Abstract: Four specimens of the pterosaur Pteranodon exhibit patterns of irregular alternating light and dark bands on the lateral surfaces of the upper jaw anterior to the nasoantorbital fenestra. Examinations reveal that the maxilla and premaxilla of Pteranodon consisted of two thin sheets of bone interconnected by regularly spaced septa with the spaces contained within presumably pneumatized, resulting in a structure analogous to modern honeycomb sandwich panels. The alternating light and dark bands resulted from waves of bone deposition moving anteriorly along the external surface of the lateral sheet of bone and laying down thin laminae of new bone while bone was simultaneously resorbed from the internal surface of the lateral sheet to maintain its thickness. The specimens that exhibit the bands were immature males and no banding was found in mature specimens or immature females. Therefore, the presence of the bands in immature males is interpreted as correlated with the enlargement and reshaping of the rostrum as males approached and attained sexual maturity.

Abstract: We report on a diminutive pterosaur specimen (MIC-V246), from the Lower Cretaceous Lagarcito Formation, which has anatomical features and general proportions that agree with those of other juvenile specimens of the filter-feeding pterosaur Pterodaustro guinazui . MIC-V246 is nearly complete, with the majority of its bones in natural articulation. The specimen is preserved within a small oval surface inferred to demarcate the outline of an egg. It includes remains of the skull and mandible, some cervical, dorsal, sacral and caudal vertebrae, ribs, gastralia, both shoulder girdles, part of the ilium, and the forelimbs and hindlimbs. The skeleton is arranged in a position similar to that of avian embryos, with the wings folded sideways, the hindlimbs flexed, and the skull tucked beneath a wing. The bones are partially covered by an irregularly distributed substance differing in texture and colour from the bony elements, and identified as remnants of the eggshell. The diminutive size of the skeleton, along with its arrangement and morphology, support the identification of this specimen as one of the very few pterosaur embryos known worldwide. Its similarity in size to other Pterodaustro specimens interpreted as hatchlings suggests that MIC-V246 was near hatching when it died.

Abstract A partial exoccipital–opisthotic from the uppermost lower Campanian (Upper Cretaceous) of the Åsen locality, Kristianstad Basin, southernmost Sweden, is described and illustrated. The fossil represents the first braincase element of a plesiosaur found in Sweden. It includes the chamber for the ampulla and utriculus, openings for the caudal vertical and horizontal semicircular canals, and four foramina for cranial nerves. The incomplete braincase can be referred to an elasmosaurid plesiosaur, and closely resembles the exoccipital–opisthotic of Libonectes morgani and a referred specimen of Aristonectes parvidens . Although we discuss putative postcranial material of the elasmosaurid subfamily Aristonectinae in the uppermost lower Campanian of southernmost Sweden, the exoccipital–opisthotic from Åsen most likely belongs to a juvenile individual of a non-aristonectine elasmosaur.

Here, we describe a juvenile Triceratops sp. skull, UCMP 136306, from the Hell Creek Formation, McCone County, Montana. The relative completeness and superb preservation of this skull contribute to an improved understanding of the cranial ontogeny, morphology, and individual variation in Triceratops . Total skull length is 120 cm long (est.). UCMP 136306 is one of the most complete Triceratops skulls of this ontogenetic stage yet known. The cranial sutures are patent, and most are overlapping with minimal sinuosity, modest interdigitation, and overlapping flat sutural surfaces. The following cranial elements are preserved and described in this study: epinasal, rostral, quadrate, quadratojugal, jugal, pterygoid, dentary, surangular, postorbital horn, parietal, squamosal, epiparietal, episquamosal, occipital condyle, supraoccipital, and exoccipital. For decades following the initial description of Triceratops by O.C. Marsh in 1889, the typical collector attitude was “bigger is better.” Emerging scientific institutions and museums with newly constructed exhibit halls demanded the biggest and newest dinosaurs. We hypothesize that this historical practice, influenced by facies and taphonomic factors in the Upper Cretaceous Hell Creek Formation, Montana (and contemporaneous formations in neighboring states), resulted in the underrepresentation of nonadult Triceratops in museum collections. This practice contributed to the false notion that nonadult Triceratops specimens are rarely preserved in the fossil record, until now.

Ceratopsid dinosaurs are notable for their common occurrences in bonebeds; however, until recently, these have not been encountered for the chasmosaurine Triceratops . The aim of this investigation is to describe the taphonomy of Quittin' Time (Museum of the Rockies locality HC-430), a Triceratops bonebed in the Hell Creek Formation, Garfield County, Montana. Using site taphonomic descriptions with an evaluation of ontogeny, inferences regarding the paleobiology of this extinct taxon are possible. The locality is associated with abundant organic material, including woody debris, large seeds, and other fragments in isolated silty lenses, all incorporated within a siltstone matrix, indicating preservation within a floodplain environment. Based on the repetition and ontogenetic stages of cranial elements, the minimum number of individuals (MNI) is three. Evidence from the location and taphonomic condition of the bones preserved in close proximity within the same siltstone unit suggests that the individuals—one young adult, one subadult, and a juvenile—likely accumulated during distinct flooding events within a narrow region of the floodplain as a result of “bloat-and-float” transport. The relatively small scale of the bonebed, both in terms of total area and number of individuals, implies that future work on Triceratops sites requires careful scrutiny of cranial elements examined within an ontogenetic framework because they are potentially critical to establishing MNI. Preservation of multiple individuals within the same unit does not necessarily provide evidence of gregarious behavior in Triceratops but rather may be a reflection of site taphonomic history and accumulation processes.