Podocnemis tatacoensis, Cadena & Vanegas, 2023

Cadena, Edwin-Alberto & Vanegas, Rubén Dario, 2023, A new fossil turtle ends the controversy on the occurrence of the extant genus Podocnemis Wagler, 1830 at the Miocene fauna of La Venta, Colombia, Geodiversitas 45 (3), pp. 127-138 : 129-132

Podocnemis tatacoensis n. sp.

( Figs 1 ; 3 )

urn:lsid:zoobank.org:act:D0A48C11-8B8C-44BE-AF28-E5348C9051B9

HOLOTYPE. — Specimen VPPLT-1727, nearly complete shell missing: left peripheral 1; the most anteromedial portion of nuchal; left costal 4; portions of left costals 2, 3, and 5; right costal 2, portions of right costal 5, peripherals 8, 9, and 10; portions of peripherals 9-11; portion of the left epiplastron, and the most anteromedial region of hyoplastron.

DIAGNOSIS. — Podocnemis tatacoensis n. sp., differs from all other extant species of Podocnemis by having eight neurals, of which neural 8 interrupts the medial contact between costals 7 and the most anteromedial portion of costals 8. It shares with P. unifilis , P. vogli and P. erythrocephala three lateral musk ducts in each hyoplastron-peripherals contact. It shares with P. unifilis , P. sextuberculata and P. negrii keeled neurals. It shares with all extant Podocnemis spp. a nuchal bone being much wider than long. It shares with all extant and many fossil pelomedusoids (except P. pritchardi ) a nearly rounded mesoplatra. It shares with all extant podocnemidids ( Podocnemis spp. , Erymnochelys madagascariensis and Peltocephalus dumerilianus ) at least one musk foramen located at the most anterior tip of the sutural contact between hyoplastron and peripherals (axillary buttress region).

TYPE LOCALITY. — La Repartidora locality (3°19’40.98”N, 75°5’58.63”W), La Tatacoa Desert, Huila Department, Colombia.

ETYMOLOGY. — ‘ tatacoensis ’, from the Tatacoa Desert.

STRATIGRAPHY, OCCURRENCE AND AGE. — Southeast from the Centro Poblado La Victoria, La Repartidora locality (3°19’40.98”N, 75°5’58.63”W), La Tatacoa Desert, Huila Department, Colombia. Lower segment of La Victoria Formation ( Guerrero 1997), Middle Miocene (Serravallian) 13.778 ± 0.081 Ma ( Flynn et al. 1997). San Alfonso Beds ( Montes et al. 2021) ( Fig. 2A ).

A Gr. Fm. M

n

.

1

Cartographic Units B AGE

(Ma)

System Series Stage MOLECULAR FOSSIL RECORD

An 0

C

5

Formation

R

n

An 5 C

.

2

5

Undifferentiated Formation

Villavieja

12.21±0.107 Ma

2.5

5.3 Peltocephalinae

Villavieja El Cardón Beds Red 23

MIOCENE Serravallian Group Honda R C

AAn 5 2 Cerbatana Cerbatana

Tatacoa

La Venta

Beds

Beds

Cong

Red

Beds. 12.93 12.512 ± ± 0.23 0.102 Ma Ma 34 56

Formation

R1 Tatacoa

Chunchullo

Chunchullo Beds

Sandstone

Sandstone Beds

Beds

13.342±0.408

P Podocnemis Podocnemis .

Ma

expansa cf pritchardi .

66

Peltocephalus Podocnemis

Victoria ABn 5 C Cerro Cerro Beds Gordo Gordo Sandstone Beds 13.651±0.107 Ma 85.74 Ma

La

13.778±0.081 Ma 100

.

La

San Alfonso Beds

Podocnemis tatacoensis n. sp.

DESCRIPTION AND COMPARISONS

Carapace

The carapace of Podocnemis tatacoensis n. sp. ( Fig. 1A, B ) is elongated (23.2 cm maximum length) with anterior (16.5 cm) and posterior (17.5 cm) regions exhibiting almost similar width. This aspect shows wide variation among podocnemidids, but it is very common that the carapace of P. expansa , P. lewyana and P. sextuberculata are wider in the posterior region, a condition maintained during their ontogeny. A similar shape is exhibited by the fossil Podocnemis pritchardi (here reattributed to the genus), but is unknown for P. medemi (here reattributed to the genus) and P. negrii ( Carvalho et al. 2002, here reattributed to the genus) due to preservation. The bone surface of P. tatacoensis n. sp. is smooth as in almost all other extant and fossil podocnemidids. The carapace exhibits a low domed shape in lateral and anterior views ( Fig. 1 C-E).

The nuchal bone of P. tatacoensis n. sp. is trapezoidal in shape, being much wider than long. This was considered to be a diagnostic feature of Podocnemis by Gaffney et al. (2011). The neural series is composed of eight bones. This contrasts all extant Podocnemis and the fossil P. negrii , which exhibit seven neurals. Some specimens of P. sextuberculata and P. lewyana exhibit six neurals, similar to the fossil P. pritchardi , as well as the extant podocnemidid Erymnochelys madagascariensis . The neural series number is unknown for P. medemi due to preservation. In the extant podocnemidid Peltocephalus dumerilianus the number of neurals can be either eight or seven. Neural 8 of P. tatacoensis n. sp. hinder a medial contact between costals 7 and the most anteromedial portion of costals 8, but does not reach the suprapygal, as can be the case of other turtles with eight neurals as for example the bothremydid Cearachelys placidoi ( Gaffney et al. 2006) . Neurals 2-4 are moderately keeled dorsally ( Fig. 3A, B ) as in P. sextuberculata , P. negrii and some P. unifilis . Podocnemis tatacoensis n. sp. has eight pairs of costals, eleven pairs of peripherals, a suprapygal and a pygal bone, as in all other extant and fossil podocnenimidids specifically and most pelomedusoids in general. Costal 1 exhibits a strong axillary scar on the ventral surface that occupies most of the central portion of the bone and projects onto peripherals 2 and 3 ( Fig. 3C, D ). The left posterior margin of the carapace of P. tatacoensis n. sp. shows a pathology affecting peripherals 10, 11 and pygal ( Fig. 3E ), potentially caused by a predator attack. There is evidence that the individual recovered from this injury via bone remodeling, expressed as a major thickening and smooth surface of bone in this region ( Fig. 3F ).

The sulci left by the scutes are well preserved in P. tatacoensis n. sp., lacking cervical scute as in all other pelomedusoids. There were five vertebral scutes, vertebral 1 reaching peripherals 1 anterolaterally as in all other podocnemidids and many other pelomedusoids. Vertebrals 2-4 had almost similar width, and vertebral 5 reached peripherals 10. Despite minor variations in the shape, all these vertebrals exhibit the same contacts between each other and pleurals, as well as covered the same bones (neurals, costals, peripherals, suprapygal, and pygal) as in all other extant and fossil podocnemidids. Podocnemis tatacoensis n. sp. had four pleural and twelve marginal scutes, as is common for podocnemidids.

Figures

FIG. 1. — Podocnemis tatacoensis n. sp. from the Middle Miocene (Serravallian), La Tatacoa Desert, Colombia: A, B, carapace in dorsal view; C, D, shell in left lateral view; D, shell in anterior view; F, G, plastron in ventral view. Abbreviations: Abd, abdominal scute; Ana, anal scute; co, costal; ent, entoplastron; epi, epiplastron; Ext, extragular scute; Fem, femoral scute; Hum, humeral scute; hyo, hyoplastron; hyp, hypoplastron; Int, intergular scute; M, marginal scute; mes, mesoplastron; mfo, musk foramina; ne, neural; nu, nuchal; P, pleural scute; pe, peripheral; Pec, pectoral scute; sp, suprapygal; py, pygal; V, vertebral scute; xip, xiphiplastron. Reconstructed bones showed in yellow shading. Scale bar: 10 cm.

FIG. 3. — Podocnemis tatacoensis n. sp. details of its anatomy: A, B, close-up of the keeled neurals 2-4; C, D, left costal 1 in ventral view, sowing the shape of the axillary scar; E, left posterior margin of the carapace showing the bone predation trauma occurred to the peripherals;F, left peripherals 10-11 where the bone healed from the injury increasing the thickness and smoothing the surface; G, H, view of the right pelvic girdle; I, J, close-up of the three lateral musk foramina of the left hyoplastron-peripherals region.Abbreviations:axs, axillary scar; co, costal; hyo, hyoplastron;ili, ilium; isc, ischium; ker, keel rigde; M, marginal scute; mfo, musk foramina; ne, neural; sp, suprapygal; P, pleural scute; pe, peripheral; pub, pubis; py, pygal; res, resin; V, vertebral scute; xip, xiphiplastron. Scale bars: A, B, E, G, H, 2 cm; C, D, 1 cm; F, I, J, 5 mm.

FIG. 2. — Stratigraphic context and temporal frame for Podocnemididae: A, chronostratigraphic context for the Honda Group (La Victoria and Villavieja formations), including the magnetostratigraphy, cartographic units, horizons and radiometric ages, as well as where the fossil podocnemidids occur including Podocnemis tatacoensis n. sp. Redrawn and modified from Montes et al. (2021); B, time of origination for the genera and some species of Podocnemididae based on the molecular hypothesis of Vargas-Ramírez et al. (2008) and fossil record (this study) for the clades that they represent.Abbreviations:Fm, formation;Gr, group;H, Holocene; L, Langhian; M, magnetostratigraphic chrons; Ma, million of years; Pleistoc., Pleistocene; Qut, Quaternary. Dotted lines indicate ghost lineage duration.