Rise of Animals 8 Flashcards
What is the Edenta?
This a group which traditionally contained anteaters, pangolins and armadillos signifying their loss or reduction of teeth
What are the similarities between pangolins, armadillos and anteaters?
These are all animals which feed on ants and termites, have long tongues, strong digging limbs and reduced or missing teeth
There are four species of pangolin in Africa and three in southeast asia while armadillos and anteaters live in the Americas
What has recent molecular evidence revealed about the relationship between pangolins, armadillos and anteaters?
It suggests that the similarities between pangolins and the other anteating mammals are a result of convergent evolution rather than shared ancestry causing pangolins to now be placed in their own separate group which forms a sister group to the carnivores while armadillos and anteaters are now placed with the sloths in a separate order known as the Xenarthra
What is the mammal group Insectivora?
This is a group which traditionally contained small, shrew-like insect eating animals such as shrews, tenrecs, moles, hedgehogs and African golden moles
This was originally placed at the base of the placental mammal tree since the earliest known placental mammals were shrew like and it was thought the ancestor or placentals was an insectivore
What has new recent molecular analysis revealed about insectivorous mammals?
That the similarities between extant insect eating mammals and the earliest fossil mammals are due to convergence
The insectivore group is polyphyletic, the new phylogenies show that two groups of African insect-eating animals, golden moles and tenrecs are not related to the main group of insectivores (despite high levels of morphological similarity) so they are now placed with other African animals in a clade called afrotheria
Shrews and mole-like animals evolved independently in Africa and in the Americas
What is included in afrotheria?
This clade now includes golden moles, tenrecs, elephant shrews, aardvarks, hyraxes, dugongs and elephants
What are the 4 main groups the new phylogeny splits eutherian mammals into?
Afrotheria, Laurasiatheria, Xenarthra and a fourth group which includes rodents, rabbits, tree shrews and primates
Since insectivore like animlas are present in all four of these great clades it is thought that insectivore like forms were the ancestors from which the other groups originated
Which of the 4 new groups of eutherian mammals show strong geographical affinities?
Afrotheria in Africa, Laurasiatheria in Europe and Asia and Xenarthra in the Americas with parallel adaptive radiations occurring in Afrotheria and Laurasiatheria for example horse like animals evolved in Asia as horses and Africa as hyraxes or anteating animals evolving as pangolins in laurasiatheria and aardvarks in afrotheria, true moles evolving in Laurasiatheria and golden moles in afrotheria
What have molecular studies revealed about the evolution of whales?
That hippos and whales are sister groups, as hippos are members of the artiodactyl group this relationship makes the group paraphyletic unless artiodactyls are united with whales in a clade known as cetartiodactyla
What are the specialized aquatic characteristics shared by whales and hippos?
A lack of hair, lack of sweat glands and the use of underwater vocalisations
What are the most important fossil relatives of whales?
Mesonychids, a group which lived from 60 to 30 MYA which is also related to the artiodactyls, however unlike moder artiodactyls whuc hare all plant eaters, mesonychids ate fish or meat and had teeth similar to those of basal whales
What resulted from phylogenetic analysis based on morphological characteristics of whales, artiodactyls and mesonychids?
These consistently resulted in trees which showed the whale as an early divergence from a sister group of mesonychids and also showed the clade of whales plus mesonychids as the sister of artiodactyls seen as a morphological group
This conflicts with the molecular phylogeny
What are the contradictions between the molecular phylogeny and the one derived by morphological analysis?
If the morphological tree is correct then the characters shared by hippos and whales must have evolved independently while if the molecular tree is correct then the characters shared by whales and mesonychods must have evolved independently
What issues doe the conflict between the molecular and morphological analysis of whale ancestry raise?
Removing fossils from an analysis combining fossil and living taxa does not simply result in the tree generated by living taxa only because fossils can supply character combinations that are missing among living clades allowing fossils to change the pattern of relationships amongst living taxa
How was the conflict between the molecular and morphological analysis of whales partially resolved?
In 2001 there was a discovery that the earliest whales, which were still terrestrial had a specialized type of double pulley ankle which is not found in mesonychids but is a characteristic of artiodactyls
This meant for the first time morphological fossil evidence shows that artiodactyls are the closest relatives of the cetaceans putting whales and artiodactlys in a group which excludes the mesonychids with some of the resemblences between these groups due to convergent evolution
