Trimerus

{{Short description|Extinct genus of trilobites}} {{for|the Italian islands|Tremiti Islands}} {{Automatic taxobox | fossil_range = {{fossil range|Llandovery|Lochkovian}} | image = Trimerus (35404778902).jpg | image_caption = Fossil of ''Trimerus (Trimerus) delphinocephalus'' from the Rochester Shale of North America, housed at the Oxford University Natural History Museum. | image2 = TrimerusDelphinocephalus.jpg | image2_caption = Reconstruction of ''Trimerus (Trimerus) delphinocephalus'' from the Rochester Shale of North America. | taxon = Trimerus | authority = Green, 1832 | type_species = ''Trimerus delphinocephalus'' | type_species_authority = Green, 1832 | subdivision_ranks = Other species | subdivision = See text }}

thumb|right|300px|An isolated fossil cephalon from the trilobite ''Trimerus (Trimerus) delphinocephalus'', missing some of the anterior portion. Collected from the Rochester Shale in Canada. Pores for setae are visible marginally.

'''''Trimerus''''' is an extinct genus of trilobite in the family Homalonotidae. ''Trimerus'' is one of North America's largest trilobites, reaching over {{convert|20|cm|in|abbr=on}} in length. It had a thorax composed of 13 segments with weak trilobation, a large subtriangular head terminating in an expanded rostral plate, a two-pronged hypostome, and a triangular pygidium. It is known from all continents except for Antarctica. Its tiny compound eyes and the shovel-like anterior of the head suggests a burrowing lifestyle, and an exoskeleton marked with many small pores which, in life, probably housed hair-like sensory setae in life, allowed the trilobite to feel which portions of its body were covered with sediment.<ref>{{cite journal |last1=Eldredge |first1=Niles |title=Observations on burrowing behavior in Limulus polyphemus (Chelicerata, Merostomata), with implications on the functional anatomy of trilobites |journal=American Museum Novitates |date=1970 |issue=2436 |url=https://digitallibrary.amnh.org/items/3f9b5aec-577c-44ef-a125-1c2c01c88930}}</ref>

==Species==

In his description of new Homalonotid species from Australia and New Zealand, Andrew Sandford divided ''Trimerus'' species into multiple subgenera to better categorize distinct populations.<ref name="Sandford">{{cite journal |last1=Sandford |first1=Andrew C. |title=Homalonotid trilobites from the Silurian and Lower Devonian of south-eastern Australia and New Zealand (Arthropoda: Trilobita: Homalonotidae) |journal=Memoirs of Museum Victoria |date=2005 |volume=62 |issue=1 |pages=1–66 |doi=10.24199/j.mmv.2005.62.1}}</ref> A number of species previously assigned to other genera were included, and a number of species previously assigned to ''Trimerus'' were excluded, variously reassigned to the trilobite genera ''Dipleura'' (''Dipleura dekayi'' has been frequently included within ''Trimerus''), ''Digonus'', ''Burmeisteria'', and ''Wenndorfia''. The following list is therefore provisional, and other sources may differ.<ref>{{cite journal |last1=Busch |first1=Richard M. |last2=Swartz |first2=Frank M. |title=Molting and Description of a New Homalonotid Trilobite from Pennsylvania |journal=Journal of Paleontology |date=1985 |volume=59 |issue=5 |pages=1062–1074 |url=https://www.jstor.org/stable/1305003 |issn=0022-3360}}</ref><ref>{{cite journal |last1=Tomczykowa |first1=Ewa |title=The trilobite subfamily Homalonotinae from the Upper Silurian and Lower Devonian of Poland |journal=Acta Palaeontologica Polonica |date=1975 |volume=20 |issue=1 |pages=3-46 |url=https://www.app.pan.pl/article/item/app20-003.html}}</ref> A handful of species also remain undescribed.

'''''Trimerus (Trimerus)''''' This group is known only from the Silurian (Wenlock to Ludlow). * Type species ''Trimerus (Trimerus) delphinocephalus'' Green, 1832 (USA, Canada, UK) ** {{extinct}}''T. (Trimerus) johannis'' Salter, 1865 (UK) ** {{extinct}}''T. (Trimerus) cylindricus'' Salter, 1865 (UK) ** {{extinct}}''T. (Trimerus) harrisoni'' McCoy, 1876 ** {{extinct}}''T. (Trimerus) vomer'' Chapman, 1912 ** {{extinct}}''T. (Trimerus) flexuosus'' Benedetto and Martel (in Baldis et al., 1976) (Argentina)

'''''Trimerus (Edgillia)''''' This group is known from the Late Silurian to the Early Devonian. Named after E. D. Gill, for his contributions to Australian paleontology, including naming a number of Homalonotid trilobites. * Type species {{extinct}}''T. (Edgillia) kinglakensis'' Gill, 1949 (Australia) ** {{extinct}}''T. (Edgillia) vanuxemi'' Hall, 1859 (USA) ** {{extinct}}''T. (Edgillia?) major'' Whitfield, 1885 (USA) ** {{extinct}}''T. (Edgillia) mongolicus'' Tchernycheva, 1937 (Mongolia) ** {{extinct}}''T. (Edgillia) grandis'' Benedetto and Martel (in Baldis et al., 1976) (Argentina) ** {{extinct}}''T. (Edgillia) jelli'' Sandford, 2005 (Australia)

'''''Trimerus (Ramiotis)''''' This group is known only from the Silurian. Named for Otis Rami, the son of the author.<ref name="Sandford" /> * Type species {{extinct}}''T. (Ramiotis) rickardsi'' Sandford, 2005 (Australia) ** {{extinct}}''T. (Ramiotis) permutus'' Tomczykowa, 1978 (nom. nov. for ''T. lobatus'' Tomczykowa, 1975) (Poland) ** {{extinct}}''T. (Ramiotis) dyaulax'' Thomas, 1977 (Saudi Arabia) ** {{extinct}}''T. (Ramiotis) salteri'' Morris, 1988 (nom. nov. for ''Homalonotus (Koenigia) ludensis'' Salter, 1865) (UK) ** {{extinct}}''T. (Ramiotis) iani'' Sandford, 2005 (Australia) ** {{extinct}}''T. (Ramiotis) otisi'' Sandford, 2005 (Australia) ** {{extinct}}''T. (Ramiotis) thomasi'' Sandford, 2005 (Australia) ** {{extinct}}''T. (Ramiotis) tomczykowae'' Sandford, 2005 (Australia)

The following species have not been assigned to a subgenus.

*{{extinct}}''T.? acuminatus'' Tromelin and Lebesconte, 1856 *{{extinct}}''T.? lehiri'' Barrois, 1886 *{{extinct}}''T. perceensis'' Clarke, 1913 *{{extinct}}''T. swartzi'' Ohern and Maynard, 1913 * {{extinct}}''T. stelmophorus'' Busch and Swartz, 1985

==References== {{reflist}}

Category:Homalonotidae Category:Articles created by Qbugbot