Chitons

Loricata is a group of reptiles that includes crocodilians and their ancestors. It was named by German naturalist Blasius Merrem in his 1820 Versuch eines Systems der Amphibien. Merrem considered it to be one of three groups of Pholidota (reptiles), the other two being Testudinata (turtles) and Squamata (lizards and snakes).^[1] Loricata was an early name for an order that includes crocodiles, alligators, and gharials, although the order is now referred to as Crocodylia.

The name Loricata gained a new phylogenetic definition in 2011. In his study of early archosaur phylogeny, paleontologist Sterling J. Nesbitt defined it as the most inclusive clade containing Crocodylus niloticus (the Nile crocodile), but not the extinct Poposaurus gracilis, Ornithosuchus longidens, or Aetosaurus ferox. Nesbitt considered the following features to be synapomorphies (distinguishing features) of Loricata:

• Four teeth in the premaxilla of the upper jaw.
• A ridge on the squamosal bone at the back of the skull.
• A projection on the squamosal that touches the infratemporal fenestra.
• A tall, narrow eye socket.
• A ridge positioned halfway along the length of the fibula for the attachment of the iliofibularis muscle.
• An articulation between the fourth tarsal bone and the bottom of the calcaneum in the ankle.
• A projection at the base of the fifth metatarsal of the foot that is separated from the end of the bone by a concave gap.

Nesbitt's phylogenetic analysis placed Crocodylomorpha and several rauisuchians within Loricata. Rauisuchidae was found to be the sister taxon of Crocodylomorpha, while prestosuchids formed a series of more basal loricatans. Loricata is the sister taxon of Poposauroidea, a group of Triassic rauisuchians. Below is a cladogram of Loricata from Nesbitt (2011):^[2]

Paracrocodylomorpha  

†Poposauroidea

  Loricata  

†Prestosuchus

     

†Saurosuchus

     

†Batrachotomus

     

†Fasolasuchus

     

†Rauisuchidae

   

Crocodylomorpha

             

França, Langer and Ferigolo (2011) found that, when added to Nesbitt's analysis (2011), Decuriasuchus was recovered as the basalmost loricatan. Its addition influenced the phylogenetic placement of Ticinosuchus as well; in Nesbitt's original analysis it was recovered outside Loricata, but when Decuriasuchus was included in the analysis, Ticinosuchus was recovered as a basal member of Loricata.^[3]

Prior to 2011, poposauroids were viewed as closer relatives of crocodylomorphs than rauisuchids and prestosuchids were. The clade Paracrocodylomorpha includes poposauroids and crocodylomorphs. Although Paracrocodylomorpha was designated to exclude rauisuchids and prestosuchids, Nesbitt found that most members of those groups are closer to crocodylomorphs than poposauroids are. Thus, the entirety of Loricata is currently considered to be a subgroup of Paracrocodylomorpha.^[2]

A clade called Paracrocodyliformes was erected in 2007 in which rauisuchids and prestosuchids were more closely related to Crocodylomorpha, and poposauroids were the most basal group.^[4] This usage is similar to Loricata.

References