Morrison Formation: Ceratosaurus as "saber-tooth" carnivore + Apatosaurine remains from Arches National Park (free pdfs)

[Ben Creisler]

Ben Creisler

bcre...@gmail.com

More Morrison papers:

Free pdf:

Taylor Oswald and Brian Curtice (2026)
A Morrison "saber-tooth"? -comparison of Ceratosaurus dentition to other theropods and Machairodontinae and its implications for Ceratosaurus predatory ecology
In: Foster et al., 2026, New Developments in the Paleontology and Geology of the Upper Jurassic Morrison Formation. New Mexico Museum of Natural History and Science Bulletin 102: 185-200
https://www.researchgate.net/publication/400054043_A_MORRISON_SABER-TOOTH_-COMPARISON_OF_CERATOSAURUS_DENTITION_TO_OTHER_THEROPODS_AND_MACHAIRODONTINAE_AND_ITS_IMPLICATIONS_FOR_CERATOSAURUS_PREDATORY_ECOLOGY


There has been significant debate over the predatory ecology of  Ceratosaurus and other large theropod dinosaurs from the Late Jurassic Morrison Formation of Western North America, with some authors positing that Ceratosaurus was a semi-aquatic predator and others positing that it fed largely on the same terrestrial herbivores as larger sympatric theropods such as Allosaurus, but avoided competition with them through some degree of niche partitioning. Here, we use linear dimensional measurements, specifically the ratios Crown Base Ratio (CBR), Crown Height Ratio (CHR), and Crown Angle (CA) to morphometrically compare the hypertrophied dentition of Ceratosaurus to the hypertrophied canines (“sabers”) of machairodont felids and other Morrison theropods to assess the morphological and, perhaps by extension, functional affinities of Ceratosaurus dentition to its Jurassic competitors and to the sabers of machairodonts, which somewhat outwardly resemble the teeth of Ceratosaurus. We also use CBR to compare the teeth of Ceratosaurus to those of spinosaurids to assess the likelihood that Ceratosaurus occupied a semi-aquatic niche. We found the teeth of Ceratosaurus to be significantly dissimilar to those of spinosaurids, casting doubt on the hypothesis that this taxon specialized in feeding on aquatic prey. We also found that the teeth of Ceratosaurus were morphometrically similar to those of machairodont sabers and actually exceeded them in some aspects of functional optimization (CBR and tooth curvature, the latter represented by CA), indicating that the hypertrophied teeth of these distantly related predators may have had similar functions. Machairodonts and other saber-toothed carnivorans are believed to have evolved the “saber-toothed” phenotype as an adaptation for quickly killing prey, thereby conserving energy and reducing competition in highly competitive, predator-dense environments, of which the Morrison Formation would be an example. Thus, similar pressures may have led to the analogous development of hypertrophied saber-like teeth adapted for killing prey quickly in both machairodonts and Ceratosaurus, albeit with key differences in their dental arrangements and biology. Ceratosaurus may have avoided especially large prey and instead favored moderately sized prey, which it could hypothetically kill with little struggle. In this way, Ceratosaurus would have saved energy and reduced competition with other theropods, such as Allosaurus and Torvosaurus, which may have competed with Ceratosaurus both indirectly for similar prey and directly through kleptoparasitism.

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Free pdf:

April Hullinger, Colin Boisvert, Gunnar T. Bivens, Brian Curtice, Ray Wilhite, and John R. Foster (2026)
Redescription of Apatosaurine Remains from Arches National Park, Utah, USA (Upper Jurassic, Morrison Formation)
In: Foster et al., 2026, New Developments in the Paleontology and Geology of the Upper Jurassic Morrison Formation. New Mexico Museum of Natural History and Science Bulletin 102: 215-231
https://www.researchgate.net/publication/400052709_Redescription_of_Apatosaurine_Remains_from_Arches_National_Park_Utah_USA_Upper_Jurassic_Morrison_Formation


Arches National Park in southeastern Utah has Mesozoic deposits spanning the Triassic to  early Late Cretaceous Periods. The Morrison Formation exposed in the park has yielded vertebrate fossils  and petrified wood; however, few of these fossils have been described. Here we redescribe fossil remains  that we assign to Apatosaurinae indet. (UMNH VP 18671 = ARCH 3151) from Arches National Park  (Utah, USA). These ten bones (nine caudal vertebrae and a right pubis) come from the Arches Apatosaur  Locality. The quarry is high in the Brushy Basin Member of the Morrison Formation, a few meters  below the contact with the Cedar Mountain Formation. Most of the caudal vertebrae were exposed or  partially embedded in matrix. The vertebrae and pubis were found roughly associated with each other,  with no duplicate material potentially representing one individual, and no other associated fauna were  found. This animal is identified as an apatosaurine based on “heart-shaped” caudal centra with limited  pneumatization and posterior articular surfaces that are slightly convex ventrally and slightly concave  dorsally. The robust pubis is also consistent with an apatosaurine or Camarasaurus identification, but the  associated caudal vertebrae provide evidence for an apatosaurine identification. These remains indicate  the presence of the geologically youngest apatosaurine from one of the stratigraphically highest sites  in the Morrison Formation. Despite this high stratigraphic placement, this specimen is smaller in size  compared to apatosaurine material found in the Oklahoma Panhandle or C. supremus from the Cope’s  Nipple locality. This apatosaurine is important to our understanding of sauropod remains from southern  Utah and from high in the Morrison, as well as exemplifying the importance of the vertebrate fossil  heritage preserved and protected within the national park system.

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[Jerry Harris]

Another one from the Morrison volume (I don't think I saw this one mentioned before...?):

Woodruff, D.C., Walker, S., Hunt, K., and Schein, J.P. 2026. The first specimen of Barosaurus (Sauropoda: Diplodocidae) from Montana: the northernmost occurrence of the genus.

https://www.researchgate.net/publication/400050346_THE_FIRST_SPECIMEN_OF_BAROSAURUS_SAUROPODA_DIPLODOCIDAE_FROM_MONTANA_THE_NORTHERNMOST_OCCURRENCE_OF_THE_GENUS

Abstract: A cervical vertebra from the Pryor Mountains of south-central Montana is the first referable specimen of the Morrison Formation diplodocine sauropod Barosaurus lentus from the state. Additionally, this specimen also represents the northernmost occurrence of the genus from the Morrison Formation to date. While localities in the northernmost extent of the Morrison Formation appear to slightly differ ecologically from classic Colorado Plateau counterparts, we can now definitively include Barosaurus within the dinosaur fauna from the northernmost extent of the formation.