The University Museum of Zoology in Cambridge has very recently closed for major refurbishment and the Map of Life team look forward to seeing the results in 2016. You can follow the redevelopment at the Inside the Cocoon Blog and plenty of online resources and events will continue to thrive while the Museum is in its ‘cocoon’… One special online resource is the Animal Bytes website, where many have left their stories of the Museum and its wonderful specimens.
At this time of change for the Museum, the Map of Life recalls some of the amazing examples of convergent evolution showcased by the specimens on display there. Many of these are explained in more detail on the Map of Life website for you to explore further! Here are just a few cases:
Lobe-finned fish like coelocanths (c. Osteolepis = stem fossil) evolved into four-legged, land-living vertebrates in the Devonian ~400 Ma. On land these early tetrapods found food plentiful food and safety from marine predation, and yet over time many tetrapod lineages independently reduced or lost their legs once again, as they returned to swimming or adopted a burrowing mode of life. Such limbless creatures include early tetrapods (e.g. Aïstopods, Crassigyrinus), amphibians (e.g. caecilians, a few salamanders), reptiles (e.g. amphisbaenians, snakes, pygopodids/’snake lizards’, anguids/’slow worms’, various skinks, ichthyosaurs and mosasaurs) and mammals (whales, dolphins and narwhals, sea cows/manatees and dugongs).
Ant eating mammals
Certain mammals from the Americas, Africa and Australia have all become specialized for eating ants, even though they are not related to each other. They all share adaptations such as a long nose, tubular tongue, body armour to protect and often a very strong front claw for destroying ants’ nests. Examples from among the Museum include specimens from all corners of the globe:
From the Americas: anteaters (Edentata) and slightly less specialised armadillos; from Asia and Africa: pangolins (Philodota); from Africa the aarvaark (Tubulidentata); from Australia the echidna or “spiny anteater” and long-nosed echidna.
The Map of Life details another remarkable convergence among ant eaters, this time involving two charismatic reptiles. The ‘thorny devil’ (Moloch horridus) of Australia is ecologically equivalent to the distantly related ‘desert horned lizard’ (Phrynosoma cornutum) of North American arid regions. Moloch is an ‘agamid’ lizard, but Phrynosoma is an ‘iguanid’, so they represent two distinct groups that have been diverging independently in Australia and North America for approximately 150 million years. Read more about Moloch and Phrynosoma here.
A number of placental and marsupial mammals independently evolved adaptations for gliding, primarily using a gliding membrane or ‘patagium’ between front and hind limbs. Placental gliders include colugos (Dermoptera, Galeopterus), scaly-tailed ‘flying squirrels’ (Anomalurus) of central Africa and flying squirrels (Petaurista) of Eurasia and North America. Marsupial gliders are the Greater Glider (Schinobates, Petauroides), feather-tailed possums (Acrobatidae) and gliding possums or phalangers of the genus Petaurus, best known as the Biak or Sugar Glider.
A wealth of extinct and living gliding reptile species have been discovered, with adaptations allowing them to gain the same advantages as gliding mammals, such as freedom to escape predators and access more resources. Some reptiles glide on membranes between their fingers (e.g. gecko Ptychozoon and lacertid Holaspis) others have projections from the body that form a wing-like membrane (Draco volans the ‘flying dragon’ and numerous extinct forms e.g. Kuehneosaurus, Xianglong and Icarosuarus), and others evolved two or four feathered wings (e.g. Aurornis and Microraptor respectively) and coexisted with or were themselves likely precursors to species capable of powered flight.