According to the current Evolutionary narrative, life began when a microscopic organism magically created itself. What that means is that life started small, then gradually got bigger. That makes many prehistoric animals and their modern counterparts very difficult to explain.
One example is crocodilians. These reptiles, while they can get pretty big today, are nothing compared to their prehistoric cousins. The largest species today is the saltwater crocodile, averaging at just over 4 - 5 meters long. That's only half as much as the purrusaurus, which is estimated to have averaged around 10 meters long. Ancient crocodilians were often so big that they may have actively hunted large dinosaurs, including the famous tyrannosaurus rex.
Surely this is backwards. If life started tiny and gradually grew, we would expect the smaller crocodilians to come first, and the larger ones to be our contemporaries. A far more logical explanation can be found in the Bible. God created all animals according to their kinds, in the space of 6 days, after which the rapid climate change that occurred over the proceeding centuries eventually killed off the last giant crocodilian.