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Male (a) and female (b) forms of Prolibytherium magnieri. P. fusus would have had similar ornaments. Art by I. Sánchez.

Paleo Profile: Pakistan’s Butterfly-Faced Beast

In any list of weird fossil mammals, the regular set of ancient beasts are trotted out. There’s always a brontothere. Uintatherium often shows up. Deinotherium isn’t a surprise, either. And while these long lost mammals are indeed wonderful, there are plenty of critters that are just as strange. One of my favorites is Prolibytherium.

Exactly what sort of beast Prolibytherium was, no one knows for sure. The herbivore has been punted around the hoofed mammal tree a bit, and, for the moment, it seems closest to a group of extinct, deer-like mammals called climacoceratids. But one thing is for sure – this mammal wore some very bizarre headgear.

The first species, named by Camille Arambourg from the 16 million year old rock of Libya, had a massive, splayed appendage growing from between its eyes and over the back of the head. And as Israel Sánchez and colleagues argued in 2010, these ornaments differed between the sexes, with probable females having minimalist spikes that more or less present the framework on which the broader male palms are supported. And now Melinda Danowitz, Rebecceca Domalski, and Nikos Solounias have named a new species of this unusual mammal, extending the range of Prolibytherium into Asia and its span back three million years.

The new species, Prolibytherium fusus, is only known from a 19 million year old braincase with the broad ornaments broken off. Yet, aside from the fractured attachments for the appendages, the back of the skull shows that this species must have had heavy appendages like its geologically younger relative. The occipital condyles – the attachment sites between the back of the skull and the front of the neck – are fused and thickened, providing greater support along the midline for carrying all that extra bone around. And, Danowitz and colleagues note, the reinforcement at the back of the skull might have had provided greater reinforcement for combat, too, although how these butterfly-faced mammals fought is so far left to our Cenozoic imagination.

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The back of the Prolibytherium fusus skill. 4 marks the fused occipital condyles. From Danowitz et al., 2015.

Fossil Facts

Name: Prolibytherium fusus

Meaning: Prolibytherium means “before Libya’s beast”, coined by Camille Arambourg in 1969 for a different species, while fusus refers to the fused occipital condyles at the back of the skull.

Age: About 19 million years old.

Where in the world?: Zinda Pir, Pakistan

What sort of critter?: A ruminant mammal of uncertain affinities.

Size: About the size of a caribou.

How much of the creature’s body is known?: A braincase with the cranial appendages broken off.


Sánchez, I., Quiralte, V., Morales, J., Azanza, B., Pickford, M. 2010. Sexual dimorphism of the frontal appendages of the early Miocene pecoran Prolibytherium Arambourh, 1961 (Mammalia, Ruminantia). Journal of Vertebrate Paleontology. doi: 10.1080/02724634.2010.483555

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