Similarities/differences between the porcupines of different Hemispheres: Erethizon vs Hystrix, part 1

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(Many thanks to Kim Cabrera @beartracker for information useful in this series of Posts.)

Among the various mammals that defend themselves by means of spines, 'porcupines'

However, the term 'porcupine' conflates two different lineages of rodents (https://animals.sandiegozoo.org/animals/porcupine). While these are similar enough to be confused in the public mind, they also differ significantly.

TAXONOMY

Any comparison is complicated by the fact that

However, I treat collectively the five species of Hystrix, namely

BODY SIZE and FORM

Erethizon and Hystrix overlap broadly in body mass, in the range 6-13 kg. However, the former is smaller-bodied than the latter.

Erethizon weighs as little as 3.5 kg when adult and lean, whereas Hystrix weighs as much as 25 kg. The heaviest, fattest specimens recorded for the two genera are 18 kg vs 27 kg.

In Erethizon, males outsize females; in Hystrix, the sexes have similar body size (https://www.tandfonline.com/doi/abs/10.1080/11250008709355592).

In https://www.youtube.com/watch?v=w4NfE9mqU64, the individual of Panthera pardus is an adult male, probably weighing more than 55 kg. By comparison, this individual of Hystrix africaeaustralis - as likely female as male - may weigh as much as 25 kg.

Both genera have small eyes (https://stock.adobe.com/sk/search/images?k=porcupine+face&asset_id=480402738 and https://stock.adobe.com/sk/search/images?k=porcupine+face&asset_id=175434829 and https://www.istockphoto.com/photo/crested-porcupine-gm90848177-2184836) and the same dental formula. However, the skulls differ surprisingly. That of Erethizon (https://animaldiversity.org/collections/contributors/skulls/erethizon/e._dorsatum/87345.lateral/) is unremarkable among rodents. By contrast, that of Hystrix (https://www.inaturalist.org/observations/36773744 and https://www.inaturalist.org/observations/17389159 and https://animaldiversity.org/collections/contributors/phil_myers/ADW_mammals/specimens/Rodentia/Hystricidae/Hystrix_indica/lateral6337/) has extremely inflated nasal and frontal bones.

The cranium also seem to differ in relative size. If Erethizon is brainier than Hystrix, this would be consistent with its play behaviour in adulthood (https://psycnet.apa.org/record/1944-03113-001) and its performance in memorising mazes (https://psycnet.apa.org/record/2005-14412-004).

The tail is proportionately larger in Erethizon (https://www.sciencephoto.com/media/1009962/view/north-american-porcupine-skeleton and https://fineartamerica.com/featured/1-north-american-porcupine-skeleton-millard-h-sharp.html and https://www.istockphoto.com/photo/north-american-porcupine-on-a-branch-gm519080646-90356241) than in Hystrix (https://paolov.files.wordpress.com/2015/03/20140227_143245.jpg and https://www.alamy.com/porcupine-skeleton-in-profile-view-after-antique-engraving-from-the-19th-century-image434355969.html).

POSTURES and LOCOMOTION

Both genera use the same gait in walking.

Erethizon:
https://www.inaturalist.org/observations/26949994 and https://www.shutterstock.com/nb/video/clip-2870482-north-american-porcupine-erethizon-dorsatum-walking-along and https://www.youtube.com/watch?v=cnos437-t18 and https://www.inaturalist.org/observations/95054372 and https://www.pond5.com/stock-footage/item/12263333-north-american-porcupine-walking-along-road-leaf-stuck-its-f.

Hystrix:
https://www.istockphoto.com/photo/porcupine-walking-gm177703348-24110328 and https://www.youtube.com/watch?v=5nbaSyg3Z1M.

Both genera prefer to commute along pathways, and Erethizon depends on creating its own pathways when commuting across deep snow.

The tracks of Erethizon (https://www.bear-tracker.com/porcpine.html) and Hystrix (https://twitter.com/bgsurvival/status/731435193278566400) are similar. In both genera, the feet are usually pointed somewhat inward in the walking gait.

However, the forefeet of the two genera differ. In Erethizon (https://natureidentification.com/how-to-identify-porcupine-erethizon-dorsatum-tracks/), the claws are long, the bare surface is rough, and the pollex is present, albeit only as a clawless pad. These features differ from Hystrix (https://www.natureinstock.com/search/preview/cape-porcupine-hystrix-africaeaustralis-adult-close-up-of-front-foot/0_11296644.html and https://www.inaturalist.org/observations/19891886).

Both Erethizon and Hystrix are able to swim (https://www.researchgate.net/publication/330451642_Behaviour_of_a_porcupine_Erethizon_dorsatum_swimming_across_a_small_boreal_stream and https://www.youtube.com/watch?v=wt1PMbVnB44). Neither genus seems capable of jumping.

However, postures and locomotion differ between the two genera in important ways.

Erethizon differs categorically from Hystrix in adopting the following postures/gaits, all of which use the muscular tail as a prop:

Erethizon is capable of hanging upside down from branches (https://natlands.org/porcupines/ and https://www.istockphoto.com/photo/north-american-porcupine-gm1285939555-382593958), but cannot locomote while doing so.

By contrast, Hystrix climbs so poorly that adults can reputedly be kept captive by walls only one metre high.

Neither Erethizon nor Hystrix has spines on the ventral surfaces. However, in Erethizon the bristly hairs here - particularly on the ventral surface of the tail - enhance friction during climbing, compensating partly for the poor development of the pollex (https://www.inaturalist.org/observations/112849002 and https://www.shutterstock.com/nb/image-photo/north-american-porcupine-erethizon-dorsatum-on-310015790 and https://www.adfg.alaska.gov/index.cfm?adfg=northamericanporcupine.main).

Erethizon seems hardly able to run (https://www.youtube.com/watch?v=4v-XGIi0O4s and https://www.shutterstock.com/nb/image-photo/porcupine-running-thru-winter-snow-colville-108288905 and https://www.alamy.com/adult-north-american-porcupine-erethizon-dorsatum-running-in-glacier-bay-national-park-alaska-united-states-of-america-north-america-image417695139.html).

Hystrix is slow-moving relative to ungulates, but is versatile in its terrestrial gaits, as follows:

to be continued...

Posted by milewski milewski, May 01, 2022 22:15

Comments

Posted by milewski 3 months ago (Flag)

Erethizon can run on the ground for short distances but they are really not well-built for running. They usually just walk. I think, if one were scared or startled, it would run for a short ways.

Posted by beartracker 3 months ago (Flag)

@beartracker Many thanks for your valuable reply.

Another question:

In my own studies of Panthera pardus, I have noticed that this felid eats the hooves of small bovids along with the flesh and cartilage. The hooves emerge intact in the feces. The point is that the big cat swallows keratinous body-parts as part of the meal, even though these are indigestible. I understand that Puma concolor is a considerable predator on Erethizon. So I would love to know whether this big cat swallows spines ('quills') along with the meal, or carefully discards them while eating. If a carnivore were to swallow spines, do you think these would lodge in its gut-walls and harm it by means of the barbs (which would presumably be fatal)? Have you ever observed the spines of Erethizon in the feces of any carnivore, or in the pellets cast by owls?

Posted by milewski 3 months ago (Flag)

As far as I know, mountain lions skin out the porcupines and the quills are not eaten. That doesn't mean a stray quill or two doesn't get accidentally eaten in the process. I haven't found quills in mountain lion feces, but that's mostly because porcupines have become quite rare in my region. Their decline is under study.

Posted by beartracker 3 months ago (Flag)

Also, I don't know if the digestive acids would soften the barbs in the predator's stomach. If not, then the barbs might cause problems inside the digestive system. I've found hooves in scats before.

Posted by beartracker 3 months ago (Flag)

Hi Uncle Antoni,
I have not had sufficient time to read the last three articles you tagged me on, due mostly to the identification craze after CNC. Can you please re-tag me after the ID period is over?
Thanks!
Ludwig

Posted by ludwig_muller 3 months ago (Flag)

@beartracker The following https://www.inaturalist.org/observations/6575340 suggests that Erethizon, when walking, tends to keep the foreclaws off the ground. (Also see https://www.pond5.com/stock-footage/item/12263333-north-american-porcupine-walking-along-road-leaf-stuck-its-f.) In your experience, do the tracks generally confirm this? If true, it might be understandable in terms of keeping the claws sharp for climbing. On the same topic, does Erethizon dig for roots, and if so does it use the foreclaws or the hindclaws?

Posted by milewski 3 months ago (Flag)

They walk so that the claw tips are what hits the ground rather than the entire 'finger.' Their tracks commonly show the palms and then just the claw tips or holes made by them. Possibly also due to having such long claws. I haven't heard that they dog for roots, although I suppose it's possible if other, more preferred, foods are lacking.

Posted by beartracker 3 months ago (Flag)

Erethizon bathygnathum, which lived in North America in the Pleistocene, seems to have been larger-bodied than E. dorsatum (https://www.floridamuseum.ufl.edu/wp-content/uploads/sites/35/2017/03/Vol-27-No-1.pdf). It was probably similar to Hystrix in body size.

Posted by milewski 3 months ago (Flag)

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