Monkeys at the transition from baboons to apes
Two extant monkey skulls,
Cercobus and Macaca (Fig 1), are similar in several views. The teeth are also similar.
The foramen magnum is distinctly different in orientation.
Figure 1. Cercobus and Macaca skulls compared. Arrows point to differences in the foramen magnum (for the spinal chord) indicating a more upright carriage of the skull in Macaca.
” data-medium-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/02/cercocebus_macaca-skulls588.gif?w=269″ data-large-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/02/cercocebus_macaca-skulls588.gif?w=584″ class=”size-full wp-image-91653″ src=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/02/cercocebus_macaca-skulls588.gif” alt=”Figure 1. Cercobus and Macaca skulls compared. Arrows point to differences in the foramen magnum (for the spinal chord) indicating a more upright carriage of the skull in Macaca. ” width=”584″ height=”652″ srcset=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/02/cercocebus_macaca-skulls588.gif?w=584&h=652 584w, https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/02/cercocebus_macaca-skulls588.gif?w=134&h=150 134w, https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/02/cercocebus_macaca-skulls588.gif?w=269&h=300 269w, https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/02/cercocebus_macaca-skulls588.gif 588w” sizes=”(max-width: 584px) 100vw, 584px” />
Figure 1. Cercobus and Macaca skulls compared. Arrows point to differences in the foramen magnum (for the spinal chord) indicating a more upright carriage of the skull in Macaca. The Macaca palate is partially blocked by the mandible.
The rotation of the foramen magnum
to a more ventral position (Fig 1) seems to be the major difference between these two sister taxa in the large reptile tree (LRT, 2336 taxa).
Figure 2. Macaca skeleton. Note the quadrupedal, typical monkey pose, not reflective of the foramen magnum rotation.
” data-medium-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/02/macaca_skeleton588.jpg?w=300″ data-large-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/02/macaca_skeleton588.jpg?w=584″ class=”size-full wp-image-91655″ src=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/02/macaca_skeleton588.jpg” alt=”Figure 2. Macaca skeleton. Note the quadrupedal, typical monkey pose, not reflective of the foramen magnum rotation. ” width=”584″ height=”408″ srcset=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/02/macaca_skeleton588.jpg?w=584&h=408 584w, https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/02/macaca_skeleton588.jpg?w=150&h=105 150w, https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/02/macaca_skeleton588.jpg?w=300&h=210 300w, https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/02/macaca_skeleton588.jpg 588w” sizes=”(max-width: 584px) 100vw, 584px” />
Figure 2. Macaca skeleton. Note the quadrupedal, typical monkey pose, not reflective of the foramen magnum rotation.
You might think
the Macaca torso would be more vertical, oriented directly below the skull, rather than posterior to it, as in all prior tetrapods including Cercobus. This then would appear to be the first stage toward tail loss and, ultimately, bipedalism in the lineage of humans.
However
the museum mount skeleton of Macaca (Fig 2) shows a typical quadrupedal monkey-like pose. A quick glance at in vivo poses show Macaca sitting on its haunches in a large fraction, perhaps a majority of those pix.
Macaca mulatta
(originally Cercopithecus mulatta, Zimmermann 1780a, b) is the extant rhesus macaque, Old World monkey. Derived from a sister to Aegyptopithecus, it is basal to Proconsul.
According to Wikipedia, “Rhesus macaque have the widest geographic ranges of any nonhuman primate, occupying a great diversity of altitudes and a great variety of habitats, from grasslands to arid and forested areas, but also close to human settlements.” They live in troops of 20-200 males and females in a ratio of 1:4. Rhesus macaques are unusual in that the youngest females tend to outrank their older sisters. Perhaps because young females are more fit and fertile. Rhesus macaques interact using a variety of facial expressions, vocalizations, body postures, and gestures. Adult male macaques try to maximize their reproductive success by entering into sex with females, both in and outside the breeding period. Females prefer to mate with males that are not familiar to her. Outsider males who are not members of the female’s own troop are preferred over higher ranking males.”
“Humans and macaques apparently share about 93% of their DNA sequence and shared a common ancestor roughly 25 million years ago.”
References
Geoffroy Saint-Hilaire E 1812. Description des mammiferes qui se trouvent en
Egypte, Description de l’Egypte. II: Mammalia. L’Imprimerie Imperiale, Paris, 752 pp.
Zimmermann EAW 1780a. Geographische Geschichte des Menschen, und der allgemein verbreiteten vierfüßigen Thiere. Zweiter Band. Enthält ein vollständiges Verzeichniß aller bekannten Quadrupeden. Weygand, Leipzig.: 1-432.
Zimmermann EAW 1780b. Geogr. Gesch. Mensch. Vierf . Thiere vol.2 p.195.
wiki/Macaca
wiki/Collared_mangabey – Cercocebus
Source: https://pterosaurheresies.wordpress.com/2025/02/12/monkeys-at-the-transition-from-baboons-to-apes/
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