Bruhathkayosaurus: a genuine giant titanosaur after all

In the late 1980s fragmentary postcranial remains from the Kallamedu Formation in Tamil Nadu, southern India, were described by Indian paleontologists P. Yadagiri and Krishnan Ayyasami as a new genus and species of carnosaurian theropod, Bruhathkayosaurus matleyi, in a paper published in 1987. However, in the 1990s the theropod placement of Bruhathkayosaurus was disputed and this taxon was soon recognized as being a titanosaurian sauropod. Due to the paucity of line drawings and photographs of the Bruhathkayosaurus material as it lay on the ground, there was online speculation that this taxon was based on fossilized tree trunks rather than genuine dinosaur bones, and varying size estimates for Bruhathkayosaurus based on the published description by Yadagiri and Ayyasami (1987) posted on internet forums precluded Bruhathkayosaurus from being touted in record books as the biggest dinosaur that ever lived. Nevertheless, various authors (e.g. Krause et al. 2006; Hone et al. 2016) have come to agree with Chatterjee (1995) that Bruhathkayosaurus matleyi is a sauropod, although the questionable validity of this taxon was further compounded by the type material falling victim to the effects of local monsoons (Galton and Ayyasami 2017). Thanks to additional published photographs of the B. matleyi type material and new morphological information on this poorly known dinosaur, it is apparent that the material of Bruhathkayosaurus is indeed from a giant titanosaur and that past hints about this dinosaur being based on non-vertebrate material do not hold water.

Photographs of the holotype ilium and paratype tibia of Bruhathkayosaurus matleyi (left) and line drawings of the B. matleyi ilium and tibia (right). From Yadagiri and Ayyasami (1987).

When Bruhhathkyosaurus was first described by Yadagiri and Ayyasami (1987), it was considered by the authors to be a very large theropod possibly comparable to or exceeding Tyrannosaurus rex in size (radius and pubis of Bruhathkayosaurus matleyi were not described or illustrated). The first author to question the theropod classification of this taxon was Olshevsky (1994), who noted that the proportions of the ilium and tibia were unusually large for a huge theropod judging from the illustrations in Yadagiri and Ayyasami (1987), therefore suggesting that Bruhathkayosaurus might not be a theropod. In a 1994 post on Dinosaur Mailing list, John Schneiderman regarded the tibia of Bruhathkayosaurus as either a sauropod or petrified wood, while Thomas Holtz Jr. in a 1995 post on the DML suggested that the type material of B. matleyi could be fossilized tree trunks due to the poor quality of the line drawings of the ilium and tibia by Yadagiri and Ayyasami (1987) Chatterjee (1995) showed that B. matleyi represented a titanosaurian sauropod by noting that the high iliac crest of the holotype ilium (GSI PAL/SR/20) and proportions of the distal femur and tibia were consistent with that of titanosaurs. Upchurch et al. (2004) tabulated Bruhathkayosaurus matleyi as a nomen dubium without any further comment, most probably aware of Chatterjee's (1995) re-assessment of Bruhathkayosaurus because that paper is not included in the bibliography for the second edition of the book The Dinosauria. Krause et al. (2006) also classified Bruhathkayosaurus as a sauropod, and Hone et al. (2016) likewise agreed with Chatterjee's (1995) identification of Bruhathkayosaurus as a titanosaur. Pal and Ayyasami (2022) provide photographs of the tibia of Bruhathkayosaurus matleyi during excavation from the Cauvery Basin and after being wrapped in a plaster jacket, and they clinch the titanosaur identification of the tibia by noting that the cnemial crest of the tibia is identical to that of titanosaurs in being smaller and less prominent than in abelisaurids, while debunking online suggestions that the B. matleyi type material is merely fossilized wood.

Now all this brings me to discussions online and published scientific literature regarding the possible size of Bruhathkayosaurus.  Mickey Mortimer wrote in a June 2001 post on the Dinosaur Mailing List that Bruhathkayosaurus most likely measured 145 feet (44.1 meters) based on measurements provided by Yadagiri and Ayyasami (1987), but in later posts on the DML he revised to size estimate for this taxon to 92-154 feet (28-47 meters). In a May 2008 post on his blog Sauropoda Vertebra of the Week, Mike Taylor suggested that Bruhathkayosaurus was 20 percent bigger than Argentinosaurus based on the length of the tibia. Although Pal and Ayyasami (2022) declined to provide a precise size estimate for B. matleyi given the limited material, they did confirm the gigantic nature of Bruhathkayosaurus by showing that its tibia was bigger than that of Argentinosaurus and Dreadnoughtus and that the width of the distal femur was bigger than that of Patagotitan. The authors also noted that the holotype ilium and paratype tibia are unlikely to belong the same individual due to size differences (the length of the ilium of B. matleyi is shorter than the ilium of the Dreadnoughtus schrani holotype), supporting Olshevshy's (1994) suggestion that the Bruhathkayosaurus material might be chimeric, but the ilium itself would still be comparable in size to those known for some large-sized titanosaurs, namely Futalognkosaurus, because its length is much greater than the longest ilia of any abelisaurid. Paul and Larramendi (2023) provide a narrower size estimate for Bruhathkayosaurus ranging from 115-148 feet (35-45 meters) with a mean length of 131 feet (40 meters). In my opinion, Bruhathkayosaurus is probably close to the lower end of the size range deduced by Paul and Larramendi (2023) for this taxon, at 120 feet (36 meters) in length, because Diplodocus hallorum and Maraapunisaurus were once considered to attain lengths of 170 feet (52 meters) and 190 feet (58 meters) respectively, only to have their size estimates reduced drastically to within 100-115 feet (30-35 meters) by later research. Regardless of the fact that the holotype ilium and paratype tibia of Bruhathkayosaurus matleyi do not appear to come from the same individual, the the tibia indicates that Bruhathkayosaurus is indeed a taxon of gigantic titanosaur as surmised online by Mickey Mortimer and Mike Taylor.

Although it is unfortunate that monsoons ended up causing the type material of Bruhathkayosaurus matleyi to disintegrate before being taken to its respective paleontological institution and there were rumors online that Bruhathkayosaurus was based on petrified wood rather than genuine dinosaur fossils even if it was clear by the mid-1990s that the original theropod classification of this taxon did not hold water, it is heartening to see that additional photographic evidence has vindicated the conclusion by Chatterjee (1995) that Bruhathkayosaurus itself is not just a titanosaur but also roughly comparable to Argentinosaurus and Diplodocus hallorum in size. Considering that Matley (1929) was the first author to report giant titanosaur remains from the Kallamedu Formation, Bruhathkayosaurus constitutes the second instance of a super-size titanosaur from this geologic unit, suggesting that giant titanosaurs had a widespread distribution across Gondwana by the Maastrichtian.

References:

Chatterjee, S., 1995. The last dinosaurs of India. The Dinosaur Report (Fall 1995): 12-18.

Galton, P.M., and Ayyasami, K., 2017. Purported latest bone of a plated dinosaur (Ornithischia: Stegosauria), a "dermal plate" from the Maastrichtian (Upper Cretaceous) of southern India. Neues Jahrbuch für Geologie und Paläontologie - Abhandlungen 285 (1): 91–96.  doi:10.1127/njgpa/2017/0671.

Hone, D.W. E., Farke, A.A., and Wedel, M.J., 2016. Ontogeny and the fossil record: what, if anything, is an adult dinosaur? Biology Letters 12 (2): 20150947. doi:10.1098/rsbl.2015.0947.

Krause, D.W., O'Connor, P.M., Rogers, K.C., Sampson, S.D., Buckley, G.A., and Rogers, R.R., 2006. Late Cretaceous terrestrial vertebrates from Madagascar: Implications for Latin American biogeography. Annals of the Missouri Botanical Garden 93 (2): 178–208. doi:10.3417/0026-6493(2006)93[178:LCTVFM]2.0.CO;2.

Matley, C.A., 1929. The Cretaceous dinosaurs of the Trichinopoly District, and the rocks associated with them. Records of the Geological Survey of India 61: 337–349.

Olshevsky, G., 1994. Bruhathkayosaurus: Bigger Than T. rex? The Dinosaur Report (Winter 1994): 12–13.

Pal, S., and Ayyasami, K., 2022. The lost titan of Cauvery. Geology Today 39: 112–116.

Paul, G.S., and Larramendi, A., 2023. Body mass estimate of Bruhathkayosaurus and other fragmentary sauropod remains suggest the largest land animals were about as big as the greatest whales. Lethaia 56 (2): 1–11. doi:10.18261/let.56.2.5.

Upchurch, P., Barrett, P.M., and Dodson, P. 2004. Sauropoda. pp. 259-322. In: Weishampel, D.B., Dodson, P., and Osmólska, A.H. (eds). The Dinosauria, second edition. University of California Press: Berkeley, CA.

Yadagiri, P., and Ayyasami, K., 1987. A carnosaurian dinosaur from the Kallamedu Formation (Maastrichtian horizon), Tamil Nadu. Geological Survey of India, Special Publications 11: 523–528.

Thoughts on paper by D'Emic (2023) regarding evolution of huge body size in sauropods

For generations, sauropod dinosaurs have starred in the popular imagination as the biggest land animals to ever walk the Earth, with interest in giant sauropods going back to the 1970s and 1980s with the discovery of the derived titanosaur Argentinosaurus and the diplodocids Diplodocus (=Seismosaurus) hallorum and Supersaurus (the giant rebbachisaurid Maraapunisaurus was seen in some publications as possibly the biggest-ever sauropod, although the missing nature of the holotype dorsal vertebra made size estimates of 190 feet guesswork, but Carpenter [2018] revised the size estimate of this genus to 105 feet, which makes sense because the initial size estimates of 170 feet for Diplodocus  hallorum was later revised to 110 feet). While children and adults alike marvel at the immense size of sauropods compared to elephants, rhinoceroses, and the extinct paraceratheres, I have not forgotten the fact that some sauropods living on island arcs in southern Europe during the Late Cretaceous which today are part of France, Spain, and Romania exhibited insular dwarfism, and that not all sauropods approached the body sizes attained by Apatosaurus, Brachiosaurus, Brontosaurus, Diplodocus, Galeamopus, Giraffatitan, and Supersaurus. Recently, D'Emic (2023) published a new paper illuminating the evolution of body size among sauropod taxa, relying on measurements of the circumferences of sauropod limb bones to propose that massive body size evolved convergently in multiple sauropod clades, while noting that select taxa of sauropods showed decreasing trends in body size. Having had the chance to read this paper, there are some noteworthy observations from the study that I wish to emphasize in detail. 

As admitted by D'Emic (2023), the patchy sauropod fossil record has constrained the focus on sauropod body size evolution to less than half of the approximately 250 described sauropod taxa, but the fact that Franz Nopcsa's interpretation of Magyarosaurus as a dwarf taxon has been vindicated by several studies (e.g. Benton et al. 2010; Stein et al. 2010) along with the small size of the short-necked dicraeosaurid Brachytrachelopan and the dwarf brachiosaurid Europasaurus shows that diminutive body size was present in more than one eusauropod clade. Although Cope's rule says that tetrapod lineages tend to increase in body size over time, it should be noted that when Edward Drinker Cope and Othniel Charles Marsh described to science the sauropod fauna of the Morrison Formation in western North America, they did not foresee that a few sauropod taxa of diminutive body size would be named in a handful of publications long after their deaths, and Magyarosaurus would be the first sauropod to be described that deviates from Cope's rule when it comes to body size in sauropods. With respect to the argument by D'Emic that the evolutionary cascade hypothesis put forward by Sander (2013) to interpret gigantism in some sauropods as being driven by anatomical and physiological innovations stemming from a nested array of historical prerequisites is best explained by ecological and life-history factors rather than any shared morphological traits, I should emphasize that the co-existence of dwarf and gigantic titanosaurs in the Late Cretaceous of Romania, Spain, and France (Stein et al. 2010; Vila et al. 2022) lends support to D'Emic's conclusion that ecological and life-history factors influenced the degree of dwarfism or gigantism among sauropod clades by showing that the insular nature of the ecosystems of the Ibero-Armorican island and Hațeg Island didn't necessarily translate into uniform dwarfism among titanosaur taxa from the Late Ceretaceous of Europe. For instance, Vila et al. (2022) note that the holotype of Abditosaurus kuehnei is substantially larger than specimens of other titanosaur taxa from the Ibero-Armorican Island as well as titanosaur specimens from the Hațeg Island, indicating that Cope's rule might apply to the evolution of body size in titanosaurs over the course of the Maastrichtian in southern Europe.

Phenogram of sauropod body size evolution over the course of the Mesozoic (from D'Emic 2023). Note that the lineages of the six eusauropod lineages that surpassed the maximum mammalian body mass are denoted by longitudinal lines highlighted in different colors (light green=non-neosauropod eusauropods; dark green=turiasaurians; blue=diplodocoids; orange=basal macronarians and non-titanosaur somphospondyls; purple=brachiosaurids; red=titanosaurs).

According to D'Emic, a total of 36 sauropod lineages independently evolved huge body sizes greater than those of other terrestrial tetrapods from the Mesozoic and Cenozoic, 32 of them belonging to the clade Neosauropoda. The discovery of isolated postcranial remains from the Bajocian-Callovian age Dongdaqiao Formation of Tibet belonging to a eusauropod over 66 feet (20 meters) long (Wei et al. 2023), two gigantic eusauropod cervical vertebrae from the Shishugou Formation of Xinjiang indicating a eusauropod 115 feet (35 meters) in length (which are referred to Mamenchisaurus sinocanadorum by Paul [2019] but considered to be of indeterminate taxonomic placement by Moore et al. [2023]), and a maximum size estimate of 105 feet (32 meters) for the Middle Jurassic mamenchisaurid Xinjiangtitan given by Wu et al. (2013), indicate that gigantic body size evolved in more than one clade of non-turiasaurian, non-neosauropod eusauropods during the Middle Jurassic, although the limited amount of material known for Mamenchisaurus sinocanadorum renders the exact size of this taxon unclear. The gigantic size of Turiasaurus relative to that of other turiasaurs makes me feel tempted to suggest that the rate of body size evolution in Turiasauria is inconsistent with Cope's rule because of the medium body size of the Early Cretaceous turiasaurs Mierasaurus and Moabosaurus and small body size of the Late Jurassic form Amanzia from Switzerland (Schwarz et al. 2020), the minor age difference between  Turiasaurus and the Yellow Cat Member of the Cedar Mountain Formation yielding Mierasaurus and Moabosaurus could suggest large-bodied turiasaurs might survived into the Valanginian-Barremian interval and that the small size of Amanzia can be best explained as a result of insular dwarfism given that much of western and central Europe was covered by seas during the Late Jurassic.

References:

Benton, M.J., Csiki, Z., Grigorescu, D., Redelstorff, R., Sander, P.M., Stein, K., and Weishampel, D.B., 2010. Dinosaurs and the island rule: The dwarfed dinosaurs from Haţeg Island. Palaeogeography, Palaeoclimatology, Palaeoecology 293 (3): 438–454. doi:10.1016/j.palaeo.2010.01.026

Carpenter, K, 2018. Maraapunisaurus fragillimus, N.G. (formerly Amphicoelias fragillimus), a basal Rebbachisaurid from the Morrison Formation (Upper Jurassic) of Colorado. Geology of the Intermountain West 5: 227–244.

D'Emic, M. D., 2023. The evolution of maximum terrestrial body mass in sauropod dinosaurs. Current Biology 33 (9): R349–R350. doi:10.1016/j.cub.2023.02.067

Paul, G.S., 2019. Determining the largest known land animal: A critical comparison of differing methods for restoring the volume and mass of extinct animals. Annals of the Carnegie Museum 85 (4): 335–358. doi:10.2992/007.085.0403

Sander, P.M., 2013. An Evolutionary Cascade Model for Sauropod Dinosaur Gigantism - Overview, Update and Tests. PLoS ONE 8(10): e78573. https://doi.org/10.1371/journal.pone.0078573

Schwarz, D., Mannion, P.D., Wings, O., and Meyer, C.A., 2020. Re-description of the sauropod dinosaur Amanzia (‘Ornithopsis/Cetiosauriscus’) greppini n. gen. and other vertebrate remains from the Kimmeridgian (Late Jurassic) Reuchenette Formation of Moutier, Switzerland. Swiss Journal of Geosciences 113: 2. https://doi.org/10.1186/s00015-020-00355-5

Stein, K., Csiki, Z., Curry Rogers, K., Weishampel, D.B., Redelstorff, R., Carballidoa, J.L., and Sander, P.M., 2010. Small body size and extreme cortical bone remodeling indicate phyletic dwarfism in Magyarosaurus dacus (Sauropoda: Titanosauria). Proceedings of the National Academy of Sciences of the United States of America 107 (20): 9258–9263. doi:10.1073/pnas.1000781107

Vila, B., Sellés, A., Moreno-Azanza, M., Razzolini, N.L., Gil-Delgado, A., Canudo, J.I., and Galobart, A., 2022. A titanosaurian sauropod with Gondwanan affinities in the latest Cretaceous of Europe. Nature Ecology & Evolution 6: 288-296. doi:10.1038/s41559-021-01651-5.

Wei, X.-F.; Wang, Q.-Y., An, X.-Y., Wang, B.-D., Zhang, Y.-J., Mou, C.-L., Li, Y., Wang, D.-B., Ma, W., and Kundrát, M., 2023. New sauropod remains from the Middle Jurassic Dongdaqiao Formation of Qamdo, eastern Tibet. Palaeoworld: in press. doi:10.1016/j.palwor.2023.02.002

Wu, W.H., Zhou, C.F., Wings, O., Sekiya, T., and Dong, Z.M., 2013. A new gigantic sauropod dinosaur from the Middle Jurassic of Shanshan, Xinjiang. Global Geology 32: 437–446.

Did early titanosaurs have non-procoelous anterior caudals and broad-crowned teeth? My thoughts on Poropat et al. 2023 paper

I remember that the description of  Rapetosaurus from Madagascar in the early 2000s demonstrated that the supposed late-surviving diplodocoids Nemegtosaurus and Quaesitosaurus are derived titanosaurs, the morphological similarities of the skulls of these taxa to diplodocids stemming from convergent evolution. Ironically, very few non-lithostrotian somphospondyl taxa preserve cranial remains, namely Diamantinasaurus, Euhelopus, Liaoningotitan, Ligabuesaurus, Mongolosaurus,  Phuwiangosaurus, Sarmientosaurus, and Tambatitanis, and the dearth of cranial remains for both basal titanosaurs and basal somphospondyls has been an obstacle to better understanding the ancestral cranial Bauplan of the most primitive titanosaurs, although Sarmientosaurus has a skull morphologically intermediate between that of basal titanosauriforms and derived titanosaurs. Recently, Poropat et al. (2023) have described a new specimen of Diamantinasaurus matildae (recovered by Poropat et al. [2021] as the sister taxon of Sarmientosaurus and Savannasaurus in the new titanosaur clade Diamantinasauria) preserving a nearly complete skull, AODF 906, illuminating aspects of the skull anatomy of this genus not preserved in referred Diamantinasaurus matildae specimen AODF 836 (described in detail by Poropat et al. 2021). Since AODF 906 reveals that Diamantinasaurus had a Sarmientosaurus-like skull and non-procoelous anterior caudal vertebrae, I have an opportunity to investigate whether the most primitive titanosaurs had broad, spatulate teeth and non-procoelous anterior caudals.

Equal-weights cladistic analysis of Diamantinasaurus matildae based on new morphological information from referred specimen AODF 906 (after Poropat et al. 2023). The figure drawings of Diamantinasaurus and Sarmientosaurus in the cladogram highlight the greater height of the rear skull relative to the snout distinguishing diamantinasaurians from lithrostrotian taxa for which skull material is known.  

In their paper erecting the name Diamantinasauria for the non-lithostrotian titanosaur clade formed by Diamantinasaurus, Sarmientosaurus, and Savannasaurus, Poropat et al. (2021) listed amphicoelous anterior caudal vertebrae as one of the distinguishing features of Diamantinasauria, but stressed that amphicoelous anterior caudals could only be assessed in Savannasaurus in contrast to the holotypes of Diamantinasaurus matildae and Sarmientosaurus musacchioi as well as referred D. matildae specimen AODF 836 lacking caudal remains even though Andesaurus has been consistently recovered as a basal titanosaur, raising the question of whether the presence of slight procoely in the anterior caudals of Andesaurus represents an independent morphological acquisition from lithostrotian titanosaurs. As Carballido et al. (2022) point out, Andesaurus has been consistently recovered as a basal titanosaur in nearly all titanosaur phylogenies, but its phylogenetic instability in some recent cladistic studies renders its role as a phylogenetic exemplar for basal Titanosauria labile, and it should be noted that the holotype of Andesaurus delgadoi is incomplete, which raises the possibility that future discoveries could render Andesaurus less basal within Titanosauria but still outside Lithostrotia. Indeed, the cladistic analysis of the titanosaur Ruixinia by Mo et al. (2023) places Andesaurus in a basal titanosaur clade that also includes Dongyangosaurus, Huabeisaurus, and Tambatitanis in a basal clade of Titan, and because Baotianmansaurus, Dongyangosaurus, Huabeisaurus and Tambatitanis share with Diamantinasaurus and Savannasaurus the presence of amphicoelous anterior caudals, it is possible that slightly procoelous in the anterior caudals of Andesaurus constitutes an autapomorphy among non-lithostrotian titanosaurs, since Poropat et al. (2023) recover Baotianmansaurus, Dongyangosaurus, and Huabeisaurus basally within Titanosauria outside Lithostrotia, like the clade Diamantinasauria. Although Hamititan from the Early Cretaceous of Xinjiang (Wang et al. 2021) is much older than Andesaurus and Diamantinasaurus, it differs from diamantinasaurians in having strongly procoelous caudal vertebrae, suggesting that some early titanosaurs had strongly procoelous anterior caudals and that others had either amphicoelous or opisthocoelous anterior caudal vertebrae because the anterior caudal vertebrae of Ninjatitan from the earliest Cretaceous of Argentina is slightly procoelous like Andesaurus (Gallina at al. 2021).

As noted by Poropat et al. (2021), the cranial material of the Diamantinasaurus matildae specimen AODF 836 is similar to the holotype of Sarmientosaurus musacchioi in having a quadratojugal with a posterior tongue-like process, a braincase with more than one ossified exit for cranial nerve V, and compressed and conical chisel-shaped teeth, but the new D. matildae specimen described by Poropat et al. (2023) demonstrates that the skull of diamantinasaurian titanosaurs was taller and acutely elevated relative to the snout, and that members of Diamantinasauria have robust dentigerous elements. I earlier mentioned that Euhelopus, Liaoningotitan, Mongolosaurus, Phuwiangosaurus, and Tambatitanis are the only non-lithostrotian somphospondyls besides diamantinasaurians that preserve extensive cranial remains, but the skulls of Diamantinasaurus and Sarmientosaurus are similar in every respect to those of brachiosaurids and differ from Euhelopus in having narrower tooth crowns, although they are not as slender as that of the basal somphospondylan Phuwiangosaurus (for which one referred specimen containing cranial and dental elements is known) or derived titanosaurs (Poropat et al. 2022, 2023). The occurrence of a relatively broad-crowned titanosauriform tooth in Santonian-age deposits in Hungary (Ősi et al. 2017) and the presence of broad-crowned teeth in the lithostrotian titanosaur Ampelosaurus (Le Loeuff 2005), in tandem with the spatulate teeth of Euhelopus and the fairly narrow tooth crowns of Diamantinasaurus, Huabeisaurus, Sarmientosaurus, and Tambatitanis, could indicate that the tooth crowns of the earliest and most primitive titanosaurs were more similar to those of Camarasaurus and Euhelopus, especially considering that the teeth of Diamantinasaurus, Huabeisaurus, Sarmientosaurus, and Tambatitanis are not as slender as those of lithostrotians such as Nemegtosaurus, Quaesitosaurus, Rapetosaurus, and Tapuiasaurus. Although the holotype of the basal somphospondyl Yongjinglong datangi does not preserve any cranial remains, it does include three teeth, all of which are somewhat similar to Euhelopus, and the basal somphospondyl Sibirotitan also had broad tooth crowns (Poropat et al. 2022). Therefore, broad-crowned teeth are most probably symplesiomorphic for the most primitive titanosaurs and a few derived titanosaurs, with conical chisel-shaped teeth and slender pencil-shaped teeth being derived states for Titanosauria. 

References:

Carballido, J.L., Otero, A., Mannion, P.D., Salgado, L., and Moreno, A.P., 2022. Titanosauria: A Critical Reappraisal of Its Systematics and the Relevance of the South American Record. pp. 269–298. 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

Gallina, P. A., Canale, J. I., and Carballido, J. L., 2021. The Earliest Known Titanosaur Sauropod Dinosaur. Ameghiniana 58 (1): 35–51. doi:10.5710/AMGH.20.08.2020.3376.

Le Loeuff, J., 2005. Osteology of Ampelosaurus atacis (Titanosauria) from Southern France. pp. 115–137. In: Tidwell, V., and Carpenter, K. (eds.). Thunder-Lizards: The Sauropodomorph Dinosaurs. Bloomington: Indiana University Press. ISBN 978-0-253-34542-4.

Mo, J., Ma, F., Yu, Y., and Xu, X., 2023. A new titanosauriform sauropod with an unusual tail from the Lower Cretaceous of northeastern China. Cretaceous Research 144: 105449.  doi:10.1016/j.cretres.2022.105449.

Ősi, A., Csiki-Sava, Z., and Prondvai, E., 2017. A sauropod tooth from the Santonian of Hungary and the European Late Cretaceous 'Sauropod Hiatus.' Scientific Reports 7: 3261. https://doi.org/10.1038/s41598-017-03602-2 

Poropat, S. F., Kundrát, M., Mannion, P. D., Upchurch, P., Tischler, T. R., and Elliott, D. A., 2021. Second specimen of the Late Cretaceous Australian sauropod dinosaur Diamantinasaurus matildae  provides new anatomical information on the skull and neck of early titanosaurs. Zoological Journal of the Linnean Society 192 (2): 610-674. doi:10.1093/zoolinnean/zlaa173 

Poropat, S.F., Frauenfelder, T.G., Mannion, P.D., Rigby, S.L., Pentland, A.H., Sloan, T. and Elliott, D.A., 2022. Sauropod dinosaur teeth from the lower Upper Cretaceous Winton Formation of Queensland, Australia and the global record of early titanosauriforms. Royal Society Open Science 9: 220381.

Poropat, S. F., Mannion, P. D., Rigby, S. L., Duncan, R. J., Pentland, A. H., Bevitt, J. J., Sloan, T., and Elliott, D. A., 2023. A nearly complete skull of the sauropod dinosaur Diamantinasaurus matildae from the Upper Cretaceous Winton Formation of Australia and implications for the early evolution of titanosaurs. Royal Society Open Science 10(4): 221618. https://doi.org/10.1098/rsos.221618   

Wang, X., Bandeira, K. L. N., Qiu, R., Jiang, S., Cheng, X., Ma, Y., and Kellner, A.W.A., 2021. The first dinosaurs from the Early Cretaceous Hami Pterosaur Fauna, China. Scientific Reports 11:14962. doi:10.1038/s41598-021-94273-7.

Ruixinia and convergences in vertebral morphology among East Asian mamenchisaurids and titanosauriforms

The past decade or so has seen a considerable increase in the number of titanosauriform taxa known from the Early Cretaceous (Berriasian-early Aptian) of East Asia (e.g. Wang et al. 2007; You et al. 2008; Azuma and Shibata 2010; Zhou et al. 2018; Wang et al. 2021), shedding light on the evolution of both titanosaurs and non-titanosaurian titanosauriforms in this region during the Berriasian-early Aptian. However, most of those taxa are based on fragmentary and/or incomplete holotypes, in some cases preserving minimal vertebral material, and although D'Emic (2012) and Mannion et al. (2019) recovered Euhelopus and some non-titanosaur somphospondyls from the Berriasian to Aptian of East Asia in a monophyletic Euhelopodidae, the recovery of Daxiatitan, Dongbetitan, Euhelopus, and Xianshanosaurus outside Titanosauriformes in some cladistic analyses of Klamelisaurus by Moore et al. (2020) combined with the fact that no caudals are preserved for Euhelopus raise questions about the degree of the convergence of cervical and caudal vertebral characters among different lineages of eusauropods which have been found in East Asia. Mo et al. (2023) have recently described a new titanosaur from the Yixian Formation of Liaoning in northeastern China, Ruixinia zhangi, on the basis of a partial articulated postcranial skeleton, constituting the first East Asian titanosauriform of the Early Cretaceous to preserve a complete caudal series. Thus, a discussion of the implications of Ruixinia for the degree of convergent evolution in the morphology of the cervical and caudal vertebrae among East Asian eusauropods found in strata from the Aalenian-Albian interval is warranted.

Elements of the holotype of Ruixinia zhangi (ELDM EL-J009) (from Mo et al. 2023)

As I have noted elsewhere, D'Emic (2012) considered bifurcated cervical neural spines and the presence of thick, subhorizontal epipophyseal–prezygapophyseal laminae on the cervical vertebrae as diagnostic for Euhelopodidae, but those characters are either homoplastic among derived eusauropods or are not exclusively shared by the taxa included by D'Emic (2012) in Euhelopodidae. When describing the cervical vertebrae of Ruixinia, Mo et al. emphasize that the preservation of the cervicals in ELDM EL-J009 make it uncertain whether the neural spines of the middle and posterior cervicals for this taxon are bifurcated, and it should be noted that very few cervical vertebrate are known for Phuwiangosaurus and Tangvayosaurus, making it uncertain if the Southeast Asian taxa assigned to Euhelopodidae by D'Emic (2012) had bifurcated neural spines or not. Also, unpublished cladistic results reported in an abstract by D'Angelo (2022) recover Erketu as a basal titanosaur closely related to Huabeisaurus, indicating that whether or not Ruixinia had bifurcated cervical neural spines, the presence or absence of bifurcation of the neural spines of the cervical vertebrae varies among basal somphospondyls and some members of  Titanosauria. The occurrence of strongly procoelous anterior caudal vertebrae in Ruixinia that was once used to diagnose derived titanosaurs but is now recognized as being present in mamenchisaurids (e.g. the holotype of Wamweracaudia keranjei was once used to assign Janenschia to Titanosauridae before being recognized as a mamenchisaurid), turiasaurians (Royo-Torres et al. 2017; Mannion et al. 2019), the basal titanosaur Hamititan (Wang et al. 2021) and the basal macronarian Bellusaurus (Jacobs et al. 1993) may suggest that strongly procoelous anterior and middle caudal vertebrae evolved convergently among different clades of derived eusauropods by the Tithonian-Berriasian. Considering that Wang et al. (2021) recover Hamititan as more derived than the basal titanosaur Andesaurus despite the younger age of the latter, it is possible that Hamititan might be closely related to Ruixinia because both taxa possess marked ventrolateral ridges on the second caudal vertebrae (compare Mo et al. 2023, fig. 6 with Wang et al. 2021, fig. 4), and Wang et al. note that the well-marked ventrolateral ridges of the anterior caudals of Hamititan are comparable to those of Xianshanosaurus. The fusion of the last six caudals of Ruixinia also deserves attention because Mo et al. point out that this morphological feature has been previously described from mamenchisaurids and the basal eusauropod Shunosaurus, but since the distal end of the tail of Ruixinia is distinct from Shunosaurus and mamenchisaurids in being rod-shaped, the fusion of the distalmost caudal vertebrae constitutes yet another caudal vertebral feature that evolved convergently in Titanosauria and non-neosauropod eusauropods.

    

Reduced consensus cladistic analysis of Ruixinia zhangi (after Mo et al. 2023).

The cladistic analysis of Ruixinia by Mo et al. provides some very important insights into the degree of convergence in the vertebral morphologies of titanosauriforms and non-neosauropod eusauropods found in East Asia. In this phylogeny, Ruixinia is recovered as a derived titanosaur closely related to the taxa Daxiatitan and Xianshanosaurus, while Dongbeititan is placed as a non-titanosaur somphospondylan, whereas Liaoningotitan is clustered with Baotianmansaurus and Diamantinasaurus in the majority of he most parsimonious trees created by the Ruixinia phylogenetic analysis. It is interesting to note that Daxiatitan, Dongbeititan, and Xianshanosaurus are recovered along with Euhelopus within the "Core Mamenchisaurus-like Taxa" clade of Mamenchisauridae in some phylogenetic analyses by Moore et al. (2020) because Dongbeititan and Euhelopus are both similar to mamenchisaurids in having more than 15 cervical vertebrae, and the anterior and middle caudal vertebrae of Daxiatitan, Dongbeititan, and Ruixinia are strongly procoelous like those of mamenchisaurids and the basal titanosaur Hamititan. Since no cervical vertebrae are preserved for Xianshanosaurus, and the Daxiatitan holotype preserves 10 cervicals, the placement of Dongbeititan outside Titanosauria in contrast to Daxititan, Ruixinia, and Xianshanosaurus being recovered as derived titanosaurs suggests that vertebral characters shared with mamenchisaurids by Daxiatitan, Dongbeititan, Ruixinia, and Xianshanosaurus are best regarded as being convergent because Mo et al. (2023) note morphological differences between Ruixinia and other titanosauriforms found in Liaoning and a few titanosaur taxa have been described as having more than 15 cervical vertebrae. For instance, although Ruixinia and Dongbeititan have a cervical vertebral count exceeding 15 and strongly procoelous anterior caudals, the presence of bifid anterior caudal neural spines in both Ruixinia and mamenchisaurids in contrast to the undivided neural spines of the anterior caudals of Dongbeititan indicates that some early-branching somphospondylan titanosauriform taxa from the Early Cretaceous of East Asia evolved strong procoelous anterior caudals convergent with those of derived titanosaurs. Additionally, the anterior caudals of the basal macronarian Bellusaurus are also strongly procoelous and were used to suggest titanosaurian affinities for this taxon by Jacobs et al. (1993), and the lithostrotian titanosaur Rapetosaurus has a total of 17 cervicals (Rogers 2009), in which case the presence of more than 15 cervical vertebrae occurs not just in mamenchisaurids, Euhelopus,  Dongbeititan, and Ruixinia but also in lithostrotian titanosaurs. Considering that Euhelopus is recovered as a basal macronarian by Dai et al. (2022), and Moore et al. (2020) note that the anterior margin of the neural spine in posterior dorsal vertebrae being level with or posterior to the rear margin of the neural arch is shared by Dongbeititan with some mamenchisaurids, it is highly probable that the anterior margin of the neural spine in posterior dorsal vertebrae being level with or posterior to the rear margin of the neural arch evolved convergently in Ruixinia and some mamenchisaurids because Daxiatitan and Euhelopus lack this character as pointed out by Moore et al. (2020).

In summary, Ruixinia is not only the third titanosauriform to be described from the Early Cretaceous of Liaoning, China, but is also the first titanosaur from the Early Cretaceous of East Asia to preserve a complete caudal vertebral series. Although several morphological features of this taxon are also found in non-titanosauriform taxa, including a high cervical vertebral count and strongly procoelous anterior and middle caudal vertebrae, the titanosaurian placement of Ruixinia indicates that the most primitive derived titanosaurs and non-titanosaurian somphospondylans from East Asia convergently evolved those characters with mamenchisaurids, turiasaurians, basal macronarians, and even some titanosaurs. By displaying an unusual combination of autapomorphic characters of the caudal region, Ruixiana itself promises to shed additional light on the presence or absence of strong procoely of the anterior and middle caudals among derived eusauropods, including somphospondylans and mamenchisaurids.

References:

Azuma, Y., and Shibata, M., 2010. Fukuititan nipponensis, a new titanosauriform sauropod from the Early Cretaceous Tetori Group of Fukui Prefecture, Japan. Acta Geologica Sinica – English Edition 84 (3): 454–462. doi:10.1111/j.1755-6724.2010.00268.x.

Dai, H., Tan, C., Xiong, C., Ma, Q., Li, N., Yu, H., Wei, Z., Wang, P., Yi, J., Wei, G., You, H., and Ren, X., 2022. New macronarian from the Middle Jurassic of Chongqing, China: phylogenetic and biogeographic implications for neosauropod dinosaur evolution. Royal Society Open Science 9 (11). 220794. doi:10.1098/rsos.220794.

D'Angelo, J., 2022. A re-evaluation of the phylogenetic relationships of the controversial Central Asian sauropod Dzharatitanis kingi. Society of Vertebrate Paleontology 82th Annual Meeting Program & Abstracts: 119. (link here)

D’Emic, M. D., 2012. Early evolution of titanosauriform sauropod dinosaurs. Zoological Journal of the Linnean Society 166: 624–671.

Jacobs, L., Winkler, D. A., Downs, W. R., and Gomani, E. M., 1993. New material of an Early Cretaceous titanosaurid saurepod dinosaur from Malawi. Palaeontology 36: 523-523.

Mannion, P. D., Upchurch, P., Schwarz, D., and Wings, O., 2019. Taxonomic affinities of the putative titanosaurs from the Late Jurassic Tendaguru Formation of Tanzania: phylogenetic and biogeographic implications for eusauropod dinosaur evolution. Zoological Journal of the Linnean Society 185: 784–909. 

Mo, J., Ma, F., Yu, Y., and Xu, X., 2023. A new titanosauriform sauropod with an unusual tail from the Lower Cretaceous of northeastern China. Cretaceous Research: in press.  doi:10.1016/j.cretres.2022.105449

Moore, A. J., P. Upchurch, P. M. Barrett, J. M. Clark, and Xu, X., 2020. Osteology of Klamelisaurus gobiensis (Dinosauria: Eusauropoda) and the evolutionary history of Middle–Late Jurassic Chinese sauropods. Journal of Systematic Palaeontology 18 (16):1299–1393.

Rogers, K. C., 2009. The Postcranial Osteology of Rapetosaurus krausei (Sauropoda: Titanosauria) from the Late Cretaceous of Madagascar. Journal of Vertebrate Paleontology 29 (4): 1046–1086. 

Royo-Torres, R., Upchurch, P., Kirkland, J.I., DeBlieux, D.D., Foster, J.R., Cobos, A., and Alcalá, L., 2017. Descendants of the Jurassic turiasaurs from Iberia found refuge in the Early Cretaceous of western USA. Scientific Reports 7 (1): 14311. doi:10.1038/s41598-017-14677-2

Wang, X., You, H., Meng, Q., Gao, C., Cheng, X., and Liu, J., 2007. Dongbeititan dongi, the first sauropod dinosaur from the Lower Cretaceous Jehol Group of Western Liaoning Province, China. Acta Geologica Sinica 81: 911–916.

Wang, X., Bandeira, K. L. N.,  Qiu, R., Jiang, S., Cheng, X., Ma, Y., and Kellner, A.W.A., 2021. The first dinosaurs from the Early Cretaceous Hami Pterosaur Fauna, China. Scientific Reports 11:14962. doi:10.1038/s41598-021-94273-7.

You, H., Li, D., Zhou, L., and Ji, Q., 2008. Daxiatitan binglingi: a giant sauropod dinosaur from the Early Cretaceous of China. Gansu Geology 17: 1–17.

Zhou, C., Wu, W., Sekiya, T., and Dong, Z., 2018. A new Titanosauriformes dinosaur from Jehol Biota of western Liaoning, China. Global Geology 37: 327–333.

Thoughts on Peterson et al. (2022) paper regarding diplodocid feeding mechanisms

Many scientific papers have published regarding the degree of tooth replacement and wear in diplodocoid and macronarian sauropods, namely diplodocids, Camarasaurus, brachiosaurids, and select titanosaurs for which skull material is known. However, very little attention until recently was paid the patterns of tooth replacement and wear in apatosaurine diplodocids, in no small part because the Apatosaurus louisae skull CM 11162, the undescribed Apatosaurus ajax specimen CMC VP-7180, and the apatosaurine specimen TATE 099 found at the Nail Quarry in Como Bluff, Wyoming in 1996, constitute the only apatosaurine skulls that preserve complete teeth (known cranial material for the Apatosaurus ajax holotype includes a braincase and two quadrates, but that's another story). Recently, Peterson et al. (2022) published a paper describing in detail for the first time TATE 099 from Nail Quarry, offering a comprehensive analysis of patterns of tooth wear and replacement for this specimen and further illuminating the nature of feeding mechanisms among flagellicaudatan diplodocoids. 

The history of the systematic placement of TATE 099 within Diplodocidae is rather interesting. It was first referred to as Apatosaurus sp. when first reported in an abstract by Connely and Hawley (1998), who suggested that Apatosaurus used its jaws in front to back sliding motion to aid in cropping and biting when eating plants. For his part, Bakker (1998) referred TATE 099 to Brontosaurus excelsus and used this specimen to claim that B. excelsus differed from Apatosaurus in having the basitubera situated far behind the occipital condyle, but provided no justification as to why TATE 099 was conspecific with B. excelsus, and due to a lack of overlapping material between TATE 099 and B. excelsus holotype, this taxonomic referral was basically ignored by many authors (e.g. Upchurch et al. 2004; Tschopp et al. 2015). In any case, Peterson et al. point out that the basitubera of Apatosaurus louisiae are positioned anterior to the occipital condyle, similar to the condition in TATE 099, and I'm heartened that the authors recognized Bakker's (1998) referral of TATE 099 to Brontosaurus excelsus as lacking basis, and instead assign it to Apatosaurus sp. based on a widely diverging basipterygoid process greater than 60 degrees and the absence of a basisphenoid/basipterygoid recess, both of which are listed as diagnostic characters for Apatosaurus by Tschopp et al. (2015).

CT scans of the maxillae and premaxillae (left) and dentary (right) of Apatosaurus specimen TATE 099 showing unerupted teeth (from Peterson et al. 2022). 3D scans of the unerupted premaxillary/maxillary and dentary teeth shown at the bottom of figures 10 and 11 in Peterson et al. (2022) are included for convenience.

The discussion section of the paper by Peterson et al. (2022) constitutes the real focus on deciphering the rate of tooth wear and replacement among diplodocids. The unerupted tooth counts for TATE 099 reported by the authors in their description of TATE 099 are 5-8 unerupted tooth crowns per alveolus in the premaxilla, 3-5 unerupted tooth crowns per alveolus in the maxilla, and 1-3 unerupted crowns per alveolus in the dentary. Even though Peterson et al. observe differences between diplodocoids and macronarians in the number of replacement teeth as well as tooth volume, shape, and replacement rate, it is quite noteworthy how the authors point out that the rebbachisaurid Nigersaurus lacks alveolar septae and has smaller replacement teeth than those of diplodocid taxa despite the both Nigersaurus and TATE 099 being comparable in the maximum number of replacement teeth. However, the authors don't comment on how the number of replacement teeth of the dentary in TATE 099 compares with that of the holotype of the rebbachisaurid Lavocatisaurus from late Aptian-early Albian deposits in Patagonia, because the latter taxon has several replacement teeth preserved in the dentary. When noting that the numbers of premaxillary/maxillary replacement teeth for TATE 099 as well as Apatosaurus premaxilla MWC 8430 and maxilla MWC 6002 described from Mygatt-Moore Quarry in Colorado by McHugh (2018) are similar, but that dentary of TATE 099 has a number of replacement teeth comparable to those of Dicraeosaurus and the macronarian Brachiosaurus, Peterson et al. (2022) propose that diplodocid taxa retained similar numbers of replacement teeth in the dentary, and interpret the higher numbers of replacement teeth in the upper jaw of Apatosaurus compared to those of diplodocines as supporting the hypothesis by McHugh (2018) that the upper jaw of Apatosaurus was more accustomed to crushing tough plant leaves than that of Diplodocus. In retrospect, the difference between apatosaurines and diplodocines in how they used their upper jaw to chew on plant material may provide another hint at morphological differences between these two diplodocid clades, because some distinguishing features between Apatosaurinae and Diplodocinae can be found in the cervical vertebrae (see Tschopp et al. 2015). Although the erupted tooth row of TATE 099 was unavailable for study by Peterson et al., the authors provide a succinct analysis of the degree of tooth replacement in this specimen based on examination of high-fidelity casts of the erupted tooth row and comparisons with the tooth rows of other sauropods because they note that the row-set tooth replacement patterns in diplodocid taxa like  Apatosaurus, Diplodocus, and Galeamopus contrast with the alternating tooth replacement patterns of the basal macronarian Camarasaurus, since the tooth row of TATE 099 has an uneven occlusal margin that creates an uneven distribution of wear facets on the teeth. 

References:

Bakker, R.T. 1998. Dinosaur mid-life crisis: The Jurassic-Cretaceous transition In Wyoming and Colorado. New Mexico Museum of Natural History and Science Bulletin 14:67-76.

Connely, M.V. and Hawley, R. 1998. A proposed reconstruction of the jaw musculature and other soft cranial tissues of Apatosaurus. Journal of Vertebrate Paleontology 18 (suppl. to volume 3): 35A.

McHugh, J.B. 2018. Evidence for niche partitioning among ground-height browsing sauropods from the Upper Jurassic Morrison Formation of North America. Geology of the Intermountain West 5:95-103.  https://doi.org/10.31711/giw.v5.pp95-103

Peterson, J. E., Lovelace, D., Connely, M., and McHugh, J.B., 2022. A novel feeding mechanism of diplodocid sauropods revealed in an Apatosaurine skull from the Upper Jurassic Nail Quarry (Morrison Formation) at Como Bluff, Wyoming, USA. Palaeontologia Electronica 25(2):a21. https://doi.org/10.26879/1216. palaeo-electronica.org/content/2022/3653-apatosaurine-feeding-mechanism

Tschopp, E., Mateus, O., and Benson, R.B.J. 2015. A specimen-level phylogenetic analysis and taxonomic revision of Diplodocidae (Dinosauria, Sauropoda). PeerJ 3:e857.  https://doi.org/10.7717/peerj.857

Upchurch, 

P., 

Tomida, 

Y., and 

Barrett, 

P.M., 2004. 

A new specimen of Apatosaurus ajax (Sauropoda: Diplodocidae) from the Morrison Formation (Upper Jurassic) of Wyoming, USA. 

National Science Museum Monographs 

26: 

1–

107

.

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.

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