Tree shrews: those post-orbit bars are long frontal processes
Ptilocercus and Tupaia
are the two tested tree shrews (Scandentia, Figs 1, 2) in the large reptile tree (LRT, 2338 taxa). According to Wikipedia, “Taxonomists continue to refine the treeshrews’ relations to primates and to other closely related clades.”
Earlier tree shrews were removed from any interrelationship with Primates by the LRT. Here they are closer to Labidolemur (Fig 1), an apatemyid ancestor of Glires, the gnawing clade. Take a look at those big, chisel-like premaxillary teeth.
Figure 1. Labidolemur (above) compared to the extant tree shrews, Ptilocercus and Tupaia, both provided with primate-like bars surrounding the orbits. These are frontal processes, not postfrontals, as in primates.
” data-medium-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/03/labidolemur-skull588.jpg?w=190″ data-large-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/03/labidolemur-skull588.jpg?w=584″ class=”size-full wp-image-92130″ src=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/03/labidolemur-skull588.jpg” alt=”Figure 1. Labidolemur (above) compared to the extant tree shrews, Ptilocercus and Tupaia, both provided with primate-like bars surrounding the orbits. These are frontal processes, not postfrontals, as in primates. ” width=”584″ height=”924″ srcset=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/03/labidolemur-skull588.jpg?w=584&h=924 584w, https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/03/labidolemur-skull588.jpg?w=95&h=150 95w, https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/03/labidolemur-skull588.jpg?w=190&h=300 190w, https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/03/labidolemur-skull588.jpg 588w” sizes=”(max-width: 584px) 100vw, 584px” />
Figure 1. Labidolemur (above) compared to the extant tree shrews, Ptilocercus and Tupaia, both provided with primate-like bars surrounding the orbits. These are frontal processes, not postfrontals, as in primates. Note the lack of canines.
At one time
Ptilocercus and Tupaia nested close to primates – when their complete orbital bars were considered postfrontals. Now those are scored as elongate frontal processes that contact the jugal. That scoring keeps them more firmly separated from Primates despite the long list of shared traits by convergence in these two arboreal clades.
Sengis, like Rhynchocyon, and numbats, like the anteating marsupial, Myrmecobius, also have ‘eyebrows’ created by frontal processes that extend posterolaterally.
Figure 2. For comparison here are Notharctus and Microcebus (to scale and enlarged) together with unrelated arboreal placentals, Labidolemur, Ptilocercus and Tupaia.
” data-medium-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/03/notharctus.labidolemur.skulls588.jpg?w=300″ data-large-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/03/notharctus.labidolemur.skulls588.jpg?w=584″ class=”size-full wp-image-92132″ src=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/03/notharctus.labidolemur.skulls588.jpg” alt=”Figure 2. For comparison here are Notharctus and Microcebus (to scale and enlarged) together with unrelated arboreal placentals, Labidolemur, Ptilocercus and Tupaia. ” width=”584″ height=”487″ srcset=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/03/notharctus.labidolemur.skulls588.jpg?w=584&h=487 584w, https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/03/notharctus.labidolemur.skulls588.jpg?w=1168&h=974 1168w, https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/03/notharctus.labidolemur.skulls588.jpg?w=150&h=125 150w, https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/03/notharctus.labidolemur.skulls588.jpg?w=300&h=250 300w, https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/03/notharctus.labidolemur.skulls588.jpg?w=768&h=641 768w, https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/03/notharctus.labidolemur.skulls588.jpg?w=1024&h=855 1024w” sizes=”(max-width: 584px) 100vw, 584px” />
Figure 2. For comparison here are Notharctus and Microcebus (to scale middle and enlarged at right) together with unrelated byt convergently similar arboreal placentals, Labidolemur, Ptilocercus and Tupaia. Primates retained canines and the postfrontal is present.
According to Wikipedia, Apatemyidae,
“Their relationships to other mammal groups are controversial; a 2010 study [Silcox, Bloch, Boyer and Houde 2010] found them to be basal members of Euarchontoglires.
The LRT does not confirm that membership. Glires and apatemyids are members of placental2. Primates are members of placental1.
This still appears to be a novel hypothesis of interrelationships.
If not, please provide a citation so I can promote it here.
PS. Some readers think the LRT cannot handle convergence.
This conjecture has been falsified time after time. Add this time to that list.
References
Silcox MT, Bloch JI, Boyer DM and Houde P 2010. Cranial anatomy of Paleocene and Eocene Labidolemur kayi (Mammalia: Apatotheria), and the relationships of the Apatemyidae to other mammals. Zoological Journal of the Linnean Society160: 773–825.
wiki/Apatemyidae
wiki/Apatemys
wiki/Labidolemur – not yet posted
wiki/Sinclairella – not yet posted
wiki/Heterohyus
Source: https://pterosaurheresies.wordpress.com/2025/03/29/tree-shrews-those-post-orbit-bars-are-long-frontal-processes/
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