What are the closest relatives to dinosaurs
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Closest Relatives to Dinosaurs: Insights from Recent Research
Silesaurids: The Non-Dinosaurian Dinosauriforms
Silesaurids as Dinosaur Precursors
Silesaurids, a group of non-dinosaurian dinosauriforms, are considered the closest relatives to crown-group dinosaurs. These creatures provide critical insights into the early stages of dinosaur evolution. The osteohistology of the Late Triassic silesaurid Sacisaurus agudoensis from Brazil reveals rapid growth patterns similar to early dinosauromorphs, although they lack the complex vascular arrangements seen in saurischian dinosaurs. This suggests that while silesaurids grew quickly, their growth rates were slower compared to most dinosaurs.
Anatomical Features of Silesaurids
The detailed anatomy of Asilisaurus kongwe, another silesaurid from the Middle Triassic of Africa, shows a mix of primitive and derived traits. This species had a unique skull and a crocodylian-like ankle, indicating high homoplasy and parallel evolutionary trends within Silesauridae and early dinosaurs. These anatomical studies underscore the importance of silesaurids in understanding the morphological transitions leading to true dinosaurs.
Lagerpetids: Bridging the Gap to Pterosaurs
Lagerpetids and Pterosaur Evolution
Lagerpetids, a group of cursorial, non-volant dinosaur precursors, have been identified as the sister group to pterosaurs. This relationship is supported by numerous shared anatomical features across the skeleton, which significantly narrows the morphological gap between the oldest pterosaurs and their closest relatives. This finding also strengthens the evidence that pterosaurs belong to the avian line of archosaurs, sharing neuroanatomical features related to enhanced sensory abilities with lagerpetids.
Dromaeosaurids: Close Relatives of Birds
Feathered Dinosaurs and Bird Evolution
Dromaeosaurids, a group of theropod dinosaurs, are among the closest relatives of birds. The discovery of Zhenyuanlong suni, a large-bodied, short-armed dromaeosaurid from the Early Cretaceous of China, provides crucial evidence of feather morphologies and distribution in these dinosaurs. This species had large wings with pennaceous feathers on the arms and tail, similar to smaller dromaeosaurids, highlighting the evolutionary link between these theropods and modern birds.
Phylogenetic Studies and Dinosaur Origins
Early Dinosaur Phylogeny
Phylogenetic studies of early dinosaurs have identified several basal forms, such as Herrerasaurus, Eoraptor, and Pisanosaurus, which help clarify the relationships among the major dinosaur clades. Silesaurus opolensis, a silesaurid, is often placed as the sister taxon to a dichotomy that includes monophyletic Saurischia and Ornithischia, further emphasizing the close relationship between silesaurids and true dinosaurs.
Biogeographical Origins
Recent analyses support the hypothesis that dinosaurs originated in southern Gondwana. This conclusion is robust despite increased taxonomic and geographic sampling and divergent phylogenetic results. The southern Gondwanan origin is consistent with the diversity of early dinosaurs and non-dinosaurian dinosauromorphs found in this region.
Conclusion
The closest relatives to dinosaurs include silesaurids and lagerpetids, which provide essential insights into the early evolutionary stages of dinosaurs and pterosaurs. Dromaeosaurids, closely related to birds, further illustrate the evolutionary continuum from non-avian theropods to modern avians. Phylogenetic and biogeographical studies continue to refine our understanding of dinosaur origins, highlighting the complexity and diversity of early dinosauriforms.
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