Odontopleurinae Burmeister, 1843

Adrain, Jonathan M. & Pérez-Peris, Francesc, 2023, Funeralaspis n. gen.: a new odontopleurine trilobite from the early Middle Ordovician (Dapingian) of Death Valley, eastern California, USA, and the classification of Ordovician odontopleurines, Zootaxa 5336 (4), pp. 509-529 : 510-512

Subfamily Odontopleurinae Burmeister, 1843

Discussion. Current understanding of the subfamily dates to the revision of the family by Ramsköld (1991a, 1991b; Ramsköld and Chatterton, 1991). Ramsköld and Chatterton (1991, p. 334) provided an outline of a new subfamilial scheme with included genera, together with a new diagnosis for Odontopleurinae ( Ramsköld and Chatterton, 1991, p. 357) . This was regarded as necessary to the main goal of that work - disentangling the phylogenetic structure and classification of what was then a polyphyletic genus, Leonaspis . It was emphasized that what was presented was preliminary and that more detailed work on the subfamilies would be presented elsewhere ( Ramsköld and Chatterton, 1991, pp. 334, 357). These subsequent works, however, never came to fruition, and the trio of 1991 papers remain the only published form of Ramsköld’s important ideas on the classification of the group.

The taxonomic history of the family can be understood as three different eras. In the first, beginning in the nineteenth century and culminating in the major review by Prantl and Přibyl (1949), what are now regarded as subfamilies were often accorded family status. Hence, Ceratocephalidae Richter and Richter, 1925, and Selenopeltidae Hawle and Corda, 1847 , have a history of treatment as distinct families. Acidaspididae Salter, 1864 (often misspelled “ Acidaspidae ”), is somewhat different, as it, too, was widely used as a family, but generally for the group now classified as Odontopleurinae . Prantl and Přibyl (1949) clarified that Odontopleuridae was the senior name for the overall taxon, though they chose to recognize it at superfamily level. It is important to note that Ramsköld and Chatterton’s (1991) taxonomic concept of Acidaspidinae was new, despite the fact that priority for its family group name dates to the mid-nineteenth century. Its earlier use at the family level was usually equivalent to the current Odontopleurinae , as reflected by the fact that Prantl and Přibyl (1949, p. 19) considered Acidaspidinae a junior subjective synonym of Odontopleuridae .

A second era of classification began in the 1950s, as Whittington and Evitt (1954, pp. 52–53) criticized the notion that the group should be considered a superfamily with separate families, arguing instead that all of the taxa should be assigned to a single family. Whittington (1956, pp. 194–195) expanded on these arguments. Where Prantl and Přibyl (1949) classified the group as a superfamily with three families ( Odontopleuridae , Ceratocephalidae, and Selenopeltidae ), Whittington (1956) understood it as a family with four subfamilies( Odontopleurinae ,Selenopeltinae, Miraspidinae Richter and Richter, 1917 [which he regarded as a senior synonym of Ceratocephalinae], and his new Apianurinae). This view was codified by Whittington in the 1959 Treatise volume ( Moore, 1959), and formed the basis for most work on the family up until 1991. It was during this period that Bruton (1965, 1966a, 1966 b, 1967, 1968a, 1968b) published his influential series of papers, work that remains foundational to the current understanding of the group.

The period since 1991 constitutes a third era of classification of Odontopleuridae . Ramsköld (1991a) demonstrated that Miraspidinae was a junior synonym of Selenopeltinae. He also considered Koneprusiinae Vaněk and Pek, 1987, a junior synonym, but in a separate paper ( Ramsköld, 1991b) considered it valid. It is now generally accepted (e.g., Chatterton et al. [2006], Adrain et al. [2008]). Ramsköld and Chatterton (1991, p. 334) then outlined the full scope of the new scheme, in which Ceratocephalinae was recognized as a subfamily (following Campbell [1977, p. 119]). This classification forms the basis for current understanding of the family.

Of most relevance to the present work was Ramsköld and Chatterton’s (1991) restriction of the scope of Odontopleurinae , as they transferred a set of genera previously classified as odontopleurines to a newly conceived Subfamily Acidaspidinae . The basis for this was the assertion that they were separate clades and hence had separate phylogenetic histories. Synapomorphies of the restricted Odontopleurinae ( Ramsköld and Chatterton, 1991, p. 357) included the presence of nine thoracic segments (in rare cases reduced to eight), a spinose or tuberculate cranidial anterior border, a narrow hypostome, a slender genal spine base, tall eyes, and a wide, rounded pygidial terminal piece. Acidaspidines universally have 10 thoracic segments, a smooth cranidial anterior border, a relatively wide hypostome, a broad genal spine base, less elevated eyes, and a narrow, pear-shaped pygidial terminal piece.

There are other features that, while not basal synapomorphies, nevertheless are unique to one or other of the groups. Prominent paired occipital spines, for example, are common in Odontopleurinae , but are not present in any species of Acidaspidinae (pairs of small spines developed in species of Dudleyaspis Prantl and Přibyl, 1949 [see Chatterton and Perry (1983, pl. 27)] are features of the posterior border found also on the fixigenal posterior border, and clearly not homologous with the paired spines of odontopleurines). A robust median occipital spine is developed by some taxa of either subfamily, but in very different ways. In odontopleurines, when a median occipital spine is developed (e.g., Edgecombeaspis Adrain and Ramsköld, 1997 ; some species of Kettneraspis Prantl and Přibyl, 1949 ), there is no median node present anterior to the spine base. In fact, the spine is developed from the occipital median node. When a robust spine is developed in species of Acidaspidinae , it is a structure developed behind the median node from the rear of the occipital ring, and hence not homologous with the median spines developed by odontopleurines. The occipital median node is usually plainly visible anterior to the base of the spine (e.g., Chatterton and Perry, 1983, pl. 21, figs 2–4, 9, pl. 23, figs 1, 7, 9, pl. 27, figs 1–3, 4, 7, etc.). In the thorax of many acidaspidines, there is a marked, lobate, posterior inflation of the posterior pleural band at and slightly distal to the thorax, where it often becomes the base of a large pleural spine (e.g., Whittington, 1956, pl. 1, figs 11, 14, 17; Chatterton and Perry, 1983, pl. 18, figs 6, 8, 10). In odontopleurines, the posterior pleural band is never expanded in this region, and runs without change in thickness into the pleural spine.

The affinity of Funeralaspis is not in doubt, even though the disarticulated silicified material cannot yield a thoracic segment count. Cranidia of F. deathvalleyensis have a finely tuberculate anterior border. A pair of small but robust median occipital spines is present. The librigenal field is broad and the eye is elevated. The base of the genal spine is narrow. The hypostome is narrow relative to its length (width approximately 1.25 times length). The thoracic posterior pleural band shows no inflation at the fulcrum. The pygidial terminal piece is broad. All are features of Odontopleurinae , and there is no question that Funeralaspis is now the earliest well known member of the subfamily.