Didelphodon and Didymoconus berkeyi now nest together in the LRT
Didelphodon and Didymoconus berkeyi now nest together
in the large reptile tree (LRT, 2338 taxa). The Wang et al 2001 description of late Oligocene Didymoconus did not mention Didelphodon (Figs 1 and 3). The authors wrote, “The family Didymoconidae is an Asian endemic group of archaic mammals with uncertain affinities in the Eocene through Oligocene.”
That means Wang et al did not know whether Didymoconus was a marsupial or a placental.
Didelphodon is a Late Cretaceous marsupial
in the LRT. Note wide flange at the posterior mandible, the wide, flat cranium, the lack of a retroarticular process of the dentary, and the jugal-jaw joint connection.
The same traits are seen in Didymoconus.
Figure 1. Didelphodon to scale with Didymoconus berkeyi. These two nest together in the LRT. Note wide flange at the posterior mandible, the wide, flat cranium, the lack of a retroarticular process of the dentary, and the jugal-jaw joint connection. Note the canine-like premolars (cyan).
” data-medium-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/10/didelphodon-didymoconus588-2.jpg?w=238″ data-large-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/10/didelphodon-didymoconus588-2.jpg?w=584″ class=”size-full wp-image-94802″ src=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/10/didelphodon-didymoconus588-2.jpg” alt=”Figure 1. Didelphodon to scale with Didymoconus berkeyi. These two nest together in the LRT. Note wide flange at the posterior mandible, the wide, flat cranium, the lack of a retroarticular process of the dentary, and the jugal-jaw joint connection. Note the canine-like premolars (cyan). ” width=”584″ height=”735″ srcset=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/10/didelphodon-didymoconus588-2.jpg?w=584&h=735 584w, https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/10/didelphodon-didymoconus588-2.jpg?w=119&h=150 119w, https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/10/didelphodon-didymoconus588-2.jpg?w=238&h=300 238w, https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/10/didelphodon-didymoconus588-2.jpg 588w” sizes=”(max-width: 584px) 100vw, 584px” />
Figure 1. Didelphodon to scale with Didymoconus berkeyi. These two nest together in the LRT. Note wide flange at the posterior mandible, the wide, flat cranium, the lack of a retroarticular process of the dentary, and the jugal-jaw joint connection. Note the canine-like premolars (cyan).
Meanwhile,
the less complete skull that is represented by a line drawing, Didymoconus colgati, Fig 2) is no longer a member of the LRT. Too few teeth, two few cranial bones = too few scores, which means it adversely affects the resolution of the other 600+ taxa.
Earlier (Jan 06 2025) Didymoconus colgatei (Fig 2) last nested with Hyaenodon, likely as a juvenile due to its smaller size and fewer teeth.
So the two Didymoconus specimens are not related to one another in the LRT.
Figure 1. Hyaenodon species + Didymoconus colgati and D berkeyi to scale.
” data-medium-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/01/hyaenodon-faces588-1.jpg?w=143″ data-large-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/01/hyaenodon-faces588-1.jpg?w=487″ class=”size-full wp-image-90902″ src=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/01/hyaenodon-faces588-1.jpg” alt=”Figure 1. Hyaenodon species + Didymoconus colgati and D berkeyi to scale.” width=”584″ height=”1229″ srcset=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/01/hyaenodon-faces588-1.jpg?w=584&h=1229 584w, https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/01/hyaenodon-faces588-1.jpg?w=71&h=150 71w, https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/01/hyaenodon-faces588-1.jpg?w=143&h=300 143w, https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/01/hyaenodon-faces588-1.jpg 588w” sizes=”(max-width: 584px) 100vw, 584px” />
Figure 2. Hyaenodon species + Didymoconus colgati and an earlier version of Didiymoconus berkeyi to scale.
Wang et al wrote,
“The presumed fossorial adaptations in didymoconids, coupled with their puncturing cheek teeth, suggest an underground life feeding on insects and worms. The prominently short and robust hand and forearm, in contrast to a slender hindlimb, is suited for strength in digging.
“Furthermore, the unusually strong cranial construction with a broad muzzle and extremely widened and flattened posterior part of skull may also be adaptations for fossorial habits.”
Figure 2. Didelphodon skeleton.
” data-medium-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/10/didelphodon_lateral588.jpg?w=300″ data-large-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/10/didelphodon_lateral588.jpg?w=584″ class=”size-full wp-image-94795″ src=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/10/didelphodon_lateral588.jpg” alt=”Figure 2. Didelphodon skeleton. ” width=”584″ height=”189″ srcset=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/10/didelphodon_lateral588.jpg?w=584&h=189 584w, https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/10/didelphodon_lateral588.jpg?w=150&h=48 150w, https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/10/didelphodon_lateral588.jpg?w=300&h=97 300w, https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/10/didelphodon_lateral588.jpg 588w” sizes=”(max-width: 584px) 100vw, 584px” />
Figure 3. Didelphodon skeleton. Note the widespread fingers and toes indicating an aquatic, otter-like lifestyle. This skeleton looks big, but Didelphodon was just a little larger than a Virginia opossum
These two taxa
are sisters to the clade that includes the recently extinct Tasmanian wolf, Thylacinus and its larger relatives, Harpagolestes macrocephalus and Andrewsarchus.
Harpagolestes macrocephalus may be a juvenile Andrewsarchus based on the shorter rostum.
Note the blunt crushing teeth in Andrewsarchus, similar to those in Didelphodon.
Figure 2. The YPM 11901 specimen of Harpagolestes macrocephalus has a skull similar enough to the much larger Andrewsarchus. The smaller specimen has a shorter rostrum, larger orbit and only three erupted molars.
” data-medium-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/01/harpagolestes-macrocephalus-ypm-11901-588.jpg?w=275″ data-large-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/01/harpagolestes-macrocephalus-ypm-11901-588.jpg?w=584″ class=”size-full wp-image-91141″ src=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/01/harpagolestes-macrocephalus-ypm-11901-588.jpg” alt=”Figure 2. The YPM 11901 specimen of Harpagolestes macrocephalus has a skull similar enough to the much larger Andrewsarchus. The smaller specimen has a shorter rostrum, larger orbit and only three erupted molars.” width=”584″ height=”637″ srcset=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/01/harpagolestes-macrocephalus-ypm-11901-588.jpg?w=584&h=637 584w, https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/01/harpagolestes-macrocephalus-ypm-11901-588.jpg?w=138&h=150 138w, https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/01/harpagolestes-macrocephalus-ypm-11901-588.jpg?w=275&h=300 275w, https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/01/harpagolestes-macrocephalus-ypm-11901-588.jpg 588w” sizes=”(max-width: 584px) 100vw, 584px” />
Figure 2. The YPM 11901 specimen of Harpagolestes macrocephalus has a skull similar enough to the much larger Andrewsarchus. The smaller specimen has a shorter rostrum, larger orbit and only three erupted molars.
These appear to be novel hypotheses of interrelationships.
If not, please provide a citation or two so I can promote them here.
References
Wang X, Downs W, Xie J and Xie G 2001. Didymoconus (Mammalia: Didymoconidae) from Lanzhou Basin, China and its strategraphic and ecological significance. Journal of Vertebrate Paleontology 21(3): 555-564.
wiki/Didelphodon
wiki/Didymoconus
Source: https://pterosaurheresies.wordpress.com/2025/10/09/didelphodon-and-didymoconus-berkeyi-now-nest-together-in-the-lrt/
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