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Sabertooth marsupials

Sunday, January 15, 2023 16:01

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Housekeeping in the marsupial subset
of the large reptile tree (LRT, 2202 taxa, Fig 1) has been both exhausting and enlightening. Early (= freshman) exposures to data years ago have been revisited. Most of the derived taxa and their interrelationships have remained unscathed. It’s the small, basal and transitional taxa that all look like mice, tiny opossums and jerboas, many known from crushed partial specimens, that are benefiting now from a second look with more taxa available for comparison. It’s a learning experience.

Figure 1. Subset of the LRT focusing on basal carnivorous marsupials. Among them are the sabertooth taxa. Vincelestes is Early Cretaceous, so more primitive taxa, some represented by extant taxa, dip back further into deep time.

The present hypothesis
indicates sabertooth marsupials, like Late Miocene Thylacosmilus (Fig 3), had their origins with rat-sized Early Cretaceous Vincelestes (Fig 2).

Figure 2. Rat-sized Early Cretaceous Vincelestes had saberteeth and maxilla that met dorsally, separating the tiny nasals from the frontals. Here shown 2x life size. The original ‘Premaxilla’ seems to be pointing to a displaced nasal here. Note the large, molars, lack of premolars.

Figure 3. From 2019, Thylacosmilus compared to Vincelestes separated by tens of millions of years. The both have maxillae conjoined dorsally to house the large canines.

The surprise today
comes from the IVPP V5235 specimen of Hapalodectes hetangensis (Fig 4). Based on this hypothesis of interrelationships this was a late survivor in the Paleocene from a Jurassic radiation. The primate-like postorbital bar fo this rat-sized taxon is lost in Vincelestes, but reappears in Thylacosmilus (Fig 3).

Figure 4. Hapalodectes, the IVPP V 5235 specimen, nests basal to the largest marsupial carnivores. This taxon retained premolars.

The IVPP specimen of Hapalodectes hetangensis
(Fig 4) was an early addition that has bounced around the LRT as taxa have been added and may continue to do so in the future. The only data I have seen is shown in figure 4. Colors added here have been shifting around over the past few years.

Figure 5. The extant tiger quoll, Dasyurus, is an extant taxa basal to the sabertooth marsupials (Fig 1) and their non-sabertooth ancestors back to the Jurassic . It has large hooked canines, but not robust saberteeth.

Hapalodectes hetangensis
(Ting and Li 1987; 4.5cm skull length; Paleocene, 55 mya; IVPP V 5235) This skull was originally considered a mesonychid, but here nests with the marsupial clade leading to sabertooth taxa with a shrinking premaxilla. Note the encircled orbits rotated anteriorly as in Thylacosmilus, convergent with primates.

Dasyurus maculatus
(Geoffroy 1796; 25-75cm snout to rump) is the extant tiger quoll or spotted tail quoll, a carnivorous, nocturnal, solitary, cat-like marsupial from Australia, New Guinea and Tasmania. A pouch that opens to the tail develops during breeding season.

Vincelestes neuquenianus
(Bonaparte 1986, Early Cretaceous, 130 mya). Derived from a sister to Haplodectes, Vincelestes is a carnivorous marsupial sister to Pataogosmilus. Note the hyper-enlarged canines and short rostrum.. Nine individuals are known. The tail is extraordinarily long and provided with deep chevrons. Skull mage from Digimorph.org and used with permission.

References
Ting S and Li C 1987. The skull of Hapalodectes (?Acreodi, Mammalia), with notes on some Chinese Paleocene mesonychids. Vertebrata PalAsiatica. 25: 161–186.

http://reptileevolution.com/thylacosmilus.htm

Source: https://pterosaurheresies.wordpress.com/2023/01/16/sabertooth-marsupials/

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