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Laurasiatheria
The Laurasiatheria families that are discussed here in detail are Chiroptera, Cetacea, Artiodactyla and Perissodactyla and Carnivora.
Order: Chiroptera
Bats evolved in the Eocene in North America. Their elongated fingers were joined by a patagium that allowed powered flight. Unlike most other mammalian Orders, bats were recognisable right from the earliest species such as Icaronycteris. Despite the Chiropetra now being one of the most speciose Orders of all placentals, all species both modern and extinct look extremely similar. Even the very earliest bats had wings that were capable of flight and rotatable feet that could be turned 180 degrees to hold onto braches when the bats hung upside down. Due to fossilised ear bones, it is believed that extinct bat forms had the same developed hearing and as with modern bats used echolocation in predation.
Example species:
Primitive bat
Icaronycteris
Length: 15 m (40 cm wingspan)
Region: North America
Time: Eocene (53-33.7 mya)
Status: Extinct
The earliest whales looked very different morphologically from what they do today. They evolved in the Eocene and had four limbs that were probably still capable of terrestrial locomotion. They would swim using their tails with an up and down motion to propel them forward. These terrestrial whales, such as Ambulocetus, probably spent most of their time on land and took to the water to hunt. Fully aquatic species such as Basilosaurus did not evolve until the end of the Eocene. These descendant species are thought to have been active predators that inhabited shallow tropical seas. Recent DNA tests have shown that whales are likely to be closely related to Artiodactyls, the hippopotamus in particular.
The first known whale was Pakicetus, found in Pakistan.
Pakicetus evolved in the middle Eocene and is presently
only known from skull material. It is thought to have been around
2 metres long and relatively terrestrial. Its delicate teeth and
body morphology suggest that Pakicetus was more designed
for splashing around in the shallows catching fish, rather than
diving to great depths like whales of today. Nevertheless, Pakicetus
possessed bones in the ear that are unique to whales, proving
that it was a direct ancestor.
Example species:
First known whale
Pakicetus
Length: 2 m
Region: Pakistan
Time: Middle Eocene
Status: Extinct
Early whale
Basilosaurus
Length: 20-25 m
Region: Shallow tropical seas
Time: Late Eocene
Status: Extinct
Order: Artiodactyla and Perrisodactlya
Hoofed mammals all belong to a group called the ungulates, which is divided into two Orders; the Perissodactyla and the Artiodactyla. The artiodactyls appeared in the Eocene and evolved into two groups; the Suiformes (pigs and hippos), and the Selenodontia (cattle, giraffes, deer, antelopes and camels). The most primiive artiodactyls were small herbivorous animals about the size of a rabbit. Diacodexis was one of the first artiodactyls. It evolved in the Early Eocene and ranged from North America, through Europe to Asia. Its skeletal structure was primitive though its legs were long and slender, presumably to enable it to leap around the grasslands in much the same way as modern deer do. Primiitive or basal artiodactyls continued into the Oligocene before they were superceded by the first Suiformes and Selenodontids in a major episode of radiation. Perissodactlys also evolved in the early Eocene. They diversified relatively quickly, still within the early Eocene, and replaced the basal placental groups to become the dominant terrestrial herbivores.
Example species:
Order: Artiodactyla
'Buffalo pig'
Daeodon
Length: 3 m
Region: North America
Time: Oligocene-Early Miocene
Status: Extinct
Deer
Cranioceras
Height: 1 m at the shoulder
Region: North America
Time: Miocene
Status: Extinct
Camel
Aepycamelus
Height: 2 m at the shoulder
Region: North America
Time: Miocene (23.5-5.3 mya)
Status: Extinct
Llama
Macrauchenia
Length: 3 m
Region: South America
Time: Pleistocene (1.75-0.01 mya)
Status: Extinct
Rhinoceros
Arsinoitherium
Length: 3.5 m
Region: Egypt, Oman and southwest Asia
Time: Eocene (53-33.7 mya)
Status: Extinct
Horse
Hipparion
Length: 1.5 m
Region: North America, Europe, Asia and Africa
Time: Miocene and Pliocene (23.5-1.75 mya)
Status: Extinct
The most primitive members of the Carnivora appeared in the late Paleocene and early Eocene. A unique character of primitive carnivores is their retractable claws. When in use the claws can be extended to varying lengths species dependant, but when out of use they retract into sheaths within the paws of the animal. The first true carnivores were a group called the Miacis. The miacoids were primitive member of the Canidae but was dapated to climbing with limb joints that closely resemble thse of modern agile predators. Miacoids had smaller brains than modern canids in comparison to their body size.
Miacis was a 30 cm long primitive member of the Canidae with retractable claws andf agile joints for climbing. It evolved in the early Tertiary and was found in Europe and North America. It also had a long tail used as a riudder when leaping around in trees, and binocular vision.
Example species:
Sabre-tooth cat
Smilodon
Length: 1.7-2.5 m
Region: North and South America
Time: Pleistocene (1.75-0.01 mya)
Status: Extinct
Cave bear
Ursus spalaeus
Length: 2.8 m
Region: Europe
Time: Pleistocene
Status: Extinct
Hyaenodont
Megistotherium osteothlastes
Length:
Region: Libya
Time: Miocene
Status: Extinct
Author: Emma-Louise Nicholls
Last updated: 20th November 2005
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