Therapsids

By | September 9, 2016

During the Permian Period, the pelycosaurs (search the article) evolved into more mammal-like animals known as therapsids. Unlike their sprawling, lizardlike ancestors, the therapsids had a more upright build that let them run and breathe more easily, allowing a more active lifestyle. The therapsids were the ancestors of mammals and became increasingly mammal-like over time.

FAMILY FACT FILE

Key features
■ Stout bodies
■ Massive heads
■ Teeth specialized to form incisors, canines, and molars
■ More upright legs than their pelycosaur ancestors

When
Therapsids appeared in the Permian Period and became the dominant animals on land. They went into decline during the age of the dinosaurs, but one family of small therapsids survived and gave rise to the mammals.

Moschops (MOE-shops)

moschops


When: 255 million years ago (Late Permian)

Fossil location: S. Africa

Habitat: Forests

Length: 8 ft (3 m)

Diet: Plants

Moschops was a heavily built plant-eater, about the size of a bear. It had stout legs, a huge, barrel shaped chest, and a short tail. The bone in the top of its skull was amazingly thick. Scientists think males may have used their massive skulls as battering rams in contests over mates, as bighorn sheep do today.
Moschops had wide jaws with short, chisel-like front teeth that met (rather than overlapping) when its mouth closed, allowing it to nip plants precisely.

EARLY HERDS?

Remains of several Moschops individuals have been found fossilized together. Perhaps these plant eaters lived in small herds for protection from predators.

Pelanomodon (PEL-an-OH-mow-don)

pelanomodon


When: 255 million years ago (Late Permian)

Fossil location: S. Africa

Length: 3 ft (1 m)

Diet: Plants

Pelanomodon was a member of a large and very successful family of plant-eating therapsids called the dicynodonts (DIE-CYE-nodonts).
The dicynodonts used toothless beaks to pluck vegetation, and most had a single pair of tusks.
Pelanomodon was a stocky, piglike dicynodont that had no tusks. Like other dicynodonts, it could slide its lower jaw forward and backward, which helped it grind the tough plants it ate.

FINE FOSSIL

pelanomodon-skull

In this remarkably well-preserved Pelanomodon skull, the bone around the beak has lots of tiny holes where blood vessels once ran.

Robertia (roe-BERT-ee-ah)

robertia


When: 255 million years ago (Late Permian)

Fossil location: S. Africa

Habitat: Woodlands

Length: 1 ft (0.4 m)

Diet: Plants

The earliest dicynodont known from good fossils is Robertia. This small plant-eater was about the size of a domestic cat and had a turtlelike beak, which it used to crop leaves. It had a pair of tusks formed from canine teeth and perhaps used them to dig for roots.

Placerias (plah-SEE-ree-ass)

placerias


When: 220–215 million years ago (Late Triassic)

Fossil location: USA

Habitat: Flood plains

Length: 6–11 ft (2–3 m)

Diet: Plants

Placerias was one of the biggest herbivores of its day, weighing about 1,300 lb (600 kg). One of the last large dicynodonts, it lived at the same time as early dinosaurs. Similar in shape and weight to a hippo, it might have wallowed in water, too, and may have used its tusks for fights and social displays as hippos do.
A find of 40 skeletons in one place suggests Placerias lived in herds.

Sinokannemeyeria (SIGH-no-CAN-eh-my-AIR-ee-ah)

sinokannemeyeria-fossil


When: 235 million years ago (Middle Triassic)

Fossil location: China

Habitat: Woodland

Length: 6 ft (2 m)

Diet: Tough vegetation, roots

This pig-sized dicynodont had a massive head, a long snout, and a huge belly to house the large intestines needed for digesting rough plant material. Like other dicynodonts, it could move its lower jaw forward and backward to shear and grind tough leaves. Its legs were short and stumpy, with a slightly sprawling gait, suggesting it was not very fast or agile on its feet. But it may have used its powerful forelimbs and small tusks to dig for roots.

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