Cimolestids (Cimolesta)
The largest cimolestid is Coryphodon, 1 metre (3.3 ft) high at the shoulder and 2.25 metres (7.4 ft) long.

Coryphodon (from Greek "point", and "tooth", meaning peaked tooth, referring to "the development of the angles of the ridges into points [on the molars].") is an extinct genus of mammal.
Coryphodon was a pantodont, a member of the world"s first group of large browsing mammals. It migrated across what is now northern North America, replacing Barylambda, an earlier pantodont. It is regarded as the ancestor of the genus Hypercoryphodon of Mid EoceneMongolia.
Coryphodon is known from many specimens in North America and considerably fewer in Europe, Mongolia, and China. It is a small to medium-sized coryphodontid who differs from other members of the family in dental characteristics.
At about 1 metre (3.3 ft) at shoulder height and 2.25 metres (7.4 ft) in body length, Coryphodon was the biggest known mammal of its time. The creature was very slow, with long upper limbs and short lower limbs, which were needed to support its weight. Coryphodon does not seem to have been in need of much in the way of defences, however, since most known predators of the time seem to have been much smaller than Coryphodon.
Coryphodon had one of the smallest brain/body ratios of any mammal, living or extinct, possessing a brain weighing just 90 grams (3.2 oz) and a body weight of around 500 kilograms (1,100 lb).
Estimates of Coryphodon"s body mass have varied considerably. Based on a regression analysis of ungulates, Uhen & Gingerich 1995 estimated the mean body mass for the type species C. eocaenus to 340 kg (750 lb), 600 kg (1,300 lb) for C. radians, and possibly as much as 700 kg (1,500 lb) for C. proterus and C. lobatus.
Since the first fossil was found in Wyoming, the taxonomy of Coryphodon and its family have been in disarray — five described genera have been synonymized with Coryphodon and thirty-five proposed species have been declared invalid.
Coryphodon evolved from the Late Paleocene C. proterus, one of the largest species found and the only one known from the ClarkforkianNALMA. The body size then decreased until C. eocaenus appears at the Clarkforkian-Wasatchian transition (55.4 Ma, near the PETM), from where Coryphodon evolved into the large species C. radians. C. radians in its turn evolved into two contemporaneous species who appear in the Early Eocene, the small C. armatus and the very large C. lobatus. These changes in size are thought to be linked to global climate change, with the size minimum in the Coryphodon lineage occurring shortly after Paleocene-Eocene boundary.
Coryphodon had a semi-aquatic lifestyle, likely living in swamps and marshes like a hippopotamus, although it was not closely related to modern hippos or any other animal known today. Coryphodon had very strong neck muscles and short tusks that were probably used to uproot swamp plants. The other teeth in the mouth were suited for processing plants that had been grabbed by browsing.
Fossils found on Ellesmere Island, near Greenland, show that Coryphodon once lived there in warm swamp forests of huge trees, similar to the modern cypress swamps of the American South. Though the climate of the Eocene was much warmer than today, plants and animals living north of the Arctic Circle still experienced months of complete darkness and 24-hour summer days. Isotopic studies of tooth enamel revealed that during the summer period of extended daylight Coryphodon would eat soft vegetation such as flowering plants, aquatic plants and leaves. However during the extended periods of darkness when plant photosynthesis was impossible, Coryphodon would switch to a diet of leaf litter, twigs, evergreen needles and most revealingly fungi, an organism and food source that does not require light to grow. Not only does this study reveal the dietary range of Coryphodon, but it also reveals the behaviour of the northern populations living within the Arctic Circle. In this respect Coryphodon did not migrate south or hibernate, it simply switched between two seasonal food sources.
Uhen & Gingerich 1995 noticed a sexual dimorphism in Coryphodon: the canines tend to be either very large or very small compared to cheek teeth, and, comparing to modern hippos, there is reason to assume males had larger canines than females.


Barylambda

Restorations of some pantodonts of the North American Paleocene. A. Coryphodon. B. Barylambda. C Titanoides primaevus. D. Caenolambda. E. Pantolambda cavirictus. E. Pantolambda bathmodon.
Barylambda is an extinct genus of pantodont mammal from the middle to late Paleocene, well known from several finds in North America. Three species of Barylambda are currently recognised.The creature likely lived a life similar of that of a modern tapir, browsing on foliage and soft vegetation. Barylambda seems to have been quite successful for an early pantodont, though eventually it seems to have been replaced in its ecosystem by other pantodonts, such as Coryphodon.
In life, Barylambda probably resembled a large tapir, with a small head and long, well-developed tail and bear-like legs. The length was about 2.5 meters with a weight around 650 kg, about the size of a pony. Barylambda was large even for a pantodont, sheer size probably protecting it from contemporary carnivores.
Like other pantodonts, Barylambda was a heavyset, five-toed plantigrade animal. The vertebrae of the tail were unusually massive; the living animal may have been able to rear up and support itself on the hind legs and tail in order to reach higher for food. Because of the generalized appearance of the teeth, the presence of well-developed canines only in males, the grinding wear and lack of shearing blades on the molars, and the animal"s heavy build strongly suggest that it was herbivorous.

Titanoides

Titanoides is an extinct genus of pantodont mammal. It was about 2 m long and weighed between 200 kg. Titanoides was one of the early Tertiary browsing mammals called pantodonts. Even though they had huge canine teeth, they were herbivores but may have been omnivores too. Their feet possessed five clawed digits and Titanoides was the largest mammal that inhabited North Dakota 60 million years ago when western North Dakota was a subtropical swampland. These animals are related to Pantolambda and had five-fingered hands, with almost equal in size fingers with terminal phalanges a bit like bear claws. All other pantodonts find the extremities of which are known to have blunt hooves at the front and rear limbs. They may have eaten roots, leaves, bark,and also probably ate small animals and carrion.


Mesoreodon major

Mesoredon major is an extinct species of oreodont belonging to the subfamily Mercoidodontinae, within the family Merycoidodontidae. It lived from 33 to 20 million years ago, in the early Miocene epoch, with a temporal range of over twelve million years. Though similar to the closely related genera Merycoidodon and Eporeodon, M. major was distinguished from both by its larger size; possessing narrower and higher crowned teeth than the former; smaller and more pit-like preorbital fossae, a higher muzzle, reduced premolars, and a more derived, upturned zygomatic arch than the latter. Mesoreodon is believed to have been ancestral to Desmatochoerus and Hypsiops.
Mesoreodon lived across the continental United States, with specimens being discovered as far as both the western and eastern seaboards. Fossils have been uncovered in the John Day formation in Oregon, the Cabbage Patch and Fort Logan formations in Montana, and in between the Brule and Gering formations in Nebraska. Specimens have also been unearthed in Florida and California.
Mesoreodon was a large grazing herbivore, with an estimated mass o 155-230 kilograms. (350-500 lbs.) It is known from several well-preserved skulls and partial skeletons. The skull of Mesoreodon was robust and mesocephalic. Like all oreodonts, Mesoreodon exhibited a pair of large, sharp canines, although it was herbivorous.
Mesoreodon specimens have been discovered with ossified vocal cords, a trait observed in extant howler monkeys. It has been suggested that Mesoreodon was capable of using loud vocalizations as a method of predator deterrent or interspecific intimidation, earning the genus the nickname of the “screaming oreodont.”