6 p., 2 fig.http://paleo.ku.edu/contributions.htm

Eaton, Theodore H., Jr.

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THE UNIVERSITY OF KANSASPALEONTOLOGICAL CONTRIBUTIONSAugust, 1965	 Paper 2A NEW WYOMING PHYTOSAURBy THEODORE H. EATON, JR.[Museum of Natural History, University of Kansas IABSTRACTThe skull of a new species of Angistorhinus, family Phytosauridae, is describedfrom the Popo Agie Member of the Chugwater Formation, Upper Triassic, FremontCounty, Wyoming. It is large but not maximum for the genus, rostrum slenderand slightly concave in dorsal outline, septomaxillaries slender, antorbital fenestraelong and spindle-shaped, skull roof of medium height and broadly curved. Theskull, including palate, is complete except for part of the roof.INTRODUCTIONThe phytosaurs are a suborder, Parasuchia, oflarge semiaquatic thecodont reptiles known fromthe Triassic of Europe and North America. Allexcept one, Paleorhinus (formerly Mesorhinus)fraasi of Germany, are found in Upper Triassicbeds. They comprise a homogeneous family, Phy-tosauridae, of which the most distinctive featuresare their structural analogies with the Crocodilia,which replaced them ecologically in the Jurassicand later periods. Unlike crocodiles, the phyto-saurs had a rostrum composed of the premaxillarybones, and the external nares were located dor-sally, at or behind the mid-point of the skull.The food was probably large fishes and the largerstereospondyl amphibians which occur commonlyin the same beds.The specimen described here is a skull, with-out lower jaw, of a new species of Angistorhinus,found in the Popo Agie Member of the Chug-water Formation, Upper Triassic, in FremontCounty, Wyoming, by a field party from the Uni-versity of Kansas Museum of Natural History inthe summer of 1960. The skull (KU 11659) isunusually well preserved in all parts except theuppermost 2 or 3 inches of the cranium, from thenasal crest posteriorly, which had been exposedto stream erosion before it was found. As is com-monly observed, the teeth had been lost fromtheir alveoli before the specimen was buried. Afew fragments of the missing parts of the skull,but no postcranial bones, were found.ACKNOWLEDGMENTSHere I wish to acknowledge assistance in the field hvRICHARD C. Fox and ROBERT D. PLATZ, and subsequentcareful work of preparation in the laboratory by thc latterand by RUSSELL R. CAMP, who finished preparing theskull for exhibit in the Museum of Natural History at theUniversity of Kansas. TO GEORGE F. CARINI, then a grad-uate student at the University of Missouri, I owe usefulinformation concerning the locality, and stratigraphythe exposures. Dr. WILLIAM A. CLEMENS and CLYDE T.WILLIAsts on a later trip to the area gave further help,especially with stratigraphie measurements. Miss KATHRYNREINHARDT drew the illustrations, except for a part addedby MERTON C. BOWMAN, who also painted the backgroundfor the museum exhibit.LOCALITY AND STRATIGAlong the northeast-facing flank of the WindRiver Range the Mesozoic and late Paleozoicsedimentary beds of the Wind River Basin aretilted upward and truncated, the more resistantrocks forming several parallel ridges at an eleva-RAPHIC RELATIONSHIPStion between 6,500 and 7,500 feet, the lower bedsbeing closest to the main slope of the range.Among these the red beds of the Triassic Chug-water Formation make a nearly continuous beltof exposures having a width of one to three2	 The University of Kansas Paleontological Contributionsmiles. They form an uneven trough boundedlaterally by the overlying buff-colored NuggetSandstone of the Jurassic. Minor ridges occur inthe Chugwater as the result of a few beds of lime-stone or hard sandstone. The Alcova LimestoneMember is the most prominent of these, with athickness of about 5 feet near the locality wherethe skull was found. Below the Alcova strati-graphically (toward the mountains) is the RedPeak Member, and above it the Popo Agie Mem-ber (pronounced "po-p6zhie"). The latter hasreceived particular attention because of the rep-tiles, stereospondyl amphibians, and fragments offishes in its upper levels.The locality for the specimen here described isthe southeast corner of section 14, Township 1North, Range 3 West, Fremont County, Wyom-ing. It is reached by following U.S. highway 287northwest 23 miles from Lander, then turningwest on the Sage Creek road to a point 11 milesfrom the highway. The Popo Agie is then onboth sides of the road, and the bone bed lies 0.25to 0.5 mile to the left (southeast) below an escarp-ment of the Nugget Sandstone. This is evidentlythe Sage Creek Locality, no. 6, of MEHL (1928)from which Borborophagus (Eupelor) wyorning-ensis and Paleorhinus parvus were collected, butin MEHL ' S map (/oc. cit., p. 170) the circle con-taining no. 6, to designate this locality, is not quiteaccurately placed in relation to the south fork ofSage Creek, and it should be in T. 1 N. instead ofT. 2 N. This is confirmed by a letter fromGEORGE F. CARINI, saying, "Dr. MEHL infcrmedn-e that his Sage Creek locality is approximatelythree miles south of the South Fork of SageCreek, just off the St. Lawrence Ranger Stationroad."The dip of the Popo Agie beds here is be-tween 10° and 15°, in a direction 20° east ofmagnetic north. In the low wash at the foot ofthe bluff capped by Nugget Sandstone is a coarselimestone 2 to 3 feet thick, which can be fol-lowed up a gentle slope to the southwest about200 yards, to where the new skull was found ina tributary dry wash, embedded in the same lay-er. From a detached boulder of this bed in thelower wash was taken a part of the interorbitalskull roof of another phytosaur (KU 11660),probably also Angistorhinus, described at theend of this paper. The soft reddish sandstone andgray shale above the limestone contain teeth offishes, labyrinthodonts, and phytosaurs, scraps oflabyrinthodont (Eupelor) and phytosaur bones,and fish scales. Presumably these beds representthe top of the Popo Agie at this locality. TheAlcova Limestone forms another escarpment fac-ing the mountains about 0.5 mile southwest. Thethickness of the Popo Agie here is about 220 feet,and the limestone containing the skull is about50 feet from the top.SYSTEMATIC DESCRIPTIONSIn his recent study of the genera of phytosaursGREGORY (1962) recognized only 5 genera in onefamily and thus greatly simplified the classifica-tion of this group. The genera known from thePopo Agie are Paleorhinus and Angistorhinus,both primitive in having the posterior temporalarches at the level of the top of the skull. Paleo-rhinus is the most primitive, with the externalflares anterior to the antorbital fenestrae, whereasin Angistorhinus and all others they are betweenthose fenestrae. A European species named Meso-rhinus fraasi, placed by GREGORY in Paleorhinus,is the only phytosaur known to retain a parietalforamen; this and its much greater age (Bunt-sandstein of the Lower Triassic) may justify re-tention of the original genus. The remaininggenera, Phytosaurus, Rutiodon, and Mystriosu-chus, are specialized in having the posterior tern-poral arches depressed to form a shelf, underlyingthe insertion of the most dorsal muscles of theneck.Four species were referred to Angistorhinusby GREGORY. Three of them, A. grandis MEHL(1913), A. gracilis MEHL (1915), and A. maximusMEHL (1928), are from the Popo Agie in Wyom-ing, and one, A. alticephalus STOVALL & WHARTON(1936), from the Dockum Group in HowardCounty, Texas. To these should be added thespecies described by CASE (1929) as Brachysuchusmegalodon, also from the Dockum of Texas, forGREGORY has recently reported (at annual meetingof Society of Vertebrate Paleontology, 1964) thatthe posterior temporal arches had been displacedby crushing from a position at the level of the topof the skull, and that they show the widening pos-teriorly that is characteristic of Angistorhinus.FIG. I [Explanation.] 	 A. Ventral view of skull, X0.17.	 B. Dorsal view of skull showing surfaces (oblique in-terrupted lines) where bone was broken away by stream erosion, X0.17.—C. Left lateral view of skull, parts aboveheavy line restored (broken lines), X0.17.A New Wyoming Phytosaur 3FIG. 1. Angistorhintts acolamnis EATON, n. sp., Upper Triassic, Wyoming (see explanation on lacing page).4	 The University of Kansas Paleontological ContributionsThus it is no longer necessary to separate Brachy-suchus from Angistorhinus, although the rostrumis relatively short.The new skull described below differs fromeach of those listed about as much as they differfrom one another, and the nature of the differ-ences seems inconsistent with ordinary individualvariation. Within the genus the most availableand significant characters are those of the skull.It would be necessary to obtain a much largerseries of skulls before the possibility of eitherhorizontal or vertical intergradation could beconsidered.Order THECODONTIA Owen, 1860Suborder PARASUCHIA Huxley, 1875Family PHYTOSAURIDAE Lydekker, 1888Genus ANGISTORHINUS Mehl, 1913ANGISTORHINUS AEOLAMNIS Eaton, n. sp.Figures 1,2Name derived from Gr. Aiohis, god of the winds, andLat. amnis, stream.Holotype. KU 11659, skull lacking lower jaw.Diagnosis. Size large but not maximum forgenus; rostrum slender (at point halfway in itslength, width goes into length 6.5 times), uppersurface gently concave; end of rostrum expandinggradually instead of abruptly; first 2 pairs of al-veoli much enlarged, not in transverse line; thirdand fourth alveoli on widening base of expandedtip; prenarial length of skull approximately equalspostnarial length; external nares between antorbi-tal fenestrae; septomaxillaries long, slender, partlyseparated by premaxillaries; antorbital fenestraelong, spindle-shaped; curvature of skull roof grad-ual, without abrupt angle at sides; orbits facingas much up as laterally; lower temporal openingextending farther forward than orbits; quadrato-jugal concealing most but not all of quadrate inlateral view; lower margin of jugal nearly straightline; pterygoids meeting to form complete vaultposterior to internal flares.Discussion. In lateral view (Fig. IC) the skullof Angistorhinus aeolamnis is of moderately slen-der proportions, less massive than that of A. mega-lodon (CASE, 1929) but somewhat heavier thanA. gracilis (MEHL, 1915). The maximum lengthof the skull is 1,164 mm.; in the mid-line, to thetip of the condyle, it is 1,043 mm. The maximumwidth, across quadratojugals, is 415 mm. Thesedimensions suggest that the total length of theanimal was between 7 and 8 meters.In Figure IC the heavy line from the front ofthe nasal crest to the orbit, across the suborbitalbar, and behind the lower temporal opening des-ignates the upper edge of the skull as it was pre-served; parts above that line are restored. Thebroken surface is also shown in Figure 1B, byareas of oblique interrupted lines. The restoration(outlined by broken lines in Figs 1B, IC, 2A, and2B) includes the contour of the dorsal surface, theshape of the temporal arches (postorbital-squa-mosal and parietal-squamosal) and the shape andposition of the external flares, as well as the pat-tern of the roof. Normal outlines of these partswere adjusted to the preserved edges of the skull.Most features of Angistorhinus aeolamnis arcclosely comparable to those of A. megalodon. Thesnout of A. aeolamnis is longer and narrower; ata point halfway back the width goes into length6.5 times, but in A. megalodon it goes 4.5. Inlateral view the high part of the nasal crest isattained much farther forward in A. aeolamnis,some 80 mm. anterior to the antorbital fenestra,but in A. megalodon the crest slopes upwardmore gradually and does not reach its upper leveluntil it is over the antorbital fenestra. CASE (/c.cit., p. 23) mentions, and shows in his Fig. 3, aslight convexity near the mid-point of the uppersurface of the premaxillary in A. megalodon,which as he says characterizes most phytosaurs;in A. aeolamnis this surface is entirely concave, asin Rutiodon carolinensis.The first 2 pairs of alveoli in the premaxillaryare much larger than others, about 23 mm. indiameter, the third 17 mm., and the fourth 12mm. The third and fourth are in the narrowinlbase of the expanded tip of the snout. The fifthalveolus has a diameter of 7.5 mm., and thosefollowing increase irregularly until, at the postenor end of the premaxillary, they are againlarge (16 to 18 mm.). Twenty-three teeth emergefrom the premaxillary on each side, but the 23rd,which apparently starts from the maxillary undera thin overlap of the premaxillary, is smaller andis comparable with the succeeding maxillary teeth(19 on the left and 18 on the right in this speci-men). They increase unevenly, the largest maxil-lary alveolus being the most posterior. The edgesof the alveoli are nearly circular and they areseparated, but in A. megalodon, which has nearlythe same number and variation in size, most al-veoli are crowded, so that the walls between themare incomplete and do not come to the surface ofthe bone. The teeth may have grown at a rateincongruent with that of the bones carrying them.In ventral view (Fig. IA) differences betweenAngistorhinus aeolamnis and A. megalodon areA New Wyoming Phytosaur 	 5FIG. 2. Angistorhinus aeolamnis EATON, n. sp., and A. sp., both Upper Triassic, Wyoming.—A, B. A. aeolaninis, dor-sal and occipital views of skull with missing parts restored (broken lines), X0.19.—C. A. sp., part of interorbital roofof specimen (KU 11660) showing position of orbits (broken lines), ventral surface on left and dorsal on right, X0.39.readily observed. The premaxillary in A. aeolam-nis sends back a long process between the pala-tine and maxillary on each side as far as a smallpalatine fenestra; this is not shown in A. mega-lodon or in other phytosaurs that I have seen fig-ured. On the medial side of the posterior maxil-lary alveoli there are 4 shallow pits in a seriesparallel to the row of alveoli; these pits evidentlyreceived the ends of the teeth of the lower jawthat were long enough to reach the bone at thatpoint. The internal nares of A. aeolamnis flareanterolatcrally between premaxillary and palatine,but those of A. megalodon do not. The length ofthe basioccipital anterior to its condyle is equal tothe width of the condyle in A. aeolamnis, but inA. megalodon the condyle is much closer toanterior end of the bone.From Angistorhinus alticephalus STOVALL &WHARTON (1936) the new species differs in sev-eral ways. The skull of A. alticephalus is unusual-ly high and steep-sided, with the external naresthe angle between the ascending edge of thenasal crest and the roof. The septomaxillaries areshort and broad as in A. gracilis and perhaps A.6	 The University of Kansas Paleontological Contributionsgrandis, but unlike A. aeolamnis and A. megalo-don. The teeth of A. alticephalus are pictured assmall and rather widely spaced. The quadrato-jugal covers the quadrate as seen from the side,but in A. aeolamnis the upper end of the quadrateis exposed and in A. megalodon the whole pos-terior edge of it can be seen. The lower temporalopening of A. alticephalus is rhomboidal.The most distinctive feature of the incom-plete skull named Angistorhinus maximus byMEHL (1928) is the deep, narrow notch betweenthe two posterior temporal arcades, which in theother species (including probably A. aeolamnis)was open at an angle of about 90 degrees. A.maxim us also shows a strong downward-pointingangle in the lower margin of the jugal, which theothers do not. In MEHL ' S figures (1913, 1915) ofA. grandis the teeth are restored as nearly uniformin size and shape except for the most anterior; thealveoli should be re-examined, I think, because inmost phytosaurs, including this genus, there is aconspicuous lack of uniformity in the series. A.grandis is also described as having only 2 pairs ofgreatly enlarged anterior teeth in a nearly trans-verse row on the deflected tip of the rostrum.Concerning mobility of the components of thephytosaur skull, it is clear that there was freedombetween the basipterygoid processes and the facetsof the pterygoids into which they fitted. There-fore, one would expect some movement of thebraincase relative to the palate, pterygoids, quad-rates, and other elements to which the latter werefirmly attached. In Angistorhinus aeolamnis (Fig.4) the basioccipital, exoccipitals, and opis . hoticsform a transverse bar, the ends of which restagainst the posterior end of the squamosal andupper end of the quadrate on each side, in whatseems to be a relatively free sliding joint. In A.megalodon, according to CASE (1929), the quad-rate and opisthotic are closely united and move asa unit against the squamosal, into which arounded dorsal head of the quadrate fits. CASEalso noted (/oc. cit., p. 18) " a distinct separationbetween the parietal and the supraoccipital, per-mitting anterior posterior movement of the supra-occipital-opisthotic-quadrate mass. The type speci-men of Leptosuchus crosbyensis [of the Dockum,placed in Rutiodon by GREGORY, 1962] shows thatthe whole brain case was loosely attached to theroof of the skull by cartilage." He added that theparietal is not firmly attached to the supraoccipi-tal in any of the specimens in the University ofMichigan collection. This may be assumed truein A. aeolamnis, although the relevant part of theskull is missing.ANGISTORHINUS sp.Figure 2CA piece of the interorbital skull roof of aphytosaur (KU 11660) (Fig. 2C) was found byROBERT D. PLATZ in a boulder of the same bed ofcoarse limestone as the skull, but about 200 yardsto the north in the lower wash. On the ventralsurface of the frontals is a smooth concavity,probably covering the anterior part of the cere-brum. From this concavity a shallow groove thatruns anteriorly presumably covered the long, slen-der olfactory lobes (compare CAMP, 1930, figs. 25,46, 47 of Machaeroprosopus). The sutures on thedorsal surface between the nasals, prefrontal, andfrontals are consistent with those of Angistorhinusbut are not adequate for determining the species.REFERENCESCAMP, CHARLES L., 1930, A study of the phyto-saurs, with description of new materialfrom western North America: Univ. Cali-fornia, Mem., v. 10, p. 1-174, pl. 1-6, 49fig.CASE, E. C., 1929, Description of the skull of anew form of phytosaur: Univ. MichiganMus. Paleontology, Mem., v. 2, p. 1-56,pl. 1-7, 24 fig.GREGORY, Josbnut T., 1962, The genera of phyto-saurs: Am. Jour. Sci., v. 260, p. 652-690,5 fig.MEHL, MAURICE G., 1913, Angistorhinus, a newgenus of Phytosauria from the Trias ofWyoming: Jour. Geology, v. 21, p. 186-191, 1 fig.	, 1915, The Phytosauria of the Trias: Same,v. 23, p. 129-165, 20 fig.	, 1928, The Phytosauria of the WyomingTriassic: Denison Univ. Bull., Jour. Sci.Lab., v. 23, p. 141-172, pl. 37-39, 9 fig.STOVALL, J. WILLIS, & WHARTON, J. B., JR., 1936,A new species of phytosaur from BigSprings, Texas: Jour. Geology, v. 44, p.183-192, 2 fig.

A new Wyoming phytosaur

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A new Wyoming phytosaur

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