and
ichthyosaurs converged on many adaptations for fast swimming.
Bodyplans Swimming animals including
fish such as
herrings,
marine mammals such as
dolphins, and
ichthyosaurs (
of the Mesozoic) all converged on the same streamlined shape. A similar shape and swimming adaptations are even present in molluscs, such as
Phylliroe. The fusiform bodyshape (a tube tapered at both ends) adopted by many aquatic animals is an adaptation to enable them to
travel at high speed in a high
drag environment. Similar body shapes are found in the
earless seals and the
eared seals: they still have four legs, but these are strongly modified for swimming. The marsupial fauna of Australia and the placental mammals of the Old World have several strikingly similar forms, developed in two clades, isolated from each other. The body, and especially the skull shape, of the
thylacine (Tasmanian tiger or Tasmanian wolf) converged with those of
Canidae such as the red fox,
Vulpes vulpes. File:Vulpes vulpes skeleton.JPG|
Red fox skeleton File:Beutelwolf fg01.jpg|Skulls of
thylacine (left),
timber wolf (right) File:Beutelwolfskelett brehm (cropped).png|
Thylacine skeleton
Echolocation As a sensory adaptation,
echolocation has evolved separately in
cetaceans (dolphins and whales) and bats, but from the same genetic mutations.
Electric fishes The
Gymnotiformes of South America and the
Mormyridae of Africa independently evolved
passive electroreception (around 119 and 110 million years ago, respectively). Around 20 million years after acquiring that ability, both groups evolved active
electrogenesis, producing weak electric fields to help them detect prey. File:Gymnotus waveform.svg|A gymnotiform electrolocation waveform File:Sternarchorhynchus oxyrhynchus.jpg|A
gymnotiform electric fish of South America File:Gnathonemus_petersii.jpg|A
mormyrid electric fish of Africa File:Elephantfish spike waveform.svg|A mormyrid electrolocation waveform
Eyes s (left) and
cephalopods (right) developed independently and are wired differently; for instance,
optic nerve (3) fibres (2) reach the vertebrate
retina (1) from the front, creating a
blind spot (4). One of the best-known examples of convergent evolution is the
camera eye of
cephalopods (such as squid and octopus),
vertebrates (including mammals) and
cnidarians (such as jellyfish). Their last common ancestor had at most a simple photoreceptive spot, but a range of processes led to the
progressive refinement of camera eyes—with one sharp difference: the cephalopod eye is "wired" in the opposite direction, with blood and nerve vessels entering from the back of the retina, rather than the front as in vertebrates. As a result, vertebrates have a
blind spot.
Flight (from forelimbs), but analogous as organs of flight in (1)
pterosaurs, (2)
bats, (3)
birds, evolved separately.
Birds and
bats have
homologous limbs because they are both ultimately derived from terrestrial
tetrapods, but their flight mechanisms are only analogous, so their wings are examples of functional convergence. The two groups have independently evolved their own means of powered flight. Their wings differ substantially in construction. The bat wing is a membrane stretched across four extremely elongated fingers and the legs. The airfoil of the bird wing is made of
feathers, strongly attached to the forearm (the ulna) and the highly fused bones of the wrist and hand (the
carpometacarpus), with only tiny remnants of two fingers remaining, each anchoring a single feather. So, while the wings of bats and birds are functionally convergent, they are not anatomically convergent. Birds and bats also share a high concentration of
cerebrosides in the skin of their wings. This improves skin flexibility, a trait useful for flying animals; other mammals have a far lower concentration. The extinct
pterosaurs independently evolved wings from their fore- and hindlimbs, while
insects have
wings that evolved separately from different organs.
Flying squirrels and
sugar gliders are much alike in their mammalian body plans, with gliding wings stretched between their limbs, but flying squirrels are placentals while sugar gliders are marsupials, widely separated within the mammal lineage from the placentals.
Hummingbird hawk-moths and
hummingbirds have evolved similar flight and feeding patterns.
Insect mouthparts Insect mouthparts show many examples of convergent evolution. The mouthparts of different insect groups consist of a set of
homologous organs, specialised for the dietary intake of that insect group. Convergent evolution of many groups of insects led from original biting-chewing mouthparts to different, more specialised, derived function types. These include, for example, the
proboscis of flower-visiting insects such as
bees and
flower beetles, or the biting-sucking mouthparts of blood-sucking insects such as
fleas and
mosquitos.
Intelligence Advanced intelligence has evolved independently in cephalopods and vertebrates. Octopus have demonstrated mammalian levels of
problem-solving, cognition, and learning behaviors. One
aquarium director even claimed his octopus specimen to have developed a sense of
personal taste as to the arrangement of its tank. Unlike other highly intelligent animals, cephalopods typically live short lives with varying levels of sociality, with the bulk of the nervous system divided between the head and limbs.
Opposable thumbs Opposable thumbs allowing the grasping of objects are most often associated with
primates, like humans and other apes, monkeys, and lemurs. Opposable thumbs also evolved in
giant pandas, but these are completely different in structure, having six fingers including the thumb, which develops from a wrist bone entirely separately from other fingers.
Primate phenotypes Convergent evolution in humans includes blue eye colour and light skin colour.
Lemurs and
humans are both primates. Ancestral primates had brown eyes, as most primates do today. The genetic basis of blue eyes in humans has been studied in detail and much is known about it. It is not the case that one
gene locus is responsible, say with brown dominant to blue
eye colour. However, a single locus is responsible for about 80% of the variation. In lemurs, the differences between blue and brown eyes are not completely known, but the same gene locus is not involved. == In plants ==