Planocraniidae

Planocraniidae is an extinct family of basal crocodylians known from the Paleogene of Asia, Europe and North America. The family was coined by Li in 1976, and contains two genera, Boverisuchus and Planocrania.[1] Planocraniids were highly specialized crocodylians that were adapted to living on land. They have extensive body armor, long legs, and blunt claws resembling hooves, and are sometimes informally called "hoofed crocodiles".[2] Most phylogenetic analyses (analyses of evolutionary relationships) place planocraniids in a basal position within Crocodylia. Some of these analyses find that planocraniids lie just outside Brevirostres, the group of crocodilians that includes alligators, caimans, and crocodiles but not gharials. Planocraniids are inferred to have first appeared in the Late Cretaceous, several tens of millions of years before they actually occur in the fossil record. This is because the earliest members of Brevirostres appear in the Campanian stage of the Late Cretaceous, and Planocraniidae, being an outgroup to Brevirostres, must have branched off before this time.[3]

Planocraniidae
Temporal range: Paleocene–Eocene
Skull of Pristichampsus geiseltalensis
Skull of Boverisuchus magnifrons in the Geisel valley museum
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Reptilia
Order: Crocodilia
Family: Planocraniidae
Li, 1976
Type genus
Planocrania
Li, 1976
Genera

Boverisuchus
Planocrania

Pristichampsidae

Prior to 2013 the term Pristichampsidae/Pristichampsinae was used for this group. However, the type specimen of Pristichampsus was found to be undiagnostic, and considered to be a nomen dubium.[1] As such, Broch (2013) transferred the other species placed in Pristichampsus to Boverisuchus, and resurrected Planocraniidae to replace Pristichampsidae/Pristichampsinae as the name for the clade.[1]

Description

Planocraniids were land-living (terrestrial) crocodylians with longer legs than living species of crocodylians. They grew to a maximum size of 2 to 3 metres (6.6 to 9.8 ft) in length.[3] Nearly complete skeletons of Boversuchus indicate that planocraniids were more heavily armored than living crocodylians, with bony plates called osteoderms tightly interlocking along the back, completely encasing the tail, and extending down the legs. The claws are blunt and have been described as hoof-like in shape,[4] suggesting that planocraniids may have been unguligrade,[5] walking on the tips of their toes like mammalian ungulates. The areas on the leg bones where muscles attach are in different positions in planocraniids than they are in living crocodylians, possibly as an adaptation to walking on land.[3]

While most crocodilians have flattened skulls, planocraniids had tall and narrow (or laterally compressed) skulls. Their teeth are also laterally compressed and not conical like those of other crocodilians. The combination of a laterally compressed skull and laterally compressed teeth is called the "ziphodont" condition. The ziphodont condition is common among terrestrial non-crocodylians crocodylomorphs that lived in the Mesozoic, but among crocodylians it is unique to planocraniids and the extinct Australian crocodile Quinkana (which is also thought to have been terrestrial).[3]

The teeth of the upper jaw completely overlap the teeth of the lower jaw when the mouth is closed, giving planocraniids an alligator-like overbite. Planocraniids also have a notch between the premaxilla bone at the tip of the upper jaw and the maxilla behind it. Living crocodiles have this notch, which provides room for the enlarged fourth tooth of the lower jaw when the mouth is closed. In planocraniids and other basal crocodyloids, the fourth tooth is small and does not fit into the notch.[3]

References

  1. ^ a b c Brochu, C. A. (2013). "Phylogenetic relationships of Palaeogene ziphodont eusuchians and the status of Pristichampsus Gervais, 1853". Earth and Environmental Science Transactions of the Royal Society of Edinburgh: 1. doi:10.1017/S1755691013000200.
  2. ^ Brochu, C. (2007). "Systematics and phylogenetic relationships of hoofed crocodiles (Pristichampsinae)". Journal of Vertebrate Paleontology. 27 (3, Suppl.): 53A. doi:10.1080/02724634.2007.10010458.
  3. ^ a b c d e Brochu, C. A. (2003). "Phylogenetic approaches toward crocodylian history" (PDF). Annual Review of Earth and Planetary Sciences. 31: 357–97. doi:10.1146/annurev.earth.31.100901.141308.
  4. ^ Langston, W. (1956). "The Sebecosuchia; cosmopolitan crocodilians?". American Journal of Science. 254 (10): 605–614. doi:10.2475/ajs.254.10.605.
  5. ^ Young, M. T.; Bell, M. A.; Andrade, M. B.; Brusatte, S. L. (2011). "Body size estimation and evolution in metriorhynchid crocodylomorphs: Implications for species diversification and niche partitioning". Zoological Journal of the Linnean Society. 163 (4): 1199. doi:10.1111/j.1096-3642.2011.00734.x.
Aldabrachampsus

Aldabrachampsus is an extinct genus of crocodylian. A horned crocodile, its incomplete remains were found on Aldabra Atoll in the western Indian Ocean. It was small (perhaps 2 to 2.5 metres (6.6 to 8.2 ft) long) and lived during the Pleistocene.Because it is known from fragmentary material, its relationships to modern crocodylians are unclear. It appears to have been a crocodylid, but could be closer to either the African dwarf crocodiles (Osteolaemus) or the true crocodiles (Crocodylus).

Alligator olseni

Alligator olseni (common name Olsen's Alligator, named after Russel Olsen) is an extinct species of alligator. They lived in the Early Miocene period, around 16-19 million years ago and possibly earlier. Their range was principally in what is now known as Florida, United States, and possibly extending into southeastern Texas.

Allodaposuchus

Allodaposuchus is an extinct genus of crocodyliforms that includes four species that lived in what is now southern Europe during the Campanian and Maastrichtian stages of the Late Cretaceous. Although generally classified as a non-crocodylian crocodylomorph, it is sometimes placed as one of the earliest true crocodylians. Allodaposuchus is one of the most common Late Cretaceous crocodylomorphs from Europe, with fossils known from Spain, Romania, and France.

Arambourgia

Arambourgia is an extinct genus of alligatorine crocodylian from Europe. It was named in 1905 and synonymized with Allognathosuchus haupti in 1990, but later reassigned as its own genus once again in 2004. It is thought to have been closely related to Hispanochampsa and Procaimanoidea. Arambourgia was likely to have been part of an early dispersal event of alligatorines from North America to Europe during the Eocene epoch. Arambourgia had non-serrated teeth and a deep altirostral snout, unlike the flatter snouts of most other alligatorids.

Boverisuchus

Boverisuchus is an extinct genus of planocraniid crocodylian known from the middle Eocene (Lutetian stage) of Germany and possibly North America. It grew to approximately three metres (10 ft) in length.

Brachyuranochampsa

Brachyuranochampsa is an extinct genus of crocodyloid crocodilians.

The only robust occurrence of Brachyuranochampsa is B. eversolei from the middle Eocene of Wyoming. Another species, B. zangerli from the lower Bridger Formation at Grizzly Buttes, has been synonymized with another primitive crocodyloid, "Crocodylus" affinis, also known from the Bridger Formation

Diplocynodontinae

Diplocynodontinae is a clade of alligatoroid crocodilians that lived from the Eocene to the Miocene in Europe. It includes 10 species and two genera, Diplocynodon and Baryphracta, although Baryphracta may be a junior synonym of Diplocynodon. The fossil range of the group may extend back into the Paleocene depending on whether remains of an alligatoroid from Berru, France belong to a diplocynodontine.

Dollosuchoides

Dollosuchoides is an extinct genus of crocodilian. It is a basal tomistomine closely related to the genus Tomistoma, of which the only extant species of tomistomine, the False gharial, is a member of. Fossils have been found from Belgium and date back to the middle Eocene. The holotype is currently housed in the Gand Museum in Belgium.

Eoalligator

Eoalligator is an extinct genus of crocodyloid crocodilian from Paleocene deposits in China.

Eusuchia

The Eusuchia ("true crocodiles") are a clade of crocodylomorphs that first appears in the Early Cretaceous with Hylaeochampsa. Along with Dyrosauridae and Sebecosuchia, they were the only crocodyliformes who survived the K-T extinction. Since the other two clades died out 35 and 11 million years ago, all living crocodilian species are eusuchians, as are many extinct forms.

Ferganosuchus

Ferganosuchus is an extinct genus of gavialid crocodilian. The genus is thought to be a tomistomine, although it has been suggested that Ferganosuchus may be a more basal gavialoid. Fossils have been found in the region of Kazakhstan and Kyrgyzstan that date back the middle Eocene. The genus is well known from fairly complete specimens, unlike most other Asian tomistomines, whose remains tend to be more fragmentary.

Globidentosuchus

Globidentosuchus is an extinct genus of basal caimanine crocodylian known from the late Middle to Late Miocene of the Middle and the Upper Members of the Urumaco Formation at Urumaco, Venezuela. It contains a single species, Globidentosuchus brachyrostris.

Harpacochampsa

Harpacochampsa is a poorly known Early Miocene crocodilian from the Bullock Creek lagerstätte of the Northern Territory, Australia. The current specimen consists of a partial skull and fragments of a slender snout reminiscent of that of a false gharial. It is tentatively placed within Mekosuchinae, though some experts disagree with this, as H. camfieldensis would be the only known mekosuchine with a long, thin snout. Its long snout demonstrates that it was a piscivore in life.

Maroccosuchus

Maroccosuchus zennaroi is an extinct tomistomine crocodylian from the early Eocene of Morocco. A recent phylogenetic assessment of Tomistoninae determined that M. zennaroi is the basalmost tomistomine.

Penghusuchus

Penghusuchus is an extinct genus of tomistomine crocodylian. It is known from a skeleton found in Upper Miocene rocks of Penghu Island, off Taiwan. It appears to be related to two other fossil Asian tomistomines: Maomingosuchus petrolica of southeastern China and Toyotamaphimeia machikanensis of Japan. The taxon was described in 2009 by Shan and colleagues; the type species is P. pani.

Planocrania

Planocrania is an extinct genus of crocodylians. Planocrania was once included in the family Pristichampsidae along with the genus Pristichampsus. Both genera were previously assigned to the subfamily Pristichampsinae within the family Crocodylidae before they were placed in their own family, the Pristichampsidae. Two species are currently known to belong to the genus. The type species, P. datangensis, was named in 1976 from material found from Nanxiong in Guangdong Province, China. A second species, P. hengdongensis, is known from Hengdong County in Hunan Province and was described in 1984.

Protoalligator

Protoalligator is an extinct genus of crocodilian which lived during the Paleocene. It is considered to be an alligatoroid, but its exact phylogeny is uncertain.

Protocaiman

Protocaiman is a caimanine genus first described in 2018. Protocaiman peligrensis, which was the first member of the genus to be identified, lived in Patagonia during the Paleocene era. The fossil was discovered in Argentina's Salamanca Formation.

Rhamphosuchus

Rhamphosuchus ("Beak crocodile") is an extinct relative of the modern false gharial. It inhabited what is now the Indian sub-continent in the Miocene. It is only known from incomplete sets of fossils, mostly teeth and skulls.Four species belonging into the genus Gavialis may be included.

Extinct crocodilian species

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