More like giant geese than deinonychosaurs, the strange, unwieldy therizinosaurs are decidedly odd members of the famously oddness-prone maniraptor clade.  Like all maniraptors, therezinosaurs are bipedal, covered in feathers, and have hands bearing three fingers each, but there the resemblance with the maniraptoran root-stock stops. 

Therizinosaurs are herbivores, and their bodies have radically changed to accommodate their vegetarian lifestyle. The hips of a therezinosaur are much wider then is normal for a maniraptor, and the pubis is swept backward in the manner of a bird or ornithischian dinosaur, to make room the large belly needed to digest plant matter. Because of its tremendous gut, the center of balance of a therezinosaur is shifted backward along its spine, and these creatures squat like sumo wrestlers, with their torsos held further up then is normal for a maniraptor. To make matters even more confusing, the tiny, non-functional hallux claw possessed by most maniraptors has, in the therizinosaurs, been greatly enlarged to make a decidedly un-maniraptorian four-toed foot. Misfits even in the varied and bizzare clade Maniraptora, and in the face of stiff competition from the hadrosaurs, ceratopsians, and other ornithischian herbivores, the therizinosaurs have nonetheless flourished in the past 130 million years, and have spread themselves across Eurasia and the Americas.

The history of Therizinosauria begins in the early Cretaceous, when small browsers like Beipiaosaurus lived in the lush forests of Asia. By the end of the Mesozoic, the therizinosaurs had expanded far into their herbivorous life-style, evolving into huge, lumbering forms like Segnosaurus and Therizinosaurus, itself. Fossil evidence is fairly poor for this time, with only a few decent remains and many puzzling fragments.  Indeed, therizinosaurs as a group were completely unknown until nearly the end of the twentieth century, and early paleontologists thought these long-necked plant eaters were late-surviving prosauropods.

In our own time-line, the therizinosaurs' history ends at the end of the Cretaceous, but in Spec, the 'sumo-dinosaurs' continued through the end of Mesozoic and into the Cenozoic with little trouble. Eocene fossils from China hint at a truly huge therizinosaurid, Neonychus, a close relative of the Cretaceous Therizinosaurus. This giant, as well as all of the close relatives of Therizinosaurus, the therizinosaurids, went extinct at the end of the Eocene, but other therizinosaur groups must have survived. Oligocene strata bear a large number of therizinosaurs, including the newly-evolved glaciotitanids (or robust therizinosaurs), and the precursors of the ceronychids were present, as well. The Miocene was a time of great diversification for the therizinosaurs, with the fleet-footed ceronychids roaming across Eurasia and North America, and the glaciotitanids expanding into a wide range of herbivore niches.

As the globe cooled during the Pliocene and then froze in the Pleistocene, therizinosaurs found themselves virtually alone in their ecosystems, more cold-tolerant than the ceratopsians and hadrosaurs and better adapted for herbivory than the oviraptors. Almost immediately, these feathery plant-eaters took over the new tundras, evolving into the forms we know today: moose-like mooras, long-necked dorsas, and mammoth arctotians.

The retreat of the Ice-Age glaciers has seen a decrease in therizinosaur diversity, especially amoung the specialized glaciotitanids. The partial thawing of Earth's polar reaches has allowed orithscian herbivores, such as the formosicorns, the cenoceratopsians, and the viriosaurs to expand northward, chewing away at the therizinosaurs' strongholds. In the frigid places, however, be they high in altitude or in latitude, these strange, lumbering maniraptors continue to dominate the large herbivore guilds.

GLACIOTITANIDAE (Yandos, lammoxes, honas, and arctotitans)

The clade to which spawned the massive arctotitan, the glaciotitanids are characterized by their robust body type, with short necks and tails. Quite successful during the Plio-Pleistocene, the glaciotitandids seem to have declined somewhat since their heyday, with the ceryonichids (see below) far outnumbering them in population and species-count. These therizinosaurs live in both Eurasia and North America, but their greatest diversity is to be found on the former of the two continents, where they occupy a range of forms.

The yando is the most southern of the modern glaciotitanids, living in the Himalayan highlands. This animal is also the most omnivorous of the robust therizinosaurs, even though plants make up the majority of its diet.  These creatures have been seen eating low-growing foliage, immature bamboo, fruits and nuts, grubs, fish, salmonites and carrion.

 

 

 

 

 

 

 

 Arctic lammoxes are found across the harshest tundras of Eurasia and North America, moving in bands a few dozen individuals before the oncoming migration of giant arctotians. These quarter-ton herbivores eat any plant material they can find, small trees, unappetizing ferns and mosses, and even lichen, which they scrape from rocks with their broad beaks. The ability to find food even on the bleak winter tundra makes lammoxes (and arctotitans, to a lesser extent) the nexus of a community of organisms the depend upon the therizinosaurs for survival, ranging from arctic plants to the bizarre caripoo. Lammoxes protect themselves and each others from polar draks with their long claws, that are also used for digging for roots.

 

The honas are the smallest of the therizinosaurs, usually weighing only about 50 kg. These miniature versions of the ice-age giants feed on seeds, berries, twigs and shoots, and occasionally small insects and reptiles. During the winter, they can sleep in small caves they dig in the snow, and even hibernate for several weeks if the weather becomes too harsh.

 

 

 

 

 

Alpicosaura nanus, the alpine hona, is the smallest therizinosaur in Spec, weighing only 20-30 kilograms. These small herbivores are adept climbers that eat a variety of foods ranging from moss to tree bark to insects.  

Male alpine honas are highly territorial, with adult cocks fiercely guarding their feeding grounds. These otherwise shy creatures will often kill each other over land disputes, but females and juveniles may travel with impunity.

 

 

 

The arctotitan is the largest of the therizinosaurs, a specialized relic left over from a chilly past. Sometimes called "woolly therizinosaurs" arctotitans are glaciotitanids, part of an ancient radiation of robust therizinosaurs that thrived during much of the Neogene.

An arctotitan's claws are long and flattened side-to-side, forming tools the massive herbivore uses to dig for food under the snow. When feeding, the arctotitan lowers its head to the ground, its spine nearly horizontal, while its great claws plow through the snow. Its long, hollow, hair-like plumage covers almost all parts of its body, including the toes.

The arctotitan species is now in something of a decline, as the Ice Age's tundras have receded. Arctotitans now live only in a narrow belt around the Arctic circle, and their extreme specialization to this habitat makes them very sensitive to environmental change.

 

(fig. 6)During the colder seasons ceronychids can often be seen resting or sleeping with their necks tucked under the arm feathers to conserve heat. Since ceronychids are more or less social the whole of the year, there is usually at least one individual always keeping watch while the others sleep.

Ceronychids (hornclaws) are the dominant herbivores of the boreal zone of the Northern Hemisphere. They evolved from small running forms long before the Ice Age, but could not compete with the massive glaciotitanids as the glaciers spread southward. Though they have changed little since, they are now the dominant plant eaters of much of temperate and polar Eurasia and North America.

As their common name implies, male hornclaws have very manual talons that are mainly used for one purpose: showing off. The claws grow slowly during their adult life, and old ceronychids can have quite impressive weapons on their hands. Ceronychids very rarely engage in serious combat, though, but the claws can be lethal when used against predators like sabre tyrants and veldraks.

The lemek was at first commonly known as the desert dorsa, or camel dorsa, before it was found not to be a member of the genus Ceronyx after all. (The old common names are still often used, though neither was ever an official one.) Paraceronychus arabicus is an unusual ceronychid for having chosen an extremely hot and arid environment instead of a chilly one. These inhabitants of the Arabian deserts can withstand long periods of drought without drinking, and often manage to get all the moisture they need from plants.

 

 

Lemeks move around the Mongolian steppes in small herds, feeding on low-growing tough plants. The large hump on their back is partly supported by enlarged neural spines, and is used to store water and food in the form of fat. It seems that lemeks don't have to drink at all, but when water is available, they tend to take advantage of it. There is another Paraceronyx species, the Arabian lemek (Paraceronyx arabicus), which is smaller and has shorter and more downy feathers.

Also called "sauropods-of-the-tundra" and "camel-geese" dorsas are slow-moving and placid creatures. These browsers usually stand still while eating, only moving their long neck to reach for the grass clumps or tender tree leaves. Dorsas inhabit the riverbanks and forest margins of Northern and central Eurasia, where, during the summer migrations, they congregate around the many marshlands formed by the melting snow.  Here the dorsas eat a variety of aquatic plants, grasses, and herbs and storing much of what they eat in the form of a fatty hump over the hips. During the winter, dorsas move deeper into the forests, where they switch to high-browsing and pluck needles of the lower branches of the pine trees, supplementing this diet with the fat they stored during the summer. 

 

Ceronychus major, the siberian dorsa is larger of the two dorsa species in Eurasia. During the summer these massive herbivores graze in swamps, plains and riversides, but during the winter they retreat to forests and switch to a diet consisting mainly of conifer needles. This change is also mirrored in the different types of stones they swallow during different parts of the year.

Species of the genus Ceronychoides, panhas and shantaks, are the only extant therizinosaurs with adaptations for cursoriality. Here pictured is an Eurasian panha Ceronychoides arctous. Panhas are generalist/grazers, smaller and rather more common than the dorsas. These rather small herbivores live in great herds of 100-200 individuals that roam the tundra and taiga.  In the summer, these habitats supply the panhas with an abundance of grasses, herbs and shrubs, but during the autumn and winter, the great panha herds must break up, small family clusters leaving plains to the lammoxes and migrating to the forests. There, the panhas live through the harsh northern winter, subsisting upon fungi, lichens and moss dug from under the snow with their long, curved claws. In the spring, the panha herds coalesce again, and the therizinosaurs mate and lay their eggs. The fast-growing calves are usually ready to follow the herd as the first snow falls on the ground. Panha breeding grounds are often located on island or river deltas where they are les accessible to predators.

 

 

The shantak (Ceronychoides gravis) is larger than its arctic cousin, the panha. Male shantaks have the proportionally longest arm claws of all extant hornclaw species

 

 

 

 

 

 

 

 

Though similar to dorsas in size and convergently similar to the robust therizinosaurs, the moora is probably more closely related to panhas. Mooras live on the taiga of Eurasia, stripping the branches off trees and bushes. They can weigh up to half a ton, but still run surprisingly fast. Mooras, in fact, looks a lot more robust than they really are because of their long hair-like plumage (especially during the winter). Like dorsas, mooras have humps on their backs for storing fat for the winter.

 

 

 

 

 

 

 (fig. 11) A male moora in winter plumage

AMERICAN THERIZINOSAURS

About 100 million years ago, a group of Asian therizinosaurs distantly related to Beipaosaurus briefly colonized a North America, spawning such Creataceous genera as Nothronychus, but these early forms failed to survive through the Tertiary. The Paleoarctic realm was repopulated with therizinosaurs during the Miocene, when primitive ceryonichids invaded North America.

During the Pliestocene, both ceronychids (hornclaws) and glaciotitanids (robust therizinosaurs) walked to America's Northern reaches via the Bering Land Bridge. As the tundras shrank, however, the robust therizinosaurs declined, leaving the ceronychids have become the dominant herbivores of America's northern reaches. These therizinosaurs are most specious in the tundra and the northern prairies of North America, and their diversity tapers off quickly south of the 55th parallel (where competition from the viriosaurs becomes fierce). On the other hand, the rarity of glaciotitanids in North America has allowed the ceryonichids to broaden their horizons, evolving a number of alpine forms.

 

 

 

 

 

 

 

 

About three million years ago, the ceryonichids migrated into South America during the Great Faunal Interchange. Although six species are known from the fossil record, only the two subspecies of the Andean Upclaw survive. In the plains, viriosaurs (basal ornithopods) could not be shaken from their dominance (this clade actually migrated north, and ousted the native small herbivores from their niches). However, the therizinosaurs did find an open niche in South America's high mountains, the Andes. The ceryonichids, had already conquered the mountains of North America and the leap from the Rockies to the Andes was, evolutionarily speaking, a short one.

The Andean upclaw exists in two distinct subspecies: A. a. peroni and A. a. bolivari. This species is spread across most of South America, from the Isthmus of Panama across the Andes to Tierra del Fuego. Although not a glaciotitanid, Altoseculus is convergent with the yando of Asia. Most of these convergences are related to size and habitat, as both species are adapted to mountain climates.

The subspecies bolivari inhabits the entire length of the Andes Mountains. These animals rarely reach lengths of over a meter.  Individuals of this the bolivari subspecies have been seen sprawling some of the highest peaks in the world, and are known to be excellent climbers. Bolivaries are herbivores, which, although they perfer coniferous foliage, will ingest most any vegetation, including alpine fruits and berries.

While A. a. bolivari is well adapted to its mountain habitat, A. a. peroni shows a slew of characters that enable it to survive in the high latitudes of Tierra del Fuego. Like the bolivari subspecies, peronies rarely reach more than a meter in length. This upclaw subspecies also favors coniferous foliage, but will eat berries and fruits if necessary.

Populations of both subspecies are known to coexist in southern South America. Generally speaking, however, the two keep quite separate ranges. It is thought that the separation of a band of A. andesensis bolivari individuals 1.5 million years ago led to the evolution of A. andesensis peroni. This second subspecies came to occupy a small range of Tierra del Fuego, quite separate from that of its close relative. The exquisite timing of A. a. peroni's reproductive cycle made it further adapted to its environment, and has proven to be the key adaptation that separates the two subspecies.

 Daniel Bensen, Matti Aumala, and Steve Brusatte

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                                                 ,=Tardox villosus (Arctic lammox)
                                     ,=Tadoxidae=|
                                    |            |                 ,=Ailurosaurus varius (Yando)
                                    |            `=Ailurosauridae=|
                                    |                              `=Alpicotardox montani (Mountain lammox)
                  ,=Glaciotitanidae=|
                 |                  |                  ,=Arctotitan gigas (Arctotitan)
                 |                   `=Arctotitanidae=|
                 |                                    |              ,=A. similis (Snow hona)
                 |                                    `=Alpicosaura=|
                 |                                                   `=A. nanus (Mountain hona)
Therizinosauria=|
                 |                   ,=Paraceronychinae=Paraceronyx mongoliensis (Lemek)
                 |                  |
                 |                ,=|                ,=Ceronyx paluditus (Dorsa)
                 |               |   `=Ceronychinae=|
                 |               |                  |                ,=K. robustus (Moora)
                 |               |                  |   ,=Kentronyx=|
                 |               |                   `=|             `=K.americensis (American moora)
                 |               |                     |
                 |               |                      `=Seculasaurus vulgaris (Common tirg)
                  `=Ceronychidae=|
                                 |
                                 |                                    ,=C. parvus (Panha)
                                 |   ,=Ceronychoidinae=Ceronychoides=|
                                 |  |                                 `=C. gravis (Shantank)
                                  `=|
                                     `=Altiseculinae=Altoseculus andesensis (Andean Upclaw) 

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