigmas will get nested. Don’t expect any celebration, acknowledgement or approbation, but that’s how you do it. Just add taxa.

References
Archer M, Hand S and Godthelp H 1988. A new order of Tertiary zalambdodont marsupials. Science 239(4847):1528-1531.
Beck RMD 2013. The osteology and systematics of the enigmatic Australian Oligo-Miocene metatherian Yalkaparidon (Yalkaparidontidae; Yalkaparidontia; ?Australidelphia; Marsupialia). J Mammal Evol DOI 10.1007/s10914-013-9236-3

wiki/Vintana
wiki/Paedotherium – not yet listed, let’s fix that!
wiki/Groeberia
wiki/Adalatherium
wiki/Yalkaparidon

Publicity
Australian.museum/learn/australia-over-time/extinct-animals/cohens-thingodonta/

Washingtonpost.com/news/speaking-of-science/wp/2016/05/27/this-odd-ancient-australian-marsupial-had-an-insatiable-appetite-for-snails/

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