bioRxiv Science⌕ Search
Home/Archive/bioRxiv

bioRxiv · 10.1101/490367

Petrosal morphology and cochlear function in Mesozoic stem therians

Harper, T.·Rougier, G.
View original source ↗Export metadata ↓

Abstract

Here we describe the bony anatomy of the inner ear and surrounding structures seen in three of the most plesiomorphic crown mammalian petrosal specimens in the fossil record. Our study sample includes the stem therian taxa Priacodon fruitaensis from the Upper Jurassic of North America, and two isolated petrosal specimens colloquially known as the Höövör petrosals, recovered from Aptian-Albian sediments in Mongolia. The second Höövör petrosal is here described at length for the first time. All three of these stem therian petrosals and a comparative sample of extant mammalian taxa have been imaged using micro-CT, allowing for detailed anatomical descriptions of osteological correlates of functionally significant neurovascular features, especially along the abneural wall of the cochlear canal.The high resolution imaging provided here clarifies several hypotheses regarding the mosaic evolution of features of the cochlear endocast in early mammals. In particular, these images demonstrate that the membranous cochlear duct adhered to the bony cochlear canal abneurally to a secondary bony lamina before the appearance of an opposing primary bony lamina or tractus foraminosus. Additionally, while corroborating the general trend of reduction of venous sinuses and plexuses within the pars cochlearis seen in crownward mammaliaformes generally, the Höövör petrosals show the localized enlargement of a portion of the intrapetrosal venous plexus. This new excavation is for the vein of cochlear aqueduct, a structure that is solely or predominantly responsible for the venous drainage of the cochlear apparatus in extant therians. However, given that these stem therian inner ears appear to have very limited high-frequency capabilities, the development of these modern vascular features the cochlear endocast suggest that neither the initiation or enlargement of the stria vascularis (a unique mammalian organ) is originally associated with the capacity for high-frequency hearing or precise sound-source localization.View Full Text

Source connections

Explore related subjects

paleontologyPreprint

Keep this discovery

Explore connections, maps & timelines

BibTeXRIS

Harper, T., Rougier, G.. 2018-12-07. Petrosal morphology and cochlear function in Mesozoic stem therians. https://doi.org/10.1101/490367

Cite the original work for its findings. Save a collection to share your selection of sources.

KEEP EXPLORING

Related preprints

bioRxiv2026

Constraining Palaeogeography and Palaeotides for the Cambrian using cnidarian medusae

The ocean tides influence key Earth system processes at a range of spatial and temporal scales. It is known that the geometry of ocean basins is the leading controller of tidal energetics, so well-constrained palaeogeographic reconstructions and tidal properties for Earths past are imperative when investigating other Earth system processes. Here, we present a novel way to constrain both deep-time tidal model results and reconstructions, by combining palaeoecology with sedimentology. We compare new palaeo-tidal model simulations for the Cambrian period, significant for the early origin and radiation of major animal fauna, to tidal proxies. One of the most abundant soft-bodied organisms preserved during this time are cnidarian medusae (jellyfish). A total of 17 cnidarian medusae localities were obtained through the literature, which had an adequate global distribution and occurred at regular intervals throughout the period of study. In some locations there were also estimates of palaeo-tidal range. Our results show a good agreement between the simulations and proxy data. In the few locations where there is disagreement, it is proposed that the palaeogeographic reconstructions are missing details, e.g., island chains, and our results allow for the palaeogeographic reconstructions to be improved. The proxy method presented is promising and can be applied to other time-periods with different marine fossils, particularly at evolutionary and extinction periods where the marginal marine environment is of importance.

paleontology↗
bioRxiv2018

Bilateral Asymmetry of the Forearm Bones as Possible Evidence of Antemortem Trauma in the StW 573 Australopithecus Skeleton from Sterkfontein Member 2 (South Africa)

The 3.67-million-year-old StW 573 Australopithecus skeleton is important for the light it sheds on the paleobiology of South African species of that genus, including, as discussed here, how the possible pathology of the specimen informs our understanding of Australopithecus behavior. The StW 573 antebrachium exhibits bilateral asymmetry, with significantly more longitudinally curved left forearm bones than right. Arguing from a comparative perspective, we hypothesize that these curvatures resulted from a fall onto a hyperextended, outstretched hand. It is unlikely that the fall was from a significant height and might have occurred when the StW 573 individual was a juvenile. This type of plastic deformation of the forearm bones is well-documented in modern human clinical studies, especially among children between the ages of four and ten years who tumble from bicycles or suffer other common, relatively low-impact accidents. Left untreated, such injuries impinge normal supination and pronation of the hand, a condition that could have had significant behavioral impact on the StW 573 individual.View Full Text

paleontology↗
bioRxiv2018

The skull of StW 573, a 3.67 Ma Australopithecus skeleton from Sterkfontein Caves, South Africa

Here we present the first full anatomical description of the 3.67 million-year-old Australopithecus skull StW 573 that was recovered with its skeleton from the Sterkfontein Member 2 breccia in the Silberberg Grotto. Analysis demonstrates that it is most similar in multiple key morphological characters to a group of fossils from Sterkfontein Member 4 and Makapansgat that are here distinguished morphologically as A. prometheus. This taxon contrasts with another group of fossils from those sites assigned to A. africanus. The anatomical reasons for why these groupings should not be lumped together (as is frequently done for the South African fossils) are discussed in detail. In support of this classification, we also present for the first time a palate (StW 576 from Sterkfontein Member 4) newly reconstructed by RJC, which has a uniquely complete adult dentition of an A. africanus. The StW 573 skull also has certain similarities with other earlier Australopithecus fossils in East Africa, A. afarensis and A. anamensis, which are discussed. One of its most interesting features is a pattern of very heavy anterior dental wear unlike that found in A. africanus but resembling that found in A. anamensis at 4.17 Ma. While StW 573 is the only hominid fossil in Sterkfontein Member 2, we conclude that competitive exclusion probably accounts for the synchronous and sympatric presence of two species of Australopithecus in the younger deposits at Makapansgat and Sterkfontein Member 4. Because the StW 573 skull is associated with a near-complete skeleton that is also described for the first time in this special issue, we are now able to use this individual to improve our understanding of more fragmentary finds in the South African fossil record of Australopithecus.

paleontology↗