How many animals have bifurcated cervical ribs?

BYU 14063, a left cervical rib of the turiasaur Moabosaurus in medial view.

A few sauropods have bifurcated cervical ribs. The most dramatic example that I know of is the turiasaur Moabosaurus (Britt et al. 2017). Mike and I got to see that material on the Sauropocalypse back in 2016, which is how we got the photo above. Royo-Torres et al. (2006) had previously described and figured bifurcated cervical ribs in Turiasaurus, but they seem to be absent in Mierasaurus (Royo-Torres et al. 2017), which is the sister taxon to Moabosaurus.

Cervical ribs of Dicraeosaurus from Janensch (1929). Note the dorsally-projecting bump on the shaft of the rib at the top.

Tschopp et al. (2015: character 217, p. 99–100, fig. 49) recognized a “posteriorly projecting spur on dorsolateral edge of [the] posterior shaft” of the cervical rib in Dicraeosaurus and some apatosaurines. That’s not a complete bifurcation, but it’s not a million miles out — at least, it’s implying that a second muscle was pulling on the cervical rib from a different direction as the first.

Sereno et al. (1999) reported that cervical ribs 3-6 of Jobaria have an “accessory anterior process”. This might mean that some of the anterior processes of the cervical ribs are bifurcated in Jobaria, but the character state is not illustrated and we have not been able to observe the relevant fossils firsthand.

Cervical ribs of Zhuchengceratops from Xu et al. (2010: fig. 7). Fifth cervical rib in lateral (I) and medial (J) views; sixth cervical rib in medial (K) and lateral (L) views.

Xu et al. (2010) described bifurcated cervical ribs in the leptoceratopsid ceratopsian Zhuchengceratops, including in their diagnosis “middle cervical ribs bifurcated due to presence of prominent accessory dorsal process (condition poorly known in other ceratopsians)”. The cervical ribs of Zhuchengceratops show a whole morphological spectrum, from an accessory dorsal process present as a tiny bump, as in Dicraeosaurus, all the way to full bifurcation. Xu et al. (2010) implied that this feature is also present in other ceratopsians including Triceratops.

So…who else? Any non-avian theropods? Weird Triassic hellasaurs? Attention-seeking salamanders? Cervical-rib-obsessed minds want to know.

References

• Britt, Brooks B., Rodney D. Scheetz, Michael F. Whiting and D. Ray Wilhite. 2017. Moabosaurus utahensis, n. gen., n. sp., a new sauropod from the Early Cretaceous (Aptian) of North America. Contributions from the Museum of Paleontology, University of Michigan 32(11):189–243.
• Janensch, Werner. 1929. Die Wirbelsäule der Gattung Dicraeosaurus. Palaeontographica, Supplement 7, 2:39–133 and plates I–VII.
• Royo-Torres, Rafael, Alberto Cobos and Luis Alcalá. 2006. A giant European dinosaur and a new sauropod clade. Science 314:1925–1927.
• Royo-Torres, Rafael, Paul Upchurch, James I. Kirkland, Donald D. DeBlieux, John R. Foster, Alberto Cobos and Luis Alcalá. 2017. Descendants of the Jurassic turiasaurs from Iberia found refuge in the Early Cretaceous of western USA. Scientific Reports 7:14311. doi:10.1038/s41598-017-14677-2
• Sereno, Paul C., Allison L. Beck, Didier. B. Dutheil, Hans C. E. Larsson, Gabrielle. H. Lyon, Bourahima Moussa, Rudyard W. Sadleir, Christian A. Sidor, David J. Varricchio, Gregory P. Wilson and Jeffrey A. Wilson. 1999. Cretaceous sauropods from the Sahara and the uneven rate of skeletal evolution among dinosaurs. Science 282:1342–1347.
• Xu X, Wang K, Zhao X, Sullivan C, Chen S. 2010. A new leptoceratopsid (Ornithischia: Ceratopsia) from the Upper Cretaceous of Shandong, China and its implications for neoceratopsian evolution. PLoS ONE 5(11): e13835. https://doi.org/10.1371/journal.pone.0013835