What's the closest relative to dinosaurs
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Closest Relatives to Dinosaurs: Insights from Recent Research
Silesaurids: The Non-Dinosaurian Dinosauriforms
Silesaurids are widely recognized as the closest relatives to crown-group dinosaurs. These non-dinosaurian dinosauriforms provide critical insights into the early evolutionary stages of dinosaurs. The osteohistology of Sacisaurus agudoensis, a Late Triassic silesaurid from Brazil, reveals rapid growth patterns similar to early dinosaurs, although they lack the complex vascular arrangements seen in saurischian dinosaurs. This simpler vascular pattern is consistent across all studied silesaurids, indicating relatively slower growth rates compared to most Dinosauria.
Asilisaurus kongwe: A Detailed Anatomical Study
Asilisaurus kongwe, another significant dinosauriform from the Middle Triassic of Tanzania, offers a comprehensive look at the anatomy of early dinosaur relatives. The detailed skeletal elements of Asilisaurus suggest it is more closely related to Silesaurus opolensis than to true dinosaurs, highlighting high homoplasy and parallel trends within Silesauridae and early dinosaur lineages. This species exhibits a mix of primitive and derived traits, such as a crocodylian-like ankle and a short foot, which are crucial for understanding the evolutionary trajectory leading to dinosaurs.
Phylogenetic Position of Early Dinosaur Relatives
Phylogenetic studies have consistently placed silesaurids, including Silesaurus opolensis, as the sister group to a dichotomy that includes monophyletic Saurischia and Ornithischia. This positioning underscores the close evolutionary relationship between silesaurids and the earliest dinosaurs, providing a clearer picture of the dinosaur family tree.
Nyasasaurus parringtoni: The Earliest Dinosauriform?
Nyasasaurus parringtoni, from the Middle Triassic of Tanzania, is either the earliest known member of Dinosauria or its sister taxon. This species exhibits a unique combination of dinosaur characteristics and an elevated growth rate similar to early dinosaurs, suggesting that the initial dinosaur radiation occurred over a longer timescale than previously thought. The African origin of Nyasasaurus supports the hypothesis of a southern Pangaean origin for Dinosauria.
Rapid Evolutionary Origins
Recent geochronologic studies have demonstrated that the temporal gap between assemblages containing only dinosaur precursors and those with the first dinosaurs was significantly shorter than previously estimated. This suggests that the origin of dinosaurs was a relatively rapid evolutionary event, occurring within a 5-10 million year interval. The initial appearance of dinosaurs did not coincide with a fundamental shift in ecosystem composition, indicating a gradual rise to dominance.
Conclusion
The closest relatives to dinosaurs are the silesaurids, a group of non-dinosaurian dinosauriforms that share several anatomical and growth characteristics with early dinosaurs. Detailed studies of species like Sacisaurus agudoensis and Asilisaurus kongwe, along with phylogenetic analyses, have solidified the position of silesaurids as the sister group to true dinosaurs. Additionally, the discovery of Nyasasaurus parringtoni and precise temporal calibrations have provided deeper insights into the rapid and complex evolutionary origins of dinosaurs. These findings collectively enhance our understanding of the early stages of dinosaur evolution and their closest relatives.
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