Oodectes: a phylogenetically miniaturized Merycoidodon
Oodectes is not a juvenile.
Oodectes (Fig 1) has a full set of adult teeth, despite the relatively large orbit, short snout and small size. Retaining juvenile traits into adulthood = neotony.
Otherwise
Oodectes has identical scores to Merycoidodon in the large reptile tree (LRT, 2332 taxa) so far as can be determined with available data (Fig 1).
Figure 3. The oreodont, Merycoidodon, compared to scale with Oodectes.
” data-medium-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2024/07/merycoidodon.skull588.jpg?w=291″ data-large-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2024/07/merycoidodon.skull588.jpg?w=584″ class=”size-full wp-image-87652″ src=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2024/07/merycoidodon.skull588.jpg” alt=”Figure 3. The oreodont, Merycoidodon, compared to scale with Oodectes.” width=”584″ height=”603″ srcset=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2024/07/merycoidodon.skull588.jpg?w=584&h=603 584w, https://pterosaurheresies.wordpress.com/wp-content/uploads/2024/07/merycoidodon.skull588.jpg?w=145&h=150 145w, https://pterosaurheresies.wordpress.com/wp-content/uploads/2024/07/merycoidodon.skull588.jpg?w=291&h=300 291w, https://pterosaurheresies.wordpress.com/wp-content/uploads/2024/07/merycoidodon.skull588.jpg 588w” sizes=”(max-width: 584px) 100vw, 584px” />
Figure 1. The oreodont, Merycoidodon, compared to scale with the much smaller sister, Oodectes.
Merycoidodon was named decades before Oodectes.
So if these two are indeed congeneric, Merycoidodon would have priority. Adult size alone likely makes them separate species.
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.
Perhaps similar, but maybe different –
Harpagolestes macrocephalus might be a juvenile Andrewsarchus. It has four molars but the fourth was a vestige (or about to erupt?). The snout was short and the orbit was larger than in related taxa, even smaller taxa like tiny Barinya (Fig 3). Those might be juvenile traits.
Harpagolestes macrocephalus and Andrewsarchus were found
a Pacific Ocean apart from each other: Wyoming and Mongolia. Some specimens referred to Harpogolestes have been recovered from Mongolia, and some of these specimens are mesonychids, not andrewsarchids.
Yes, convergence can be difficult to untangle.
Andrewsarchus and kin (Fig 2) used to nest with Mesonyx and Sinonyx in the LRT. Now they nest more primitively in the LRT among the marsupials along with extant Myrmecobius (Fig 3), a taxon about the size of Barinya.
Figure 3. The skulls of Myrmecobius (left) and Barinya (right) to scale plus Myrmecobius in vivo. DGS colors added here.
” data-medium-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/01/myrmecobius_barinya588.jpg?w=300″ data-large-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/01/myrmecobius_barinya588.jpg?w=584″ class=”size-full wp-image-91146″ src=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/01/myrmecobius_barinya588.jpg” alt=”Figure 3. The skulls of Myrmecobius (left) and Barinya (right) to scale plus Myrmecobius in vivo. DGS colors added here. ” width=”584″ height=”555″ srcset=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/01/myrmecobius_barinya588.jpg?w=584&h=555 584w, https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/01/myrmecobius_barinya588.jpg?w=150&h=143 150w, https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/01/myrmecobius_barinya588.jpg?w=300&h=285 300w, https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/01/myrmecobius_barinya588.jpg 588w” sizes=”(max-width: 584px) 100vw, 584px” />
Figure 3. The skulls of Myrmecobius (left) and Barinya (right) to scale plus Myrmecobius in vivo. DGS colors added here.
Merycoidodon culbertsoni
(Leidy 1848; Late Eocene to Late Oligocene, 38–16 mya; 1.4 m in length)
Oodectes herpestoides
(Wortman 1901; late Paleocene to Middle Eocene, known from skull only).
Andrewsarchus mongoliensis
(Osborn 1924; middle Eocene, 45 mya; AMNH 20135; 83cm skull length).
Harpagolestes macrocephalus
(Worthman 1901; late Paleocene, 50 mya.
References
Leidy J 1856. Notices of extinct Vertebrata discovered by Dr. F. V. Hayden, during the
expedition to the Sioux country under the command of Lieut. G. K. Warren. Ibid., vol. 8, pp. 311-312.
Osborn HF 1924. Andrewsarchus, giant mesonychid of Mongolia. American Museum Noviattes 146: 1-5.
Wortman JL 1901. Studies of Eocene Mammalia in the Marsh Collection, Peabody Museum. The American Journal of Science, series 4 12(70):281-296.
wiki/Oodectes
wiki/Merycoidodon
wiki/Andrewsarchus
wiki/Harpagolestes
Source: https://pterosaurheresies.wordpress.com/2025/01/16/oodectes-a-phylogenetically-miniaturized-merycoidodon/
