Bulletin of Big Bend Paleo-Geo An Open Access Publication from Mosasaur Ranch Museum, Terlingua and Lajitas, Texas All rights reserved This was a private report in 2003 on my thoughts on Platecarpus planifrons. Now we know they were abundant at least in the Big Bend area of Texas. Excuse my grammar Platecarpus planifrons sp.,an early Platecarpinae Mosasaur from the Big Bend area of Texas, ( Terlingua, and Lajitas area,brewster County, Texas. ) Ken Barnes, amateur paleontologist, MOSASAUR RANCH MUSEUM and Geologic Research Center, Lajitas, and Terlingua, Texas, 79852 NOTE : This is only a rough draft of my personal description of my presently private collection of fossils.july, 30, 2003. Ken Barnes, HC 65, Box 300, Alpine, Texas, 79830, phone 432-371-2445. ABSTRACT Platecarpus planifrons is a species of Mosasaur not very well known or described. These specimens are from an early Platecarpinae, ( late Coniacian ), from the upper Boquillas formation, west of Big Bend National Park. Platecarpus planifrons is distinguished from later Platecarpinae ( P. tympaniticus Cope 1869, P. ictericus Cope 1871, etc. ), by not having a dorso medial ridge on the frontal, the quadrates are lighter built with a sharp medial edge of the quadrate shaft, the prefrontal and postorbitofrontal do not meet on the ventral side of the frontal over the orbit, there is a buttress between these two elements.the only published, description of Platecarpus planifrons, that I am aware of, was described as Clidastes planifrons Cope 1875, page 135, and plates XXII and XXIII. Later Williston called it Platecarpus planifrons, Williston, 1898, page 188. INTRODUCTION There have been few published descriptions,(?), of Mosasaurs from the Big Bend area of Texas. I am working on 18 + Mosasaurs in this area on private land west of Big Bend National Park, of which most are Tylosaur nepaeolicus, but a few of these are Platecarpus planifrons. Referred specimens are, ( KB M -11 ), ( KB BB M 13 ),( KB BB M 5 ), and ( KB M 3 SC ), which is the stomach contents of a 7.5 meter +/- Tylosaur nepaeolicus # KB M 3. EXPLANATION of my numbering system is ; KB = Ken Barnes ; BB = Bill Bourbon ( found by ) ; M = Mosasaur ; SC = stomach content ; the number is the order in which they were found. STRATIGRAPHY - All of these fossils were found in the upper Boquillas formation, not far, 50 to 150 feet +/-, below the gradational contact with the Pen formation. The Pen formation is a grey to yellow clay gradating downward into the upper Boquillas formation which is blue grey to yellow flaggy poor limestone and marl in beds from 1 to 6 inches thick that weather into fissile bedding. Inoceramus undulatoplicatus, ( IUP ), is a guide fossil of stratigraphic time, not 1
an index fossil of a certain formation, in this area the formations were named lithostratigraphicly, page 1, Geology of Big Bend National Park, The University of Texas publication NO. 6711,1967. In the Big Bend Ntl. Park, IUP is found near the top of the upper Boquillas fm. 50 +/- miles East of my locations. West of the park IUP has only, so far, been found by me 90 + feet up into the Pen fm ;( See figure #1). IUP was also found by me in the baked, pyroxene-hornfels zone, Pen fm. clay one mile north of Study Butte, Texas, off the east end of Bee mtn. This is also the only location of a?clidastes sp., I have seen in this area, it was found by Gorden Bell when I was showing him IUP locations. DESCRIPTION OF FOSSILS FOUND SKULL PARTS QUADRATES Referred specimens ; ( KB M 11 ), Fig. 2 ; ( KB BB M 5 ), ( KB BB M 13 ), and ( KB M 3 - SC ), Fig. 2 A. The quadrate is one of the most useful bones to identify the species in Mosasaurs. The right quadrate of KB M 11 is identical in shape to the right quadrate of KB BB M 13, the right quadrate of KB BB M 5 is poorly preserved, but identifiable as the same species as the above. The left quadrate of KB M 3 SC was very young, and in the stomach content of a Tylosaur nepaeolicus and is missing some thin and small parts, but is identifiable as the same species as above. Note this stomach content has two more small quadrates in poor shape, and jumbled with other small fossils, but one seems to be the right mate to this one. Here I will describe and compare the quadrates of KB M- 11, Fig. 2, with two quadrates ( YPM # 40434, and YPM # 1277 ), Fig. 3, and Fig. 3 A. I observed and sketched these two quadrates on loan to Gordon Bell at the South Dakota School of Mines lab. at Rapid City, South Dakota in June, 1994. YPM # 40434 is the left quadrate of Platecarpus planifrons, personal communication with Gordon Bell, SDSM, June 1994. YPM # 1277, ( P. Felix ), is figured to be Platecarpus ictericus by Dale Russell, Yale University Bulletin 23, pg. 155. These quadrates from KB M - 11, and YPM # 40434 are comparable with Clidastes Planifrons, 2
( Platecarpus planifrons, Williston ), Cope 1875, pg. 135 137, plate XXII, fig. 5, 5a, 5b,upper pt. right quadrate, and fig. 6, 6a, 6b, lower pt. left quadrate. In all respects the right quadrate of KB M 11 is identical to YPM # 40434, except opposite side and smaller. The medial edge, one half way up the quadrate shaft, is sharp as in YPM # 40434, not broad and rounded as in YPM # 1277. The anterodorsal side of the quadrate has a deep grove as in YPM # 40434, which is shallow in YPM # 1277. The anteromedial edge of the suprastapedial process has a straight narrow small ridge beginning about the stapedial pit and going down the suprastapedial process, Fig. 2 Right and left Quadrates ( KB M 11 ) Posterior view Anterior view Medial view 0 5 3
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Fig. 2 A Quadrates Anteromedial Posterolateral KB BB M 5 Right KB BB M 13 Right Tympanum KB M 3 SC Left 0 5 cm 5
Fig. 3 My ( Ken Barnes ) sketch, June, 1994, at Gorden Bell `s Laboratory, South Dakota School of Mines, ( Yale Peabody Museum specimens ) Left quadrate of Platecarpus planifrons, ( YPM # 40434 ) Anterior Posterior Medial Left quadrate of Platecarpus ictericus, ( YPM # 1277 ) 0 5 cm 6
Fig. 3 A Deep grove Straight and narrow ridge YPM # 40434 Thick, thumb like Not so deep grove Broad, rounded and curved Rounded edge YPM # 1277 0 5 cm To a point 7
forming the posteromedial edge of the stapedial notch.this is the case with YPM # 40434, YPM # 1277 has a broad rounded curved ridge here. The lower end of the suprastapedial process ends quite abruptly with an indention on the posteroventral tip which creates a rounded sharp ventral edge, more like YPM # 40434, but somewhat like YPM # 1277. The stapedial pit is an inverted teardrop in shape, and there is only a thin layer of bone between the pit and the stapedial notch, as in YPM # 40434.The infrastapedial process is large as in both other quadrates, but shaped like YPM #40434. It begins along the posteroventral, rounded, articular edge of the quadrate shaft, and rises posterodorsomedialy towards the tip of the suprastapedial process and ends lateroventraly short of this tip. From this point there is a thin sheet of bone rising and thickening to form the anterolateral side of the stapedial notch. Between this thin sheet of bone and the medial sharp edge of the quadrate shaft there is a deep rounded grove. One quarter of the way up the flat medial side of the quadrate shaft there begins another small grove, it rises to terminate with the sharp medial edge of the quadrate shaft just below the stapedial pit. A very thin layer of crescentric bone extends outwards from the anterolateral edge of the quadrate shaft forming the tympanic ala, this is fragmented on this quadrate with some of it still in the matrix, and part of the squamosal postorbitofrontal shafts are adhered to the anterior side of the quadrate here. The dimensions of this right quadrate is ; medial edge of shaft is 54 mm tall ; lower articular surface is 25 mm across ; suprastapedial process is 38 mm from top of shaft to tip. The left quadrate of, KB M 11, is the same shape as the right, except opposite, and it has been slightly crushed front to back closing off the stapedial notch. Note : The right quadrate of KB BB M -13 is well preserved and even has the tympanum preserved, See fig. 2 A. FRONTAL ; KB M 11, see Fig. 4, 4-A,4-B The frontal, parietal, and right postorbitofrontal squamosal, are articulated. The frontal of Platecarpus planifrons is its name sake, ( flat frontal ), it dose not have a dorsomedial ridge on the frontal as does other Platecarpinae. DESCRIPTION of the dorsal side of the frontal ; The premaxillae attach onto a narrow dorsomedial grove on the anterior tip of the frontal. The external nares invade the frontal between this anterior tip of the frontal and anterolateral projections that laterally contact the prefrontals. The lateral edges of the orbits is a straight line parallel with the opposite side, then diverges laterally at about 45* and then forms a fairly sharp curve around and towards the midline, this curved area overlaps the postorbitofrontal, which underlies the frontal to a point only slightly under the parallel part of the orbits. The posterior edge of the frontal has two posterior projecting triangles that overlaps part of the parietal, between the triangular parietal table and the anterolateral projecting bar of the parietal. The anterior part of the triangular parietal table only slightly invades the posterior edge of the frontal. This specimen has very small vein like ridges on the dorsal side, probably from crushing. See Fig. 4 A. DESCRIPTION of the ventral side of the frontal; 8
There is a small anterolateral buttress between the sutures for the prefrontal, and the postorbitofrontal, on the underside of the parallel sides of the frontal over orbits. The prefrontal and postorbitofrontal do not contact each other as they do in other Platecarpinae. The olfactory grove is Y in shape medial to posterior limit of the parallel sides of the orbits, with two groves angling posterolateraly for about ½ the distance to the posterior edge of the frontal. From this Y,anteriorly the olfactory grove is narrow and deep to a point just anterior to the anterior limit of the parallel sides of the orbits, at which point it widens to form a large triangular excavation anteriorly to join the external nares. There is a thickening or buttress under the posterolateral wing of the frontal onto which the postorbitofrontal attaches. Note : This frontal from KB M 11 is comparable with Clidastes planifrons, ( Platecarpus planifrons, Williston ) Cope 1875 pages 135 137, plate XXII, figures 1 and 2, including the buttress between postorbitofrontal and prefrontal, no dorsomedial ridge, and parietal only slightly invades the frontal. PARIETAL KB M 11 ; see Fig. 4, 4-A, 4-B Note : The parietal, the right postorbitofrontal, and squamosal are articulated. DESCRIPTION of the dorsal side of parietal ; The triangular parietal table is prominent with its anterolateral corners squared off and anterolateraly in contact with a small posterior projecting triangular part of the frontal.the parietal foramen is medially oval in shape and centered in the triangular parietal table, well posterior to the frontal. The parietal only slightly invades the posterior part of the frontal. There is a thick bar projecting from under the anterolateral side of the parietal table anterolateraly and contacting the posterolateral side of the small posterior projecting triangle part of the frontal, contacting the posterior part of the frontal wing, and contacting the dorsomedial part of the postorbitofrontal. There is a fan of bone between the ventral side of this bar and the ventral side of the medial part of parietal that underlies the small triangular posterior projecting part of the frontal. From the posterior acute apex of the triangular parietal table the posterior part of the parietal slowly widens to form a narrow Y with each parietal bar slowly curving posterolateraly to contact the anteromedial projecting wing of the squamosal. I have most of the triangular parietal table of KB - BB M 13, it is shaped identical to the one described above except smaller and the parietal foramen is more rounded. Note; This parietal is approximately 37 % longer posteriorly than the parietal of P. ictericus as depicted in Text fig. 83, dorsal view of the skull of Platecarpus ictericus, ( reconstructed after AMNH # 1820 x 3/8) on page 150 Yale Univ. bulletin # 23. Text fig. 83, above depicts the parietal invading the frontal extensively, and the parietal bars turning abruptly posterolateraly towards the squamosal. This is not so with the parietal of KB M 11, the parietal only slightly invades the frontal, and the parietal bars form a along smooth curve posterolateraly to the squamosal. DESCRIPTION of the ventral side of the parietal ; The parietal foramen is a large oval in shape tapering to form a smaller, ½ size, oval opening to the dorsal side. There is a long narrow ridge beginning at the suture for the supraoccipital at the rear widening to form a long triangle anteriorly to contact the frontal, with the parietal foramen 9
centered in the broad part of this triangle. Either side of this ridge is a skirt of bone extending a short distance lateroventraly. Anterolateraly from the anterior part of this long triangle there is a wing of bone that underlies the small triangle of the frontal and makes contact with the postorbitofrontal. Note ; This parietal is comparable with Cope 1875, page 135, plate XXII, fig. 1 & 2. SUPRAOCCIPITAL ; KB M 11, see fig. 5. Note : This bone is buried in the matrix with only the posterior side exposed. DESCRIPTION of the supraoccipital. This bone has a knuckle shaped suture to contact the underside of the parietal, and skirts around the perimeter to contact the parietal, prootic and opisthotic. PROOTIC OPISTHOTIC complex, KB M 11, see, fig. 5. DESCRIPTION of prootic opisthotic complex. These elements are fused and viewed as one in each ½, left and right.the left side is still in the matrix with the brain case side exposed, see fig 5. The right side is free from the matrix, see fig. 5, except the distal part which is imbedded in the matrix, and in contact with the spoon shaped supratemporal. These element are normal as far as can be seen, only a cat scan could reveal the foramen etc. POSTORBITOFRONTAL SQUAMOSAL complex, KB - M 11, see fig 4, and fig 5. DESCRIPTION of the left postorbitofrontal squamosal complex. These elements are broken and separated from the frontal and still imbedded in the matrix.the anterior part of the postorbitofrontal, see fig. 4, is bird wing in shape with its dorsal side exposed. The bird wing part of the postorbitofrontal is deeply concave dorsally to fit under the rounded buttress on the ventral side of the frontal wing. The anterior part of the bird wing feathers out to a thin fan to fit the suture on the ventral side of the frontal and butt up against the buttress between this element and the prefrontal. There is a small square bone protruding laterally from the lateral shoulder which should extend ventrally to accept the jugal. The posterior part of the postorbitofrontal and squamosal, see fig. 5, are broken off and overlying the left opisthotic wing still in the matrix. These elements are very long and the dorsal side of the posterior end of the squamosal is exposed and shovel in shape with an anteromedialy directed wing to contact the parietal bar over the supratemporal. DESCRIPTION of the right postorbitofrontal squamosal complex. The right side, see fig. 4, is articulated with the frontal and parietal with the feathered out wing tip stopping just short of the small buttress on the ventral side of the frontal to separate it from the suture for the prefrontal. Broken off and buried medial side down is a small square bone extending latterly from the lateral shoulder of the postorbitofrontal which should extend ventrally to accept the jugal. This bone should have an internal buttress to fit the grove in the posterodorsomedial end of the jugal. The postorbitofrontal bar has a broad connection with the 10
posterior shoulder of the postorbitofrontal and tapers posteriorly joining the squamosal bar,( the separation between them is not visible and part of it is adhered to the anterior shaft of the right quadrate ), tapering more rapidly and curving slightly posterolateraly to the shovel shaped posterior end. There is an impression in the matrix indicating a small wing directed a short distance anteromedialy to join the parietal bar over the supratemporal. RIGHT JUGAL of, KB M 11, see fig. 5. DESCRIPTION of right jugal. The jugal is a curved L in shape with the posterodorsal end being quite broad with a grove on the dorsolateral side to attach to the medial side of a ventrally directed square bone off the postorbitofrontal. The ascending shaft of the jugal narrows and curves ventroanterioly then thins laterally and extends anteriorly in a feather shape under the orbit. Note : There is no posterior tuberosity at the crux of the curve in this jugal. BASIOCCIPITAL BASISPHENOID ; KB M 11, see fig. 6. DESCRIPTION of the basioccipital basisphenoid complex. These two elements are fused in this specimen with a suture line crossing the medullary cavity. At the posterior end of the medullary cavity, and anterior to the occipital condyle, there are two large foramen interring into the basioccipital for the basilar artery. there is a small septum of bone separating these two foramen, and they are slightly offset from each other with the right one being more to the posterior. Just anterior to these two large foramen there are two small openings, ( foramen? ), in the floor of the medullary cavity. In the floor of the medullary cavity of the anterior part of the basisphenoid there is a small ridge of bone with a small foramen (? ) on either side. There may be two very small foramen just anterior to the suture line. In a lateral grove in the basisphenoid above the basipterygoid process, and below the lateral shelf of bone from the rough dorsal side of the basisphenoid there is a foramen entering from the posterior, the exits to the anterior are obscure. Note : These elements need to be cat scanned to determine routs of foramen, etc. BASIOCCIPITAL of KB BB M 5 ; The occipital condyle is all I have, it is broken off but has two groves for the basilar artery. LEFT ARTICULAR SURANGULAR, KB M 11 See figure 7 VERTEBRA KB M 11 has 2 vertebra, one cervical with free hypapophyses, other indt. KB BB M 5 has many vertebra in poor shape, found on the surface, caudal vertebra have free haemal arches. KB M 3 SC this stomach content has many vertebra, one with zygosphenes preserved, caudal vertebra have free haemal arches. 11
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Photos Platecarpus planifrons KB M 11, KB M 3 SC, KB BB M 5, & KB BB M 13 13
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KB M 14, Tylosaur nepaeolicas, (now found to be Tylosaur Kansasensis) 27
Platecarpus planifrons KB M 3 SC, stomach content of a Tylosaur nepaeolicus 28
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Platecarpus planifrons KB BB M 13 31
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Platecarpus planifrons KB BB M 5 34
DISCUSSION AND QUESTIONS ; This Mosasaur was described by E. D. Cope ( 1875 ) pg 135 137 as Clidastes planifrons, probably because the postorbitofrontal and prefrontal do not contact each other under the frontal over the orbit, as is the case with Clidastes. Williston (1898) pg. 188 calls it Platecarpus planifrons. Lane (1943) calls it a doubtfully valid species. Dale A. Russell, (1967) Yale University Bulletin 23 pg. 182, calls it nomen vanum. I have enough evidence that this Mosasaur is valid, and was an early species, (late Coniacian),and it occupied the same waters as Tylosaur nepaeolicus, at least the young or small ones. The largest one I have, (KB M 11), would be only about three meters long. The smallest ones I have are 3 in the stomach content of KB M 3, a 7.5 meter long Tylosaur nepaeolicas, they would be only 1 + meter long. Did larger ones occupy deeper waters? Were they a dead end and went extinct, or did they evolve into later Platecarpinae? Did Clidastes occupy different waters or did they show up later? The only Clidastes I have seen is in the Pen formation above the Boquillas formation, near the IUP beds. REFERENCES COPE, E. D. ( 1875 ) U. S. Geological Survey of the Territories, Cretaceous Vertebrates. Vol. II 1875, Page 135 137 and plates XXII and XXIII. 35
LANE, H. H., ( 1943 ) A Survey of the Fossil Vertebrates of Kansas, page 317. MAXWELL, R. A., J. T. LONSDALE, R. T. HAZZARD, J. A. WILSON. ( 1967 ). Geology of Big Bend National Park, Brewster County, Texas. University of Texas Bureau of Economic Geology Publication no. 6711, 320 pages. RUSSELL, D. A., ( 1967 ), Yale University Peabody Museum of Natural History Bulletin no. 23, 240 pages. WILLISTON, S. W.,( 1898 ) Geological Survey of Kansas Vol. IV, Paleontology, part I, Upper Cretaceous, page 188. 36