Biology

Recently-discovered tarantula sports a mysterious back horn

Recently-discovered tarantula ...
Although other types of baboon tarantulas also have horns on their back, the structures are much harder and shorter
Although other types of baboon tarantulas also have horns on their back, the structures are much harder and shorter
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Although other types of baboon tarantulas also have horns on their back, the structures are much harder and shorter
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Although other types of baboon tarantulas also have horns on their back, the structures are much harder and shorter
This is an individual of the newly described species (Ceratogyrus attonitifer) in defensive posture 
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This is an individual of the newly described species (Ceratogyrus attonitifer) in defensive posture 
The purpose of the spider's back horn remains unknown
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The purpose of the spider's back horn remains unknown

Many times, when new species are discovered, the characteristics that set them apart can only be appreciated by scientists. That isn't the case with the Ceratogyrus attonitifer tarantula, however – the thing has a long, soft horn protruding out of its back, and nobody knows why it's there.

A member of the existing baboon tarantula family, C. attonitifer was first discovered when several female specimens were collected between 2015 and 2016 in the miombo-tree forests of central Angola. They were gathered by scientists taking part in the National Geographic Okavango Wilderness Project, which is aimed at exploring the biodiversity of Africa's Okavango Delta.

Although some other baboon spiders do also have "back horns," the appendages are much harder and shorter than that of the newly-classified species. In all cases, the purpose of the structure remains unknown.

This is an individual of the newly described species (Ceratogyrus attonitifer) in defensive posture 
This is an individual of the newly described species (Ceratogyrus attonitifer) in defensive posture 

Thanks to information provided by local indigenous people, however, some things are known about C. attonitifer's behaviour. Known as "chandachuly" by tribes in the area, the spider is said to prey mostly on insects, with females enlarging existing tarantulas' burrows instead of digging their own. Additionally, its venom is reportedly not dangerous to humans, although fatalities have occurred from bites getting infected.

A paper on the findings was recently published in the journal African Invertebrates. And the Latin name "Ceratogyrus attonitifer," incidentally, roughly translates to "bearer of astonishment."

Source: Pensoft Publishers

4 comments
PAV
I postulate that it is there to deter predators such as the tarantula hawk. https://en.m.wikipedia.org/wiki/Tarantula_hawk
Expanded Viewpoint
But being as soft as it is, and with no venom in it to defend against wasps. that explanation doesn't hold any water. If the removal of this back horn doesn't affect the life of the spider, then it would be safe to say that it's just a genetic anomaly, a mutation that occurred due to some chromosome damage, and it has been passed on for who knows how many generations. Many years ago, a spontaneous mutation was seen in the rosettes in the coat pattern of a Leopard's back, near the tail. No one knows how or why it happened, but it did, and it was evidently passed on. Randy
amazed W1
Looks suspiciously like an ear to me, specially with a shape that could channel sound energy down towards its back. But agreed if its there only on females then it probably evolved because males found it attractive, like the lyre bird's lyre which attracts females in that case.
Imran Sheikh
Probably an old model of Tarantula Spider with an Antenna ;-)