Yet another marsupial to placental transition: Sminthopsis to Macroscelides
As long-time readers know,
the large reptile tree (LRT, 2342 taxa) recovered more than one genesis for the placenta in eutherian mammals. This confirmed earlier studies by Wortman 1902, who published on this long before the advent of phylogenetic analysis and software.
Figure 1. The marsupial, Sminthopsis compared to the larger placental, Macroscelides, now sister taxa in the LRT.
” data-medium-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/11/sminthopsis.macroscelides588.jpg?w=147″ data-large-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/11/sminthopsis.macroscelides588.jpg?w=501″ class=”size-full wp-image-95389″ src=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/11/sminthopsis.macroscelides588.jpg” alt=”Figure 1. The marsupial, Sminthopsis compared to the larger placental, Macroscelides, now sister taxa in the LRT. ” width=”584″ height=”1194″ srcset=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/11/sminthopsis.macroscelides588.jpg?w=584&h=1194 584w, https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/11/sminthopsis.macroscelides588.jpg?w=73&h=150 73w, https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/11/sminthopsis.macroscelides588.jpg?w=147&h=300 147w, https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/11/sminthopsis.macroscelides588.jpg 588w” sizes=”(max-width: 584px) 100vw, 584px” />
Figure 1. The marsupial, Sminthopsis compared to the larger placental, Macroscelides, now sister taxa in the LRT. The two are shown to scale and with Sminthopsis enlarged/ Note the prepubes in Sminthopsis, lacking in Macroscelides.
Today
an extant dasyurid marsupial, the dunnart Sminthopsis (Figs 1–3) now nests with the larger, but broadly similar extant placental, the putative sengi, Macroscelides (Figs 1–3) is traditionally linked to another, more dissimilar sengi, Rhynchocyon (Fig 3).
Both featured taxa are nocturnal insectivorous hoppers.
Sminthopsis is more primitive and smaller.
Figure 2. The skulls of Sminthopsis and Macroscelides not to scale.
” data-medium-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/11/sminthopsis-macroscelides-skull588.jpg?w=280″ data-large-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/11/sminthopsis-macroscelides-skull588.jpg?w=584″ class=”size-full wp-image-95391″ src=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/11/sminthopsis-macroscelides-skull588.jpg” alt=”Figure 2. The skulls of Sminthopsis and Macroscelides not to scale. ” width=”584″ height=”627″ srcset=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/11/sminthopsis-macroscelides-skull588.jpg?w=584&h=627 584w, https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/11/sminthopsis-macroscelides-skull588.jpg?w=140&h=150 140w, https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/11/sminthopsis-macroscelides-skull588.jpg?w=280&h=300 280w, https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/11/sminthopsis-macroscelides-skull588.jpg 588w” sizes=”(max-width: 584px) 100vw, 584px” />
Figure 2. The skulls of Sminthopsis and Macroscelides not to scale. The phylogenetic distance here is great in these two extant taxa. That implies an early split. Even so, they nest together in the LRT. Note the marsupial-like perforation of the palate in Macroscelides.
At present,
Macroscelides represents a clade of one placental taxon derived from Sminthopsis. Today Macroscelides is found in Namibia and South Africa. Sminthopsis is restricted to Australia.
That means the two taxa split apart when the two continents split apart 140 mya near the start of the Cretaceous Period (145–66mya) at that time near the then warm South Pole with a low sun during the long day cycles and no sun during the long night cycles.
Figure 3. Sminthopsis compared to Macroscelides and the unrelated sengi, Rhynchocyon.
” data-medium-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/11/rhynchocyon_macroscelides_sminthopsis_compared.jpg?w=188″ data-large-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/11/rhynchocyon_macroscelides_sminthopsis_compared.jpg?w=584″ class=”size-full wp-image-95394″ src=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/11/rhynchocyon_macroscelides_sminthopsis_compared.jpg” alt=”Figure 3. Sminthopsis compared to Macroscelides and the unrelated sengi, Rhynchocyon. ” width=”584″ height=”931″ srcset=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/11/rhynchocyon_macroscelides_sminthopsis_compared.jpg?w=584&h=931 584w, https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/11/rhynchocyon_macroscelides_sminthopsis_compared.jpg?w=94&h=150 94w, https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/11/rhynchocyon_macroscelides_sminthopsis_compared.jpg?w=188&h=300 188w, https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/11/rhynchocyon_macroscelides_sminthopsis_compared.jpg 588w” sizes=”(max-width: 584px) 100vw, 584px” />
Figure 3. Sminthopsis compared to Macroscelides and the unrelated sengi, Rhynchocyon. Here Sminthopsis is more closely related to Macroscelides than Macroscelides is to Rhynchocyon.
Sminthopsis crassicaudata
(Gould 1844; 6-9 cm long with 5-7cm tail, Australia) is the extant fat-tailed dunnart, a mouse-like insectivorous carnivorous marsupial with an open pouch. The lifespan is less than 2 years. This genus prefers extreme, semi-arid environments. Daily torpor enables this niche. Prepubes are present. This taxon gave rise to Macroscelides a placental, convergent with other placentals.
Macroscelides proboscideus
(Shaw 1800, 10-30cm) is the extant round-eared elephant shrew or sengi. It is not a sister to Scutisorex, the hero shrew, nor related to Rhynchocyon another traditional sengi. Macroscelides is not related to elephants either, contra Wikipedia. The cranium is expanded with acoustic space on this nocturnal desert dweller. Diet includes insects, shoots and roots. The limbs are long and slender, making it one of the fastest small mammals.
This appears to be a novel hypothesis of interrelationships.
If not, please provide a citation so I can promote it here. Apparently no one saw this coming. Let me know if otherwise.
References
Gould J 1844. Proceedings of the Zoological Society of London 1844:103-108.
Shaw G 1800. General zoology or systematic natural history. Vol. I. Part 2. Mammalia. London: Printed for G. Kearsley.
wiki/Macroscelides
wiki/Sminthopsis
Source: https://pterosaurheresies.wordpress.com/2025/11/25/yet-another-marsupial-to-placental-transition-sminthopsis-to-macroscelides/
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