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Abstract Almadasuchus figariiis a basal crocodylomorph recovered from the Upper Jurassic levels of the Cañadón Calcáreo Formation (Oxfordian–Tithonian) of Chubut, Argentina. This taxon is represented by cranial remains, which consist of partial snout and palatal remains; an excellently preserved posterior region of the skull; and isolated postcranial remains. The skull of the only specimen of the monotypicAlmadasuchuswas restudied using high‐resolution computed micro tomography.Almadasuchushas an apomorphic condition in its skull shared with the closest relatives of crocodyliforms (i.e. hallopodids) where the quadrates are sutured to the laterosphenoids and the otoccipital contacts the quadrate posterolaterally, reorganizing the exit of several cranial nerves (e.g. vagus foramen) and the entry of blood vessels (e.g. internal carotids) on the occipital surface of the skull. The endocast is tubular, as previously reported in thalattosuchians, but has a marked posterior step, and a strongly projected floccular recess as in other basal crocodylomorphs. Internally, the skull ofAlmadasuchusis heavily pneumatized, where different air cavities invade the bones of the suspensorium and braincase, both on its dorsal or ventral parts.Almadasuchushas a large basioccipital recess, which is formed by cavities that excavate the basioccipital and the posterior surface of the basisphenoid, and unlike other crocodylomorphs is connected with the basisphenoid pneumatizations. Ventral to the otic capsule, a pneumatic cavity surrounded by the otoccipital and basisphenoid is identified as the rhomboidal recess. The quadrate ofAlmadasuchusis highly pneumatized, being completely hollow, and the dorsal pneumatizations of the braincase are formed by the mastoid and facial antra, and a laterosphenoid cavity (trigeminal diverticulum). To better understand the origins of pneumatic features in living crocodylomorphs we studied cranial pneumaticity in the basal members of Crocodylomorpha and found that: (a) prootic pneumaticity may be a synapomorphy for the whole clade; (b) basisphenoid pneumaticity (pre‐, postcarotid and rostral recesses) is a derived feature among basal crocodylomorphs; (c) quadrate pneumatization is acquired later in the history of the group; and (d) the rhomboidal sinus is a shared derived trait of hallopodids and crocodyliforms. The marine thallatosuchians exhibit a reduction of the pneumaticity of the braincase and this reduction is evaluated considering the two phylogenetic positions proposed for the clade.
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New genus and species of djadochtatheriid multituberculate (Allotheria, Mammalia) from the Upper Cretaceous Bayan Mandahu Formation of Inner Mongolia
The superfamily Djadochtatherioidea is a distinctive clade of multituberculates from Upper Cretaceous beds of Mongolia and Inner Mongolia, China. Because many of the 11 included genera are known from skulls, more is known about the cranial anatomy of djadochtatherioids than any other clade of multituberculates. Within Djadochtatherioidea, the most diverse and widely accepted group is the family Djadochtatheriidae. Within the family, the basal genus, Kryptobaatar Kielan-Jaworowska, 1970, is small with a skull length of about 30 mm, whereas the other four genera, Djadochtatherium Simpson, 1925, Catopsbaatar Kielan-Jaworowska, 1994, Tombaatar Rougier et al., 1997, and Mangasbaatar Rougier et al., 2016, have skulls approximately twice as long. Here, we describe a new genus and species, Guibaatar castellanus, based on a single specimen from the Upper Cretaceous Bayan Mandahu Formation, Inner Mongolia that we refer to Djadochtatheriidae. Guibaatar is represented by a relatively complete rostrum, a partial right braincase, and partial lower jaws. As revealed by CT scanning, the specimen is a juvenile, with deciduous enlarged upper and lower incisors with permanent replacements forming, m2 erupting, and M2 forming. Based on the preserved cranial parts, we estimate the skull length to be approximately 50 mm, but as an adult, Guibaatar would have been in the size range of the larger djadochtatheriids. Phylogenetic analysis including Guibaatar, known djadochtatherioids, and outgroups places Guibaatar within Djadochtatheriidae, as sister to a clade of Mangasbaatar and Catopsbaatar. We suspect the relationships of djadochtatherioids are likely to be refined given the announcements by other researchers that skulls are known for the djadochtatheriids Tombaatar and Djadochtatherium, which were previously represented by incomplete material.
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- Award ID(s):
- 1654949
- PAR ID:
- 10160590
- Date Published:
- Journal Name:
- Annals of Carnegie Museum
- Volume:
- 85
- Issue:
- 4
- ISSN:
- 1943-6300
- Page Range / eLocation ID:
- 285-327
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.2992/007.085.0401
