Egg shapes found in a Jurassic monotreme

Recent housekeeping in the LRT
finally got around to Agilodocodon (Fig 1), now a Middle Jurassic monotreme. The fossil is complete and articulated. Several small ovals appear on the fossil. These could be eggs.

“Monotreme eggs have a leathery shell. The eggs are retained inside the mother’s body for at least a couple of weeks. During that time, the mother provides the eggs with nutrients. Platypus females lay their eggs in a burrow.”

Figure 1. Agilodocodon in situ, as originally traced. DGS colors added here. ” data-image-caption=”

Figure 1. Agilodocodon in situ, as originally traced. DGS colors added here. Yellow ovals are possible eggs.

” data-medium-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2024/11/agilodocodon588.gif?w=193″ data-large-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2024/11/agilodocodon588.gif?w=584″ class=”size-full wp-image-89813″ src=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2024/11/agilodocodon588.gif” alt=”Figure 1. Agilodocodon in situ, as originally traced. DGS colors added here. ” width=”584″ height=”908″ srcset=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2024/11/agilodocodon588.gif?w=584&h=908 584w, https://pterosaurheresies.wordpress.com/wp-content/uploads/2024/11/agilodocodon588.gif?w=96&h=150 96w, https://pterosaurheresies.wordpress.com/wp-content/uploads/2024/11/agilodocodon588.gif?w=193&h=300 193w, https://pterosaurheresies.wordpress.com/wp-content/uploads/2024/11/agilodocodon588.gif 588w” sizes=”(max-width: 584px) 100vw, 584px” />

Figure 1. Agilodocodon in situ, as originally traced. DGS colors added here. Yellow ovals are possible eggs.

According to Wikipedia – Agilodocodon
“Agilodocodon was a genus of shrew-sized docodont from the Middle Jurassic, believed to be the earliest known tree-climbing mammaliaform.”

The LRT recognizes no mammaliaforms, just mammals, starting with Megazostrodon and including docodonts listed by Averianov 2010.

Agilodocodon scansorius
(Meng et al 2015; Middle Jurassic; BMNH 001138; 13 cm long) is considered a tree-climbing pre-mammal, but here nests between Krusatodon and Lactodens among the monotremes, a clade not mentioned by Meng et al, who wrote, “This fossil expands the range of known locomotor adaptations in docodontans to include climbing, in addition to digging and swimming.”

The authors wrote,
“Docodontans are extinct early mammaliaforms without living descendants, but they
were widespread and abundant in Laurasia during the Mesozoic (1–9). Mammaliaforms
bear key evidence of the earliest evolution of mammalian characteristics.”

In the LRT Agilodocodon has two living descendants, the platypus, Ornithorhynchus, and the echidna, Tachyglossus.

In the LRT “the earliest evolution of mammalian characteristics” belong to egg-laying monotremes. The authors don’t mention eggs or Lactodens, but compare the molar shape to Krusatodon and three other taxa based on jaws + teeth not tested in the LRT.

Figure 3. Manus of Eomaia (right) and Ornithorhynchus (left). Note the relatively long phalanges of the platypus, Ornithorhynchus, which is a swimmer, not a climber. ” data-image-caption=”

Figure 3. Manus of Eomaia (right) and Ornithorhynchus (left). Note the relatively long phalanges of the platypus, Ornithorhynchus, which is a swimmer, not a climber.

” data-medium-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2024/11/platypus-eomaia_manus588.jpg?w=300″ data-large-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2024/11/platypus-eomaia_manus588.jpg?w=584″ class=”size-full wp-image-89821″ src=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2024/11/platypus-eomaia_manus588.jpg” alt=”Figure 3. Manus of Eomaia (right) and Ornithorhynchus (left). Note the relatively long phalanges of the platypus, Ornithorhynchus, which is a swimmer, not a climber. ” width=”584″ height=”423″ srcset=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2024/11/platypus-eomaia_manus588.jpg?w=584&h=423 584w, https://pterosaurheresies.wordpress.com/wp-content/uploads/2024/11/platypus-eomaia_manus588.jpg?w=150&h=109 150w, https://pterosaurheresies.wordpress.com/wp-content/uploads/2024/11/platypus-eomaia_manus588.jpg?w=300&h=217 300w, https://pterosaurheresies.wordpress.com/wp-content/uploads/2024/11/platypus-eomaia_manus588.jpg 588w” sizes=”(max-width: 584px) 100vw, 584px” />

Figure 2. Manus of Eomaia (right) and Ornithorhynchus (left). Note the relatively long phalanges of the platypus, Ornithorhynchus, which is a swimmer, not a climber.

The authors wrote,
“In Agilodocodon, the phalanges are elongate relative to the metacarpals. The phalangeal index [PI: (combined length of proximal + intermediate phalanges)/(length of metacarpal) × 100] is 137% for manual ray 3, typical of primates and arboreal marsupials, carnivorans, and rodents, but well above the range of this index for terrestrial mammals.”

The related monotreme platypus, Ornithorhynchus (Fig 2) has an even larger PI for manual ray 3, yet is known as a swimmer and a digger, not a tree climber – but can climb small waterfalls. Ornithorhynchus is not mentioned in the authors’ 2015 text.

References
Averianov AA et al (3 co-authors) 2010. New docodontians from the Middle Jurassic of Siberia and reanalysis of docodonta interrelationships. Proceedings of the Zoological Institute RAS. 314 (2): 121–148.
Meng Q-J, Ji Q, Zhang Y-G, Liu D, Grossnickle DM and Luo Z-X 2015. An arboreal docodont from the Jurassic and mammaliaform ecological diversification. Science. 347 (6223): 764–768. doi:10.1126/science.1260879.

wiki/Agilodocodon