Pucadelphys enters the LRT

Known from Early Paleocene fossils in Bolivia,
with a phylogenetic genesis in the early Jurassic, Pucadelphys andinus (Figs. 1-3), nests in the large reptile tree (LRT, 1870+ taxa) just prior to the extant arboreal didelphid, Caluromys (Figs. 3-4). These taxa nest as omnivores between the largely herbivorous marsupials and the largely carnivorous marsupials, not far from the omnivorous ancestors of placentals.

35 partial skeletons are known
from mouse-like Pucadelphys, dying en masse within ten feet of each other, perhaps during a flash flood. This was originally considered odd because usually marsupials are territorial and isolated from one another (kangaroos are exceptions to this trend). Twelve are female. Six are male with larger heads and larger canines. Five were juveniles. Ladeveze et al. 2011 concluded, “the early Palaeocene P. andinus population at Tiupampa was a socially interacting group, characterized by gregariousness, male–male competition and polygyny.”

Figure 3. Photo of gregarious didelphids from Astúa et al. 2015. ” data-medium-file=”https://pterosaurheresies.files.wordpress.com/2021/06/gregarious_didelphid588.jpg?w=200″ data-large-file=”https://pterosaurheresies.files.wordpress.com/2021/06/gregarious_didelphid588.jpg?w=584″ src=”https://pterosaurheresies.files.wordpress.com/2021/06/gregarious_didelphid588.jpg” alt=”Figure 2. Photo of gregarious didelphids from Astúa et al. 2015.” class=”wp-image-56450″ />

Later, Astúa et al. 2015
reported the first evidence of gregarious denning in didelphids supported by photos (Fig. 2)

Surprisingly
Pucadelphys phylogenetics are rather difficult to find. Pucadelphys is al so close to Caluromys geographically. Prepubes are present on both taxa.

Figure 1. Pteropus and Caluromys compared in vivo and three views of their skulls. Caluromys is in the ancestry of bats and shows where they inherited their inverted posture. ” data-medium-file=”https://pterosaurheresies.files.wordpress.com/2018/08/pteropus_caluromys588.jpg?w=138″ data-large-file=”https://pterosaurheresies.files.wordpress.com/2018/08/pteropus_caluromys588.jpg?w=471″ src=”https://pterosaurheresies.files.wordpress.com/2018/08/pteropus_caluromys588.jpg” alt=”Figure 1. Pteropus and Caluromys compared in vivo and three views of their skulls. Caluromys is in the ancestry of bats and shows where they inherited their inverted posture.” class=”wp-image-32694″ />

References
Astúa D et al. 2015. First evidence of gregarious denning in opossums (Didelphimorphia, Didelphidae), with notes on their social behaviour. Biol. Lett. 11: 20150307.
http://dx.doi.org/10.1098/rsbl.2015.0307
Ladeveze S, de Muizon C, Beck R, Germain D and Cespedes-Paz R 2011. Earliest evidence of mammalian social behaviour in the basal Tertiary of Bolivia Nature, 474, 83-86 DOI: 10.1038/nature09987
Marshall LG and De Muizon C 1988. The Dawn of the Age of Mammals in South America. National Geographic Research 4:23-55.
Marshall LG, de Muizon C and Sigogneau-Russsell D 1995. Pucadelphys andinus (Marsupialia, Mammalia) from the early Paleocene of Bolivia. Part I: The locality of Tiupampa: age, taphonomy and mammal fauna. Mémoires du Muséum national d’histoire naturelle 165: 11–20.

https://www.nbcnews.com/id/wbna42960300