Laurasiatheria Clade (11)
Animals of the Laurasiatheria evolved on the northern supercontinent of
Laurasia after the breakup of Pangea. The diversity in form, habitat, and
size in this group is astounding and contains the largest and among the
smallest of all mammals. The Laurasiatheria includes 7 or 8 orders
depending on how the cetaceans and artiodactyls are lumped together into a group
called the Cetartiodactyla. This group (here treated as a superorder)
is an unlikely collection of animals like pigs, cows, camels together with
whales and dolphins.
As remarkable as the collection seems, the relationship
has been confirmed by fossil, molecular, and anatomical evidence (Thewissen
and Williams 2002). Furthermore, the emerging story of whale evolution has
become one of the most exciting demonstrations of macroevolution to have emerged
in vertebrate paleohistory.
The former order Insectivora, which turned out to be a polyphyletic
assemblage of taxa (Douady et al. 2002), contained tenrecs, ottershrews,
and golden moles (see afrotherian
insectivores) as well as diverse groups of laurasiatherians: shrews,
moles, and hedgehogs (of the order Eulipotyphla). These are small
animals with elongate muzzles and superficially similar to the earliest
mammaliformes like Morganucodon (see Figure 2). The order is
represented by three extant families and extinct groups that push its initial
radiation well into the Cretaceous.
The shrews (Figure 24) occur on all
continents except Antarctica and Australia.
Shrews form two major groups:
red-toothed shrews (Europe, northern Asia
and North America) and white-toothed shrews (Africa and southern Asia).
These tiny animals have a very high metabolic rate and must eat nearly
their own body weight in insects each day.
Moles (Figure 25) and desmans are
fossorial and aquatic animals of North America
and Eurasia. Moles are adapted to burrowing with large digging claws and weak hind
legs; small eyes and ears. Desmans
look like fat shrews (they are aquatic) with webbed feet.
(Figure 26) and rat shrews are terrestrial mammals of
, and Eurasia to
. They are plantigrade and some have
enlarged incisors. Early forms were dog-sized and covered with stiff hairs.
Later forms evolved the spines characteristic of today’s hedgehog. Like
moles, they are are good diggers and are omnivorous. Some
are good climbers and swimmers.
The bats (Chiroptera) are the second-most speciose order of mammals
with more than 1,100 living species (~22% of all living mammals).
Bats use fingers 2-5 as the
frame for their wings. The shoulder
girdle together with the ribs, scapula, and sternum, is adapted for the
attachment of large flight muscles.
Also, their hind feet can swivel so that they are turned backwards. The origin of flight in bats remains something of a mystery.
They separated from the other mammals, most likely a common ancestor to
the Eulipotyphla, around the end of the Cretaceous (Teeling et al. 2005,
Cao et al. 2000). The earliest known fossils of bats are from the
upper Paleocene, and they clearly are bats with elongated digits of the
manus, the hallmark of powered flight in that order. The discrepancy
was explained by Teeling et al. (2005) who determined that the fossil
record of bats underestimates their fossil history by 61%. The
relatively sudden elongation of bat digits was explored by Sears et al.
(2006) who noted that although bat digits begin development much smaller than
even those of mice, the expression of Bmp protein causes the elongation of
the digits (artificial addition to mouse embryos also promoted digit
elongation). Hockman et al. (2008) also observed that Sonic
hedgehog, which controls Bmp, makes a second round of expression causing
the forelimb digits to elongate. This evolution through developmental changes (now
referred to as evo-devo) could explain the very rapid and profound change
in digit length in bats. However, Cooper and Tabin (2008) suggest
that we should be cautious about being lured by such a siren's song
because we do not have early fossils and, therefore, do not know what
utility early minor elongations in bat digits might have had.
Aside from flight, the most distinctive character of many bats is
a sonar system that seems to have evolved more than once in the order (Teeling
et al. 2002, Eick
et al. 2005). Echolocating bats emit high-frequency sounds using the
larynx (14,000 to 100,000 hz) through the mouth or the nose. The
integration of the echoes with the emitted sound allows the flying animal
to navigate through complex terrain with minimal light while locating prey
items. Aside from the sound-emitting and neural modifications,
(Eick et al. 2005), other morphologies like relatively large and elaborate
ears and many with nose-leaves also function in echolocation. The earliest microbats (e.g. Gunnell et al.
2003), indeed the earliest placental mammals found in sub-Saharan Africa,
had an enlarged cochlea, which showed that they likely possessed
echolocation in the Eocene.
order is divided between two suborders, commonly called megabats and
microbats (after Dobson 1875). The megabats are the flying foxes
(Figure 27) and Old World fruit bats, which occupy a single family, the Pteropodidae. They are large bats of
the tropics and subtropics of Africa, southern and central Asia, Australia, and
the Pacific islands. Some are
quite large and have wingspans up to 1.7m. Most,
however, are much smaller. Pteropodids have a
suite of unique characters that include: a second finger with a claw, elongated
bony palate, no more than four upper and four lower incisors, relatively simple ears
and small cochlea, tail absent or, if present, much reduced.
They eat fruit or nectar.
The microbats (see Figure 28) tend to be insectivores, but some
are fruit-eating, blood-eating, or fish-eating. Distributed into 16
families, the microbats contain 84% of all bat species. Mainly, they
are small animals, an index finger without a claw and a relatively long tail.
Microbats are found from the tropics through temperate latitudes.
Teeth broad with many cusps. Most
are sociable and some hibernate.
During the past 30 years molecular and anatomical work have not
supported the traditional subordinal classification. Pettigrew et
al. (1989) and Pettigrew (1991) saw a strong relationship between the
brain anatomy of primates-flying lemurs and the megabats. They
proposed that bats and mammalian flight were polyphyletic. That is,
the microbats were related to the insectivores while the megabats were
related to the primates and similarities between the two groups was
superficial. Simmons et al. (1991), in a response to Pettigrew's
assertions outlined the need for more anatomical and molecular work
coupled with phylogenetic analysis. The initial molecular work (e.g.
Baker et al. 1991, Hucheon et al. 1998) supported the monophyly of the
Chiroptera; however, they also suggested that the microbat-megabat
dichotomy was a false one. Furthermore, Eick et al. (2005), Hutcheon
and Kirsch (2004, 2006), and Teeling et al. (2000, 2002, 2003, 2005) demonstrated that five superfamilial groupings of bats occurred.
Also, in the emerging subordinal structure, megabats (Pteropodidae)
clustered within a clade that included five formerly microbat
families. So, molecular phylogenetics confirmed the monophyly of
bats, but restructured the organization at the subordinal level.
Now the standard classification of bats is that of Simmons (2005)
as modified by Hutcheon and Kirsch (2006). Springer et al. (2001)
named the two suborders Yinpterochiroptera and Yangochiroptera.
Hutcheon and Kirsch (2006) objected to such names because they had little
information and were taxonomically inconsistent and suggested the names
Pteripodiformes (superfamilies Pteropodoidea and Rhinolophoidea) and
Vespertilioniformes (superfamilies Emballonuroidea, Noctilionoidea, and
The odd-toed ungulates (Perissodactyla) include two major groups:
Hippomorpha (the horse forms) and Ceratomorpha (horned forms). The
living hippomorphs (horses, asses, and zebras) are relatively large
herbivores of open habitats, particularly grasslands, through the Old
World. They also have a single digit (The modern domestic horses
were derived from wild stock like the surviving Przewalski's Horse, see
Figure 29). However, the Eocene
horses, like Hyracotherium (Figure 30), were woodland browsers with 4 toes. As they began to make use
of more open habitats, the animals became larger and reduced the number of
toes to one. At the same time, the legs grew longer, which made them
very fast. The
browsing molar was small while the grazing molar became large and able to
withstand the abrasion of the silica in grass.
Ceratomorpha taxa were and remain much more diverse than the
hippomorphs. Though the name means "horned forms", some of
the ceratomorph taxa do not have horns.
Among the first to appear in this line were the
enormous brontotheres (also called titanotheres, Figure 31) during the Eocene.
These were large animals that resembled rhinoceros with a catapult-shaped
horn on the nose. They were not true odd-toed animals.
Although their hind feet had three toes, their front feet had
four. Though massive, they likely could not the tougher
vegetation, especially the grasses, that began to appear in open
habitats in the Eocene.
Chalicotheres (Miocene to Pleistocene) looked like a large ape with
hooves and a horse's head (Figure 32). Their forelegs were very long and the
hind legs were short. They may have been able to walk bipedally or
Tapirs (Figure 33) are terrestrial animals that range from southern
Mexico to Venezuela. A fourth species
occurs in Burma, Thailand south to
Sumatra. The tapirs radiated from animals
that looked like Eocene horses. Then,
the surviving lineage developed a short proboscis, which evolved independently
to the proboscis of the afrotherians.
Living rhinoceroses are restricted to open areas of south-central Asia
Africa. They are large animals with thick
skin and one or two horns made of compressed hairs.
Rhinos evolved from animals that resembled Eocene horses.
By the Oligocene, the rhino line had produced the largest terrestrial
mammal that ever evolved, Paraceratherium+
(Figure 34; syn: Indricotherium; Baluchitherium).
Horned rhinoceroses radiated in the Miocene.
Carnivora + Pholidota
The carnivora have a particular dental formula that includes: a pair
of carnassial teeth. They are best known for the canines, which are
long and adapted for piercing or puncturing. The feet are modified
as clawed paws. The carnivores are divided into two modern natural
groups: Feliformia and Caniformia, cat forms and dog forms,
respectively. They can be recognized by the type of tympanic bulla:
feliforms have an ossified tympanic bula that has an internal septum, the
caniforms do not have an internal septum. The earliest carnivores were the
miacids (Figure 35), semiarboreal
cat-like or weasel-like animals that appeared in the Paleocene perhaps
allied with a line of early ungulates (Wesley-Hunt and Flynn 2005). They
did not have an ossified tympanic bulla. Recognizable members of the
carnivora appeared in the Eocene and radiated to all continents and
The feliforms are the civets, mongooses, aardwolves, hyneas, and
cats (Figure 36). Most of them are digitigrade and striped or
spotted. The felids (the cat family) have retractable claws.
The caniforms are more diverse and include dogs, wolves, bears, raccoons
mustelids (otters, weasels, etc., Figure 38) and the pinnipeds (Figure 39). The
results of Arnason et al. (2006) indicate that the seals are sisters to the walrus + sealion
clade and that the sealions separated from the seals before the middle
Pangolins (Pholidota, Figure 40) make up a group of anteaters
called scaly anteaters, sister group to the carnivores.
These animals are toothless and covered with armored overlappingd scales.
They, too seem to have appeared in the Eocene.
This group that includes the
odd-toed ungulates (Artiodactyla) and the whales (Cetacea) was identified
as a clade by Thiewissen et al. (2001). The unlikely grouping of
animals as different as pigs, deer, and whales was a major insight into
the origin of whales, one of the great enigmas of vertebrate
evolution. The earliest members of the clade were the zhelestids,
arctocyonids and the mesonychids. The zhelestids were present in the
upper Cretaceous but their position is uncertain. Though accepted as
placental mammals (Archibald et al. 2001), the zhelestids seem to be
paraphyletic and basal to both the glires and the ungulates. The
zhelestids persisted into the Paleocene.
Arctocyonids (Figure 41) were Paleocene
herbivores that superficially resembled sheep-sized dogs (Benton
2005). The molars, which were very large and adapted to crushing,
indicated their herbivorous nature. They were somewhat diverse with
some taxa becoming arboreal, having muscular limbs and even the suggestion
of a prehensile tail.
Mesonychids (Figure 42) also resembled large
wolves, but these, unlike the arctocyonids were carnivores (Benton
2005). They had a plantigrade stance with paw-like feet ending
in toes, each of which had a small terminal hoof. These hoofed
carnivores had teeth like certain early cetaceans and toes like
ungulates. Though once considered the ancestors of the cetaceans,
mesonychids are now thought to be sisters to the cetacean + artiodactyl
clade (Thewissen and Williams 2002).
They appeared in the Paleocene and died out in the Eocene.
The artiodactyls, the even-hooved
ungulates, are divided into two extant groups: the Suiformes (pig-forms)
and Selenodontia (moon-teeth). The sister groups derived from a
basal ungulate group, the dichobunids, which were herbivorous
browsers. These basal artiodactyls had multiple digits on the front
and hind feet (4-5 toes). Each digit terminated in a small toe;
however, only digits 3 and 4 bore weight, a condition seen in all
artiodactyls. Also, the dichobunids had a diagnostic double-pulley
astragalus (heel bone) that is characteristic of all artiodactyls.
They appeared in the lower Eocene and disappeared in the Oligocene.
Suiformes appeared in the upper
Oligocene and persist today as pigs, peccaries (Figure 43), and hippos
(Figure 44). In
general, they are omnivores with bulbous cusps on their molars and large
canines that emerge from their mouths. Their stomachs may have 2
chambers (pigs) or 3 chambers (peccaries and hippos), but they are never
ruminating (regurgitate food to chew as a cud).
Selenodonts appeared in the Eocene
and underwent several diversifications. In general, all members of
this group tend to be animals of open habitats, usually grasslands or open
woodlands as grazers or browsers, respectively. The key character is
the occurrence of a lunate pattern on the surfaces of certain cheek
teeth. Also, the upper incisors are very reduced or missing
altogether and the lower incisors bite against a horny pad in most.
There are two clades within the selenodonts: tylopods and ruminants.
Only camels (Figure 45), which have a 3 chambered ruminating stomach, represent the
tylopod line today. The ruminants, well represented today as deer
antelope, giraffes, and bovids, etc., have 3-4 chambered ruminating
stomachs and true horns or antlers.
Cetaceans (whales and dolphins)
Cetaceans either are sisters to the
artiodactyls or emerged from within the artiodactyls and are sisters to
hippos. The distinction is important. If whales are sisters to
the artiodactyls at large, then there could be an order Cetacea and a
related order Artiodactyla. However, if the whales emerged from
within the recognized artiodactyls, particularly the suiforms, then the
clades would become much more complicated with the selenodonts as an
isolated group and the suiforms separated into pigs and peccaries as one
clade and hippos and whales as a second clade. Until this is sorted
out, we will retain the more traditional classification. Most
morphologically-based phylogenetic analyses show the cetaceans as sisters
to the artiodactyls (e.g. Benton 2005, Thewissen et al. 2007, and Gatesby
and O'Leary 2001). However, molecular analyses (e.g. Price et al. 2005, and Nikaido et al.
2001) seem to point to the
hippos as the closest living relatives to the cetaceans.
appeared in the Eocene, much earlier than the earliest known remains of
hippos, as semiaquatic carnivores, similar to crocodiles in lifestyle
(summarized in O'Leary et al. 2004). Though the mesonychids were
considered the likely precursors of cetaceans (e.g. O'Leary et al. 2001),
information from an impressive set of fossil animals from the Eocene of
Pakistan and India across to North Africa, show a relatively complete
series of animals that transitioned from terrestrial carnivore/scavengers
to fully aquatic leviathans in relatively short time. Among the earliest known in the line was Pakicetus
(the whale of Pakistan, Figure 47), a most unlikely whale ancestor. It was an
amphibious animal that clearly was able to move effectively over terra
firma. Ambulocetus (the walking whale, Figure 48) was more
transitional in its form and lifestyle. Thewissen et al. (1994, 1996),
Thewissen and Fish 1997, and Madar et al. (2002) describe an animal that
was at home in the water and on land. It had a long crocodilian-like
head and inhabited fringing swamps and marshes of the Tethys Sea.
Because it was a carnivore but equally slow on land and the water, likely
lived as an ambush predator.
The transition to a more whale-like
body with nostrils moving higher on the head, the pectoral limbs becoming
paddle-like, the reduction and loss of the hind limbs seems to have
occurred somewhat rapidly. By the middle Eocene, animals that would
be recognized as whales (e.g. Dorudon, Maiacetus, and Basilosaurus,
had appeared (Gingerich et al. 2009). They had small hind legs, and
long tails that probably had flukes. The further transition to
modern whales involved elongation of the skull and the development of the
melon organ, a structure involved in echolocation. Also,
the hind limbs either disappeared or remained as bony elements that were
not attached to the vertebral column.
Modern whales are divided into two
groups: the toothed whales, which may not be monophyletic and the baleen
whales, which seem to be monophyletic. Though Price et al. (2005)
treat them as separate clades, fossils of toothed whales come from
deposits as old as the Miocene and the baleen whales seem to have arisen
more recently in the Oligocene (Benton 2005). All modern whales have
well-developed echolocation abilities and seem to be quite social with
various forms of communication.
All toothed whales are carnivores
and feed on fish, other mammals (including other whales), and
squids. The Sperm Whale (Figure 50), which can grow to be up to 18m long, have a
head that occupies about one-third of the body and an enormous melon
organ. They feed primarily on giant squids for which they can dive
up to 1,000m. This group also includes Orcas, Dolphins, and Pilot
Whales. Some of the toothed whales are native to brackish and fresh
The baleen whales include the
largest animals that have ever lived on the earth (e.g. Blue Whale, Figure
All of these animals are adapted to straining their food from water or
suspended mud through overlapping sheets of baleen in their mouths.
The Blue Whale fills its enormous pleated mouth cavity with
plankton-containing water and then forces it through the baleen with its
tongue. This way, the animal can strain out hundreds of kilograms of
krill, a planktonic crustacean, with each mouthful.
Other whales like Right Whales have equally large heads but no throat
pleats and strain out much smaller crustaceans like copepods. Gray
Whales are somewhat unusual in their method of feeding. They scoop
up bottom mud from which they strain out crustaceans.
| Euarchonotoglires (12)
The Euarchonotoglires (Clade
12), sometimes called the Supraprimates, have two major monophyletic sister
groups: Glires (rodents, rabbits, and hares) and Euarchonta (primates,
tree shrews, and flying lemurs). They are sisters to
the Laurasiatheria in a clade called Boreoeutheria (Clade 10).
group seems to have appeared in the late Cretaceous, when it separated
from the Laurasiatherian line (Benton 2005). The Plesiadapiformes,
an early group of arboreal mammals, were the earliest known members of the
euarchontoglires and appeared to be sisters to the primates. Animals
like Purgatorius (Figure 52) had bodies that resembled primates, even to the
extent of having nail-like claws, but their heads were long and
squirrel-like with the eyes on the sides rather than the front.
Although many aspects of these animals seemed basal, their teeth were
highly modified with distinctive incisors and molars. The derived
nature of their dentition suggests that they did not give rise to any
particular groups in the euarchontoglires. Indeed, Wible et al.
(2007) show them as non-placental mammals altogether.
to Benton (2005), the primates have three major sets of adaptations:
agility in the trees, large brain and acute diurnal vision, and parental
care. Clearly, these are not synapomorphies, nor are they restricted
to the primates, but they can explain the features of large forward-set
eyes and grasping manus and pes.
The primates are
roughly divided into three major groups: Strepsirrhini, Haplorhini, and
Anthropoidea. The strepsirrhini (the curly nostrils, also referred
to as the Lemuriformes) include somewhat primitive adapiformes and lemurs. The
adapiformes were lemur-like animals and among the most abundant of the early
primates (lower Eocene to the upper Miocene).
They had a relatively long snout, small orbits, and dentition that indicated
are alive today and restricted to Madagascar, southeast Asia, and Africa
south of the Sahara. In general, they have an elongate fox-like face
and all members of the group have a
tooth comb made of forward pointing incisors and canines (feeding and grooming)
and a toilet claw on the second toe. Though most are nocturnal, some like
the Woolly Lemur (Figure 53) are diurnal and move about on the ground in social
groups. Lemurs and their relatives tend to be omnivores, but a few
like the Aye-Aye (Figure 54) have become specialists and have elongate fingers for
probing wood for insects.
The Haplorrhini (the simple noses, also
referred to as the dry noses) as defined by Wilson and Reeder (2005) has
two major groups: the Tarsiformes and the Simiiformes. The
tarsiforms include the tarsiers (Figure 55), which are insectivores with relatively large heads, small snouts, and large orbits.
They likely are related to the Omomytidae, which were small tree-dwelling
mammals and among the oldest primates (Eocene).
(the monkey forms) form two great monophyletic groups: Platyrrhini (flat
noses) and Catarrhini (the hook noses). The platyrrhines are New
World Monkeys which occur in the tropics and subtropics of North and South America. They usually live in troops and
are omnivorous. Generally arboreal, the platyrrhines have prehensile tails and nails.
Examples include Spider Monkeys and Howler Monkeys (Figure 56), both of which can move
through the forest canopy with great agility using their tails as fifth
hands. All of them except the Marmosets and Tamarinds, have have 36 teeth, 4 more teeth than other primates.
catarrhines are the Old World Monkeys and Apes, which in general have 32
teeth. Unlike many of the platyrrhines, none of the catyrrhines have
prehensile tails. This line seems to have appeared in the upper
Eocene. The early catarrhines like Aegyptopithecus appear to have
been close to the point of divergence between the Old World Monkeys and
the Apes. Animals that clearly were Old World Monkeys appeared by
the late Miocene. Today, they occur throughout warm
regions of the Eastern Hemisphere
except Australia and Madagascar. Although
at home in the trees, the Old World Monkeys do not have prehensile
tails. Examples include well-known groups like baboons (Figure 57)
and macaques (Figure 58).
The Old World Monkeys tend to be
somewhat omnivorous with a general diet of fruit, leaves, and small invertebrates. They
have cheek pouches that aid in the immediate collection and
transportation of bulky food items.
The old world monkeys seem to have diverged from the ape ancestors by adaptations toward
foliverous (leaf-eating) diet.
The apes appeared in the lower Miocene
and the earliest (Proconsul) walked on all four feet, which were
ape-like. The earliest apes also had small molars and very large
canines. They were somewhat similar to the tree-dwelling gibbons
today. Most of the living apes are in the Hominidae, the family in
which our species occurs. The basal hominids also appeared in the
Miocene and seemed to be equally at home in trees and on the ground.
The hominid apes include two living subfamilies: the Ponginae (orangutans)
and the Homininae [humans, chimps (Figure 59), and gorillas]. Chimpanzees
and gorillas are poorly represented in the fossil record; however, the human
(bipedal) line has
quite an elaborate record with at least 15 species. Read
more about Hominin Evolution.
Tree Shrews and
Living sister groups to the primates include the
tree shrews and colugos or flying lemurs. Both groups appeared by
the Eocene and persist as line of low diversity, mostly of southeastern
Asia. Tree shrews (Figure 60) occupy deciduous forests of
central and southeastern Asia. They are
small and very squirrel-like (but
with 5 toes). Unlike squirrels, they have
auditory bullas and complete zygomatic arches.
Flying Lemurs or Colugos
(Figure 61) are arboreal herbivores of southeastern Asia to the Philippines. They have an expandable flap of skin
that connects the shoulder to the forefeet, hindfeet, and tip of the tail.
With the expanded membrane, they can glide up to 100m.
Colugos are about the size of a squirrel and feed by scraping leaves with
their incisors from which they gather material with their long tongues.
The rodents and hares are very speciose and comprise more
than 40% of all living mammals. The basal rodents may have appeared in the
upper Cretaceous with small rat-like animals like Zalambdalestes
(Figure 62) and Kulbeckia. Archibald et al. (2001) affirm the
relationship of these taxa in a group called the glires. That view
is not universally accepted, though. Misawa and Janke (2003) reject
the monophyly of the glires and claim that the hares and rabbits (Lagomorpha)
are part of the clade that includes humans, dogs, and cows. With
that in mind, I present the views of Benton (2005) and Wilson and Reeder
(2005), who propose that the glires are formed by two great orders:
Rodentia (rodents) and Lagomorpha (hares and rabbits).
are characterized by having deep-rooted incisors
which grow continuously through their lives.
The incisors are followed by a gap (diastema), a premolar and the molars. The
typical rodent digit plan (4 on the forefeet and 5 on the hind feet) can
be variable with fewer digits on both feet. Typically,
rodents are small animals that are found on most continents. They
range in habitat from fossorial, arboreal, or semi-aquatic
environments. Traditionally, the rodents have been divided into two
large suborders (Sciurognathi and Hystricognathi) divided according to the
structure of the jaw, the insertions of jaw muscles, and the structure of
the zygomatic arch. Molecular phylogenetics, however, discovered a
somewhat hidden diversity, especially within the former Sciurognathi,
which Wilson and Reeder (2005) divide into three groups that they
interpret as suborders: Sciuromorpha (squirrel forms), Castorimorpha
(beaver forms), and Myomorpha (mouse forms). The former
Hystricognathi is almost unchanged with most of the families of the
hystricognaths now found in the Hystricomorpha
(porcupine forms). The major difference is the removal of two
families in the Anomaluromorpha (the
scaly-tailed forms) as a separate suborder. So, in all, Wilson and
Reeder (2005) recognize five rodent suborders.
include squirrels and dormice. Squirrels (Figure 63) occur on all continents except
Antarctica, Australia, and southern
South America. They range from arboreal
(e.g. Gray Squirrel) to fossorial (e.g. Chipmunk) animals,
they eat nuts and seeds, but supplement their diets with other things like fungi,
small birds, sap, etc. Dormice are mainly herbivorous, but
do eat small invertebrates and other mice; found from northern Africa
across to central Asia. They resemble chipmunks with short
limbs and broad feet tipped by curved claws (4 foredigits and 5 hinddigits).
include an unlikely mix of taxa including beaver, pocket gophers, and
kangaroo rats. Beavers are found throughout the northern temperate zone of the Northern Hemisphere. Semiaquatic
herbivores (they feed on bark and leaves and fell small trees) with a coat of
long outer fur and dense underfur. They
build lodges of sticks and mud and their activities modify depth and flow rates
of lakes and streams. Beavers have a strongly-built skull that is flattened in profile; jaws are
especially powerful. Their
epiglottis lies above the soft palate and can be sealed off with the tongue; so,
they can gnaw underwater without getting water in their lungs.
Pocket Gophers (Figure 64) are fossorial animals of North
and Central America. A distinguishing
character is fur-lined cheek pouches
(pockets). They are stout with short
neck and powerful digging legs with feet (5 digits) that are broad tipped with
strong claws. They have short,
almost hairless tails, small eyes and ears.
Rats and Pocket Mice are fossorial
herbivorous (mainly seed eaters) animals of deserts and dry grasslands of North
America and also of wet and dry tropical forests of northern South America.
These animals are adapted to leaping and hopping with very long hind legs
(Kangaroo Rats are almost bipedal). Like
Pocket Gophers, they
have large fur-lined cheek pouches.
The Myomorphs include about a fourth
of all living mammals. They include mice, rats, gerbils, hamsters,
lemmings, and voles. Most members of this group are small animals.
They have exploited almost all terrestrial habitats on earth and are found
on all continents except Antarctica. Myomorphs have two very unequal
groups: Dipodidae (two-feet) and Muroidea (mouse-like).
The dipoids include a single
family of small kangaroo-like jumping mice. These include most of
the jumping mice of the Northern Hemisphere. Jerboas (Figure 65) show features
of the family almost to an extreme. They can move about by
leaping, hopping or walking on their hind legs, a true bipedal stance.
muroids include most of the common rodents including rats (Figure 66), mice,
hamsters, voles, gerbils, lemmings, and muskrats. The
relationships between humans and members of this groups are mixed.
Rats and mice can be extremely destructive to agriculture and human
dwellings. They have been implicated as carriers of the vectors of
disease such as Bubonic Plague. Once confined to Eurasia, the
Brown Rat has been carried over land and sea as an invasive in many
areas. The Brown Rat also is used in scientific research and
can make nice pets. Other murids like the Deer Mouse are important
components of natural communities in North America. So, all in
all, the group gets mixed reviews.
Amomaluromorphs are the Scaly-Tailed
Squirrels and Springhares (Figure 67) of Africa. The two groups are very
different from each other. The Scaly-Tailed Squirrels are
arboreal herbivores of
the forests of central Africa. These animals resemble flying
squirrels, and almost all have gliding membranes.
The underside of the tail has two rows of scales, a character that gives
the suborder its name. Springhares (Springhaas) are rabbit or
kangaroo-like nocturnal herbivorous rodents of southern Africa. They hop and also move in a
quadrupedal gait. The pinnae of the
ears are sparsely-haired and they have large eyes.
The animals are good diggers and are somewhat fossorial.
have a dentary with
a distinctive broad flange for the insertion of jaw muscles.
Among the largest of the rodents occur in this group which includes Pacas,
Mole Rats, Guinea Pigs, Chinchillas, Pacaranas, Porcupines (both
New World and Old World families), Capybaras, and Nutrias. The following descriptions are not exhaustive of the group but serve to introduce the
diversity of the suborder.
Pacas (Figure 68) are animals of tropical forests in Central and South America. These animals are very large (up
to 12kg). They have stout bodies
with long legs and no tails. The
forefeet have 4 toes and three toes on the hindfeet, and the claws are almost hoof-like. Their
skulls are massive with large zygomatic arches (the jugal does not connect with
the lacrimal). They are terrestrial
animals and good diggers.
Mole Rats (Figure 69) are fossorial animals in Africa, south of the
Sahara Desert. Their legs are short and strong
with small ears and eyes. Their
incisors are massive, procumbent, and lack the yellow pigment characteristic
of rodents. The animals are highly
fossorial and herbivorous. They range
from solitary to colonial animals with social structures reminiscent of the
social bees. Some
are naked, but most have a thick fur.
Cavies (Figure 70) are diurnal animals which occur over most of
South America. They occur in two major groups the
cavies with compact bodies (like Guinea Pigs) and almost rabbit-like (Patagonian
Hares). They have rootless incisors,
and flat crowns. They are herbivores
with many areas of specialization (e.g. leaves, fruits, grasses). They
do not hibernate.
Chinchillas are herbivores of the
central and southern Andes, Patagonia, and Southern South America. Chinchillas have a fine fur with
compact bodies and pronounced tails. Their
hind legs are longer than the front legs, and their
paws have fleshy pads. The forefeet
have 4 toes that are highly mobile and can be used for grasping.
They jump bipedally but generally move about quadripedally.
All are colonial and have large behavioral repertoires.
(Figure 71) are animals of the New World
tropics. They have slender bodies,
relatively large heads, long legs, and short tails.
The hindlegs are longer than front legs and the feet are tipped with
sharp, hoof-like claws. Fur is long
and coarse with a distinctive sheen. Normally,
they are solitary. They are good
Pacaranas are animals of the foothills and slopes of the Andes
in northern South America. They have
broad, massive heads with very long vibrissae and short legs with a plantigrade stance.
The incisors are large and powerful allowing them to eat a
variety of stems, leaves, and fruits. Little
is known of the living animals because they are rare. Josephhoartigasia
(Figure 72) lived about 2-4 million years ago in the area of Uruguay and weighed
nearly 1000kg making it the largest known rodent that has ever lived (Rinderknecht
and Blanco 2008).
New World Porcupines (Figure 73) occur
from the Arctic coast of North America through Central America
to northern Argentina. All have hairs modified into
spines with barbs. They are solitary nocturnal animals with weak eyesight and good sense of smell.
have prehensile tails.
Capybaras (Figure 74) are large rodents found in the tropics of
South America. They have stout bodies with short
and deep heads. Their ears and eyes
are small, and their nostrils sit high on the rostrum, apparently adaptations to
a semi-aquatic lifestyle.
Their legs are not particularly long, but the forelegs are shorter than
the hind legs; also, they have 4 digits on their front legs and 3 on their hind
legs. Capybaras feed on aquatic plants.
Porcupines are terrestrial
animals of Africa
and Asia and are distinguished from the New World Porcupines by having quills without barbs.
Their bodies are stout and their legs are short terminating in feet with
plantigrade stance (5 digits each foot). They
are good diggers and construct burrows.
Generally omnivorous, they
eat many kinds of plants and carrion.
Nutrias (Figure 75) are semi-aquatic animals of Central and
South America, but they have become distributed over much of the world, where they are
destructive exotic invasive animals. They are robust
for rodents and have numerous adaptations to an aquatic life: webbed hind feet
(5 digits and 4 on the forefeet), small ears, small eyes, the tail is long,
almost naked and round. Their pelts have a
thick underfur. Nutrias are herbivores and feed on land and in the water.
Also, they are good diggers,
making burrows in the banks of streams or lakes.
They are social and usually live in groups of 10-15.
Lagomorphs (rabbits, hares, and pikas)
Rabbits, hares, and
Like rodents, the lagomorphs have incisors that are deep rooted and grow
continuously. However, they have a
second small pair of incisors in the upper jaw. They appeared in the
Rabbits (Figure 76) and hares are globally distributed animals of grasslands, forests, and tundra.
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The hindlimbs are long and longer than the forelimbs.
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are distinctive and arched with a broad zygomatic arch.
They may be solitary or live in small groups.
Females are larger than males. Many
species flourish in the presence of humankind and can become agricultural pests.
(Figure 77) are animals of open plains and steppes of western North America
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