The horns of the African aurochs and its evolutionary implications

I did a post on the African aurochs, Bos primigenius mauretanicus, a few years ago. The African aurochs is said to be morphologically very similar if not identical to the European aurochs, so that van Vuure (2005) concludes it might be exclusively geographical [1]. The only difference to the European aurochs mentioned in my old article is the fact that bulls likely had a colour saddle. However, there might be morphological differences in the horns of the African aurochs, which have previously not been recognized in the literature. 

 

In 2015, the oldest aurochs skull found so far was described [2]. It is from Tunisia and is very large-horned. But what was interesting to me about the horns was not their size, but their shape and orientation relative to the skull. They have an angle of 40° relative to the snout, which is narrower than in the European aurochs, where the range of angles of the horns relative to the snout is between 50 and 80° on average, and larger in single exceptions (such as in the skull exhibited at Horsholm). Also, the horns seem to be dorsoventrally compressed at the base or proximal half, while the distal end of the horn seems to be round in cross section. 

Due to the age of the skull (700.000 years), I was unsure whether to classify it as a member of B. p. mauretanicus, or maybe as a basal aurochs that lived before subspecies differentiation. 

However, I recently found a depiction of another African aurochs skull, that, because of its geologically younger age, certainly is a member of B. p. mauretanicus. The anatomical drawing is from a work from 1931 and is labelled as Bos opisthonomus, which is a junior synonym of B. p. mauretanicus. It shows the same anatomy as the 700.000 years old skull from Tunisia: horns facing forwards in a narrow angle (35°) and dorsoventrally compressed at the base or proximal half. The image is from Duerst (1931) [3]. 

An anatomical drawing of an African aurochs skull, from Duerst 1931

Thus, it seems that these two traits (dorsoventrally compressed horns at the base, horns facing forwards in an angle sharper than in the European aurochs), were general anatomical traits of the African aurochs. That the horns of the African aurochs faced forwards in a sharp angle also fits historic descriptions, because Herodotos describes that in North Africa there were bovines with horns so long and forwards-facing that they had to graze backwards [1]. Likely this referred to the African aurochs. Also ancient depictions of African aurochs show horns growing parallel to the snout, what suggests that the horns were facing forwards in a narrow angle. In European aurochs, and sometimes also domestic cattle, the horns were/are oval in cross section at the base as well (in Pleistocene European aurochs more so than in Holocene ones) [1], but this trait is definitely more expressed in the African aurochs. 

 

Apparently, the aurochs varied in horn orientation from subspecies to subspecies. While the African aurochs had the narrowest angle, the Indian aurochs and possibly B. p. suxianensis had the largest angle, and the European aurochs was in between. Whether the difference in horn orientation has a functional purpose or if the variation was merely a result of genetic drift is unclear to me. 

 

It is interesting to speculate about the evolutionary implications of the horn anatomy of B. p. mauretanicus. There are two conflicting hypotheses on the origin of Bos and the aurochs. One of the hypotheses postulates that Bos and the aurochs in particular evolved in Africa from Pelorovis oldowayensis, the other one suggests that Bos originated from Leptobos in Asia, and the aurochs from the very large-horned Bos acutifrons in India. The fact that the horns of the Indian aurochs are more upright than those of the other aurochs subspecies seems to support the latter hypothesis, as the horns of Leptobos are rather upright. However, the fact that the horns of the African aurochs have such a narrow angle between horns and snout and the dorsoventrally compressed horn bases support the origin from Pelorovis oldowayensis, as this species has horns with a very narrow angle relative to the snout and dorsoventrally compressed horns. Other cranial traits seem to support an origin from Leptobos, on the other hand. The origin of Bos probably can only be resolved by finding more fossils of relevant taxa. 

 

Literature

 

[1] van Vuure: Retracing the aurochs – history, morphology and ecology of an extinct wild ox. 2005. 

[2] Martinez-Navarro et al.: The early middle Pleistocene archaeopaleontological site of Wadi Sarrat (Tunisia) and the earliest record of Bos primigenius. 2014. 

[3] Duerst: Grundlagen der Rinderzucht – eine Darstellung der wichtigsten für die Entwicklung der Leistungen und der Körperformen des Rindes ursächlichen, physiologisch-anatomischen, zoologisch-paläontologischen, entwicklungsmechanischen und kulturhistorischen Tatsachen und Lehre. 1931. 

 

 

Differences between the Quagga Project zebras and the quagga

The Quagga Project likes to call their zebras “Rau quagga”, after the founder of the project Reinhold Rau. That is why I made the post Please don’t call it quagga. The advocates of the name “Rau quagga” state that it is O.K. to call the zebras that way because the “Rau” in “Rau quagga” underlines that they are different animals from the quagga. I, however, think it is not legitimate to call something that is not a quagga a “quagga”, with or without the “Rau” in front of it. Calling those zebras “Rau zebra” would be more adequate if the zebras of the Quagga Project need a name, because they are zebras in any case. 

 

Names aside, I made a post on the differences between the quagga and other zebras not so long ago. I think it is time to have a look at the differences between the zebras of the Quagga Project and the quagga. 

The Quagga Project focuses only on the pelage colour characteristics. The coat colour of the Quagga was variable to a certain degree. I tried to capture this diversity in a drawing, using the preserved quagga skins as a reference: 

 

The quagga was variable in the extent of the striping, but there are some general differences between the quagga and the zebras of the Quagga Project. 

The striping is supposed to link the zebras of the QP with the quagga, and indeed the amount of reduction of the striping that has been achieved is impressive, but there are some clear differences in the stripe pattern of the quagga and the zebras of the QP. 

1) In many of the zebras of the QP the stripes on the neck alternate between broad, solid black stripes and faint, narrow stripes. This was not the case in the quagga. All quagga skins show that the quagga had exclusively broad, solid black stripes on the neck. 

2) The stripes on the face of the zebras of the QP are very narrow, producing a broad white space between them. In the case of the quagga, the stripes on the face are rather broad, with only a narrow quite area in between them. 

The second clear difference in coat colour between the zebras of the QP and the quagga is the base colour, i.e., the colour between the stripes on the trunk. In the quagga the base colour of the trunk was brown, sometimes more intense sometimes less intense, but always brown. The base colour of the trunk on the zebras of the QP has some brownish shade but is not nearly intense as in the quagga specimen documented. The QP is aware of that and hopes they will achieve that brown base colour in the future. 

Another possible difference is the length of the mane. I have the suspicion that the quagga had a shorter mane than other plains zebras, based on the photographs and the preserved skins. The zebras of the QP have rather long manes compared to the documented specimen of quagga. This is only my suspicion; it would have to be verified by measuring the manes of the preserved quagga skins. 

 

Another very important difference between the quagga and the zebras of the quagga project is the fact that the quagga does not share any mitochondrial haplotypes with the living plains zebra subspecies (see my article linked above). There is no reason to assume the case is any different in the zebras of the QP, so therefore the animals are also genetically different. 

 

The quagga and the zebras of the QP are superficially similar because an amount of stripe reduction on leg and trunk has been achieved in the latter, but that is it. There is no justification for calling the zebras of the QP quagga or “Rau quagga”, they are simply plains zebras with a reduced stripe pattern. General differences, such as in the striping on the anterior part of the body or the lack of a brown base colour on the trunk will remain. The project hopes to achieve the brown base colour one day, but I wonder if this is possible without new mutations enabling an increased production of pigment on the trunk area.

 

I am writing this not in order to criticize the QP, not at all. I just think that we should always stay objective and should not declare the revival of an extinct animal that is still dead as a dodo based on superficial similarity. I am happy that there is the QP, because their zebras could be very useful for outbreeding with quaggas if one individual or a few individuals could be genetically resurrected using genome editing one day.