I looked at this skeletal of Majungasaurus http://www.skeletaldrawing.com/theropods/majungasaurus and I noticed it has very strange features even for an abelisaur. Why did it have such thin nueral spines on its caudal vertebrae? Why did it have a fused coracoid and scapula? Its body is very streamlined, does this indicate a semi aquatic lifestyle? Why did it have short legs?

Sorry if I am asking too many questions, I am an enthusiast that wants to learn more!

I don't know about the caudal neural spines. In general, it seems that different species often have differences in their bones that are without any obvious reason based on lifestyle. These can be the result of genetic drift -- i.e. they are selectively neutral. Or they could be affected by the same genes that are being positively selected for other reasons: most genes do more than one thing.

Fusion of the scapular and coracoid is common in fully mature dinosaurs, but many individuals that we think of as mature (e.g. the huge brachiosaur in the atrium of the Museum Für Naturkunde Berlin) are actually not skeletally mature. So we're used to see unfused scapulocoracoids. My best guess is just  that the Majungasaurus skeleton that reconstruction is based on happened to be fully mature.

I wouldn't rule out a semi-aquatic lifestyle, but you'd need more to go on that just a vague, general sense of body shape.