Милодон.

Так об этом уже давно говорили. Только разве это был мегалоникс?

В Сев. Америку до великого обмена могли попасть именно не очень крупные животные - по островам. Также как в Южную Америку кавиаморфные грызуны и приматы. А когда ленивцы попали в Сев. Америку?

Ground Sloths
As mentioned in our Xenarthrans section, sloths developed in South America 60 to 65 million years ago. Since this time, sloths have ranged in size from that of a small dog to as large as an elephant. The larger of these ancient sloths lived their lives either partially or completely on the ground. By the Oligocene epoch (35 million years ago), three groups of ground sloths had emerged. The first group was the family Megalonychidae, the ancestors of present-day Choloepus (two-toed sloths). The second was the family Megatheriidae, to which the genus Megatherium belongs. The third group was the largely land-dwelling Mylodontidae family. The latter two of these three families are now extinct, although three-toed sloths (family Bradypodidae) show an affinity to Megatheriidae.

Scientists distinguish between the ancient ground sloth families by the number of digits, number and size of teeth, and shape of the skull. Fossils found in Haiti and Puerto Rico indicate that some smaller ground sloths survived into modern times, perhaps as recently as 600 years ago. Research indicates that these smaller specimens weighed between 50 to 155 pounds (23 to 70 kg), and bear a resemblance to Choloepus in their skull and bone structure.

Giant Ground Sloths
The largest of the various species of ground sloths, such as and Megatherium americanum and Lestodon armatus, are known popularly as "giant ground sloths". The most recent fossil remains of giant ground sloths date back to 10,000 to 12,000 years ago. The remains of some of these giant creatures, such as Megalonyx, have been unearthed as far north as the Arctic Circle in Canada.

Giant ground sloth bones were first unearthed in Brazil in 1789. The creature was named Megatherium, meaning "giant beast", by Georges Cuvier in 1796. Megatherium americanum was a huge, elephant-sized beast that grew up to 20 feet (6 meters) in length and weighed up to 7,000 pounds (3,175 kg). M. americanum possessed massive claws 12 inches (30 centimeters) in length, which allowed it to defend itself against other terrestrial predators, such as the powerful saber-toothed tiger. Members of the Mylodontidae family, such as Mylodon, also possessed an interesting defensive charcteristic: small, pebble-sized bones just beneath the skin called "dermal ossicles". These bones make the skin very tough and resistant to injury. (Modern-day tortoises and many other reptile species also possess dermal ossicles.)

These great beasts, however, were not necessarily predators. Giant ground sloths' claws were also suited for digging and ripping up the vegetation that it used for food. Some scientists believe M. americanum was an omnivorous scavenger, whose diet consisted of both left-over animal kills as well as the leaves and roots of trees - similar to some modern-day species of armadillos.

M. americanum moved its mass from place to place on four legs, but could easily stand solely on its larger, more powerful hind legs to better reach food high in the treetops. Giant ground sloths also apparently walked upon the sides of their feet when traveling from place to place: a condition called a "pedolateral" foot.

Exactly why these huge creatures have disappeared is still unknown. It is possible that the ground sloths' numbers dwindled over time due to a combination of climate changes, predators (including early humans), and the inability to effectively compete for food and resources. While scientists piece together this mystery, the giant ground sloths continue to capture the imagination of both young and old alike.

Вика пишет что 9 млн лет назад, значит в миоцене. А вот антильских островов они достигли гораздо раньше. Может они вплавь туда отправились, ленивцы отлично плавают.
Кстати говорят они могут быть очень шустрыми, но кадров я пока таких не встречал.

Тhalassocnus был из мегатериид, а в миоцене попали в Северную Америку мегалонихиды, это самое успешное семейство ленивцев.
А почему решили что он был полуводным?

Насколько валидно семейство Orophodontidae?

Crazy Zoologist :

Кстати кто в курсе на основании чего двупалых ленивцев помещают в семейство мегалонихид? У последних три пальца на передних лапах. Это важный признак.

По ряду не менее важных признаков - отсутствию у двупалого слуховой буллы ( у брадипуса она есть),наличию клыковидных передних зубов и др.

Тоже самое, судя по всему. К тому же некоторые мелкие формы мегалонихид с Антил также вели, видимо, полудревесный образ жизни. Некоторые специалисты считают, что, возможно, современный унау ведет начало от них.
Почему брадиподиды отдельное семейство? Отличаются по ряду признаков - строением зубов, например. К тому же пока пробел в палеонтологической летописи не позволяет с точностью установить филогенетические связи трехпалых ленивцев, ясно лишь, что ближе они к мегатериидам.

А кто из ленивцев ступал НОРМАЛЬНО на стопу?

Сайт с статьями о Ксенартрах!   http://globalanimals.ru/category/ksenar … itayushhie

ТОчно!

Ребята,кто автор?Есть у кого большего размера?