| Laganosuchus | |
|---|---|
 | |
| Lower jaws ofL. thaumastos | |
Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Reptilia |
| Clade: | Archosauria |
| Clade: | Pseudosuchia |
| Clade: | Crocodylomorpha |
| Family: | †Stomatosuchidae |
| Genus: | †Laganosuchus Sereno and Larsson,2009[1] |
| Type species | |
| †Laganosuchus thaumastos Sereno and Larsson, 2009 | |
| Other species[2] | |
| |
Laganosuchus is anextinctgenus ofstomatosuchidcrocodyliform. Fossils have been found fromNiger andMorocco and date back to theUpper Cretaceous.[1][2]
The name means "pancake crocodile" from theGreekλαγανον,laganon ("pancake") andσοῦχος,souchos ("crocodile") in reference to the shallow depth of the skull, which is characteristic of all stomatosuchids. It has been nicknamed "PancakeCroc" byPaul Sereno and Hans Larsson, who first described the genus in a monograph published inZooKeys in 2009 along with other Saharan crocodyliformes such asAnatosuchus andKaprosuchus.[3]
Thetype species isL. thaumastos (meaning 'the astonishing pancake crocodile' from Greek θαυμαζω,thaumazo "I astonish" in reference to its unusual form) from theCenomanian-ageEchkar Formation in Niger, holotype MNN IGU13. A second species,L. maghrebensis (making a reference to the place of discovery), is known from theKem Kem Beds in Morocco, which are also Cenomanian in age; its holotype is UCRC PV2.[4]
Both species ofLaganosuchus are known only from theirlower jaws, those ofL. thaumastos almost complete save for the leftretroarticular process and those ofL. maghrebensis only from a fragment of thedentary bone.L. thaumastos had a total jaw length of 838 mm and a jaw length from tip toarticular facet of 750 mm, of which 490 mm actually boreteeth. Across the jaws, the total width of the lower jaw ranged from around 140 mm at thesymphysis to 240 mm at the articular facets, widening fairly evenly all the way along. All the teeth were simple straight spikes, with the first pair the largest and the rest of the teeth decreasing in size towards the back of the mouth. Each side of the mouth bore 24 teeth, relatively evenly spaced save for the sixth and seventh, thedental alveoli of which have merged. Each side of these jaws is gently bowed outwards horizontally, curving more strongly towards the symphysis of the two dentary bones from the seventh alveolus forwards. The symphysis itself is relatively small and weak compared to other crocodyliforms, suggesting a very weak bite, although the bones are fully fused. The jaws are also bowed slightly, curving downwards from the articular facet and then back upwards to the symphysis of the jaws. Each of the dentary bones is very slender, only about 22 mm wide even at the slightly thickened 'chin' of the symphysis. WhileL. thaumastos has a small crest running along the lingual side of the dentary to thicken it, this feature is not present inL. maghrebensis. Thesplenial is a very thin sheet of bone in both species; it stretches much of the way along the lower jaws, but does not participate in the symphysis as the dentary does. The anterior end of the splenial differs between the two species; inL. thaumastos it is bifurcated, whereas inL. maghrebensis the anterior end of the splenial comes to a simple point.[1]
Although the posterior end of the lower jaw is not preserved inL. maghrebensis, inL. thaumastos thecoronoid process isrugose, low and broad transversely, thickened by thesurangular on the lingual side of the jaw, possibly signifying the attachment of powerfulmuscles to close the long, heavy jaws - a task that would be difficult underwater due to the large surface area between them. The externalmandibular fenestra is very much reduced, forming little more than a slit. There is an unusually smalladductor fossa just in front of the saddle-shaped articular facet of theglenoid; on the right side this saddle-shaped facet has irregular edges and shows some signs ofbone disease, for unknown reasons. The retroarticular process is triangular in cross-section with slightly concave sides. Both theangular and theprearticular bones have thin posterior rami that entirely overlap thearticular laterally and medially, leaving only the top and bottom faces of the articular open.[1]
L. thaumastos has the first two teeth in each dentary tilted forwards, and these would probably have projected out from the mouth below matching teeth in thepremaxilla. Between each alveolus, the dorsal margin of the alveolar row forms a ridge that slopes downwards labially in concave depressions between the alveoli, probably indicating strongly interdigitating teeth that fitted together to form a kind of 'fish trap'. Most of the teeth are broken or missing, but a few were being replaced when the specimen died and have so been preserved in their crypts; they are straight, perfectly symmetrical spikes with no ornamentation, carinae or recurvature. InL. maghrebensis, however, the fourth tooth in the dentary is slightly larger than the first and there is no procumbency of the first dental alveoli, so its front teeth would not have projected forwards in the same fashion.[1]
Both species ofLaganosuchus would have been between 4–6 metres (13–20 ft) in total length, a comparatively large proportion of which would have been the large flattened head. It is possible that they hadgular sacs beneath their throats, just as their relativeStomatosuchus may have done, but there is no fossil evidence either to support or disprove this theory. The jaws would have been unable to be opened or closed at speed or with much power due to their length relative to all the possible muscles that could be used to close them.[1]
According to Sereno and Larsson,L. thaumastos was an approximately 6 m (20 ft) long, squat fish-eater with a 1 m (3.3 ft) flat head.[3] It would have stayed motionless for hours, waiting for prey to swim into its open jaws with spike-shaped teeth.[3][5] These teeth would have fitted together tightly so that no fish trapped in the mouth could escape.
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