| Kayentavenator | |
|---|---|
Scientific classification | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Clade: | Dinosauria |
| Clade: | Saurischia |
| Clade: | Theropoda |
| Clade: | Tetanurae |
| Genus: | †Kayentavenator Gay,2010 |
| Species: | †K. elysiae |
| Binomial name | |
| †Kayentavenator elysiae Gay, 2010 | |
Kayentavenator (meaning "Kayenta hunter") is a genus of smallcarnivoroustetanurandinosaur that lived during theEarly Jurassic Period; fossils were recovered from theKayenta Formation of northeastern Arizona and were described in 2010.[1]
Theholotype specimen ofK. elysiae is a juvenile, as shown by unfusedneural spines[1] and would have stood about 0.5 metres (1.6 ft) high at the hip. The adult size ofKayentavenator is unknown. The inclusion of apubic fenestra is one of the characteristics thatGay uses to setKayentavenator apart from the contemporaneous, and better knownDilophosaurus.[1] AsDilophosaurus lacks a pubic fenestra as a subadult or an adult,[2] it is unlikely that it had one during any stage ofontogeny.Apomorphies include an ellipsoidacetabulum, the greatertrochanter and the head of the femur having been fused, a mediodistal crest that extends 50% ofthe length of the femur, as well as a prominent accessorycondyle on the medial femoral condyle, a groove in dorsal surface of the femoral head that extends out from the centerline of the body, and highly constricted ("waisted") caudal vertebra centra.[1]
The only known fossils ofKayentavenator were excavated by theUniversity of California Museum of Paleontology from theNavajo Reservation inArizona. It was briefly described in 2003[3] and was fully described in 2010 based on a partialfossilskeleton, consisting of part of the pelvis, partial hindlimbs, and vertebrae.[1]
| Cladogram of Theropods (Gay 2010[1]) | |||||||||||||||||||||||||||||||||||||||
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Timothy Rowe originally assigned the holotype specimen ofKayentavenator to thecoelophysoidSyntarsus kayentakatae (nowMegapnosaurus kayentakatae orCoelophysis kayentakatae).[4] It is unlikely thatKayentavenator is actually congeneric withMegapnosaurus kayentakatae due to the number of tetanuran characters thatKayentavenator possesses andM. kayentakatae lacks, such as thepubic fenestra and a sharp ridge on the medial side of thetibia.[1] Acladistic analysis of the remains showedKayentavenator to lie outside ofCoelophysidae, and was closer toAllosaurus.[1] This would makeKayentavenator the oldest knowntetanuran from North America. The fragmentary remains ofKayentavenator make this open to further interpretation.
Mortimer (2010) noted the uncertainty of whetherKayentavenator is a validly named taxon based on the rules of ICZN and the absence of published evidence thatKayentavenator is the same taxon asS. kayentakatae, while questioning whetherKayentavenator is a tetanurine.[5][6] In the 2012 conference abstract,Martin Ezcurra treatedKayentavenator as a junior synonym ofS. kayentakatae based on his unpublished phylogenetic matrix.[7] In 2017, Ezcurra treated the holotype ofKayentavenator as a specimen ofS. kayentakatae.[8]
The only known specimen ofKayentavenator, UCMP V128659, was recovered from the Silty Facies Member of theKayenta Formation, in northeastern Arizona. A definitive radiometric dating of this formation has not yet been made, and the available stratigraphic correlation has been based on a combination of radiometric dates from vertebrate fossils, magnetostratigraphy, and pollen evidence.[9] It has been surmised that the Kayenta Formation was deposited during theSinemurian andPliensbachian stages of the Early Jurassic Period or approximately 199 to 182 million years ago.[10] The Kayenta Formation is part of the Glen Canyon Group that includes formations not only in northern Arizona but also parts of southeastern Utah, western Colorado, and northwestern New Mexico. The formation was primarily deposited by rivers. During the Early Jurassic period, the land that is now the Kayenta Formation experienced rainy summers and dry winters. By the Middle Jurassic period it was being encroached upon from the north by a sandy dune field that would become theNavajo Sandstone.[11] The animals were adapted to a seasonal climate and abundant water could be found in streams, ponds and lakes.
Kayentavenator shared itspaleoenvironment with other dinosaurs, such as several theropods includingDilophosaurus,Coelophysis kayentakatae, and the "Shake N Bake" theropod, thebasalsauropodomorphSarahsaurus,[12]heterodontosaurids, and the armored dinosaursScelidosaurus andScutellosaurus. The Kayenta Formation has produced the remains of three coelophysoid taxa of different body size, representing the most diverse ceratosaur fauna yet known.[13] The Kayenta Formation has yielded a small but growing assemblage of organisms.[14] Vertebrates present in the Kayenta Formation at the time ofKayentavenator includedhybodont sharks, indeterminatebony fish,lungfish, salamanders, the frogProsalirus, thecaecilianEocaecilia, the turtleKayentachelys, asphenodontian reptile, various lizards, and thepterosaurRhamphinion. Also present were thesynapsidsDinnebitodon,Kayentatherium,Oligokyphus,morganucodontids,[15] the possible early true mammalDinnetherium, and aharamiyid mammal. Several earlycrocodylomorphs were present includingCalsoyasuchus,Eopneumatosuchus,Kayentasuchus andProtosuchus.[14][15][16][17]
Vertebrate trace fossils from this area includedcoprolites[18] and the tracks oftherapsids, lizard-like animals, and dinosaurs, which provided evidence that these animals were also present.[19] Non-vertebrates in this ecosystem included microbial or "algal" limestone,[18] freshwater bivalves, freshwater mussels and snails,[11] andostracods.[20] The plant life known from this area included trees that became preserved as petrified wood.[16]
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