| Concavenator | |
|---|---|
 | |
| Holotype specimen in articulation | |
Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Reptilia |
| Clade: | Dinosauria |
| Clade: | Saurischia |
| Clade: | Theropoda |
| Clade: | †Carcharodontosauria |
| Genus: | †Concavenator Ortega et al.2010 |
| Species: | †C. corcovatus |
| Binomial name | |
| †Concavenator corcovatus Ortega et al. 2010 | |
Concavenator (meaning "Cuenca hunter") is agenus ofcarcharodontosauriandinosaur that lived inSpain during theEarly Cretaceous epoch, about 125 million years ago. The genus contains a single species,Concavenator corcovatus, named and described in 2010 from a nearly complete skeleton collected from the Las Hoyas fossil site of theLa Huérguina Formation.
Concavenator was a medium-sized carcharodontosaurian, reaching about 5–6 m (16–20 ft) in length and 320–400 kg (710–880 lb) in weight. Unlike most carcharodontosaurians, the neural spines of the last dorsal (back) vertebrae were tall, creating asail-like structure.
The firstfossil remains ofConcavenator were recovered fromlimestone slabs of Las Hoyas locality (considered aKonservat-Lagerstätten; deposits of exceptional fossil preservation) ofCuenca Province,Spain, which belongs toLa Huérguina Formation. The remains were represented by an articulated, nearly complete skeleton of a theropod dinosaur individual encased in limestone, comprising the skull, ten cervical vertebrae, thirteen dorsal vertebrae (with the last two presenting an unusual elongation), five sacral vertebrae, thirty caudal vertebrae, a partial pectoral girdle and arm, the pelvic girdle and partial legs, as well as ribs. This specimen was also found preserving integument traces, such as scale impressions on the feet and tail, which is characteristic of many of thelithographic limestones within La Huérguina Formation.[1]
In 2010, the specimen was catalogued MCCM-LH 6666 and described by paleontologists Francisco Ortega, Fernando Escaso, and José Luis Sanz, used as theholotype for naming the new genus and species of carcharodontosaurid dinosaurConcavenator corcovatus. The specimen belongs to the collection of theScience Museum of Castilla-La Mancha. Thegeneric name,Concavenator, is derived from theLatinConca, in reference to the region of discovery, the Cuenca Province, andvenator, which means hunter. Thespecific name,corcovatus, is taken from the Latincorcovatus, giving a glimpse onto the hump-like structure formed by the elongated dorsal vertebrae. In their description, the team noted that some anatomical elements had to be leftunprepared (without removing the encasing rock), given the delicate nature of the preserved integument traces.[1] Though initially described in 2010, a series of monographs about the taxon and holotype were published later, including examinations of the feet integument in 2015,[2] as well as several anatomical redescriptions of the specimen in 2018.[3][4][5]
Concavenator was a medium-sized carcharodontosaurian, reaching 5–6 m (16–20 ft) long and 320–400 kg (710–880 lb).[6][7][8] It possessed several unique features, including the two extremely tall vertebrae in front of the hips that formed a tall, narrow, pointed crest (possibly supporting a hump) on the dinosaur's back.[1] The function of such crests, however, is currently unknown. Paleontologist Roger Benson from theUniversity of Cambridge speculated that one possibility is that "it is analogous to head-crests used in visual displays", but the Spanish scientists who discovered it noted it could also be a thermal regulator.[9]
Concavenator had structures resembling quill knobs on itsulna, a feature known only in birds and other feathered theropods, such asdromaeosaurids. Quill knobs are created by ligaments which attach to the feather follicle and, since scales do not form from follicles, the authors ruled out the possibility that they could indicate the presence of long display scales on the arm. Instead, the knobs have been thought to probably anchor simple, hollow, quill-like structures. Such structures are known in bothcoelurosaurs, such asDilong, and in someornithischians, likeTianyulong andPsittacosaurus. If the ornithischian quills are homologous with bird feathers, their presence inConcavenator and otherallosauroids would be expected.[1] However, if ornithischian quills are not related to feathers, the presence of these structures inConcavenator would show that feathers had begun to appear in earlier, more primitive forms than coelurosaurs.
Feathers or related structures would then likely be present in the first members of the cladeNeotetanurae, which lived in theMiddle Jurassic. No impressions of any kind of integument were found near the arm, although extensive scale impressions were preserved on other portions of the body, including broad, rectangular scales on the underside of the tail, bird-like scutes on the feet, and plantar pads on the undersides of the feet.[1]
However, the significance of the 'quill knobs' remains controversial, as some amount of skepticism has been raised among experts on the validity of the interpretation that the ulnar bumps represent quill knobs.[10] Christian Foth and colleagues noted that the quill knobs ofConcavenator were on the anterolateral side of the ulna. They suggest they were intermuscular lines that acted as tendon attachments.[11] The hypothesis that the bumps along the ulna represented muscular insertion points or ridges was subsequently examined and the results were presented at the 2015 meeting of theSociety of Vertebrate Paleontology. Elena Cuesta Fidalgo, along with two of the researchers who initially describedConcavenator (Ortega and Sanz), attempted to reconstruct its forearm musculature to determine if the ulnar bumps would be explained as an inter-muscular ridge. They identified the insertion point for the major arm muscles and determined that the row of bumps could not have been located between any of them. They found that the only possibility was that the bumps could be an attachment scar for theM. anconeus muscle. However, this is unlikely because this muscle normally attaches to a smooth surface without marks or bumps on the underlying bone. They argued that the most likely explanation for the bumps was their initial interpretation as feather quill knobs. The authors admitted that it was unusual for quill knobs to form along the posterolateral surface of the bone, but also noted that the same arrangement is found in some modern birds, like theMoorhen.[12]
In 2018, Cuesta Fidalgo published her doctorate thesis on the anatomy ofConcavenator, which argued that the ulna was preserved in lateral view. This means that the ulnar bumps were positioned posterolaterally instead of anterolaterally as Cau and Mortimer claimed. Cuesta Fidalgo noted that theproximal part of the ulna is affected by fracturing and abrasion, with certain features that would have shifted when compared to their position in the bone while the animal was alive. For example, in the fossil, the lateral process of the ulna is positioned further posteriorly than the ulnar bumps. InAllosaurus andAcrocanthosaurus, the lateral process is on the lateral (rather than posterior) part of the bone, which would seem to support the ulnar bumps being anterolateral in position if the lateral process was truly preserved in lateral orientation inConcavenator. However, Cuesta Fidalgo described how the lateral process was distorted posteriorly when compared to the bumps and was not valid evidence for the claim that the ulna had shifted into anterior view. The ulna's distortion (as well as genus-specific proportions) means that precise comparisons toAllosaurus andAcrocanthosaurus would be misleading.[13] As Cuesta Fidalgo and her colleagues explained in 2015, the ulnar bumps could not be an intermuscular line if the bone is preserved in lateral view.[12] Cuesta Fidalgo and her colleagues pointed out that these bumps on the ulna are posterolateral, which is unlike that of interosseous ligaments.[3]
In their 2022 description of the giganotosaurinMeraxes,Concavenator was recovered as an early-diverging member of the Carcharodontosauridae, in an unresolvedpolytomy withEocarcharia,Lajasvenator, andLusovenator. The results of theirphylogenetic analyses are displayed in thecladogram below:[14]
Media related toConcavenator at Wikimedia Commons
Data related toConcavenator at Wikispecies
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