This suggests that the presence of the pouch plays a crucial role by providing a safe environment for continued development after birth, but its evolution is tied to trade-offs between offspring quantity and maternal investment.

Ancestral state reconstructions show that the pouch has been gained and lost multiple times during marsupial evolution, although the ancestral marsupial condition remains uncertain, but most likely corresponding to pouch absence.

We used phylogenetic comparative methods to investigate the relationship between pouch presence, body mass and litter size across 195 species. Our results show that the probability of pouch presence increases with body mass and decreases with litter size.

This is the question we set out to answer in a recent article published online by the journal Evolution. This article was written in collaboration with Daniel Casali, Gabby Guilhon, and @rmissagia.bsky.social, and is also part of Mariah Yoshikawa's master's thesis.
doi.org/10.1093/evol...

The paper was also recently published in the journal Ichnos and you can find it here: doi.org/10.1080/1042...

If you're interested, come check our poster on Saturday, November 15th, 4 PM. #SVP2025

This work was developed by me and may coauthors, @sergiolages.bsky.social, Leonardo de Melo Carneiro, Luana Cardoso de Andrade, and Rafael Costa da Silva.

In the case of N. fissuratus, the perpetuator was likely sparassodont metatherians, one of the few compelling evidence of this kind of predator-prey in the South American fossil record.

These large punctures on the symphiseal part of the jaws are consistent with predation by metatherians, as practiced by living didelphids

We describe a new ichnospecies, Nihilichnus fissuratus isp. nov., which are constituted of symmetrical marks on the mandibles, likely from antagonistic teeth.