Recent paleontological research has elucidated the evolutionary mechanisms driving cranial robustness and forelimb reduction in theropod dinosaurs, alongside the identification of a bipedal crocodile relative from the Triassic Period.

近期的古生物研究闡明了驅動獸腳類恐龍頭骨強壯化與前肢縮減的演化機制，同時鑑定出一個三疊紀時期的雙足行走鱷魚親戚。

The correlation between cranial development and limb atrophy in carnivorous dinosaurs has been quantified through a study published in the Proceedings of the Royal Society B. Researchers, led by Charlie Scherer of University College London, posit that the escalation of body mass among herbivorous prey necessitated a transition toward cranial-centric hunting strategies. This selective pressure favored the development of robust skulls—characterized by increased bite force and specific bone-fusion patterns—which rendered forelimbs functionally redundant. This evolutionary trajectory occurred independently across five theropod lineages, including the tyrannosaurs, carcharodontosaurs, megalosaurs, ceratosaurs, and abelisaurs. While apex predators like Tyrannosaurus rex exhibited extreme cranial robustness and minimal forelimb utility, other lineages, such as Spinosaurus and Megaraptor, maintained substantial arm mobility, suggesting divergent predatory methodologies.

肉食性恐龍頭骨發育與肢體萎縮之間的關聯，已透過發表在《英國皇家學會會報B》的一項研究量化。由倫敦大學學院的 Charlie Scherer 領導的研究人員認為，草食性獵物體積的增加，使得狩獵策略必須轉向以頭骨為中心。這種選擇壓力促使了強壯頭骨的發展——其特徵為咬合力增加與特定的骨融合模式——進而使得前肢在功能上變得多餘。這種演化軌跡在五個獸腳類譜系中獨立發生，包括暴龍類、叉齒龍類、巨龍類、角龍類與阿貝力龍類。雖然像暴龍這樣的頂級掠食者表現出極端的頭骨強壯化與極低的前肢實用性，但其他譜系如棘龍與巨爪龍仍保持相當的手臂靈活性，顯示出分歧的掠食方法。

Regarding the persistence of vestigial limbs in T. rex, co-author Paul Upchurch suggests a genetic constraint. He hypothesizes that the genes responsible for forelimb development may be pleiotropic, performing essential functions in other anatomical regions, thereby preventing the total elimination of the limbs despite their lack of primary utility.

關於暴龍保留退化肢體的原因，共同作者 Paul Upchurch 認為存在基因限制。他假設負責前肢發育的基因可能是多效性的，在其他解剖區域執行重要功能，因此儘管前肢缺乏主要用途，仍無法被完全消除。

Parallel to these findings, the discovery of Labrujasuchus expectatus at Ghost Ranch, New Mexico, demonstrates convergent evolution within the archosaur lineage. Despite its phylogenetic classification as a relative of the crocodile, L. expectatus exhibited a bipedal stance, a toothless beak, and reduced forelimbs. Dr. Alan Turner characterizes this as a successful adoption of a body plan typically associated with theropod dinosaurs, filling a critical stratigraphic gap in the Shuvosauridae family and illustrating the experimental nature of Triassic morphology.

與這些發現平行的是，在新墨西哥州 Ghost Ranch 發現的 Labrujasuchus expectatus，展示了主龍類譜系內的趨同演化。儘管其系統分類被視為鱷魚的親戚，但 L. expectatus 表現出雙足站立、無齒喙與縮減的前肢。Alan Turner 博士將其描述為成功採用了通常與獸腳類恐龍相關的身體構造，填補了 Shuvosauridae 科中一個關鍵的地層缺口，並說明了三疊紀形態的實驗性質。

Current evidence indicates that prehistoric anatomical configurations were heavily influenced by prey dynamics and genetic complexities, resulting in diverse manifestations of bipedalism and cranial specialization.

目前證據顯示，史前解剖構造深受獵物動態與基因複雜性影響，導致雙足行走與頭骨特化出現了多樣的表現形式。