Brachytrachelopan is a short-necked sauropod dinosaur from the Late Jurassic (Oxfordian to Tithonian) of Argentina. The holotype and only known specimen (Museo Paleontológico Egidio Feruglio MPEF-PV 1716) was collected from an erosional exposure of fluvial sandstone within the Cañadón Calcáreo Formation on a hill approximately 25 kilometres (16 mi) north-northeast of Cerro Cóndor, Chubut Province, in west-central Argentina, South America. Though very incomplete, the skeletal elements recovered were found in articulation and include eight cervical, twelve dorsal, and three sacral vertebrae, as well as proximal portions of the posterior cervical ribs and all the dorsal ribs, the distal end of the left femur, the proximal end of the left tibia, and the right ilium. Much of the specimen was probably lost to erosion many years before its discovery. The type species is Brachytrachelopan mesai. The specific name honours Daniel Mesa, a local shepherd who discovered the specimen while searching for lost sheep. The genus name translates as "short-necked Pan", Pan being the god of the shepherds.
Rauhut et al. 2005
Rauhut et al. 2005
This taxon's very short neck (approximately 40% shorter than other dicraeosaurids and the shortest of any known sauropod) is evidence that this lineage specialized to fill an ecological niche not exploited by other members of this infraorder. Small for a sauropod, Brachytrachelopan measured less than 10 metres (33 ft) in length. Rauhut et al. (2005, 670) note that the high degree of fusion present between the preserved neural arches and their respective centra, as well as fusion between the sacral centra, sacral neural arches, and sacral neural spines is evidence that the holotype does not represent a juvenile animal. Hence, the small body size is not a relic of ontogeny.
Rauhut et al. (2005, 670) diagnose Brachytrachelopan as differing from all other sauropods in the following respects: "...individual cervical vertebrae being as long as, or shorter in anteroposterior length than, high posteriorly. Further apomorphies...include a pronounced, pillar-like centropostzygapophyseal lamina in the cervical vertebrae, a pronounced anterior inclination in the mid-cervical neural spines, with the tip of the spine extending beyond the anterior end of the centrum, and anterior dorsal neural spines one to six with vertical bases and anteriorly flexed tips."
Following a cladistic analysis of 27 sauropod taxa and 154 anatomical characters, Rauhut et al. (2005, 671-672; Fig. 2) assigned Brachytrachelopan to the Dicraeosauridae, proposing that, within this clade, it should be considered to have a sister group relationship to the Late Jurassic African taxon Dicraeosaurus, instead of to Amargasaurus from the Lower Cretaceous of South America. Rauhut et al. (2005, 671) conclude this is indicative of a rapid evolutionary radiation and dispersal of the Dicraeosauridae following the separation of the continents of the Southern and Northern Hemispheres during the latest Middle Jurassic.
The following cladogram by Tschopp and colleagues (2015) shows the presumed relationships between members of the Dicraeosauridae:
Rauhut and colleagues in 2005 noted that the tendency towards shorter-necks seen in dicraeosaurids, and most evident in Brachytrachelopan, runs counter to the lengthening of the neck seen in most sauropod lineages (brachiosaurids, titanosaurs, diplodocids, etc.) and indicates that this group of sauropods was "progressively adapting for low browsing and might have been specialized on specific food sources, as has been suggested for Amargasaurus and Dicraeosaurus." Moreover, the morphology of the cervical neural arches in Brachytrachelopan would have significantly restricted dorsal flexion of neck and most likely indicates that this sauropod was specialized to a diet of plants "growing at heights of between about 1 and 2 m." Rauhut and colleagues also suggested that diet may have been a limiting factor in body size among dicraeosaurids, and that this may have placed them in the same ecological niche as "large low-browsing iguanodontian ornithopods." Such large iguanodontians are absent from the Late Jurassic Gondwanan sediments that have produced all known fossils of dicraeosaurids, while they are abundant in similar ecosystems of the same age in North America, where dicraeosaurids are absent. This may indicate that large iguanodontians and dicraeosaurids (especially Brachytrachelopan) were ecological analogs, resulting from parallel evolution in two distantly related dinosaurian lineages.
Amargasaurus (; "La Amarga lizard") is a genus of sauropod dinosaur from the Early Cretaceous epoch (129.4–122.46 mya) of what is now Argentina. The only known skeleton was discovered in 1984 and is virtually complete, including a fragmentary skull, making Amargasaurus one of the best-known sauropods of its epoch. Amargasaurus was first described in 1991 and contains a single known species, Amargasaurus cazaui. It was a large animal, but small for a sauropod, reaching 9 to 10 meters (30 to 33 feet) in length. Most distinctively, it sported two parallel rows of tall spines down its neck and back, taller than in any other known sauropod. In life, these spines most likely could have stuck out of the body as solitary structures that supported a keratinous sheath. An alternate hypothesis, now less favored, postulates that they could have formed a scaffold supporting a skin sail. They might have been used for display, combat, or defense.
Amargasaurus was discovered in sedimentary rocks of the La Amarga Formation, which dates back to the Barremian and late Aptian stages of the Early Cretaceous. A herbivore, it shared its environment with at least three other sauropod genera, which might have exploited different food sources in order to reduce competition. Amargasaurus probably fed at mid-height, as shown by the orientation of its inner ear and the articulation of its neck vertebrae, which suggest a habitual position of the snout 80 centimeters (31 inches) above the ground and a maximum height of 2.7 meters (8.9 feet). Within the Sauropoda, Amargasaurus is classified as a member of the family Dicraeosauridae, which differs from other sauropods in showing shorter necks and smaller body sizes.Bajadasaurus
Bajadasaurus is a genus of sauropod dinosaur from the Early Cretaceous epoch (late Berriasian to Valanginian stages) of northern Patagonia, Argentina. It was first described in 2019 based on a single specimen found in 2010 that includes a largely complete skull and parts of the neck. The only species is Bajadasaurus pronuspinax. The genus is classified as a member of the Dicraeosauridae, a group of comparatively small and short-necked sauropods that lived from the Early or Middle Jurassic to the end of the Early Cretaceous.
Bajadasaurus sported bifurcated, extremely elongated neural spines extending from the neck vertebrae. Similar elongated spines are known from the closely related and more completely known Amargasaurus. Various possible functions have been proposed for these spines in Amargasaurus, with the 2019 description of Bajadasaurus suggesting that they could have served as passive defense against predators in both genera. The skull was gracile and equipped with around 44 teeth that were pencil-shaped and restricted to the front of the jaws. The eye openings of Bajadasaurus were exposed in top view of the skull, possibly allowing the animal to look forwards while feeding. Bajadasaurus was discovered in sedimentary rocks of the Bajada Colorada Formation, and its environment resembled a braided river system. It shared its environment with other dinosaurs including the sauropod Leinkupal and different theropods.Brasilotitan
Brasilotitan is a genus of titanosaurian sauropod dinosaur from the Late Cretaceous (early Maastrichtian) Adamantina Formation of Brazil. The type species is Brasilotitan nemophagus.Dicraeosauridae
Dicraeosauridae is a family of diplodocoid sauropods who are the sister group to Diplodocidae. Dicraesaurids are a part of the Flagellicaudata, along with Diplodocidae. Dicraeosauridae includes genera such as Amargasaurus, Suuwassea, Dicraeosaurus, and Brachytrachelopan. Specimens of this family have been found in North America, Africa, and South America. Their temporal range is from the Early or Middle Jurassic to the Early Cretaceous. Few dicraeosaurids survived into the Cretaceous, the youngest of which was Amargasaurus.The group was first described by German paleontologist Werner Janensch in 1914 with the discovery of Dicraeosaurus in Tanzania. Dicraeosauridae are distinct from other sauropods because of their relatively short neck size and small body size.The clade is monophyletic and well-supported phylogenetically with thirteen unambiguous synapomorphies uniting it. They diverged from Diplodocidae in the Mid-Jurassic, as evidenced by the diversity of dicraeosaurids in both South America and East Africa when Gondwana was still united by land. However, there is some disagreement among paleontologists on the phylogenetic placement of Suuwassea, the only genera of the Dicraeosauridae to be found in North America. It has been characterized as a basal dicraeosaurid by some and a member of the Diplodocidae by others. The placement of Suuwassea within Dicraeosauridae or Diplodocidae has substantial biogeographic implications for the evolution of Dicraeosauridae.Dicraeosaurus
Dicraeosaurus (Gr. δικραιος, dikraios "bifurcated, double-headed" + Gr. σαυρος, sauros "lizard") is a genus of small diplodocoid sauropod dinosaur that lived in what is now Tanzania during the late Jurassic. It was named for the spines on the back of the neck. The first fossil was described by paleontologist Werner Janensch in 1914.Diplodocoidea
Diplodocoidea is a superfamily of sauropod dinosaurs, which included some of the longest animals of all time, including slender giants like Supersaurus, Diplodocus, Apatosaurus, and Amphicoelias. Most had very long necks and long, whip-like tails; however, one family (the dicraeosaurids) are the only known sauropods to have re-evolved a short neck, presumably an adaptation for feeding low to the ground. This adaptation was taken to the extreme in the highly specialized sauropod Brachytrachelopan. A study of snout shape and dental microwear in diplodocoids showed that the square snouts, large proportion of pits, and fine subparallel scratches in Apatosaurus, Diplodocus, Nigersaurus, and Rebbachisaurus suggest ground-height nonselective browsing; the narrow snouts of Dicraeosaurus, Suuwassea, and Tornieria and the coarse scratches and gouges on the teeth of Dicraeosaurus suggest mid-height selective browsing in those taxa. This taxon is also noteworthy because diplodocoid sauropods had the highest tooth replacement rates of any vertebrates, as exemplified by Nigersaurus, which had new teeth erupting every 30 days.Ferganasaurus
Ferganasaurus was a genus of dinosaur first formally described in 2003 by Alifanov and Averianov. The type species is Ferganasaurus verzilini. It was a sauropod similar to Rhoetosaurus. The fossils were discovered in 1966 in Kyrgyzstan from the Balabansai Formation and date to the Callovian stage of the Middle Jurassic.Flagellicaudata
Flagellicaudata is a clade of Dinosauria. It belongs to Sauropoda and includes two families, the Dicraeosauridae and the Diplodocidae.Gravisauria
Gravisauria is a clade of sauropod dinosaurs consisting of some genera, Vulcanodontidae and Eusauropoda.Huangshanlong
Huangshanlong is a genus of mamenchisaurid dinosaurs native to the Anhui province of China. It contains a single species, Huangshanlong anhuiensis. H. anhuiensis represents, along with Anhuilong and Wannanosaurus, one of three dinosaurs fround in Anhui province.Jiutaisaurus
Jiutaisaurus is a genus of sauropod dinosaur from the Quantou Formation of China. Jiutaisaurus was a sauropod which lived during the Cretaceous. The type species, Jiutaisaurus xidiensis, was described by Wu et al. in 2006, and is based on eighteen vertebrae.Kaijutitan
Kaijutitan (meaning "Kaiju titan" after the type of Japanese movie monsters) is a genus of basal titanosaur dinosaur from the Sierra Barrosa Formation from Neuquén Province in Argentina. The type and only species is Kaijutitan maui.Lingwulong
Lingwulong is a genus of dicraeosaurid sauropod dinosaur from the Early or Middle Jurassic Yanan Formation in Lingwu, Yinchuan, Ningxia Hui, China. The type and only species is L. shenqi, known from several partial skeletons. It is the earliest-aged neosauropod ever discovered, as well as the only definite diplodocoid from east Asia. Its exact age is uncertain, but it lived between the late Toarcian and Bajocian ages, with an midpoint estimate age of 174 Ma.Pilmatueia
Pilmatueia is a diplodocoid sauropod belonging to the family Dicraeosauridae that lived in Argentina during the Early Cretaceous.Shunosaurus
Shunosaurus, meaning "shu lizard", is a genus of sauropod dinosaur from Early Jurassic (Oxfordian) beds in Sichuan Province in China, approximately 159±2 million years ago. The name derives from "Shu", an ancient name for the Sichuan province.Suuwassea
Suuwassea (meaning "ancient thunder") is a genus of dicraeosaurid sauropod dinosaur found in the Upper Jurassic strata of the Morrison Formation, located in southern Carbon County, Montana, United States. The fossil remains were recovered in a series of expeditions during a period spanning the years 1999 and 2000, described by J.D. Harris and Peter Dodson in 2004. They consist of a disarticulated but associated partial skeleton, including partial vertebral series and limb bones.Tambatitanis
Tambatitanis is an extinct genus of titanosauriform dinosaur from the Early Cretaceous (probably early Albian) of Japan. It is known from a single type species, Tambatitanis amicitiae. It was probably around 14 meters long and its mass was estimated at some 4 tonnes. It was a basal titanosauriform and possibly belonged to the Euhelopodidae.Tengrisaurus
Tengrisaurus (meaning "Tengri lizard") is a genus of lithostrotian sauropod, from the Early Cretaceous (Barremian-Aptian), of the Murtoi Formation, Russia. It was described in 2017 by Averianov & Skutschas. The type species is T. starkovi.Vulcanodontidae
The Early Jurassic sauropod dinosaurs Zizhongosaurus, Barapasaurus, Tazoudasaurus, and Vulcanodon may form a natural group of basal sauropods called the Vulcanodontidae. Basal vulcanodonts include some of the earliest known examples of sauropods. The family-level name Vulcanodontidae was erected by M.R. Cooper in 1984. In 1995 Hunt et al. published the opinion that the family is synonymous with the Barapasauridae. One of the key morphological features specific to the family is an unusually narrow sacrum.