Lizard-lions

Lizard-Lions are a large carnivorous reptile that lives in the bogs and swamps of the Neck in Westeros. They are so-named because they grow to the size of Lions. Lizard-Lions are semi-aquatic and attack the unwary who wander through the Neck.

House Reed, the ruling House of the Crannogmen of the Neck, use a black Lizard-Lion as their Heraldry.

In the books
In the A Song of Ice and Fire novels, Lizard-Lions are the only species of crocodilian known to inhabit the entire continent of Westeros - it is unknown if similar species exist in the other continents. Like their real-life analogues, they are ambush predators that hunt by lying entirely still in the water, resembling floating logs.

Exactly what kind of crocodilian Lizard-Lions are supposed to represent is unknown: names such as "crocodile", "alligator", or "caiman" do not exist in their fictional world. Author George R.R. Martin has stated that not every species of animal in Westeros has a direct one-for-one equivalent to a real-life species of animal. For example, Martin said that Shadowcats have no direct real-life analogue: they are larger than cougars (mountain lions) but smaller than tigers, and don't look quite like either. Thus, it is uncertain if Lizard-Lions are real-life crocodiles or alligators known by a different name, or a unique fictional variant. It is also unknown if they are roughly the same size as normal crocodilians, or even larger.

In the first book, as the Stark-Baratheon caravan passes south over the Neck (corresponding to the episode "The Kingsguard"), Arya Stark says that she hopes to see a Lizard-Lion. In the second book, when Meera and Jojen Reed join Bran Stark, Bran is curious about Lizard-Lions and asks them what they are like (as they don't live in the cold regions north of the swamps).