The study of the biogenic remains from the excavations of the medieval town of Rusokastro, discovered in 2021, is once again the work of archaeozoologist Dr. Georgi Ribarov. He identified bones from domestic animals such as horse, donkey, cattle, buffalo, sheep, goat, cat and duck. Among the wild animals there are bones of wild boar, red deer, fallow deer, roe deer, fox, wild cat, wild rabbit, hedgehog and others. New species discovered in 2021 and undiscovered in previous seasons are the squirrel, the night heron, the little heron and the crow. Shells of black mussels, oysters and snails, which were consumed after cooking, were also found. In 2021, quite a lot of round and bison bones have been discovered - no longer single specimens, but dozens of bones from these long-extinct animals. Among the most interesting finds are bones from birds of prey, which were used after domestication in hunting small wild animals and birds. Curious and important are the discovered bones of dogs - greyhounds, which have definitely been selected. These are tall, long-legged animals that have been bred to chase game. One of the dogs was the size of a wolf.