Eusauropoda

Eusauropods Temporal range: Early Jurassic—Late Cretaceous, 184.5–66  Ma PreꞒ Ꞓ O S D C P T J K Pg N
Skull of Jobaria
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Reptilia
Clade:	Dinosauria
Clade:	Saurischia
Clade:	† Sauropodomorpha
Clade:	† Sauropoda
Clade:	† Gravisauria
Clade:	† Eusauropoda Upchurch, 1995
Subgroups
† Cetiosauridae † Mamenchisauridae † Turiasauria † Neosauropoda Uncertain affinity and basal genera † Algoasaurus ? † Asiatosaurus ? † Atlasaurus ? † Bagualia † Barapasaurus ? † Bellusaurus † Cetiosauriscus † Chebsaurus † Chondrosteosaurus ? † Ferganasaurus ? † Huashanosaurus † Jinchuanloong † Jobaria † Klamelisaurus ? † Kotasaurus ? † Lapparentosaurus † Liubangosaurus ? † Nebulasaurus † Ohmdenosaurus ? † Qinlingosaurus ? † Rhoetosaurus ? † Shunosaurus † Spinophorosaurus ? † Tharosaurus † Volkheimeria ?

Eusauropoda (meaning "true lizard foot") is a derived clade of sauropod dinosaurs. Eusauropods represent the node-based group that includes all descendant sauropods starting with the basal eusauropods of Shunosaurus , and possibly Barapasaurus , and Amygdalodon , but excluding Vulcanodon and Rhoetosaurus . ^[1] The Eusauropoda was coined in 1995 by Paul Upchurch to create a monophyletic new taxonomic group that would include all sauropods, except for the vulcanodontids. ^[2]

Eusauropods are herbivorous, quadrupedal, and have long necks. They have been found in South America, Europe, North America, Asia, Australia, and Africa. ^[3] The temporal range of Eusauropoda ranges from the early Jurassic to the Latest Cretaceous periods. ^[1] The most primitive forms of eusauropods are not well-known because the Vulcanodon cranial material is not available, and the distribution of some of these shared derived traits that distinguish Eusauropoda is still completely unclear. ^{[1] [4]} However the discovery of Tazoudasaurus , which does preserve cranial material, did help refine some of the characteristics. ^[5]

Description

Eusauropods are long-necked, strictly herbivorous, obligate quadrupeds. ^[6] They have a highly specialized set of skeletal adaptions due to their large size, and are graviportal. ^[7]

Teeth and mouth

Yates and Upchurch described eusauropod evolution as moving towards a "bulk-browsing mode of feeding". They describe the development of lateral plates on the alveolar margins of tooth-bearing bones. These plates can be used to strip foliage, the eusauropod's "U-shaped" jaws create a wide bite, and their loss of "fleshy cheeks" increased the gape. ^[7] The crowns of eusauropod teeth also have "wrinkled enamel textures", but it is unclear what this meant for their feeding habits. ^[1]

Head and neck

Main article: Sauropod neck posture

Reconstruction of selected sauropod necks, showing posture and length

The skull length of the basal eusauropod, Patagosaurus , is about 60 centimetres (24 in). ^[8] One of the most basal eusauropods, Shunosaurus , has two characteristic features of the eusauropod elongated neck: the incorporation of the equivalent of the first dorsal vertebra into the cervical region of the spine, and the addition of two cervical vertebra in the middle of the cervical vertebrae. ^[4]

Other synapomorphies of Eusauropoda includes a retracted position of the external nares. Unlike prosauropods and theropods, which have a snout with smooth, unprotruding alveolar and subnarial regions, eusauropods have snouts with "stepped anterior margins". Further distinguishing features of eusauropods include the absence of the contact between the squamosal and the quadratojugal, the absence of the anterior (front) process of the prefrontal, and a distally elongated anterior ramus of the quadratojugal. Separating the anteroventral process of the nasal from the posterolateral process of the premaxilla, eusauropods also have a long maxilla that forms the posteroventral margin of the external naris. ^[1]

Feet and limbs

Eusauruopods are hypothesized to have had a semi-digitigrade foot posture, demonstrated by footprint evidence. ^[4] This differs from from theropods and prosauropods, which had a digitigrade pes (foot) where the heel and metatarsals were lifted off the ground. Eusauropods show asymmetry in their metatarsal shaft diameters where metatarsal I was broader than the others, suggesting that their weight was mostly assumed by their inner feet. ^[1] According to Steven Salisbury and Jay Nair, basal eusauropods retained four pedal unguals (the toe bones which supported claws) but reduced their phalangeal count in their fourth digit to three. ^[9] The metatarsus in eusauropods is less than a quarter of their tibial length, unlike sauropod outgroups that have long hindlimbs and metatarsus that are almost half of their tibial length. ^[4]

Distribution

Eusauropods are found on all major continents, with diplocodoids being widespread in the Northern Hemisphere, and titanosaurs being found in Southern Hemisphere. However, basal eusauropods that do not fall into either group are fairly well represented. ^[10]

Early eusauropods such as Volkeimeria and Amygdalodon, and more derived eusauropods such as Patagosaurus have been found in South America. ^[8] Volkeimeria is classified as a basal eusauropod, though in 2004 Paul Upchurch was suspicious of its placement, because of its "opisthoceolous cervical centra, the absence of a femoral anterior trochanter, and laterally projecting cnemial crest of the tibia", and instead thought it may be a generic sauropod. ^[10]

African eusauropods may include Spinophorosaurus , from Niger, although that taxon may instead be closer to Vulcanodon and outside Eusauropoda. ^{[3] [9]} Also, Atlasaurus was found in Morocco, and Jobaria was found in Niger. However, both genera have been found as possible Macronarians, but Atlasaurus was found to be a turiasaurian, and Jobaria a eusauropod, by a phylogenetic analysis of Xing in 2012. ^{[3] [10]}

In Europe, the clade Turiasauria has been found in France, Spain, and possibly England, with multiple genera from the same locality in Spain. ^{[10] [11]} Cetiosaurus skeletons have also been found in England, along with the possibly eusauropod genera Cardiodon and Oplosaurus , known only from teeth. ^[10]

The family Mamenchisauridae is found widespread throughout Asia. A majority of the genera are found in China, although a possible specimen of Mamenchisaurus has been found in Thailand. ^{[3] [10]} Also in China, the basal eusauropod Nebulasaurus taito was found to be a sister taxon to Spinophorosaurus, and more derived than Mamenchisauridae, but less derived than Patagosaurus, and the genus Shunosaurus is likely one of the most basal eusauropods. ^{[3] [10]} The genus Barapasaurus has been found in India, and may represent a cetiosaurid, a basal eusauropod, or a genus outside Eusauropoda. ^{[3] [9] [10]}

Paleobiology

The data around sauropod evolution, as Novas points out, is largely based on a few formations mostly in the Northern Hemisphere. However, other beds in places such as Tanzania, specifically the Canadon Asfalto and Canadon Calcereo formations, reveal a more diverse and widespread paleobiology of eusauropods in the Late Jurassic period. ^[8]

Classification

Cladogram of Eusauropoda after Gomez et al. (2024): ^[12]

Sauropoda	Antetonitrus Ingentia Lessemsaurus Ledumahadi Pulanesaura Gongxianosaurus Amygdalodon NHMUK PVR 36834 Archaeodontosaurus Volkheimeria Sanpasaurus Vulcanodon Tazoudasaurus Eusauropoda Shunosaurus Barapasaurus Patagosaurus Bagualia Nebulasaurus Spinophorosaurus Tonganosaurus Mamenchisauridae Cetiosaurus Turiasauria Jobaria Neosauropoda

Cladogram of Sauropoda after Holwerda et al. (2021): ^[13]

Sauropoda	Vulcanodon Tazoudasaurus Barapasaurus Spinophorosaurus Volkheimeria Eusauropoda Shunosaurus Cetiosauridae Cetiosaurus oxoniensis Patagosaurus Cetiosaurus Rutland specimen Mamenchisauridae Omeisaurus Mamenchisaurus Turiasauria Jobaria Neosauropoda

Cladogram after Li et al. (2025): ^[14]

Eusauropoda	Shunosaurus Omeisaurus Mamenchisauridae Jobaria Lapparentosaurus Jinchuanloong Turiasauria Neosauropoda

References

1. Wilson, J.A.; Curry-Rogers, K.A. (2005). The Sauropods: evolution and paleobiology. Berkeley: University of California Press. ISBN   978-0-520-24623-2.
2. Upchurch, P (1995). "The evolutionary history of sauropod dinosaurs" (PDF). Philosophical Transactions of the Royal Society of London B. 349 (1330): 365–390. Bibcode:1995RSPTB.349..365U. doi:10.1098/rstb.1995.0125.
3. Xing, Lida (2013). "A new basal eusauropod from the Middle Jurassic of Yunnan, China, and faunal compositions and transitions of Asian sauropodomorph dinosaurs". Acta Palaeontologica Polonica. doi: 10.4202/app.2012.0151 .
4. Wilson, J.A.; Sereno, P.C. (1998). "Early Evolution and Higher-Level Phylogeny of Sauropod Dinosaurs" (PDF). Journal of Vertebrate Paleontology. 18 (2): 1–79. Bibcode:1998JVPal..18S...1W. doi:10.1080/02724634.1998.10011115.
5. Allain, Ronan; Aquesbi, Najat; Dejax, Jean; Meyer, Christian; Monbaron, Michel; Montenat, Christian; Richir, Philippe; Rochdy, Mohammed; Russell, Dale; Taquet, Philippe (May 2004). "A basal sauropod dinosaur from the Early Jurassic of Morocco" . Comptes Rendus Palevol. 3 (3): 199–208. Bibcode:2004CRPal...3..199A. doi:10.1016/j.crpv.2004.03.001.
6. Taylor, M.P.; Wedel, M.J. (2013). "Why sauropods had long necks; and why giraffes have short necks". PeerJ. 1: e36. doi: 10.7717/peerj.36 . PMC   3628838 . PMID   23638372.
7. Yates, A.M.; Bonnan, M.F.; Neveling, J.; Chinsamy, A.; Blackbeard, M.G. (2009). "A new transitional sauropodomorph dinosaur from the Early Jurassic of South Africa and the evolution of sauropod feeding and quadrupedalism". Proceedings of the Royal Society B: Biological Sciences. 277 (1682): 787–794. doi:10.1098/rspb.2009.1440. PMC   2842739 . PMID   19906674.
8. Novas, F.E. (2009). The age of dinosaurs in South America. Bloomington: Indiana University Press. ISBN   978-0-253-35289-7.
9. Nair, J.P.; Salisbury, S.W. (2012). "New anatomical information on Rhoetosaurus Longman, 1926, a gravisaurian sauropodomorph dinosaur from the Middle Jurassic of Queensland, Australia". Journal of Vertebrate Paleontology. 32 (2): 369–394. doi:10.1080/02724634.2012.622324. S2CID   85317450.
10. Upchurch, P. (2004). "Sauropoda". In Weishampel, D.B.; Osmolska, H.; Dodson, P. (eds.). The Dinosauria (2nd ed.). University of California Press. pp.  261–299. ISBN   0-520-24209-2.
11. Royo-Torres, R.; Cobos, A.; Luque, L.; Aberasturi, A.; Espilez, E.; Fierro, I.; Gonzalez, A.; Mampel, L.; Alcala, L. (September 2009). "High European sauropod dinosaur diversity during Jurassic-Cretaceous transition in Riodeva (Teruel, Spain)". Palaeontology. 52 (5): 1009–1027. Bibcode:2009Palgy..52.1009R. doi: 10.1111/j.1475-4983.2009.00898.x .
12. Gomez, Kevin L.; Carballido, José L.; Pol, Diego (2024-10-14). "Cranial anatomy of Bagualia alba (Dinosauria, Eusauropoda) from the Early Jurassic of Patagonia and the implications for sauropod cranial evolution". Journal of Systematic Palaeontology . 22 (1). Bibcode:2024JSPal..2200471G. doi:10.1080/14772019.2024.2400471. ISSN   1477-2019.
13. Holwerda, Femke M.; Rauhut, Oliver W. M.; Pol, Diego (2021-07-22). "Osteological revision of the holotype of the Middle Jurassic sauropod dinosaur Patagosaurus fariasi Bonaparte, 1979 (Sauropoda: Cetiosauridae)" . Geodiversitas. 43 (16). doi:10.5252/geodiversitas2021v43a16. ISSN   1280-9659.
14. Li, Ning; Zhang, Xiaoqin; Ren, Xinxin; Li, Daqing; You, Hailu (2025-05-23). "A new eusauropod (Dinosauria, Sauropodomorpha) from the Middle Jurassic of Gansu, China". Scientific Reports. 15 (1): 17936. Bibcode:2025NatSR..1517936L. doi:10.1038/s41598-025-03210-5. ISSN   2045-2322. PMC   12102329 . PMID   40410409.