Tiny, flat-head Jurassic marsupials and their larger flat-head descendants
I missed these hypothetical interrelationships earlier.
So did all prior authors. The large reptile tree (LRT, 2322 taxa) gradually brought this to my attention as part of the ongoing housekeeping in the marsupial clade.
This is presently a very fragile hypothesis. Distant outgroup inclusion or exclusion reverberates here.
The flat-head marsupials,
(Fig 1) some of them tiny and from the Middle Jurassic, now nest together in the LRT (Fig 2). Some, like Didelphodon, are former Late Cretaceous borhyaenids. Boryhyaena is from the Miocene and it is very similar.
Figure 1. Flat-head marsupials from Hadrocodium to Didelphodon.
” data-medium-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2024/07/didelphodon-asiatherium-mayulestes588.jpg?w=129″ data-large-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2024/07/didelphodon-asiatherium-mayulestes588.jpg?w=440″ tabindex=”0″ role=”button” class=”size-full wp-image-87495″ src=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2024/07/didelphodon-asiatherium-mayulestes588.jpg” alt=”Figure 1. Flat-head marsupials from Hadrocodium to Didelphodon. ” width=”584″ height=”1358″ />
Figure 1. Flat-head marsupials from Hadrocodium to Didelphodon. Dental formula: 4-1-3-4.
Some of these taxa
(Fig 1) are among the smallest of all mammals and vertebrates. The orbit is open dorsally on skulls at least twice a wide as tall (measured at the orbit) and the orbit is a small fraction of the large temporal opening.
I’m working on this problem.
Figure 2. Subset of the LRT focusing on basal Mammalia and the flat-head marsupials.
” data-medium-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2024/07/basal.metatheria588.jpg?w=146″ data-large-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2024/07/basal.metatheria588.jpg?w=499″ tabindex=”0″ role=”button” class=”size-full wp-image-87498″ src=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2024/07/basal.metatheria588.jpg” alt=”Figure 2. Subset of the LRT focusing on basal Mammalia and the flat-head marsupials. ” width=”584″ height=”1198″ />
Figure 2. Subset of the LRT focusing on basal Mammalia and the flat-head marsupials.
This novel hypothesis of interrelationships
is so fragile that it fell apart when Vincelestes was matched to Callistoe. Then it came back together when a long list of placentals (sans Carnivora) was added. Creodonts and carnivores still mess each other’s nodes and branches.
I’m working on this problem, too. Baby steps.
References
Burger BJ 2013. A new species of the archaic primate Zanycteris from the late Paleocene of western Colorado and the phylogenetic position of the family Picrodontidae.PeerJ 1(1):e191
Crowell JW, Wible JR and Chester SGB 2024. Basicranial evidence suggests picrodontid mammals are not stem primates. Biology Letters 20: 20230335.
https://doi.org/10.1098/rsbl.2023.0335
Luo Z-X, Crompton AW and Sun A-L 2001. New Mammaliaform from the Early Jurassic and Evolution of Mammalian Characteristics. Science 292 (5521): 1535–1540. Bibcode:2001Sci…292.1535L. doi:10.1126/science.1058476. PMID 11375489.
Matthew WD 1917. A Paleocene bat. Bulletin of the American Museum of Natural History. 37, 569–571.
wiki/Hadrocodium
wiki/Zanycteris – not yet posted
Source: https://pterosaurheresies.wordpress.com/2024/07/15/tiny-flat-head-jurassic-marsupials-and-their-larger-flat-head-descendants/
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