An Early Warning

A reconstruction of Panderavis shows it's rake like claws, with which it dug furrows in the soil to find its food. Opportunistic local animals walk alongside Panderavis, looking for morsels left over from its feasting.

During those times, a small discovery of immense implications warned humanity that it might not be alone.
On a newly colonized world, engineers had stumbled across the remains of a puzzling creature, considered so because it had every hallmark of terrestrial animals on an alien planet. Justifiably named Panderavis pandora, the colossal fossil belonged to a bird-like creature with enormous claws. Later research determined it to be a highly derived therizinosaur, from a lineage of herbivorous dinosaurs that died out millions of years ago on Earth.
While every other large land animal on that colony world had three limbs, a copper based skeletal system and hydrostatically operated muscles; Panderavis was a typical terrestrial vertebrate with calcium-rich bones and four extremities. Finding it there was as unlikely as finding an alien creature in Earth’s own strata.
For some, it was irrefutable proof of divine creation. The religious resurgence, fueled at first by mankind’s apparent loneliness in the heavens, got even more intensified.
Others saw it differently. Panderavis had shown humans that entities; powerful enough to visit Earth, take animals from there and adapt them to an alien world, were at large in the galaxy. Considering the time gulf of the fossil itself, the mysterious beings were millennia older than humanity when they were capable of such things.
The warning was clear. There was no telling what would happen if mankind suddenly ran into this civilization. A benevolent contact was obviously preferred and even expected, but it paid to be prepared.
Silently, humanity once again began to build and stockpile weapons, this time of the interplanetary potency. There were terrible devices, capable of nova-ing stars and wrecking entire solar systems. Sadly, even these preparations would prove to be ineffectual in time.