Amargatitanis

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Amargatitanis
Temporal range: Barremian-Early Aptian
~129.4–123  Ma
Amargatitanis Skeletal.svg
Skeletal reconstruction, known material in teal
Scientific classification OOjs UI icon edit-ltr.svg
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Clade: Dinosauria
Clade: Saurischia
Clade:† Sauropodomorpha
Clade:† Sauropoda
Superfamily:† Diplodocoidea
Family:† Dicraeosauridae
Genus:† Amargatitanis
Apesteguía 2007
Species:
†A. macni
Binomial name
†Amargatitanis macni
Apesteguía 2007

Amargatitanis (meaning "Amarga giant") is a genus of dicraeosaurid sauropod dinosaur (a type of large, long-necked quadrupedal herbivorous dinosaur) from the Barremian-age (Lower Cretaceous) La Amarga Formation of Neuquén, Argentina. It is known from a single, incomplete postcranial skeleton consisting of a partial hindlimb, ischium, and two vertebrae. These remains were unearthed by Argentine paleontologist José Bonaparte in 1983 during an expedition by the Museo Argentino de Ciencias Naturales and later described as a new genus and species, Amargatitanis macni by Sebastián Apesteguía. The genus name comes from the words Amarga, where the fossils were collected, and titanis meaning "titan". Its species name is in reference to the MACN (Museo Argentino de Ciencias Naturales ), where the remains are stored.

Contents

Though initially thought to be a titanosaur, recent research has found it to be a dicraeosaurid, a group of short-necked, smaller sauropods. It reached around 12 meters (39.7 feet) long and 3.5 metric tons (3.9 short tons) according to one estimate. Like other dicraeosaurids, it has robust limbs, a long tail, and tall neural spines . However, much of its anatomy can only be inferred due to the lack of preserved bones. It lived in a diverse ecosystem that included higher browsing titanosauriforms and smaller, lower browsing dicraeosaurids like Amargatitanis itself.

Discovery and naming

Portrait of Sebastian Apesteguia, describer of Amargatitanis. Sebastian Apesteguia.jpg
Portrait of Sebastián Apesteguía, describer of Amargatitanis.

During an expedition by the Museo Argentino de Ciencias Naturales from March 11th to 16th of 1983, Argentine paleontologist José Bonaparte collected several fossils from four sites along the La Amarga stream in Neuquén, Argentina. At site number "1", an associated skeleton of a large sauropod was unearthed by Bonaparte who noted the discovery in his personal journal. Bonaparte initially recorded the specimen as being from the Pichi Picún Leufú Formation, although they were subsequently determined to be from the La Amarga Formation. These remains were taken to the Museo Argentino de Ciencias Naturales where they were cataloged under the specimen number MACN PV N53. [1] [2]

The skeleton remained undescribed until 2007, when Argentine researcher Sebastián Apesteguía named it Amargatitanis macni. The genus name comes from Amarga, where the holotype was found, and titanis meaning "titan". Its species name, macni, is to honor the Museo Argentino de Ciencias Naturales (MACN). [2] Apesteguía erroneously assigned a scapula (MACN PV N34) and six caudal vertebrae (MACN PV N51) to the specimen, despite coming from other rock layers and being found in 1986. [1] [3] It was originally assigned to the group Titanosauria due to the anatomy of the scapula and caudal vertebra, but a 2016 reanalysis of the holotype (MACN PV N53) fossils demonstrated that Amargatitanis was instead a dicraeosaurid dipolodocoid. The study, authored by researcher Pablo Gallina, also removed MACN PV N34 and N51 from the holotype material, which were referred to an indeterminate titanosauriform, and considered only the dicraeosaurid bones to be from the genus. Since Gallina's paper, several phylogenetic studies have recovered Amargatitanis as a dicraeosaurid. [4] [5] [6]

Fossil record

Amargatitanis macni is known from a single specimen, the holotype MACN PV N53, which was found in the Barremian-aged Puesto Antigual Member of the La Amarga Formation, approximately 129 to 123 million years old. This specimen represents a mature individual [7] and consists of an incomplete anterior caudal vertebra, an incomplete middle caudal vertebra, an incomplete right ischium, and most of the right hind limb, including the femur, partial tibia and fibula, astragalus, and the distal half of the first metatarsal. Field notes indicate that two phalanges and another metatarsal of this specimen were also collected, but as of 2016 they could not be located. [1] A pair of anterior dorsal vertebrae from a dicraeosaurid that were also found in the La Amarga Formation, MOZ-Pv 6126-1 and MOZ-Pv 6126-2, could be additional remains of Amargatitanis, or belong to the other La Amarga Formation dicraeosaurid, Amargasaurus. [3]

Description

Life restoration Amargatitanis LM.png
Life restoration

As a dicraeosaurid, Amargatitanis would have resembled better known members of the family such as Dicraeosaurus and Amargasaurus , which had shorter necks than most other sauropods and long neural spines extending from the vertebrae of the neck and trunk. [8] It was a small sauropod, [9] with one study estimating its mass at 11.406 metric tons (12.573 short tons), slightly larger than the same study's estimate for Amargasaurus of 10.195 metric tons (11.238 short tons). [10] Mass estimates for Amargasaurus have been noted to vary widely depending on the method used, [11] and studies using other methods, not yet applied to Amargatitanis, have found Amargasaurus to weigh 3.304 metric tons (3.642 short tons) [12] to 4.376 metric tons (4.824 short tons). [13]

From what is known of the caudal (tail) vertebrae of Amargatitanis, they generally resemble those of other dicraeosaurids. The centra (or "bodies") of these vertebrae are typical of flagellicaudatans, with gently concave anterior (front) faces and flat posterior (backside) faces. The prezygapophyseal centrodiapophysial fossae, which are deep depressions on the anterior surface of the transverse processes of the caudal vertebrae found in most diplodocoids and some macronarians, differ from other sauropods in that they contain a thin vertical lamina (sheet of bone). [1] The caudal vertebrae of Amargatitanis resemble those of Pilmatueia, but not most other dicraeosaurids, in lacking ventrolateral ridges. [14] The ischium generally resembles that of other flagellicaudatans, although it resembles the brachiosaurid Giraffatitan in that much of its posterior margin is straight. [1]

The hind limb bones generally resemble those of other dicraeosaurids. The femur is distinctive in that it is much wider at its proximal (upper) end than at its distal (lower) end, whereas in other sauropods, including Dicraeosaurus, both ends are approximately equal in width. [1] A similar condition may have been present in another dicraeosaurid, Pilmatueia . [15] As in other dicraeosaurids, the lateral (outer) border of the femur is gently curved and lacks the distinct lateral bulge characteristic of titanosauriforms. The tibia has a low cnemial crest , similar to that of Dicraeosaurus and Amargasaurus and unlike the higher cnemial crest found in most macronarians. The posterior fossa of the astragalus differs from other sauropods in being deep and crescent-shaped, and in the arrangement of the foramina (openings) within it. The distal end of the first metatarsal has an oval shape, rather than being constricted in the middle to form distinct medial and lateral condyles as in Dicraeosaurus. The metatarsal has a distinct posterolateral (pointing both to the side and backwards) projection, as in other flagellicaudatans. [1]

Classification

Apesteguía originally hypothesized in 2007 that Amargatitanis was a member of Titanosauria, a group of large, macronarian sauropods, based on features of the femur and scapula. However, two later papers argued that these titanosaurian traits were instead a misinterpretation of broken elements. [16] [1] In 2012, D'Emic in turn regarded Amargatitanis as a nomen dubium and that the fossils could not be from the same individual, making it a chimera. [17] A 2016 study by Pablo Gallina found that characteristics such as the lack of a lateral bulge on the femur and presence of procoelous vertebrae (centra being concave at the front and convex at the back) meant Amargatitanis belonged to the family Dicraeosauridae. This claim was supported by phylogenetic analyses conducted by Gallina and later studies, which typically found Amargatitanis at the base of the family. [15] [5] [1] In 2022, researcher Guillermo Windholz and colleagues argued that South American dicraeosaurids formed a clade based on their biogeography and results of phylogenetic analyses, with Amargatitanis being especially closely related to Pilmatueia and Bajadasaurus. They also hypothesized that Dicraeosauridae originated in North America, with the earliest known genera being Suuwassea and Smitanosaurus . [18] [14]

Bajpai and colleagues, in 2023, recovered Amargatitanis as an advanced dicraeosaurid in polytomy with Pilmatueia and a group containing Brachytrachelopan, Dicraeosaurus , and the contemporary Amargasaurus. The results of their phylogenetic analyses are shown in the cladogram below: [5]

Diplodocoidea

Life history

In a 2021 paper, two Argentine researchers, Guillermo J. Windholz and Ignacio A. Cerda, examined the bone histology of Amargatitanis using thin sections from a femur. The study sought to evaluate the age of the specimen by counting the number and spacing of cyclical growth marks (concentric lines similar to the growth rings of a tree), which formed in periods of slow growth. Sauropods are thought to be characterised by high rates of continuous growth, and, as a consequence, cyclical growth marks usually form only after sexual maturity is reached. Growth continued after sexual maturity, with adult size being reached much later. [7]

The femur of Amargatitanis bears 19 cyclical growth marks, indicating that the individual was at least 19 years old at the time of death. The six outermost growth marks are closely spaced, a structure known as an external fundamental system, indicating that the individual had not only reached sexual maturity but also its adult size. This assessment is supported by the extensive remodeling of the cortical bone, a trait associated with anatomical and sexual maturity. The high number of cyclical growth marks seen in Amargatitanis is unusual for sauropods, and possibly indicates that some sauropods grew discontinuously rather than continuously. [7]

Paleoenvironment

Skeleton of Amargasaurus, a sauropod that coexisted with Amargatitanis. Amargasaurus1 Melb Museum email.jpg
Skeleton of Amargasaurus , a sauropod that coexisted with Amargatitanis.

Amargatitanis stems from sedimentary rocks of the La Amarga Formation, which is part of the Neuquén Basin and dates to the Barremian and late Aptian of the Early Cretaceous. Most vertebrate fossils, including Amargatitanis, have been found in the lowermost (oldest) part of the formation, the Puesto Antigual Member. This member is approximately 29 meters (95 ft) in thickness and mainly composed of sandstones deposited by braided rivers. [19] The sauropod fauna of the La Amarga Formation was diverse and included the basal rebbachisaurid Zapalasaurus , the dicraeosaurid Amargasaurus, and unnamed remains of basal titanosauriforms. [2] [20] The high diversity suggests that different sauropod species exploited different food sources in order to reduce competition. Basal titanosauriforms showed proportionally longer necks, longer forelimbs, and broader tooth crowns than dicraeosaurids and rebbachisaurids, suggesting greater feeding heights. [21] Amargatitanis and Amargasaurus probably fed above ground level at heights of up to 2.7 meters (8.9 ft), as evidenced by the anatomy of their neck and inner ear. Rebbachisaurids like Zapalasaurus presumably fed at ground-level, while basal Titanosauriforms exploited food sources at higher levels. [21]

Other dinosaurs of the La Amarga Formation include an indeterminate stegosaur; predatory dinosaurs include the small ceratosaur Ligabueino , and the presence of a large tetanuran is indicated by teeth. [22] Other than dinosaurs, the formation is notable for the cladotherian mammal Vincelestes , the only mammal known from the Early Cretaceous of South America. [23] Crocodylomorphs are represented by the trematochampsid Amargasuchus. [24]

Related Research Articles

<span class="mw-page-title-main">Titanosauria</span> Extinct clade of dinosaurs

Titanosaurs were a diverse group of sauropod dinosaurs, including genera from all seven continents. The titanosaurs were the last surviving group of long-necked sauropods, with taxa still thriving at the time of the extinction event at the end of the Cretaceous. This group includes some of the largest land animals known to have ever existed, such as Patagotitan, estimated at 37 m (121 ft) long with a weight of 69 tonnes, and the comparably-sized Argentinosaurus and Puertasaurus from the same region.

Agustinia is a genus of sauropod dinosaur from the Early Cretaceous of South America. The genus contains a single species, A. ligabuei, known from a single specimen that was recovered from the Lohan Cura Formation of Neuquén Province in Argentina. It lived about 116–108 million years ago, in the Aptian–Albian stages of the Early Cretaceous Period.

<i>Bonitasaura</i> Extinct genus of dinosaurs

Bonitasaura is a genus of titanosaurian dinosaur hailing from uppermost layers of the Late Cretaceous (Santonian) Bajo de la Carpa Formation, Neuquén Group of the eastern Neuquén Basin, located in Río Negro Province, Northwestern Patagonia, Argentina. The remains, consisting of a partial sub-adult skeleton jumbled in a small area of fluvial sandstone, including a lower jaw with teeth, a partial vertebrae series, and limb bones, were described by Sebastian Apesteguía in 2004.

<i>Amargasaurus</i> Dicraeosaurid sauropod dinosaur genus from the Early Cretaceous period

Amargasaurus is a genus of sauropod dinosaur from the Early Cretaceous epoch 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 13 meters 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 could have stuck out of the body as solitary structures that supported a keratinous sheath. An alternate hypothesis, now more favored, postulates that they could have formed a scaffold supporting a skin sail. They might have been used for display, combat, or defense.

<span class="mw-page-title-main">Dicraeosauridae</span> Extinct family of dinosaurs

Dicraeosauridae is a family of diplodocoid sauropods who are the sister group to Diplodocidae. Dicraeosaurids 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, Asia, Africa, and South America. In 2023, a dicraeosaurid fossil was discovered in India for the first time. 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.

<i>Brachytrachelopan</i> Extinct genus of dinosaurs

Brachytrachelopan is a short-necked sauropod dinosaur from the Late Jurassic of Argentina. The holotype and only known specimen 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.

Amargasuchus is an extinct genus of crocodylomorph. It was a member of the Trematochampsidae, an enigmatic family of mesoeucrocodylians. Fossils have been found from the La Amarga Formation in Argentina and date back to the Barremian and Aptian stages of the Early Cretaceous. Amargasuchus inhabited a terrestrial paleoenvironment that existed during the Early Cretaceous in the Neuquén basin and was characterized by a system of braided rivers, lakes, and alluvial plains. Sauropod, abelisauroid, and stegosaurian dinosaurs have also been found existing in the Neuquén basin at this time.

<i>Elaltitan</i> Extinct genus of dinosaurs

Elaltitan is an extinct genus of large lithostrotian titanosaur sauropod dinosaur known from the Late Cretaceous of Chubut Province, southern Argentina. It contains a single species, Elaltitan lilloi.

<i>Katepensaurus</i> Extinct genus of rebbachisaurid dinosaurs

Katepensaurus is an extinct genus of rebbachisaurid sauropod dinosaur known from the Late Cretaceous of south-central Chubut Province of central Patagonia, Argentina. It contains a single species, Katepensaurus goicoecheai.

<i>Leinkupal</i> Extinct genus of reptiles

Leinkupal is a genus of diplodocine sauropod known from the Early Cretaceous of the Bajada Colorada Formation, southeastern Neuquén Basin in the Neuquén Province of Argentina. It contains a single species, Leinkupal laticauda.

<i>Taurovenator</i> Extinct genus of reptiles

Taurovenator is a large carcharodontosaurid theropod from the late Cretaceous Huincul Formation of Argentina that lived during the Cenomanian age of the Late Cretaceous. It is monotypic, containing only one species, T. violantei.

<i>Pilmatueia</i> Sauropod dinosaur genus from the early Cretaceous Period

Pilmatueia is a diplodocoid sauropod belonging to the family Dicraeosauridae that lived in Argentina during the Early Cretaceous. Its type and only species is Pilmatueia faundezi. Pilmatueia was probably closely related to other South American dicraeosaurids such as Amargasaurus. Pilmatueia had relatively pneumatic vertebrae compared to other dicraeosaurids, which were otherwise characterized by a reduction in pneumaticity relative to other sauropods. Pilmatueia dates to the Valanginian, an age of the Cretaceous period for which dinosaur faunas are poorly known.

<i>Bajadasaurus</i> Genus of sauropod dinosaur

Bajadasaurus is a genus of sauropod dinosaur from the Early Cretaceous epoch 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 relatively small and short-necked sauropods.

<i>Meraxes</i> Genus of carcharodontosaurid dinosaurs

Meraxes is a genus of large carcharodontosaurid theropod dinosaur from the Late Cretaceous Huincul Formation of Patagonia, Argentina. The genus contains a single species, Meraxes gigas.

Ruixinia is an extinct genus of somphospondylan titanosauriform dinosaur from the Early Cretaceous (Barremian) Yixian Formation of China. The genus contains a single species, Ruixinia zhangi. The Ruixinia holotype is a partial articulated skeleton with the most complete series of caudal vertebrae known from any Asian titanosauriform.

<i>Chucarosaurus</i> Genus of titanosaurian dinosaurs

Chucarosaurus is an extinct genus of titanosaurian dinosaur from the Late Cretaceous Huincul Formation of Argentina. The genus contains a single species, C. diripienda, known from various limb and pelvic bones.

<i>Garumbatitan</i> Genus of somphospondylan sauropod dinosaurs

Garumbatitan is an extinct genus of somphospondylan sauropod dinosaur from the Cretaceous Arcillas de Morella Formation of Spain. The genus contains a single species, G. morellensis, known from multiple partial skeletons.

Sidersaura is an extinct genus of rebbachisaurid sauropod dinosaur from the Late Cretaceous Huincul Formation of Argentina. The genus contains a single species, S. marae, known from the remains of four individuals. Sidersaura represents one of the largest known rebbachisaurids.

Campananeyen is a genus of rebbachisaurid sauropod dinosaur from the Late Cretaceous (Cenomanian) Candeleros Formation of Argentina. The genus contains a single species, Campananeyen fragilissimus, known from a fragmentary skeleton.

References

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  16. ↑ Mannion, Philip D.; Upchurch, Paul; Barnes, Rosie N.; Mateus, Octávio (2013). "Osteology of the Late Jurassic Portuguese sauropod dinosaur Lusotitan atalaiensis (Macronaria) and the evolutionary history of basal titanosauriforms" (PDF). Zoological Journal of the Linnean Society. 168: 98–206. doi:10.1111/zoj.12029.
  17. ↑ D'Emic, M. D. (2012). "The early evolution of titanosauriform sauropod dinosaurs" (PDF). Zoological Journal of the Linnean Society. 166 (3): 624–671. doi: 10.1111/j.1096-3642.2012.00853.x .
  18. ↑ Whitlock, John A.; Mantilla, Jeffrey A. Wilson (2020-12-10). "The Late Jurassic sauropod dinosaur ' Morosaurus' agilis Marsh, 1889 reexamined and reinterpreted as a dicraeosaurid". Journal of Vertebrate Paleontology. 40 (6): e1780600. Bibcode:2020JVPal..40E0600W. doi:10.1080/02724634.2020.1780600. ISSN   0272-4634.
  19. ↑ Leanza, Héctor A; Apesteguı́a, Sebastián; Novas, Fernando E; de la Fuente, Marcelo S (2004-02-01). "Cretaceous terrestrial beds from the Neuquén Basin (Argentina) and their tetrapod assemblages". Cretaceous Research. 25 (1): 61–87. Bibcode:2004CrRes..25...61L. doi:10.1016/j.cretres.2003.10.005. ISSN   0195-6671.
  20. ↑ Windholz, Guillermo J.; Baiano, Mattia A.; Bellardini, Flavio; Garrido, Alberto (2021-01-01). "New Dicraeosauridae (Sauropoda, Diplodocoidea) remains from the La Amarga Formation (Barremian–Aptian, Lower Cretaceous), Neuquén Basin, Patagonia, Argentina". Cretaceous Research. 117: 104629. Bibcode:2021CrRes.11704629W. doi:10.1016/j.cretres.2020.104629. ISSN   0195-6671.
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  23. ↑ Bonaparte, José F. (2008). "On the phylogenetic relationships of Vincelestes neuquenianus: Short Review". Historical Biology. 20 (2): 81–86. doi:10.1080/08912960802164470. ISSN   0891-2963.
  24. ↑ Chiappe, Luis M. (1988-12-01). "A new trematochampsid crocodile from the Early Cretaceous of north-western Patagonia, Argentina and its palaeobiogeographical and phylogenetic implications". Cretaceous Research. 9 (4): 379–389. Bibcode:1988CrRes...9..379C. doi:10.1016/0195-6671(88)90009-2. ISSN   0195-6671.
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