The tropical grasslands, when they developed and spread halfway through the Tertiary, were a totally novel environment for the great reptiles. Grass is a remarkably tough substance, and a grass-eating animal needs a number of extreme specializations to allow it to survive. Grass is full of hard silica and so it causes a great deal of wear to teeth. A grass-eating animal needs teeth that are constantly growing or frequently replaced. Complex digestive systems are needed to break down and extract nutrients from the substance of grass. On top of all that, a big grassland-living animal needs to have long legs to allow it to run away from danger. In some places, such as the prairies of the Nearctic realm, dinosaurs developed quite happily into grass-eating forms. However, on the savannas of the Ethiopian realm, dinosaurs were not able to establish a foothold. They were beaten to it by their cousins – the pterosaurs. A group of pterosaurs abandoned their powers of flight as soon as the tropical grasslands spread, and they became the main grass-eating animals of the Ethiopian realm. The lank is now the most highly specialized of these, and the one that has become most unlike its flying ancestor. The body has remained short but the forelimbs and hind limbs have become long and equal in length. The neck and face are also long – all plains-living features.
The long face of the lank means that its eyes are still above the level of the grass even when its snout is grazing at the grass roots. It can thus keep an eye open for danger. On the open plains danger can be seen coming from afar, and the lank’s long legs give it the speed needed to escape from predators. The lank runs with a pacing motion – both legs at the same side moving in the same direction at the same time. This prevents the long legs from becoming entangled.
It is difficult to believe that the lank’s front legs are evolved from pterosaurs’ wings. The fourth finger, that once supported the flight membrane, now carries the animal’s weight and has a hoof on the end. The three small claws that once acted as a hand are now only used for grooming the animals fine fur.