Pleurodira Cope, 1865

De La Fuente, Marcelo S., Maniel, Ignacio, Jannello, Juan Marcos, Sterli, Juliana, Garrido, Alberto C., Garcia, Rodolfo A., Salgado, Leonardo, Canudo, José I. & Bolatti, Raúl, 2017, Unusual shell anatomy and osteohistology in a new Late Cretaceous panchelid turtle from northwestern Patagonia, Argentina, Acta Palaeontologica Polonica 62 (3), pp. 585-601 : 588-596

Pleurodira Cope, 1865

Panchelidae Joyce, Parham, and Gauthier, 2004 Genus Rionegrochelys de la Fuente, Maniel, and Jannello nov.

Type species: Rionegrochelys caldieroi sp.nov.; see below.

Etymology: From Río Negro Province ( Argentina) and from Greek chelys, aquatic turtle.

Diagnosis.—As for the type species by monotypy.

Rionegrochelys caldieroi de la Fuente, Maniel,

and Jannello sp. nov.

Figs. 4–6 .

Etymology: In honour of the late Ing. Victorino Caldiero (1945–1999), for his contribution to the project of developing the southern margin of Cipolletti, Rio Negro Province, Argentina.

Holotype: MPCA-AT 258 ; carapace and plastron of an adult specimen. Type locality: Northern flank of the Parrita site (39º18 ʹ 13 ʺ S; 68º24 ʹ 35 ʺ W), El Anfiteatro, Río Negro Province, Argentina.

Type horizon: Upper Cretaceous, Plottier Formation, according to Musacchio (2006) and Musacchio and Vallati (2007), this horizon is Coniacian–Santonian in age, but Garrido (2010, 2011) more recently referred this horizon to the upper Coniacian–lower Santonian.

Material.— MPCA-AT 30 , right lateral edge of carapace with plastral bridge suture ; MPCA-AT 29 , right hypoplastral bone ; MPCA-AT 26 , isolated plates of a carapace. All from type locality and horizon .

Diagnosis.— Rionegrochelys caldieroi can be diagnosed as a panchelid pleurodire by the suturing of the pelvic girdle to the shell, the presence of a cervical scute, only one suprapygal bone, and vertebral scutes that are narrower than the pleural scutes. It shares with South American panchelids and Chelodina : vertebral 1 wider than vertebral 2 and axillary buttresses parallel or adjacent to costal rib 1. It differs from other panchelids by the following unique combination of characters: the first vertebral scute is twice as wide as long and subrectangular in shape, a prominent and discontinuous mid-carapace crest, a strong nuchal notch, peripheral bones 2–11 with strongly gutter ends, posterior margin of the vertebral 5 in the carapace is three lobe shaped, the plastron longer than the carapace, an anteriorly wide thoracic vertebra 1 that is tapered posteriorly in ventral view, in its heart-shaped carapace, and in its wide and short cuneiform mesoplastra crossed by a humeropectoral sulcus.

Description.— Carapace: The carapace of the holotype of Rionegrochelys caldieroi is low and wide (length/width ratio 1.03) with a strong nuchal notch (reaching peripheral 1), moderately large in size (carapace length 430 mm), and equivalent in size to Lomalatachelys neuquina ( Lapparent de Broin and de la Fuente 2001) . Contrary to other Cretaceous panchelid species (e.g., Bonapartemys bajobarrealis , Yaminuechelys gasparinii ) and extant South American and Australasian chelids (e.g., Phrynops hilarii, MHNSR H-1550, NHMUK 86-3-10-1; Emydura macquarii, QMJ 61586, QMJ 78979), where the maximum width is at the margin of the seventh and eight peripheral bones, in Rionegrochelys caldieroi the greatest width is at the margin of the fourth peripheral bones ( MPCA-AT 258 carapace maximum width 410 mm). The nuchal notch, the carapace width/length ratio of 1.03, and the curved lateral margins of the posterior peripherals produce a heart-shaped carapacial outline. Although this carapace shape is a characteristic of this species, intraspecific variation in carapace outline is recognized in some chelid species (e.g., Chelus fimbriatus, Pritchard and Trebbau 1984 ; Sánchez Villagra et al. 1995). These authors point out that the carapace outline of this extant species can be oval, subquadrangular with straight lateral sides, or with expanded anterior or posterior margins. However, the heart-shaped outline of the Rionegrochelys caldieroi carapace is an unusual shape for both extant and extinct panchelid turtles ( Maniel and de la Fuente 2016).

The carapace of Rionegrochelys caldieroi is decorated with relatively sharp longitudinal crests on the costal bones, as in some Australasian chelids (e.g., Elseya novaeguineae, USNM 313654). Along the midline, a discontinuous keel is recognized from the first neural bone to the suprapygal bone. Although the carapace decoration partially obscured sutures between bones in several sectors, the shell seems to be formed, as in crown pleurodires, by one nuchal, eight neurals, 16 costals, 22 peripherals, one suprapygal, and one pygal bone ( Maniel and de la Fuente 2016).

The strong nuchal emargination is formed by the first peripheral and the nuchal bone. This emargination is deeper than the condition recognized in Yaminuechelys gasparinii and Y. maior ( de la Fuente et al. 2001; Bona and de la Fuente 2005). Although the nuchal notch of Rionegrochelys caldieroi is strongly developed, it is not reaching the first costal as in Araripemys barretoi ( Meylan 1996) . The anterior peripherals, the bridge peripherals, and the posterior peripherals show a strong gutter. Each gutter end is coincident with a marginal scute that extends over half of two consecutive peripheral bones. The posterior free margin of the peripheral bones is slightly indentation in coincidence with the marginal scutes. A more extreme condition can be recognized in the panpleurodire Platychelys oberndorferi ( Bräm 1965) and in the chelid Chelus fimbriatus (Sánchez-Villagra et al. 1995) which is formed by a strong indentation of the posterior peripheral bones.

The nuchal bone is twice as wide as long, with a wide cervical scute. Although the costal-neural sutures of the first and second neural bones are not apparent on the left side in dorsal view, they are recognized in visceral view, these neural bone are subquadrangular in shape. The third to fifth neurals are also sub quadrangular, while the sixth and seventh neural bones are hexagonal. The anterior neural bones are relatively wide as in the extant Chelus fimbriatus . This neural pattern with predominant sub quadrangular prezygapophysis

C

neural bones deviates from the more frequent chelid condition characterized by narrow quadrangular or hexagonal neural bones ( Pritchard 1988). The suprapygal bone is quite large and subpentagonal in shape, while the pygal is nearly trapezoidal. The eighth pair of costal bones contacts one another along the carapace midline. The first to fourth costals have parallel lateral sides, while the lateral end of the fifth and seventh costal bones is much narrower than the lateral end of the adjacent elements.

Costals 1–8 are preserved on both sides of the holotype. As is typical in turtles, costal 1 is the largest costal bone.

is also wider than long. This bone contacts anteromedially the nuchal, anterolaterally peripherals 1–3, laterally peripheral 4, medially neural 1 and 2, and posteriorly costal 2. Costal 2 contacts anteriorly costal 1 and laterally peripherals 4 and 5. Both costals 2 contact posteriorly costals 3. Both costals 3 contact laterally peripherals 5 and 6, medially neurals 3 and 4, and posteriorly costal 4. Costals 4 contact laterally peripherals 6 and 7, medially neurals 4 and 5, and anteriorly and posteriorly costals 3 and 5, respectively. Costals 5 contact anteriorly and posteriorly costals 4 and 6, respectively, laterally peripherals 6 and 7, and medially neurals 5 and 6. Costals 6 contact laterally peripherals 8 and 9, medially neurals 6 and 7, anteriorly costal 5, and posteriorly costal 7. Costals 7 contact laterally peripherals 9 and 10, and medially neurals 7 and 8. Costals 8 contact each other in the midline of the carapace and anteriorly contact neural 8

and costal 7, laterally peripherals 10 and 11, and posteriorly the suprapygal. The suprapygal is pentagonal and contacts anterolaterally costal 8 and posterolaterally peripheral 11. The pygal is trapezoidal in shape and contacts anteriorly the suprapygal and laterally both peripherals 11.

The peripheral bones are relatively narrow in the anterior free margin and slightly wider in the posterior one. Peripheral 1 is the largest and, like the other peripherals of the anterior margin, is trapezoidal in outline. This bone contacts the nuchal medially, peripheral 2 laterally, and costal 1 posteriorly, as is usual in turtles. Peripheral 2 contacts peripheral 1 medially, peripheral 3 laterally and costal 1 posteriorly. The third to seventh peripheral bones contribute to the bridge. As well as the second peripheral, the bridge peripherals, and the eighth to eleventh peripheral bones are characterized by strongly dorsally curved, gutterlike margins. The axillary buttress fits between the third peripheral and the first costal, while the inguinal buttress is attached between the seventh peripheral and the lateral extreme of the fifth costal. As is typical in pleurodires, the ilia in Rionegrochelys caldieroi are sutured to the carapace ( Gaffney and Meylan 1988). The iliac suture extends over the posterior area of the seventh costal, the eighth costal, and the anterolateral edge of the suprapygal. A different condition is seen in Yaminuechelys gasparinii and Y. maior where this suture extends over the eighth costal and the anterolateral edge of the suprapygal.

The cervical scute is wider than long. The vertebral scutes are strongly marked on the carapace. The first and fifth vertebral scutes are the widest. The first vertebral scute is twice as wide as long and subrectangular in shape. This scute covers most of the nuchal bone, the caudal-medial portions of both peripherals 1, the medial part of both costals 1, and probably half of neural 1. A slightly sinuous intervertebral sulcus between vertebral scutes 1 and 2 crosses the caudal portion of neural 1. The second and third vertebral scutes are slightly wider than long and subquadrangular in outline. Vertebral scute 2 covers the caudal portion of neural 1, neural 2, and most of neural 3, a small mediocaudal portion of costal 1, the medial part of both costals 2, and a portion of the anteromedial part of costal 3. The intervertebral sulcus between vertebrals 2 and 3 crosses at least neural 3 and both costals 3 in their medial part. Vertebral scute 3 covers the caudal medial portion of both costals 3, the medial part of both costals 4, neural 4, and most of the medial portion of both costals 5. The intervertebral sulcus between vertebrals 3 and 4 with an anteriorly marked inflection crosses both costals 5 in their medial portion, and the posterior part of neural 5. By contrast, vertebral 4 is slightly longer than wide and pentagonal in shape. This vertebral scute covers neurals 6–8, the caudal medial part of costals 5, the medial part of costals 6 and 7, and the cranial medial part of costals 8. The intervertebral sulcus between vertebrals 4 and 5 crosses both costals 8. The fifth vertebral scute is slightly wider than long and characterized by a three lobed posterior margin. This vertebral scute covers part of the caudal portion of both costals 8, most of the suprapygal, and small portion of the proximal margins of the pygal and peripheral bones 11. Four pairs of pleural scutes are recognized in Rionegrochelys caldieroi as is usual in turtles. Pleural 1 is slightly longer than wide and covers the posterolateral portion of peripheral 1, the medial part of peripherals 2–4, the central and lateral part of costal 1, and the cranial centrolateral portion of costal 2. Pleural 2 is wider than long and covers costals 2–4. Pleural 3 is also wider than long and covers costals 4–6. Pleural 4 is as wide as long and covers costals 6–8. The interpleural sulci between pleural scutes cross costals 2, 4, and 6 as usual in turtles. The sulcus between pleural 4 and vertebral 5 crosses costals 8.

On the anterior margin of the carapace, marginal scutes 1–4 are recognized. Marginal scutes 4–8 are also identified on the right and left peripheral bridge. Although the intermarginal sulcus between marginal 1 and 2 is scarcely discernible, marginal scute 1 is subrectangular in shape, as does marginal scute 2. Marginal scute 1 covers the proximolateral sector of the nuchal and only the cranial medial part of peripheral 1. Marginal scutes 2–4 also cover two peripheral bones each without extending onto costal bone 1. From marginal scutes 5–11 (with the exception of marginal 10), the scutes cover the costal bone and show an alternating pentagonal and rectangular outline. Marginal 12, pentagonal in shape, covers the pygal, peripheral 11, and the suprapygal.

Plastron: The plastron of the holotype of Rionegrochelys caldieroi is preserved in good condition. It is medium sized (450 mm length along the midline) and slightly longer than the carapace (430 mm length along the midline). The anterior and posterior lobes are nearly equal in length. The bridge (= axillo-inguinal distance) is about 70% of the anteroposterior length of the posterior plastral lobe. The relative length of the bridge of Rionegrochelys caldieroi is greater than in long necked chelids such as Yaminuechelys and Hydromedusa or short necked chelids such as Prochelidella portezuelae ( de la Fuente 2003) and Phrynops geoffroanus ( AMNH 79048, USNM 306646), but it is shorter than the bridge of other extinct species (e.g., Bonapartemys bajobarrealis ; see Lapparent de Broin and de la Fuente 2001).

The broad anterior plastral lobe (width/length ratio 1.71) in Rionegrochelys caldieroi is U-shaped. As in the panpleurodire Platychelys oberndorferi ( Bräm 1965) and the chelid Chelus fimbriatus ( AMNH 70638, USNM 64154), the anterior lobe extends beyond the anterior margin of the carapace. The posterior plastral lobe of Rionegrochelys caldieroi is as long as wide. The lateral margins of the posterior lobe are curved and have a strong femoral-anal notch, as is usual in species of the Phrynops geoffroanus complex (see Rhodin and Mittermeier 1983). The anal notch in Rionegrochelys caldieroi is U-shaped as in Bonapartemys bajobarrealis and Lomalatachelys neuquina , and unlike the V-shaped condition of Yaminuechelys gasparinii among extinct chelids. However, intraspecific variation of this feature has been pointed out in some fossil and extant pleurodires ( Wood and Díaz de Gamero 1971; Cadena et al. 2008; Ferreira et al. 2016).

The epiplastra in Rionegrochelys caldieroi are long and broad with a relatively short medial contact. These bones are partially separated by a large, rounded entoplastron. Between the large hyo and hypoplastra, the mesoplastra are located. They are cuneiform and they are relatively long in comparison to those of Yaminuechelys spp. The xiphiplastra show slight interdigitating sutures with the hypoplastra. They are broad, but deeply notched at the limit imposed of the femoral-anal sulcus. On their visceral surface, the pubis and ischium are attached by a suture to the xiphiplastron. The pubic scar is lateral in position and obliquely oriented at an obtuse angle with respect to the plastral midline, whereas the ischial scar is L-shaped with the short branch of the L extended on the xiphiplastral tips and the longer one oriented slightly obliquely towards the shorter. The xiphiplastral tips end in nearly blunted margins.

As in other pleurodires, Rionegrochelys caldieroi has six pairs of plastral scutes (extragular, humeral, pectoral, abdominal, femoral, and anal) and one odd scute (gular). The plastron has a simple extragular-gular scheme with small extragular scutes on the epiplastra and a small, subtriangular gular scute over the anterior margin of the entoplastron. The large entoplastron is crossed posteriorly by the humero-pectoral sulcus, which is unusual among South American panchelids. An entoplastron crossed by this sulcus can otherwise be seen in some Australasian species, such as Elseya novaeguineae ( USNM 313654), E. schultzei and E. rhodini

Thompson et al. 2015), E. flaviventralis (Thompson and Georges 2016) , Emydura macquarii ( NHMUK 86-8-26-5), and Rheodytes leukops ( QM J 85198). The interfemoral sulcus is longer than any of the other median sulci of the plastron. The interanal sulcus and gular scutes are the shortest, whereas the interpectoral sulcus is longer than the interhumeral or interabdominal sulci. This peculiar plastral formula is recognized in some specimens of extant Chelus fimbriatus e.g., USNM 64154). Although many authors have used these midline contact lengths of plastral scutes to characterize species of turtles, Lovich and Ernst (1989) and Sánchez-Villagra et al. (1995) reported a great amount of intraspecific variation in extant turtles such as Mauremys reevesii , Graptemys pulchra , Platemys platycephala , and Chelus fimbriatus . The lateral cuneiform mesoplastra are crossed by the pectoro-abdominal sulcus. A similar condition can be seen in other extinct Patagonian species of panchelid turtles e.g., Bonapartemys bajobarrealis , Linderochelys rinconensis , Lomalatachelys neuquina , Prochelidella portezuelae ,

Yaminuechelys gasparinii , Y. maior ) and platychelyid panpleurodire such as Notoemys oxfordiensis , Notoemys laticentralis , and Platychelys oberndorferi (see Bräm 1965; de la Fuente and Iturralde-Vinent 2001; de la Fuente et al. 2001, 2007; Lapparent de Broin and de la Fuente 2001; de la Fuente 2003; Bona and de la Fuente 2005; Lapparent de Broin et al. 2007; Cadena and Joyce 2015).

Pelvic girdle: The pelvic girdle is represented by both right and left halves in the holotype ( Figs. 4 , 5 ). Each one is tri-radiate in lateral view. As is typical in pleurodires, the pubis and ischium of each half are attached by suture to the xiphiplastron. The iliac blade of the ilium expands dorsally to be attached by suture to the carapace. The pubis is sutured only by the lateral process, whereas the ischium is suturally attached by a broad surface extending from its symphysis to a lateral process. As is typical in pleurodires, the pubis and ischium are separated from each other by a large and confluent thyroid fenestra.

Thoracic vertebrae. At least six dorsal vertebrae are preserved in the holotype of Rionegrochelys caldieroi . Among

Fig. 8. Shell bone histological section of the panchelid turtle Rionegrochelys caldieroi gen. et sp. nov. (MPCA-AT 26) from Parrita site, Upper Cretaceous. → A. Black and white processed image from costal element. B. Close view of external cortex in costal element showing a resorption line. External cortex of peripheral element showing structural fibers (C), a resorption line and lamellar bone (D). E. Vascularization in external cortex of costal element. F. General view of cancellous bone of peripheral element. G. Transition in the orientation of PFB (parallel-fibered bone) in the internal cortex of costal element.Abbreviations: BL, bone lacunae; ISF, interwoven structural collagenous fibre bundles; LB, lamelar bone; PFB, parallel-fibred bone; RL, resorption line; SF, structural fiber; ShF, Sharpey’s fibres; SO, secondary osteon; SVC, simple vascular canal; TB, bone trabeculae; VCO, vascular canal opening to the external surface.

them, the first, second, and third are in articulation and in good condition, allowing detailed description ( Fig. 6 ). All contacts of the preserved thoracic vertebrae are platycoelous synchondroses. Thoracic vertebra 1 is well preserved and is as long as wide. The anterior articular end is concave facing anteriorly and slightly ventrally. It is also as wide as long. In ventral view, thoracic vertebra 1 is wide anteriorly and tapered posteriorly. A different condition is seen in other extant and extinct crown chelids ( Fig. 7 ), where an hourglass shape is the most common pattern recognized in the ventral view of the first thoracic vertebra. The well-developed prezygapophyses face medio-dorsally and are laterally strongly divergent. Thoracic rib 1 is articulated with the anterior end of thoracic vertebra 1, whereas thoracic rib 2 is articulated between the posterior end of thoracic vertebra 1 and the anterior end of thoracic vertebra 2. Thoracic vertebra 2 is longer than the first one, and longer than wide. Its anterolateral end contacts thoracic rib 2, whereas its posterolateral end contacts thoracic rib 3. Thoracic vertebra 3 is also slightly longer than wide like the second one. The anterolateral margin of this thoracic vertebra contacts thoracic rib 3, whereas the posterolateral margin contacts thoracic rib 4.

Paleohistology.—The microanatomy shows a compact diploe structure with the external and internal cortex framing in the interior area of cancellous bone (Fig. 8A). The external cortex is thicker, double in size compared with the internal cortex. The cancellous bone is well developed, occupying 70% of the cross-sectional area in peripheral elements and less than 50% in costal elements. The osteohistology of all the shell elements is described together. Variation among samples is mentioned if applicable.

External cortex: The external cortex is mostly composed of primary bone. In the peripheral plates, primary bone consists of interwoven bundles of structural collagenous fibers. On the other hand, costal plates are formed by mineralized collagenous fibers arranged parallel/sub-parallel to the external surface. These fibers exhibit two main orientation, which are parallel and transversal to the progression of the element (Fig. 8B, C). Sharpey´s fibers are present in the costal plates. They are short and oriented mostly perpendicularly or oblique to the outer surface. Resorption lines associated with successive episodes of bone resorption and deposition are clearly observed in the outer (ornamented) portion of the cortex of one peripheral and one costal plate Fig. 8B, D). Vascularization is mostly formed by simple vascular canals that run in parallel or perpendicular to the anteroposterior axis. Simple vascular canal openings to the external surface can be clearly made out (Fig. 8E). Some primary osteons are also observed and these commonly anastomose. Secondary osteons are more commonly distributed in the inner (i.e., perimedulary) portion of the cortex. These osteons are more abundant in some costal plates, in which they even reach the outer cortex (Fig. 8B). Secondary osteons have bone composed of alternating lamellae (Fig. 8B). Bone cell lacunae are commonly arranged following the orientation of the structural fibers in which they are embedded.

Short canaliculi are preserved. Growth marks are present, mostly discontinuous, and not easily discerned.

Cancellous bone: The cancellous bone is quite massive and strongly remodeled. Short trabeculae appear in the costal elements and long ones in the peripheral elements. The trabeculae themselves are composed of centripetally deposited secondary lamellar bone formed over different growth generation with variation in the orientation of each lamella. Intertrabecular spaces are generally small and circular or sub-circular in section. Interstitial areas within the trabecular bone are composed by primary and secondary bone, as seen in the external cortex. Flattened bone cell lacunae follow the centripetally deposited lamellar bone linings (Fig. 8F).

Internal cortex: The internal cortex is composed mainly of parallel-fibered bone matrix that can locally form lamellar bone. In one costal element, the fibers are parallel to the latero-medial axis in the central area (which corresponds to the rib), and gradually change their arrangement toward the suture margins, where they become parallel to the anteroposterior axis (Fig. 8G). This is made visible by the monorefringent properties of the bone in the center and the birefringent properties toward the margins, as well as by the change in the shape of the bone cell lacunae, which are circular/ sub-circular in section in the center and strongly elongated and flattened toward the suture margins. Vascularization is typically poor (mainly avascular in several cases). Some simple vascular canals and primary osteons appear to be longitudinally oriented. At least five lines of arrested growth are visible (Fig. 8G).

Sutures: The structure of sutures could be studied in the three costal elements. The microanatomical structure is typically “peg and socket”. The matrix principally consists of woven bone. Dense Sharpey´s fibers are oriented parallel to the protrusions in all samples. In some samples, Sharpey´s fibers continue into the cancellous bone.

The results of the compactness parameters calculated for a costal element of Rionegrochelys caldieroi using BONE PROFILER Software were: modeled compactness 80.6%, lowest compactness at the center 11.1% (SE 0%), modeled compactness at the center 70.5%, compactness at the maximum periphery 87% (SE 0%), modeled compactness at the periphery 87.2%, compactness at the transition between cancellous bone and compact bone (point P) 36% (SE 0.6%), and the slope of compactness change at point P 1.15 (SE 0.008%).

Stratigraphic and geographic range.— El Anfiteatro, Río Negro Province, Argentina. Plottier Formation ( upper Coniacian–lower Santonian ), Rio Neuquén Subgroup, Neuquén Basin .

Figures

Fig. 4. Photographs of the holotype of the panchelid turtle Rionegrochelys caldieroi gen. et sp. nov. (MPCA-AT 258) from Parrita site, Upper Cretaceous. Carapace in dorsal (A) and visceral (B) views. Plastron in ventral view (C). Carapace and plastron in anterior (D) and lateral (E) views. Note suturally attached pelvic girdle.

Fig. 5. Explanatory drawings of the holotype of the panchelid turtle Rionegrochelys caldieroi gen. et sp. nov. (MPCA-AT 258) from Parrita site, Upper Cretaceous. Carapace in dorsal (A) and visceral (B) views. Plastron in ventral view (C). Carapace and plastron in anterior (D) and lateral (E) views. Note suturally attached pelvic girdle.

Fig. 6. The holotype of the panchelid turtle Rionegrochelys caldieroi gen. et sp. nov. (MPCA-AT 258) from Parrita site, Upper Cretaceous. Thoracic vertebrae 1–3 in dorsal (A), ventral (B), and lateral (C) views. Photographs (A1–C1) and explanatory drawings (A2–C2).

Fig. 7. Comparison of thoracic vertebrae 1–3 in some extinct and extant pleurodiran turtles. A. Chelodina colliei Gray, 1856 (NHMUK 64-12-22-66). B. Elseya dentata (Gray, 1863) (NHMUK 76-5-19-27). C. Rionegrochelys caldieroi gen. et sp. nov. (MPCA-AT 258). D. Chelus fimbriatus (Schneider, 1783) (MZUSP 2619). E. Phrynops hilarii (Duméril and Bibron, 1835) (MHNSR H-1550). F. Platemys platycephala (Schneider, 1792) (MHNSR H-1554). G. Rheodytes leukops Legler and Cann, 1980 (QMJ 7693). H. Acanthochelys macrocephala (Rhodin, Mittermeier, and McMorris, 1984) (MACN H-8288). I. Hydromedusa tectifera Cope, 1870 (MHNSR-H 1615). J. Mesoclemmys nasuta (Schweigger, 1812) (MACN H-11967). K. Podocnemis sextuberculata Cornalia, 1849 (MZUSP 2501). L. Pelomedusa subrufa (Bonnaterre, 1789) (SMF 7953). M. Yaminuechelys gasparinii de la Fuente, Lapparent de Broin, and Manera de Bianco, 2001 (MPA 86-86-IC). Scale bars 20 mm.