Phacopoidea Hawle and Corda, 1847

Sandford, Andrew C. & Holloway, David J., 2006, Early Silurian phacopide trilobites from central Victoria, Australia, Memoirs of Museum Victoria 63 (2), pp. 215-255 : 219

Superfamily Phacopoidea Hawle and Corda, 1847 Family Phacopidae Hawle and Corda, 1847

Remarks. In his seminal review of the Phacopidae in which he established the genera Acernaspis and Ananaspis, Campbell (1967) proposed a classification of the family that he considered to be ʻhorizontalʼ in the sense of Simpson (1961). His approach was criticised by some workers (e.g. Eldredge, 1973: 292) as creating paraphyletic and polyphyletic taxa, an outcome that was acknowledged by Campbell (1977: 26). Nevertheless, Acernaspis and Ananaspis have been universally recognised, and the former has come to be accepted as monophyletic ( Ramsköld and Werdelin, 1991: 61).

Ananaspis continues to present more problems than Acernaspis because it embraces greater variability in characters such as the width of the cheeks in relation to that of the glabella, the relative lengths (exsag.) of L2 and L3, the size of the eye and the position of its lower margin in respect to the lateral border furrow, the depth of the vincular furrow medially and the strength of its notching laterally, the glabellar sculpture (but in relation to this character see remarks on Acernaspis below), and the width and degree of taper of the pygidial axis. These characters, many of which were regarded by Campbell (1967) and later workers as diagnostic of Ananaspis , are expressed to differing degrees and in a variety of combinations in the species assigned. Ramsköld and Werdelin (1991) restricted Ananaspis to a small number of species of Ludlow and Lochkovian ages [ A. orientalis ( Maksimova, 1968) , to which Ramsköld and Werdelin ascribed a possible Ludlow age, is from the Kokbaital Horizon of Central Kazakhastan, now known to be early Lochkovian; Talent et al., 2001: 61]. Several other species previously assigned to Ananaspis , and of late Llandovery–late Wenlock age, were referred to by Ramsköld and Werdelin as ʻ Ananaspis ʼ or incertae sedis, and said to represent ʻ…a number of monospecific (or nearly so) genera … between Acernaspis and Ananaspis ʼ ( Ramsköld and Werdelin, 1991: 56). We are not in complete agreement between ourselves on the relationships of these species which include ʻ Phacops ʼ typhlagogus Öpik, 1953 , redescribed below. However, it is difficult to identify any consistently developed characters that could be used to distinguish such species from others assigned to Ananaspis s.s. by Ramsköld and Werdelin, or to be sure that the latter species are more closely related to eachotherthantosomeofthespeciesexcludedfrom Ananaspis by those authors. Consequently Ananaspis is more broadly conceived herein than by Ramsköld and Werdelin.