A best-kept secret of the marsupial lion

The name 'marsupial lion' suggests that Thylacoleo carnifex (https://www.youtube.com/watch?v=dGsteaaM7Pk and https://prehistoric-fauna.com/Thylacoleo and https://en.wikipedia.org/wiki/Thylacoleo_carnifex and https://phys.org/news/2018-12-first-ever-skeleton-thylacoleo-australia-extinct.html and https://australian.museum/learn/animals/mammals/thylacoleo-carnifex/#:~:text=A%20study%20of%20the%20skull,a%20tooth%20specialized%20for%20carnivory and http://www.naturalworlds.org/thylacoleo/introducing/presenting/presenting_tc_1.htm) - which became extinct perhaps thirty thousand years ago - was an Australian counterpart to the big cats of other continents.

However, there is a big problem: the dentition of Thylacoleo lacks any tooth capable of puncturing the flesh of prey animals. There is therefore ultimately no analogy with the canine teeth of Carnivora.

In profile, the front teeth do project from the jaws suggestively (https://cosmosmagazine.com/history/palaeontology/secrets-of-australias-marsupial-lion-revealed/).

However, a frontal view (https://skull-blog.tumblr.com/image/35002390335 and https://phys.org/news/2016-08-elbows-extinct-marsupial-lion-unique.html and https://indaily.com.au/news/science-and-tech/2016/02/18/australias-marsupial-lion-claws-its-way-out-of-the-darkness/) reveals that these are incisors, so bunched together as to invalidate the explicit or implicit attempts that have been made by previous authors (e.g. https://zslpublications.onlinelibrary.wiley.com/doi/abs/10.1111/j.1469-7998.2007.00389.x and https://www.sciencedirect.com/science/article/abs/pii/S0944200608000032) to interpret them as stabbers.

Nobody doubts that Thylacoleo was a 'top predator', because it possesses an extreme version of carnassial cheek-teeth (https://en.wikipedia.org/wiki/Carnassial and https://www.publish.csiro.au/zo/zo9880565).

However, the basic difference in canine dentition means that the marsupial lion was no more similar to a lion than a kangaroo is to a bighorn sheep. There is some analogy, but the differences are more significant than the similarities.

So how did Thylacoleo - which seems to have been slow-moving - procure food without biting in the way conventional for carnivores?

The staple prey of Thylacoleo were presumably extinct species of marsupials (e.g. https://en.wikipedia.org/wiki/Zygomaturus). Is it possible that Thylacoleo specialised on pouch-young (https://en.wikipedia.org/wiki/Pouch_(marsupial))?

If Pleistocene herbivores in Australia were like their living relatives, they were prepared to sacrifice their pouch-young to breed another day.

When chased to a point of distress (but not yet wounded), mothers of kangaroos evict juveniles from the pouch and tend not to reclaim them even if both mother and offspring happen to escape the attempted predation (e.g. see https://www.dpaw.wa.gov.au/images/documents/plants-animals/monitoring/sop/sop_care_of_evicted_pouch_young_v1.1_2017.pdf and https://veteriankey.com/veterinary-aspects-of-hand-rearing-orphaned-marsupials/ and https://www.northgeorgiazoo.com/zoo-am-i-blog/ask-a-zookeeper-sacrificing-babies).

Pouch-young of several species of marsupials have vocal cords capable of shrill cries. However, mothers seem deaf to the calls of the jettisoned, and neither mother nor pouch-young seems capable of restoring the former cosy maternal relationship even when the offspring have survived the attack.

This suggests that Thylacoleo might have been able to forage by harassing adults persistently, as opposed to having to kill them.

Faunas worldwide contain various examples of animals, including insects, lizards, fishes and rodents, that seem to sacrifice parts of their bodies as appeasements to predators. In a sense, the jettisoning or yielding of pouch-young can be seen as an extension of this syndrome, albeit one impossible for eutherian ('placental') mammals because of their built-in commitment to the protection of foetuses on pain of death of the mother herself.

Thylacoleo had a pair of retractable, probably hooked claws, one on each pollex (thumb, https://www.smithsonianmag.com/science-nature/how-changing-climate-may-have-killed-marsupial-lion-180970866/). It is possible that these filled in for the missing canines (https://phys.org/news/2016-08-elbows-extinct-marsupial-lion-unique.html). What is equally likely, however, is that these claws were used to force open the maternal pouch.

Judging from its bone-structure and its living relatives, Thylacoleo had a slow pace of life, a modest appetite, flat feet, and the kind of somnolent metabolic economy we see in the koala (https://en.wikipedia.org/wiki/Koala).

The largest herbivorous marsupials, presumably included among its prey, may have reproduced even more slowly than rhinos. If each adult female of Diprotodon (https://en.wikipedia.org/wiki/Diprotodon) raised an offspring only once every five years, then for any top predator to kill more than one adult in every 50 per year would risk eventual extermination of the population.

Hence the idea of a more sustainable mode of predation: one specialising on foetus-like juveniles and forgoing the need for canine teeth.

As a demographic clue based on the living fauna: kangaroos can reach 27 years old, whereas the domestic sheep (Ovis aries) is usually spent by 10 years. If each female kangaroo gives birth once every year, she can hypothetically afford to sacrifice 15 pouch-young and still replace herself and the father before she dies.

The pie of ecological niches has been sliced in unusual ways in Australia. This is the only place on Earth with hopping mammals as large as humans (kangaroos, https://en.wikipedia.org/wiki/Kangaroo), large herbivores digging complex tunnels (Vombatus and Lasiorhinus, https://en.wikipedia.org/wiki/Wombat), moles surviving in the interior deserts of any continent (Notoryctes, https://en.wikipedia.org/wiki/Marsupial_mole), and a non-flying mammal that eats only nectar and pollen (Tarsipes, https://en.wikipedia.org/wiki/Honey_possum#:~:text=The%20honey%20possum%20or%20noolbenger,Banksia%20coccinea%20and%20Adenanthos%20cuneatus.).

With such an array of odd precedents, is it not possible that Australia also claims the only pouch-raiding predator ever to have evolved?

Posted on Δεκέμβριος 24, 2021 0800 ΠΜ by milewski