所有現(xiàn)存鱷魚類動(dòng)物，包括crocodiles,、alligators和gavialoids，都是半水生的。但它們據(jù)信是從被稱為Sphenosuchians的陸地祖先進(jìn)化來(lái)的,。來(lái)自中國(guó)西北戈壁沙漠的一個(gè)新發(fā)現(xiàn)的Sphenosuchian化石，促使研究人員重新思考鱷魚類動(dòng)物進(jìn)化過(guò)程中可能經(jīng)歷的一些事件,。新發(fā)現(xiàn)的化石是徹底陸生的,，然而卻與現(xiàn)存鱷魚類動(dòng)物密切相關(guān)?？雌饋?lái),，現(xiàn)存鱷魚類動(dòng)物堅(jiān)硬的頭骨（非常適合在水中捕獲獵物）最初是由其體形小、比較細(xì)弱的陸地形式用來(lái)鉗住獵物,、并將獵物鉗緊的,。這種頭骨的有用之處只是后來(lái)才在水環(huán)境中得到驗(yàn)證。
A Middle Jurassic 'sphenosuchian' from China and the origin of the crocodylian skull
The skull of living crocodylians is highly solidified and the jaw closing muscles are enlarged1, allowing for prey capture by prolonged crushing between the jaws. Living species are all semi-aquatic, with sprawling limbs and a broad body that moves mainly from side-to-side2; however, fossils indicate that they evolved from terrestrial forms. The most cursorial of these fossils3-6 are small, gracile forms often grouped together as the Sphenosuchia, with fully erect, slender limbs; their relationships, however, are poorly understood5, 7-10. A new crocodylomorph from deposits in northwestern China of the poorly known Middle Jurassic epoch possesses a skull with several adaptations typical of living crocodylians. Postcranially it is similar to sphenosuchians but with even greater adaptations for cursoriality in the forelimb. Here we show, through phylogenetic analysis, that it is the closest relative of the large group Crocodyliformes, including living crocodylians. Thus, important features of the modern crocodylian skull evolved during a phase when the postcranial skeleton was evolving towards greater cursoriality, rather than towards their current semi-aquatic habitus.
Figure 1 Results of a maximum parsimony phylogenetic analysis. Strict consensus of 81 trees; length = 109, consistency index (CI) = 0.569, retention index (RI) = 0.659. Junggarsuchus is the closest relative of the Crocodyliformes and the Sphenosuchia are paraphyletic. See Supplementary Information for details of the analysis.
Figure 2 Junggarsuchus sloani holotype skull. a, b, Left lateral view. c, d, Dorsal view. e, f, Occipital view. a, angular; aof, antorbital fenestra; bo, basoccipital; bs, basisphenoid; cf, carotid foramen; d, dentary; eo, exoccipital; f, frontal; j, jugal; la, lacrimal; mf, external mandibular fenestra; mx, maxilla; n, nasal; o, orbit; p, parietal; pa, palpebral; pf, prefrontal; pl, palatine; pm, premaxilla; po, postorbital; pt, pterygoid; q, quadrate; qf, quadrate fenestra; qj, quadratojugal; rp, retroarticular process; sa, surangular; saf, surangular foramen; sc, sagittal crest; soc, supraoccipital; sq, squamosal; stf, superior temporal fenestra. Scale bar, 5 cm.
Figure 3 Postcranial skeleton of Junggarsuchus sloani. a, Skeleton in left lateral view. b, Left humerus with hemispherical head in proximal view. c, Posteroventrally facing glenoid fossa of left scapula in distal view. d, Left carpus and manus in posteroventral view (arrow points to reduced fifth metacarpal). e, f, For comparison, the living Alligator mississippiensis left humerus and shoulder in lateral view (e) showing the hemi-sellar glenoid fossa, and left hand in dorsal view (f) showing the asymmetry of the digits and carpals, the rounded ulna–carpal contact (arrow) and the single distal carpal (stippled area is cartilaginous). dc, distal carpal; g, glenoid fossa; h, humerus; hh, head of humerus; hyp, hypapophyses; ra, radius; rl, radiale; sc, scapula; ue, ulnare; ul, ulna; I–V, digits of hand. f was modified from ref. 16. Scale bars, 4 cm (a) and 1 cm (b–d).
