Department of Biology, George Washington University, Washington D.C., United States of America.
PeerJ. 2024 Apr 30;12:e17277. doi: 10.7717/peerj.17277. eCollection 2024.
Squamata (lizards, snakes, and amphisbaenians) is a Triassic lineage with an extensive and complex biogeographic history, yet no large-scale study has reconstructed the ancestral range of early squamate lineages. The fossil record indicates a broadly Pangaean distribution by the end- Cretaceous, though many lineages (e.g., Paramacellodidae, Mosasauria, Polyglyphanodontia) subsequently went extinct. Thus, the origin and occupancy of extant radiations is unclear and may have been localized within Pangaea to specific plates, with potential regionalization to distinct Laurasian and Gondwanan landmasses during the Mesozoic in some groups.
We used recent tectonic models to code extant and fossil squamate distributions occurring on nine discrete plates for 9,755 species, with Jurassic and Cretaceous fossil constraints from three extinct lineages. We modeled ancestral ranges for crown Squamata from an extant-only molecular phylogeny using a suite of biogeographic models accommodating different evolutionary processes and fossil-based node constraints from known Jurassic and Cretaceous localities. We hypothesized that the best-fit models would not support a full Pangaean distribution (i.e., including all areas) for the origin of crown Squamata, but would instead show regionalization to specific areas within the fragmenting supercontinent, likely in the Northern Hemisphere where most early squamate fossils have been found.
Incorporating fossil data reconstructs a localized origin within Pangaea, with early regionalization of extant lineages to Eurasia and Laurasia, while Gondwanan regionalization did not occur until the middle Cretaceous for Alethinophidia, Scolecophidia, and some crown Gekkotan lineages. While the Mesozoic history of extant squamate biogeography can be summarized as a Eurasian origin with dispersal out of Laurasia into Gondwana, their Cenozoic history is complex with multiple events (including secondary and tertiary recolonizations) in several directions. As noted by previous authors, squamates have likely utilized over-land range expansion, land-bridge colonization, and trans-oceanic dispersal. Tropical Gondwana and Eurasia hold more ancient lineages than the Holarctic (Rhineuridae being a major exception), and some asymmetries in colonization (e.g., to North America from Eurasia during the Cenozoic through Beringia) deserve additional study. Future studies that incorporate fossil branches, rather than as node constraints, into the reconstruction can be used to explore this history further.
有鳞目（蜥蜴、蛇和蚓蜥）是一个起源于三叠纪的谱系，具有广泛而复杂的生物地理历史，但没有大规模的研究重建早期有鳞目谱系的祖先范围。化石记录表明，到白垩纪末期，有鳞目动物的分布范围广泛，但许多谱系（例如，Paramacellodidae、Mosasauria、Polyglyphanodontia）随后灭绝。因此，现存辐射的起源和占据情况尚不清楚，可能局限于泛大陆的特定板块，在某些群体中，中生代期间可能存在区域性分化，分别形成古北大陆和冈瓦纳大陆的陆地。
我们使用最近的构造模型，对 9 个离散板块上现存和化石有鳞目动物的分布进行编码，其中包括 3 个灭绝谱系的侏罗纪和白垩纪化石限制。我们使用一套生物地理模型，根据已知的侏罗纪和白垩纪地点的进化过程和化石节点约束，从一个仅基于现生物种的分子系统发育中对有鳞目动物的冠群祖先范围进行建模。我们假设，最佳拟合模型不会支持有鳞目动物冠群起源的泛大陆（即包括所有区域）分布，而是会显示出在正在分裂的超大陆内特定区域的区域化，可能在北半球，那里发现了大多数早期有鳞目化石。
纳入化石数据重建了泛大陆内的局部起源，现存谱系早期在欧亚大陆和劳亚古陆的区域化，而冈瓦纳大陆的区域化直到白垩纪中期才发生在 Alethinophidia、Scolecophidia 和一些冠群壁虎类谱系中。尽管现存有鳞目动物生物地理学的中生代历史可以概括为欧亚大陆起源，然后从劳亚古陆扩散到冈瓦纳大陆，但它们的新生代历史非常复杂，有多个方向的多次事件（包括二次和三次再殖民化）。正如之前的作者所指出的，有鳞目动物可能利用了陆上范围扩张、陆桥殖民化和跨洋扩散。冈瓦纳热带地区和欧亚大陆比全北极地区（Rhineuridae 是一个主要例外）拥有更古老的谱系，一些殖民化的不对称现象（例如，新生代通过白令海峡从欧亚大陆到北美洲的扩散）值得进一步研究。未来的研究可以将化石分支纳入重建，而不是作为节点约束，以进一步探索这段历史。
