Lizard-lions

Lizard-lions are large carnivorous reptiles that live in the bogs and swamps of the Neck in Westeros. House Reed, the ruling house of the Crannogmen, employ as their sigil a black lizard-lion on a grey-green field.

Range
Lizard-lions are only found in the swamps of the Neck, the narrow isthmus that connects the North to the rest of Westeros.

Biology
Lizard-lions are semi-aquatic reptiles, so-named because they grow to the size of Lions. They are carnivorous, and have teeth like daggers.

Lizard-lions have also been known to attack unwary men who wander through the Neck.

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.

Another species of large reptile exists in the jungles of Yi Ti in eastern Essos, known as "basilisks", apparently roughly dog-sized and venomous. Many have been imported to Qarth or Slaver's Bay where they are set against dogs in fighting pits for entertainment. They may be only distantly related to lizard-lions.

In the first book, as the Stark-Baratheon caravan passes south over the Neck, corresponding to the episode "The Kingsroad", 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.