Apterodon: now a phylogenetically miniaturized Prodinoceras in the LRT
Two rarely described taxa,
the ‘most basal uintathere’ 3m, long-skulled, Late Paleocene, Prodinoceras (Figs 1–3) and the much smaller, dog-sized, long-skulled ‘hyaenodont’ Late Eocene, Apterodon (Fig 1) are in the spotlight today. Presently in the LRT Apterodon nests as a descendant of the much larger Prodinoceras. That means phylogenetic miniaturization = kids having kids = precocious sexual maturity and neotony appears to be at work here.
These two long-cranium taxa (Fig 1) have not been compared together before, but the LRT put them together by including them in the same wide gamut matrix file. Note the short rostrum and lack of premaxillary teeth in Apterodon. These are juvenile traits relative to Prodinoceras. That lack of teeth could be a result of loss during taphonomy.
Sorry it took so long to recognize these synapomorphies,
but the moment of discovery was well worth the wait.
Figure 1. Little Apterodon here compared to much larger and earlier Prodinoceras. Phylogenetic miniaturization appears to be at work here.
” data-medium-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/11/apterodon_macrognathus_skull588.jpg?w=88″ data-large-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/11/apterodon_macrognathus_skull588.jpg?w=301″ class=”size-full wp-image-95190″ src=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/11/apterodon_macrognathus_skull588.jpg” alt=”https://en.wikipedia.org/wiki/Apterodon” width=”584″ height=”1986″ srcset=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/11/apterodon_macrognathus_skull588.jpg?w=584&h=1986 584w, https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/11/apterodon_macrognathus_skull588.jpg?w=44&h=150 44w, https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/11/apterodon_macrognathus_skull588.jpg?w=88&h=300 88w, https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/11/apterodon_macrognathus_skull588.jpg 588w” sizes=”(max-width: 584px) 100vw, 584px” />
Figure 1. Little Apterodon here compared to much larger and earlier Prodinoceras. Phylogenetic miniaturization appears to be at work here.
Phylogenetically later descendants,
like Masrasector (Fig 1), continue this phylogenetic trend with a smaller cranial crest and smaller overall size.
Earlier
the large reptile tree (LRT, 2339 taxa) nested Masrasector basal to much larger fanged taxa, like Titanoides and Barylambda, at the base of the slow-moving, herbivorous sloth and glyptodon clade.
Figure 2. Prodinoceras skeleton from Piveteau (1961), after Flerov (1952). Length approximately 2.9 m.
” data-medium-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2024/10/prodinoceras.skeleton588.jpg?w=300″ data-large-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2024/10/prodinoceras.skeleton588.jpg?w=584″ class=”size-full wp-image-89344″ src=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2024/10/prodinoceras.skeleton588.jpg” alt=”Figure 2. Prodinoceras skeleton from Piveteau (1961), after Flerov (1952). Length approximately 2.9 m.” width=”584″ height=”235″ srcset=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2024/10/prodinoceras.skeleton588.jpg?w=584&h=235 584w, https://pterosaurheresies.wordpress.com/wp-content/uploads/2024/10/prodinoceras.skeleton588.jpg?w=150&h=60 150w, https://pterosaurheresies.wordpress.com/wp-content/uploads/2024/10/prodinoceras.skeleton588.jpg?w=300&h=121 300w, https://pterosaurheresies.wordpress.com/wp-content/uploads/2024/10/prodinoceras.skeleton588.jpg 588w” sizes=”(max-width: 584px) 100vw, 584px” />
Figure 2. Prodinoceras skeleton from Piveteau (1961), after Flerov (1952). Length approximately 2.9 m.
This match came as a phylogenetic surprise.
Apparently no one expected Prodinoceras to be ancestral to a lineage of much smaller, neotonous taxa, like Apterodon and Masrasector (Fig 1), nor the sloth connection.
The hypothetical origin of Prodinoceras
is shown below (Fig 3) in graphic form.
Figure 4. The origin of Prodinoceras from Didelphis and a series of transitional taxa of various sizes.
” data-medium-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/11/didelphis_descendants588.jpg?w=66″ data-large-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/11/didelphis_descendants588.jpg?w=224″ class=”size-full wp-image-95195″ src=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/11/didelphis_descendants588.jpg” alt=”Figure 4. The origin of Prodinoceras from Didelphis and a series of transitional taxa of various sizes. ” width=”584″ height=”2670″ srcset=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/11/didelphis_descendants588.jpg?w=584&h=2670 584w, https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/11/didelphis_descendants588.jpg?w=33&h=150 33w, https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/11/didelphis_descendants588.jpg 588w” sizes=”(max-width: 584px) 100vw, 584px” />
Figure 4. The origin of Prodinoceras from Didelphis and a series of transitional taxa of various sizes. Compare this drawing of Prodinceras to the photograph of the longer skull in figure 1.
Prodinoceras martyr
(Matthew, Granger and Simpson 1929, Late Paleocene, 2.9 m long) is traditionally considered the most basal uintathere. In the LRT it nests between Trigonostylops and the much smaller Apterodon.
Apterodon macrognathus
(Fischer 1880; Eocene to Oligocene, IVPP V 12385) is traditionally a member of the Hyaeodontida, a clade within Creodonta. Here Apterodon phylogenetically follows the much larger Prodinoceras and precedes Masrasector, an ancestor to sloths and glyptodons and several transitional taxa. Most specimens are from Egypt. The type genus is from Germany.
This appears to be a novel hypothesis of interrelationships.
If not, please provide a citation so I can promote it here.
References
Matthew WD, Granger W and Simpson GG 1929. Additions to the fauna of the Gashato Formation of Mongolia. American Museum Noviates 376: 1–12.
wiki/Prodinoceras
wiki/Apterodon
Source: https://pterosaurheresies.wordpress.com/2025/11/17/apterodon-now-a-phylogenetically-miniaturized-prodinoceras-in-the-lrt/
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