thunder lizard out
arcanodon next (if only I could find the previous sketches this time...)

I hope it is clear enough, details for stuff this big in a drawing the size of a hand can get messy
anyway, it's the classic body of a sauropod with the nastier turtle-like mouth I could make and flat bony plates running all over the main body like in the stegadon and the bastiladon, offering protection and a solid base for pointier bony protrusions, in particular near the head, shoulders, hips and at some point not too far from the end of the tail
the howdah is made to resemble a pyramid, it is in fact divided into 2 parts, 3 if we take into consideration that the lower is split to accommodate the spines of the creature (at some point the spines get cut and worked on by the skinks to offer a more stable base)
at the top of the pyramid is the starcaller, inspired by the original version of the engine of the gods in lustria, it is composed by multiple rotating rings (even the small cone under it is supposed to be a spinning platform for the complex rites of the skink priest), but as always happens with lizardmen stuff and old ones tech, designs vary
ideally it would work like a long range artillery: Casting down meteors, comets or lasors from the stars
manned by 8-10 skinks, this would represent the smaller thunder lizards, the ones easier to control and train
like the engine of the god it's a powerful artifact capable of interacting with the geomantic grid to draw power but the starcaller in particular is thought to be able to contact the old ones and in times of celestial alignments the slann order to move it to a particular location and perform a ritual
sometimes they do so personally, riding the beast themselves
obviously the starcaller is put on top of the thunder lizards because they are sacred, the land creatures with the closest link, and nearer heads to the stars
but superstition and religion often complement a more realistic reason: The thunder lizards are among the few beasts capable of bearing the weight of the artifact