The Frontoparietal Fossa and Dorsotemporal Fenestra of Archosaurs and Their Significance for Interpretations of Vascular and Muscular Anatomy in Dinosaurs

Abstract

The attachments of jaw muscles are typically implicated in the evolution and shape of the dorsotemporal fenestra on the skull roof of amniotes. However, the dorsotemporal fenestrae of many archosaurian reptiles possess smooth excavations rostral and dorsal to the dorsotemporal fossa which closely neighbors the dorsotemporal fenestra and jaw muscle attachments. Previous research has typically identified this region, here termed the frontoparietal fossa, to also have attachment surfaces for jaw‐closing muscles. However, numerous observations of extant and extinct archosaurs described here suggest that other tissues are instead responsible for the size and shape of the frontoparietal fossa. This study reviewed the anatomical evidence that support soft‐tissue hypotheses of the frontoparietal fossa and its phylogenetic distribution among sauropsids. Soft‐tissue hypotheses (i.e., muscle, pneumatic sinus, vascular tissues) were analyzed using anatomical, imaging and in vivo thermography techniques within a phylogenetic framework using extant and extinct taxa to determine the inferential power underlying the reconstruction of the soft tissues in the skull roofs of dinosaurs, pseudosuchians, and other reptiles. Relevant anatomical features argue for rejection of the default hypothesis—that the fossa was muscular—due to a complete lack of osteological correlates reflective of muscle attachment. The most‐supported inference of soft tissues is that the frontoparietal fossa contained a large vascular structure and adipose tissue. Despite the large sizes and diverse morphologies of these fossae found among dinosaur taxa, these data suggest that non‐avian dinosaurs had the anatomical foundation to support physiologically significant vascular devices and/or vascular integumentary structures on their skull roofs. Anat Rec, 303:1060–1074, 2020. © 2019 Wiley Periodicals, Inc.

The braincase of <em>Bissektipelta archibaldi</em> — new insights into endocranial osteology, vasculature, and paleoneurobiology of ankylosaurian dinosaurs

“…A bifurcating groove extends posterodorsally PALAEONTOLOGY from the internal foramen for CN VII and indicates the course of CN VIII (Fig. 3A); a similar reconstruction of this region was made for some ornithopods (Hopson, 1979;Sobral et al, 2012). The internal opening of the metotic foramen (MF) is just posterior to the otic capsule.…”

“…The morphology of the inner ear and braincase vasculature of ZIN PH 1/16 are described in separate sections below. The brain of Bissektipelta loosely fitted the endocranial cavity as is common for many non-avian dinosaurs and for reptiles in general (Hopson, 1979;. Thus, the produced endocast is more a cast of the meninges (including endocranial venous sinuses) rather than the brain itself.…”

“…10), most sauropods , and some theropods (e.g., Sampson and Witmer, 2007). Dorsal expansions of dinosaur endocasts have been interpreted as an unossified gap plugged with cartilage in life (Hopson, 1979) or as corresponding to extensive dural sinuses that may have surrounded the pineal complex (Sampson and Witmer, 2007;. In Bissektipelta, the only structure of the endocast that may correspond to the pineal complex is a conspicuous median vessel (medVs, Fig.…”

“…Notably, the pineal complex, optic chiasm, and the neurohypophysis are all diencephalic derivates. However, the external pineal (parietal) foramen was lost early in archosauriform evolution (Hopson, 1979;character 63 in Nesbitt, 2011); extant birds have a pineal that lies internally within the braincase, adjacent to the skull roof (Ralph, 1970). Thus, we doubt that the median canal of Bissektipelta contained a pineal/parapineal organ that was exposed on the dorsal surface of the skull roof and consider the structure a vascular canal.…”

Paleobiology in the 21st Century

“…"Contemporary paleobiology" is something of an oxymoron; however, this special issue of The Anatomical Record focuses on a wide variety of topics in which contemporary paleobiologists engage themselves. This of course includes taxonomic descriptions of new taxa and descriptions of new specimens (including a profoundly large and old specimen of Tyrannosaurus rex; Persons et al, 2020, in this issue), but it also includes work on behavior (Arbour and Zanno, 2020, in this issue), histology (Hedrick et al, 2020, in this issue), flight mechanics in extinct taxa (Torres et al, 2020, in this issue), vascular patterns in extinct taxa (Porter and Witmer, 2020, in this issue), and analyses exclusively on extant taxa (Angst et al, 2020, in this issue). There are many additional avenues and techniques that contemporary paleobiologists use to understand extinct organisms, and the range presented in this issue is certainly not exhaustive.…”