The role of Ambolestes in Marsupialia vs Metatheria

Marsupialia
was a clade erected by Iliger in 1811 to include mammals with pouches.

Back then few fossils were known. Fossils don’t preserve pouches.

Metatheria
was erected by Huxley 1880 to include all mammals more closely related to marsupials than to placentals. It contains all marsupials as well as many extinct non-marsupial relatives.

Non-marsupials?

What if non-marsupials turn out to be marsupials
based on phylogenetic bracketing after analysis?

The large reptile tree (LRT) uses the last common ancestor (LCA) method for determining clade memberships. All clade members, sans exceptions (see below), probably had a pouch. They need not have had any particular trait using the LCA method.

Figure 1. Ambolestes in situ and newly reconstructed. ” data-image-caption=”

Figure 1. Ambolestes in situ and newly reconstructed.

” data-medium-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2024/07/ambolestes-zhoui-skull-recon588.jpg?w=300″ data-large-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2024/07/ambolestes-zhoui-skull-recon588.jpg?w=584″ tabindex=”0″ role=”button” class=”size-full wp-image-87574″ src=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2024/07/ambolestes-zhoui-skull-recon588.jpg” alt=”Figure 1. Ambolestes in situ and newly reconstructed.” width=”584″ height=”341″ />

Figure 1. Ambolestes in situ and newly reconstructed.

Bi et al 2018 described Ambolestes
(Fig 1), which they described as a eutherian. Bi et al also labeled Sinodelphys a eutherian.

In the LRT Ambolestes is a marsupial and Sinodelphys is a monotreme. Marsupials arise from a Ukhaatherium ancestor in the Triassic. Placentals arise from the placental without a pouch, a Monodelphys ancestor in the Early Jurassic.

The LRT does not confirm Bi et al 2018 due to taxon exclusion.

Gallus et al 2015 attempted to ‘disentangle’ marsupial orders
by using genomes. They did not include fossils and deep time genomic studies too often fail, as this one failed.

The LRT does not confirm Gallus et al 2015 due to taxon exclusion.

Figure 3. Little Pucadelphys is now a sister to Lycopsis in the LRT. ” data-image-caption=”

Figure 3. Little Pucadelphys is now a sister to Lycopsis in the LRT.

” data-medium-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2024/07/lycopsisskull-588.jpg?w=224″ data-large-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2024/07/lycopsisskull-588.jpg?w=584″ tabindex=”0″ role=”button” class=”wp-image-87566 size-full” src=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2024/07/lycopsisskull-588.jpg” alt=”Figure 3. Little Pucadelphys is now a sister to Lycopsis in the LRT.” width=”584″ height=”783″ />

Figure 2. Little Pucadelphys is now a sister to Lycopsis in the LRT.

According to Wikipedia – Pucadelphys
“Pucadelphys is an extinct genus of non-marsupial metatherian.”

Hence the reason for the preface (above).

In the LRT Early Paleocene Pucadelphys now nests with Miocene Lycopsis on one branch, and Late Paleocene Danjiangia + Hapalodectes hetangenesis (Fig 3) on another branch. All are marsupials in the LRT.

Figure 1. Danjiangia and its LRT ancestors, the IVPP V5235 specimen of Hapalodectes and Pucadelphys. ” data-image-caption=”

Figure 1. Danjiangia and its LRT ancestors, the IVPP V5235 specimen of Hapalodectes and Pucadelphys.

” data-medium-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2024/07/danjiangia-recon588.jpg?w=185″ data-large-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2024/07/danjiangia-recon588.jpg?w=584″ tabindex=”0″ role=”button” class=”size-full wp-image-87554″ src=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2024/07/danjiangia-recon588.jpg” alt=”Figure 1. Danjiangia and its LRT ancestors, the IVPP V5235 specimen of Hapalodectes and Pucadelphys.” width=”584″ height=”945″ />

Figure 3. Danjiangia and its LRT ancestors, the IVPP V5235 specimen of Hapalodectes and Pucadelphys.

Traditionally Lycopsis is considered to be a sprassodont.
“Sparassodonta were once considered to be true marsupials, but are now thought to be a separate side branch that split before the last common ancestor of all modern marsupials.  Almost all sparassodonts have an exceptionally shortened snout—most especially thylacosmylids.”

Exceptionally the snout is long in Lycopsis.

According to Wikipedia – Danjiangia
“Danjiangia is a genus of the extinct family Brontotheria.”

According to the LRT Early Eocene Danjiangia (Fig 2) arose from marsupials like Hapalodectes and Pucadelphys.

“According to phylogenetic studies, it shares some similarities with Lambdotherium, which in turn is assigned a position either within the (early) Brontotheria or within the independent family Lambdotheriidae”. Originally Wang 1995 considered Danjiangia to be the original representative of the Chalicotheriidae.

In the LRT Lambotherium (Cope 1880; Eocene, 50mya) is a placental horse.

Figure 6. Monodelphls and pups exposed as no pouch is present in this basal placental taxon. Note the tail is not bushy. ” data-image-caption=”

Figure 6. Monodelphls and pups exposed as no pouch is present in this basal placental taxon. Note the tail is not bushy.

” data-medium-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2016/10/monodelphis_and_pups588.jpg?w=300″ data-large-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2016/10/monodelphis_and_pups588.jpg?w=584″ tabindex=”0″ role=”button” class=”size-full wp-image-24463″ src=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2016/10/monodelphis_and_pups588.jpg” alt=”Figure 6. Monodelphls and pups exposed as no pouch is present in this basal placental taxon. Note the tail is not bushy.” width=”584″ height=”554″ />

Figure 4. Monodelphls and pups exposed as no pouch is present in this basal placental taxon. Note the tail is not bushy.

Since placentals in the LRT arose from marsupials
like tiny pouch-less Monodelphis (Fig 4), monophyletic placentals remain a clade within Marsupialia. Perhaps we should refer to traditional marsupials (with pouches) as non-placental marsupials. That would make Iliger happy. Not sure about Huxley.

Think of traditional marsupials in the same way as non-avian dinosaurs, non-avian theropods and other such hyphenated clade names.

This appears to be a novel hypothesis of interrelationships.
If not, let us know so I can promote that earlier citation here.

References
Bi S, Zheng X, Wang X, Cignetti NE, Yang S, Wible JR 2018. An Early Cretaceous eutherian and the placental–marsupial dichotomy. Nature. 558 (7710): 390–395.
Gallus S, Janke A, Kumar V, Nilsson MA 2015. Disentangling the relationship of the Australian marsupial orders using retrotransposon and evolutionary network analyses. Genome Biology and Evolution. 7 (4): 985–992.
Wang Y 1995. A new primitive Chalicothere (Perissodactyla, Mammalia) from the early Eocene of Hubei, China. Vertebrata PalAsiatica 33(2):138-159

wiki/Lophiodon
wiki/Litolophus
wiki/Danjiangia in German
wiki/Metatheria
wiki/Marsupial