Is this organism a fish? Fish do exhibit vertical tail alignment, and this organism does have a vertical tail. Yet, this organism lacks gills. Look closely and nose slats are apparent on the beak. The absence of gills in an organism that appears to be highly adapted to aquatic living and the presence of nose slats militate heavily against this being a fish. What other features can we examine? Though this picture does not illustrate these features, we know that this organism had a three-chambered heart, gave birth to live young after a gestational period in an internal egg sack, and may have even had endothermic, temperature regulatory characteristics.
What kind of organism is this? This is a reptile and it belongs to the reptilian suborder ichthyopterygia. Several dozen species of this suborder have been classified form the fossil record including the above pictured ichthyosaurus, one of the earliest classified representatives. Much like the later whales, the common ancestor(s) of this suborder descended from land ancestors who returned to the water. In this case, evolutionary pressures caused reptilian exaptations to be restructured into highly fish-like structures and morphologies. Yet, the distinctly though possibly disadvantageous reptilian features such as air breathing remain.
The ichthyosaurus, as a representative for its suborder, presents numerous challenges to creationism. First, if God created everything ex nihilio, then why make creatures that boast traits demanding an explanation beyond, "God did it." These traits include the obvious terrestrial ancestry. A God who creates false histories is a liar. Second, if the ichthyopterygia present in the fossil record were buried in the Flood, which is the uniform young-earth creationist explanation for the rock layers in which they are found, why are they not found with whales and dolphins which share not only incredible degrees of morphological similarity but also share profoundly overlapping ecological niches. The same depositional pressures which would have favored the deposition of ichthyopterygia in Jurassic layers would have likewise captured cetaceans such as whales and dolphins.
Really, I have only tiped the iceberg with the above questions. The ichthyopterygia are loaded with characteristics that demand an evolutionary ancestry and that defy creationism. Yet, my point in bringing them up is that they represent one of the ways in which creationism failed me as an explanatory model for the observational data from biology. And, I am speaking about more than just the ichthyopterygia—I am referring to each and every species and subspecies that I have ever encountered both in print and with my own hands. There are too many devilish details that defy creationist explanation so many that, "…if they should be written every one, I suppose that even the world itself could not contain the books that should be written" (John 21:25).