Cambrian

Wanneria walcottana (Wanner, 1901), IUPC C-158, cast of holotype in Wanner (1901, pl. xxxi, fig. 1, United States National Museum [USNM] 56807), Emigsville Member, Kinzers Formation (Cambrian Series 2, Stage 4), Pennsylvania (fig. 1).

Specimen is a cast of the original. It is complete, flattened, 115.21 mm long (sag.) and 77.42 mm (tr.) across the posterior cephalon margin. The specimen shows a malformation on the left side. The distal sections of the second and third pleural spines are fused into one spine, 16.82 mm from the axial lobe. This fused section extends laterally to the genal spine and is 14.61 mm long (tr.).

Asaphiscus wheeleri Meek, 1873, IUPC 101527, Wheeler Formation (Drumian, Miaolingian), House Range, western Utah (fig. 2).

The specimen is complete, 45.51 mm long (sag.) and 30.34 mm (tr.) across the posterior cephalon margin. The sixth to eighth right thoracic pleurae and associated spines are malformed, showing a V-shaped indentation that extends 4.5 mm toward the axial lobe. The sixth pleural segment has a section that is 3.47 mm longer (exsag.) than the rest of the segment. Lateral to this is a 1.3 mm (exsag.) long V-shaped indentation. The seventh segment is reduced by 4.5 mm (exsag.) and terminates at the overlengthened section of the sixth segment (tr.). The eighth segment has a bifurcation 4.08 mm (tr.) from the axial lobe, resulting in an additional, 2.49 mm long (tr.) spine that is deflected anteriorly.

FIGURE 3.

Cast of malformed Dorypyge bispinosa from the Changhia Formation (Drumian, Miaolingian). IUPC C-145. A. Complete specimen showing reduced fourth right pygidial spine. B. Close up of box in A, showing reduced spine (white arrow). Specimen coated in ammonium chloride. Image converted to grayscale. Scale bars: A, 5 mm; B, 2 mm.

Dorypyge bispinosa Walcott, 1905, IUPC C-145, cast of holotype in Walcott (1905, pl. 8, fig. 3, USNM 57886), Changhia Formation (Drumian, Miaolingian), Shandong, North China (fig. 3).

Specimen is a cast of a partial pygidium, 10.2 mm long (sag.), 17.03 mm wide (tr.) at the anterior margin. The fourth right pygidial spine is 1.19 mm long (exsag.) compared with the fourth pygidial spine on the left side that is 10.15 mm long (i.e. only 11.7% the exsag. length). This reduced spine also appears to be partially fused with the fifth right pygidial spine at its base.

Ordovician

Isotelus iowensis (Owen, 1852), IUPC 18400-5. Elgin Member, Maquoketa Formation (Upper Ordovician, Katian), Missouri (fig. 4).

Specimen is an isolated cephalon, 30.38 mm long (sag.) and 55.26 mm wide (tr.) across the posterior margin. Specimen has an asymmetrical W-shaped indentation on the right side. The indentation extends 4.10 mm from the lateral border. The anteriormost section of indentation shows rounding. The lateral border width (tr.) is consistent along the malformation margin.

FIGURE 4.

Malformed Isotelus iowensis from the Elgin Member, Maquoketa Formation (Upper Ordovician, Katian). IUPC 18400-5. A. Complete specimen. B. Close up of box in A, showing W-shaped indentation in cephalon (white arrow). Specimen coated in ammonium chloride. Images converted to grayscale. Scale bars: A, 10 mm; B, 2 mm.

On the Malformations

Malformations are split into three main sections: injuries, teratologies, and neoplasms (Owen, 1985; Babcock, 1993, 2003, 2007; see above, Terminology). Here, we see no evidence for round or ovate structures, excluding the possibility of neoplasms in the examined material (Babcock, 1993, 2003, 2007; De Baets et al., 2022). We document examples of injuries in the form of reduced and malformed spines and indentations, and possible evidence for teratological structures. The nature of these examples is discussed below.

Wanneria walcottana has a single malformation on the left side of the thorax—distal fusion of the second and third pleural spines (fig. 1). There is no clear indication of an indentation or possible callusing proximal to the malformation. This seems to reflect abnormal recovery and fusion of the spines, as the original injury is no longer observable (see Šnajdr, 1981, Owen, 1985 and Bicknell et al., 2022a, for other examples).

Dorypyge bispinosa is diagnosed by the presence of the considerably longer (sag.) and proximally much wider (tr.) fourth and fifth pygidial spines (Palmer, 1968; Zhang and Jell, 1987). The holotype of the taxon (fig. 3A); however, has a reduced fourth right pygidial spine that is merged at the base with the fifth. Two possible explanations for the malformation are presented:

At present, both options are possible. The means of determining which is more likely necessitates more material from the type locality. This research direction is pertinent as the taxon has been considered only briefly beyond the original work (Walcott, 1905; Zhang and Jell, 1987; Wasserman, 1999; Peng et al., 2006), reflecting the limited collected material.

V-shaped indentations are commonly considered evidence of failed predation (Rudkin, 1979; Conway Morris and Jenkins, 1985; Rudkin, 1985; Nedin, 1999; Bicknell and Paterson, 2018; Bicknell et al., 2022b). The indentation in IUPC 101527 (fig. 2B) suggests an example of failed predation, aligning with other examples of malformed Asaphiscus wheeleri (Vorwald, 1982; 1984; Owen, 1985; Babcock, 1993; Eaton, 2019; Bicknell et al., 2022b), and bolstering the record of thoracic injuries on A. wheeleri (see Bicknell et al., 2022b). We can therefore consider possible predator groups within the Wheeler Formation. Artiopodans with gnathobasic spines on the protopodal regions of the walking legs (Whittington, 1975, 1980; Bruton, 1981; Stein, 2013; Zacaϊ et al., 2016; Bicknell and Pates, 2020), priapulid worms (Conway Morris and Robison, 1986), and radiodonts (Vorwald, 1984; Babcock, 1993; Bicknell and Holland, 2020) have commonly been highlighted as possible predators. As Cambrian priapulid worms were smaller than documented examples of injured A. wheeleri specimens (Conway Morris, 1979; Vorwald, 1984), we can exclude this group. Biomechanical, fluid dynamic, and kinematic analyses of Anomalocaris canadensis Whiteaves, 1892, have demonstrated that select radiodont frontal appendages were ineffective at handling biomineralized prey (De Vivo et al., 2021; Bicknell et al., 2023b). However, other radiodonts within the deposit may have been capable of processing trilobite exoskeleton (see Pates and Daley, 2017; Pates et al., 2018, 2021; De Vivo et al., 2021). Functional morphological (Bruton, 1981; Stein, 2013; Zacaï et al., 2016; Bicknell et al., 2018a, 2021; Holmes et al., 2020) and biomechanical models (Bicknell et al., 2018a, 2021) of artiopodans with gnathobases on their walking legs have demonstrated that a selection of these morphologies could have processed re-enforced prey. We propose that arthropods with gnathobasic spines on walking legs, or radiodonts, such as Caryosyntrips Daley and Budd, 2010, were the likely predators of A. wheeleri (Briggs et al., 2008; Pates and Daley, 2017; Pates et al., 2018, 2021).

The Asaphiscus wheeleri specimen also presents unique data regarding injury recovery. Reduction in the seventh pleural spine width (tr.) is accommodated by the overdevelopment of the sixth and the eighth pleural spines (fig. 2B). These segments may have had additional resources allotted to them to fill in the space. This demonstrates compensatory exoskeletal hypertrophy in trilobites (Babcock, 1993, 2003, 2007).

Malformed Isotelus iowensis have not previously been documented. Furthermore, records of malformed Isotelus DeKay, 1824, are rare within the literature (see note in Berg, 1992). Despite this, there is abundant evidence of malformed asaphid trilobites. Abnormalities on asaphids have been attributed to molting complications (Ludvigsen, 1979; Wandås, 1984; Bicknell and Smith, 2023), teratological development (Tjernvik, 1956), parasitic infestation (Ross, 1957; Owen, 1985), and failed predation (Tjernvik, 1956; Šnajdr, 1979a; Rudkin, 1985; Bicknell et al., 2023c; Bicknell and Kimmig, 2023; Zong et al., 2023). Within these, cephalic malformations have been considered evidence of injuries (Schmidt, 1906; Owen, 1985; Zong et al., 2023) and possible pathologies (Ross Jr, 1957; Owen, 1985). There are no other records of W-shaped injuries in asaphids. This injury shape is comparable to cephalic indentations attributed to failed predation on Cambrian trilobites (Hall, 1859; Babcock, 1993, 2003; Bicknell et al., 2018b). As such, we attribute this injury to possible failed predation. However, the injury size is minute compared to the cephalon. The specimen was likely attacked during a soft-shelled stage and was only slightly damaged. This aligns with the proposals that Isotelus species could have been targeted by Ordovician eurypterids using capture-basket-like raptorial appendages (Caster and Kjellesvig-Waering, 1964; Schmidt et al., 2022a, 2022b).

On Dark Collections

The examination of dark collections and dark specimens has become a core research theme for museums over the past decade (Smith and Blagoderov, 2012; Marshall et al., 2018). This examination has highlighted the historical nature of often underexplored material. Even more so, these collections house material from rare or completely inaccessible fossil sites, representing the only means of understanding understudied regions (Monfils et al., 2020). The Indiana University Paleontological Collection is one such example. During the early stages of the collection, the material was on display in a grand gallery. However, a series of catastrophes and unfortunate administrative decisions, including a fire, a “great housecleaning,” and decades of neglect led to a marked decline (Lane, 2000; Sturgeon et al., 2019). Despite this, over the past 15 years, the paleontology faculty at Indiana University have renewed the curation, making the collection available to researchers once more.

One subsection contained within the IUPC is the Deiss material. Charles Deiss was the former chair of the department, state geologist, and director of the Indiana Geological and Water Survey (Lane, 2000). His collection of trilobites includes casts of types created from the holdings of museums around the world, and specimens from the northern Rocky Mountains. Deiss used the latter to build a biostratigraphic record for the Cambrian of North America (Deiss, 1936, 1938, 1939, 1940; Howell et al., 1944; Lochman et al., 1944). While the scope of his research was largely biostratigraphic, there are many lines of inquiry (such as injuries discussed herein) that can be assessed with this material. As the Deiss collection contains over 700 lower Paleozoic fossils, this material will continue to present more insight into animals from this time period.