A New Extinct Emydid Turtle From the Lower Pliocene of Oklahoma

Part 1

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A New Extinct Emydid Turtle from the Lower Pliocene of Oklahoma

EDWIN C. GALBREATH

University of Kansas Publications Museum of Natural History

Volume 1, No. 16, pp. 265-280, plate 1 August 16, 1948

University of Kansas LAWRENCE 1948

UNIVERSITY OF KANSAS PUBLICATIONS, MUSEUM OF NATURAL HISTORY

Editors: E. Raymond Hall, Chairman; H. H. Lane, Edward H. Taylor

Volume 1, No. 16, pp. 265-280, plate 1 August 16, 1948

UNIVERSITY OF KANSAS Lawrence, Kansas

PRINTED BY FERD VOILAND, JR., STATE PRINTER TOPEKA, KANSAS 1948

22-3340

A New Extinct Emydid Turtle from the Lower Pliocene of Oklahoma

EDWIN C. GALBREATH

In the summer of 1946 a party from the University of Kansas Museum of Natural History visited exposures of the Laverne formation in Beaver County, Oklahoma, at the invitation of Dr. Stuart Schoff of the United States Geological Survey. When examining the marl beds an Emydid turtle was discovered which appears to be an unnamed species of the genus Chrysemys. A description of the new species follows.

Chrysemys limnodytes, new species

Holotype.--University of Kansas Museum of Natural History No. 7676, vertebrate paleontological collection, a turtle consisting of a fragmental anterior portion of a carapace, left part of the plastron, and several marginals collected by the 1946 paleontological field party of the University of Kansas Museum of Natural History.

Geological Age and locality.--Marl beds of the Laverne formation, early Pliocene age, in SW 1/4 Sec. 15, T. 4 N., R. 25 ECM, Beaver County, Oklahoma. The specimen was removed from the marl immediately below the fossil leaf zone (see Chaney and Elias, 1936; Frye and Hibbard, 1940).

Diagnosis.--Size large (see measurements) and differing from other species of Chrysemys in having: The anterior end of the carapace broadly concave, the posterolateral marginals not greatly flared, the posterior end of the plastron broadly indented, the carapace more sculptured and relatively wider.

Description of type.--The specimen had been badly damaged before preservation, and had suffered further damage from exposure before discovery. The anterior and posterior lobes of the plastron had been folded over the bridge, forming a three-ply thickness of bone. Of the carapace, only the following parts are known: Fragment of the nuchal; right 1st, 7th, 8th, and 9th marginals, left 1st, 2d, 7th, 8th, 9th, and 11th marginals; costals 1-5 on the right side; costals 1-4 on the left side; and 1st, 2d, 3d, and 4th neurals. The left half of the plastron is relatively complete, lacking only the epiplastron and entoplastron. The left 7th, 8th, and 9th marginals are joined to the plastron at the inguinal buttress, and the right 7th, 8th, and 9th marginals are attached to the fifth costal. The carapace has smooth contours with no keel present, but on the lower half of the costals there are seven or eight ridges, and the remaining surface of the costals and neurals are rugose. The marginals lack ridges, and the posterolateral marginals are not serrated. The anterior end of the carapace has a broad shallow notch. The first neural is rounded, and the 2d, 3d, and 4th are hexagonal, with the broad ends forward. Anterior margins of the 2d and 3d neurals are concave, and the anterior margin of the 4th neural is straight.

The sulci bounding the scutes are moderately impressed. The width of the first vertebral scute, anteriorly and posteriorly, is less than the width of the second vertebral scute. The costal scutes join the marginal scutes on the marginal plates.

The plastron, broadly indented at the posterior end, does not have the posterior lobe flared laterally as it is in Recent species of Chrysemys, and lacks any pronounced notch at the femoro-anal suture. The humero-pectoral sulcus crosses the plastron behind the entoplastron in a straight line, and reaches the border anterior to the axillary notch. The pectoro-abdominal suture is anteriorly convex at the sides and concave at the midline.

A comparison of this carapace and plastron with a series of specimens of Recent Chrysemys picta and Pseudemys scripta of approximately the same size reveals characters indicated in the following chart:

================================================================== RECENT Chrysemys | Chrysemys limnodytes | RECENT Pseudemys --------------------+------------------------+-------------------- Not serrated. | Posterolateral | Serrated. | marginals not serrated.| --------------------+------------------------+-------------------- Not notched. | Carapace with broad | Notched. | shallow notch at | | anterior end. | --------------------+------------------------+-------------------- Occasional faint | Plastron does not have | Distinct notch at notch at femoro-anal| a pronounced notch at | femoro-anal suture. suture. | femoro-anal suture. | --------------------+------------------------+-------------------- Posterior lobe of | Posterior lobe of | Posterior lobe of plastron flares | plastron does not | plastron does not laterally. | flare laterally. | flare laterally. --------------------+------------------------+-------------------- Carapace smooth. | Carapace has smooth | Carapace has | contours. | depressions and | | elevations. --------------------+------------------------+-------------------- Old specimens | Seven or eight ridges | Ridges cover occasionally have | on lower half of | costals. five or six ridges | costals. | near border of | Remaining surface of | costals. | costals and neurals | | rugose. | --------------------+------------------------+-------------------- No ridges on | No ridges on | May or may not marginals. | marginals. | have ridges on | | marginals. --------------------+------------------------+-------------------- Nuchal smooth. | Nuchal smooth. | Nuchal has ridges. --------------------+------------------------+-------------------- Carapace not | Probably arched less | Greatly arched. greatly arched. | than in Pseudemys, | | but more than in any | | Recent Chrysemys. | --------------------+------------------------+-------------------- Keel often present | No keel present. | Keel often present. at birth, but soon | | lost. | | --------------------+------------------------+-------------------- Anterior and | Anterior and posterior | Anterior width of posterior widths of | widths of first | first vertebral first vertebral | vertebral scute less | scute less than scute approximately | than width of second | posterior width, same as width of | vertebral scute. | or both dimensions second vertebral | | less than width of scute. | | second vertebral | | scute. --------------------+------------------------+-------------------- Ribs do not tend | Ribs not prominent on | Ribs tend to be to be prominent on | costals. | prominent on costals. | | costals. --------------------+------------------------+--------------------

Hay attached considerable taxonomic importance to the characters of the nuchal and I find its characters to be fairly constant in the specimens of Emydidae examined. Although the nuchal of Chrysemys limnodytes is incomplete, it can be distinguished from the nuchals described by Hay as types of his several fossil Emydids. Differences in the nuchal, together with those in the carapace and plastron, serve to distinguish the species from other genera of the Emydidae.

When the specimen is compared with Chrysemys timida Hay, of the Nebraska Pleistocene, many similarities, mostly of generic rank, are seen. Chrysemys limnodytes is broader in relation to length than is either C. timida or any Recent specimen examined of the same size. The greatest allowance possible in estimating the length of C. limnodytes fails to bring the ratio of its breadth to length within the range of Recent specimens of similar size. Data from 96 specimens of Recent Chrysemys picta show that the ratio of length to width is not affected by sex, but that the ratio does vary with the age of the specimen. In young animals the length and width are approximately equal, but with further growth the length becomes relatively greater. Specimens in the length group of 135 to 144 mm. have the widths ranging from 71 to 81 per cent of the lengths. In all specimens larger than this, the ratio is in the low seventies, and the largest specimen, 177 mm. in length, has the width of the carapace amounting to only 74 per cent of the length. The fossil species, C. timida, with a length of 160 mm., has the width amounting to 75 per cent of the length, and C. limnodytes, with an estimated length of 180 mm., has the width amounting to 80.5 per cent of the length. C. timida is widest anteriorly, whereas C. limnodytes and the other species of the genus are widest posteriorly. Less obvious differences between the two fossils are the narrower anterior margin of the nuchal, the concave anterior end of the carapace, the sculptured surface of the carapace, and the relatively wider neurals and longer vertebrals of C. limnodytes.

DIMENSIONS OF THE TYPE SPECIMEN

(In millimeters)

Part 2

Total length of carapace, 180 (estimated); greatest width of carapace, 145 (estimated); height of carapace, more than 50.

Length of plastron, 165 (estimated); width of plastron, 130 (estimated); length of anterior lobe, 45 (estimated); width of anterior lobe, 75 (estimated); length of posterior lobe, 62; width of posterior lobe, 82; length of bridge from axillary to inguinal notch, 60.

PLATES OF THE CARAPACE AND PLASTRON

Nuchal: Width of anterior margin, 12 (estimated); greatest width, 37 (estimated); length at midline, 35 (estimated).

First neural: Greatest width, 13; length at midline, 17. Second neural: Greatest width, 16; length at midline, 14. Third neural: Greatest width, 18; length at midline, 16. Fourth neural: Greatest width, 18; length at midline, 16.

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