Abstract
Therocephalia is one of the major therapsid clades and ranges from the middle Permian to Middle Triassic. The earliest therocephalians were large-bodied predators whose fossils are common in middle Permian rocks of South Africa, but have received little study. Here we present a redescription of the skull of the early therocephalian Lycosuchus based on a specimen from the middle Permian Tapinocephalus Assemblage Zone of the South African Karoo Basin. By using a computed tomographic (CT) reconstruction of this specimen, we describe for the first time several endocranial characters of this taxon including a highly ramified maxillary canal and the inner ear, which is characterized by a lengthened lateral semicircular canal, a feature previously only known from the anomodont Kawingasaurus among non-mammalian therapsids, and the presence of a cochlear recess, so far only known within Therocephalia from the highly specialized Triassic taxon Microgomphodon. We also provide new insights into patterns of tooth replacement in lycosuchids, which have proven controversial for this taxon. Craniodental characters generally support the placement of Lycosuchus as the most basal taxon in therocephalian phylogeny. The morphology of the maxillary canal and inner ear reveal a mosaic of features indicating a complex history of character acquisition and loss in Therocephalia, comparable to that of cynodonts.
Highlights
The advent of widely-used computed tomographic (CT) imaging on fossil specimens has allowed paleontologists unprecedented access to the once-obscure internal features of vertebrate crania
Therocephalia is a species-rich and ecomorphologically varied group ranging from the middle Permian to the Middle Triassic, with highest diversity in the late Permian (Abdala et al, 2008; Huttenlocker et al, 2011; Huttenlocker, 2014; Huttenlocker and Smith, 2017).The earliest known representatives of this group have been reported from the middle Permian Eodicynodon Assemblage Zone (AZ) in the Karoo Basin of South Africa (Abdala et al, 2008), and they are the most abundant group of predatory therapsids in the subsequent, middle–earliest late Permian Tapinocephalus and Pristerognathus AZs, with hundreds of known specimens (Smith et al, 2012)
Our redescription of Lycosuchus vanderrieti based on a computed tomographic reconstruction of the skull of the specimen MB.R.995 provides new insights into the internal cranial morphology of this taxon
Summary
The advent of widely-used computed tomographic (CT) imaging on fossil specimens has allowed paleontologists unprecedented access to the once-obscure internal features of vertebrate crania. Therocephalia is a species-rich and ecomorphologically varied group ranging from the middle Permian to the Middle Triassic, with highest diversity in the late Permian (Abdala et al, 2008; Huttenlocker et al, 2011; Huttenlocker, 2014; Huttenlocker and Smith, 2017).The earliest known representatives of this group have been reported from the middle Permian Eodicynodon Assemblage Zone (AZ) in the Karoo Basin of South Africa (Abdala et al, 2008), and they are the most abundant group of predatory therapsids in the subsequent, middle–earliest late Permian Tapinocephalus and Pristerognathus AZs, with hundreds of known specimens (Smith et al, 2012) Despite their abundance, these early therocephalian taxa have received little study relative to their later Permo-Triassic relatives. Lycosuchids are characterized by relatively short, broad snouts and reduction of the postcanine dentition (van den Heever, 1994; Abdala et al, 2008, 2014a)
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