The Shankland Name
The definitive work on Scottish names is The Surnames of Scotland: Their origin, meaning and history by George F. Black. This book provides where possible the derivation of the name, where in Scotland it is found, and lists the earliest references to people of that name. The relevant entries for the names we are interested in are reproduced below (by kind permission of the publishers, Birlinn Ltd. of Edinburgh).
SHANKILAW. Local. Alexander Shankilaw, burgess of Lanark, 1671, and other two of the name.
SHANKLAND, SHANKLIN. Local. Grissell Shankiland in Cowhill, 1682 (Dumfries) and William Shankiland in Galtuay, Kirkcudbright, 1689. Shankland is said to be an Ayrshire place name, but I cannot find it in the Retours. Shanklin is said to be a common name in Stirlingshire.
Compared to other entries in the book, this is rather inconclusive! However, there is no lack of theories as to the origins of the name, such as Simon Grundy's investigation, "Here's Tae Us! Wha's like us!".