The Validity of Supersaurus vivianae

Supersaurus vivianae is a Diplodocid Sauropod (one of many from the Morrison formation). The holotype (BYU 9025) is a scapulocoracoid 2.2m long. Jensen described this as a Brachiosaurid, along with UltrasaurusDystylosaurus (Jensen, 1985). Later, Jensen realized Supersaurus was a Diplodocid, and he transferred the dorsal from Ultrasaurus (which was the holotype of Ultrasaurus) to Supersaurus (as he realized it was a posterior Diplodocid dorsal, not an anterior Brachiosaurid dorsal) & made the holotype of Ultrasaurus the giant 2.5m scapulocoracoid. (Jensen, 1987). Curtice, Stadtman, & Curtice (1996), knowing that the ICZN does not allow the holotype to be transferred, & thus Ultrasaurus (which by this point had been renamed Ultrasauros, because a small, non-diagnostic, fragmentary, piece of crap Sauropod from South Korea had been named Ultrasaurus in 1983) became a junior synonym of Supersaurus, with the giant scapulocoracoid referred to Brachiosaurus. Curtice & Stadtman (2001) referred Dystylosaurus to Supersaurus. Thus the Jensen Three became the Jensen One.

 

In 2007, a new specimen, WDC-DMJ-021, nicknamed Jimbo, was described. Jimbo is a rather complete Diplodocid skeleton. Lovelace, Hartman, & Wahl (2007) referred it to Supersaurus. However, Jimbo does not preserve a scapula or a coracoid. So what was their reasoning for this referral? They referred Jimbo to Supersaurus based on the similarities to the other postcranial elements (cervicals, dorsals, caudals, etc) from the Dry Mesa Quarry.

 

supersaurus-jimbo-skeletal-sh

Fig. 1. Skeletal restoration of Jimbo, compared to Barosaurus lentusBrontosaurus louisae. Skeletals by Scott Hartman. Used for educational purposes only.


In 2016, an SVPCA abstract was released by Mike Taylor & Matt Wedel of SVPOW! In this abstract,  they refer (rather convincingly) a pair of three cervicals (from BYU quarry  3GR) belonging to a 33-37m Barosaurus. They also refer BYU 9024 (from Dry Mesa quarry), the longest cervical known at 137cm, to Barosaurus, after originally being referred to Supersaurus by both Jensen (1987) & Lovelace, et al (2007). This belongs to a Titanic 45+m Barosaurus specimen. As well, Taylor & Wedel (in press) state that because of lack of cervical bifurcation & a pronounced ventral keel, Dystylosaurus can’t be referred to Supersaurus, or any other Diplodocid for that matter. Thus Dystylosaurus is most likely a valid genus once more. As well, the Ultrasauros scapulocoracoid, referred to Brachiosaurus (Curtice, et al 1996; Taylor, 2009), most likely doesn’t belong to Brachiosaurus, & is likely a valid genus (Paul, 2012). So the Jensen One had once more become the Jensen Three.

This creates a multitude of problems. Jimbo was referred to Supersaurus based on comparisons with the other Diplodocid postcranial material at Dry Mesa. This won’t work if the postcranial is more than Supersaurus. We know for sure there’s a Barosaurus & a Dystylosaurus present at the site, & we can’t just automatically assume all of the other Dry Mesa material is Supersaurus. So let’s take a look at Supersaurus vivianae in detail. The first step is to look at the holotype specimen, BYU 9025. Tschopp, Mateus, & Benson (2015) listed six characters that distinguish BYU 9025 from Diplodocus:

362. Angle between the acromial ridge and scapular blade – This differs between the right and left scapulocoracoids from the type locality, and the range overlaps with the range in other diplodocid species, although it’s closer to the apatosaurine average than the diplodocine average.
366. Orientation of glenoid – This is variable (perhaps ontogenetically) in apatosaurines, and individually varies in Diplodocus carnegii. Supersaurus has the typical non-apatosaurine state.
367. Shape of acromial edge of blade – Individually variable in DiplodocusSeismosaurus and lacks a clear phylogenetic signal elsewhere.
369. Ovate muscle scar on lateral face of blade at base – Variable in Brontosaurus parvus and Seismosaurus hallorum.
370. Subtriangular projection at base of blade, posterior to the glenoid – Individually variable in B. parvus and S. hallorum.
371. Distal expansion of blade – Individually variable in B. parvus, with BYU 1252-18531 being the only diplodocid to resemble Supersaurus in this regard.

So the takeaway here is that both Brontosaurus parvus UW 15556 & BYU 1252-18531 differ in a few scapular characters, & that Diplodocid scapulae may not be particularly reliable for diagnosing a species or genus. Jimbo is definitely a distinct taxon, but given that we can’t say for sure what Dry Mesa material is & is not Supersaurus, I recommend for the moment to retain Jimbo as “Supersaurus” sp., & to wait until we discover a new specimen which has overlap with both Jimbo & BYU 9025. At the moment, I still leave both as Supersaurinins (along with Dinheirosaurus, Australodocus, Tornieria). Another thing to realize is we continue to underestimate Morrison Sauropod diversity (which will definitely be a post at another time). Tally ho folks, & we will have more Sauropod stuff soon!

References


  1. Curtice, B.; Stadtman, K. (2001). “The demise of Dystylosaurus edwini and a revision of Supersaurus vivianae“. In McCord, R.D.; Boaz, D. Western Association of Vertebrate Paleontologists and Southwest Paleontological Symposium – Proceedings 2001. Mesa Southwest Museum Bulletin 8. pp. 33–40.
  2. Curtice, B., Stadtman, K., and Curtice, L. (1996) “A reassessment of Ultrasauros macintoshi (Jensen, 1985).” Pp. 87-95 in M. Morales (ed.), The Continental Jurassic: Transactions of the Continental Jurassic Symposium, Museum of Northern Arizona Bulletin number 60.
  3. Jensen, J.A. (1985). “Three new sauropod dinosaurs from the Upper Jurassic of Colorado.” Great Basin Naturalist, 45: 697-709.
  4. Jensen, J.A. (1987). “New brachiosaur material from the Late Jurassic of Utah and Colorado”. The Great Basin Naturalist 47 (4): 592–608.
  5. Lovelace, D. M.; Hartman, S. A.; Wahl, W. R. (2007). “Morphology of a specimen of Supersaurus (Dinosauria, Sauropoda) from the Morrison Formation of Wyoming, and a re-evaluation of diplodocid phylogeny”. Arquivos do Museu Nacional 65 (4): 527–544.
  6. Paul, Gregory S. (2012). “Some Notes on the Diverse Brachiosaurid Sauropods of the Late Jurassic of North America, Europe and Africa”
  7. Taylor, M.P. (2009). “A Re-evaluation of Brachiosaurus altithorax Riggs 1903 (Dinosauria, Sauropod) and its generic separation from Giraffatitan brancai (Janensch 1914).”Journal of Vertebrate Paleontology, 29(3): 787-806.
  8. Taylor, M.P., & Wedel, M. J. (In press). “How big did Barosaurus get?” SVPCA Liverpool 2016 Abstracts: 30.
  9. Tschopp, E., Mateus O., & Benson R. B. J. (2015). “A specimen-level phylogenetic analysis and taxonomic revision of Diplodocidae (Dinosauria, Sauropoda).” PeerJ. 3, e857.
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