Deep dive into Gallagher et al. (2025) paper on sauropod coloration

This week, a paper was published by Gallagher et al. (2025) taking a step towards tackling the question of what color neosauropods were by deducing the coloration of four diplodocid specimens from the Late Jurassic Morrison Formation of Montana. A handful of sauropod specimens have been found with skin impressions preserved, including the holotype of Haestasaurus becklesii, but until now there was no published investigation into the possible coloration of neosauropod sauropods.

For all purposes and intents, the sauropod specimen sample size subjected to analysis by Gallagher et al. is assigned by the authors to Diplodocus sp. even though Gallagher et al. note that ongoing research on the systematics of Morrison diplodocoids may lead to a change in the generic classification of the specimens found in the Mother's Day Quarry. Given the results of analysis of the melanosomes found in the skin impressions of the Mother's Day Quarry diplodocine specimens, the coloration extrapolated for these specimens was either unique to Diplodocus or widespread among diplodocines because figuring out the coloration of Barosaurus, Supersaurus, and Galeamopus is impossible due to a lack of specimens with skin impressions for those genera. In retrospect, discovery of apatosaurine specimens with skin impressions preserving melanosomes might tackle the question of how apatosaurine coloration compares with that of diplodocine diplodocids.

Microbodies of diverse morphology from a small section of stratum corneum from Diplodocus specimen CMC VP 20858 (after Gallagher et al. 2025)

The discussion by Gallagher et al. (2025) of the taphonomy of the scales of the juvenile Diplodocus specimens is quite breathtaking. Their explanation of why melanosome impressions are preserved in the integument of Diplodocus takes into account the nature of the siltstone in which the skin was preserved because epidermal scales are usually preserved as three-dimensional moulds, and the authors note that fossils from the Burgess Shale and two hadrosaur skins are preserved with clay minerals. The comments by Gallagher et al. about microbody positioning in dinosaur scales are quite interesting. When noting the difficulty in finding melanosome impressions in juvenile Diplodocus specimens, the authors express concerns about previous dinosaur scale studies reporting a lack of melanosome impressions or melanin chemical signatures in their specimens. Their recommendation that future studies on dinosaur scales investigate the possibility of their specimens being preserved similar to the juvenile Diplodocus specimens makes sense because Borealopelta is the only non-avian dinosaur taxon for which skin coloration is known (Brown et al. 2017).

Generally speaking, the paper by Gallagher et al. (2025) is a first step in deciphering the coloration of sauropod dinosaurs given that dino-artists have only historically guessed at sauropod coloration when creating illustrations of sauropod dinosaurs. By demonstrating that Diplodocus had varied coloration rivaling birds and mammals, it promises to shed new light on what the color of diplodocid scales was like.   

References:

Brown, C.M., Henderson, D.M., Vinther, J., Fletcher, I., Sistiaga, A., Herrera, J., and Summons, R.E., 2017. An Exceptionally Preserved Three-Dimensional Armored Dinosaur Reveals Insights into Coloration and Cretaceous Predator-Prey Dynamics. Current Biology 27 (16): 2514–2521.e3. doi:10.1016/j.cub.2017.06.071

Gallagher, T., Folkes, D., Pittman, M., Kaye, T. G., Storrs, G. W., and Schein, J., 2025. Fossilized melanosomes reveal colour patterning of a sauropod dinosaur. Royal Society Open Science. 12 (12) 251232. doi:10.1098/rsos.251232.

Thoughts on Alamosaurus paper by Paul (2025)

The titanosaur Alamosaurus has long been the only titanosaur to be described from the latest Cretaceous of North America, and numerous titanosaur remains from the Maastrichtian of Laramidia have long been referred to the genus, including postcranial skeleton USNM 15560 from the North Horn Formation of Utah and a postcranial remains from Big Bend National Park. However, a handful of sauropod workers have questioned the referral of some of these specimens on grounds of anatomical overlap or a lack of shared diagnostic features, even going as far as to suggest that more than one species is present among referred Alamosaurus specimens. Now, Paul (2025) has come out with a new paper revising the taxonomic attribution of specimens referred to Alamosaurus, erecting Utetitan zellaguymondeweyae for USNM 15560 and restricting Alamosaurus sanjuanensis to remains found in New Mexico.

Same scale comparison of select postcranial elements of Maastrichtian titanosaurs from North America (after Paul 2025). Arrows point to morphological features listed by Paul as diagnostic for Alamosaurus and Utetitan.   

The morphological criteria for distinguishing Utetitan from Alamosaurus given by Paul (2025) deserve some attention. The diagnoses of these two genera given in the paper are primarily based on scapular and ischial characters, and while D'Emic et al. (2011) diagnose Alamosaurus sanjuanensis on the basis of scapular and caudal characters, ischial features which Paul (2025) cites to distinguish Alamosaurus from Utetitan would suggest that USNM 10487 could be distinct from USNM 15560. However, since USNM 10486 and USNM 10487 were found far apart and belong to distinct individuals, it is unclear if Alamosaurus possessed the ischial characters cited as diagnostic for Utetitan. Paul lists a robust femur as another diagnostic trait for Utetitan, but he does not compare the proportions of the femur belonging to BYU 9087 with those of TKM 009 from the Hall Lake Formation of southern New Mexico. Lastly, Paul's erection of the subfamily Utetitaninae to accommodate Alamosaurus and Utetitan is problematic because most of the diagnostic characters cited by Paul for Utetitaninae are confined to very limited anatomical regions of the skeleton and cladistic analyses (e.g. Navarro et al. 2022) consistently place Alamosaurus as a saltasaurid, either an opisthocoelicaudiine or a saltasaurine.

In his discussion of the stratigraphy of specimens referred to Alamosaurus, Paul (2025) suggests that a 5-6 million year timespan for Maastrichtian titanosaurs from North America is improbable because it is abundant time for taxa to experience substantial evolution, especially at the species level. Although not cited by Paul, an abstract presented at the 2018 SVP conference hints at the specimen TMM 41541-1 being a distinct taxon from USNM 15560. Also, the specimen BIBE 45854 (described by Tykoski and Fiorillo 2017) from the lower part of the Black Peaks Formation in southern Texas not only hails from the late Maastrichtian like Utetitan and juvenile specimen TMM 43621-1 but also has been recovered as a member of Lognkosauria by Navarro et al. (2022) in contrast to Alamosaurus, indicating that the giant lognkosaurians and smaller saltasaurids co-existed in southern Laramidia during the late Maastrichtian. Paul's provisional referral of all titanosaur material from the Ojo Alamo Formation of New Mexico on grounds of biochronology should be taken with a grain of salt because Paul (2025) does not compare the humerus TKM007 and femur TKM009 (both from the Hall Lake Formation) to the Utetitan specimen BYU 9087 or any isolated titanosaur humeri and femora from the Javelina Formation. Given the yet-as-unpublished data indicating the distinctness of TMM 41541-1 from Utetitan and the cladistic results of Navarro et al. (2022) finding Alamosaurus and BIBE 45854 in different positions within Titanosauria, it seems probable that more than two titanosaur taxa existed in New Mexico during the early to middle Maastrichtian.

The paper by Paul (2025) is by no means the last word on the topic of titanosaur diversity in Laramidia during the Maastrichtian, but it helps to highlight the pitfalls of referring all Maastrichtian titanosaur remains to Alamosaurus absent shared diagnostic features or overlap with the A. sanjuanensis holotype specimen.

References:

D’Emic, M.D., Wilson, J.A., and Williamson, T.E., 2011. A sauropod dinosaur pes from the latest Cretaceous of North America and the validity of Alamosaurus sanjuanensis. Journal of Vertebrate Paleontology 31: 1072–1079.

Navarro, B.A., Ghilardi, A.M., Aureliano, T., Díaz, V.D., Bandeira, K.L.N., Cattaruzzi, A.G.S., Iori, F.V., Martine, A.M., Carvalho, A.B., Anelli, L.E., Fernandes, M.A., and Zaher, H., 2022. A new nanoid titanosaur (Dinosauria: Sauropoda) from the Upper Cretaceous of Brazil Ameghiniana 59(5): 317–354. doi:10.5710/AMGH.25.08.2022.3477

Paul, G.S., 2025. Stratigraphic and anatomical evidence for multiple titanosaurid dinosaur taxa in the Late Cretaceous (Campanian-Maastrichtian) of southwestern North America. Geology of the Intermountain West 12: 201–220. doi:10.31711/giw.v12.pp201-220 

Tykoski, R.S., and Fiorillo, A.R., 2017. An articulated cervical series of Alamosaurus sanjuanensis  Gilmore, 1922 from Texas—new perspective on the relationships of North America’s last giant sauropod. Journal of Systematic Paleontology 15: 339–364.

Veracity of Ikejiri's (2005) biochronology for Camarasaurus

The basal macronarian Camarasaurus is the most common sauropod genus from the Morrison Formation of western North America, with numerous specimens spanning the long vertical range in the Morrison. Twenty years ago, Ikejiri (2005) devised a biostratigraphic framework for Camarasaurus using Turner and Peterson's (1999) idea of stratigraphically correlating Morrison dinosaur quarries, creating five biozones for the genus: (1) No Camarasaurus zone (early-middle Kimmeridgian); (2) Camarasaurus grandis zone (late Kimmeridgian); (3) Camarasaurus lentus zone (late Kimmeridgian-early Tithonian); (4) Transition Zone (Kimmeridgian-Tithonian boundary); and (5) Camarasaurus supremus zone (Tithonian). However, a number of recent papers afford me the opportunity to test the validity of the biochronological framework for Camarasaurus created by Ikejiri (2005).

In his discussion of Camarasaurus biochronology, Ikejiri notes that the holotype of Camarasaurus lentus (YPM 1910) falls within the C. grandis Zone, as does the holotype of Camarasaurus lewisi (BYU 9047), and that the type locality for C. lentus is stratigraphically outside the C. lentus zone. He therefore raises the possibility that C. lentus and C. lewisi could be synonyms of C. grandis, stressing that some characters cited as diagnostic for C. lewisi by a number of authors could result from intraspecific variation. However, unpublished cladistic results in Tschopp et al. (2014) find Camarasaurus lewisi to be a distinct species, and Woodruff and Fowler (2017) provide no info on the stratigraphic position within the Morrison Formation of a juvenile Camarasaurus specimen described by the authors from Montana. Thus, more than one Camarasaurus species is present in the C. grandis zone, and overlap between the C. grandis and C. lentus calls into question the distinctness of these two biochronological zones.   

When establishing the No Camarasaurus Zone, Ikejiri (2005) notes that Haplocanthosaurus is the only sauropod genus reported from Dinosaur Zone 1 of Turner and Peterson (1999). Notwithstanding the fact that the presence of Haplocanthosaurus in this zone reported by Turner and Peterson is undescribed, the absence of Camarasaurus from Dinosaur Zone 1 may hold water because of the paucity of dinosaur localities from the lower part of the Salt Wash Member, but also the fact that knowledge of sauropod evolution in North America during the Bathonian-Oxfordian interval is limited. Future studies could demonstrate that any potential camarasaurid discoveries in the lower part of the Salt Wash Member could constitute a taxon generically distinct from Camarasaurus. The Transition Zone is problematic because Ikejiri (2005) refers Camarasaurus specimens from Oklahoma to C. supremus in the text of his paper but lists them as Camarasaurus sp. and possibly referrable to C. supremus in the "Systematic Paleontology" section of his paper. Thus, a re-appraisal of the Oklahoma Camarasaurus material is needed to determine if it referable to C. supremus or C. lentus. The Camarasaurus supremus Zone, however, can be judged to be valid because occurrences of Camarasaurus supremus are restricted to Dinosaur Zone 4 of Turner and Peterson (1999). In their description of the skull of Camarasaurus specimen BHI 6200, Woodruff et al. (2021) mention Camarasaurus supremus as a possible candidate for the identity of BHI 6200, but the authors provided no info on where in the Morrison Formation BHI 6200 comes from, so it is unclear if BHI 6200 is from the C. supremus zone. 

In summary, Ikejiri's (2005) biochronology for Camarasaurus is somewhat tenuous, with only the No Camarasaurus Zone and Camarasaurus supremus Zone standing up to scrutiny, and the validity of the C. grandis and C. lentus Zones being undercut by the distinctness of C. lewisi. The Transition Zone does not hold up to scrutiny because the Camarasaurus material found in Oklahoma and used by Ikejiri to infer a biochronological overlap between C. lentus and C. supremus is yet to be re-evaluated, and the No Camarasaurus Zone and Camarasaurus supremus Zone are apparently valid based on current fossil evidence.

References:

Ikejiri, T., 2005, Distribution and biochronology of Camarasaurus (Dinosauria, sauropoda) from the Jurassic Morrison Formation of the Rocky Mountain Region. New Mexico Geological Society, 56th Field Conference Guidebook, Geology of the Chama Basin 2005: 367-379.

Tschopp, E., Mateus O., Kosma R., Sander M., Joger U., & Wings O., 2014. A specimen-level cladistic analysis of Camarasaurus (Dinosauria, Sauropoda) and a revision of camarasaurid taxonomy. Journal of Vertebrate Paleontology. Program and Abstracts: 241-242.

Turner, C.E. and Peterson, F., 1999. Biostratigraphy of dinosaurs in the Upper Jurassic Morrison Formation of the Western Interior, U.S.A. pp. 77–114. In: Gillette, D.D. (ed.), Vertebrate Paleontology in Utah. Utah Geological Survey Miscellaneous Publication 99-1.

Woodruff, D.C., and Foster, J.R., 2017. The first specimen of Camarasaurus (Dinosauria: Sauropoda) from Montana: The northernmost occurrence of the genus. PLoS One 12:e0177423.

Woodruff, D.C., Wilhite, D.R., Larson, P.L., and Eads, M., 2021. A new specimen of the basal macronarian Camarasaurus (Dinosauria: Sauropoda) highlights variability and cranial allometry within the genus. Volumina Jurassica 19: 109–30. http://dx.doi.org/10.7306/vj.19.5. 

About the Transylvanian titanosaur paper by Diez Diaz et al. (2025)

The lithostrotian titanosaur Magyarosaurus has long been significant for demonstrating the presence of dwarf titanosaurs in the latest Cretaceous of Europe, but until recently an up-to-date re-appraisal of the titanosaur material referred to Magyarosaurus in the past was lacking, although the description of the similarly dwarf-sized Paludititan by Csiki et al. (2010) signaled that more than one taxon of titanosaur existed in the Late Cretaceous of Romania. Now, Diez Diaz et al. (2025) have come out with the long-overdue revision of nominal titanosaur taxa assigned to Magyarosaurus from the latest Cretaceous of Transylvania, confirming suspicions about more than one genus being represented in the material referred to Magyarosaurus by von Huene (1932).

Lectotype and paralectotype of Petrustitan hungaricus (NHMUK R.3853) (from Diez Diaz et al. 2025)

As a prelude to the "Systematic palaeontology" section of their paper, Diez Diaz et al. provide a relatively short overview of a number of publications making the case for the existence of more than one titanosaur species in Transylvania, including Stein et al. (2010) and the paper by Csiki et al. (2010) describing the new titanosaur taxon Paludititan nalatzensis. They note that McIntosh (1990) found it conceivable that more than one taxon is represented in the titanosaur material assigned by von Huene (1932) to Magyarosaurus, and the paper by Mocho et al. (2023) identifying four distinct titanosaur caudal morphotypes from the Hațeg Island region provides the authors with an impetus to clarify the taxonomy of Transylvanian titanosaurs based on overlap and shared characters between type specimens and referred material for Magyarosaurus dacus, M. hungaricus, and M. transsylvanicus.

The assortment by Diez Diaz et al. of name-bearing and "Rosetta Stone" Transylvanian titanosaur specimens into "individuals" and "assemblages" in quite creative. The authors rely on locality data for these specimens and specimen preservation and registry notes when labeling the type material of Magyarosaurus dacus as an assemblage and the type remains of Petrustitan hungaricus as an individual while referring to a number of non-type specimens from select localities with duplicate elements as assemblages. This is important because the type material of P. hungaricus comprises only a left fibula and tibia, the former which nevertheless allowed for Diez Diaz et al. (2025) to compare NHMUK R.3853 to Magyarosaurus dacus by overlapping with the fibulae included in type material for M. dacus. Paradoxically, Diez Diaz et al. neglect to designate one of the fibulae included in the hypodigm for Magyarosaurus transsylvanicus by von Huene (1932) as the lectotype of transsylvanicus even though they demonstrate that the hypodigm for this species is a composite of Magyarosaurus and indeterminate titanosaur remains, with the fibulae belonging to M. dacus and the vertebrae and forelimb remains being indeterminate beyond Titanosauria.

The phylogenetic analysis of Transylvanian titanosaurs by Diez Diaz et al. (2025) is quite breathtaking. Although Cury Rogers (2005) recovered Magyarosaurus as a lithostrotian titanosaur, her cladistic analysis found that taxon to be of uncertain placement within Lithostrotia. Given that Magyarosaurus is a dwarf taxon, its placement within Saltasauridae by Diez Diaz et al. indicates that Magyarosaurus itself arose from African saltasaurids that evolved insular dwarfism after colonizing island chains in southern Europe. The authors' recovery of Paludititan as closely related to or within Lognkosauria differs from the placement of Paludititan as a member of Lirainosaurinae in the phylogeny by Mocho et al. (2024), On the other hand, Nemegtosaurus falls outside Saltasauridae in the cladistic analysis by Diez Diaz et al. (2025), while the equal weights analysis finds Malawisaurus to be sister to a clade composed of Andesaurus, Baotianmansaurus, Daxiatitan, Dongyangosaurus, Huabeisaurus, and Xianshanosaurus. The placement of Nemegtosaurus outside Saltasauridae is most likely a fluke because it is coeval with Opisthocoelicauda, but the Diez Diaz et al. cladistic analysis is in lockstep with the phylogeny in Han et al. in placing Huabeisaurus as a late-surviving basal titanosaur. The recovery of Petrustitan as sister to Antarctosaurus, Vahiny, and Jainosaurus could attest to Antarctosaurus-like titanosaurs evolving insular dwarfism after entering Europe from North Africa because Diez Diaz et al. (2025) assess Petrustitan as a dwarf titanosaur. 

In summary, the paper by Diez Diaz et al. (2025) is kind of a magnum opus with respect to the alpha-taxonomy of Transylvania's titanosaur fauna because it re-evaluates all nominal referred species of Magyarosaurus in light of the description of Paludititan over a decade ago. Moreover, the authors of this paper demonstrate that the titanosaur fauna from Hațeg Island comprises both insular dwarfs and large-bodied forms judging from the large size of the newly described taxon Uriash. By refining the cladistic position of the Transylvanian titanosaurs, this paper will be useful for future discussions of the biogeography of derived titanosaurs as they relative to the inter-relationships of lithostrotians. 

References:

Curry Rogers, K. A., 2005. Titanosauria: A Phylogenetic Overview. pp. 50-103. In: Curry Rogers and Wilson (eds), The Sauropods: Evolution and Paleobiology. University of California Press: Berkeley.

Csiki, Z., Codrea, V., Jipa-Murzea, C., and Godefroit, P., 2010. A partial titanosaur (Sauropoda, Dinosauria) skeleton from the Maastrichtian of Nǎlaţ-Vad, Haţeg Basin, Romania. Neues Jahrbuch fur Geologie und Palaontologie – Abhandlungen 258 (3), 297–324.

Díez Díaz, V., Mannion, P.D., Csiki-Sava, Z., and Upchurch, P., 2025. Revision of Romanian sauropod dinosaurs reveals high titanosaur diversity and body-size disparity on the latest Cretaceous Hațeg Island Island, with implications for titanosaurian biogeography. Journal of Systematic Palaeontology 23 (1): 2441516. doi:10.1080/14772019.2024.2441516

Han, F., Yang, L., Lou, F., Sullivan, C., Xu, X., Qiu, W., Liu, H., Yu, J., Wu, R., Ke, Y., Xu, M., Hu, J., and Lu, P., 2024. A new titanosaurian sauropod, Gandititan cavocaudatus gen. et sp. nov., from the Late Cretaceous of southern China. Journal of Systematic Palaeontology 22 (1): 2293038. doi: https://doi.org/10.1080/14772019.2023.2293038.

McIntosh, J.S., 1990. Sauropoda. pp. 345-401. In: Weishampel, D.B., Dodson, P., and Osmólska, H., (eds.) The Dinosauria, 1st edition. Berkeley: University of California Press. 

Mocho, P., Pérez-García, A., and Codrea, V. A., 2023. New titanosaurian caudal remains provide insights on the sauropod diversity of the Hațeg Island (Romania) during the Late Cretaceous. Historical Biology 35 (10): 1881–1916.

Mocho, P., Escaso, F., Marcos-Fernández, F., Páramo, A., Sanz, J. L., Vidal, D., and Ortega, F., 2024. A Spanish saltasauroid titanosaur reveals Europe as a melting pot of endemic and immigrant sauropods in the Late Cretaceous. Communications Biology 7: 1016. doi:10.1038/s42003-024-06653-0

Stein, K., Csiki, Z., Curry, K., Weishampel, D. B., Redelstorff, R., and Carballido, J. L., 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.

von Huene, F., 1932. Die fossile Reptil-Ordnung Saurischia, ihre Entwicklung und Geschichte. Monographien zur Geologie und Palaontologie, Series 1, 4: 1–361.

Thoughts on Danison et al. (2024) paper on Saurophaganax

Diplodocids have been previously documented from the Morrison Formation of Cimarron County, western Oklahoma, thanks to postcranial remains described by Stovall (1938) and Carpenter & McIntosh (1994), and while most of these specimens are juvenile, dorsal vertebra OMNH 1670 reported by Stovall (1938) represents a giant individual compared to other apatosaurine specimens found in western Oklahoma. Now, Danison et al. (2024) have published a paper demonstrating that the material assigned to Saurophaganax maximus Chure, 1995 includes remains from the caudal region belonging to a diplodocid and that the holotype dorsal neural arch OMNH 1123 is more likely to be a sauropod rather than a theropod. 

Holotype dorsal neural arch of Saurophaganax maximus (from Danison et al. 2024)

The morphological criteria employed by Danison et al. (2024) evaluating the systematic placement of the holotype dorsal neural arch of Saurophaganax maximus is quite breathtaking. As noted by these authors, the accessory lamination present in this specimen is typical of sauropods and while upturned diapophyses are seen in theropods, this feature in OMNH 1123 is also present in juvenile diplodocid vertebrae. In his paper describing Saurophaganax maximus, Chure (1995) considered the accessory laminae autapomorphic for Saurophaganax but did not compare OMNH 1123 to the dorsal vertebrae of any sauropods from the Morrison Formation. By comparing OMNH 1123 with Apatosaurus dorsal vertebra OMNH 1366 (also found in western Oklahoma), Danison et al. effectively leave open the possibility that OMNH 1123 could be a diplodocid sauropod when taking serial position and ontogeny into account, bearing in mind the fact that no valid theropod taxon from the Morrison Formation has accessory laminae on the vertebrae. 

The re-identification by Danison et al. of six mid-caudal chevrons (OMNH 1102, 1104, 1438, 1439, 1684, and 1685) assigned to S. maximus as belonging to Diplodocidae is worthy of attention. As pointed out by Dansion et al., no quarry map for Kenton Quarry 1 (type locality for Saurophaganax maximus) is known to exist, calling into question Chure's (1995) referral of the chevrons to the same taxon as OMNH 1123 and the allosaurid remains for which the authors erect the name Allosaurus anax. Since there are duplicate hindlimb elements assigned to the S. maximus hypodigm, it made perfect sense for Danison et al. to evaluate the question of whether the mid-caudal chevrons represent an individual different from OMNH 1123. The fact that Danison et al. assign the atlas OMNH 1135 to Neosauropoda indeterminate is quite noteworthy given the presence of Camarasaurus in Kenton Quarry 1 (Carpenter and McIntosh 1994), which shows that two different neosauropod clades co-exist in the Morrison Formation of western Oklahoma. In other words, the atlas and mid-caudal chevrons constitute the new addition to the fossil record of Morrison sauropods from western Oklahoma.

References:

Carpenter, K., and McIntosh, J., 1994. Upper Jurassic sauropod babies from the Morrison Formation. pp. 265-278. In Carpenter, K., Hirsch, K., and Horner, J., (eds.) Dinosaur Eggs and Babies. New York, NY: Cambridge University Press.

Chure, D.J., 1995. A reassessment of the gigantic theropod Saurophagus maximus from the Morrison Formation (Upper Jurassic) of Oklahoma, USA; pp. 103–106 in A. Sun and Y. Wang (eds.). Sixth Symposium on Mesozoic Terrestrial Ecosystems and Biota, Short Papers. China Ocean Press: Beijing, China.

Danison, A., Wedel, M., Barta, D., Woodward, H., Flora, H., Lee, A., and Snively, E., 2024. Chimerism in specimens referred to Saurophaganax maximus reveals a new species of Allosaurus (Dinosauria, Theropoda). Vertebrate Anatomy Morphology Palaeontology 12 (1): 81-114. https://doi.org/10.18435/vamp29404

Stovall, J.W., 1938. The Morrison of Oklahoma and its dinosaurs. Journal of Geology 46:583-600.

Ardetosaurus and implications for degree of diplodocine diversity in the Morrison Formation

Since the publication of the paper by Tschopp et al. (2015), a number of individuals (e.g. Prothero 2019) have had a number of misgivings about the taxonomic scheme for Morrison diplodocids in Tschopp et al. (2015) by arguing that ecosystems in western North America was not suited to support a great many taxa of diplodocids because of Morrison diplodocids being oversplit. However, this opinion overlooks the fact that the Morrison Formation itself spans 10 million years and that the presence of Haplocanthosaurus in the type locality as Supersaurus (Boisvert et al. 2024) demonstrates the co-existence of diplodocids with basal diplodocoids in the lower part of the Brushy Basin Member of the Morrison Formation. Recently, van der Linden et al. (2024) have described a new taxon Morrison diplodocine diplodocid, Ardetosaurus viator, from the Howe-Stephens Quarry in northern Wyoming, increasing the diversity of diplodocines in the Morrison Formation to eight. Therefore, I will take the liberty of the bearing of Ardetosaurus upon the question of the true number of diplodocine diplodocids from the Morrison Formation.

Skeletal reconstruction of Ardetosaurus viator (after van der Linden et al. 2024)

In their paper, van der Linden et al. neglect to provide a detailed cladistic analysis because they note that the description of Ardetosaurus viator is part of a broader collaborate project regarding the systematics of Diplodocoidea. It is understandable that the authors refrain from testing the cladistic position of the new taxon because their planned collaborative phylogeny of Diplodocoidea incorporates new diplodocoid specimens, but exhaustive comparison by the authors of Ardetosaurus with other diplodocines reveals hints about possible cladistic position of Ardetosaurus relative to other members of Diplodocinae. For instance, as noted by van der Linden et al., Ardetosaurus is similar to Barosaurus lentus in having elongated cervical vertebrae, so there is a possibility that Ardetosaurus itself could be more closely related to Barosaurus and Supersaurus than to other Morrison diplodocines. If so, then those three taxa (and possibly Dinheirosaurus) most likely form a distinct clade of diplodocines with elongated necks, and diplodocines from the Morrison Formation might have exhibited a degree of cladistic diversity with respect to evolving a variety of neck lengths in response to the emergence of different types of ferns and cycads in Morrison times. After all, the presence of four different taxa of dicraeosaurids in the Morrison Formation (see Whitlock and Wilson Mantilla 2020) may suggest a similar diversity pattern of diplodocine diplodocids in the Brushy Basin Member of the Morrison Formation as a result of dynamism of the Morrison ecosystems by the late Kimmeridgian.

Given the assignment of Ardetosaurus to Diplodocinae by van der Linden et al. (2024), it is important to note that the interpretation by Maidment and Muxworthy (2019) of the Morrison Formation as being more dynamic, more spatially varied, and temporally changing over the time it was deposited begs the question of the possible upper limit of diplodocine diversity in the Morrison. While the diversity of Morrison diplodocines exceeds the number of valid apatosaurine species, van der Linden et al. note that ontogeny and stratigraphy of the Morrison Formation may affect estimates of diversity of diplodocines throughout the Morrison Formation. Indeed, the type locality of Ardetosaurus viator is low in the upper part of the Salt Wash Member of the Morrison Formation, whereas Supersaurus vivianae has only been found in the lower part of the Brushy Basin Member, and Galeamopus remains occur in both the Salt Wash and lower Brushy Basin Members. The holotype of Ardetosaurus viator is assessed by van der Linden et al. (2024) as mature, in contrast to the holotype of Kaatedocus siberi being a juvenile, so the low stratigraphic position of Howe-Stephens Quarry compared to localities which have yielded known remains of Barosaurus, Diplodocus, Galeamopus, and Supersaurus may indicate that diplodocine diversity in the Salt Wash Member was low compared to a gradual increase over the timespan of the Brushy Basin Member. In other words, the evolution of Morrison ecosystems noted by Maidment and Muxworthy (2019) over the timespan of the Morrison Formation indicates that the relative growth in the diversity of Morrison diplodocines increased over time in response to changes in ecosystems in western North America over the span of time in which the Morrison Formation was deposited. For instance, a growth in Morrison diplodocine diversity during the late Kimmeridgian-Tithonian might have filled ecological niches left by the disappearance of Haplocanthosaurus from the fossil record by the late Kimmeridgian.

References:

Boisvert, C., Curtice, B., Wedel, M., and Wilhite, R., 2024. Description of a new specimen of Haplocanthosaurus from the Dry Mesa Dinosaur Quarry. The Anatomical Record: 1–19. http://doi.org/10.1002/ar.25520

Maidment, S.C.R., and Muxworthy, A., 2019. A chronostratigraphic framework for the Upper Jurassic Morrison Formation, western U.S.A. Journal of Sedimentary Research 89 (10): 1017–1038. https://doi.org/10.2110/jsr.2019.54

Prothero, D., 2019.The Story of the Dinosaurs in 25 Discoveries. New York, NY: Columbia University Press.

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 

van der Linden, T.T.P., Tschopp, E., Sookias, R.B., Wallaard, J.J.W., Holwerda, F.M., and Schulp, A.S., 2024. A new diplodocine sauropod from the Morrison Formation, Wyoming, USA. Palaeontologia Electronica 27(3):a50. https://doi.org/10.26879/1380 

Whitlock, C., and Wilson Mantilla, J., 2020. The Late Jurassic sauropod dinosaur 'Morosaurus' agilis Marsh, 1889 reexamined and reinterpreted as a dicraeosaurid. Journal of Vertebrate Paleontology DOI: 10.1080/02724634.2020.1780600

   

Thoughts on phylogenetic analysis of Qunkasaura by Mocho et al. (2024)

The description of the derived titanosaur Abditosaurus by Viel et al. (2022) upended the long-standing view that all titanosaur taxa described from the Campanian-Maastrichtian of the Ibero-Armorican island (now northeastern Spain and southern France) were dwarf, insular forms because known specimens of Abditosaurus kuehnei are larger than Ampelosaurus, Lirainosaurus, Magyarosaurus, and other dwarf titanosaurs from the Late Cretaceous of Europe. Now, Mocho et al. (2024) have described yet another non-dwarf titanosaur from the Late Cretacrous of Spain, Qunkasaura pintiquiniestra, which hails from the type locality of the co-eval titanosaur Lohuecotitan pandafilandi in Lo Hueco, south-central Spain. While Qunkasaura constitutes the newest addition to an already-burgeoning inventory of lithostrotian titanosaurs from the Ibero-Armorican realm, there are aspects of the phylogenetic analysis of this taxon by Mocho et al. (2024) that are quite novel and worth discussing.

Phylogenetic analysis of Qunkasaura pintiquiniestra by Mocho et al. (2024) showing bifurcation of Saltasauroidea into Lohuecosauria and a Rapetosaurus+Overosaurus clade.

The most tangible taxonomic action concocted by Mocho et al. as a result of their cladistic analysis of Qunkasaura involves a shake-up of the phylogenetic nomenclature for and interrelationships of taxa outside South America assigned to Saltasauridae. The creation of the new name Lohuecosauria for a clade within Saltasauroidea comprising Lirainosaurinae, Saltasauridae, and Isisaurus by the authors constitutes a bold effort to tackle the interrelationships of Saltasaurus-like lithostrotians because the cladistic analysis by Mocho et al. (2024) differs from the phylogeny of Diez Díaz et al. (2018) in recovering Lirainosaurinae as closely related to Saltasauridae rather than as sister to Lognkosauria, suggesting that lirainosaurines may have evolved in Gondwana prior to the Maastrichtian and became the dominant titanosaur clade in Europe by the Maastrichtian. In particular, Carballido et al. (2022) noted that the Sallam et al. (2018) phylogeny recovering Opisthocoelicauda within Lirainosaurinae (which would have meant Opisthocoelicaudiinae having priority over Lirainosaurinae) in contrast to the results by Diez Díaz et al. rendered the exact cladistic position of Lirainosaurinae unclear, and by finding Lirainosaurinae to be basal to Isisaurus and Saltasauridae, Mocho et al. do an outstanding job of tackling the question of whether Opisthocoelicaudia is closely related to members of Lirainosaurinae, because the saltasaurid Ibirania described from the late Santonian-early Campanian of southeastern Brazil by Navarro et al. (2022) is a dwarf taxon like many members of Lirainosaurinae, implying that the dwarfism evolved independently within different clades of Lohuecosauria during the Santonian-Maastrichtian interval.    

The recovery of Nemegtosaurus as closely related to Lognkosauria by Mocho et al. (2024) is quite remarkable. Diez Díaz et al. (2018) and Sallam et al. (2018) also find Nemegtosaurus to be the sister taxon of Rinconsaurus, Muyelensaurus, Lognkosauria, Aeolosaurus, and Gondwanatitan, but the placement of Nemegtosaurus within Colossosauria as closely related to Lognkosauria should be taken with a grain of salt because of marginal overlap between the few postcranial elements assigned to the holotype of N. mongoliensis from the type locality of this taxon by Currie et al. (2018) and postcranial remains of lognkosaurian taxa but also the younger age of Nemegtosaurus compared to lognkosaurian taxa included in the phylogeny by Mocho et al. except Garrigatitan and Puertasaurus. Still, Mocho et al. (2024) agree with Wilson et al. (2016) and Navarro (2019) that Rapetosaurus does not group with Nemegtosaurus to the exclusion of other derived lithostrotians, especially as their cladistic analysis finds Rapetosaurus and Tapuiasaurus to be distantly related despite overlap between known skeletal elements for those taxa. As a matter of fact, cladistic analyses by Navarro et al. (2022) and Gorcsak et al. (2023) recover Nemegtosaurus and Opisthocoelicaudia within Saltasauridae, which makes sense when considering that few postcranial elements are known for Nemegtosaurus despite overlap with those of Opisthocoelicaudia.

Mocho et al.'s note of caution on the cladistic positions of Garrigatitan and Normanniasaurus as well the Algora titanosaur within Colossosauria is quite reasonable. While I agree that newly discovered titanosaur material from Cenomanian-age deposits in Algora, Spain may shift the cladistic position of the Algora taxon to a different spot within Lithostrotia, the placement of Normanniasaurus within Colossosauria could still stand because a number of topologies in Mannion et al. (2019) happen to recover Normanniasaurus as sister to Lognkosauria and Aeolosaurus despite the incompleteness of the N. genceyi holotype. Although Mocho et al. (2024) call into question the tentative referral of some specimens to Garrigatitan, making their cladistic recovery of Garrigatitan as a lognkosaurian tenuous, Garrigatitan could still be a member of Colossosauria despite being based on incomplete material because the cladistic results in Mocho et al. (2024) demonstrate the co-existence of two distinct clades of saltasauroids in the Campanian-Maastrichtian of Europe.   

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.; Pol, D. (eds.). South American Sauropodomorph Dinosaurs. Record, Diversity and Evolution. Cham, Switzerland: Springer. doi:10.1007/978-3-030-95959-3. 

Currie, P. J., Wilson, J.A., Fanti, F., Mainbayar, B., and Tsogtbaatar, K., 2018. Rediscovery of the type localities of the Late Cretaceous Mongolian sauropods Nemegtosaurus mongoliensis and Opisthocoelicaudia skarzynskii: Stratigraphic and taxonomic implications. Palaeogeography, Palaeoclimatology, Palaeoecology 494:5–13. doi:10.1016/j.palaeo.2017.10.035. 

Díez Díaz, V., Garcia, G., Pereda-Suberbiola, X., Jentgen-Ceschino, B., Stein, K., Godefroit, P., and Valentin, X., 2018. The titanosaurian dinosaur Atsinganosaurus velauciensis (Sauropoda) from the Upper Cretaceous of southern France: New material, phylogenetic affinities, and palaeobiogeographical implications. Cretaceous Research. 91: 429–456. doi:10.1016/j.cretres.2018.06.015

Gorscak, E., Lamanna, M. C., Schwarz, D., Díez Díaz, V., Salem, B. S., Sallam, H. M., and Wiechmann, M. F., 2023. A new titanosaurian (Dinosauria: Sauropoda) from the Upper Cretaceous (Campanian) Quseir Formation of the Kharga Oasis, Egypt. Journal of Vertebrate Paleontology e2199810. doi:10.1080/02724634.2023.2199810.

Mannion, P. D., Upchurch, P., Jin, X. and Zheng, W. 2019. New information on the Cretaceous sauropod dinosaurs of Zhejiang Province, China: impact on Laurasian titanosauriform phylogeny and biogeography. Royal Society Open Science 6: 191057. doi:10.1098/rsos.191057

Mocho, P., Escaso, F., Marcos-Fernández, F., Páramo, A., Sanz, J. L., Vidal, D., and Ortega, F., 2024. A Spanish saltasauroid titanosaur reveals Europe as a melting pot of endemic and immigrant sauropods in the Late Cretaceous. Communications Biology 7: 1016. doi:10.1038/s42003-024-06653-0

Navarro, B.A., Ghilardi, A.M., Aureliano, T., Díaz, V.D., Bandeira, K.L. N., Cattaruzzi, A.G.S., Iori, F.V., Martine, A.M., Carvalho, A.B., Anelli, L.E., Fernandes, M.A., and Zaher, H., 2022. A new nanoid titanosaur (Dinosauria: Sauropoda) from the Upper Cretaceous of Brazil. Ameghiniana 59(5): 317–354. doi:10.5710/AMGH.25.08.2022.3477

Sallam, H., Gorscak, E., O'Connor, P., El-Dawoudi, I., El-Sayed, S., and Saber, S., 2018. New Egyptian sauropod reveals Late Cretaceous dinosaur dispersal between Europe and Africa. Nature 2 (3): 445–451.

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.

Wilson, J. A., D. Pol, A. B. Carvalho, and H. Zaher. 2016. The skull of the titanosaur Tapuiasaurus macedoi (Dinosauria: Sauropoda), a basal titanosaur from the Lower Cretaceous of Brazil. Zoological Journal of the Linnean Society 178(3):611–662.