An extinct canid ('Canis rubronegrus') hiding in plain sight in the domestic dog (Canis familiaris)? part 2

@ludwig_muller @ptexis

...continued from https://www.inaturalist.org/posts/56803-an-extinct-canid-canis-rubronegrus-hiding-in-plain-sight-in-the-domestic-dog-canis-familiaris-part-1#

I have just read Smith et al. (2017, https://www.publish.csiro.au/zo/zo17040), which contains important data and analyses.

Please note that the terms 'braininess' and 'EQ', as I use them in this Post, are not synonymous.

This is mainly because EQ (encephalisation quotient)

• was designed as a species-specific index of braininess relative to the allometric expectations from body mass, and
• is poorly applicable to the domestic dog (Canis familiaris), with its extreme range of breeds.

EQ in canids tends to complicate rather than to clarify the picture of relative braininess. This is because the domestic dog varies so much in body mass (according to breed) that the ancestral body mass is obscure.

Despite the above complications, Smith et al. (2017) found that

• the wolf (Canis lupus) is indeed brainier than the domestic dog, with no overlap,
• the coyote (Canis latrans) and the Eurasian jackal (Canis aureus) seem brainier than the wolf, notwithstanding the fact that the former two spp. are about three-fold smaller-bodied (about 10 kg) than the latter (30 kg), and
• the black-backed jackal (Lupulella mesomelas) and particularly the side-striped jackal (Lupulella adusta) - despite being 'jackals' - are less brainy than like-size, wild spp. of Canis.

I have reshuffled the data in Smith et al. (2017) as follows, to list all those spp./breeds with body mass about 10 kg, in decreasing order of EQ:

• Boston terrier 8 kg EQ 164
• pug 8 kg EQ 158
• coyote (Canis latrans) 10.5 kg EQ 153
• miniature schnauzer 7 kg EQ 152.5
• dachshund 8 kg EQ 145
• miniature poodle 8 kg EQ 145
• fox terrier 8 kg EQ 144
• Eurasian jackal (Canis aureus) 9 kg EQ 142
• dingo 13 kg, EQ 137
• wirehaired fox terrier 9 kg EQ 135
• standard schnauzer 8 kg EQ 135
• New Guinea singing dog (Canis hallstromi) 11 kg EQ 124.5
• black-backed jackal (Lupulella mesomelas) 8 kg EQ 121.5
• short-eared dog (Atelocynus microtis, wild canid of South America) 9 kg EQ 119
• beagle 14.5 kg EQ 117.5
• cocker spaniel 13 kg EQ 116
• bush dog (Speothos venaticus, wild canid of South America) 6 kg EQ 102
• side-striped jackal (Lupulella adusta) 11 kg EQ 86

How do we interpret the fact that EQ in various breeds of the domestic dog exceeds that in various like-size wild canids? Part of the answer is that EQ was originally conceived as a species-specific quotient.

When applied to breeds within a species, EQ becomes subject to interpretation because of the uncertainty of 'typical' body mass, as follows: EQ exaggerates braininess in small-bodied breeds, and understates braininess in large-bodied breeds.

I assume that the EQ corresponding with the 'real' species-specific EQ of the domestic dog is about 1.0, corresponding to body mass about 20 kg.

Please bear in mind that the point of Smith et al (2017) was the braininess of the dingo relative to the domestic dog; all wild canid spp. were ancillary to their study.

On the above basis, the following picture emerges from Smith et al. (2017).

The domestic dog (excluding the dingo) is less brainy than both the wolf and the Eurasian jackal (C. aureus). It is true that the difference is greater relative to the wolf than relative to the Eurasian jackal. However, relating this to the question of the real main wild ancestor of the domestic dog is rather subjective.

It seems likely that 'Canis rubronegrus' would likewise have been brainier than the domestic dog, based on the finding that all three extant wild spp. of Canis (wolf, coyote, and Eurasian jackal) are brainier than the domestic dog.

So, the data analysed by Smith et al. (2017) do not necessarily undermine the possibility that the domestic dog, with its anthropogenic decephalisation, was mainly derived from an extinct jackal-like (relatively omnivorous, non-gregarious) species rather than the specialised carnivore that is the wolf.

However, the data do suggest that my hypothetical ancestral species, 'Canis rubronegrus', was larger-bodied (about 20 kg) than extant jackals (about 10 kg).

The kelpie breed, with its wild-type conformation and colouration, has body mass 11-20 kg (https://www.perplexity.ai/search/What-is-the-ToObfrkBRw2sKkYuQVAdLg).

The wild ancestor must have been somewhat large-bodied, on average, than the kelpie, if we are to make sense of the EQ values of jackal-size (about 10 kg) breeds of the domestic dog.

In other words, I suggest that 'Canis rubronegrus' was jackal-like in diet and sociality, more than in body size. This would be consistent with Bergmann's rule (https://en.wikipedia.org/wiki/Bergmann%27s_rule), if the ancestral species lived at the northern limit of the vegetated landscape in the Ice Age.

Posted on May 24, 2024 05:17 PM by milewski