19Ultraconserved genomic elements (UCEs), are generally treated as independent 20 loci in phylogenetic analyses. The identification pipeline for UCE probes is agnostic to 21 genetic identity, only selecting loci that are highly conserved, single copy, without 22 repeats, and of a particular length. Here we characterized UCEs from 12 phylogenomic 23 studies across the animal tree of life, from birds to marine invertebrates. We found that 24 within vertebrate lineages, UCEs are mostly intronic and intergenic, while in 25 invertebrates, the majority are in exons. We then curated 4 different sets of UCE 26 markers by genomic category from 5 different studies including; birds, mammals, fish, 27Hymenoptera (ants, wasps and bees) and Coleoptera (beetles). Of genes captured by 28UCEs, we find that many are represented by 2 or more UCEs, corresponding to non-29 overlapping segments of a single gene. We considered these UCEs to be non-30 independent, merged all UCEs that belonged to a particular gene, constructed gene and 31 species trees, and then evaluated the subsequent effect of merging co-genic UCEs on 32 gene and species tree reconstruction. Average bootstrap support for merged UCE gene 33 trees were significantly improved across all datasets. Increased loci length appears to 34 drive this increase in bootstrap support. Additionally, we found that gene trees 35 generated from merged UCEs were more accurate than those generated by unmerged 36 and randomly merged UCEs, based on our simulation study. This modest degree of 37 UCE characterization and curation impacts downstream analyses and demonstrates the 38 advantages of incorporating basic genomic characterizations into phylogenomic 39 analyses. 40 41 3