New digital braincase endocasts of two species of Desmatosuchus and neurocranial diversity within Aetosauria (Archosauria: Pseudosuchia)

Abstract

In the present contribution we revise, figure, and redescribe several isolated braincases of the iconic aetosaur Desmatosuchus from the Placerias Quarry locality, Chinle Formation, Arizona, United States. The detailed study of the isolated braincases from the UCMP collection allowed us to assign them at the species-level and recognize two species of Desmatosuchus for the Placerias Quarry: D. spurensis and D. smalli. The former can be distinguished from the latter by the presence of a transverse sulcus on the parietals, deep median pharyngeal recess on the basisphenoid, almost no gap between the basal tubera and the basipterygoid processes, and the exoccipitals meeting at the midline. The presence of D. smalli at the Placerias Quarry has not been previously reported. Based on the braincases UCMP 27408, 27410, 27407, three new brain endocasts were developed through CT scan images, reconstructing the most complete endocranial casts known for an aetosaur, including the encephalon, cranial nerves, inner ear, and endocranial vasculature. The cranial endocasts also exhibited some differences between both species of Desmatosuchus, with D. spurensis having a distinguishable dural expansion and markedly asymmetric anterior and posterior semicircular canals of the labyrinth. Additionally, the combination of osteological features and the endocranial casts allowed us to identify and discuss the presence of an ossified orbitosphenoid on the anteriormost region of the braincase among aetosaurs. Furthermore, we were able to reinterpret some of the observations made by previous authors on the endocast of the holotype of Desmatosuchus spurensis (UMMP VP 7476) and provide some insight into their neurosensory capabilities.

Paleoneurology and neuroanatomical notes on the South American “rauisuchian” Saurosuchus galilei from the Ischigualasto formation, San Juan, Argentina

“…The labyrinth height is approximately three‐quarters the dorsoventral extension of the utricle‐lagena region, and this elongate proportion is reported among various archosaurs (e.g., D . spurensis , von Baczko, Desojo, Gower, et al, 2022; von Baczko, Desojo, Trotteyn, & Stocker, 2022; Parasuchus hislopi , Stocker et al, 2016). However, it differs from that of extinct and extant crocodylians (e.g., Alligator mississippiensis : OUVC 9761; Gavialis gangenticus ; Gr .…”

The endocast of Euparkeria sheds light on the ancestral archosaur nervous system

“…CN V (trigeminal) is placed below the hindbrain and is relatively large in comparison to other archosauriforms, but not as large as in Desmatosuchus and other aetosaurs (Baczko et al . 2018, 2021). CN IX, X, and XI converge on the large fenestra ovalis, which connects to the ear system.…”

Cranial osteology and paleoneurology of Tarjadia ruthae: An erpetosuchid pseudosuchian from the Triassic Chañares Formation (late Ladinian‐?early Carnian) of Argentina

“…These elements are partially preserved in both recently collected articulated skulls, being represented by an anterior fragment of the right side in CRILAR‐Pv 495 and the posterolateral process of the right side in CRILAR‐Pv 478. In addition, the parietals are also partially preserved in MCZ 9319 (von Baczko et al, 2023). The anterior region of the parietal is dorsoventrally thick and strongly ornamented; it contacts anteriorly with the frontal and anterolaterally the postfrontal.…”

“…The participation of the supraoccipital in the dorsal border of the foramen magnum is a condition widespread among early archosauriforms, including the erpetosuchids Parringtonia gracilis (Nesbitt et al, 2018) and Archeopelta arborensis (Desojo et al, 2011). A better preserved supraoccipital is available in the referred specimen MCZ 9319 described by Arcucci and Marsicano (1998), recently analyzed by von Baczko et al (2023). In this specimen, the external surface of the supraoccipital possesses an incipient median vertical ridge that separates shallowly concave surfaces from each other.…”