The greatest portraits convince by the subtlest means. In a Rembrandt self-portrait, the least curl of his lip seems to proclaim the man. Velázquez could make the shadowy folds of a velvet tunic tell us all we need to know about some long-dead duke. Royal portraits follow established conventions but the cunning brush of a Goya could allow a hidden personality to peep out from behind the stiffest pose. In such portraits, through the droop of an eyelid or the flourish of an upraised hand, we seem to glimpse the flitting essence of a self. What is a master portraitist to do, then, when his sitters are specimens rather than individuals, and stand garbed not in silks and satins but in feathers and fur?

Such was the challenge faced by Jean-Baptiste Oudry (1686-1755), perhaps the finest painter of animals who ever lived. How to capture the image of, say, a cassowary, that flightless cousin of the ostrich, so that from the horny ridge on its skull to its naked and scaly legs the depiction is pure quintessence of cassowary and yet, somehow, as individual as any duke? In Oudry’s 1745 portrait of this gangling bird, it turns its head backward to reveal an eye of aristocratic amber and seems, for all its ugliness, on the verge of footing a delicate minuet. This and a dozen other majestic animal paintings — some not exhibited for over a century — are reproduced in “Oudry’s Painted Menagerie: Portraits of Exotic Animals in Eighteenth-Century Europe” (The J. Paul Getty Museum, 166 pages, $39.95), edited by Mary Morton. This lavishly produced and quite beautiful book, which contains seven essays on the painter and his work by leading experts in 18th century art, serves as a catalogue to an exhibition of Oudry’s masterpieces opening this fall at Houston’s Museum of Fine Arts.

Oudry enjoyed great success in his long career, combining artistic brilliance with a keen nose for opportunity. Louis XV was his principal patron, but Oudry’s work attracted other royal collectors from around Europe. One of these was Christian Ludwig II, duke of Mecklenburg-Schwerin, whose son Friedrich persuaded his father to purchase Oudry’s “menagerie series” in 1750. (The series has remained in the ducal collection at Schwerin, Germany, since that time.) Oudry is probably best known today for his classic illustrations to La Fontaine’s “Fables.” In those 276 drawings, one for each fable, he created animals which are fully animal from snout to hoof; and yet, these hogs and donkeys, though real enough to squeal and bray, betray sly reminders of human traits. The five years he spent on this labor of love taught Oudry to depict animals which were both anatomically accurate in every detail and surprisingly lively; they are beasts whose individuality pounces from every page.

At first sight, the more regal portraits of the “menagerie series” seem to have little in common with the barnyard critters of the “Fables.” The snarling “Hyena Attacked by Two Dogs” sports a glossy pelt a princess might covet. The “demoiselle crane,” improbably sharing a woodland glade with a toucan and a tufted crane, displays long silky tufts swept back from her head like a flying tiara. These are noble creatures all, the living trophies of a king, and portrayed as such. Oudry often sketched from life at the Royal Menagerie at Versailles, and many of his enchanting sketches, executed in chalk on pale blue paper, are reproduced in the book. The life sketches reveal how hard Oudry worked to catch his subjects on the quick. As a result, his finished portraits ripple with vitality beneath their pomp.

The most astonishing painting of the series, and a masterpiece in its own right, is Oudry’s colossal portrait of a rhinoceros. This life-size painting, not shown for some 150 years, is of a celebrated Indian rhino named Clara who arrived in Rotterdam in July 1741. Clara spent much of the next two decades on European tour, creating a wave of “rhinomania” among the fashionable (as Ms. Morton notes, hair ribbons “à la rhinoceros” suddenly became the vogue in Paris). Oudry saw Clara when she made a long stopover in Paris in 1749; as his careful sketches show, he studied every inch of her armor-plated anatomy. The final painting, which measures 10 by 15 feet, overwhelmed its first viewers as much by its sheer size as by its artistry. One of the most interesting chapters in the book is by Mark Leonard, a conservator at the Getty Museum, which restored the badly damaged portrait that had been kept rolled up and in storage for decades. Now repaired, retouched, and revarnished, Clara has emerged from her long hibernation.

Oudry presents her in side view in a rocky landscape; a soft light touches each bump on her hide and makes her single horn gleam. This is a surprisingly affectionate portrait and the affection lies not only in Oudry’s scrupulous observation but in an unusual sense of empathy on the painter’s part. Seen in profile, Clara’s eye fixes the viewer alertly. Her glance is shy and yet sophisticated. This is a rhino who has seen the world, who has witnessed the vanities of the court and the swings of fashion, and who finds us as odd and every bit as exotic as we find her.

eormsby@nysun.com