Architecture of the bronchial tree in Cuvier’s dwarf caiman (Paleosuchus palpebrosus)

We imaged the lungs of five Cuvier's dwarf caiman (Paleosuchus
palpebrosus) via computed tomography (CT) and micro-computed tomography
(μCT) and compared these data to the lungs of the American alligator
(Alligator mississippiensis). These data demonstrate anatomical
commonalities between the lungs of P. palpebrosus and A. mississippiensis,
and a few notable differences. The structural similarities are (a) a
proximally narrow, distally widened, hook-shaped primary bronchus; (b) a
cervical ventral bronchus that branches of the primary bronchus and
immediately makes a hairpin turn toward the apex of the lung; (c) a
sequential series of dorsobronchi arising from the primary bronchus caudal
to the cervical ventral bronchus; (d) intraspecifically highly variable
medial sequence of secondary airways; (e) sac-like laterobronchi; and (f )
grossly dead-ended caudal group bronchi in the caudal and ventral aspects
of the lung. The primary differences between the two taxa are in the
overall number of large bronchi (fewer in P. palpebrosus), and the number
of branches that contribute to the cardiac regions. Imaging data of both a
live and deceased specimen under varying states (postprandial, fasting,
total lung capacity, open to atmosphere) indicate that the caudal margin
and position of the lungs shift craniocaudally relative to the vertebral
column. These imaging data suggest that the smooth thoracic ceiling may be
correlated to visceral movement during ventilation, but this hypothesis
warrants validation. These results provide the scaffolding for future
comparisons between crocodilians, for generating preliminary
reconstructions of the ancestral crocodilian bronchial tree, and
establishing new hypotheses of bronchial homology across Archosauria.

我们通过计算机断层扫描（computed tomography, CT）和显微计算机断层扫描（micro-computed tomography, μCT）对5只库维耶侏儒凯门鳄（Paleosuchus palpebrosus）的肺脏进行了成像，并将这些数据与美国短吻鳄（Alligator mississippiensis）的肺脏数据进行了比较。这些数据揭示了P. palpebrosus与A. mississippiensis肺脏之间的解剖学共性，以及若干显著差异。结构相似性包括：（a）近端狭窄、远端扩张的钩状主支气管；（b）自主支气管分支的颈腹侧支气管，其随即呈发夹状转向肺尖；（c）在颈腹侧支气管尾侧，自主支气管依次发出的一系列背支气管；（d）种内高度变异的内侧次级气道序列；（e）囊状外侧支气管；（f）肺脏尾侧及腹侧区域大体呈盲端的尾组支气管。两个类群间的主要差异在于大型支气管的总数（P. palpebrosus中数量更少）以及参与心脏区域构成的分支数量。对活体和死亡标本在不同状态下（餐后、空腹、肺总量、暴露于大气）的成像数据表明，肺脏的尾缘及位置会相对于脊柱发生颅尾向移位。这些成像数据提示，光滑的胸腔顶部可能与通气过程中的内脏运动相关，但该假设仍需验证。这些结果为未来鳄类间的比较、鳄类祖先支气管树的初步重建，以及建立主龙类（Archosauria）支气管同源性的新假设提供了基础框架。