Most current designations of mid-cambrian trilobites

[Paleome]

 I know that what used to be called Alokistocare is now Altiocculus.  Where does Amecephalus fit into this?

[Nanosaurus]

I believe Amecephalus is now the preferred name for both Alokistocare and Altiocculus. But, I will let others chime in as this is not my specialty.

[piranha]

They are all valid genera in the Alokistocaridae family:

 

 

Previously named species assigned to Altiocculus include: Alokistocare harrisi Robison, 1971, and A. harrisi? of the Wheeler Shale or Marjum Formation of Utah; A. sinuatum Rasetti, 1951, and A. cataractense Rasetti, 1951, of the Eldon Formation of British Columbia; and A. americanum (Walcott, 1916; Schwimmer, 1989) from the Appalachians. New species include: A. drumensis and A. concavus from the Swasey Limestone of Utah; and A. cf. A. harrisi from the Eldorado Formation of Nevada. Species of Altiocculus are differentiated primarily on the construction of their frontal area. Alokistocare harrisi is the only species of Altiocculus that is known from complete exoskeletons. The holaspid specimens have consistently 32 thoracic segments, 9 more than Alokistocare species (Robison, 1971). However, this species is not used as the type species because the specimens are compressed in shales and they do not retain their original convexity (Robison, 1971; personal observations).

 

Sundberg, F.A. 1994

Corynexochida and Ptychopariida (Trilobita, Arthropoda) of the Ehmaniella Biozone (Middle Cambrian), Utah and Nevada.

Natural History Museum of Los Angeles County - Contributions in Science, 446:1-137  PDF LINK

 

 

Alokistocare can be differentiated from Altiocculus (which includes species previously assigned to Alokistocare) because the cranidium of Alokistocare has non-elevated palpebral lobes [17], moderate downsloping of the anterior area of the fixigena [26], longer posterior area of the fixigena [27], elongated swelling parallel to the anterior border furrow [29], and circular or no swelling in the preglabellar area [30]. Its pygidium has weak anterior pleural bands [43], anterolateral comers that have a flatter slope [47], and a wider border at the anterolateral comers [48].

 

Alokistocare and Amecephalus (type species A. piochensis) have either been synonymized (Resser, 1935; Palmer, 1954; Robison, 1971; Palmer and Halley, 1979) or recognized as separate genera (Rasetti, 1951; Poulsen, 1958; Fritz, 1968; see below). However, Alokistocare can be differentiated from the older Amecephalus by its more rounded frontal lobe [5], axial furrow outline that is straight concave [10], distinct occipital ring [14], well defined anterior border furrow [23], wider posterior area of the fixigena [28], genal spines are moderate length with a narrow groove [34, 35], border wider at anterolateral comers [48], and anterior pleural bands that project into the pygidial border [49]. Thus, Amecephalus is here reinstated and includes Amecephalus piochensis, A. laticaudum, A. cleora, and A. idahoense. Further analysis is needed to determine which other species belong to Amecephalus.

 

Sundberg, F.A. 1999

Redescription of Alokistocare subcoronatum (Hall and Whitfield, 1877), the Type Species of Alokistocare, and the Status of Alokistocaridae Resser, 1939B (Ptychopariida: Trilobita, Middle Cambrian). Journal of Paleontology, 73(6):1126-1143  PDF LINK

[Paleome]

Thank you so much. Yes, I have seen Alokistocare and Amecephalus synonymized, and there are differences in nomenclature between the books I have. 

 

In case you didn't see it yet, I wanted to thank you also for your insight into the ornate inarticulate brachiopods which possessed honeycomb type structures. 

[piranha]

14 hours ago, Paleome said:

Thank you so much. Yes, I have seen Alokistocare and Amecephalus synonymized, and there are differences in nomenclature between the books I have. 

 

In case you didn't see it yet, I wanted to thank you also for your insight into the ornate inarticulate brachiopods which possessed honeycomb type structures. 

 

 

Thanks -- glad to assist!