Alone in the World; single species families

I've long been intrigued by organisms which have no close relations, having separated off from their ancestral line very long ago. I'm not just talking about animals and plants which are the only ones in their genus - indeed it is claimed (and I've not attempted to verify it!) that there are more animal genera with just one species than of any other number! I'm talking about a whole family with only one genus, which in turn has only one species. What this means is that the species has been alone with no close relatives for millions of years, and almost certainly ten of millions. 

This in turn means - at least it seems so to me - one of two things, though I've never actually read a discussion of it. Either the species has been living for a long time in a very stable environment, and perhaps in a small area, so that it hasn't ever split into separate populations which in time evolved into separate species, or all its sister-species for some reason became extinct. However that's as far as I'm going the pursue the 'whys' today, preferring to introduce you to some of these special species and simply admire them. 

At the end I'm going to go a step further and offer you some really ancient animals and plants which are the only survivors of an entire Order!

There are about 30 singleton bird families of the 230-odd living families recognised. I have chosen to use the International Ornithological Congress (IOC) list as my standard taxonomy, in large part due to their excellent website which is updated (with explanations) every three months. Let's meet some of them.

Family Dromaiidae.
Emu Dromaius novaehollandiae father and chicks, northern Flinders Ranges, South Australia.
This one is perhaps borderline, as two Emu species - from Kangaroo Island and from King Island in the Bass Strait
between Victoria and Tasmania - may have become extinct in the early years of the 19th century.
The 'may' does not refer to any doubts over their extinction, sadly, but to whether they were indeed
full species. Many think they were (including me for what it's worth) but IOC does not.

Family Anseranatidae.
Magpie Geese Anseranas semipalmata, Territory Wildlife Park, south of Darwin (but these are wild birds).
A strange Daffy Duck lookalike, with knobbed head, half-webbed feet and odd breeding habits, whose ancestor
apparently split from the waterbird line before the extinction of the dinosaurs 65 million years ago, long before
the more modern ducks/geese/swans family arose.
Once found across south-eastern Australia, now common only in the tropics of Australia and New Guinea
(though I feel that they're making a slow recovery in the south).

Family Scopidae.
Hamerkop Scopus umbretta, Entebbe Botanic Gardens, Uganda.
Widespread in sub-Saharan Africa and Madagascar, its resemblance to herons is coincidental.
Its closest relatives are probably pelicans and the Shoebill (coming up) but flamingos
seem to be in there somewhere too...
'Hamerkop' is from Afrikaans meaning 'hammer head'.

Family Balaenicipitidae.
Shoebill Balaeniceps rex, Murchison Falls NP, Uganda.
A remarkable bird and a large one, up to 1.5 metres tall, found in swamps of central eastern Africa.
The huge sharp-edged bill apparently evolved to eat large fish, notably catfish and lungfish,
but frogs and reptiles, including monitor lizards and young crocodiles, are also taken.

Family Eurypygidae.
Sunbittern Eurypyga helias, Manu Special Reserve, Amazonian Peru.
A lovely bird which has only recently lost its even more special status as a single-Order bird,
being now placed in the same Order as an another member of the single-family club, the equally enigmatic
Kagu of New Caledonia.

Family Aramidae.
Limpkin Aramus guarauna, Manu Special Reserve, Amazonian Peru.
It looks rather like an ibis, but is apparently closest to (though still distant from) the cranes.
It is found throughout eastern and northern South America, central America and the Caribbean, and Florida.

Family Pluvianidae.
Egyptian Plover Pluvianus aegyptius, Benoué NP, central Cameroon.
Once thought to be an aberrant pratincole, it is now recognised as being somewhere near
the true plovers and painted snipes.
It is found by rivers in a band across Africa south of the Sahara.

Family Steatornithidae.
Oilbird Steatornis caripensis, Yasuni NP, Ecuadorian Amazonia.
A remarkable fruit-eating nocturnal bird - the only one in the world - from the north of
South America. They nest in caves and are among the very few birds to echo-locate.
They seem to be closest to the frogmouths and nightjars, as theirs superficial appearance seems to suggest,
but there are some who would put them in their own order.
This one remarkably appeared above our canoe on a creek one night.

Family Donacobiidae.
Black-capped Donacobius Donacobius atricapilla, Yasuni NP, Ecuador.
This one is the unwitting cause of considerable controversy; until recently it was thought to be
an unusual mockingbird, then a wren, but current thinking puts it in its own family (though not all agree)
with its nearest relations being in Africa. A bold, curious bird found along waterways throughout much of the
northern half of South America.

Family Coerebidae.
Bananaquit Coereba flaveola Umbrellabird Lodge, southern Ecuador.
Another controversial one, which has been swapped between the tanagers, to a sorry 'unknown status',
to being placed in its own family, though again not all yet agree with this.
It's a bold familiar little bird around lodges and feeders across northern South America and the Caribbean.
'Quit' is apparently a Jamaican-English name for a small bird, but there the trail of its origin ends!

We'll come back to one more remarkable single-species bird family towards the end, but meantime, how about mammals? There are relatively few compared with birds, but there are some familiar ones, and Australia has more than its share.

Family Ornithorhynchidae.
Platypus Ornithorhynchus anatinus, Tidbinbilla Nature Reserve, near Canberra.
One of only two groups of monotremes (along with the four species of echidnas), the
only egg-laying mammals. It is also, along with the Water Rat, the only fully aquatic endemic
Australian mammal.

Family Phascolarctidae.Koala Phascolarctos cinereus, Mount Eccles/ Budj Bim National Park, Victoria.
(And I can't believe I don't have a better picture than this!)
The ancestral koala parted from its relatives that were to become the two species of living
wombat (and many extinct ones) some 40 million years ago.

Family Myrmecobiidae.
Numbat Myrmecobius fasciatus, Perth Zoo.
A termite specialist, once found across southern Australia but now restricted to a few isolated
colonies in the south-west. It is placed with the Australian marsupial carnivores, and was possibly
closest to the sadly late Thylacine, but its ancestor seems to have gone its own way more than
30 million years ago.

Family Thylacinidae.
A moving tribute to the magnificent big marsupial carnivore, Launceston, Tasmania.
It was deliberately driven to extinction in the 1930s in Tasmania, having been extirpated on
the mainland with the arrival of the Dingo some 4000 years ago.
(I wrote about it in more detail some time ago, here.)

 Family Dugongidae.Dugongs Dugong dugon, Shark Bay, Western Australia; you rarely if ever see a whole one at once!
There are only four members of the Order Sirenia; the other three, the manatees, form a separate family.
The Dugong is found in warm shallow seas from Australia and through south-east Asia,
as well as on the east coast of India and the east coast of Africa.
The sirenians are the only fully vegetarian marine mammals.

The old South American rodents are an ancient group, having arrived from Africa by rafting some 30 or more million years ago, like the South American monkeys. A couple of large aquatic species form their own families.

Family Myocastoridae.
Coypu Myocastor coypus, Chepu River, Isla de Chiloé, Chile.
I wrote about them very recently here.

Family Hydrochoeridae.
Capybara Hydrochoerus hydrochaeris, Tambopata NP, southern Peru (plus a couple of Giant Cowbirds).
The world's largest rodent, up to 130cm long and weighing up to 65kg, living in groups of dozens.
Some would put it in the family Caviidae with guinea pigs, but I find the competing claim convincing.
(I hope to have a better photo by the end of the year!)

I don't think I can illustrate any singly-species plant families, though in Australia the Albany Pitcher Plant Cephalotus follicularis, Family Cephalotidae, is a good example.

Which brings us to the real isolates - sole members of an entire Order! Among mammals the wonderful Aardvark Orycteropus afer is the only one I can think of. Among reptiles the sole example (I am almost sure) is the ancient New Zealand Tuatara Sphenodon punctatus, Family Sphenodonidae, Order Rhynchocephalia. The key thing is that they are not lizards, but something far older.

Among living plants, the Gingko and the Welwitschia apparently fall into the category, though modern plant taxonomy can be pretty hard to keep up with!

Family Ginkgoaceae, Order Ginkgoales.
Gingko Ginkgo biloba, growing as a street tree in Canberra.
Native to China, it is known from 260 million year old fossils.

Family Welwitschiaceae, Order Welwitschiales.
Welwitschia Welwitschia mirabilis, Damaraland, Namibia.
(A scan of a faded slide, but this is too fascinating a plant to ignore!)
The plant comprises just two constantly-growing leaves, which are shredded by wind.
The plant can be almost 10m across. Individual plants are believed to be in excess of 1000 years old.

And we'll finish with a bird, one of just two species in the world which represent entire Orders (the other being the Cuckoo-roller of Madagascar, which I'm hoping to see in a few weeks!).

Family Opisthocomidae, Order Opisthocomiformes.
Hoatzins Opisthocomus hoazin, Tambopata NP Peru, above, and at dusk, Yasuni NP Ecuador, below.
A large but sluggish bird, found throughout the Amazon basin. Its somnolence is largely due to its diet;
it lives almost entirely on leaves, and is the only species of bird which digests leaves by bacterial action,
like a herbivorous mammal. The fermentation chamber is so large that it is has largely displaced the sternum,
the keelbone which anchors the great flight muscles, so it is essentially flightless.
Chicks can drop into the water to escape danger and dive and swim, climbing back out again with
the assistance of sharp claws on fingers two and three.
All this is pretty amazing, but they've had 64 million years of evolution to come up with
unique adaptations. They're one of the things I most look forward to when I go back to the Amazon.

There are very many wonderful and surprising things in this wonderful and surprising world; among them are the organisms without close relatives. I hope you've enjoyed meeting a few of them.

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