By Darren Naish
Deer are strongly associated with Eurasia and North America and less so with the other regions of the world. In this brief article – part of which is an excerpt from my 2013 article on the conservation status of South American mammals (Naish 2013) – I’m going to say a few things about the deer of South America. For South America, you see, is home to approximately 17 living deer species. These include the Marsh deer Blastocerus dichotomus, Pampas deer Ozotoceros bezoarticus, the highland-dwelling Andean deer or huemuls or guemals (genus Hippocamelus), the forest-dwelling brockets (Mazama), and the tiny pudus (Pudu). Endemic subspecies of White-tailed deer Odocoileus virginianus also occur in northern South America.
These deer span a range of body sizes and shapes. The Marsh deer is the largest of the lot: males can weigh up to 150 kg. Sexual dimorphism is pronounced, the legs are long and slender, the hooves are long and spreading, and the antlers are amber, heavy and four-pronged. The Pampas deer is a tropical grassland deer, typically with three-tined antlers. Andean deer are stocky, short-legged deer (70-90 cm tall at the shoulder), the males of which have short, forked antlers. They are somewhat goat-like (or, arguably, klipspringer-like) in ecology, behaviour and anatomy and are specialised for life in steep, rocky terrain. Two species are recognised: the Huemul or South Andean or Chilean huemul H. bisculus of the far southern Andes and the Taruka H. antisensis of the northern Andes.
Brockets are a diverse and confusing group of South and Central America that generally have short, spike-like antlers, slender limbs and an arched back. They vary substantially in pelt colour and in fact they’re pretty variable overall, on which read on. Finally, pudus are tiny deer – the smallest of the whole group – that occur from the Colombian Andes all the way south to Chile and Argentina. They can be just 25 cm tall at the shoulder, 60 cm in total length, and weigh as little as 5.8 kg. The legs are short and thick, the hooves are slender, and the antlers are thin spikes.
According to molecular phylogenies (e.g., Pitra et al. 2004, Duarte et al. 2008), all South American deer are part of the same clade as reindeer and caribou (Rangifer), moose (Alces), white-tailed deer and kin (Odocoileus), and roe deer (Capreolus). The idea that all endemic South American deer are close kin was first proposed by Miranda Ribeiro in 1919 and has been repeatedly endorsed since the 1940s (Geist 1999). The names Capreolinae, Odocoileinae and Neocervinae are variously used for this clade. Because they have the so-called telemetacarpalian condition (where the second and fifth metacarpals are represented by distal splints), they are also sometimes termed the telemetacarpalian deer. In the ‘opposite’ condition – the plesiometacarpalian one, typical of Old World deer – those same metacarpals are only represented by proximal splints.
Within the clade, the South American taxa form a sub-clade that includes Odocoileus. This is interesting: does it mean that Odocoileus – mostly associated with North America – originated in South America before moving north? Or is it that all capreolines/odocoileines* originated in North America before Blastocerus, Pudu, Hippocamelus, Mazama and so on invaded South America independently of one another? This is the sort of problem where we hope that fossils might help. Alas, while there are a fossils of these groups, and fossils of a whole bunch of taxa that seem to be part of this group but are now wholly extinct, there aren’t enough to help resolve this issue. Duarte et al. (2008) looked at morphological and molecular characters across South American deer. They found Odocoileus to be deeply nested within the South American clade, and also posited that many of the divergence events within the clade happened during the early part of the Pliocene. In other words, before the Central American land-bridge formed. The conclusion: those different lineages did indeed make the crossing into South America on several occasions, perhaps as many as eight times!
However… here I should say how the idea of a single ‘land-bridge event’ between 3 and 2.5 million years ago has been disrupted by recent discoveries. Proboscideans, peccaries, tapirs and the dromomerycine Surameryx (Prothero et al. 2014) in South America, and sloths in North America, indicate that animals were crossing north and south as early as the late Miocene – that is, from about 9.5 million years ago onwards – via a terrestrial connection termed the Baudo Pathway. This idea is new (post-2000 – the announcement in that year of the gomphothere Amahuacatherium in the Miocene sediments of Peru being one of the key instigators) and has only really been elaborated upon since about 2008. Might it have ramifications for our ideas on when those deer lineages arrived in South America? It might. For now, I’ll leave that idea there and will aim to revisit it in future.
* Also spelt – less frequently – as ‘odocoilines’.
Incidentally, Duarte et al. (2008) found Mazama – the brockets – to be radically non-monophyletic. The rainforest-dwelling red brockets belonged to three clades separated by Odocoileus, and the savannah-woodland-dwelling grey brockets belonged to two clades separated by an Ozotoceros + Hippocamelus clade, and by Blastocerus. If this is accurate, the deer conventionally classified together in Mazama evolved independently on four or five separate occasions and our traditional concept of this genus has well and truly been artificial. That said, it has sometimes been noted that Mazama is highly variable chromosomally, genetically and morphologically, the bewildering variety of forms meaning that any attempt to understand brocket diversity and evolution has to be considered provisional. This is made all the more difficult by the fact that new brocket species and subspecies have been described on fairly regular occasion.
Several of the South American deer are in danger of extinction. The South Andean or Chilean huemul persists as approximately 600 animals in Argentina and 1500 in Chile. Some estimates suggest that a decline of about 99% relative to the numbers present in pre-Columbian times has occurred, and the decline appears to be continuing. The Argentine population is fragmented into about 60 small, isolated groups. This reduction has partly been caused by hunting, domestic dog depredation, and habitat loss and fragmentation stemming from agricultural encroachment (Povilitis 1998). Ecological competition from alien Red deer Cervus elaphus and vulnerability to diseases carried by sheep may also be contributing to the huemul’s decline.
This is but a brief introduction to South American deer and I aim to discuss certain of them at great length in future. More deer soon!
While I’m here, some announcements. Note that there is now a Tet Zoo patreon page. Many thanks to those who have pledged support; I hope you’re enjoying the sneak-peeks you’re getting of assorted works-in-progress. Also, there’s now a Tet Zoo wiki. Already it’s grown to impressive proportions but, as a crowd-sourced endeavour, it may well benefit from your input. Or it may not, your call.