Perijasaurus and implications for Early-Middle Jurassic eusauropod paleobiogeography in the Western Hemisphere

The South American country of Colombia has received some attention in some media outlets because its government beginning in the mid-2010s engaged in peace talks with the Marxist insurgent groups FARC (Revolutionary Armed Forces of Colombia) and ELN (National Liberation Army), leading to a peace agreement with FARC in 2016 under President Juan Manuel Santos that led to FARC abandoning its guerrilla activities and disbanding to allow many of its members to take part in the Colombian political process. Somewhat lost in talk about Colombia, however, is the fact that it has yielded its own Mesozoic tetrapods, including plesiosaurs, marine turtles, ichthyosaurs, and even a titanosauriform sauropod, Padillasaurus. Recently, Rincón et al. (2022) erected the new genus and species Perijasaurus lapaz for a sauropod dorsal vertebra (UCMP 37689) described from the Early to Middle Jurassic La Quinta Formation of eastern Colombia by Langston and Durham (1955), the species name referring to the town of La Paz near which this specimen was excavated and the fact that the 2016 peace agreement between Bogota and FARC made it possible to relocate the site in Colombia that yielded the holotype of P. lapaz. Given that Patagonia has yielded almost all Jurassic sauropod taxa from South America,  and Perijasaurus is quite significant as the first eusauropod from the Hettangian-Callovian interval to described from a locality in the Western Hemisphere north of Patagonia, I am dedicating this post to giving a synopsis of how Perijasaurus affects knowledge of eusauropod paleobiogeography in the Western Hemisphere during the Early-Middle Jurassic interval.

To give an introductory preview of how Perijasaurus affects state-of-the art knowledge of eusauropod paleobiogeography in the Western Hemisphere, it should be noted that the fossil record of Early-Middle Jurassic eusauropods from this region of the world is mostly concentrated in Patagonia, Argentina, with an extreme dearth of sauropod body and trace fossils in localities in the Western Hemisphere outside Patagonia, in contrast to the abundance of eusauropod taxa unearthed in Hettangian-Callovian deposits of East Asia, Europe, Niger, and Madagascar. For instance, fragmentary sauropod remains described from the Toarcian-age La Boca Formation of southwestern Mexico by Fastovsky et al. (1995) and an isolated caudal vertebra from the Summerville Formation of New Mexico (Lucas and Heckert 2000) constituted the only evidence for sauropod body fossils from the Hettangian-Callovian interval in North American until Rivera-Sylva and Espinosa-Arrubarrena (2020) described fragmentary diplodocid remains collected from the Bathonian-Callovian age Otlaltepec Formation in east-central Mexico in the late 1980s. I have always suspected that sampling biases are mostly responsible for the patchy record of sauropod in western North America from the Toarcian-Callovian interval because sauropod trackways are known from Bajocian-Bathonian deposits in Mexico (Ferrusquía-Villafranca et al. 1978, 1995, 1996). Outside Patagonia, dinosaur trackways have been described from Early-Middle Jurassic deposits in southeastern Brazil and northern Chile (see Weishampel et al. 2004), and together with Perijasaurus show that there maybe additional sauropod fossils from fossiliferous Early-Middle Jurassic deposits in South America outside Patagonia waiting to be unearthed or described to science.

Select views of the holotype of Perijasaurus lapaz (UCMP 37689) (after Rincón et al. 2022) 

When placing the phylogenetic position of Perijasaurus obtained by Rincón et al. (2022) in the broader context of eusauropod biogeography during the Toarcian-Callovian interval, it should be pointed out that the recovery of Perijasaurus in a polytomy with Cetiosaurus, Mamenchisauridae, Neosauropoda, Turiasauria, Jobaria, and a non-neosauropod clade formed by Bagualia, Nebulasaurus, Patagosaurus, and Spinophorosaurus raises questions about the timing of the paleogeographical dispersal of some derived eusauropod lineages from Patagonia to the northern Andes, Africa, Australia, and other regions of the worlds from which sauropod taxa dating to the Toarcian-Callovian have been recorded. For instance, the upper unit of the La Quinta Formation that yielded the Perijasaurus lapaz holotype spans the Toarcian-Aalenian boundary, whereas the Cañadón Asfalto Formation that has yielded Bagualia, Patagosaurus, and Volkheimeria plus a few unnamed taxa has been dated to the middle-late Toarcian based on radiometric dating (Pol et al. 2022). Despite the P. lapaz holotype comprising only a single dorsal vertebra, the late Toarcian-early Aalenian age of Perijasaurus combined with the revised age of the Cañadón Asfalto Formation, but also the fact that the mamenchisaurid Tonganosaurus hails from deposits dating to the Pliensbachian, could indicate that eusauropods had immigrated to northern South America and western North America (e.g. Mexico) by the end of the Early Jurassic. In support of this hypothesis, the North American landmass, including present-day Mexico, was mostly attached to South America until the eve of the Middle Jurassic, by which time Pangaea had begun to break up and the Caribbean Seaway started to form, and East Asia was mostly isolated from the Western Hemisphere (Iturralde-Vinent 2003, fig. 1). Moreover, the Bathonian-Callovian age of the Otlaltepec Formation  makes it probable that eusauropods began migrating to Mexico and eventually most of western North America beginning in the Toarcian because the unit of the the La Quinta Formation that has yielded Perijasaurus lapaz is comparable in age to the La Boca Formation, and present-day Mexico and Central America are adjacent to northwestern South America and therefore must have served as a land bridge for tetrapods to disperse into western North America prior to North America breaking away from South America in the Middle Jurassic. Although Rincón et al. (2022) recover a eusauropod clade comprising  Bagualia, Nebulasaurus, Patagosaurus, and Spinophorosaurus, the cladistic analysis by Holwerda et al. (2021) places Patagosaurus as the sister taxon of Cetiosaurus in a monophyletic Cetiosauridae, and the recovery of Spinophorosaurus as a member of Mamenchisauridae by Ren et al. (2023) combined with the Pliensbachian age of Tonganosaurus indicates that more derived eusauropods began achieving a global distribution by the Toarcian-Aalenian. Alternate placements of Perijasaurus within Eusauropoda as sister to either Haplocanthosaurus or the Turiasauria+Neosauropoda clade hinted at by Rincón et al. could hold water in future studies not only due to the P. lapaz holotype comprising a single element but also because the co-existence of the early-diverging eusauropod Archaeodontosaurus and turiasaurian  Narindasaurus in the Bathonian of Madagascar suggests that both basal and derived eusauropods were also coeval in western North America by the late Toarcian/early Aalenian.  

In summary, Perijasaurus is a chronologically important eusauropod taxon for providing new data on the biogeography of basal and derived eusauropods not only because it the oldest eusauropod from a Western Hemispheric locality outside Patagonia but also in that its discovery in northwestern South America provides hints at the timing of the dispersal of eusauropods into western North America given the current dearth of sauropod body fossils in the Hettangian-Callovian interval. Despite the limited amount of material known for the holotype, it demonstrates that eusauropods began spreading into areas of South America and eventually Mexico at lower latitudes over the course of the Toarcian stage of the Early Jurassic due to the presence of sauropod remains from Toarcian and Bathonian-Callovian deposits in Mexico and New Mexico, and thus constitutes the first non-Patagonian eusauropod genus from the Early to Middle Jurassic of the Western Hemisphere. Given that no sauropod body fossils were reported from the Early to Middle Jurassic of western North America until the 1980s, not to mention dinosaur tracks from deposits of Hettangian-Toarcian and Callovian age in Brazil and Chile, Perijasaurus lapaz itself will be of use in helping track the early evolution and paleobiogeography of eusauropods in areas of the Western Hemisphere north of Patagonia, namely the vicinity of the northern Andes and western North America.

Referennces: 

Fastovsky, D.E., Clark, J.M., Strater, N.H., Montellano, M., Hernandez, R., and Hopson, J.A., 1995, Depositional environments of a Middle Jurassic Terrestrial Vertebrate Assemblage, Huizachal Canyon, Mexico. Journal of Vertebrate Paleontology 15(3): 561–575.

Ferrusquía-Villafranca, I., Applegate., S.P., and Espinosa-Arrubarrena, L., 1978. Rocas volcanosedimentarias mesozoicas y huellas de dinosaurios en la región suroccidental pacífica de México. Revista Mexicana de Ciencias Geológicas 2 (2): 150-162.

Ferrusquía-Villafranca, I., Jiménez-Hidalgo, E., and Bravo-Cuevas, V. M., 1995, Jurassic and Cretaceous dinosaur footprints from México: additions and revisions, Journal of Vertebrate Paleontology 15 (Suppl. to No. 3):28A.

Ferrusquía-Villafranca, I., Jiménez-Hidalgo, E., and Bravo-Cuevas, V.M., 1996, Footprints of small sauropods from the Middle Jurassic of Oaxaca, southeastern Mexico. pp. 119-126. In: Morales, M. (ed.), The Continental Jurassic. Museum of Northern Arizona Bulletin 60.

Iturralde-Vinent, M.A., 2003. The conflicting paleontologic versus stratigraphic record of the formation of the Caribbean Seaway. pp. 75–88. In: Bartolini, C.R., Buffler, B.J., and Blickwede, J.F., (eds.), The Circum-Gulf of Mexico and the Caribbean: Hydrocarbon Habitats, Basin Formation, and Plate Tectonics. American Association of Petroleum Geologists Memoir 79: Tulsa, Oklahoma.

Holwerda, F. M., Rauhut, O. W. M., and Pol, D., 2021. Osteological revision of the holotype of the Middle Jurassic sauropod dinosaur Patagosaurus fariasi Bonaparte, 1979 (Sauropoda: Cetiosauridae). Geodiversitas 43 (16): 575-643. https://doi.org/10.5252/geodiversitas2021v43a16. 

Langston, W., Jr., and Durham, J.W., 1955. A sauropod dinosaur from Colombia. Journal of Paleontology 29 (6):1047–1051.

Lucas, S.G., and Heckert, A.B., 2000. Jurassic dinosaurs in New Mexico. New Mexico Museum Of Natural History and Science Bulletin 17:43-46.

Pol, D., Gomez, K., Holwerda, F.H., Rauhut, O.W.M., and Carballido, J.L., 2022. Sauropods from the Early Jurassic of South America and the Radiation of Eusauropoda. pp. 131-136. In: Otero, A., Carballido, J.L., and Pol, D. (eds.), South American Sauropodomorph Dinosaurs. Record, Diversity and Evolution. Cham, Switzerland: Springer. ISBN 978-3-030-95958-6.

Ren, X.X, Jiang, S., Wang, X.R., Peng, G.Z., Ye, Y., Jia, L., and You, H.L., 2023. Re-examination of  Dashanpusaurus dongi (Sauropoda: Macronaria) supports an early Middle Jurassic global distribution of neosauropod dinosaurs. Palaeogeography, Palaeoclimatology, Palaeoecology 610: 111318. doi:10.1016/j.palaeo.2022.111318.

Rincón, A.F., Raad Pájaro, D.A., Jiménez Velandia, H.F., Ezcurra, M.D., and Wilson Mantilla, J.A., 2022. A sauropod from the Lower Jurassic La Quinta Formation (Dept. Cesar, Colombia) and the initial diversification of eusauropods at low latitudes. Journal of Vertebrate Paleontology 42 (1): e2077112. doi:10.1080/02724634.2021.2077112

Rivera-Sylva, H. E., and Espinosa-Arrubarena, L., 2020, Remains of a diplodocid (Sauropoda: Flagellicaudata) from the Otlaltepec Formation Middle Jurassic (Bathonian-Callovian) from Puebla, Mexico. Paleontologia Mexicana 9 (3): 145-150.

Weishampel, D.B., Barrett, P.M., Coria, R.A., Le Loeuff, J., Xu, X., Zhao, X., Sahni, A., Gomani, E.M.P., and Noto, C.R., 2004, Dinosaur distribution. pp. 517-606. In: Weishampel D.B., Dodson, P., and Osmólska, H., (eds.), The Dinosauria, second edition. Berkeley, CA: University of California Press.