Notoemys zapatocaensis, RUEDA & GAFFNEY, 2005

RUEDA, EDWIN ALBERTO CADENA & GAFFNEY, EUGENE S., 2005, Notoemys zapatocaensis, a New Side-Necked Turtle (Pleurodira: Platychelyidae) from the Early Cretaceous of Colombia, American Museum Novitates 3470 (1), pp. 1-20 : 13-15

Notoemys zapatocaensis ( fig. 6 ) show differ­

ences with those in Notoemys laticentralis . The first marginal lies on the nuchal and peripheral 1, as in N. laticentralis , and marginal 2 extends from peripheral 1 onto peripheral 2, as in N. laticentralis . Marginal 3, however, is a small, oval scale, lying on the edge of peripheral 2, and not extending onto peripheral 3. This may be related to the apparent reduction of peripheral 3, which seems to be a small ossification in the peripheral 2–peripheral 4 suture (see above). Marginal 4 barely extends onto peripheral 2, a condition not found in N. laticentralis , Platychelys , or other pleurodires, which have marginal 4 lying on peripherals 3 and 4. As in N. laticentralis and Platychelys , the anterior marginals are short and restricted to the edges of the peripherals and do not extend onto the costals.

Marginal 5 is not preserved; marginals 6 to 11 are very similar to those in N. laticentralis . The 8th and 10th marginals are fivesided rather than four­sided, as they extend medially along the sulci between pleurals. This is in both N. zapatocaensis and N. laticentralis (and seems to be in N. oxfordiensis ), but not Platychelys . There are no supramarginals or anal/pygal scales in Notoemys , as occur in Platychelys .

SHELL SHAPE AND SURFACE TEXTURE

Notoemys and Platychelys are characterized by a shell that has a wide, straight, anterior edge, rounded anterolateral margins followed by the widest part of the shell around costals 4 and 5, with a distinctive posterior taper and nearly straight margins. Notoemys differs from Platychelys in having the lateral edges more parallel rather than more rounded. Notoemys zapatocaensis fits this pattern closely. It differs from other Notoemys only in having a more pronounced degree of serration on marginals 7 to 11, but it is not serrated to the degree seen in Platychelys . The anterior half of the shell in N. zapatocaensis is not well enough preserved to see if these marginal sulci are also more deeply incised.

The carapace surface ( fig. 3 ) has a large number of circular pits, particularly in the area of the vertebral scales. The shell surface is well preserved and shows a smooth surface with a slight, irregular granulation. There is distinct doming along the midline, rising to a protuberance just anterior to the posterior sulcus of each vertebral, in the same position as the much higher projections seen in Platychelys . Notoemys laticentralis has a low, midline ridge that is not divided by the vertebrals. In a few places on the pleurals and vertebrals of IPN 15­EAC 140120031, the surface shows a very slight radiating pattern of ridges, similar to that in Platychelys . N. laticentralis has a smooth surface, particularly well preserved in the type, that shows no ridges and no pleural doming.

PLASTRON BONES

HYPOPLASTRON: Most of the right and left hypoplastra are preserved ( figs. 9 , 10 ). The anterior margin shows the contact with the mesoplastron. Dorsomedially, the margin is broken, and the bone is thin, but there is no sign of a fontanelle. Medially, both hypoplastra meet on the midline. Posteromedially, both hypoplastra show a thin, natural edge, indicating a possible narrow fontanelle, just anterior to the xiphiplastron contact. The femoral–abdominal sulcus is not visible, although the area where it is usually located is present on both sides.

XIPHIPLASTRON: Most of both xiphiplastra are present ( figs. 9 , 10 , 11 ), but broken along their medial edges, so there is no midline contact. There is no indication of a fontanelle on the xiphiplastron; the medial margins are all broken edges. On the ventral surface, there is a clear anal–femoral sulcus, with an indentation on the lateral xiphiplastron margin. The xiphiplastron narrows posteriorly and comes to a rounded margin, as in Platychelys . There is an anal notch, also as in Platychelys . Although Notoemys laticentralis is not well preserved in this area, what is known is entirely consistent with the Colombian xiphiplastron.

The pubic scar ( fig. 11 ) is covered by the pubis on both sides, but it is clearly wide and relatively large, and reaches the lateral margin of the xiphiplastron, in contrast to podocnemidids and bothremydids. The ischiac scar is visible on the left side; the ischium is in contact on the right side. The ischiac scar is relatively large, reaching the lateral edge of the xiphiplastron. The scar is roughly triangular, but widens medially to reach the midline, in contrast to bothremydids and podocnemidids.

PELVIS

ILIUM: The ilium ( fig. 8 ) is preserved on both sides, with thoracic ribs 9, 10, and 11 reaching it. These are very similar in position to those in Platychelys . The iliac articulation is on costals 7 and 8 in Notoemys zapatocaensis . It seems that the medial edge of peripherals 10 and 11 lie just against the ilium, so that the sutural scar does not quite reach the peripherals. The suprapygal is less clear, but it also does not seem to have the iliac scar on it, although this is not clear anteriorly. The ilium blade is elongate, without a lateral process seen in pelomedusids and podocnemidids. The ilium neck is shorter than it is in Pelomedusoides. The acetabulum shows the usual tripartite formation; it is best preserved on the right side. The articulation surface is wider and oval as in Platychelys , rather than more circular as in Pelomedusoides.

PUBIS: The right pubis is in articulation and nearly complete, although much is obscured by matrix. The anterior process is damaged on both sides and the shape of the pubic scar ( fig. 11 ) can only be seen in a few places, but it is relatively wide, as in Platychelys , rather than narrow as in Pelomedusoides. The thyroid fenestra is poorly preserved, but enough can be seen to show that it was confluent and large as in Platychelys , not small as in Proganochelys . The pubis contact goes right to the edge of the xiphiplastron, as in Platychelys . It is not retracted from the edge as in Pelomedusoides.

ISCHIUM: Most of the right ischium is present, but its medial margin is missing. The ischium scar ( fig. 11 ) is preserved on the left xiphiplastron and some of the left ischium can be articulated on it. The right ischium is disarticulated from the acetabulum and moved posterodorsally. The ischium of Notoemys has a wider shaft than in Pelomedusoides and its posterior process is more like a sheet of bone than a column.

Figures

Fig. 6. Notoemys zapatocaensis, n.sp. Restoration of carapace in dorsal view. Scales labeled on left, bones on right.

Fig. 3. Notoemys zapatocaensis, n.sp. IPN IS­EAC140120031. Dorsal view of carapace.

Fig. 9. Notoemys zapatocaensis, n.sp. IPN IS­EAC140120031. Ventral view of shell with plastron elements.

Fig. 10. Notoemys zapatocaensis, n.sp. Key to figure 9.

Fig. 11. Notoemys zapatocaensis, n.sp. Restoration of known plastron elements. Scales labeled on left, bones on right.

Fig. 8. Notoemys zapatocaensis, n.sp. Key to figure 7.