| Planocraniidae | |
|---|---|
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| Skeleton ofBoverisuchus magnifrons | |
Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Reptilia |
| Clade: | Archosauria |
| Clade: | Pseudosuchia |
| Clade: | Crocodylomorpha |
| Clade: | Neosuchia |
| Clade: | Eusuchia |
| Family: | †Planocraniidae Li, 1976 |
| Type genus | |
| Planocrania Li, 1976 | |
| Genera | |
Planocraniidae is anextinctfamily ofeusuchiancrocodyliforms known from thePaleogene ofAsia,Europe andNorth America. The family was coined by Li in 1976, and contains threegenera,Boverisuchus,Duerosuchus andPlanocrania.[2][3] Planocraniids were highly specialized crocodyliforms that were adapted to living on land. They had extensive body armor, long legs, and blunt claws resembling hooves, and are sometimes informally called "hoofed crocodiles".[4]
Prior to 2013, the term Pristichampsidae/Pristichampsinae was used for this group. However, thetype specimen ofPristichampsus was found to be undiagnostic, and considered to be anomen dubium.[2] As such, Brochu (2013) transferred the other species placed inPristichampsus toBoverisuchus, and resurrected Planocraniidae to replace Pristichampsidae/Pristichampsinae as the name for theclade.[2] Brochucladistically defined Planocraniidae asPlanocrania hengdongensis and crocodyliforms more closely related to it than toAlligator mississippiensis (American alligator),Crocodylus niloticus (Nile crocodile),Gavialis gangeticus (gharial),Thoracosaurus macrorhynchus,Allodaposuchus precedens, orHylaeochampsa vectiana.
Phylogenetic analyses based purely onmorphological data have generally placed planocraniids in abasal position within thecrocodiliancrown group. Some of these analyses have found that planocraniids lie just outsideBrevirostres, a group that includesalligators,caimans, andcrocodiles but notgharials.[2][5][6] However, molecular studies usingDNA sequencing have found the group Brevirostres to be invalid upon finding that crocodiles andgavialids are more closely related than alligators.[7][8][9][10][11]
A 2018tip dating study by Lee & Yates using bothmolecular,morphological andstratigraphic data instead recovered the planocraniids outside crown groupCrocodylia. Below is acladogram from that study:[10]
In 2021, Rio & Mannion conducted a newphylogenetic study using a heavily modified morphological data set, and also noted the lack of consensus and difficulty in placing Planocraniidae. In their study, they recovered Planocraniidae within Crocodylia, as thesister group toLongirostres, as shown in the cladogram below:[1]
Planocraniids were land-living (terrestrial) crocodyliforms with longer legs than living crocodilians. They grew to a maximum size of 2 to 3 metres (6.6 to 9.8 ft) in length.[12] Nearly complete skeletons ofBoverisuchus indicate that planocraniids were more heavily armored than living crocodilians, with bony plates calledosteoderms tightly interlocking along the back, completely encasing the tail, and extending down the legs. The claws were blunt and have been described as hoof-like in shape,[13] suggesting that planocraniids may have been unguligrade,[14] walking on the tips of their toes like mammalianungulates. The areas on the leg bones where muscles attach were in different positions in planocraniids than they are in living crocodilians, possibly as an adaptation to walking on land.[12]
While most crocodilians have flattened skulls, planocraniids had tall and narrow (orlaterally compressed) skulls. Their teeth were also laterally compressed and not conical like those of modern crocodilians. The combination of a laterally compressed skull and laterally compressed teeth is called the "ziphodont" condition.[12]
The teeth of the upper jaw completely overlapped the teeth of the lower jaw when the mouth was closed, giving planocraniids an alligator-like overbite. Planocraniids had a notch between thepremaxilla bone at the tip of the upper jaw and themaxilla behind it. Living crocodiles also have this notch, which provides room for the enlarged fourth tooth of the lower jaw when the mouth is closed. In planocraniids the fourth tooth was small and did not fit into the notch.[12]
The evolution of Planocraniidae occurred after theK-T extinction whenniches were open. Because of the lack of competition, the Planocraniidae evolved to hunt on land, which would have been almost impossible with thedinosaur clades existing.[15]
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