A cell may have either haploid (n) or diploid (2n) number of chromosomes. The chromosomes number is determined based on the process of cell division undergone by the cell ( that is either mitotic or meiotic division).
A chromosome is assigned a number based on its apparent size, with chromosome 1 being the longest. Longer chromosomes would be expected to have more genes on them than shorter chromosomes. Genes that are on different chromosomes will be inherited independently, while genes that are closely positioned to each other on the same chromosome will be inherited together due to a concept called linkage.
The number of distinct chromosomes in a cell determines what is called ‘chromosome number’ (note that this is singular). Humans have a chromosome number of n=23, but most of our cells (since we are diploid) will have 46 chromosomes (2 of each). Each species have a characteristic chromosome number ranging from n=1 up to n>1000. Since the chromosome number indicates how all the genes are split up into different groups, the organisms with higher chromosome numbers will have (in theory) more independent sorting of their genes within their sex cells (gametes), potentially allowing for a greater chance of their offspring having more variety.
A trilobite. Trilobites became extinct about 250 million years ago while a ammonite became extinct around the same time as dinosaurs(65 million years ago). You wouldn't find a human skull or a dinosaur footprint
