Athenar bermani: A new species of Diplodocoid Sauropod from the Late Jurassic Morrison Formation of Dinosaur National Monument, Utah.

In 1913 prolific American fossil hunter Earl Douglass excavated a Sauropod braincase and partial skull roof from the Carnegie Quarry site at Dinosaur National Monument in Utah. This made its way to the collection of the Carnegie Museum in Pittsburgh, where it was given the specimen number CM 26552, and was largely forgotten for half a century (to give some context, Douglass excavated over 300 tonnes of material, including many complete skeletons of Jurassic Dinosaurs such as Diplodocus, Dryosaurus, Stegosaurus, Barosaurus, Camarasaurus, and Brontosaurus, which may have left museum staff a bit busy).

In 1978, palaeontologists David Berman and John McIntosh published a study in which they revised the genera Diplodocus and Camarasaurus, in which they assigned the specimen CM 26552 to Diplodocus. However, since that time our understanding of Sauropods as a group has developed significantly, notably in that proportional differences, which could change significantly as Sauropods grew, are no longer given the same emphasis, with modern palaeontologists instead placing more emphasis on character states (discrete features which can be present or absent).

In a paper published in the journal Palaeontologica Electronica in October 2025, John Whitlock of the Department of Science and Mathematics at Mount Aloysius College and the Section of Vertebrate Paleontology at the Carnegie Museum of Natural History, Juan Pablo Garderes and Pablo Gallina of the Consejo Nacional de Investigaciones Científicas y Técnicas, the Argentina and Fundación de Historia Natural Félix de Azara, and the Centro de Ciencias Naturales, Ambientales y Antropológicas at Universidad Maimónides, and Matthew Lamanna, also of the Section of Vertebrate Paleontology at the Carnegie Museum of Natural History, formally redescribe specimen CM 26552, assigning it to a new species and genus.

Based upon their inspection of CM 26552, Whitlock et al. conclude that it should be placed in the Dicraeosauria, a sub-group of the Diplodocidae, the skulls of which can be determined by (1) the presence of postparietal and frontoparietal fenestrae, (2) the exclusion of the basioccipital from the dorsal margin of the occipital condyle by the exoccipitals, (3) the presence of a distinct prong on the squamosal, (4) the contribution of the frontal to the margin of the supratemporal fenestra, (5) an expanded crista prootica, (6) a free dorsal margin of the antotic process, (7) the presence of a “shelf” overhanging the foramen for the trigeminal (V) nerve, and (8) the flat distal margin of the paroccipital process.

Braincase CM 26552 in anterior (A), (C) and posterior (B), (D) views. Abbreviations: BO, basioccipital; BS, basisphenoid; BT, basal tubera; CPR, crista prootica; EO-OP, exoccipitalopisthotic; F, frontal; LS, laterosphenoid; OS, orbitosphenoid; P, parietal; PO, postorbital; POP, paroccipital process; PR, prootic; S, shelf overhanging the opening for cranial nerve V; SOC, supraoccipital; SQ, squamosal; I, opening for cranial nerve I; II, opening for cranial nerve II; IV, opening for cranial nerve IV; V, opening for cranial nerve V. Whitlock et al. (2025).

Within that group, however, specimen CM 26552 shows a unique combination of features, not seen in any other genera, plus one unique character state,  the presence of a ‘tooth’ in the parietal/opisthotic suture, which has not previously been seen. For this reason, Whitlock et al. assign CM 26552 to a new species and genus, under the name Athenar bermani, where 'Athenar' honours the musician Athenar, 'for whom no better palaeontological comparison exists than a broken skull', and 'bermani' honours palaeontologist David Berman, who did so much of the fundamental modern work on Diplodocoid skulls at Carnegie Museum of Natural History and was responsible for the initial description of the specimen. 

Given the limited material available, no size estimate is made for Athenar bermani, although Whitlock et al. note that it appears to have been larger than the mature Diplodocus CM 11161, but shows incomplete fusion of many of the sutures of the braincase, suggesting that the specimen was a subadult at its time of death. 

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Stegosaurs from the Late Jurassic Morrison Formation of Montana.

The Stegosauria is a group of Ornithischian (Bird-hipped) Dinosaurs that is characterised by the possession of a series of plates and spikes that extend from the neck to the tail in two parasagittal rows. The best known genus of the group, Stegosaurus, is from the Upper Jurassic of the western USA, but members of the group are known from all continents except for Antarctica and Australia, and their temporal range extends from the Middle Jurassic to the late Early Cretaceous. Despite the iconic status of Stegosaurs among Dinosauria, they are poorly known as fossils, with most genera being known from single partial skeletons and/ or fragmentary remains. Consequently, they have received relatively little attention, and much remains unknown about their palaeobiology.

In a paper published in the journal Acta Palaeontologica Polonica on 5 August 2019, Cary Woodruff of the Great Plains Dinosaur Museum and Field Station, the Department of Ecology and Evolutionary Biology at the University of Toronto, and the Royal Ontario Museum, David Trexler of the Two Medicine Dinosaur Center, and Susannah Maidment of the Department of Earth Sciences at the Natural History Museum, describe two sets of Stegosaur remains from the Late Jurassic Morrison Formation of Montana, an area further north than any that have previously produced described Stegosaur remains.

The Upper Jurassic Morrison Formation of the western United States comprises the deposits of rivers and floodplains that were laid down in a broad shallow basin over about 10 million years in the Kimmeridgian (157.3-152.1 million years ago and Tithonian (152.1-145.0 million years ago). The deposits host a diverse and well-preserved Dinosaurian fauna that includes such well-known taxa as Apatosaurus, Diplodocus, and Stegosaurus. The Dinosaurs of the southern part of the Morrison Basin, from Colorado, Utah, and southern Wyoming, have been intensively studied for about 150 years, but those from northern outcrops in northern Wyoming and Montana are much less exploited. An increasing body of evidence suggests that northern Morrison faunas were somewhat different to their southern counterparts but further exploration in this part of the basin is needed.

The first specimen described by Woodruff et al., GPDM 205, was collected in 2004 by the Judith River Dinosaur Institute from the 5E Ranch, owned by the Hein family, in the Little Snowy Mountains of Fergus County, Montana. The specimen is now housed at the Great Plains Dinosaur Museum in partnership with the Judith River Foundation. GPDM 205 was collected in close proximity to Camarasaurus sp. specimen GPDM 220. Unfortunately, neither field notebooks nor quarry maps exist for the excavation of this specimen, so Woodruff et al. do not possess any documentation regarding taphonomy. However, Susanneh Maidment visited the 5E Ranch quarry in 2005 and was told by the excavation crew that the specimen was found disarticulated, and stratigraphically above the Camarasaurus remains. 

The material assigned to GPDM 205 comprises a prepared humerus, ulna, and radius, plus an unprepared coracoid, fragmentary scapula, humerus, and ulna. During the 2005 field season, at the time of Susanneh Maidment’s visit, a carpal and some poorly preserved dermal plates from this specimen were also recovered. Several other Stegosaur specimens were discovered during the 2005 field season at the 5E Ranch quarry, and were excavated over subsequent years. These specimens currently reside in a private collection, and thus are unavailable for study.

Left humerus of Stegosaur GPDM 205 from the 5E Ranch, Little Snowy Mountains, Fergus County, Montana, USA; in anterior (A₁), posterior (A₂), lateral (A₃), medial (A₄), dorsal (A₅), and ventral (A₆) views. Woodruff et al. (2019).

The second specimen, GPDM 178, was collected in 2003 and 2004 by the Judith River Dinosaur Institute near the town of Giffen, Cascade County, Montana, on land belonging to the Yurek family. Elements were initially found eroding out of a hill adjacent to the Yurek’s house. The distal end of the right tibia was the first element recovered, and it was not immediately recognised as a fossil. For a period of time, this 'black rock'  served as a door stop until construction of a pole barn on the hill started, and further elements were discovered below the surface. At this time the Yurek family contacted the Judith River Dinosaur Institute, and the excavation commenced. The specimen is now housed at the Great Plains Dinosaur Museum in partnership with the Judith River Foundation 

 Partial right tibia of Stegosaur GPDM 178, near Giffen, Cascade County, Montana; in medial (A₁, A₆), lateral (A₂, A₇), anterior (A₃, A₅), dorsal (A₄), and ventral (A₈) views. (A₁)–(A₄) proximal end, (A₅)–(A₈), distal end. Woodruff et al. (2019).

GPDM 178 consists of a partial skeleton including both crania and post-crania. Several field jackets that are labelled as dorsal ribs or vertebrae await preparation. Only those elements prepared to-date are described, though the skeletal reconstruction for this specimen includes all elements collected as recorded in the quarry log.

Skeletal reconstruction of the stegosaurs GPDM 178 (A) and GPDM 205 (B) scaled together based on humeral lengths. Black, elements preserved in each specimen; gray, missing elements. Human scale is the Artemision Bronze featuring the deity of Zeus as 1.83 m in height. Woodruff et al. (2019).

Three genera of Stegosaur have previously been described from the Morrison Formation, Alcovasaurus, Hesperosaurus, and Stegosaurus, though unfortunately neither of the Montana specimens is complete enough to assign them to a specific genus, as useful diagnostic features are not preserved.

The specimens GPDM 178 and 205 represent the northernmost Stegosaurs found to-date, and GPDM 178 is the northernmost Dinosaur fossil thus far recovered from the entire Morrison Formation. Interestingly, according to a Works Progress Administration report from 1938, a 'Stegosaurus' was found at Sheep Creek, 25 miles north of Great Falls, Montana. If true, then this specimen is the northernmost Morrison Formation dinosaur, as GPDM 178 was found near equivalent distance southeast of Great Falls, Montana. Unfortunately, this report does not mention what material was collected or where it was sent. Searching for this material in Montana institutions with historic palaeontological collections and the National Museum of Natural History has yielded no results. Therefore Woodruff et al. believe that these remains, if true, have subsequently been lost or discarded. Thus by default, GPDM 178 is the northernmost record of the Stegosauria.

(A) Map of the USA with indicated the state of Montana, were the Stegosaur specimens GPDM 178 and GPDM 205 were found. (B) Map of Montana with the extent of the Morrison Formation in green, and the general locations of GPDM 178 and GPDM 205 indicated by the Stegosaurus skull silhouettes. Woodruff et al. (2019).

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Maraapunisaurus fragillimus: Edward Drinker Cope’s giant Sauropod revisited, reclassified, and downsized (a bit).

In 1878 Oramel and Ira Lucas of Garden Park, Colorado, excavated a gigantic neural spine (projection on the top of a vertebra) from the Cope’s Nipple location of the Late Jurassic Morrison Formation, and shipped it to Edward Drinker Cope at the Academy of Natural Sciences of Philadelphia. Cope carefully examined, measured and illustrated this specimen, concluding that it came from a Diplodocid Sauropod Dinosaur, and reconstructed it as having come from a Vertebra over six feet (220 cm) high, which he named Amphicoelis fragillimus. Sadly, the specimen was lost some time between this description being made and Cope’s collection being curated at the American Museum of Natural History after his death, leaving modern scientists only Cope’s illustrations to go on. This is unfortunate, since it has been estimated that if the measurements of the specimen are correct, and it did come from a Diplodocid, then the animal that produced it would have been 58 m in length, by far the largest Dinosaur known, and dwarfing even modern Baleen Whales, which has led to some scientists making the opposite conclusion, that Cope’s measurements were inaccurate or even wildly exaggerated.

In a paper published in the journal Geology of the Intermountain West on 19 October 2018, Kenneth Carpenter of the Prehistoric Museum at Utah State University Eastern, and the University of Colorado Museum of Natural History re-examines Cope’s illustrations of the giant neural spine, and draws new conclusions about the affinities of the specimen, and the nature of the animal that produced it.

The controversial vertebra and Edward D. Cope who described the specimen in 1878. Carpenter 2018. 

When Cope was examining the specimen, very few Sauropods were known, and less than a year had passed since the first description of a North American species. This meant that there were very few Sauropod specimens to compare the neural spine to. Of the available specimens, one struck Cope as being particularly likely, Amphicoelias altus, one of the first described Diplodocids (though this term was not coined until the 1920s), with the similarity apparently so great that Cope described the specimen as a new species within the same genus, Amphicoelias fragillimus.

Illustrations of different sauropod dorsals made by Cope to show why he thought that the neural spine of "Amphicoelias" fragillimus (A) was most similar to that of Amphicoelias altus (B) than to Camarasaurus supremus (C) mid-dorsal and (D) more posterior mid-dorsal. Scale bar is 1 m. Carpenter 2018.

Diplodocids were large animals, among the largest Sauropods and therefore Dinosaurs of any kind, but their vertebrae had relatively small centra (disks) with a large neural spine located above. Interpreted as the neural spine of a Diplodocid, Cope's specimen calculated to have come from a vertebra six foot four inches (1.93 m) high, which in turn has been used to suggest an animal 58 m in length. 

This is excepionally large, even for a Sauropod Dinosaur, and has provoked some extreme scepticism among palaeontologists, some of whom have gone as far as to sugest that Cope's measurements were inaccurate. Carpenter, however, notes that Cope's measurements and illustrations were generally considered to be excellent, and that, where they can be checked against still extant specimens, appear to be highly reliable. Instead he puts forward an alternative theory, that Cope's specimen comes not from a Diplodocid, but instead from a Rebbachisaurid, a group of Dinosaurs entirely unknown in Cope's day, and which had rather different proportions. To this end he proposes that the name Amphicoelias fragillimus is wrong for the neural arch, since Amphicoelias refers to a genus of Diplodocid Dinosaurs, which was described prior to the specimen, and therefore suggests a new genus name, Maraapunisaurus, meaning 'Huge Reptile'.

Comparison of the neural spine of Maraapunisaurus fargillimus restored as a Rebbachisaurid (A), and the dorsal vertebrae of Rebbachisaurus garasbae (B), and Histriasaurus boscarollii (C). Increments on scale bars are 10 cm. Carpenter 2018.

Like Diplodocids, Rebbachisaurids were big animals, but their proportions were somewhat different, with their vertebrae typically composing a large, wide centra surmounted by a large neural arch, with the whole structure being far larger compared to the overall size of the animal; interpreted as a neural arch from a Rebbachisaurid, Carpenter estimates that Cope's specimen would have come from a vertebra 2.4 m in height, but that this would have come from an animal only 30.3 m in length (big, but not absurd - and it has never been doubted that the vertebra came from a big animal).

Body comparisons of Maraapunisaurus as a 30.3-m-long Rebbachisaurid (green) compared with previous version as a 58-m-long Diplodocid (black). Lines within the silhouettes approximate the distal end of the diapophyses (i.e., top of the ribcage). Carpenter 2018.

The Rebbachisaurids as a group are currently known only from South America, Africa and Europe, and only from the Cretaceous, which at first sight seems a problem for the assignment of the specimen to this group. However, the Rebbachisaurids are considered to be the sister group to the Diplodocids (hence having neural spines similar enough to be mistaken), and therefore the two groups must have had a common ancestor living in one place, so finding an ancestral Rebbachisaurid living in an area known to have been home to early Diplodocids is not especially surprising, particularly as North America was probably still attached to Europe in the Late Jurassic, and Europe subsequently came into contact with North Africa, while West Africa was still attached to South America, creating a pathway known to have been used by other groups.

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A new species of Diplodocid Dinosaur from the Late Jurassic of northern Wyoming.

Diplodocids were members of the Sauropod group of Dinosaurs, noted for their extremely long necks and tails; they were less massive than the related Titanosaurids and Brachiosaurs, but were longer and more slender, making them probably the longest animals ever to live; the longest species, Diplodocus and Supersaurus, are thought to have reached around 34 m, making them longer than a Blue Whale (though considerably less massive). The ecology of the Diplodocids is somewhat mysterious; their light frame and long bodies makes it seem unlikely that they had the musculature to lift their necks very high, and they had relatively short legs compared to other Sauropods, ruling out Giraffe-style treetop feeding. Some palaeontologists have described them as 'Dachshund' Dinosaurs.

In a paper published in the Journal of Systematic Palaeontology on 27 January 2013, Emanuel Tschopp of the Faculdade de Ciências e Tecnologia at the Universidade Nova de Lisboa and Octávio Mateus of the Museu da Lourinhã describe a new species of Diplodocid Dinosaur from the Late Jurassic Morrison Formation at Howe Quarry near Shell,Wyoming.

The new Dinosaur is named Kaatedocus siberi, where the Crow word 'Kaate' (small) has been combined with the element '-docus' (beam) from Diplodocus, to make 'small-beam' or 'small-Diplodocus', and 'siberi is in honour of Hans-Jakob Siber, who founded the Sauriermuseum Aathal, near Zurich, and who was involved in the organization and funding of the expedition which found the new specimen, as well as its subsequent preparation and curation.

Kaatedocus siberi is described from a partial skull and a series of cervical (neck) vertebrae. It is thought to have been a young animal, with weekly fused bones and a head and neck length of about 3.8 m and a total body length of 14 m. 

The reconstructed skull of Kaatedocus siberi in right lateral view. (A) Photograph. (B) Drawing. Light grey areas in (B) are reconstructed parts. Abbreviations: a: articular;  aof: antorbital

fenestra; bt: basal tuber; d: dentary;  f: frontal;  ltf: laterotemporal fenestra; m: maxilla; o: orbit;

os: orbitosphenoid; p: parietal; pm: premaxilla; po: postorbital; popr: paroccipital process;  pra: proatlas; q: quadrate; qj: quadratojugal; sq: squamosal. Scale bar is 5 cm. Tschopp & Mateus (2013).

The reconstructed skull of Kaatedocus siberi in right lateral view. (A) Photograph. (B) Drawing. Abbreviations: a: articular; aof: antorbital fenestra; bt: basal tuber; d: dentary; f: frontal; la: lacrimal; ls: laterosphenoid; ltf: laterotemporal fenestra; m: maxilla; o: orbit; p: parietal; paof: preantorbital fossa; po: postorbital; popr: paroccipital process; pre: pre-epipophysis; pro: prootic; q: quadrate; qj: quadratojugal; sa: surangular; sq: squamosal. Scale bar is 5 cm. Tschopp & Mateus (2013).

The reconstructed skull of Kaatedocus siberi in dorsal view. (A) Photograph. (B) Drawing. Abbreviations: a: articular; aof: antorbital fenestra; f: frontal; ls: laterosphenoid; m: maxilla; n: external nares; o: orbit; p: parietal;  pm: premaxilla; po: postorbital; popr: paroccipital process; ppfo: postparietal foramen; pra: proatlas; q: quadrate; sq: squamosal. Scale bar is 5 cm. Tschopp & Mateus (2013).

Life reconstruction of the skull of Kaatedocus siberi. Note the lateral spur on the lacrimal and the palpebral element covering the orbit. Illustration by Davide Bonadonna in Tschopp & Mateus (2013).

See also Dwarf Titanosaur eggs from the Haţeg Basin in Romania, A Mamenchisaurid Sauropod Dinosaur from Thailand, A Titanosaur from the Antarctic and An American Titanosaur.

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