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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