| Librostoma Temporal range:
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|---|---|
| |
| Asaphus lepidurus | |
Scientific classification 
| |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Arthropoda |
| Class: | †Trilobita |
| Subclass: | †Librostoma Fortey, 1990[1] |
| Orders | |
| |
Librostoma is a subclass of trilobites defined by having a natant hypostome, which is a hypostome (mineralized trilobite mouthpart) that is free from the anterior doublure and aligned with the anterior of the glabella,[4] this is unlike a conterminant hypostome, which is attached to the exoskeleton.[5]
They are a large and long lasting group, with some of the candidates for the first trilobites being librostomes in the order ptychopariida; and all post-Devonian[b] trilobites being in the order proetida, whom are librostomes.
The monophyly of the group has been questioned, with Whittington (2003) placing some genera (Hemibarrandia, Lakaspis, Peraspis and Symphysurina) of the asaphid family Nileidae in the order Corynexochida.[6]
- ^ Ontogeny, hypostome attachment and trilobite classification. RA Fortey, Palaeontology, 1990
- ^ Cite error: The named reference
Gonwas invoked but never defined (see the help page). - ^ Bignon, Arnaud; Waisfield, Beatriz G.; Vaccari, Emilio; Chatterton, Brian D. E. (2020). "Reassessment of the Order Trinucleida (Trilobita)". Journal of Systematic Palaeontology. 18 (13): 1061–1077. Bibcode:2020JSPal..18.1061B. doi:10.1080/14772019.2020.1720324. S2CID 212995185.
- ^ "The Hypostome".
- ^ Whittington, H. B. "Reflections on the Classification of the Trilobita". University of Cambridge.
- ^ Whittington, Harry B. (2003). "The trilobite family Nileidae: morphology and classification". Palaeontology. 46 (4): 635–646. Bibcode:2003Palgy..46..635W. doi:10.1111/1475-4983.00313.
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