Hippodraco

Hippodraco (meaning "horse dragon") is a genus of iguanodontian ornithopod dinosaur that lived in North America during the Early Cretaceous period. It contains a single species, H. scutodens, for which the holotype is an immature individual cataloged as UMNH VP 20208.[1]

Hippodraco Temporal range: Early Cretaceous, 139–134.6 Ma PreꞒ Ꞓ O S D C P T J K Pg N ↓
Diagram showing known elements of the holotype specimen
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Clade:	Dinosauria
Order:	†Ornithischia
Suborder:	†Ornithopoda
Clade:	†Styracosterna
Genus:	†Hippodraco McDonald et al., 2010
Type species
†Hippodraco scutodens McDonald et al., 2010

Discovery

Stratigraphy and taphonomy of the type locality, with quarry map (B)

The holotype of Hippodraco, UMNH VP 20208, was discovered in 2004 by Andrew R. C. Milner. It is a fragmentary specimen including a fragmented skull and dentary teeth, vertebrae (dorsal, caudal and cervical), a right humerus, a right scapula, a left ischium, a right tibia, a right femur, and left metatarsals.[1][2][3][4]

It was later named in 2010 by Andrew T. McDonald, James I. Kirkland, Andrew R. C. Milner, Scott K. Madsen, Donald D. DeBlieux, Jennifer Cavin and Lukas Panzarin. The generic name Hippodraco is a combination of the Greek word hippos ("horse") and the Latin word draco ("dragon"). It refers to the elongated shape of the skull, which resembles a horse skull. The specific name scutodens is a combination of the Latin words scutum (meaning shield) and dens (meaning tooth), and it references the shield-shaped dentary tooth crowns. UMNH VP 20208 was unearthed from the Yellow Cat Member of the Cedar Mountain Formation, Utah, at a site known as Andrew's Site, dating from the Valanginian stage in the Early Cretaceous period.[1]

Description

Size compared to a human

Hippodraco is a relatively small iguanodontid, with the holotype reaching 4.5 m (15 ft) in length. Holtz estimated its weight between 227 to 454 kg (500.4 to 1,000.9 lb).[5] However, a large orbital in the skull indicates that the specimen is immature. The left side of the skull is well preserved, although the right side is very fragmented. The left dentary is preserved on the skull along with teeth, which, have shield-shaped crowns. The lacrimal bone closely resembles those of Dakotadon and Theiophytalia. [1]

Life restoration

Vertebrae indicates a characteristic iguanodont body shape. Most of the body remains are gracile, such as the right humerus and scapula, the right tibia and femur are fragmented, having irregular surfaces. The nearly-complete metatarsus is very similar to those of Camptosaurus and Iguanodon.[1]

Classification

Partial skull in left and medial view

In 2010 and 2011 cladistic analyses of McDonald and colleagues, Hippodraco has been recovered as a basal member of the Styracosterna and its closest relative was Theiophytalia.[1][6][7][8]

Ankylopollexia	Camptosaurus   Styracosterna   Uteodon         Hippodraco     Theiophytalia         Iguanacolossus       Lanzhousaurus       Kukufeldia       Barilium     Hadrosauriformes

Paleoenvironment

Hippodraco (lime-yellow, left) and other fauna from the Yellow Cat Member of the Cedar Mountain Formation

The holotype of Hippodraco was unearthed from the Upper Yellow Cat Member of the Cedar Mountain Formation.[1] Contemporaneous fauna from the Upper Yellow Cat include the fellow ornithopod Cedrorestes, sauropods (Cedarosaurus and Moabosaurus), theropods (Martharaptor and Nedcolbertia), the nodosaurid Gastonia, and the giant dromaeosaurid Utahraptor.[9][10][11] Other dromaeosaurids with fragmentary remains are also known from the formation: an indeterminate eudromaeosaur (UMNH VP 20209) and an indeterminate velociraptorine (UMNH VP 21752).[12]

References

1. McDonald AT, Kirkland JI, DeBlieux DD, Madsen SK, Cavin J, et al. (2010). "New Basal Iguanodonts from the Cedar Mountain Formation of Utah and the Evolution of Thumb-Spiked Dinosaurs". PLoS ONE. 5 (11): e14075. doi:10.1371/journal.pone.0014075. PMC 2989904. PMID 21124919.
2. Maffly, B. "Two new dinosaur species found at Utah site". The Salt Lake Tribune. Retrieved 13 August 2020.
3. Dell'Amore, C. (8 December 2010). ""Horse Dragon," Colossus Dinosaurs Found in Utah". National Geographic News. Retrieved 13 August 2020.
4. Black, R. "Two New Dinosaurs From Utah: Hippodraco and Iguanacolossus". Retrieved 13 August 2020.
5. Holtz, T. R.; Rey, L. V. (2007). Dinosaurs: The Most Complete, Up-to-Date Encyclopedia for Dinosaur Lovers of All Ages. Random House. Supplementary Information 2012 Weight Information
6. Andrew T. McDonald (2011). "The taxonomy of species assigned to Camptosaurus (Dinosauria: Ornithopoda)" (PDF). Zootaxa. 2783: 52–68. doi:10.11646/zootaxa.2783.1.4.
7. McDonald, A. T. (2012). "Phylogeny of Basal Iguanodonts (Dinosauria: Ornithischia): An Update". PLoS ONE. 7 (5): e36745. doi:10.1371/journal.pone.0036745.
8. Boyd, Clint A.; Pagnac, Darrin C. (2015). "Insight on the anatomy, systematic relationships, and age of the Early Cretaceous ankylopollexian dinosaur Dakotadon lakotaensis". PeerJ. 3: e1263. doi:10.7717/peerj.1263.
9. Paul, Gregory S. (2016). The Princeton Field Guide to Dinosaurs (2nd Edition). Princeton, New Jersey: Princeton University Press. pp. 151, 163, 229, 252, 314, 319, 326, 327. ISBN 9780691167664.
10. Kirkland, J.I. (December 1, 2016). "The Lower Cretaceous in East-Central Utah—The Cedar Mountain Formation and its Bounding Strata". Geology of the Intermoutain West. 3: 1–130.
11. Lockley, Martin G.; Buckley, Lisa G.; Foster, John R.; Kirkland, James I.; DeBlieux, Donald D. (2015). "First report of bird tracks (Aquatilavipes) from the Cedar Mountain Formation (Lower Cretaceous), eastern Utah". Palaeogeography, Palaeoclimatology, Palaeoecology. 420: 150–162. doi:10.1016/j.palaeo.2014.12.014.
12. Senter, P.; Kirkland, J. I.; Deblieux, D. D.; Madsen, S.; Toth, N. (2012). Dodson, Peter (ed.). "New Dromaeosaurids (Dinosauria: Theropoda) from the Lower Cretaceous of Utah, and the Evolution of the Dromaeosaurid Tail". PLoS ONE. 7 (5): e36790. doi:10.1371/journal.pone.0036790. PMC 3352940. PMID 22615813.