Earth Times Logo
RSS Feed Google+ Facebook Twitter Linked In Pinterest



Evolution of placental lizards gave us advanced skinks,

By Dave Armstrong - 23 Aug 2016 23:0:1 GMT
Evolution of placental lizards gave us advanced skinks,

Eumecia anchietae is a skink from Kenya which has evolved leglessness, in parallel with the snakes The key adaptation here is its extreme matrotrophic placentation, with tiny, yolkless eggs and the parallel there would be with early mammals.Skink image; Credit: © royalsocietypublishing

Lizards are lowly reptiles and look similar to small versions of the most ancient dinosaurs? Wrong! While 20% of lizards and snakes have adopted live bearing around 100X over for reproduction, some have even turned to the placental solution we find in most mammals.

This condition even has its own name, especially suited to this evolutionary success story. Matrotrophy means the most extreme adaptation of the mother for a complete placental nutrient supply. Eggs were the vertebrate solution to life on land, containing yolk as a nutrient supply. Then blood-transfer as seen in eutherian mammals is unlikely in reptiles, with the suggestion that histotrophic-transfer takes place from epithelial cells in the uterus to cells in the placenta. 3 groups of skinks (mabuyid lizards), 66 species in total, supply their embryos completely from maternal sources.

The researchers from Villanova University in the US and the Natural History Museums of Port Elizabeth in South Africa, Geneva in Switzerland and Zoologische Staatssammlung Munchen, in Germany were led by Margarita Metallinou of the former institution. They present their paper in the Biology Letters of the Royal Society with the explanatory title A single origin of extreme matrotrophyin African mabuyine skinks.

They extracted DNA from sample tissues collected during expeditions to Zambia and Angola and used molecular clock settings to work out tree models for the phylogenetic relationships. Asian skinks separate from 2 other genera and a large Afro-Neotropical group as sister groups. All the extreme matrotrophic groups have tiny eggs and could have evolved this habit just once, or possibly up to 3 times. The evidence points to a single or double evolutionary moment, in Africa and maybe once again in the Neotropics.

This leaves us with a remarkable similarity between the successful early mammals and their various methods of placentation and this advanced placentation of small lizards. We have to remember that similar reptiles gave rise to our hairy ancestors as well as these squamates. Perhaps we should consider them as much closer to us than we have previously, at least in habits and parental investment in their offspring. To confirm that, here is one of the most remarkable skinks, because it is a social reptile, native to the Solomons.