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Historical Biology An International Journal of Paleobiology

ISSN: 0891-2963 (Print) 1029-2381 (Online) Journal homepage: http://www.tandfonline.com/loi/ghbi20

Paleobiology of the Late sclerorhynchid , mira (: ), from based on new anatomical data

Phillip C. Sternes & Kenshu Shimada

To cite this article: Phillip C. Sternes & Kenshu Shimada (2018): Paleobiology of the sclerorhynchid sawfish, Ischyrhiza mira (Elasmobranchii: Rajiformes), from North America based on new anatomical data, Historical Biology, DOI: 10.1080/08912963.2018.1452205 To link to this article: https://doi.org/10.1080/08912963.2018.1452205

Published online: 30 Mar 2018.

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Paleobiology of the Late Cretaceous sclerorhynchid sawfish, Ischyrhiza mira (Elasmobranchii: Rajiformes), from North America based on new anatomical data

Phillip C. Sternesa and Kenshu Shimadaa,b,c

aDepartment of Biological Sciences, DePaul University, Chicago, IL, USA; bDepartment of Environmental Science and Studies, DePaul University, Chicago, IL, USA; cSternberg Museum of Natural History, Fort Hays State University, Hays, KS, USA

ABSTRACT ARTICLE HISTORY We describe seven associated skeletal remains of Ischyrhiza mira, a Late Cretaceous sclerorhynchid sawfish, Received 20 December 2017 from the ‒lower of Tennessee and Alabama, U.S.A., to decipher its paleobiology. Accepted 11 March 2018 Ischyrhiza mira had about 16 or 17 functional spines and about the same number of replacement spines on KEYWORDS each side of the rostrum in which tall erect spines occupied the anterior one-half to two-third of the rostrum Anatomy; batoid; ; followed posteriorly by smaller spines. Whereas small hat-shaped dermal denticles were distributed on the ; rostrum, large thorn-like dermal denticles were present on the dorsal side of the body characteristic of sluggish, benthic batoids. We concur with the interpretation that specimens previously identified as rostral spines of Peyeria are actually enlarged thorn-like dermal denticles of a sclerorhynchid. We suggest that the ratio between the rostrum length and total body length of sclerorhynchids was generally about 1:3.27. Our vertebra-based ontogenetic analysis of I. mira gives an age estimate of 12.4 for a 190-cm-long individual, the size at birth of about 0.5 m, and the maximum possible length for the of no more than 3 m. Compared to extant pristid , I. mira probably became sexually mature much earlier with a slightly faster rate of rostrum development.

Introduction Arkansas, Georgia, Mississippi, , and New Mexico as well as from Alberta, (Cappetta and Case 1975a; Lauginiger Sclerorhynchidae (Elasmobranchii: Rajiformes) is an extinct and Hartstein 1983; Case and Schwimmer 1988; Russell 1988; batoid group of ‘sawfishes’sensu lato found in Cretaceous Welton and Farish 1993; Beavan and Russell 1999; Peng et al. rocks nearly worldwide (Kriwet and Kussius 2001). Like the 2001; Becker et al. 2006; Spielmann et al. 2009; Cicimurri et al. extant sawfishes (: Pristidae) and 2014; Bice and Shimada 2016). Most reported remains of I. mira (Pristiophoriformes: Pristiophoridae) (Ebert et al. 2013; Naylor consist of isolated rostral spines and oral teeth. Some associated et al. 2016), sclerorhynchids are characterised by a dorsoventrally skeletal remains of the species, including a partial rostrum from flattened body with an elongate, spinous rostrum considered the of Alabama (Mehling et al. 2012; Maisey to have evolved independently of pristids and pristiophorids 2013), are known, but those associated specimens have received (Kriwet 2004; Wueringer et al. 2009). One of the sclerorhy- little attention, and the paleobiology of I. mira remains largely nchids is the Ischyrhiza Leidy 1856 known from various unknown. Upper Cretaceous deposits nearly worldwide, including Africa (I. In this paper, we examine seven sets of associated skele- nigeriensis Tabaste 1963), western Eurasia (I. germaniae (Albers tal remains of Ischyrhiza mira from lower Campanian‒lower and Weiler 1964); I. viaudi Cappetta 1981; I. serra Nessov 1997), and South America (I. hartenbergeri Cappetta 1975) (note: some Maastrichtian marine deposits in Tennessee and Alabama species have been transferred to other sclerorhynchid genera, (Figure 1), including the aforementioned partial rostrum from such as I. iwakiensis Uyeno and Hasegawa 1986, to the Mooreville Chalk of Alabama (Figure 2). None of them Gervais 1852; and I. texana Cappetta and Case 1975b to Kiestus preserves oral teeth that would confirm whether teeth referred Cappetta and Case 1999). In North America, Cappetta (2012) to as I. mira (e.g. Welton and Farish 1993) do indeed belong to lists four species of Ischyrhiza to be valid: I. avonicola Estes 1964 the species, and these associated specimens are mostly disar- and I. mira Leidy 1856 from the ‒Maastrichtian, I. geor- ticulated and highly partial. Nevertheless, they are significant giensis Case, Schwimmer, Borodin, and Leggett 2001 from the because they offer a wealth of paleobiological information about , and I. monasterica Case and Cappetta 1997 from the the fossil sawfish because, besides the rostrum, they include Maastrichtian. Among them, I. mira is the most common species associated sets of rostral spines, dermal denticles, and verte- in which it has been reported from New Jersey, Delaware, , brae. We first describe the morphology and variation of each

CONTACT Phillip C. Sternes [email protected] © 2018 Informa UK Limited, trading as Taylor & Francis Group

Published online 30 Mar 2018 2 P. C. STERNES AND K. SHIMADA

Figure 1. Stratigraphic and geographic distribution of associated skeletal specimens of Ischyrhiza mira Leidy 1856 examined in this study. (a) generalised Upper Cretaceous stratigraphy of western Tennessee and western Alabama with triangular arrows to the right pointing to stratigraphic positions of respective specimens (stratigraphic information based on Mancini et al. 1996, Figure 2, and Ikejiri et al. 2013, Figure 3). (b) generalised paleogeographic map of North America during middle Late Campanian showing oceanic mass in white, land masses in dark gray, and position of Tennessee and Alabama in light gray (map based on Kauffman1984 , Figure 12). (c) close-up view of Tennessee and Alabama showing locality of each specimen.

anatomical element in I. mira and then make various paleobi- chondrichthyan and seven osteichthyan taxa as well as 14 tet- ological inferences such as its ontogenetic growth pattern and rapod taxa, including two taxa are known from the life history strategies. (Ikejiri et al. 2013). The is characterised by glauconitic fine sand and sandy calcare- Geographical and stratigraphic context ous clay interbedded by thin indurated fossiliferous sandstone beds (Raymond et al. 1988). At least nine chondrichthyan taxa, The specimens ofIschyrhiza mira described in this paper come four osteichthyan taxa, and eight tetrapod taxa including from the Mooreville Chalk (lower Campanian), the Bluffport two are known (Ikejiri et al. 2013). The upper part of Marl Member (mid‒upper Campanian) of the Demopolis the Coon Creek Formation consists of silty to clayey sand with Chalk Formation, and the upper part of the Ripley Formation local siderite concretions (Ebersole 2016). Fossil (lower Maastrichtian) in Alabama as well as from the upper are rare in the formation, but reported taxa include at least 11 part of the Coon Creek Formation (upper Campanian) in chondrichthyan and nearly 20 osteichthyan as well as 11 Tennessee (Figure 1). These rock units are marine depos- reptile taxa, including a and a dinosaur (Whetstone its that formed along the eastern‒southern shoreline of the 1977; Gibson 2008). Besides I. mira, taxa reported from all Late Cretaceous Mississippi Embayment that connected to four stratigraphic units include texanus, the southern end of the to the west ‘’ appendiculata, pristodontus, ichthy- (Figure 1(b)). The Mooreville Chalk consists of fossiliferous odectiforms ( sp. and/or sp.), chalk and chalky marl (Raymond et al. 1988). It is rich in fossil spp. as well as one or more taxa of testudines, (e.g. vertebrates, including at least 23 chondrichthyan species, 26 sp.), marine crocodilians, and dinosaur (e.g. osteichthyan fish species, and 39 tetrapod taxa including five hadrosaur) (Gibson 2008; Ikejiri et al. 2013). Whereas most of dinosaur and two avian taxa (Ikejiri et al. 2013). The Bluffport these fish taxa are marine components (e.g. Everhart 2017), the Marl Member represents the upper part of the Demopolis fact that dinosaurs have been found in all these stratigraphic Chalk and consists of massive chalky marl, clayey chalk, units indicates that the shoreline must have been not so far and calcareous clay (Raymond et al. 1988). At least seven from those locations. HISTORICAL BIOLOGY 3

Figure 2. Rostral specimen of Ischyrhiza mira Leidy 1856, from Upper Cretaceous Mooreville Chalk of Alabama (AMNH FF 20388): anterior to top in (a)–(f); cross-sectional views looking anteriorly in (g); schematic drawing of rostrum in cross-sectional view in (h) and (i). a, rostrum in dorsal view and four associated disarticulated rostral spines (bracket = portion enlarged in Figure 2(c) and (d); top arrow, portion enlarged in Figure 4(a); bottom arrow = position of cross-section illustrated in Figure. 2(g); (b) rostrum in right lateral view (bracket = portion enlarged in Figure 2(e); arrow = portion enlarged in Figures. 2(f) and 4(b)); (c) close-up image of mid-section of rostrum in dorsal view showing four articulated right rostral spines (portion indicated by bracket in Figure 2(a)); (d) close-up image of mid-section of rostrum in right lateral view showing four articulated right rostral spines (portion indicated by bracket in Figure 2(a)); (e) close-up image of anterior portion of rostrum in ventral view showing two articulated left rostral spines (portion indicated by bracket in Figure 2(b)); (f) close-up image of mid-section of rostrum in ventrolateral view showing scattered dermal denticles near articulated right rostral spines (portion indicated by top one-third of bracket in Figure 2(a)); (g) cross-section of rostrum (portion pointed by bottom arrow in Figure 2(a)); (h) interpretive schematic drawing of cross-section of rostrum illustrated in Figure 2(g) showing organization of calcified cartilage (gray portions); (i) reconstructed cross- section of rostrum with rostral spine on one side based on Figure 2(g) and (h). Notes: Abbreviations: b = position of buccopharyngeal nerves; hc = hyaline cartilage; mc = medial canal; r (with number) = rostral spine code (see Appendix 1); so = position of superficial ophthalmic nerves; wc = wood-like cartilage. Bar scale = 2 cm (not to scale in i).

Systematic paleontology (Figures 2 and 3). All the described specimens are housed in the following three institutions: American Museum of Natural Unless otherwise specifically noted, all specimens described History, Fossil Fishes collection (AMNH FF), New York, U.S.A.; in this paper consist of associated remains of Ischyrhiza mira Memphis Pink Palace Museum (MPPM), Tennessee, U.S.A.; and that contain at least one taxonomically diagnostic rostral spine 4 P. C. STERNES AND K. SHIMADA

Figure 3. Associated remains of Ischyrhiza mira Leidy 1856 from Upper Cretaceous of Alabama and Tennessee (d = dermal denticle; r = rostral spine; v = vertebra; unlabeled elements = calcified cartilage fragments; see Appendices 1 and 2 for measurements of each rostral spine and vertebra identified by respective code number). (a) MPPM 2013.8.3; (b) RMM 2943; (c) RMM 6003; (d) RMM 1245; (e) RMM 1924; (f) RMM 2503 (note: smaller calcified cartilage fragments not illustrated in (a), (b), (e), and (f)). Notes: Bar scale = 1 cm. [Planned for page width].

McWane Science Center, Birmingham, Alabama, U.S.A., that Cohort Euselachii Hay 1902 manages collection of Red Mountain Museum (RMM) no longer Superorder Compagno 1973 in operation. Many of the examined specimens contain multiple Order Rajiformes Berg 1940 fragments of calcified cartilage consistent with those observed by Suborder Sclerorhynchoidei Cappetta 1980 Becker et al. (2005); however, most of them are too fragmentary Family Sclerorhynchidae Cappetta 1974 for meaningful descriptions. Anatomical descriptions presented Genus Ischyrhiza Leidy 1856 below focus on preserved skeletal elements that are anatomically Ischyrhiza mira Leidy 1856 informative. Although sclerorhynchids may merit placement into its own order Sclerorhynchiformes (see Kriwet 2004), we follow Materials Cappetta’s (2012) taxonomic scheme for the purpose of this paper. Class Huxley 1880 AMNH FF 20388, rostrum with six articulated and four dis- Subclass Elasmobranchii Bonaparte 1838 articulated rostral spines from upper part of Ripley Formation HISTORICAL BIOLOGY 5

(lower Maastrichtian) in western Lowndes County, Alabama anterior end of the rostrum (Figure 2(e)) and four of which are (Figure 2; same specimen briefly discussed by Mehling et al. left spines present near the middle of the rostrum (Figure 2(c), (2012) and Maisey (2013)); MPPM 2013.8.3, seven rostral spines, (d)). Some spines are slightly displaced, but the two portions eight vertebrae, and at least 42 calcified cartilage pieces from of articulated rostral spines suggests that there was a ‘diastema’ upper part of Coon Creek Formation (upper Campanian) in between two adjacent ‘functional spines’ that measured roughly northwestern Decatur County, Tennessee (Figure 3(a)); RMM 40 mm on average where a ‘replacement spine’ developed (also 1245, one rostral spine, two dermal denticles, and 14 vertebrae see below). The articulated rostral spines in AMNH FF 20388 from Mooreville Chalk (lower Campanian) in Dallas County, indicate that the side with the cutting edge continuing linearly Alabama (Figure 3(d)); RMM 2503, 50 rostral spines and at least to the root is the anterior side, and that the side with the concave 11 calcified cartilage pieces from lower part of Mooreville Chalk cutting edge at the crown base area represents the posterior side (lower Campanian) in central Greene County, Alabama (Figure (Figure 2(c)). In addition, AMNH FF 20388 shows that each 3(f)); RMM 1924, two rostral spines and at least 122 calcified rostral spine tends to curve ventrally in which the trend is more cartilage pieces from lower part of Mooreville Chalk (lower prominent in smaller rostral spines than the larger ones (Figure Campanian) in central Greene County, Alabama (Figure 3(e)); 2(d)). RMM 2943, two rostral spines, three vertebrae, and at least 34 calcified cartilage pieces form Bluffport Marl Member (mid‒ Rostral spines upper Campanian) of Demopolis Chalk Formation in eastern The rostral spines of Ischyrhiza mira vary in size and shape Sumter County, Alabama (Figure 3(b)); RMM 6003, five ros- within each individual, but they overall conform to Welton and tral spines and two dermal denticles from upper part of Ripley Farish’s (1993, p. 141) description. Each spine consists of a thick, Formation (upper lower Maastrichtian) in northeast Wilcox smooth-surfaced crown with sharp anterior and posterior cutting County, Alabama (Figure 3(c)). edges that extend the entire length except at the crown base. The anterior margin of the crown and root is continuous and straight, Description whereas the posterior margin of the spine at the crown-root junc- tion is concaved, making the entire posterior edge sinuous. The Rostrum root is generally shorter and more massive than the crown, and The rostrum of AMNH FF 20388 has a total preserved length of it is basally expanded with bifurcated scalloped root lobes sep- 55 cm (Figure 2(a)‒(b)). Much of it is taphonomically slightly arated by a median longitudinal furrow. Appendix 1 lists meas- compressed laterally, but it gradually widens from about 2.3 cm urements of all rostral spines with a complete crown preserved at its anterior end to about 5.0 cm at the posterior end. The in all the associated specimens we examined (see Figure 5(a) maximum dorsoventral height of the rostrum as preserved is for measured variables). 2.8 cm (Figure 2(b)). However, its posterior end is dorsoven- The six articulated rostral spines preserved in the anterior trally crushed taphonomically suggesting that it could have been half of the rostrum of AMNH FF 20388 are tall and erect and slightly greater in height than the anterior end, especially con- are overall similar in size and shape (Figure 2(a)‒(f)), but one sidering the pattern of the widening of the rostrum posteriorly. of the associated four disarticulated teeth (r9 in Figure 2(a)) On both dorsal and ventral sides, two parallel grooves run is short and is curved posteriorly, suggesting the presence of longitudinally through the entire length of the rostrum that intraindividual variation in spine morphology and size. Such represent the positions of ophthalmic nerves and the positions variation is evident in RMM 2503 (Figures 3(f), 5(b)-(d)) that of bucco-pharyngeal nerves, respectively (Figure 2(a), (g), (h)). contains 50 disarticulated rostral spines, constituting the largest The main body of the rostrum consists of tessellated cartilage known set of rostral spines of Ischyrhiza mira. Many spines are formed by a layer of small (0.5‒1 mm) prismatic calcified car- incomplete, but the tallest spine in the specimen is erect and tilage blocks, but a thin layer of fibrous cartilage referred to as measures about 19.0 mm in total apicobasal spine height, 7.0 mm the ‘wood-like cartilage’ (e.g. Kirkland and Anguillόn-Martίnez in total anteroposterior spine (root) length, and 11.8 mm in api- 2002; Maisey 2013) covers each superficial ophthalmic nerve cobasal crown height (r10 in Appendix 1). The smallest spine (Figures 2(i), 4(a)). Each lateral margin of the rostrum is marked in RMM 2503 has a posteriorly curved crown and measures by two parallel longitudinal ridges. The two root lobes of each about 8.3 mm in total apicobasal spine height, 4.8 mm in total rostral spine (see below) articulated with the two ridges, likely anteroposterior spine (root) length, and 5.2 mm in apicobasal by collagenous fibers in life. In addition, broken surfaces of the crown height (r4 in Appendix 1; Figure 5(d)). Rostral spines rostrum showing its cross-sectional view reveal the presence of that fall in between those two extreme ends are intermediate in a longitudinally-directed medial canal within the rostrum that size and shape (e.g. Figure 5(c)), although there are more tall is defined by a layer of tesserae forming a tube (Figure 2(g)‒(h)). erect teeth represented in the associated specimen than shorter, Between the outer layer of tessellated cartilage and inner tubu- posteriorly-curved rostral spines. The largest complete rostral lar tessellated cartilage for the medial canal is a void filled with spine in our sample is represented in AMNH FF 20388 (r3 in matrix that is assumed to have been occupied by hyaline cartilage Figure 2(c)), and measures 44.0 mm in total apicobasal spine in life (Figure 2(g)‒(h); Becker et al. 2005). Based on AMNH FF height, 12.1 mm in total anteroposterior spine (root) length, 20388, Figure 2(i) shows a schematic drawing of the organization and 23.3 mm in apicobasal crown height (r3 in Appendix 1). of the rostrum in Ischyrhiza mira in life. Although not all rostral spines may be represented in each AMNH FF 20388 preserves a total of ten rostral spines, consist- set, the following order of specimens reflects the likely sequence ing of four disarticulated and six articulated spines (Figure 2(a), of sizes of individuals from the largest to the smallest based on (b)). Two of the articulated ones are right spines located near the the apicobasal height of the preserved tallest rostral spine in each 6 P. C. STERNES AND K. SHIMADA

specimen, including an estimated height if incomplete: AMNH base exhibiting vascularization pits and a slightly posteriorly-di- FF 20388, RMM 6003, MPPM 2013.8.3, RMM 2943, RMM 2503, rected, apically-tapering ‘cusp’ showing many apicobasally-ori- RMM 1245, and RMM 1924. ented ridges and grooves (Figure 4(c)‒(f)). The better-preserved, slightly larger of the two denticles in RMM 1245 (Figure 4(d)) is Dermal denticles 19.1 mm in presumed anteroposterior length, 12.2 mm in width, Our examined specimens include two broad types of dermal and 11.9 mm in maximum preserved height. The better-preserved, denticles: those that are small and distributed along the lateral slightly larger of the two denticles in RMM 6003 (Figure 4(f)) margins of the rostrum (i.e. ‘rostral dermal denticles’), and those is 32.0 mm in presumed anteroposterior length, 19.4 mm in that are large and considered to have come from the dorsal side width, and 30.4 mm in maximum preserved height. The four of the post-rostrum body (i.e. ‘non-rostral dermal denticles’). non-rostral dermal denticles show that the demarcation between Rostral dermal denticles are recognised in AMNH FF 20388, the basal portion and the flanks of the ‘cusp’ is less pronounced and they are found near the base of rostral spines (Figure 2(f)). in larger specimens. The apex of all of them is not complete, but These denticles are oval in outline in apical view and measure it appears to be worn at least for RMM 1245 (Figure 4(c)). When 1.5‒2.5 mm in maximum dimension (Figure 4(b)). They are hat- viewed anteriorly (or posteriorly), the ‘cusp’ is symmetrical in shaped each with a rounded knob-like rise that is well-demar- the largest denticle (Figure 4(f)) suggesting that it was likely sit- cated from the flat basal margin. Although none of the rostral uated along the sagittal line somewhere on the back, whereas the dermal denticles exhibits the basal surface, it is assumed to be flat. remaining three denticles (Figure 4(c)‒(e)) are slightly inclined Non-rostral dermal denticles are represented by two samples to one side, suggesting that each of them came from either the each in RMM 1245 and RMM 6003 (Figure 3(c), (d)). The den- right or left side of the dorsal body surface. Isolated dermal den- ticles in RMM 6003 (Figure 4(e), (f)) are larger and more robust ticles of similar size and morphology are also known at least that those in RMM 1245 (Figure 4(c), (d)). However, they all have from Late Cretaceous marine deposits of Alabama (e.g. RMM a laterally-compressed cone shape with a flat or slightly concaved 2504: not Figured).

Figure 4. Calcified cartilage and dermal denticles of Ischyrhiza mira Leidy 1856 from Upper Cretaceous Mooreville Chalk of Alabama. (a) close-up image of dorsal surface of rostrum (AMNH FF 20388; portion indicated by top arrow in Figure 2(a)) showing two types of calcified cartilage, tessellated prismatic cartilage (left half) and ‘wood- like’ cartilage (right half); (b) close-up image of ventral surface of rostrum (AMNH FF 20388; portion indicated by arrow in Figure 2(b)) showing several small, hat-shaped dermal denticles; (c) and (d), two dermal denticles in RMM 1245 in (from left to right) apical, basal, anterior, and left lateral views (d1 and d2 in Figure 3d); (e) and (f), two dermal denticles in RMM 6003 in (from left to right) apical, basal, anterior, and left lateral views (d1 and d2 in Figure 3(c)). Notes: Bar scale = 5 mm in (a) and (b); 1 cm in (c)‒(f). HISTORICAL BIOLOGY 7

Figure 5. Rostral spines of Ischyrhiza mira Leidy 1856. (a) rostral spine measurements (not to scale); (b)‒(d), three of 50 associated rostral spines (RMM 2503; cf. Figure 3(f)) in (from left to right) dorsal, anterior, ventral, and basal views showing intra-individual morphological variation range ((c) = left rostral spines but their images reversed to depict right rostral spines as in (b) and (d); (b) = r6, (c) = r1, and (d) = r4 of RMM 1245 in Appendix 1); (e) large isolated rostral spine of I. mira (RMM 6095) from Ripley Formation of Alabama (image reversed for purpose of comparison); (f) large isolated rostral spine of Ischyrhiza sp. (AMNH FF 2305) in dorsal (left) and anterior (right) views; (g) line drawing of mid-section of rostrum in AMNH FF 20388 showing four articulated right rostral spines (cf. Figure 2(c); dark gray = functional spine; light gray = replacement spine); (h) restored organization of right rostral spines in life showing direction of spine replacement (curved arrow) as functional spine becomes lost (straight arrow) (cf. Figure 5(g); dark gray = functional spine; light gray = replacement spine); (i) restored organization of right rostral spines showing inferred position of lateral edge of skin cover (vertical lines) and externally exposed portions of rostral spines (dark gray) in life (cf. Figure 5(h); light gray = portions of rostral spines embedded in soft tissue in life). Notes: Abbreviations: bCL, anteroposterior crown length at crown base; CH, apicobasal crown height; CT, dorsoventral crown thickness at crown base; mCL, maximum anteroposterior crown length; SH, total apicobasal total rostral spine height; SL, total anteroposterior rostral spine length; ST, total dorsoventral rostral spine thickness. Bar scale = 1 cm.

Vertebrae RMM 1245 (Figure 3(d)) contains the smallest vertebrae MPPM 2013.8.3, RMM 1245, and RMM 2943 preserve multiple among the three vertebrae-bearing specimens. The small sizes vertebral centra, some of which are complete whereas others are of vertebrae are at odds given that the single associated rostral fragmentary or heavily distorted taphonomically. The centra are spine in the specimen is much larger than the rostral spines in circular, biconcave (i.e. amphicoelous), and not perforated in which the other two specimens. The two articular surfaces of one of the dorsoventral height is nearly equal to the transverse width, the vertebrae in particular have distinctively unequal widths whereas the anteroposterior length is always shorter than the height (diameters), measuring 10.6 mm and 11.7 mm, separated by an or width (Figure 6). Articular surfaces as well as broken surfaces anteroposterior centrum length of 6.7 mm (v3 in Appendix 2; generally exhibit several concentric ‘growth bands’ (also see below). Figure 6(a)). This vertebra is interpreted to be the anterior-most The largest centrum, assumed to be the trunk vertebra, is present in centrum in the vertebral column in which the smaller articular RMM 2943 (v1 in Figure 3(b)). It is incomplete and taphonomically surface is thought to be the anterior side that was likely artic- distorted, but its diameter is estimated to be about 27.2 mm and the ulated with the ‘occipital centrum’ of the neurocranium in life. anteroposterior length about 11.4 mm (v1 in Appendix 2). Large trunk vertebrae are also found in MPPM 2013.8.3 (v1 in Figure 3(a)), one of which is 26.0 mm in diameter and 9.5 mm in length Discussion (v1 in Appendix 2; Figure 6(b)). One pair of depressions that are Rostral anatomy 13.4 mm apart occur on the dorsal side representing the attach- ment sites for the bases of the neural arch (dorsal view depicted Most sclerorhynchids are taxonomically identified by their ros- in Figure 6(b)). Likewise, one pair of depressions that are 8.7 mm tral spines. Unlike the modern pristids, the rostral spines of apart occurs on the ventral side and represent the attachment sites sclerorhynchids are not embedded in the alveoli of the rostral for the cartilaginous ribs (ventral view depicted in Figure 6(b)). cartilage and are replaced continuously during life (Slaughter 8 P. C. STERNES AND K. SHIMADA

Figure 6. Vertebrae of Ischyrhiza mira Leidy 1856 from Upper Cretaceous of Alabama and Tennessee. (a) anterior-most(?) vertebra in RMM 1245 (cf. Figure 3(d)) in (from left to right) anterior, posterior, left lateral, dorsal, ventral, and anterolateral views (v3 in Appendix 2); (b) one of eight vertebrae in MPPM 2013.8.3 (cf. Figure 3(a)) in (from left to right) articular, lateral, dorsal (top) and ventral (bottom), and anterolateral views (v1 in Appendix 2); (c) transverse broken surface of centrum in one of 14 vertebrae in RMM 1245 (cf. Figure 3(d)) showing nine growth bands in total (circles) (v11 in Appendix 2); (d) transverse broken surface of centrum in one of three vertebrae in RMM 2943 (cf. Figure 3(b)) showing five growth bands in total (circles) (v1 in Appendix 2); close-up image of articular surface showing growth bands in one of eight vertebrae in MPPM 2013.8.3 (cf. Figure 2(a), 6(b)) showing observable six growth bands plus putative position of seventh growth band (square) along edge of centrum (v1 in Appendix 2). Notations: asterisks (*) = position of center of vertebra; b, band representing vertebral size at birth; circles, positions of observable growth bands; square, putative position of growth band during process of its formation. Bar scale: (a), (b) = 1 cm; (c)‒(e) = 0.5 cm.

and Springer 1968). On the other hand, the replacement mode generally of equal size in the middle portion of their rostrum. of the rostral spines in sclerorhynchids is similar to that in pris- This pattern is also true for I. mira based on the six rostral spines tiophorids in which, when a functional rostral spine was lost, a articulated with the anterior half of the rostrum in AMNH FF similar-sized replacement spine that had developed immediately 20388 in which they all range 33.4+‒44.0 mm in total apicobasal posteriorly within the integument against the rostral cartilage height (r1‒r6 in Appendix 1). AMNH FF 20388 also includes became erect and moved into the position of the lost spine to four disarticulated rostral spines (see bottom right of Figure become functional (Welten et al. 2015; Figure 5(h), (i)). In other 2(a)), one of which is posteriorly curved and is only 15.0 mm words, a functional spine and its replacing spine form a pair in total apicobasal height (r9 in Appendix 1). The small rostral (Welten et al. 2015), and at least two pairs of spines are evident spine is morphologically equivalent to the smallest complete in the articulated rostral spines in AMNH FF 20388: the func- rostral spine in RMM 1245 (Figure 5(d)) that was found with tional spine (r1) and its replacement (r2) that is taphonomically many tall, erect rostral spines (Figures 3(f), 5(b)) similar to the displaced: (Figure 2(e)) and the next preserved functional spine six articulated spines in AMNH FF 20388 (Figure 2(c), (e)). We (r3) and its replacement (r4: Figures 2(c), 5(g)). The fifth and interpret the small rostral spines to have come from near the sixth preserved spines (r5 and r6) are functional spines, but their posterior-most portion of the rostrum. This interpretation would replacement spines are not preserved in the specimen (Figure imply that the anterior one-half to two-third of the rostrum in 2(c)). Like the rostral spine of the extant pristiophorids, the integ- I. mira was equipped with tall erect rostral spines, and spines ument is assumed to have covered the root of each functional became shorter and more curved towards the posterior end of spine as well as the entire replacement tooth (Figure 5(i)). the rostrum. This spine organization would have meant that, in Based on skeletal remains of non-Ischyrhiza sclerorhynchids, life, the apices of rostral spines on either side must have been Kriwet (2004) observed that rostral spines in sclerorhynchids are lined up relatively evenly even though the rostrum widened HISTORICAL BIOLOGY 9

posteriorly. One possible exception is the second smallest rostral two-third of the rostrum is occupied by large tall spines followed spine preserved in RMM 2503, r13 (Figure 3(f); Appendix 1), posteriorly by smaller spines (see above), the rostrum length of that has a short but relatively erect crown, possibly representing 58 cm would give a space for about 16 or 17 functional spines an anterior-most spine in the rostrum; however, its exact posi- with the same number of replacement spines. Under this assump- tion cannot be ascertained at the present time. tion, each side of the rostrum likely had a total of about 32 or 34 The development of rostral spines in sclerorhynchids is more spines, and the entire rostrum would have had about 64 or 68 comparable to that of pristiophorids than to pristids (Underwood spines in all. The presence of 50 rostral spines in RMM 2503 is et al. 2015). In pristiophorids, the total number of rostral spines in accordance with this interpretation. varies from species to species from 34 (Pristiophorus nudipinnis Günther 1870) to as many as 86 (P. japonicus Günther 1870) Dermal denticle anatomy (Ebert et al. 2013). The largest set of associated rostral spines, RMM 2503, contains 50 rostral spines including many tall, erect ‘Dermal denticles’ sensu lato are ubiquitously present in chon- ones as well as a few smaller, posteriorly curved ones (Figure drichthyans including placoid scales, and show high levels of 3(f)). Exactly how many of them represent left spines or right interspecific and intraindividual variations (e.g. Reif 1982; Raschi spines is difficult to ascertain because about two-thirds of them and Tabit 1992). This present report represents the first descrip- are incomplete, but the fact that the smallest spine in the spec- tion of rostral and non-rostral dermal denticles in Ischyrhiza imen (Figure 5(d)) is not represented in pair suggests that the mira. We presume the small hat-shaped rostral dermal denticles specimen does not contain all the rostral spines that existed in distributed along the spinous margin of the rostrum (Figures life. Whereas RMM 2503 suggests that at least 50 rostral spines 2(f), 4(b)) to have added extra protection to the rostrum against (or at least 25 spines on either side of the rostrum) were present abrasion. On the other hand, the large, laterally-compressed con- in each individual of Ischyrhiza mira, the question remains as ical dermal denticles (Figure 4(c)‒(f)) were possibly sparsely dis- to how many in all were originally present in one rostrum. We tributed ‘thorns’ on the dorsal surface of the behind the address this question based on AMNH FF 20388 that has an esti- rostrum. In extant batoids, multiple types of thorns are known mated total rostrum length of 58 cm (55 cm in preserved length, on the dorsal side of the body, including alar and malar thorns plus estimated missing length of 3 cm based on comparisons on pectoral fins that occur specifically to males in some rajoids with other sclerorhynchids: Figure 7(f) based on Figure 7(a)‒ as well as ‘generalized thorns’ (McEachran and Konstantinou (e)). Because one functional spine accompanies one replacing 1996, Figure 2) such as rostral, orbital, interorbital, interspirac- spine as a pair (Figure 5(h)), and because the anterior one-half to ular, nuchal, mid-scapular, scapular, and interdorsal thorns as well as median, parallel, and lateral rows of thorns that extend to the back of the tail (Yearsley and Last 2016, Figure 6.2). All the non-rostral dermal denticles present in RMM 1245 and RMM 6003 are different from one another in shape and size (Figure 4(c)‒(f)), suggesting that they likely must have come from differ- ent parts of the body. They are likely those of ‘generalized thorns’ and not of alar or malar thorns because they are characterised by a form with an ‘upright, blunt stellate base’ (not with a ‘tilted tip sharp or pungent’: sensu Yearsley and Last 2016, Figure 6.4; see also McEachran and Konstantinou 1996). However, their exact thorn types as well as the exact total number, specific types, and distribution pattern of thorns present in I. mira can only be speculated based on the present fossil record. Nevertheless, the role of these non-rostral dermal denticles is interpreted to be that of Reif’s (1982) ‘Type 2’ that is characterised by sluggish, benthic swimmers and agrees with the assumed life style of sclerorhy- nchids (see below for further discussion). It is noteworthy that the non-rostral dermal denticles, espe- Figure 7. Restored (a, f, g) and preserved (b‒e) body outlines of Late Cretaceous cially the two large ones in RMM 6003 (Figure 4(e), (f)), are sclerorhynchid sawfishes (body lengths standardised using two anatomically reminiscent to the rostral spine of Peyeria libyca Weiler 1935. homologous positions in a‒f: upper horizontal line = inferred position of mouth indicated by gently curved line based on position of upper and lower jaws; lower Cappetta (1987) listed the taxon to be an extinct pristid but also horizontal line = position of posterior end of pectoral fin base). (a) restored noted that ‘Peyeria could also represent dermal thorns of some body outline of atavus Woodward 1889 in dorsoventral view by Woodward (1892, p. 531); (b) preserved body outline of Lebanopristis hiram batoids’ (p. 158). Subsequently, Cappetta (2012) considered (Hay 1903) in dorsoventral view based on photograph by Cappetta (1980, pl. Peyeria to be ‘dermal thorns of the sclerorhynchid , 2, Figure 3); (c)‒(e) preserved body outlines of S. atavus in dorsoventral view with which it is always associated’ (p. 383). We concur with the based on photographs by Cappetta (1980, pl. 3, Figures 1–3); (f) restored body outline of generalised sclerorhynchids, including Ischyrhiza mira Leidy 1856 in interpretation that specimens previously assigned to Peyeria dorsoventral view suggested in this present study based on Figure 7(b)‒(e) (dark are likely ‘dermal thorns’ (i.e. enlarged dermal denticles) gray shade = silhouette of AMNH FF 20388 showing its inferred position in life); because of their strong resemblance with the dermal denticles (g) restored body outline of generalised sclerorhynchids, including I. mira that ‒ reached up to about 2 m TL, in left lateral view suggested in this present study of Ischyrhiza mira described here (Figure 4(c) (f)). This would based on Figure 7(f) and extant pristiophorid sawsharks (e.g. Compagno 1984, p. mean that such dermal thorns may have been widely present 131‒132). in sclerorhynchids. 10 P. C. STERNES AND K. SHIMADA

Body form and body size about 4.6 m TL. Amalfitano et al. (2017) also noted that the largest individuals could have reached as much as almost 5.8 m The body form of Ischyrhiza is not known, but reasonable infer- TL but this is based on the rostrum only comprising 20‒22% of ences can be made based on closely related sclerorhynchids the TL in adult living pristids (e.g. see Thorson 1982). However, with known articulated skeletons. A number of body restora- Amalfitano et al.’s (2017) specimen preserved a nearly complete tions of various sclerorhynchids are known (e.g. Wueringer et rostrum that measured 115 cm, and if the 1:3.27 ratio (see above) al. 2009, Figure 1a), but they generally lack explanations about is used, the individual of Onchosaurus would have measured restoration methods and exact sources. One exception is that about 376 cm TL, that is still considerably large for sclerorhy- by Woodward (1892; see also Cappetta 2012; Figure 378B) who nchids but smaller than their original estimate of 4.6 m TL. There presented a body restoration of Sclerorhynchus atavus Woodward is nothing to preclude that the body plan of Onchosaurus was 1889 (Figure 7(a)), by noting the ‘general form and proportions drastically different from other sclerorhynchids, and Amalfitano of the trunk … are based upon the type-specimen of Squatina et al.’s (2017) TL estimation method required many assumptions. crassidens’ whereas ‘the proportions of the rostrum are inferred Thus, we consider our estimation of 376 cm TL for the individual from the type-specimen of rostrum Sclerorhynchus atavus’ (p. to be more realistic. Regardless, both Amalfitano et al.’s (2017) 530). Subsequently, Cappetta (1980) presented photographs study and our present work suggest that at least some species of of three well-preserved skeletons of S. atavus (Figure 7(c)‒ sclerorhynchids exceeded well over 1 m TL (cf. Cappetta 1974; (e)) and a nearly complete skeleton of another sclerorhynchid, Wueringer et al. 2009). Lebanopristis hiram (Hay 1903) (Figure 7(b)). Comparison of Woodward’s (1892) body outline, that is not based on complete specimens, with the outline of each sclerorhynchid skeleton Ontogenetic growth illustrated by Cappetta (1980) reveals two major inaccuracies in ‘Growth bands’ in vertebrae have been used commonly to Woodward’s restoration (Figure 7). First, the anterior extremity determine the ontogenetic age and growth pattern of modern of the rostrum in S. atavus is sharply pointed and not as blunt elasmobranchs (Cailliet et al. 2006; Goldman et al. 2012). Three as depicted by Woodward (1892). Second, the body length pos- specimens of Ischyrhiza mira described here contain vertebral terior to the pectoral fins is found to be much longer than that centra: MPPM 2013.8.3 (Figure 3(a)), RMM 1245 (Figure 3(d)) illustrated by Woodward (1892). In addition, Cappetta’s (1980) and RMM 2943 (Figure 3(b)). Closer examination of those verte- study revealed the presence of two closely-spaced dorsal fins brae reveals the presence of growth bands on the articular surface positioned immediately anterior to the caudal fin at least in S. and broken surfaces (Figure 6(c)‒(e)). Each vertebra generally atavus. By taking these pieces of information into account, Figure shows a distinct band near its center that is considered to be the 7(f) shows a revised body outline of S. atavus, which can also be size of the centrum at birth, and each subsequent major ‘band’ considered as a generalised body plan of sclerorhynchids, includ- towards the rim of the centrum that generally follows multiple ing Ischyrhiza, especially because it is also nearly identical to the finer ‘rings’ is considered to be an annual growth band. When overall body outline of L. hiram (Figure 7(b)). Figure 7(g) shows the total number of bands are counted, RMM 1245 is considered a tentative outline of the generalised sclerorhynchid body plan to be about 9 years old (Figure 6(c)), RMM 2943 to be 5 years in lateral view in which the body depth and caudal fin morphol- old (Figure 6(d)), and MPPM 2013.8.3 to be almost or at 7 years ogy are inferred based on extant pristiophorid sawsharks (e.g. old (Figure 6(e); see below for further explanation). Vertebrae Compagno 1984, p. 131 ‒132). Both extant pristid sawfishes and in RMM 1245 are the smallest compared to those in RMM 2943 extinct sclerorhynchids have 213‒240 vertebrae (Amalfitano et and MPPM 2013.8.3, and yet, they have the greatest band counts al. 2017), but the total vertebral count in Ischyrhiza is unknown among the three specimens. This is because centra in RMM 1245 at the present time. likely represent anterior-most vertebrae in the vertebral column The ratio between the rostrum length (RL) and total length in life, whereas vertebrae in the other two specimens likely came (TL) in the revised generalised sclerorhynchid body plan (Figure from the trunk region that would have been the largest vertebrae 7(f)) is about 1:3.27. Assuming that the body outline of Ischyrhiza in the vertebral column of each individual. Regardless, in all three closely resembled that shown in Figure 7(f), I. mira represented specimens, the distance between the ‘birth band’ and the first by AMNH FF 20388 with an estimated rostrum length of band has the widest interval and the interval to each subsequent 58 cm (see above) is calculated to be about 190 cm TL using outer band becomes successively narrower in general (Figure the ratio. The estimated size of 190 cm TL is much smaller than 6(c)‒(e); see band interval (‘BI’) in Table 1 explained further the reported maximum size in modern pristids that is around below). This observation suggests a rapid growth during the 7 m TL (Weigmann 2016), but it is much larger than Cappetta first one or two years after birth, and the growth rate gradually (1974) and Wueringer et al.’s (2009) accounts who noted that decreased through ontogeny. sclerorhynchids reached only about 70‒100 cm TL. The indi- The crown height (CH) of the tallest rostral spine preserved vidual represented by AMNH FF 20388 is comparably large for in MPPM 2013.8.3 (Figure 3(a)) is tall and erect and measures I. mira based on the size of its rostral spines (e.g. Appendix 1, 16.4 mm (r2 in Appendix 1). This measurement is 79.0% of the but also see below). However, we note that even larger sclerorhy- average crown heights of the eight tall erect rostral spines in nchids did exist. For example, Amalfitano et al. (2017) described AMNH FF 20388, i.e. 20.75 mm (r1‒r8 in Appendix 1; Figure a partial, disarticulated skeleton of Onchosaurus pharao (Dames 2). If the percentage of 79.0% is applied to the estimated TL of 1887) from the upper Turonian of Italy. Based on the extrapolated 190 cm TL and the rostrum length (RL) of 58 cm for AMNH FF vertebral column length, rostrum length, and length of rostrum 20388 (see above), the estimated TL and RL for MPPM 2013.8.3 as proportion of body size, they estimated the individual to be are 150 cm TL and 46 cm RL, respectively. This assumption then HISTORICAL BIOLOGY 11

Table 1. Raw measurements (BN, CR, and BI) taken from vertebra of Ischyrhiza mira Leidy 1856 (MPPM 2013.8.3: Figure 6(e)) and derived measurements (pCR, TL, RL, and CH; see below and text for explanation) as well as reported TL of three extant species of Linck 1790 (P.cla., P.pec., and P.pri.) for comparison. Abbreviations in listed sequence: BN, band number assumed to be equivalent to ontogenetic age (0 = band at birth, or circumference of centrum at birth); CR, centrum radius at each band; BI, band interval from previous band; pCR, percent centrum radius from center of vertebra; TL, estimated total length of entire fish; RL, anteroposterior length of rostrum; CH, apicobasal crown height of rostral spine; P.cla, reported TL of P. clavata Garman 1906 (data from Thorburn et al. 2008; n = 5) as example of ‘small’ extant Pristis that reaches up to about 318 cm TL (Weigmann 2016); P.pec, reported TL of P. pectinata Latham 1794 (approximation based on Figure 6 of Scharer et al. 2012; n = 15) as example of ‘large’ extant Pristis that reaches up to at least 553 cm TL and may be as much as 760 cm TL (Weigmann 2016); P.pri, reported TL of P. pristis (Linnaeus 1758) (= P. microdon Latham 1794: data from Thorburn et al. 2007; n = 10) as example of ‘large’ extant Pristis that reach up to at least 700 cm TL (Weigmann 2016). BN CR BI pCR TL CH RL P.cla. P.pec. P.pri. (‘Age’) (mm) (mm) (%) (cm) (cm) (mm) (cm) (cm) (cm) 0 4.4 ‒ 34.9 52 5.7 16 <87 ~50 <80 1 6.4 2.0 50.8 76 8.3 23 90 ~150 100 2 8.2 1.8 65.1 98 10.7 30 ~115 ~220 150 3 9.3 1.1 73.8 111 12.1 34 160 ~260 200 4 10.5 1.2 83.3 125 13.7 38 ‒ ~310 ‒ 5 11.4 0.9 90.5 136 14.8 42 ‒ ~340 ‒ 6 12.0 0.6 95.2 143 15.6 44 ‒ ~360 ‒ 7a 12.6 0.6 100 150b 16.4c 46d ‒ ~370 ‒ Notes: Actual seventh band (a) is not evident but inferred to have been close to, or at the onset of, its formation (see text); each TL is calculated from estimated TL (b) for MPPM 2013.8.3 (see text); each CH is calculated from measured CH of tallest rostral spine (c) in MPPM 2013.8.3 (Table 1); each RL is calculated from estimated RL (d) for rostrum in MPPM 2013.8.3 (see text).

allows us to tentatively extrapolate the possible TL and RL as time (i.e. the time it takes for a fish in a population to reach near

well as CH at the time of each band formation as the vertebra its mean maximum length), and t0 the theoretical time at zero of MPPM 2013.8.3 (Figure 6(b), (e)) developed ontogenetically length. Strictly speaking, data for the VBGF analysis must be in life. Although only six growth bands are discernible in the taken from multiple specimens that are randomly sampled from vertebra not counting the band that represented the size of the a population for independent measurements. Measurements vertebra at birth (Figure 6(e)), the distance between the last taken from one vertebra here provide dependent measurements, (sixth) band and the outer edge of the articular surface suggests so the statistical operations in our study must be viewed experi- that the seventh band must have been close to, or at the onset mental with a hypothetically supposition that the 8 BN-TL pairs of, its formation along the edge. Thus, we treat the edge of the (including BN 0: Table 1) were obtained from eight different, articular surface to mark the seventh band, or band number (BN) randomly sampled individuals. With this supposition, the VBGF 7, meaning that the individual represented by MPPM 2013.8.3 experimentally fitted to the data to correlate the BN values with was approximately 7 years old at the time of its death. TL values using the least squares method (Table 1) is statisti- To examine the ontogenetic pattern based on the vertebra cally significant (non-linear regression: R2 = 99.9%; p < 0.001). in MPPM 2013.8.3 (Figure 6(e)), we measured the distance of Parameter estimates for the function are 51.910 cm TL for the –1 each band from the center of the vertebra, the centrum radius length at birth (L0), 176.250 cm TL for L∞, and 0.222 yr for k (CR), that formed the basis of our TL extrapolation when each (line ‘a’ in Figure 8(a)). Furthermore, if these VBGF parameter band formed (Table 1). We also measured the distance between estimates are applied to Natanson et al.’s (2006) equation for the

each band and its immediately previous band (i.e. BI: Table 1). estimated age at 95% of L∞, i.e. Longevity = (1/k)ln{(L∞ – L0)/ We then assumed that the outer-most band, BN 7, formed when [L∞(1 – x)]} with x = L(t)/L∞ = 0.95, the estimated longevity for the individual was 150 cm TL. Next, the CR value for BN 7, I. mira is calculated to be 11.923 years.

12.6 mm, was considered 100%, and the percent distance of all Our L0 of 51.910 cm TL is practically identical to our back-cal- other bands, each from the center of the vertebra (pCR), was culation of size at birth of 52 cm TL although the exact reproduc- obtained (Table 1). Then, the TL of the fish at each band position tive mode is speculative for Ischyrhiza mira (Table 1). Whereas (or at the time of each band formation) was calculated according modern pristids give birth to live pups, it is noteworthy that to each respective pCR value (Table 1). Similarly, by considering this estimated size at birth of 52 cm TL for I. mira is similar the tallest measured CH of 16.4 mm and extrapolated RL of to the reported smallest free-swimming extant pristids meas- 46 cm in MPPM 2013.8.3 (see above) to be 100%, CH of the uring as small as 43 cm TL, although they are more commonly fish at each band formation was calculated according to each in the range of 0.6‒0.9 m TL (e.g. Thorson 1976; Peverell 2005;

respective pCR value (Table 1). Scharer et al. 2012; Last et al. 2016). In contrast, our obtained L∞ The von Bertalanffy growth function (VBGF: von Bertalanffy of 176.250 cm TL is considerably low given that the estimated size 1938) is the most common quantitative method used to describe for AMNH FF 20388 is 190 cm TL (see above). It is important the growth of modern elasmobranchs (e.g. Cailliet and Goldman to point out that the estimated asymptotic length expressed by

2004; Goldman 2004), and the technique has also been applied L∞ does not represent the maximum possible length but rather to some extinct elasmobranchs (e.g. Shimada 2008; Cook et al. the average length-at-age, meaning that some individuals may

2011; Newbrey et al. 2015). The VBGF parameters for Ischyrhiza be larger or smaller than any calculated L∞ value (Francis 1988). mira were obtained through the Desmos Inc. graphing software However, there are several other reasons that may explain this (www.desmos.com) using the following form of VBGF that discrepancy. First, because our VBGF analysis is manifested describes the length (L) as a function of the age of the animal with many assumptions, including the TL estimation made for ‒k(t ‒ t0) (t): L(t) = L∞ (1 ‒ e ), where L∞ is the estimate of asymptotic AMNH FF 20388 that formed the basis for the TL estimation for maximum length, k the rate constant with units of reciprocal MPPM 2013.8.3 was by means of comparing crown heights of 12 P. C. STERNES AND K. SHIMADA

Figure 8. Growth models of Ischyrhiza mira Leidy 1856 based on vertebral growth bands in MPPM 2013.8.3 (Figure 6(e); see text). (a) von Bertalanffy growth function (VBGF: a) and power function (b) fitted to data points that show relationship of number of vertebral growth bands (BN, or ‘age’ of individual in years) with total length (TL); (b) VBGF (a) and power function (b) fitted to data points that show relationship of BN with crown height C( H) of rostral spines; (c) linear function fitted to data points that show relationship of CH with TL; d, linear function fitted to data points that show relationship ofTL with rostrum length (RL) in I. mira (a: this study) compared with that in (b) male Pristis pristis (Linnaeus 1758) (= P. microdon Latham 1794: data from Thorburn et al. 2007, Figure 6; n = 22) in (c) female P. pristis (data from Thorburn et al. 2007, Figure 6; n = 37), and in (d) P. clavata Garman 1906 (data from Thorburn et al. 2008, Figure 3; n = 31 consisting of 13 females and 18 males combined). their rostral spines. Second, the total BN we obtained could be 141) noted that rostral spines of I. mira reach to ‘50 + mm,’ and an underestimated count especially given that significant under- Cappetta (2012, p. 376) noted the maximum spine size for the estimation can happen in vertebra-based age assessments even genus to be ‘up to 6 cm high.’ To our knowledge, the largest ros- on extant elasmobranchs (Passerotti et al. 2014; Harry 2017). tral spine that can be confidently assigned to I. mira is one of the Third, where the VBGF curve is likely specific for a population three spines catalogued as RMM 6095 with a total spine height of of I. mira, AMNH FF 20388 and MPPM 2013.8.3 come from about 58 mm and a CH of about 32 mm. Spines with >20 mm CH chronologically and geographically different populations (lower are uncommon, and those with >25 mm CH are exceptionally Maastrichtian of Alabama vs. upper Campanian of Tennessee). rare for I. mira; nevertheless, our VBGF analyses for both BN-TL Fourth, variation range of rostral spine sizes in I. mira could and BN-CH based on MPPM 2013.8.3 with an assumed TL of have been exceptionally wide or could have exhibited differences 150 cm are likely underestimating the actual growth parameters. in sex given that, for example, cases of sexual dimorphism in In order to compensate the probable underestimation without the TL-RL relationship (female > male: Thorson 1973) and in altering our original data, we experimentally generated a best-fit the number of rostral spines in each rostrum (female < male: power function using the same BN-TL and BN-TL plots used for Thorburn et al. 2007) are known in extant pristids. our VBGF analyses. The best-fit curve for the BN-TL relationship The VBGF is generally applied to fit its curve for plots has an equation of TL = 66.083(BN + 0.539)0.412 with R2 = 0.997 between the age of the fish (based on BN) with the size of the (line ‘b’ in Figure 8(a)), and that for the BN-CH relationship fish. However, we here experimentally derived a VBGF curve to CH = 7.194(BN + 0.549)0.414 with R2 = 0.998 (line ‘b’ in Figure fit plots between BN and CH (line ‘a’ in Figure 8(b)) where, in 8(b)). The BN-TL power curve (line ‘b’ in Figure 8(a)) suggests

this instance, L0 represents the CH at birth, L∞ the estimate of that the individual represented by AMNH FF 20388 with an asymptotic maximum CH, and k the rate constant with units of estimated TL of 190 cm died at age 12.4 years. The BN-CH power reciprocal time in terms of the time it takes for a rostral spine to curve (line ‘b’ in Figure 8(b)) shows that the estimated age at reach near its mean maximum length. The resulting curve has death for AMNH FF 20388 is also 12.4 years if the average CH –1 L0 of 5.689 mm CH, L∞ of 19.289 mm CH, and k of 0.220 yr . of 20.75 mm among the eight tallest spines is used. However, The L∞ of 19.289 mm CH is quite close to the average crown individuals with a rostral spine of 23.3 mm CH (largest spine in heights of the eight tall erect rostral spines in AMNH FF 20388, AMNH FF 20388) and 32 mm CH (largest spine to our knowl- 20.75 mm CH. However, it is also important to note that the edge in RMM 6095) would have come from individuals that were tallest rostral spine in AMNH FF 20388 measures 23.3 mm CH 16.6 and 36.4 years old, respectively. If the age of 36.4 years old (r3 in Appendix 1). In addition, Welton and Farish (1993, p. is applied to the BN-TL power curve (line ‘b’ in Figure 8(a)), HISTORICAL BIOLOGY 13 the size of the individual would have been 292.805 cm TL, or 2011). AMNH FF 2305 is one such example that is represented nearly 3 m TL. by an isolated rostral spine questionably from the Cretaceous of Because the aforementioned power functions are purely New Jersey, U.S.A. (Figure 5(f)). It is morphologically different experimental, we generated a graph that directly correlates each with rostral spines of I. mira, such as its slight concavity along the CH value with a respective TL value in Table 1. The data points in anterior cutting edge and anteriorly curved posterobasal margin the graph (Figure 8(c)) show a perfect linear relationship because of the root (Figure 5(a)‒(e) vs. Figure 5(f)); thus, it is identi- each CH-TL plot is based on its respective pCR value, which itself fied only as Ischyrhiza sp. It is significant because it is gigantic, represents an extrapolated value, with the assumption that BN 7 measuring 66.5 mm in total spine height, and although its CH corresponds to 150 cm TL. The linear relationship has a function measures 39 mm, it is estimated to be about 40 mm CH originally of TL = 9.173·CH ‒ 0.192. In Figure 8(c), the line extends beyond considering its slightly abraded crown apex. If it is assumed to 150 cm TL for our purpose here, showing that an individual be the tallest rostral spine in the individual, the CH of 40 mm of Ischyrhiza mira with largest known rostral spines measuring would yield an estimated TL of 367 cm for the fish represented by 32 mm CH (RMM 6095) would have measured 293.345 cm TL, AMNH FF 2305 based on the CH-TL linear function in Figure or nearly 3 m TL. This result suggests that the power functions 8(c), although both the estimated TL of 367 cm as well as the discussed above (line ‘b’ in Figure 8(a), (b)) may indeed ade- CH of 40 cm give an unrealistic age of 62‒63 years old for the quately capture the BN-TL and BN-CH relationships of I. mira. individual using both BN-TL and BN-CH power functions (line It is noteworthy that the size of Ischyrhiza mira that appears to ‘b’ in Figure 8(a), (b)). This fact demonstrates that all the growth have rarely exceeded 2 m TL and likely not beyond 3 m TL is in functions shown in Figure 8(a)‒(c) are tentative growth models striking contrast with modern pristid sawfishes in which all five specifically for I. mira, and that their direct application to other pristid species under two genera (Anoxypristis White and Moy- taxa is inappropriate. Thomas1941 and Pristis Linck 1790) attain at least 3.1 m TL and as much as 7.3 m TL depending on the species (Last et al. 2016; Additional paleobiological inferences Weigmann 2016). Because modern pristids reach, or is inferred to reach, sexually maturity generally not until at least about Modern pristid sawfishes (Anoxypristis and Pristis) all live in 2‒4 m TL (e.g. Thorson 1976; Peverell 2005; Thorburn et al. 2007, shallow waters that are typically no deeper than 100 m, and 2008; Last et al. 2016), it is quite possible that I. mira reached they also commonly enter estuaries and rivers (Last et al. 2016; sexual maturity much earlier than the extant pristids. Although Weigmann 2016). Likewise, sclerorhynchids are thought to be our VBGF-based growth parameters for I mira (L0 = 51.910 cm benthic fishes that typically inhabited shallow coastal waters –1 TL; L∞ = 176.250 cm TL; k = 0.222 yr ; longevity = 11.923 years), (Wueringer et al. 2009), although at least some sclerorhynchids should be considered as conservative estimates due to probable (e.g. ) are known to occur in open marine depos- underestimation, it is worth pointing out that our power func- its (Smith et al. 2015). Because of their dorsoventral-flattened tion-based age estimate of 12.4 years for a 190-cm-TL individual body with a spinous rostrum like the extant pristids, the lifestyle and that of 36.4 years old for an individual that had a 32-mm-CH of sclerorhynchids have been inferred to be similar to that of rostral spine (see above) are not necessarily unrealistic given extant pristids, such as using the rostrum for searching for food that at least one extant pristid species has an estimated lifespan through the substrate and stunning and slashing prey (Schaeffer of 30 years (Thorson 1982). 1963; Wueringer et al. 2009; Last et al. 2016). Furthermore, the A few studies have shown the relationship between TL and elongated rostrum could have allowed the expansion of the sen- RL in extant pristids, and although a non-linear function was sory system (e.g. ampullae of Lorenzini) as well as self-defense fitted to data in those studies, the plot distributions were practi- through its lateral swipes as seen in extant pristids (Wueringer cally linear (Thorburn et al. 2007, Figure 6; Thorburn et al. 2008, et al. 2009). Given the fact that at least some dinosaurs ventured Figure 3; Figure 8(d)). At least one species has shown to have a into shallow waters and even could have had piscivorous diet (e.g. slight difference between the two sexes, but they all show a sim- possibly feeding on sawfishes: Ibrahim et al. 2014), ilar growth pattern of their rostrum (lines ‘b’‒’d’ in Figure 8(d)). it is not beyond of the realms of possibility that I. mira could In contrast, line ‘a’ in Figure 8(d) shows the correlation between have encountered dinosaurs in shallow waters that forced the each TL value with a respective RL value for Ischyrhiza mira. Like fish to use its spinous rostrum for self-defense especially because Figure 8(c), its data points also show a perfect linear relation- dinosaur remains do co-occur with I. mira in Late Cretaceous ship because each plot represents a theoretical TL value and a rocks of Tennessee and Alabama (see above). theoretical RL value based on their respective pCR value, which again itself represents an extrapolated value with the assumption Conclusion that BN 7 corresponds to 150 cm TL. The linear relationship has a function of RL = 0.306·TL ‒ 0.226. The line is drawn up to Ischyrhiza mira is a commonly found sclerorhynchid in North 190 cm TL that corresponds to about 58 cm RL seen in AMNH America traditionally known primarily by isolated rostral spines. FF 20388. One conclusion that can be drawn from Figure 8(d) is In this study, we studied seven specimens of I. mira consisting that the rate of rostrum development through growth in I. mira of associated elements, such as rostral spines, vertebrae, dermal is slightly faster than that in extant pristids. denticles, and calcified cartilage pieces, from Campanian‒lower In the fossil record of North America, I. mira is the most Maastrichtian of Tennessee and Alabama with the goal to make commonly reported species of Ischyrhiza. However, rostral spines inferences about the paleobiology of the species. In I. mira, the that are similar to I. mira but differ in minute anatomical detail anterior one-half to two-third of the rostrum was occupied by are also known (e.g. ‘Ischyrhiza sp. aff. I. mira’ by Bourdon et al. a row of large tall spines followed posteriorly by smaller, more 14 P. C. STERNES AND K. SHIMADA curved spines. One functional spine accompanied one replacing Beavan NR, Russell AP. 1999. An elasmobranch assemblage from the spine as a unit in which about 16 or 17 functional spines were terrestrial-marine transitional lethrbridge coal zone (dinosaur park present along one side of the rostrum with the same number formation: Upper Campanian), Alberta, Canada. J Paleontol. 73:494– 503. of replacement spines developed within the integument, mean- Becker MA, Chamberlain JA Jr, Brady D. 2005. Rostral morphology of ing that one rostrum likely held about 64 or 68 spines in all. the Late Cretaceous sawfish, Ischyrhiza mira, from the lower Navesink Ischyrhiza mira had small hat-shaped rostral dermal denticles Formation (Campanian-Maastrichtian), Monmouth County, New around the bases of rostral spines as well as large thorn-like Jersey. NE Geol Environ Sci. 27:37–48. non-rostral dermal denticles likely on the dorsal side of the body Becker MA, Chamberlain J, Wolf G. 2006. Chondrichthyans from the Arkadelphia Formation (Upper Cretaceous: Upper Maastrichtian) of characteristic of sluggish, benthic swimmers. The body form res- Hot Spring County, Arkansas. J Paleontol. 80:700–716. toration of I. mira based on nearly complete skeletons of closely Berg LS. 1940. Classification of fishes both recent and fossil. Leningrad: related sclerorhynchids suggests that the ratio between the ros- Trudy Zool Inst. Akad Nauk SSSR. 5:346–517. trum length and total body length of sclerorhynchids was about von Bertalanffy L.1938 . A quantitative theory of organic growth (inquiries 1:3.27 in general, meaning that I. mira with a rostrum length of on growth laws II). Hum Biol. 10:181–213. Bice KN, Shimada K. 2016. Fossil marine vertebrates from the Codell 58 cm would have measured about 190 cm TL. Sandstone Member (middle Turonian) of the Upper Cretaceous Carlile Based on the vertebral growth bands recognised in a 7-years- Shale in Jewell County, Kansas, USA. 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Appendix 1. Measurements of each rostral spine with measurable complete crown height in millimeters in each associated specimen of Ischyrhiza mira Leidy 1856. Rostral spine codes (‘r’) are arbitrarily assigned reference number for each measured rostral spine in each associated specimen (see Figures 2(a)‒(f), 3; rostral spines with immeasurable crown height, that are indicated as ‘r’ without any number, are excluded from this appendix; ST and CT for r6‒r26 in RMM 2503 could not be measured because they are mounted as museum display). Abbreviations: SH = apicobasal spine height; SL = anteroposterior spine length; ST = dorsoventral spine thickness; CH = apicobasal crown height; bCL = anteroposterior crown length at base; mCL = maximum anter- oposterior crown length; CT = dorsoventral crown thickness at crown base.

Catalog number Rostral spine code SH SL ST CH bCL mCL CT AMNH FF 20388 r1 40.2 11.9 8.9 22.2 8.0 8.2 4.0 AMNH FF 20388 r2 40.2 12.3 9.0 22.0 9.3 8.8 4.0 AMNH FF 20388 r3 44.0 12.1 9.2 23.3 9.4 10.0 4.3 AMNH FF 20388 r4 33.4+ 10.0 7.5 22.7 9.2 9.7 3.9 AMNH FF 20388 r5 41.3 12.5 8.1 22.0 9.0 9.8 4.1 AMNH FF 20388 r6 37.2 10.8 7.7 19.5 5.7 7.1 4.0 AMNH FF 20388 r7 29.4 11.5 7.0 18.3 6.2 8.0 3.8 AMNH FF 20388 r8 28.1 9.5 7.1 16.0 5.9 7.7 3.1 AMNH FF 20388 r9 15.0 7.3 5.5 6.1 4.1 4.6 2.9 MPPM 2013.8.3 r1 25.3 6.7 6.5 14.8 5.3 4.7 3.1 MPPM 2013.8.3 r2 28.6 ‒ ‒ 16.4 5.3 5.2 3.3 MPPM 2013.8.3 r3 25.3 6.2 6.8 15.2 5.1 4.7 3.3 MPPM 2013.8.3 r4 25.1 6.7 6.5 14.6 5.2 5.1 3.8 MPPM 2013.8.3 r5 26.2 7.7 6.6 14.7 5.5 5.4 3.2 MPPM 2013.8.3 r6 26.8 ‒ ‒ 15.8 5.3 5.2 3.6 MPPM 2013.8.3 r7 ‒ ‒ ‒ 14.6 5.3 5.2 3.7 RMM 1924 r1 15.8 5.9 4.2 8.8 3.6 3.2 1.6 RMM 2503 r1 10.8 5.6 4.8 5.9 2.9 3.0 1.8 RMM 2503 r2 15.0 5.3 ‒ 7.9 3.4 3.6 1.5 RMM 2503 r3 ‒ ‒ ‒ 7.6 3.6 3.5 1.8 RMM 2503 r4 8.3 4.8 4.2 5.2 2.7 2.7 1.5 RMM 2503 r5 12.5 ‒ ‒ 9.2 3.4 3.3 2.2 RMM 2503 r6 17.9 6.8 ‒ 10.8 3.8 3.9 ‒ RMM 2503 r7 17.5 8.4 ‒ 10.0 3.2 3.4 ‒ RMM 2503 r8 17.2 6.3 ‒ 8.8 4.1 4.3 ‒ RMM 2503 r9 14.1 5.5 ‒ 8.5 3.0 3.4 ‒ RMM 2503 r10 19.0 7.0 ‒ 11.8 4.0 4.5 ‒ RMM 2503 r11 16.1 ‒ ‒ 9.1 3.0 4.2 ‒ RMM 2503 r12 17.0 8.0 ‒ 9.4 4.0 4.4 ‒ RMM 2503 r13 10.0 4.1 ‒ 4.9 2.9 3.2 ‒ RMM 2503 r14 18.1 7.9 ‒ 11.2 3.8 4.1 ‒ RMM 2503 r15 16.5 6.5 ‒ 10.1 3.5 4.0 ‒ RMM 2503 r16 17.0 7.0 ‒ 10.9 4.1 4.7 ‒ RMM 2503 r17 13.1 4.9 ‒ 8.1 3.2 3.3 ‒ RMM 2503 r18 15.0 5.2 ‒ 8.5 3.0 3.4 ‒ RMM 2503 r19 16.0 6.0 ‒ 9.0 3.5 3.9 ‒ RMM 2503 r20 17.5 6.2 ‒ 9.3 4.0 4.2 ‒ RMM 2503 r21 ‒ ‒ 10.1 4.0 4.1 ‒ RMM 2503 r22 18.1 6.3 ‒ 10.0 3.2 4.0 ‒ RMM 2503 r23 17.1 6.0 ‒ 10.1 3.5 4.0 ‒ RMM 2503 r24 ‒ ‒ ‒ 8.0 4.0 4.2 ‒ RMM 2503 r25 ‒ ‒ ‒ 10.2 3.8 4.3 ‒ RMM 2503 r26 ‒ ‒ ‒ 10.1 3.2 3.7 ‒ RMM 2943 r1 20.1 ‒ 5.8 11.7 3.7 3.6 1.6 RMM 2943 r2 18.5 ‒ ‒ 11.6 3.3 4.0 2.0 RMM 6003 r1 29.2 9.6 9.3 14.9 5.8 6.3 3.3 RMM 6003 r2 ‒ ‒ ‒ 19.0 7.1 8.4 4.8 RMM 6003 r3 ‒ 9.1 8.0 11.8 6.3 3.5 3.8 18 P. C. STERNES AND K. SHIMADA

Appendix 2. Measurements of each vertebral centrum in millimeters in each associated specimen of Ischyrhiza mira Leidy 1856;. Vertebra codes (‘v’) are arbitrarily assigned reference number for each measured centrum in each associated specimen (see Figure 3; vertebrae with immeasurable diameter, that are indi- cated merely as ‘v’ without any number, are excluded from this appendix). Single asterisk (*) indicates estimated value; double asterisks (**) indicate larger of the two measurements (see text). Abbreviations: D = lateral width (i.e. = approximate diameter); L = anteroposterior length.

Catalog number Vertebra code D L MPPM 2013.8.3 v1 26.0 9.5 MPPM 2013.8.3 v2 25.3 9.2 MPPM 2013.8.3 v3 21.8 10.1 MPPM 2013.8.3 v4 25.6. 10.3 MPPM 2013.8.3 v5 25.8 9.3 MPPM 2013.8.3 v6 25.9 10.8 MPPM 2013.8.3 v7 26.0 10.7 MPPM 2013.8.3 v8 25.2* 7.3 RMM 1245 v1 11.5 7.0 RMM 1245 v2 11.8 7.4 RMM 1245 v3 11.7** 6.7 RMM 1245 v4 12.7 7.5 RMM 1245 v5 12.9 7.7 RMM 1245 v6 11.7 7.3 RMM 1245 v7 12.1 7.3 RMM 1245 v8 12.3 7.4 RMM 1245 v9 12.2 7.4 RMM 1245 v10 12.5 7.4 RMM 1245 v11 12.6 8.0 RMM 2943 v1 27.2 11.4 RMM 2943 v2 23.2* ‒