| Knoetschkesuchus | |
|---|---|
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| Type specimen ofKnoetschkesuchus langenbergensis | |
Scientific classification | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Reptilia |
| Clade: | Archosauria |
| Clade: | Pseudosuchia |
| Clade: | Crocodylomorpha |
| Clade: | Crocodyliformes |
| Clade: | Eusuchia |
| Family: | †Atoposauridae |
| Genus: | †Knoetschkesuchus Schwarzet al., 2017 |
| Type species | |
| Knoetschkesuchus langenbergensis Schwarzet al., 2017 | |
| Species | |
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Knoetschkesuchus is a genus of smallatoposauridcrocodylomorph from theLate Jurassic ofGermany andPortugal. Two species are known: the German speciesK. langenbergensis, described by Schwarz and colleagues in 2017 based on two partial skeletons and various isolated bones; and the Portuguese speciesK. guimarotae, named from over 400 specimens including several partial skeletons.Knoetschkesuchus was a small and short-snouted crocodilian, measuring about 55 centimetres (22 in) in length, that primarily fed on small prey, includinginvertebrates,amphibians, andmammals. This specialization towards small prey ecologically separatedKnoetschkesuchus from most of the other diverse crocodilians that it lived with in the island ecosystem of JurassicEurope.
Both species were formerly recognized as belonging toTheriosuchus;K. guimarotae was initially named asT. guimarotae, and specimens ofK. langenbergensis were initially referred toT. pusillus upon their discovery. Schwarz and colleagues recognized a number of characteristics that united these two taxa to the exclusion of other species ofTheriosuchus; in particular,Knoetschkesuchus only has two distinct types of teeth, lacking the leaf-shaped teeth seen in other atoposaurids. Other distinguishing traits include the relatively wide skull, and the presence of theantorbital and mandibular fenestrae in all life stages.
The material of the type species ofKnoetschkesuchus,K. langenbergensis, comes from amarlylimestone bed (numbered as Bed 83, not Bed 93 as reported by some publications) containingrecrystallizedmicriticintraclasts, located within the Langenberg Quarry in theHarz Mountains nearGoslar,Lower Saxony,Germany. These deposits have been dated to the UpperKimmeridgian stage of theJurassic—specifically, to the regional equivalent of the Upper Kimmeridgian known as the Mittleres Kimmeridge,[1] and belong to theSüntel Formation.[2] Although well-preserved, fossils from this quarry were recovered generally by regular blasting operations in the quarry.[3]
Specimens belonging toKnoetschkesuchus are stored at theDinosaurier-Freilichtmuseum Münchehagen (hereafter denoted by DFMMh/FV) inRehburg-Loccum, Germany. They are: thetype specimen DFMMh/FV 200, the partial skeleton of an adult with a skull; DFMMh/FV 605, the complete skull of a juvenile; DFMMh/FV 261, an isolatedangular; DFMMh/FV 790.12, an isolated leftdentary; DFMMh/FV 279, an isolatedfemur; DFMMh/FV 790.11, an isolatedmetatarsal; and DFMMh/FV 325, a partial skeleton includingosteoderms, vertebrae, and ribs.Stereomicroscopy was used to examine the specimens, which were described in a 2017 paper published by Daniela Schwarz, Maik Raddatz, and Oliver Wings.[3]
The genus nameKnoetschkesuchus combines the family name of Nils Knötschke, a researcher at the DFMMh who was responsible for the collection, curation, and preparation of Langenberg Quarry specimens, with the common crocodilian suffixsuchus, from the Greeksouchos ("crocodile"). Meanwhile, the species namelangenbergensis is in reference to the provenance of this species from the Langenberg Quarry.[3]
Schwarzet al. also assigned an additional species toKnoetschkesuchus,K. guimarotae, which was originally classified as a species ofTheriosuchus. As reflected by the specific name,K. guimarotae originates from thelignite layers of the Guimarota quarry, located nearLeiria,Portugal. There are two primary vertebrate-bearing lignite strata within the so-called Guimarota-strata, which are separated by marly limestone and respectively known as the "Fundschichten" and "Ruafolge" subunits;K. guimarotae is known from both of these layers. They have been assigned to theAlcobaça Formation, a subunit of theAbadia Formation,[4] which has been dated to the Kimmeridgian on the basis of fossilostracods.[5][6][7]
The remains ofK. guimarotae are stored at the Institute of Geological Sciences of theFree University of Berlin (hereafter IPFUB). Alongside the type specimen IPFUB Gui Croc 7308—which consists of a partial skull with jaws, a vertebra from thesacrum, and two osteoderms—over 400 additional specimens are known, most of them consisting of single isolated bones. Among these, the more complete specimens are IPFUB Gui Gui Croc 7352 (tail vertebrae, femur, osteoderms); 7441 (osteoderms andulna); 7545 (dorsal vertebrae,ischia, osteoderms); 7564 (femur,humerus, osteoderms); 7634 (dorsal vertebrae, rib, osteoderms); and 8037 (cervical and dorsal vertebrae, and osteoderms). More specimens are known, but they remain unprepared. Some specimens show the marks of scavenging.[5]
As with other members of theAtoposauridae,[3]Knoetschkesuchus is very small, withK. guimarotae measuring only 55 centimetres (22 in) long at maximum.[5] Typical of the group, both species werequadrupedal, bearing long and slender limbs.[8] The backs of both of the known species are covered with two rows of bony rectangular osteoderms, centred at the midline, that are wider than they are long.[3] Each osteoderm bears a keel running longitudinally, although the keels are less-developed inK. langenbergensis.[3] In at leastK. guimarotae, the osteoderms on the tail have sharper and higher keels; the ones near the back of the tail tend to be longer than they are wide, unlike the other osteoderms, and are also vaulted. Thevertebrae ofK. guimarotae are additionallyamphicoelous, or concave at both ends;[5] while initially proposed as a unique trait,Theriosuchus pusillus bears amphicoelous vertebrae as well.[3][9] The skull and jaws, which exhibit a number of characteristics that separateKnoetschkesuchus from other atoposaurids, are described in further detail below.
The skull ofKnoetschesuchus is relatively short, with the snout taking up 47% of skull length inK. langenbergensis and 42% inK. guimarotae,[5] which allows them to be classified as brevirostrine crocodilians.[10] Along the side of the snout are two undulations, a smaller one on thepremaxilla and a larger and broader one on themaxilla. The jaggedsuture between the premaxilla and maxilla is angled towards the front of the skull inK. langenbergensis and towards the back inK. guimarotae.[5] Along the midline of the snout are the thin and wedge-likenasals; the nostrils, which face upwards, are clearly separated by the nasals inK. guimarotae,[5] but it is not clear that this is the case inK. langenbergensis.[3]
At the back, the nasals are separated by thefrontal inK. langenbergensis, the back third of which is somewhat vaulted. The portion of the frontal between the eyes is one-third the width of the entire skull in both species, but it widens further back to form the front of the skull roof. Theprefrontal is straight along its contact with the frontal and nasal (about half of the bone is in contact with each), but forms an angle between the margin of the eye socket and the lacrimal on the other side. This angle is rounded inK. guimarotae such that the bone is oval-shaped,[5] but very pointed inK. langenbergensis such that the bone is triangular.[3]
The main body of the lacrimal is a rounded square with both faces of the bone are concave. Its contact with the nasal is rather limited in both species. The oval-shapedantorbital fenestra is small, being only 9% the length of the eye socket; its presence is unique to both species of the genus among atoposaurids. Meanwhile, the eye socket is large and oval, being 54% longer than it is tall. The drop-shapedpalpebrals project out from the tops of the eye sockets. In both species, the back two-thirds of the inner surface of the palpebral is slightly concave. Both species have asquamosal in which the back third is bevelled; inK. langenbergensis, the outer margin is somewhat convex.[3]
Viewed from the top, theparietal increases in width at the back; the increase is small inK. langenbergensis, such that the bone is overall rectangular, but the difference is larger inK. guimarotae. The back of the bone bears a small notch inK. langenbergensis and a general concavity inK. guimarotae that slightly exposes the underlyingsupraoccipital.[5] Thepostorbital bears two branches that join with a gentle curve, separated by an angle of 130° inK. langenbergensis. Thesupratemporal fenestra is roughly square inK. guimarotae[5] but has a thinner back end inK. langenbergensis. In both species, the maximum distance between the supratemporal fenestrae is about a third of the total width of the top of the skull. The trapezoidalinfratemporal fenestra is 1.5 times as long as it is wide inK. langenbergensis.[3]
On the bottom of the skull, thepterygoid is about twice as wide as it is long. At the front of the pterygoid is a small projection that extends backwards to form a ridge, on either side of which is a furrow-like depression (the choanal groove) containing thechoanae. InTheriosuchus, unlikeKnoetschkesuchus, the choanae are embedded in a wider bowl-like depression. Additionally, in both species, the bottom surface of the pterygoid is somewhat concave. Extending forward from either side of the pterygoid is the ectopterygoid; in both species, this bone is constricted near the middle to form an hourglass-like shape, but inK. langenbergensis it is also somewhat twisted to the side. The back of the bone is very concave in both species.[3][5]
Forming the sides of the back of the skull is theexoccipital, which surrounds most of theforamen magnum. TheEustachian tube extends downwards across thebasoccipital andbasisphenoid; these bones are thickened on either side of the tube inK. langenbergensis.K. guimarotae has a small rounded foramen beside the tube on the basoccipital, and a tuberosity bearing a ridge above.[5] On the front of the basoccipital in both species, there are two rounded depressions near the bottom. The basisphenoid resembles a triangular hatchet in shape when viewed from the side.[3]
InK. guimarotae, the two halves of the dentary diverge from each other at an angle of 20° near the front, then 40° near the back.[5] It also bears two convexities on the bottom of the jaw, one at the third and fourth teeth and another at the eighth to tenth teeth. The latter convexity is replaced by a concavity inK. langenbergensis. In both species, the top margin of the jaw behind the tooth row slopes upwards in a straight line. The side of the dentary is pitted, albeit much more densely so inK. langenbergensis. Near the back of the dentary in both species, the pits are replaced by longitudinal grooves. On the interior of the jaw, thesplenial bears an oval foramen behind the level of thesymphysis in both species, and the top of the bone bears a low and roughened crest inK. guimarotae.[3][5]
The tip of the angular is situated close to the midpoint of the bone inK. langenbergensis rather than being at the back as inK. guimarotae.[5] In both species, the back of the angular contributes to the retroarticular process. The inner surface of the angular is roughened inK. guimarotae, and the top margin of the inner wall transitions from an upward-projecting tip at the front to a low, rounded crest at the back;[5] the same margin maintains its height along the angular inK. langenbergensis. Thesurangular bears a thin, forward-projecting process that, inK. langenbergensis, extends forward to the back of the tooth row and bears a groove on the bottom.[5] The presence of the oval-shaped[5] external mandibular fenestra is unique to the genus among atoposaurids.[3]
Both species ofKnoetschkesuchus have only two distinct types of teeth, uniquely among atoposaurids. Other atoposaurids have a third type of leaf-shaped teeth. The first type of teeth, found near the front of the jaw, are conical, slightly constricted at the base, and curved slightly inwards.[5] A subtype is represented by the canine-like or pseudocaniniform teeth. They are the fourth and fifth maxillary teeth, and are enlarged (about twice the size of the other maxillary teeth), more pointed, and more constricted at the base. The second type of teeth, which constitutes the rest of the teeth, are shaped like thin lanceheads, with a wide base and a narrower tip; inK. guimarotae all of the tips are sharp,[5] but inK. langenbergensis they gradually become blunter.[3]
There are 5 premaxillary teeth in both species,[5] the fourth of which is about a third larger relative to the others. The maxilla has 12 distinct sockets inK. langenbergensis. Excluding the pseudocaniniforms, the maxillary tooth size remains roughly constant but gradually decreases after the pseudocaniniforms in both species; all tooth sockets after the twelfth are replaced by a continuous trough. In total,K. guimarotae had at least 15 maxillary teeth,[5] andK. langenbergensis 17 or 18. Meanwhile, the dentary exhibits 21 teeth inK. langenbergensis and at least 20 inK. guimarotae.[5] Like the maxilla, distinct sockets for dentary teeth are replaced by a groove from the eleventh tooth backwards inK. langenbergensis.[3]
When the known specimens ofK. langenbergensis were first described in a preliminary fashion by a 2006 paper from Hans-Volker Karlet al., they were referred to the genusTheriosuchus. This was on the basis of the short skull, divided nostrils, large eye sockets compared to the supratemporal fenestrae, and the bevelled side of the squamosal. Specifically, they recognized its similarity toT. pusillus on the basis of its osteoderms and teeth, although they noted that the orientation of the back of the skull was different and that leaf-shaped teeth were absent. These differences were attributed toK. langenbergensis probably representing a different life stage ofT. pusillus compared to the type specimen.[11][12] A 2016 analysis of the relationships of the Atoposauridae, from Jonathan Tennantet al., tentatively supported the affinity of these specimens withT. pusillus on account of the teeth being situated in a groove (a trait unitingT. pusillus and"T." guimarotae in their analysis), the presence of pseudocaniniform teeth, and the lance head-shaped teeth near the back of the jaw. However, they noted that the nasals essentially completely divide the nostrils to the exclusion of other bones, which is not seen in the genus ofTheriosuchus.[12]
However, the taxonomy ofTheriosuchus itself is somewhat convoluted. Many recent taxonomic studies have not provided an explicit set of characteristics that unite species ofTheriosuchus and separate them from other atoposaurids;[13][14][15] the only such diagnoses that have been produced were given by Steve Salisbury andDarren Naish in 2011,[16] and Jeremy Martinet al. in 2010.[17] In 2016 Mark Younget al. criticized these diagnoses, noting that many characters were either more widely distributed among the Atoposauridae, difficult to assess, or—in the case of the latter diagnosis—not present at all. Younget al. provided an alternative diagnosis containing nine traits, mostly involving teeth; however, they also noted that there was variation among the expression of these traits, which calls into question themonophyly ofTheriosuchus.[13]K. langenbergensis differs from this diagnosis in four out of nine traits,[13] which Schwarzet al. cited as a basis for both the generic separation ofKnoetschkesuchus and the necessity of revising the diagnosis further.[3]
According to Schwarzet al., seven traits uniteK. langenbergensis andK. guimarotae, and separate them from other species referred toTheriosuchus. These include the presence of only two unique tooth morphotypes; the choanae being placed in shallow grooves rather than a bowl-like depression; the relatively wide top of the skull; the presence of antorbital and mandibular fenestrae in all life stages; and the relatively limited contact between the lacrimal and nasal. Additionally,K. langenbergensis differs from other species in lacking teeth with low crowns; having a longer maxillary symphysis; having a crest on the side of the downward-projecting process of the postorbital; having overlap between the postorbital and the front of the squamosal; and a rectangular parietal that does not form part of the supratemporal fenestra.[3]
In the 2017 description ofK. langenbergensis, Schwarzet al. used the 2015phylogenetic dataset of Alan Turner,[18] which was revised to remove irrelevant characteristics, addK. langenbergensis andT. grandinaris, and correct flaws in the coded traits ofK. guimarotae (due to low-resolution images, inaccuracies in the original reconstruction, and the acquirement of new data). The phylogenetic trees recovered by this analysis consistently found that Atoposauridae, represented byKnoetschkesuchus,Theriosuchus, andAlligatorium, forms a monophyletic clade. Within this clade, a close relationship betweenK. langenbergensis andK. guimarotae, excluding otherTheriosuchus species, was strongly supported, providing further evidence of these two species forming a separate genus. In some trees,T. grandinaris was also close toKnoetschkesuchus. Themost parsimonious arrangement is reproduced below.[3]
| Eusuchia |
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Being relatively small,Knoetschkesuchus would have mainly fed on invertebrates and possibly small vertebrates (including amphibians and mammals). The same diet is observed in modern juvenile crocodilians of the same size class.[5]
During the Kimmeridgian, Europe was covered by the shallowinlandTethys Ocean, with exposed landmasses being a series of scattered archipelagos.[19][20] Highly variable sea levels[21] supported a highly diverse insular crocodilian fauna, with biodiversity (that of atoposaurids in particular) being driven strongly byallopatric speciation.[22] The two species ofKnoetschkesuchus were part of similar faunas, in both of which they functioned as small predatorsecologically partitioned from the other contemporary crocodilians; it is likely that these faunas originated through dispersal over larger landmasses.[3] A similar faunal exchange occurred with theWessex-Weald Basin ofEngland.[23]
The Langenberg Quarry, whereK. langenbergensis is known from, is part of the Lower Saxony Basin, which would have been part of the landmass associated with the Rhenisch, Bohemian, and London-BrabantMassifs. During the Kimmeridgian, it would have been a shallow marine environment; however, this does not imply thatK. langenbergensis was marine, since the animals and plants of the Langenberg Quarry were probably transportedallochthonously (albeit only by a short distance) from the surrounding islands. Brackish and freshwater sediments are also present in the quarry, which implies that there was occasional freshwater influx.[3] Twigs and conifer cones indicate that thearaucarianBrachyphyllum was present at the site.[24]
BesidesK. langenbergensis, other crocodilians from the Langenberg Quarry include the marineMachimosaurus hugii andSteneosaurus aff. brevirostris,[11] which would have lived offshore and fed on turtles and fish; and the amphibious generalistGoniopholis simus,[11] which subsisted on a diet of both shelly and soft prey like modern alligators.[3] The quarry is best known as the type locality of thebrachiosauridsauropoddinosaurEuropasaurus holgeri, which was aninsular dwarf.[25] Isolated teeth show that there were at least four different types oftheropods present at the locality, including themegalosauridTorvosaurus sp. as well as an additional megalosaurid and indeterminate members of theAllosauridae andCeratosauria;[26] theropod tracks from two different species (not identifiable to the family level) are also known.[1] Remains attributable todiplodocids (possibly also dwarfed) andstegosaurs have also been found,[24] alongside an indeterminatedsungaripteridpterosaur.[27]
Non-archosaurs are also present in the Langenberg Quarry. These include aparamacellodidlizard;[28] theturtlesThalassemys sp.,[29]Plesiochelys etalloni,[30] and a juvenileeucryptodiran;[31]plagiaulacidmultituberculate,[32]dryolestid, anddocodontmammals known from teeth;[24] themammaliaformStorchodon;[33] a diverseactinopterygian fish fauna dominated byLepidotes sp. but also includingMacromesodon sp.,Proscinetes sp.,Coelodus sp.,Macrosemius sp. (orNotagogus sp.),Histionotus sp.,Ionoscopus sp.,Callopterus sp.,Caturus sp.,Sauropsis sp.,Belonostomus sp., andThrissops subovatus;[34] and five morphotypes ofhybodonts plus theneoselachiansPalaeoscyllium sp., two distinctSynechodus sp., and two distinctAsterodermus sp.[35]
The Guimarota locality is located in the eastern Lusitanian Basin, which is part of the Iberian Meseta.[3] The vertebrate-bearing Guimarota-strata was deposited in a brackishlagoon that periodically received both freshwater and saltwater influxes.[4] Ecologically, the environment would have been akin to a modernmangrove swamp.[36][37] Plants known from megafossils include the horsetailsEquisetum andSchizoneura; theseed fernCaytonia; thecycadOtozamites; the araucariaBrachyphyllum;Ginkgo; and thecharophytealgaePorochara. Additionally, plant families known only from pollen includelycopods,forked ferns, possiblescaly tree ferns (which may bematoniaceans ordicksoniaceans instead),royal ferns, theseed fernSphenopteris,cypresses, andpines.[38] Most of the preserved organisms probably originated from around the swamp, although there may have been minimal transportation by water currents.[37]
Many crocodilians are known from the Guimarota mine. The marineMachimosaurus hugii is again present,[39] as isGoniopholis (although as a different species,G. baryglyphaeus).[40] Additionally,Bernissartia sp.,Lisboasaurus estesi, andLusitanisuchus mitracostatus have also been found;[41] the latter two were small, being less than 50 centimetres (20 in) in length, and likely also fed on insects likeK. guimarotae.[3] Dinosaurs from Guimarota are mainly known from teeth, and include a brachiosaurid, which is also rather small in size; theropods, includingStokesosaurus sp. (known from body fossils),Compsognathus sp., allosaurids, a ceratosaur similar toCeratosaurus, a taxon similar to the phylogenetically problematicRichardoestesia, dromaeosaurids,troodontids, andarchaeopterygiforms; and theornithopodsPhyllodon henkeli and aniguanodont similar toCamptosaurus.[42] Other diverse vertebrates, includingchondrichthyans,osteichthyans,albanerpetontidamphibians, turtles, lizards,rhamphorhynchid pterosaurs, and docodont and dryolestid mammals (includingHenkelotherium guimarotae) are also present. Invertebrates are represented by ostracods andmolluscs.[3]
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