K. R. K. JÃger, Z.-X. Luo & T. Martin (2019)
Postcranial Skeleton of Henkelotherium guimarotae (Cladotheria, Mammalia) and Locomotor Adaptation.
Journal of Mammalian Evolution (advance online publication)
X-ray computed tomography of the cladotherian Henkelotherium guimarotae from the Kimmeridgian Guimarota coal mine (Portugal) adds new information on its postcranial skeleton. Contrary to earlier description, the humerus of Henkelotherium shows a plesiomorphic cladotherian condition similar to that seen in Dryolestes leiriensis in having individual radial and ulnar condyles on the anterior aspect of the distal joint, whereas the posterior aspect appears to be trochlear. The scapula is also more plesiomorphic than previously assumed in having a laterally flared crest on the inferior margin. In this regard, it is similar to the scapula of spalacotherioid "symmetrodontans" such as Zhangheotherium but more derived than the latter, in having a larger supraspinous fossa. The hind limb is similar to that of small extant therians, which is interpreted to be assocated with an upright limb posture. The previously proposed hypothesis of an arboreal lifestyle for Henkelotherium is corroborated by a number of skeletal features such as large humeral entepicondyles, prominent digital flexor tubercles, elongated and slender tail vertebrae, as well as a high pedal phalangeal index of 153%.
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Aitor NavarroâDÃaz, Borja EsteveâAltava & Diego RasskinâGutman (2019)
Disconnecting bones within the jawâotic network modules underlies mammalian middle ear evolution.
Journal of Anatomy (advance online publication)
The origin of the mammalian middle ear ossicles from the craniomandibular articulation of their synapsid ancestors is a key event in the evolution of vertebrates. The richness of the fossil record and the multitude of developmental studies have provided a stepwise reconstruction of this evolutionary innovation, highlighting the homology between the quadrate, articular, preâarticular and angular bones of early synapsids with the incus, malleus, gonial and ectotympanic bones of derived mammals, respectively. There are several aspects involved in this functional exaptation: (i) an increase of the masticatory musculature; (ii) the separation of the quadrate bone from the cranium; and (iii) the disconnection of the postâdentary bones from the dentary. Here, we compared the jawâotic complex for 43 synapsid taxa using anatomical network analysis, showing that the disconnection of mandibular bones was a key step in the mammalian middle ear evolution, changing the skull anatomical modularity concomitant to the acquisition of new functions. Furthermore, our analysis allows the identification of three types of anatomical modules evolving through five evolutionary stages during the anatomical transformation of the jawbones into middle ear bones, with the ossification and degradation of Meckel's cartilage in mammals as the key ontogenetic event leading the change of anatomical modularity.
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