Euhelopus

Euhelopus is a genus of sauropod dinosaur that lived between 145 and 133 million years ago during the Berriasian and Valanginian stages of the Early Cretaceous^[1] in what is now Shandong Province in China. It was a large quadrupedal herbivore. Like sauropods such as brachiosaurs and titanosaurs, Euhelopus had longer forelegs than hind legs. This discovery was paleontologically significant because it represented the first dinosaur scientifically investigated from China: seen in 1913, rediscovered in 1922, and excavated in 1923 and studied by T'an during the same year.^[2] Unlike most sauropod specimens, it has a relatively complete skull.^[3]

Euhelopus Temporal range: Berriasian-Valanginian ~145–133 Ma PreꞒ Ꞓ O S D C P T J K Pg N
Reconstructed skeleton in Japan
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Clade:	Dinosauria
Clade:	Saurischia
Clade:	†Sauropodomorpha
Clade:	†Sauropoda
Clade:	†Macronaria
Clade:	†Titanosauriformes
Clade:	†Somphospondyli
Family:	†Euhelopodidae
Genus:	†Euhelopus Romer, 1956
Type species
†Euhelopus zdanskyi (Wiman, 1929)
Synonyms
Helopus Wiman, 1929 (preoccupied)

Euhelopus was a long-necked sauropod similar to Mamenchisaurus, but its affinities are controversial. Most studies favor a close relationship between Euhelopus and titanosaurs, rather than mamenchisaurids.

Description

 

Size comparison

Size

Since its original description, Euhelopus has often been considered a rather large sauropod. It has been thought to weigh about 15–20 tonnes (17–22 tons) and attain an adult length of 15 metres (49 feet).^[4] Later estimates have downsized this considerably. In 2016, Gregory S. Paul estimated the weight at 3.5 tonnes (3.9 tons) and the body length at 11 metres (36 feet).^[5] Benson et al. estimated its mass as 5,924 kg.^[6] Larramendi et al. later estimated its mass as 3,628 kg.^[7]

Overall anatomy

Euhelopus was a relatively long-necked sauropod, with a 4-meter neck^[8] composed of 17 cervical vertebrae.^[a] The presacral vertebrae had a camellate pneumatic structure, made of many small pneumatic chambers, as is characteristic of titanosauriforms and some mamenchisaurids.^[1][9] Pneumatic chambers even extended into the ilium,^[1] as occurs in many titanosaurs.^[10] The humerus was apparently nearly as long as the femur, although there is some uncertainty in this ratio, as it is not certain that the humerus and femur from which this ratio was calculated belong to the same individual, and the femur in question is incomplete.^[1]

Distinguishing anatomical features

The original diagnosis by Wiman is outdated. A diagnosis is a statement of the anatomical features of an organism (or group) that collectively distinguish it from all other organisms. Some of the features in a diagnosis may be autapomorphies. An autapomorphy is a distinctive anatomical feature that is unique to an organism or group.

 

Restoration

According to a study by Jeffrey A. Wilson and Paul Upchurch in 2009, Euhelopus can be distinguished based on, among others, these autapomorphies:^[1]

• The teeth are inclined to the front as proven by the edge of the enamel at the front of the tooth running more in the direction of the top and a front buttress also located more closely to the top.
• The axis, the second neck vertebra, has a hollow at the rear of its neural spine, with three deeper pneumatic depressions in it.
• The postaxial cervical vertebrae, the neck vertebrae behind the axis, have variably developed epipophyses and more subtle "pre‐epipopophyses" below the prezygapophyses, projections on the front of the ridge between the prezygapophysis and the vertebral body.
• The cervical neural arches have an epipophyseal‐prezygapophyseal lamina, a horizontal ridge running from the epipophysis to the prezygapophysis, separating two pneumatocoels by dividing the usual depression at the side base of the neural spine.
• In the neck vertebrae the pleurocoels are reduced to foramina, smaller openings.
• In the neck vertebrae the neural spines are reduced in height and length.
• The third neck vertebra has a neural spine with a transversely flattened forwardly directed process.
• The anterior cervical vertebrae have three costal spurs between the tuberculum and capitulum, the heads of their ribs.
• The neck rib shafts are strongly positioned below the vertebral body due to an appending parapophysis and a long section between the two rib heads.
• The middle presacral neural spines, of the rear neck and front back, are divided or forked, and in the neck base and anterior dorsal vertebrae bear a median tubercle that is at least as large as the metapophyses, the prongs of the fork, resulting in a "trifid" condition.
• The middle and posterior dorsal parapophyseal and diapophyseal laminae are arranged in a "K" configuration.
• The presacral pneumaticity extends into the ilium, which thus is permeated by air chambers.

Discovery and naming

 

Cast of the holotype skull on display in Japan

The original discovery was by a Catholic priest, Father R. Mertens, in 1913. He showed some remains he had excavated to the German mining engineer Gustav Behaghel who in 1916 sent three vertebrae to the head of the Geological Survey of China Ding Wenjiang ("V.K. Ting"). This was probably the first occasion dinosaur bones from China were scientifically studied. With help of another Catholic priest, Father Alfred Kaschel, the site was rediscovered in November 1922 by Johan Gunnar Andersson and Tan Xichou. In March 1923, the Austrian student Otto Zdansky excavated two skeletons at sites about three kilometres apart and the holotype was studied by H. C. T'an, also in 1923.^[2]

It was originally described and named Helopus, meaning "Marsh Foot", by the Swedish paleontologist Carl Wiman in 1929, after the Greek ἕλος, helos, "swamp", and πούς, pous, "foot".^[11] The name refers to the marshy area of the finds and to truga, Swedish swamp shoes, which according to Wiman resembled the wide feet of the animal.^[11] This name however, already belonged to a bird because the Caspian tern had once been named Helopus caspius Wagler 1832. The sauropod dinosaur was therefore renamed Euhelopus (True marsh-foot) in 1956 by Alfred Sherwood Romer.^[12] There proved to be a plant genus (a grass) with the same generic name, Euhelopus. However, a genus in one biological kingdom may have a name that is used as a genus name in another kingdom, so Euhelopus was allowed. The type species is Helopus zdanskyi. The combinatio nova is Euhelopus zdanskyi. The specific name honours Zdansky.^[11]

 

Left premaxilla and maxilla

Specimen PMU 24705 (formerly PMU R233) forms according to Wilson & Upchurch the holotype,^[1] descriptive basis, for the species Euhelopus zdanskyi.^[3] It represents one of the skeletons found by Zdansky, named "Exemplar a" by Wiman, who did not formally assign a holotype.^[11] This is the original skeleton found by Mertens.^[11] Specimen PMU 24705 consists of a partial skeleton with skull and lower jaws comprising these bones: the rostral part of the left nasal; a partial right jugal; the tapered jugal process of the postorbital, partially excavated; the dorsal process of the right quadratojugal; the fragmented left pterygoid (another fragment might be the right splenial, but it is too fragile to be removed from its matrix),^[3] a series of twenty-five presacral vertebrae and the left thighbone.^[11]

The second skeleton, of an individual about as large as the holotype, was designated "Exemplar b" by Wiman.^[11] It was by Wilson & Upchurch referred to Euhelopus. This specimen PMU 24706, formerly PMU 234, comprises nine articulated dorsal vertebrae and the sacrum, two dorsal ribs, a nearly complete pelvis, and a right hindlimb lacking the fifth metatarsal and several pedal phalanges.^[4]

Both specimens are housed in the collection of the Paleontological Museum of Uppsala University, in Uppsala, Sweden, where the mounted skeletons are displayed since the 1930s.^[1]

In 1923, Zdansky lacked the time to finish the excavation of the holotype.^[11] In the autumn of 1934, C. C. Young and M. N. Bien returned to the locality and recovered a left scapulocoracoid, right coracoid and right humerus. Young described these remains, as well as the vertebrae Behagel had sent to Ting, in 1935. Young assigned all of these remains to Euhelopus zdanskyi except the incomplete right coracoid, and suggested that they probably belonged to the type specimen.^[13] Yang and Bien's scapulocoracoid and humerus and Ting's vertebrae were designated "exemplar c" by Wilson & Upchurch in 2009. They were informed in 2007 that this material could no longer be located in the Chinese collections.^[1]

Classification

 

Reconstructions of the skull

 

Left dentary and surangular bones

Wiman in 1929 was uncertain about the affinities of Helopus and placed it in a Helopodidae of its own.^[11] Yang made this a Helopodinae, first within the Morosauridae, then within the Brachiosauridae. Romer in 1956 created a Euhelopodinae.^[12] In 1990, John Stanton McIntosh placed Euhelopus in the Camarasauridae.^[14]

The phylogenetic affinities of Euhelopus are controversial, and it has been variously interpreted as having close affinities to Mamenchisaurus-like taxa^[15][9] or as being grouped together with titanosaurs in the clade Somphospondyli.^[16][1][17] The clade containing Euhelopus and its close relatives is known as Euhelopodidae, but the ambiguity over Euhelopus's affinities has caused considerable uncertainty regarding the membership of Euhelopodidae.^[17] Most studies favor the somphospondyl hypothesis for Euhelopus, but the lack of research on the anatomy of Mamenchisaurus-like sauropods has inhibited a rigorous test of the relationship between them and Euhelopus.^[9]

Wilson and Upchurch (2009) noted that cladistic assessments suggest that Euhelopus belonged to a clade of sauropods, the Euhelopodidae, that originated during an interval of geographic isolation and was endemic to this geographical range in China. It is not clear if the Euhelopodidae are monophyletic.^[1] Euhelopus demonstrates phylogenetic affinity to the taxon Titanosauria. Traditional claims that Euhelopus, Omeisaurus, Mamenchisaurus and Shunosaurus form the monophyletic family “Euhelopodidae” are not supported by new phylogenetic analysis.^[18] The cladogram below follows José L. Carballido, Oliver W. M. Rauhut, Diego Pol and Leonardo Salgado (2011).^[18]

Camarasauromorpha	Camarasaurus Europasaurus Galvesaurus Tehuelchesaurus Janenschia Tastavinsaurus Euhelopus Chubutisaurus Wintonotitan Titanosauriformes  Brachiosauridae Phuwiangosaurus Titanosauria

Paleoecology

 

Restorations of the head

Provenance and occurrence

The type material for Euhelopus was excavated at the Mengyin Formation in Shandong (Shantung) Province, China. The specimens were collected by Otto Zdansky in 1923, in green/yellow sandstone and green/yellow siltstone.

The Mengyin Formation dates to the Berriasian-Valanginian.^[19] It was previously regarded as having been deposited during the Barremian or Aptian stages of the Cretaceous period, about 129 to 113 million years ago. During the 1990s it was mistakenly thought the formation might date from the Late Jurassic.^[1]

Footnotes

1. The position of the cervicodorsal transition in Euhelopus is uncertain, and it is possible that the 18th vertebra in the series should also be considered as part of the neck.^[1]

References

1. Wilson, Jeffrey A.; Upchurch, Paul (2009). "Redescription and reassessment of the phylogenetic affinities of Euhelopus zdanskyi (Dinosauria:Sauropoda) from the Early Cretaceous of China". Journal of Systematic Palaeontology. 7 (2): 199–239. doi:10.1017/S1477201908002691. S2CID 84505064.
2. T'an, H. C. (1923). New research on the Mesozoic and early Tertiary geology in Shantung. Geological Survey of China Bulletin 5:95-135
3. Poropat, Stephen F.; Kear, Benjamin P. (2013-11-21). "Photographic Atlas and Three-Dimensional Reconstruction of the Holotype Skull of Euhelopus zdanskyi with Description of Additional Cranial Elements". PLOS ONE. 8 (11): e79932. doi:10.1371/journal.pone.0079932. PMC 3836988. PMID 24278222.
4. "Euhelopus." In: Dodson, Peter & Britt, Brooks & Carpenter, Kenneth & Forster, Catherine A. & Gillette, David D. & Norell, Mark A. & Olshevsky, George & Parrish, J. Michael & Weishampel, David B. The Age of Dinosaurs. Publications International, LTD. p. 70. ISBN 0-7853-0443-6.
5. Paul, G.S., 2016, The Princeton Field Guide to Dinosaurs. Second Edition, Princeton University Press p. 224
6. Benson, Roger B. J.; Campione, Nicolás E.; Carrano, Matthew T.; Mannion, Philip D.; Sullivan, Corwin; Upchurch, Paul; Evans, David C. (2014-05-06). "Rates of Dinosaur Body Mass Evolution Indicate 170 Million Years of Sustained Ecological Innovation on the Avian Stem Lineage". PLOS Biology. 12 (5): e1001853. doi:10.1371/journal.pbio.1001853. ISSN 1545-7885. PMC 4011683. PMID 24802911.
7. Larramendi, Asier; Paul, Gregory S.; Hsu, Shu‐yu (2020-12-01). "A review and reappraisal of the specific gravities of present and past multicellular organisms, with an emphasis on tetrapods". The Anatomical Record. 304 (9): 1833–1888. doi:10.1002/ar.24574. ISSN 1932-8486. PMID 33258532. S2CID 227243708.
8. Taylor, Michael P.; Wedel, Mathew J. (2013-02-12). "Why sauropods had long necks; and why giraffes have short necks". PeerJ. 1: –36. doi:10.7717/peerj.36. ISSN 2167-8359. PMC 3628838. PMID 23638372.
9. Moore, Andrew J.; Upchurch, Paul; Barrett, Paul M.; Clark, James M.; Xu, Xing (2020-05-28). "Osteology of Klamelisaurus gobiensis (Dinosauria, Eusauropoda) and the evolutionary history of Middle–Late Jurassic Chinese sauropods". Journal of Systematic Palaeontology. 18 (16): 1299–1393. doi:10.1080/14772019.2020.1759706. ISSN 1477-2019. S2CID 219749618.
10. Gorscak, Eric; O'Connor, Patrick M.; Stevens, Nancy J.; Roberts, Eric M. (2014-07-29). "The basal titanosaurian Rukwatitan bisepultus (Dinosauria, Sauropoda) from the middle Cretaceous Galula Formation, Rukwa Rift Basin, southwestern Tanzania". Journal of Vertebrate Paleontology. 34 (5): 1133–1154. doi:10.1080/02724634.2014.845568. ISSN 0272-4634.
11. C. Wiman. 1929. "Die Kreide-Dinosaurier aus Shantung" [The Cretaceous dinosaurs from Shantung]. Palaeontologia Sinica, Series C 6(1): 1-67
12. A.S. Romer. 1956. Osteology of the Reptiles, University of Chicago Press 772 pp
13. Young, C. C. (1935). "Dinosaurian remains from Mengyin, Shantung". Bulletin of the Geological Society of China. 14 (4): 519–533. doi:10.1111/j.1755-6724.1935.mp14004004.x.
14. McIntosh, J.S. 1990. "Sauropoda". Pp. 345-401 in: Weishampel, D.B., Dodson, P. & Osmólska, H. (eds) The Dinosauria. University of California Press, Berkeley
15. Upchurch, Paul (1995-09-29). "The evolutionary history of sauropod dinosaurs". Philosophical Transactions of the Royal Society of London. Series B: Biological Sciences. 349 (1330): 365–390. doi:10.1098/rstb.1995.0125. eISSN 1471-2970. ISSN 0962-8436.
16. Wilson, Jeffrey A.; Sereno, Paul C. (1998-06-15). "Early evolution and higher-level phylogeny of sauropod dinosaurs" (PDF). Society of Vertebrate Paleontology Memoir. 5: 1–68. doi:10.2307/3889325. ISSN 1062-161X. JSTOR 3889325.
17. D'Emic, Michael D. (2012). "The early evolution of titanosauriform sauropod dinosaurs". Zoological Journal of the Linnean Society. 166 (3): 624–671. doi:10.1111/j.1096-3642.2012.00853.x. hdl:2027.42/94293. ISSN 0024-4082. S2CID 54752135.
18. José L. Carballido; Oliver W. M. Rauhut; Diego Pol & Leonardo Salgado (2011). "Osteology and phylogenetic relationships of Tehuelchesaurus benitezii (Dinosauria, Sauropoda) from the Upper Jurassic of Patagonia". Zoological Journal of the Linnean Society. 163 (2): 605–662. doi:10.1111/j.1096-3642.2011.00723.x. hdl:11336/71888.
19. Xu, Jianqiang; Li, Zhong (2015). "Middle-late Mesozoic sedimentary provinces of the Luxi and Jiaolai areas: implications for tectonic evolution of the North China Block". Journal of Asian Earth Sciences. 111: 284–301. doi:10.1016/j.jseaes.2015.07.008.