Nicrosaurus (/nɪkroʊˈsɔrəs/) is an extinct genus of phytosaur reptile that lived during the Late Triassic period. Although it looked like a crocodile (and probably lived like the more terrestrial crocodylomorphs), it was not closely related to them, instead being an example of parallel evolution.

The main difference between Nicrosaurus (and all other phytosaurs) and modern crocodiles is the position of the nostrils. Nicrosaurus's nostrils, or external nares, were placed directly in front of the forehead (much like modern-day cetaceans, such as whales, dolphins, and porpoises), whereas in crocodiles, the nostrils are positioned on the end of the snout. A 2013 study has also found that the ilium of Nicrosaurus is quite distinctive from all other phytosaurs. The genus was named by German paleontologist, Dr. Eberhard Fraas, in 1866, possibly after the Neckar river of southwestern Germany, near which it was found.

Some distinguishing anatomical features of Nicrosaurus are the external nares at the skull roof level, the dorsoventrally compressed and rounded posterior squamosal processes, the broad and heavy rostrum and a strong prenarial crest.

Nicrosaurus may have been more terrestrial than other phytosaurs. Occurring in marginal-lacustrine or outrightly terrestrial settings, it bears longer limb bones, a straighter femur and a deeper pelvis than other phytosaurs. Combined with its unusually deep upper jaw and heterodont teeth, it was most likely a secondarily terrestrial predator, probably not at all dissimilar from terrestrial crocodylomorphs like sebecians.

Nicrosaurus dentition is highly heterodont, the tooth shapes varying from wide, laterally compressed blade teeth to cylindrical, recurved caniniform teeth.

In terms of jaw morphology, a full prenarial crest is a distinctive anatomical feature for Nicrosaurus kapffi. In both the upper and lower jaw, the dentition has five morphologically separated arrays of teeth: tip-of-snout set, premaxilla set, maxilla set, tip-of-mandible set, and dentary set. Moving posteriorly in all of these sets, except the tip-of-the-snout and tip-of-mandible sets, tooth morphology starts out relatively simple and undifferentiated and gradually changes, resulting in a morphocline. The upper dentition is considered to be tripartite.

The anteriormost teeth, or carinae, of the premaxilla set in Nicrosaurus kapffi are enlarged and strongly curved. These are usually the largest teeth of the upper jaw. Much of the other anterior teeth in this set, as well as in the maxilla, are difficult to distinguish from one another.

The anteriormost teeth of the premaxilla are firmly anchored and labially vaulted.