Mammal evolution summarized in the LRT

Here’s the mammal subset
of the large reptile tree (LRT, 2340 taxa, about 620 synapsids, Fig 1). Apologies for the tiny type size. The larger original (without color) is linked here. Details below the image.

Figure 1. Mammal subset of the LRT. ” data-image-caption=”

Figure 1. Mammal subset of the LRT.

” data-large-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2026/05/mammal-clades588-1.jpg?w=361″ src=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2026/05/mammal-clades588-1.jpg” alt=”Figure 1. Mammal subset of the LRT.” class=”wp-image-96407″ />

Monotremes, Marsupials and Placentals
In the LRT these three mammal subclades are recovered similar to traditional studies – except for the double appearance of placental reproduction.

Placental One taxa
Monodelphis domestica gave rise to Alcidedorbignya, a traditional basal pantodont, but more primitive in the LRT placental one clade. Both are South American taxa, likely post-asteroid in origin. Basal members of these taxa retain the plesiomorphic canine.

Deltatherium (Early Paleocene, New Mexico) gave rise to terrestrial, herbivorous Pantodonta (includes Condylarthra, Artiodactyla (including Perissodactylia and Mysticeti) and to a split between Primates and Carnivora. Primates include bats and colugos. Carnivora includes Carnivoramorpha and Creodonta.

Placental Two taxa
Petaurus, the extant marsupial sugar glider gave rise to one clade of placental Multituberculates (including the extant aye-aye Daubentonia + Rodents (including plesiadapiformes and manatees) and one clade of initially morphologically similar placental tree shrews. In turn, tree shrews (Scandentia) gave rise to shrews, moles, hedgehogs, moonrats, sengis, tenrecs and ultimately a much larger clade of pakicetids, archaeocetids and odontocetes.

No placental 2 members retained the plesiomorphic canine (see below).

Given the Early Jurassic age of some multituberculates, this clade of placental 2 taxa is much older than the generally larger placental 1 taxa that gave rise to cattle, humans and cats.

Figure 2. Asioryctes is basal to Leptictis in the LRT and retains small, slender canines (orange). ” data-image-caption=”

Figure 2. Asioryctes is basal to Leptictis in the LRT and retains small, slender canines (orange).

” data-large-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/05/asioryctes-longrostrum-cutout588.jpg?w=584″ src=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/05/asioryctes-longrostrum-cutout588.jpg” alt=”Figure 2. Asioryctes is basal to Leptictis in the LRT and retains small, slender canines (orange).” class=”wp-image-93053″ />

The plesiomorphic canine
was almost lost in Asioryctes (Fig 2) and completely lost in akynodont marsupials and their placental 2 descendants, which often had premolar 1 replace the lost canine in structure and use.

The canine issue is one aspect of mammal phylogeny
that seems to have been recovered for the first time here in the LRT. Please send citations of earlier reports of this in mammals (other than humans, who apparently have a rare double-rooted dental condition.

Of course,
trait-based analyses that include fossils, do not recover the same cladograms as gene-based analyses that do not include fossils. Apparently something intervenes over millions of years that corrupts certain genes without affecting the genes that produce the gradual morphology recovered in trait-based analyses like the LRT.

References
wiki/Mammal
/wiki/Placentalia
wiki/Marsupial
wiki/Monotreme