Kubantadens

Kubantadens Temporal range: Early Cretaceous, 130–120 Ma PreꞒ Ꞓ O S D C P T J K Pg N
Mounted K. horridus skeleton cast, Collinebourg Natural History Museum
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Dinosauria
Order:	Theropoda
Family:	Joanusauridae
Genus:	Kubantadens Jour & Leon, 1933
Type species
†Kubantadens horridus Jour & Leon, 1933

Kubantadens is an extinct genus of large joanusaurid theropod dinosaur from the Kubagne Archipelago of the Early Cetaceous period of Sarpolevantia, in modern southwestern Yonderre. The genus, known from several dozen specimens ranging from nestling juveniles to mature adults, is recognized as a single species, Kubantadens horridus. K. horridus was a derived member of the joanusauridae lineage limited in age and in geographical range to the Kubagne Archipelago, living c. 130-120 million years ago. Having seemingly outcompeted every other terrestrial carnivore larger than 50 kilograms (110 lb), Kubantadens would have been the dominant apex predator of the Kubagne Archipelago ecosystem, occupying the various predatory niches of the ecosystem throughout its growth stages. Kubantadens is an often-used example of island gigantism, with fully-grown adults being estimated at almost 50% larger by mass than its closest ancestor Joanusaurus and almost two-thirds larger by mass than its nearest contemporary continental relative Metriacanthonychus.

Like other joanusaurids, Kubantadens was a large bipedal carnivorous dinosaur characterized by stocky hind limbs and extensive ornamentation of the skull bones, having horn-like protrusions over the eyes. While a single specimen, KBD 1814, has been estimated at 14.5 metres (48 ft), the average adult Kubantadens appears to have measured somewhere around 12 metres (39 ft) to 13 metres (43 ft) from nose to tail. Mass estimates for Kubantadens range from c. 1,600 kilograms (3,500 lb) to 2,500 kilograms (5,500 lb) for modal adult weight (not maximum), although the largest known specimen KBD 1814 has been estimated at anything from 2,500 kilograms (5,500 lb) to 4,000 kilograms (8,800 lb)..

Kubantadens is significant for a number of reasons: for one, it is a textbook example of island gigantism in theropod dinosaurs. The specimen KBC 1117 is also strong evidence for substantial parental care in derived joanusaurids, and by extension gives evidence to parental care in extinct theropods in general. Finally, it being the only large predator in its environment, predation on herbivores and trace fossils of large theropods can definitely be attributed to Kubantadens rather than on the Sarpolevantine mainland where multiple large theropods would have existed simultaneously, thus allowing a more definite understanding of the genus' paleoecology.

Discovery and naming

The specimen KBD 1814, the largest known Kubantadens, on display in Sainte-Catherine

Kubantadens was first discovered in 1932 by Yonderian paleontologists Jour & Leon. Based on an incomplete mandible and premaxilla as well as a complete arm, pubis and tail, Kubantadens was immediately recognized as a derived joanusaurid based on its triangular pubic boot and the pronounced chevron bases on its tail having anterior and posterior bone growth. While Falco Jour briefly entertained the idea of the fossilized skeleton being a large Joanusaurus specimen, Joanus Leon soon convinced his colleague that their find, KBP 2003, was in fact a new, closely related genus. Jour & Leon published their findings in 1933 as A Giant Joanusaurid from Cretaceous Kubagne based on their single specimen. Based on the location of the find and the large teeth of the mandible, the duo named the animal Kubantadens horridus, translating as "frightful tooth from Kubagne".

More finds followed throughout the latter Great War period including a preserved ground nest with three nestling juveniles in situ, indicating or at least suggesting substantial parental care from Kubantadens as the nestlings appeared to be beyond hatchling size by some margin. The largest known specimen of Kubantadens, KBD 1814, was discovered in 1984. KBD 1814 sported a mostly complete skeleton, missing the very tip of its tail, its right arm and right femur.

Description

Kubantadens is thought to have been one of the largest joanusaurid dinosaurs, and by extension one of the largest theropod dinosaurs, although even Kubantadens was dwarfed by its relatives Vollardisaurus and Levaretyrannus, not to mention the largest of the caphirosaurids like Caphirosaurus. While the specimen KBD 1814 has been estimated by Horner et al. at 14.5 metres (48 ft), the average adult Kubantadens would have more likely measured somewhere around 12 metres (39 ft) to 13 metres (43 ft) from nose to tail. Mass estimates for Kubantadens range from c. 1,600 kilograms (3,500 lb) to 2,500 kilograms (5,500 lb) for the average mature adult, although the largest known specimen KBD 1814 has been estimated to range from 2,500 kilograms (5,500 lb) to 4,000 kilograms (8,800 lb)..

Kubantadens was a typical large bipedal theropod, having a massive skull on a short neck, a long, slightly sloping tail, and reduced forelimbs. Each premaxilla (the bones that formed the tip of the snout) held five teeth with D-shaped cross-sections, and each maxilla (the main tooth-bearing bones in the upper jaw) had between 14 and 17 teeth; the number of teeth does not exactly correspond to the size of the bone. Each dentary (the tooth-bearing bone of the lower jaw) had between 14 and 17 teeth, with an average count of 16. The teeth became shorter, narrower, and more curved toward the back of the skull. All of the teeth had saw-like edges. They were shed easily, and were replaced continually, making them common fossils.

The skull had a pair of horn-like protrusions above and in front of the eyes. These horns were composed of extensions of the lacrimal bones, and varied in shape and size from animal to animal. The horns of Kubantadens were most likely used as socio-sexual signaling structures to attract mates and potentially to ward off or fight other Kubantadens. Like other joanusaurids, and indeed most derived theropods, Kubantadens had hollow spaces in the neck and anterior back vertebrae; such spaces, which are also found in modern theropods (that is, the birds), are interpreted as having held air sacs used in respiration. The rib cage was broad, giving it a barrel chest, especially in comparison with less derived joanusaurids like Magnalophosaurus. The forelimbs of Kubantadens were short in comparison to the hindlimbs and had three fingers per hand, tipped with large, strongly curved and pointed claws. The legs were not as long or suited for speed as those of later joanusaurids like Sentinellasaurus or Velocivenator, and the claws of the toes were also less developed. Skin impressions exist in relation to an adult Kubantadens' thigh, showing large diamond-shaped scales of roughly 2.7 square centimetres (0.42 in²) each.

Classification

Kubantadens life restoration

Kubantadens is classified taxonomically as a member of joanusauridae, making it a derived joanusaur. Kubantadens is most likely directly descendeded from Joanusaurus davignoni, having seemingly come about immediately around the extinction of the former. As such Kubantadens is considered a polytomic sister taxon to Metriacanthonychus, which is also thought to be the most direct descendant of Joanusaurus. The reason for the divergent evolution of the two taxa is most likely to be found in the vastly different conditions and ecosystem that Kubantadens found itself in on the Kubagne Archipelago to that which Metriacanthonychus experienced on the Sarpolevantine mainland.

Despite the genus' longevity of c. ten million years, Kubantadens is generally only considered to consist of a single species, K. horridus. While specimens of newer Kubantadens (that is, closer to 120 million years old than 130 million years old) tend to be larger than their predecessors, in keeping with Bergmann's Law, the newer specimens do not appear to be sufficiently different to justify naming as a subspecies. The discrepancy in size has also been suggested to simply reflect the randomness of fossil preservation, rather than a trend towards an increase in size.

Joanusauroidae	Projoanusaurus Magnalophosaurus Sarponychidae Joanusauridae Everardtadens Joanusaurus Metriacanthonychus Kubantadens

Paleoecology

Cast of a Kubantadens skeleton

Like other theropod dinosaurs, Kubantadens was homeothermic, a type of "warm-bloodedness" on a level somewhere between mammals and lizards, giving it a stable core body-temperature. The high metabolism as a result of the homeothermy would have supported rapid growth. While estimates vary, it has been suggested that Kubantadens would have taken around 16-20 years to grow to full size. Kubantadens' cranial construction suggests a strong and fast bite, and various features of the rear part of the skull indicate that it would have been well-suited for moving the skull sideways in relation to the front neck vertebrae, making it adept at swiping bites on the horizontal plane.

By far the largest carnivore in its environment, Kubantadens would have been an apex predator feeding on herbivorous dinosaurs, pterosaurs, mammals and in all likelyhood other Kubantadens opportunistically. A 2004 study suggested opportunistic cannibalism had taken place between Kubantadens, having studied some Kubantadens specimens with tooth marks in the bones that could only be attributed to another Kubantadens based on their size. The tooth marks were identified in the humerus, tibia and metatarsals, and this was seen as evidence for opportunistic scavenging, rather than wounds caused by intraspecific combat. The study suggested that it would have been difficult in a fight to reach down to bite in the feet of a rival, making it more likely that the bitemarks were made on a carcass. As the bitemarks were made in body parts with relatively scantly amounts of flesh, it is suggested that the Kubantadens was feeding on a cadaver in which the more fleshy parts had already been consumed.

Based on the specimen KBC 1117 of three nestling juveniles in situ in a ground nest, Kubantadens has been suggested to exhibit substantial parental care for their offspring. Similar behaviour has since been evidenced in other joanusaurids, not least in Sentinellasaurus where a specimen was found in relation to a nest with large theropod eggs. This supports the wider argument that joanusaurid dinosaurs, and mesozoic theropods in general, exhibited parental care.

See also

• Joanusaurids
• Kubagne Archipelago
• Paleontology in Yonderre
• History of paleontology