| Chindesaurus | |
|---|---|
 | |
| Skeletal reconstruction ofChindesaurus bryansmalli. Known elements in white and light grey, and unknown in dark gray. Missing elements based onTawa hallae. | |
Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Reptilia |
| Clade: | Dinosauria |
| Clade: | Saurischia |
| Genus: | †Chindesaurus Long & Murray,1995 |
| Species: | †C. bryansmalli |
| Binomial name | |
| †Chindesaurus bryansmalli Long & Murry, 1995 | |
| Synonyms | |
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Chindesaurus (/ˌtʃɪndɪˈsɔːrəs/CHIN-diss-OR-əs) is an extinctgenus of basalsaurischiandinosaur from theLate Triassic (213-210million years ago) of thesouthwestern United States. It is known from a single species,C. bryansmalli, based on a partial skeleton recovered fromPetrified Forest National Park inArizona. The original specimen was nicknamed "Gertie", and generated much publicity for the park upon its discovery in 1984 and airlift out of the park in 1985. Other fragmentary referred specimens have been found in Late Triassic sediments throughout Arizona,New Mexico, andTexas, but these may not belong to the genus.[1]Chindesaurus was abipedalcarnivore, approximately as large as awolf.[2]
Chindesaurus's classification is debated, and various papers have had different conclusions on its affinities. Its fossils were originally believed to belong to "prosauropods" (basalsauropodomorphs), but its original description and numerous subsequent papers argued that it was aherrerasaurid[3][4][5] or herrerasaurian.[6] A 2019 redescription of itsholotype consideredChindesaurus to be atheropod closely related toTawa, a slightly smaller dinosaur known from the Hayden Quarry ofGhost Ranch, New Mexico.[1]
Although many specimens have been referred toChindesaurus, only one specimen has enough material to remain within the genus with certainty.[1] This specimen,holotype PEFO 10395, is a partial skeleton, found withinPetrified Forest National Park inApache County, Arizona. PEFO 10395 was discovered in 1984 by Bryan Small, who recovered the skeleton from a bluemudstone layer in theChinle Formation's Upper Petrified Forest Member.[3][8][1] Based onU-Pb dating of overlying and underlying units, the mudstone layer was deposited about 213 to 210 million years ago, during theNorian stage of theTriassic.[1]
PEFO 10395 mainly consists ofvertebrae, limb bones, and hip fragments. Vertebrae include several partialcervical (neck)dorsal (back), andcaudal (tail) vertebrae, along with twosacral (hip) vertebrae, achevron, andrib fragments. Each of the three bones making up the hip (theilium,pubis, andischium) are represented by isolated fragments. Leg bones include a complete rightfemur, the upper part of the left femur, an incomplete righttibia, and a rightastragalus bone of the ankle.[1][3] A single serrated tooth has also been considered as part of the specimen,[9] but this may be in error.[10]
When the holotype specimen was discovered, it was nicknamed "Gertie" (afterGertie the Dinosaur) and received much publicity. "Gertie" was subsequently airlifted by helicopter on June 6, 1985, and brought to theUniversity of California Museum of Paleontology (UCMP) inBerkeley, CA, where it was prepared over the next several years.[1] The anniversary of the airlift and the media interest it generated for Petrified Forest National Park is celebrated at the park every year. It was also initially known as the "Chinde Point dinosaur", referring to an overlook close to the site where it was recovered. "Gertie" was described and given abinomial name by R.A. Long and P.A. Murry in1995. Thegeneric name combines Chinde Point with theGreek word "sauros" (σαυρος) (meaning "lizard"). Thespecific name,bryansmalli, honors Bryan Small, who discovered the skeleton.[3]
Native American staff and consultants of the national park have long voiced disapproval over the name of Chinde Point.[11][12][7] The area was named after theNavajo wordchindi (ataboo concept referring to an unhealthy negative miasma left at a person's place of death). Several apocryphal explanations for the origin of the name are recorded by theU.S. Board on Geographic Names (BGN).[11][7] A new name, Hózhó Point, was proposed in 2019[11] and formally adopted in September 2023,[7] after approval by theNavajo,Hopi,Zuni,Tohono O'odham, andPascua Yaqui. Two other overlooks in the park acquiredHopi andZuni names (Tatàypi Point and Hamilili Point, respectively) after negotiations with the Hopi Tribe.[7] Hózhó is a Navajo word which expresses positive concepts such as balance, harmony, and beauty.[11][7]
Several more incomplete specimens have been referred to the genus. These specimens consist of various vertebrae and femur fragments found throughout the American southwest. Eight referred specimens are stored at PEFO (Petrified Forest National Park, AZ), where the holotype was discovered. Two are stored at the UCMP (University of California Museum of Paleontology), where the holotype was prepared. Up to six more are stored at theNew Mexico Museum of Natural History and Science (NMMNH) inAlbuquerque, NM, with at least several of them having been discovered in theBull Canyon Formation ofNew Mexico.[10][1] A complete femur, GR 226, was discovered in 2006 at the Hayden Quarry of Ghost Ranch, NM, where it is now stored.[13][1]
Though most specimens referred toChindesaurus hail fromNorian-age formations of Arizona and New Mexico, there are exceptions: TMM 31100–523, which consists of a proximal femur, was discovered in theCarnian-ageColorado City Formation ofTexas. It is currently housed in the collections of theTexas Memorial Museum inAustin, TX. A similar case involves UMMP 8870, a partial ilium first described in 1927. It was recovered from the Carnian?-ageTecovas Formation of Texas, and now housed at theUniversity of Michigan (UMMP) inAnn Arbor, MI.[3][1] However, UMMP 8870 may represent a separate species of early dinosaur,Caseosaurus crosbyensis.[9][5] The referred Texas specimens ofChindesaurus were at one point believed to be the oldest dinosaur fossils in the world.[3]
Though specimens referred toChindesaurus are widely distributed and sometimes well-preserved, none of them exhibit features unique to the genus. The referral of two specimens (NMMNH P16656 and NMMNH P17325) toChindesaurus came under question as soon as 2007.[10] Marshet al. (2019) argued that only the holotype specimen ofChindesaurus should be considered as belonging to the genus. They removed all specimens except for the holotype from the genus, placing the rest as indeterminate material from theChindesaurus +Tawa clade of their analysis.[1]
Long & Murry reconstructedChindesaurus with a stout body, long legs, a fairly long neck, and a total estimated length of 3 to 4 meters (9.8 to 13.1 feet).[3] Benson & Brusatte (2012) suggested thatChindesaurus was smaller, up to 2 to 2.3 metres (6.6 to 7.5 ft) in length.[14] Holtz (2012) estimated thatChindesaurus had a length of about 2 meters (6.6) feet and a weight equivalent to that of a wolf (23–45 kg, or about 50-100 pounds).[2] The skeletal anatomy ofChindesaurus is incompletely known, so these full body estimates are very rough approximations. The holotype specimen may not be fully grown due to its unfused ankle and dorsalneurocentral sutures. However, these features may not be fully correlated with development in early dinosaurs, and the specimen has other traits indicating a post-juvenile stage, such as a trochanteric shelf and fused caudal neurocentral sutures.[1]
Thecervical (neck)vertebrae, at least near the head, had a low keel along the front half of their lower edge. They also had a pair of shallow oval-shaped depressions on their sides, similar to those found inTawa,Liliensternus, andCryolophosaurus. Thedorsal (trunk) vertebrae are deep, wide, and fairly short (from front-to-back), closer to the condition in herrerasaurids rather thanTawa andcoelophysoids. Both the sides and the lower edge of each dorsal are constricted, and small pockets lie below the sutures with theneural arch. These pockets, known ascentrodiapophysealfossae, are ancestral to dinosaurs but lost by mosttheropods.Neural spines expand outwards and backwards, forming "spine-tables", structures which are otherwise only observed inHerrerasaurus andDilophosaurus among potential theropods.[3][10][1]
The two preservedsacral (hip) vertebrae are wide and not fused to each other. The assumption thatChindesaurus had only two sacrals has been vital to its traditional identity as a herrerasaurid.[3] The rear side of the first sacral has a vertical ridge extending up to a large pit, which may be ahypantrum. Large sacral ribs extend outwards from the front half of each sacral vertebrae. The sacral ribs have an inverted T-shaped cross-section when seen from the side. Thecaudal (tail) vertebrae are large at the base of the tail and elongated towards the tip of the tail. Several low ridges extend towards theprezygapophyses at the front of the distal caudal vertebra. The prezygapophyses themselves are fairly short, unlike those ofherrerasaurids or most theropods. Aneural spine rises up abruptly in the last third of each caudal.Chevrons curve backwards and are thinnest at their mid-length.[3][1]
The postacetabular process (rear blade) of theilium is low, with a horizontal ridge on its inner edge and a large roughly-textured tubercle on its outer surface. These characteristics are also known inCaseosaurus. There is no distinct brevis fossa, also likeCaseosaurus and herrerasaurids. Both the pubic and ischiadic peduncles of the ilium expand lengthwise towards their lower edges. Unlike herrerasaurids, the supraacetabular crest of the ilium does not extend as far forwards as its contact with the pubis. Thepubis is thin, straight, and slightly curved back, widening slightly towards the ilium. On the other hand, theischium seems to widen slightly away from the ilium.[10][1]
Thefemur is large and sigmoid, with a smooth, rectangular femoral head. LikeTawa (but unlike coelophysoids), the anterior trochanter has the appearance of a bulbous ridge, not separated from the shaft by a cleft. However,Chindesaurus lacks a groove at the top of its femoral head, possesses a trochanteric shelf, and has a dorsolateral trochanter which is low and rounded, traits which contrast withTawa. Thefourth trochanter is low and located further distally than that ofHerrerasaurus. The lower end of the femur has two distinct condyles which are triangular in cross-section. Thetibia is very similar to that ofTawa in several respects. For example, the rear face of the upper end of the tibia is nearly straight, with the exception of a large notch on its medial half and a smaller notch slightly lateral to it. Moreover, the cnemial crest running down the front of the tibia is quite low, <35% the total anteroposterior thickness of the bone. Finally, the lower end of the tibia has a large and triangular posterolateral process which extends downwards and outwards from the rest of the bone, a trait also shared byLesothosaurus andGuaibasaurus. The front edge of theastragalus has a deep and broad cleft which subdivides the bone vertically. This cleft actually extends onto the lower surface of the bone, giving it a characteristic "glutealiform" shape shared withTawa. There is a distinct ascending process on the upper and outer part of the astragalus, surrounded by a system of pits, ridges, and depressions which connect to the tibia.[10][1]
Chindesaurus has been difficult to classify, and has been recovered in several different positions at the base of thesaurischian family tree. When it was first discovered in 1984, the fossil specimen which would eventually be namedChindesaurus was thought to be a "prosauropod" (basalsauropodomorph).[15][3][1] When it was finally described and named a decade later by Long & Murry (1995), they regarded it as aherrerasaurid. This interpretation has been followed by many paleontologists since then, often supported byphylogenetic analyses.[3][4][16][17][18][5]
Nesbittet al. (2007) and Irmiset al. (2007) argued thatChindesaurus was a probablebasalsaurischian dinosaur, and noted that it shares a wide range of characteristics with several lineages of basal saurischians, making any classification problematic.[10][13] Rauhut (2003) noted that the medially expandedbrevis shelf ofChindesaurus resembles that of "crurotarsans" (pseudosuchians), unlike that of most dinosaurs, which is usually laterally expanded.[19]
A partial ilium originally assigned toChindesaurus, from theTecovas Formation ofTexas, was later placed in its own genus and species,Caseosaurus crosbyensis, by Huntet al. (1998).[9] Langer (2004) argued that this separation was probably in error, and that the two forms represent the same species.[20] Nesbittet al. (2007) corroborated this, stating that the differences betweenCaseosaurus andChindesaurus cited by Huntet al. (1998) were probably a result of size-related variation. However, Nesbittet al. refrained from formally synonymizing the two taxa due to the fragmentary nature ofChindesaurus's ilium.[10] Baron & Williams redescribedCaseosaurus in 2018, and considered it to be a valid herrerasaurian taxon closely related to, but not within, the familyHerrerasauridae, in the larger clade Herrerasauria.[5] An analysis by Novaset al. (in 2021) also placedChindesaurus as a non-herrerasaurid herrerasaurian, forming a clade withDaemonosaurus andTawa (also see below)[6]
The following is acladogram based on the phylogenetic analysis by Sueset al. (2011), one of many studies which argued thatChindesaurus is aherrerasaurid.[17]
A phylogenetic analysis by Cabreiraet al. (2016) found an unusual result, whereChindesaurus was placed as the sister taxon ofTawa hallae, a carnivorous dinosaur from the Hayden Quarry ofGhost Ranch inNew Mexico.[21]Tawa lived at roughly the same time as the holotype specimen ofChindesaurus, and material referred toChindesaurus has also been found at the Hayden Quarry.[13][1] ThoughChindesaurus was often considered a herrerasaurid andTawa was often considered a theropod, this study suggested that neither position was correct. Instead, it placed theChindesaurus +Tawaclade within basal Saurischia, prior to the split between sauropodomorphs and theropods.[21] AChindesaurus +Tawa clade was also found in a revision to Baronet al. (2017)'s controversialOrnithoscelida hypothesis.[22]
The hypothesis of close relations toTawa was elaborated upon in 2019, when the holotype specimen ofChindesaurus was redescribed by Adam D. Marsh, William G. Parker, Max C. Langer, and Sterling J. Nesbitt. They included a phylogenetic analysis which placed theChindesaurus + Tawa clade in the base of Theropoda, a similar position to that first described forTawa.Their sister-taxon relationship was supported by oneapomorphy, or unique derived trait: a posterior margin of the proximal end of the tibia which is divided by two notches. It was also supported by the absence of an oblique ligament sulcus on the rear of the femoral head, a low cnemial crest and prominent posterolateral process of the tibia, and a low astragalus with a prominent anterior groove. The authors noted that two right tibiae from theCooper Canyon Formation may be referable to this clade based on their possession of two notches on posterior margin of the proximal tibia.Guaibasaurus may also belong to the clade based on its tapering posterolateral process of the distal end of the tibia.[1]
The following cladogram represents the phylogenetic analysis of Marshet al. (2019), recovering aChindesaurus +Tawa clade in basal Theropoda:[1]
The UpperPetrified Forest National Park member of theChinle Formation was an ancient floodplain wherephytosaurs,rauisuchids,archosaurs,pseudosuchians, and othertetrapods lived and competed with the dinosaurChindesaurus and its relativeCoelophysis for resources. This paleoenvironment also had abundantlungfish andclams.
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