Zeller U A
Folia Primatol (Basel). 1986;47(2-3):61-80. doi: 10.1159/000156266.
The structure of the tympanic region of the skull of Ptilocercus lowii was studied in an embryo of 30 mm crown-rump length and in 5 osteocrania. As in Tupaia, the anterior wall of the bulla of Ptilocercus is not completed by a tympanic process of the alisphenoid, contrary to earlier reports. Ptilocercus resembles Tupaia in the following derived characters. The ventral wall of the tympanic cavity is formed by a rostral entotympanic and by a caudal tympanic process of the petrosal. The entotympanic develops in primary connection with the tubal cartilage. The tympanic aperture of the auditory tube is bordered by the entotympanic. The ring-shaped tympanicum is covered by the entotympanicum and is aphaneric. The musculus tensor tympani is lacking. Among mammals, these characters can be regarded as synapomorphic for the Tupaiidae, that is, to have been present in the common ancestor of the two subfamilies. From the evidence of the tympanic region, the Tupaiidae, therefore, form a monophyletic group. Besides these synapomorphies, there are remarkable differences between Ptilocercus and Tupaia in the structure of the bulla. In Ptilocercus the bulla is smaller and less pneumatized than in Tupaia. An anterior intrabullar septum, present in Tupaia, is lacking in Ptilocercus. The epitympanic wing of the alisphenoid is smaller in Ptilocercus than in Tupaia. A lateral prefacial commissure of the tegmen tympani is present in Ptilocercus, but absent in Tupaia. The caudal tympanic process of the petrosal is larger in Ptilocercus than in Tupaia. These characters are autapomorphic for the Ptilocercinae and for the Tupaiinae, respectively. They demonstrate that the auditory bulla of Ptilocercus and that of Tupaia have evolved independently to a considerable extent. An early phylogenetic separation of their respective ancestors seems likely. The tympanic region of the skull provides no evidence for close relationships of the tree shrews to the primates or to any other eutherians. The classification of the Tupaiidae in a separate order, Scandentia, is supported.
对一只头臀长30毫米的胚胎及5个骨质颅骨标本的细纹睡鼠颅骨鼓室区域结构进行了研究。与笔尾树鼩属不同，细纹睡鼠的鼓泡前壁并非由翼蝶骨的鼓室突完成，这与早期报道相反。细纹睡鼠在以下衍生特征上与笔尾树鼩属相似。鼓室的腹侧壁由岩骨的吻侧内鼓骨和尾侧鼓室突形成。内鼓骨在发育过程中与咽鼓管软骨有原始连接。咽鼓管的鼓室口以内鼓骨为界。环形鼓膜被内鼓骨覆盖，难以辨认。鼓膜张肌缺失。在哺乳动物中，这些特征可被视为树鼩科的共有衍征，也就是说，在这两个亚科的共同祖先中就已存在。因此，从鼓室区域的证据来看，树鼩科形成一个单系类群。除了这些共有衍征外，细纹睡鼠和笔尾树鼩属在鼓泡结构上也存在显著差异。细纹睡鼠的鼓泡比笔尾树鼩属的更小，气化程度更低。笔尾树鼩属没有笔尾树鼩存在的鼓泡内前中隔。细纹睡鼠的翼蝶骨鼓室上翼比笔尾树鼩属的更小。细纹睡鼠有鼓膜盖的外侧面前连合，而笔尾树鼩属没有。细纹睡鼠的岩骨尾侧鼓室突比笔尾树鼩属的更大。这些特征分别是细纹睡鼠亚科和笔尾树鼩亚科的自有衍征。它们表明，细纹睡鼠和笔尾树鼩属的听泡在很大程度上是独立进化的。它们各自祖先可能在系统发育上很早就已分离。颅骨的鼓室区域没有提供证据表明树鼩与灵长类或任何其他真兽类有密切关系。树鼩科归入独立的树鼩目得到了支持。
