Jaguar (
Panthera onca)
Care Manual
8
Association of Zoos and Aquariums
addition
to physical characteristics, they use a number of techniques at the molecular level, seeking to
understand how organisms are genetically connected to one another and to construct family trees that
demonstrate the relationships. Systematists take into account geographic, genetic, behavioral,
chronological and other circumstances that may have served as isolating mechanisms to create new
species over time.
The last taxonomic revision of
Panthera onca into subspecies was published in 1939 (Pocock, 1939).
Pocock measured skull characters and grouped specimens according to their collection localities, revising
the number of species and races of jaguar downward from 24 to eight, as follows:
Table 3: Jaguar subspecies (Pocock, 1939)
Nomenclature
Taxonomist
Described
Geographic range
P. onca onca
Linnaeus
1758
Venezuela, south and
east to Rio Grande do Sul in
Brazil
P. onca palustris
Ameghino
1888
Matto
Grosso, Paraguay and northeastern Argentina
P. onca peruviana
Blainville
1843
Coastal Perú
P. onca centralis
Mearns
1901
Central America, El Salvador to Colombia
P. onca hernandesii
Gray
1857
Western México
P. onca arizonensis
Goldman
1932
Eastern
Arizona to Sonora, México
P. onca veraecrucis
Nelson & Goldman
1933
Southeastern México to central Texas
P. onca goldmani
Mearns
1901
Yucatán peninsula to Guatemala and Belize
However, he concluded that individual variation among specimens outweighed any true systematic
differentiation; his subspecies were based only on the geographic origins of the study skulls at the British
Museum (Pocock, 1939).
Larson’s 1997 re-evaluation of jaguar subspecific taxonomy began with Pocock’s revision based on
skull morphology and then applied the same criteria and statistical analysis to a different study set of 170
skulls of known geographic origin. Her study concluded that clinal variation
exists from north to south, but
it emphasized that there is more variation within subspecies than between subspecies (Larson, 1997).
While skull morphology is by no means the only criterion on which to base jaguar taxonomy, it was, and
continues to be, a primary method used alongside molecular genetics techniques.
This was strongly reinforced by Eizirik,
et al. (2001) in their analysis of mitochondrial DNA (mtDNA)
differences and microsatellite location in somatic DNA. This study revealed very weak phylogeographic
differentiation. While it indicates that jaguars from the southern part of the range are significantly different
from those in the northern part of the range, a much less marked difference appears between populations
living Central America and those from northern South America. The Amazon River and the former Darien
Straits, between what is now Panama and Colombia, were posed as geographic isolators. A comparison
with similar studies in other species suggested that, as a species, jaguars might be in an expansion and
rapid growth phase of habitat exploitation. Under such conditions, along with the counter-pressures of
habitat fragmentation
and persecution, broad genetic diversity without deep geographic differentiation
could be expected (Eizirik
et al., 2001). Today the living jaguar is seen as monotypic:
Panthera onca
without subspecies.
The paleontology and historical biogeography of jaguars is complex and is a story that continues to
be written. Most of the evidence is fragmentary or implied, and it is subject to frequent revision. Ecological
and taxonomic conclusions have often been drawn from subtle skeletal differences among incomplete or
solitary specimens, some of which are ultimately shown to result from sexual dimorphism or normal
individual variation (Kurtén, 1973). Tying the DNA analyses of mutation rates to physical evidence in the
form of confidently dated fossils is important when identifying a speciation event (Johnson
et al., 2006),
but this is not always accomplished. Meanwhile, ongoing fossil discoveries push the earliest appearance
farther back in time and often spread the geographic range further afield than previously thought.
In a relatively short span of geologic time, modern big cats diversified and colonized Asia, Europe,
and the Americas. It has been suggested that their speciation relied more upon ecological divergence
than geographic separation (Mattern & McLennan, 2000). Many species in the genus
Panthera have died
out, with fairly frequent new fossil discoveries continuing to be reported. Glaciations and regional climatic
changes during the past three million years alone likely opened
and closed migration routes, altered
regional habitats, and perhaps isolated populations of big cat species. As the jaguar’s predecessors and
ancestors spread across the globe from their presumed central Asian origin, factors in their evolution
Jaguar (
Panthera onca)
Care Manual
9
Association of Zoos and Aquariums
were time, space, climate fluctuation, and physical obstacles. From our present perspective, these factors
also obscure the relationships among extinct and living species. They make it difficult to identify clear
pathways from jaguars’ beginnings to where the species is today, and it is evident that the complete story
has not yet been told (Mattern & McLennan, 2000).
The earliest identified member of the genus
Panthera, described in 2013, lived more than 4.4 million
years ago in Tibet. This recent discovery more than doubled the genus’ age in
the fossil record and firmly
establishes its geographic home in Asia. It also pushes a hypothetical origin of
Panthera back to 10.7
million years before the present. This directly affects the timing of the jaguar’s appearance.
The proposed new phylogenetic tree suggests that approximately 7.7 million years ago, the clade
—
a
group consisting of a common ancestor and all its descendants
—
containing the modern jaguar (
Panthera
onca), leopard (
P. pardus), and lion (
P. leo) along with the extinct American ‘lion’ (
P. atrox) and cave lion
(
P. spelaea) diverged from the group which gave rise to the tiger (
P. tigris) and snow leopard (
P. uncia). It
also suggests that the last common ancestor shared by jaguars and the leopard-lion group itself lived
some 6 million years ago (Tseng
et al., 2013).
Fossil specimens still classified as jaguars have been dated at between 1.8 and 2 million years old in
both Arizona (Kurtén, 1973) and Bulgaria (O’Regan & Turner, 2004). Similar specimens tentatively dated
older than 2.4 million years have also been unearthed in the Netherlands (O’Regan & Turner, 2004; Mol,
van Logchem & de Vos, 2011). So, the jaguar must have arisen in Asia, expanding its range westward
into Europe and east to North America throughout the Pleistocene, or even earlier.
Based upon geography, the Plio-Pleistocene Eurasian jaguar is referred to as
Panthera onca
gombaszogensis (Wagner, 2011) and the North American is called
P. onca augusta (Simpson, 1941)
.
Nevertheless, this allows us to assume a more or less contiguous ancient jaguar population across
Europe, Asia, and North America (Hemmer, Kahlke & Vekua, 2001; Kurtén, 1973). Plant and animal
material found in association with both subspecies indicate forest vegetation and abundant water; this is
still the modern jaguar’s preferred habitat. So, while other
Panthera species diversified by exploiting new
niches as the cats found them or as the landscapes themselves developed (e.g. lion onto savannah, and
snow leopard into high, rocky mountains), the jaguar seems to have stayed true to its original ecosystem,
exploiting major watercourses as corridors for expansion
—
as they still do
—
across the northern
hemisphere and, later, into South America (Rabinowitz, 2014).
Fossils indicate the paleo-jaguar being as much as 25 percent larger than today’s largest jaguars
even as relatively recently as 10,000 years before the present. As a result of this and
other skeletal
similarities among North America’s Pleistocene felines, there has been confusion and disagreement
regarding their placement. For example,
Panthera atrox, perhaps the largest true cat of all time, has been
variously described as a lion, a transitional species linking lions and jaguars, a jaguar ancestor, a jaguar
and a sister species to the jaguar. Its first conclusive appearance in the fossil record is much later than
the jaguar’s, and when it is included in recent phylogenetic trees constructed with combined
physical/molecular characters,
P. atrox is placed after the jaguar, making the sister species explanation
appear most likely (Kurtén, 1973; Christiansen, 2008; Tseng
et al., 2013).
Fossilized jaguars dated to the Pleistocene have been unearthed as far north as Pennsylvania and as
far south as Paraguay, yet it disappeared from North America not long after, as did many of the other
megafauna. The jaguar reappeared during recent times. DNA evidence suggests that approximately 500
generations ago, South American jaguars re-colonized the northern continent and underwent a dramatic
population explosion (Eizirik
et al., 2001).
Mean generation time for zoo jaguars in the United States today is just over seven years (Association
of Zoos and
Aquariums, 2013), permitting a rough calculation of 3,500 years ago for the re-colonization of
North America. Molecular analysis of the jaguar’s evolutionary events tends to place them more recently
than indicated by the admittedly sparse fossil record (Eizirik,
et al., 2001; Christiansen, 2008). So, it is
probably safe to say that the big paleo-jaguar declined and disappeared along with most of the
Pleistocene megafauna as climatic changes reworked North American habitats; however, its smaller,
ever-adaptable descendants in northern South America filled the ecological void the paleo-jaguars left.
Upon the jaguars’ return, they faced pressure and competition from a relatively new arrival on the scene:
humans.
Ecological information preceding 1970, when available, consists mainly of anecdotes and notes on
the animal’s natural history (Humboldt, 1852 & 1853; Rengger, 1830; Azara, 1838; Roosevelt, 1914;
Cherrie, 1930; Miller, 1930; Krieg, 1948; Leopold, 1959; Brock, 1963).