I think the concept could be worked up more: make them look more like dino-cozies maybe with a pom-pom on top? I would say that it could be a joke about them being cold-blooded except that they weren't... exactly. But most people aren't going to know that.
However, the linework needs to be heavier and more confident, the design a bit larger and the colours punchier, especially the colour of the tee. That grey is just bleh.
Ok, so heavier lines? brighter colours? its not meant to be a joke in any way about them being dinosaurs cold blooded its just some nice dinosaurs in knit wear! Maybe it does need something else for threadless. I just wish some of the tshirt designs that are artists own styles got made. It always seems that to get high votes they need to conform to the same style...hmm...remember moops? (was that what it was called? the tee with little rabbit like creatures and a skull) i love that tshirt we need more of that kind of thing!!
I'd like to see more artistic tees too, and I like your drawing style, but the image simply needs more impact. It is lost on the tee. Heavier lines and more colour would help a lot. Presentation also has a great effect on a score. Use a small version of the tee template to show the placement of your design, but present the design itself on a colour field as large as you can so that people can see the detail.
Look at some of the printed designs to get ideas for presentation.