#kogaionidae

[obscurefossils]

Hainina belgica

Hainina was a genus of multituberculate mammal from the Late Cretaceous and Early Paleogene. Its type species is H. belgica. Three other species are also known, those being H. godfriauxi, H. pyrenaica, and H. vianeyae. Known fossils were found in the Hainin Formation in Belgium as well as the Pyrenees Mountains in Spain and the Cernay Formation in Cernay, France; additional, unassigned fossils were discovered in the Densus-Ciula Formation and Jibou Formation, both in Romania. Hainina is one of the few multituberculate mammals from Europe to survive the K-Pg extinction into the Paleogene.

Hainina belgica is named for its place of discovery, the Hainin Formation in Belgium. H. godfriauxi is named for I. Godfriaux, who worked on the fossil. H. pyrenaica is also named for its place of discovery, the Pyrenees. H. vianeyae is named in honor of Monique Vianey-Liaud, the first author to study it.

Hainina's autapomorphies include its textured and ornamented enamel, a trait that none of the other Kogaionidae members share.

Hainina is part of the Kogaionidae family along with three other genera, Barbatodon, Kogaionon, and Litovoi. This family is placed as one of the most basal members of Cimolodonta, second only to Bryceomys. Kogaionids lived on the Hațeg Island, which was practically devoid of any mammalian competition at the time. This allowed at least some genera to develop red-pigmented teeth, a trait now only found in modern rodents and shrews. Hainina specimens consist of multiple teeth, as is common for mammals of the time period. These consist entirely of premolars and molars.

Original paper: Description for H. belgica and H. godfriauxi; description for H. pyrenaica and H. vianeyae

Wikipedia article: https://en.wikipedia.org/wiki/Hainina

[alphynix]

Island Weirdness #10 -- The Kogaionids

Multituberculates were a group of rodent-like mammals that originated back in the Early Jurassic, at a point on the mammalian family tree between the origin of monotremes and the earliest therians (represented today by marsupials and placentals).

While they were an incredibly successful group, found around the world in large numbers, in Late Cretaceous Europe multis had become incredibly rare and restricted to just a single place: Hațeg Island.

Isolated there, they evolved into a unique family known as the kogaionids, diverging from their ancestral mostly-herbivorous diet to instead become specialized insectivores with distinctly red iron-pigmented teeth and huge blade-like lower premolars.

Skull of Barbatodon (from fig 2 in Smith T, Codrea V (2015) Red iron-pigmented tooth enamel in a multituberculate mammal from the Late Cretaceous Transylvanian “Haţeg Island.” PLoS ONE 10(7): e0132550. doi: 10.1371/journal.pone.0132550  || CC-BY-4.0 )

Some of them also had oddly domed skulls and proportionally tiny brains, along with highly acute senses of smell, eyesight, balance, and motor control.

Kogaionon ungureanui was one of the first kogaionids to be discovered, and gives its name to the group as a whole. Although known only from a skull, it was probably rat-sized, around 30cm long (~12").

Unusually for island species, which are often ecologically fragile and vulnerable, the kogaionids’ insectivorous habits allowed them to successfully survive through the end-Cretaceous mass extinction 66 million years ago while the Hațeg dinosaurs and pterosaurs perished. And when conditions changed and their island home became reconnected to the rest of Europe they rapidly spread out and became common across the entire region for a further 10 million years, only finally disappearing in the early Eocene about 56 million years ago.

[alphynix]

Litovoi tholocephalos, a multituberculate mammal from the Late Cretaceous of Romania (~70-66 mya). Living on what was at the time the large offshore Hațeg Island, this rat-sized animal (about 25cm /10″ long) was part of a lineage of insectivorous multis called the kogaionids, with the same sort of red-colored enamel on its teeth as other species like Barbatodon.

Its brain was surprisingly tiny proportional to its size -- one of the smallest known brain-to-body ratios of any mammal, and more similar to those of non-mammalian cynodonts -- but it also seems have been highly specialized for processing sensory input, with relatively enormous regions associated with smell, eyesight, balance, and motor control. The olfactory bulbs of its brain were so enlarged, in fact, that they caused its skull to bulge out into an unusually dome-shaped forehead.

Its reduced brain size may have been due to limited food availability on its isolated island home. Brains are very metabolically expensive organs, and some other extinct island mammals like hippos, hominids, and goats are also known to have evolved smaller brain sizes. Modern shrews even seasonally shrink their own brains during winter for similar energy-saving reasons.

[alphynix]

They just described Litovoi, the dumbest mammal ever. Also little pachycephalosaur-like multie.

Well, it’s a Hațeg Island species, of course it’s weird.

But we can’t really make any judgements about its intelligence. Yes, its brain/body mass ratio was very low for a mammal, but still similar to that of ancestral mammaliaformes and cynodonts -- so relatively “primitive”, but that doesn’t necessarily mean “stupid”. Since it also had well-developed and enlarged brain regions associated with smell, eyesight, and balance/motor-control, it was probablyactually highly specialized for something.

The overall reduction in brain size was likely due to limited food resources -- big brains are very metabolically expensive, and modern shrews even shrink their own brains during winter for the same sort of reason.

I also can’t find any evidence of the domed skull being convergent with headbutting animals. The dome shape apparently comes from the skull having to accommodate around the highly expanded olfactory bulbs of the brain -- I don’t see any mention of the sort of reinforced thickened bone that would indicate pachy-like behavior.