PERUSING THE PACARANA - A TERRIER-SIZED ‘TERRIBLE MOUSE’

A captive pacarana (public domain)

There are over 2,200 species of modern-day rodent currently known to science, but only a handful are so radically different from all others that they have been assigned an entire taxonomic family all to themselves. However, the extraordinary – and exceptionally large - rodent documented here (and which also happens to be one of my favourite mammals) has indeed received that rare accolade. Moreover, as will now be revealed, the history of its scientific discovery - and rediscovery - is just as remarkable as it is.

The year 1904 was a momentous year for mice, for it marked the rediscovery of a truly astonishing and extremely mysterious, controversial rodent that science had dubbed 'the terrible mouse', due to the fact that it was as large as a fox terrier!

Needless to say, any mouse the size of a small dog is no ordinary mouse, and in truth this species is not a bona fide mouse at all. If anything, it more closely resembles a long-tailed, spineless porcupine in general shape, and sports a handsome grey-black pelage decorated with longitudinal rows of white spots, which compares well with that of the South American common paca or spotted cavy Cuniculus paca, which is a fairly large relative of the guinea pig (but not the world's third largest rodent, as certain websites erroneously claim).

Common pacas (© HumedoTepezc/Wikipedia)

Indeed, in its native Andean homeland, the 'terrible mouse' is known locally as the pacarana ('false paca'). Yet it is neither paca nor porcupine either. Instead, as noted above, it is sufficiently removed from all living rodents to require its very own taxonomic family, Dinomyidae, thereby making it one of the most important mammalian discoveries of the past 150 years - not to mention one of the most elusive. Several prehistoric relatives of the pacarana have subsequently been described from fossil remains, and some of these were quite enormous in size (one, Josephoartigasia monesi, which lived 4-2 million years ago during the Pliocene and early Pleistocene epochs, was the size of a bison and is the largest rodent presently known to have existed). However, no other living dinomyids have been discovered, thus making the pacarana the very last representative of its entire lineage.

Josephoartigasia monesi reconstruction inspired by the pacarana (© Nobu Tamura/Wikipedia)

Measuring up to 100 cm long and weighing as much as 15 kg, the pacarana is the world's third largest living rodent (exceeded only by the capybaras and beavers – but not by the paca, see above), and was discovered in 1873 by Prof. Constantin Jelski, curator of Poland's Cracow Museum. Financed by Polish nobleman Count Constantin Branicki, Jelski was engaged in zoological explorations in Peru when, one morning at daybreak, he observed an extremely large but wholly unfamiliar rodent. It had very long whiskers and a fairly lengthy tail, and was wandering through an orchard in the garden of Amablo Mari's hacienda near Vitoc, in the eastern Peruvian Andes. He swiftly dispatched the poor creature, and sent its skin and most of its skeleton back to Warsaw, where it gained the attention of Prof. Wilhelm Peters, Berlin Zoo's director, who meticulously studied its anatomy. Recognising that this huge rodent represented a dramatically new species, by the end of 1873 he had published a scientific description of it, in which he named it Dinomys branickii - 'Branicki's terrible mouse'. The pacarana had made its scientific debut.

19^th-Century engraving of the pacarana specimen encountered by Jelski

Peters's studies disclosed that its anatomy was a bewildering amalgamation of features drawn from several quite different rodent families. In terms of its pelage and limb structure, it compared well with the paca, but unlike the five-toed (pentadactyl) configuration of the latter's paws the pacarana's each possessed just four toes. Many of its cranial and skeletal features (not to mention its long, hairy tail) also set it well apart from the paca, especially the flattened shape of the front section of its sternum (breast bone), and the development of its clavicles (collar bones).

19^th-Century engraving of the common paca for comparison purposes with the previous engraving of a pacarana

Certain less conspicuous features of its anatomy were reminiscent of the capybara, but various others (including the shape of its molar teeth) corresponded most closely with those of the chinchillas. There were also some additional characteristics that seemed to ally it with the West Indies’ coypu-like hutias. Little wonder then that Peters elected to create a completely separate taxonomic family for it!

The pacarana was clearly a major find - yet no sooner had it been discovered than it vanished. For three decades nothing more was heard of this 'false paca', and zoologists worldwide feared that it was extinct.

Dr Emil Goeldi (public domain)

Then in May 1904, Dr Emilio Goeldi (1959-1917), director of Brazil's Para (now Belem) Museum, received a cage containing two living pacaranas (an adult female and a subadult male). These precious animals had been sent from the upper Rio Purus, Brazil, and proved to be extremely docile, inoffensive creatures, totally belying their 'terrible mouse' image. They were swiftly transferred to Brazil's Zoological Gardens, but tragically the adult female died shortly afterwards, following the birth of the first of two offspring that she was carrying.

Rare, early 20^th Century photograph of a captive pacarana

In 1919, a more unusual-than-normal pacarana was described by Alipio de Miranda Ribeiro. Instead of being greyish-black in colour, it was brown, so Ribeiro designated it as the type specimen of a new species, christened D. pacarana. Three years earlier, the first pacarana recorded from Colombia had been collected (near La Candela, Huila); in 1921, this became the type of a third species, D. gigas. During the early 1920s, a series of pacaranas was procured by Edmund Heller from localities in Peru and also Brazil, so that by the 1930s a number of museum specimens existed, which were then examined carefully by Dr Colin Sanborn in the most detailed pacarana study undertaken at that time. Publishing his findings in 1931, he revealed that D. pacarana and D. gigas were nothing more than varieties of D. branickii, which meant that only a single species existed after all.

Brown-furred (or faded black-furred?) taxiderm pacarana specimen at the Berlin Natural History Museum (© Markus Bühler)

A rarely-glimpsed, nocturnal inhabitant of mountain forests, the pacarana feeds on leaves, fruit, and grass, usually associates in groups of four and five, and is hunted as a source of food by its Indian neighbours, but little else is known about its lifestyle in the wild state. It is currently classed as a vulnerable species by the IUCN, yet as a result of its secretive habits and relatively inconspicuous habitat it may be more abundant than hitherto suspected (nowadays it is known to be fairly common, for instance, in Bolivia’s Cotapata National Park).

Taxiderm pacarana at Tring Natural History Museum, Hertfordshire, England (© Dr Karl Shuker)

Due to this species’ notoriously elusive nature, however, down through the years zoos have prized pacaranas almost as much as giant pandas - which is why early 1947 was a singularly memorable time for Philadelphia Zoo. It was then that it received an innocuous-looking crate from legendary animal dealer Warren Buck of Camden, New Jersey, with the laconic remark: “Here’s a new one on me. Maybe you know what it is”. When the crate was opened, to everyone astonishment it contained a living pacarana! And just like Goeldi’s twosome, it proved to be delightfully tame and affectionate, showing no inclination to bite, and liking nothing better than to greet its visitors with a cheerful grunt and to sit upright on its hindlegs crunching a potato or carrot gripped firmly between its forepaws.

Of the handful of captive pacaranas obtained more recently and exhibited at such zoos as Zurich (the first to breed them), Basle, and San Diego (where I was fortunate enough to see my first live pacaranas in 2004), most have been of similarly pacific temperament. Indeed, they actively seek out their human visitors to nuzzle them and rub themselves against their legs almost like cats, or even to be picked up and carried just like playful puppies - truly a species with no desire whatsoever to live up to its formidable Dinomys designation!

Pacarana depicted on a postage stamp issued by Equatorial Guinea

Finally: Demonstrating that not only the pacarana but also the true pacas may well have some extra-large surprises in store for science is an exciting recent discovery made in Brazil by Dutch zoologist Dr Marc van Roosmalen. There are three currently-recognised species of true paca. Namely: the above-mentioned common paca C. paca; the smaller, longer-furred, and less-familiar mountain paca C. taczanowskii; and Hernandez's mountain paca C. hernandezi, described and named as recently as 2010 after mitochondrial DNA analyses confirmed its separate taxonomic status from the mountain paca. These are almost-tailless rodents normally no more than 60 cm long (often less), averaging 7 kg in weight, and adorned with usually four longitudinal rows of white spots on each side of their blackish-brown-furred body

Mountain paca (© WebmasterRioblanco/Wikipedia)

However, just a few years ago, Marc encountered – and collected – in Brazil a much larger form of true paca, known locally as the paca concha. It appears to have a very wide distribution range, and is distinguished from the two recognised species by its greater size (weighing up to 13 kg), its lighter fur colour, and the merging of most of its spots into longitudinal lines.

The holotype of the currently-undescribed giant paca (© Dr Marc van Roosmalen)

In a scientific paper currently awaiting publication, Marc has named this extra-large form as a new species. Several suspected specimens of giant paca are held at Brazil’s Museu Paraense Emilio Goeldi, where Marc’s holotype of this potential new species, killed for food by a local hunter on 28 May 2006 near Tucunaré, has been deposited. So perhaps Count Branicki’s false paca now has a rival among the real pacas in terms both of physical stature and of complete surprise to the zoological community, thanks to its unexpected discovery.

This ShukerNature post is an expanded version of my pacarana account in my Encyclopaedia of New and Rediscovered Animals.