Family of the Week: the Lily-Walkers

The family Jacanatheriidae is made up of tiny mammals that are closely related to the small Deinognathids, namely Feresetta. The family was originally named Olodactylidae, but I thought Jacanatheriidae was a name to better describe the physical features of this family. This is one of few cases I have where I didn't name the family after the original genus I thought up, but preferred the more descriptive name. These little trelatebrates are very much like today's jacana birds. Their bone structure is mostly made up of air sacs, making these mammals lighter than they appear. They have long necks and the body is covered in thick, woolly fur. The fur is thicker than it is in modern cats, and aids in keeping the animal afloat if it should fall in the water. The tail is usually long and counterbalances the head and neck. The eyes are large and almond-shaped and placed in the front of the face. The ears are small, diamond-shaped and have a furry backside and naked in front. The arms are almost non-existent and generally covered up by the thick fur, but the fingers are long and slender and are about the only things visible from the forelimbs. The hind legs however, are their most remarkable features. The legs are long and slender, the toes are oversized and arrow-shaped. The tips of their toes are flattened to help them stay buoyant. The oversized toes enable these animals to move easily over aquatic plants, like lilypads and hyacinth. The toes are very flexible and capable of forming to whatever it is the animal is standing on. These animals live their lives among the water plants. This is where they eat, sleep, mate, and give birth and raise their young. So these animals prefer to live in swampy areas where there is a heavy covering of plants on the surface. These animals almost never set foot on dry land. They are mostly small animals and very light-weight. No species is over 10 inches tall, with the neck fully extended, or weighs more than a pound. They are carnivorous, the diet consists mainly of fish, crustaceans, mollusks, and insects. Most hunt like herons, darting their heads into the water to capture their prey. But slow-moving prey, like snails or slugs, they simply reach into the water with their jaws and snatch it up. Most species are usually only social during the breeding season, or they may live in couples.

The largest species in this group is Xescophotus. It is also the only species that has a totally naked head and neck. They also have fleshy "wattles" on the upper jaw and chin areas. During the breeding season, the males' flesh turns from charcoal black to bright pink, and the wattles turn bright red and purple. The females are highly turned-on by this dramatic change in clothing. But after the breeding season, the males' flesh goes back to a dull charcoal black color. After they have mated, males and females may go their separate ways.

Ziphidromas is also a unique species in that it has the longest muzzle, in proportion to it's size than any other species. The nostrils of this animal are also placed higher on the muzzle than any other species in this family. When this animal hunts, it feels under the water's surface with it's highly-sensitive muzzle. It can stand motionless for hours on end, waiting for the muzzle tip to feel a fish pass by. Then they quickly shut their jaws on the hapless fish and bring it to the surface to be consumed. Ziphidromas is one of few species in this family to live in groups of more than 4 individuals.

Female jacanatheriids give birth to several fawns, usually no more than 4 at a time. She will usually give birth on a lily pad, most of the time it is one that is shady, and well away from any others in her herd. She gives birth very quickly, almost one right after another. The fawns then take refuge on the mother's belly, clinging to her thick fur. This also allows them to suckle, and if the mother has to leap into the water to avoid danger, the fur on the belly stores enough air for the fawns to still breathe until the danger passes. Often all that is visible of the babies are the long toes dangling from the mother's belly. The color of the fawns is determined by the color of the mother's belly. But most of their fawns are born with stripes or spots on the body, which fade away with age.

Predators of jacanatheriids are plenty, especially predatory bats, snakes, mongooses, predatory birds, deinognathids, caroroos, large, predatory fish, and almost any other predator, large or small, that can wade into the water to get at them. The lily-walkers usually dip into the water to avoid danger, and can stay submerged for up to 5 minutes until the danger passes. For underwater predators like fish, these animals usually leap onto a branch or hide in the reeds to avoid them. They can move very fast, in spite of their long toes.