Peloroplites
| Peloroplites | |
|---|---|
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| Peloroplites skeletal reconstruction on display at the USU Eastern Prehistoric Museum, Price, Utah. | |
Scientific classification 
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| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Clade: | Dinosauria |
| Clade: | †Ornithischia |
| Clade: | †Thyreophora |
| Clade: | †Ankylosauria |
| Family: | †Nodosauridae |
| Subfamily: | †Polacanthinae |
| Genus: | †Peloroplites Carpenter et al., 2008 |
| Species: | †P. cedrimontanus
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| Binomial name | |
| †Peloroplites cedrimontanus Carpenter et al., 2008
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Peloroplites (meaning “monstrous heavy one”) is a monospecific genus of nodosaurid dinosaur from Utah that lived during the Late Cretaceous (Cenomanian to lower Turonian stage, 98.2 to 93 Ma) in what is now the Mussentuchit Member of the Cedar Mountain Formation. The type and only species, Peloroplites cedrimontanus, is known from a partial skull and postcranial skeleton. It was named in 2008 by Kenneth Carpenter and colleagues. Peloroplites was 6 metres (20 feet) long and weighed 2 tonnes (4,410 lbs), making it one of the largest known nodosaurids, and came from a time when ankylosaurids and nodosaurids were attaining large sizes.[1][2]
Discovery and Naming
In 2001, a skeleton of a large
The generic name, Peloroplites, is derived from the Greek words “peloros” (monstrous, gigantic) and “hoplites” (heavily armed), and as a subjunctive, a heavily armed soldier. The specific name, cedrimontanus, is derived from the Latin words “cedrus” (Cedar) and “mont-“ (mountain), in reference to the Cedar Mountain Formation.[1]
Carpenter et al. (2008) suggested that some of the large nodosaurid material from the Ruby Ranch Member of the Cedar Mountain Formation that has been questionably identified as Sauropelta may actually belong to Peloroplites. If the material does belong to Peloroplites, then it would extend the stratigraphic range based on a specimen described by Warren and Carpenter (2004). However, one specimen tentatively referred to Sauropelta cannot be assigned to either that genus or to Peloroplites. The specimen was obtained from the Poison Strip Sandstone Member of the Cedar Mountain Formation and assigned to Hoplitosaurus by Bodily (1969) based on the morphology of the spines. The compressed, triangular spines of the specimen are characteristic of polacanthines, which also includes Hoplitosaurus. Carpenter et al. (2008) considered that the specimen probably represents an unnamed large polacanthine.[1]
Description
Size and distinguishing traits
Carpenter et al. (2008) originally gave Peloroplites an estimated length of 5-5.5 metres (16-18 feet).[1] However, Gregory S. Paul in 2016 gave a higher estimate of 6 metres (20 feet) and a weight of 2 tonnes (4,410 lbs).[2]
Carpenter et al. (2008) diagnosed Peloroplites based on the lack of premaxillary teeth, occiput sloping forwards and towards the back, the absence of a prominent lateral temporal notch towards the back as in Sauropelta, small and blunt squamosal horns, paroccipital process projecting from the sides, a vertical quadrate that isn’t anteriorly bowed or sloped on the underside of the front, a very short odontoid, a short axis centrum which is as long as it is tall, and similar coracoid to scapula proportions to Animantarx and Edmontonia.[1]
Cranium
The
Only the rear portions of the left and right
Postcrania
The total vertebral count of Peloroplites is unknown and the
The right scapula and coracoid are coossified and are almost complete. The scapula has a damaged acromion process, which appear to be pathological due to avulsion of the deltoideus clavicularis. The remains of the acromion process indicates that it had a similar position on scapula as Edmontonia. The scapular blade is intermediate in shape between curved and straight. The posterior margin of the scapula is rounded and, like most ankylosaurs, is large and deep. The coracoid almost as long as the scapula and is pierced by the coracoid foramen. Parts of the humeri are known and enough of the crest remains to show that the humeral shaft is elongated in a similar condition to Sauropelta, Edmontonia, Animantarx, and Gastonia. The radial and ulnar condyles are widely separated. The radius more closely resembles that of Edmontonia as the radius lacks the extreme expanded ends seen in Sauropelta. The ulna is long and straight unlike the bowed ulna of Sauropelta or the short and massive of Cedarpelta and Gastonia. The olecranon process partially overhangs the humeral notch. The carpals are unknown and a partial manus was found in loose association with some of the forelimb material. The manus has a complete set of metacarpals. The metacarpals have proximal ends that are faceted and fit close against one another. Metacarpal I is sub-rectangular and has a subtriangular proximal end, a condition similar to that of ceratopsians. In addition, metacarpal I is the largest in the manus and no distal condyles. The rest of the metacarpals are hourglass shaped and have expanded proximal and distal ends. Metacarpal II has a subtriangular proximal end and weakly separated distal condyles. As in other ankylosaurs, metacarpal III is the most robust and longest metacarpal in the manus. The distal condyles of metacarpal III are separate unlike Sauropelta and Nodosaurus. Metacarpal IV is roughly the same length as metacarpal I and is subpentagonal. The distal condyles of metacarpal IV form a single surface rather than being separate. The smallest metacarpal in the series is metacarpal V, although it is slightly more robust than metacarpal IV. Metacarpal V has a rounded distal end, with no development of condyles that are separated. All the phalanges are anteroposteriorly short, have very shallow proximal articular surfaces and lack distal condyles. Due to the shortness of the phalanges, the lateral collateral ligament pits are absent. Phalanx I-1 is the largest and the longest of the phalanxes. The distal unguals are disc-shapes as they are wider than long and rounded.[1]
A 2011 study by Philip J. Senter suggested that the metacarpal configuration of Peloroplites and other ankylosaurs were positioned in a vertical semi-tube configuration, similar to that of sauropods, as the metacarpals are wedge-shaped in proximal view which fit tightly in such position without gaps between the proximal gaps and proximal surfaces.[3] A right ilium and left pubis represent the only material of the pelvis. The preacetabular process of the pelvis diverges 55° unlike Sauropelta where it diverges 39° and 28° in Edmontonia. However, the degree of divergence might possibly be an artefact of not having a complete medial surface. The postacetabular process is broad and short. Additionally, the lateral surface is almost straight rather than concave. The pubis is robust and has a lateral face that forms the anterior wall of the acetabulum. The preacetabular process is short, straight and thick, while the postpubic process is short and angled posteroventrally. Both the left and right femora are complete and are relatively straight shafted. The head of the femora are set at a slight upward angle. The left femur preserves an oblique transverse ridge that is present below the greater trochanter but is damaged and better seen on the right femur. The cnemial crest of the tibia is short and rounded in profile. The tibial shaft is thick throughout its length and astragalus is not fused to the distal end of the tibia. Only a right metatarsal and ungual are known of the hindfoot. The metatarsal is proportionally shorter and more robust than the metacarpals of the manus. As in Sauropelta, the proximal end of the metatarsal is sloped laterally in anterior view and the distal condyles are well developed. The ungual is broad throughout its length.[1]
Phylogeny
Carpenter et al. (2008) originally placed Peloroplites within Nodosauridae but did not conduct a phylogenetic analysis to determine its exact relationships within the clade.[1] Thompson et al. (2012) recovered Peloroplites as sister taxon to Polacanthus, a position also recovered by Chen et al. (2013).[4][5] However, Yang et al. (2013) found Peloroplites to be sister taxon to both Taohelong and Polacanthus, while Zheng et al. (2018) found it to be sister taxon to Taohelong and a large clade containing more nested taxa such as Nodosaurus, Edmontonia, Struthiosaurus and Europelta.[6] Rivera-Sylva et al. (2018) placed Peloroplites as sister taxon to Sauropelta, Taohelong and a clade containg more nested taxa.[7]
A phylogenetic analysis conducted by Rivera-Sylva et al. (2018) and modified by Madzia et al. (2021) is reproduced below.[7][8]
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The results of an earlier analysis by Thompson et al. (2012) are reproduced below.[4]
Paleobiology
Peloroplites is known from the uppermost part of the Cedar Mountain Formation, a layer known as the Mussentuchit Member. The layer was originally interpreted as being of
Peloroplites was contemporaneous with the basal
References
- ^ S2CID 129480044.
- ^ a b Paul, G.S., 2016, The Princeton Field Guide to Dinosaurs 2nd Edition, Princeton University Press
- S2CID 198121272.
- ^ a b Richard S. Thompson, Jolyon C. Parish, Susannah C. R. Maidment and Paul M. Barrett, 2012, "Phylogeny of the ankylosaurian dinosaurs (Ornithischia: Thyreophora)", Journal of Systematic Palaeontology 10(2): 301–312
- S2CID 128421549.
- ^ Yang J.-T.; You H.-L.; Li D.-Q.; Kong D.-L. (2013). "First discovery of polacanthine ankylosaur dinosaur in Asia" (PDF). Vertebrata PalAsiatica (in Chinese and English). 51 (4): 265–277.
- ^ S2CID 134924657.
- S2CID 245111393.
- ^ PMID 30479889.
- JSTOR i406457.
- PMID 20179896.
- PMID 30820466.
- ^ Kirkland, Lucas and Estep, (1998). "Cretaceous dinosaurs of the Colorado Plateau." in Lucas, Kirkland and Estep (eds.). Lower and Middle Cretaceous Terrestrial Ecosystems. New Mexico Museum of Natural History and Science Bulletin, 14, 79-89.
- ^ Carpenter, K., Kirkland, J.I., Burge, D.L., & Bird, J. 1999. Ankylosaurs (Dinosauria: Ornithischia) of the Cedar Mountain Formation, Utah, and their stratigraphic distribution. In: Gillette, D. (Ed.) Vertebrate Paleontology in Utah. Utah Geological Survey Miscellaneous Publication 99-1. Pp. 243-251.
- ^ ISBN 9781557916341. Retrieved 6 January 2022.
- S2CID 44146129.
- ^ S2CID 131449530.
