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Cingulates t Bryan Patterson Curator, Fossil Mammals Department of Geology Field Museum of Natural History Chicago, Illinois 60605-2496 Agassiz Professor Museum of Comparative Zoology Harvard University Cambridge, Massachusetts 02138 tWalter Segall Research Associate Department of Zoology Field Museum of Natural History Chicago, Illinois 60605-2496 William D. Turnbull Curator, Fossil Mammals Department of Geology Field Museum of Natural History Chicago, Illinois 60605-2496 Accepted March 22, 1988 Published November 30, 1989 Publication 1405 PUBLISHED BY FIELD MUSEUM OF NATURAL HISTORY © 1989 Field Museum of Natural History ISSN 0096-2651 PRINTED IN THE UNITED STATES OF AMERICA a u o o CO 3 •c o o a CO o M F a fc H 2 03 oo ^_» g § £ •c c 20 FIELDIANA: GEOLOGY described. Due to the extensive union between tympanic and squamosal, the sulcus malleolaris becomes obscured early. It is plainly visible in the young Chaetophr actus, and the tip of the processus malleolaris may be seen forming part of the bulla wall in some adults. In the interior of the bulla the tympanic fuses with the adjacent portion of the processus cristae facialis of the periotic [petrosal]. A very well developed external auditory meatus, which ossifies early in postnatal ontogeny, is pres- ent. It is inclined dorsolateral^ and the porus pre- sents upward and outward, the inclination being more pronounced in the smaller Zaedius. The ven- tral and anterior surfaces of the meatus ossify from the anterior crus of the tympanic, which in these forms is very much more extensive than the pos- terior, and come into sutural contact with the mas- toid process, which forms the greater part of the posterior wall. In old individuals the suture be- comes obliterated. Lateral to the stylomastoid fo- ramen, the meatus sends down a short, blunt pro- cess in some individuals. The posterior crus, which is small in comparison with the anterior although equal in relative size to the posterior crura in the Priodontes and Dasypus groups, is largely con- cealed by the mastoid process in lateral view and contributes very little to the posterior wall. The dorsal wall, lateral to the tympanic ring, is formed largely by the squamosal, the anterior crus con- tributing at the margin. In the very young speci- men of Chaetophr actus, the meatus has barely be- gun to ossify and there are traces of a cleft extending medially between the crura. This is an interesting point of resemblance to the eutatines and to the Tertiary euphractines described below. The glenoid surface is high on the skull and slightly convex. Posterior to it is a large, deep re- cess in the squamosal that extends back above and internal to the auditory meatus; the large post- glenoid foramen opens in the caudal extremity of the recess. The structure of this area is a charac- teristic feature of the entire Euphractus group. The entotympanic has sutural contacts with the exoccipital posteriorly— the contact here extend- ing ventrally almost to the level of the condyle, the basioccipital, and to a slight extent the basi- sphenoid medially. It reaches the pterygoid ante- riorly, the two bones forming a short crest above the level of the Eustachian opening. Laterally, it extends above the anterior margin of the tympan- ic, between this element and the alisphenoid, to the squamosoalisphenoid junction, as in Cabas- sous and Tolypeutes. Internally, the entotympanic is smooth, and its posterior extremity forms a sharp, prominent transverse ridge that continues upward into the crista facialis. There is no trace, in this or any other xenarthran, of a septum bullae, a structure that frequently occurs in other mam- mals with a compound bulla. Anteroexternally it fuses extensively in adult specimens with the pro- cessus cristae facialis. The medial wall of the bone is thickened and cancellous. The aperture for the Eustachian tube is completely surrounded by this element and by the tympanic. The entotympanic may be a compound bone, formed from rostral and caudal elements in these genera, but the ma- terial at hand, even the young individual of Chae- tophractus, throws no light on the matter. The paleontological evidence suggests, however, that the part, if any, played by the caudal portion was minor. The tympanohyal is in the usual position. It is clearly visible in very young specimens, in which it may be seen as a thin strip of bone lying medial to the united crura of the tympanic, but later be- comes fused with the surrounding elements. A slight depression for the reception of the stylohyal sometimes remains to mark its position in Eu- phractus, into which, as noted by van Kampen (1 905), the tip of the otherwise fused tympanohyal occasionally protrudes. The ventral surface of the pars petrosa of the periotic shows no outstanding peculiarities. The promontorium is prominent but not as globular as in Dasypus, being quite similar to that of Tol- ypeutes. The processus cristae facialis is a very well developed, gently concave bony plate that is rounded anteriorly and sharply triangular poste- riorly. As noted above, it fuses during postnatal ontogeny with the tympanic and entotympanic. The recessus epitympanicus passes directly into a large epitympanic sinus, which extends anteriorly beneath the posterior part of the recess behind the glenoid articulation and posteriorly into the pars mastoidea. In the young specimen of Chaetophr ac- tus already referred to, it is partially divided by a horizontal septum into two portions, of which the lower, and smaller, appears to correspond in part to the posterior evagination of the recessus epi- tympanicus seen in Cabassous and Tolypeutes. Van Kampen noted the presence of an epitympanic sinus in Euphractus and Zaedius but was uncertain as to whether it lay wholly in the squamosal. Our material shows that it is bounded medially by the periotic. In correlation with the width of the cranium, the pars mastoidea is widely exposed on the oc- cipital surface. It forms the whole of the mastoid PATTERSON ET AL.: EAR REGION IN XENARTHRANS. I. CINGULATES 21 process, which is wide transversely, compressed anteroposteriorly, and inclined anteroventrally. The relations between this process and the tym- panic have been described above. The process is in contact laterally for most of its length with the outgrowth from the anterior crus of the tympanic; the rounded tip may project for a very short dis- tance in some specimens. The posterior face bears a small protuberance near the center. Between the process and the exoccipital there is a wide, shallow groove [leading from the mastoid foramen]. No trace of a paroccipital process is present. The internal carotid enters a canal in the ante- rior part of the entotympanic, and passes to the cranial cavity via the concealed foramen lacerum medium in all specimens but one of Zaedius, all of C. (E.) villosus, and slightly under half of E. sexcinctus. In the single Zaedius and the remaining E. sexcinctus, there is a groove in the entotym- panic, and the foramen lacerum medium is visible in the dried skull. The artery enters the cranial cavity by a small opening situated directly dorsal to the foramen lacerum medium and posterolater- al to the sella turcica. A second artery enters the skull immediately anterointernal to the foramen lacerum posterior and runs anteriorly in a canal, formed by the entotympanic below, periotic lat- erally and basioccipital medially, that opens in the cranial cavity at the posterolateral extremity of the sella. Several small squamosal foramina, rarely a single large one, occur above the porus in Eu- phractus. In Zaedius there is usually a single fo- ramen above and behind the porus, and occasion- ally one or two smaller ones as well. The mastoid foramen is in the usual position with a channel running ventrally from it, which is only excep- tionally bridged over in part by bone. Above it is a second, smaller venous opening. Both foramina lead into canals that pass anteriorly above the au- ditory region, through the diploe in this very thick part of the cranial wall, to open in the postero- lateral part of the cerebral cavity. Here the dorsal of the two canals (which becomes ventral in po- sition posteriorly) receives a sinus that enters the cerebral cavity through a venous opening in the posterior part of the orbit. Both canals are in com- munication with each other posteriorly and also with the transverse sinus, the canal from the post- glenoid foramen, the subsquamosal foramina, and the numerous small venous openings in the vicin- ity of the squamosoparietal suture. The foramen lacerum posterior, as usual, is oval and situated between exoccipital and entotympanic. The course of the facial nerve in armadillos of the Euphractus group is rather unusual. The nerve follows the usual course within the tympanic cav- ity and then turns laterally to pass through a canal formed by the pars mastoidea posteriorly and the tympanohyal and posterior crus of the tympanic posteriorly. On emerging from this canal at the foramen stylomastoideum definitivum, it runs an- teroventrolaterally along the sulcus in the anterior face of the mastoid process— and hence lies within the external auditory meatus— and finally leaves the skull at a point near the tip of the mastoid process, between this element and the outgrowth of the anterior crus of the tympanic. In young animals, this is in a slit between the two, but as ossification of the crus progresses the point of exit is converted into a foramen, a "foramen stylo- mastoideum tertium," so to speak. fPaleuphractus Kraglievich, 1934 Two skulls of Paleuphr actus argent inus Moreno and Mercerat, FMNH PI 44 12 (fig. 8C) and P 1 4442, from the Andalgalense of Catamarca, have been available for study. Both have suffered to some extent from distortion and breakage. The tympanic, as far as revealed, is very similar to those of Zaedius and Euphratus, differing only in the structure of the anterior crus. In degree of enlargement and lateral projection, this portion of the bone is comparable to that of Zaedius but it is not reflected posteriorly to floor the meatus. The well-defined ventral slit, here V-shaped, between anterior crus and mastoid process is therefore present, as in all extinct euphractine genera now known. The relation of the anterior wall of the tympanic to the deep recess, posterior to the glenoid surface, is precisely as in the living forms. The boundary between tympanic and entotym- panic is visible in the posterior half of the bulla. It corresponds closely with conditions seen in the young specimen of Euphractus [Chaetophractus] described above, except that here again, as in Proeuphr actus, there is a gap posteriorly between the two elements and no contact between exoc- cipital and entotympanic at the level of the con- dyle. The gap is smaller than in that form and is confined entirely to the posterior face of the bulla. This lack of ossification in the immediate vicinity of the tympanohyal, coupled with the absence of any indication of a division in the entotympanic of the young Euphractus [Chaetophractus], strong- ly suggests that the caudal portion of the entotym- 22 FIELDIANA: GEOLOGY panic played a very minor role, if indeed it par- ticipated at all, in the formation of the bone. The ventral surface of the pars petrosa of the periotic is comparable in all respects with that of Euphractus. The same is true of the pars mastoi- dea, save that the mastoid process projects freely in the cranioventral direction, due to the lack of reflection of the anterior crus of the tympanic. All foramina that can be seen in the auditory region differ in no respect from those of the living forms, except that due to the lesser degree of os- sification of the anterior crus, there is no "foramen stylomastoideum tertium" between crus and mas- toid process. tion between entotympanic and exoccipital at the level of the condyle. It is rather remarkable to find these primitive characters persisting in so large and specialized a form. Both available specimens appear to be fully grown, so that the lack of os- sification can hardly be regarded as due to im- maturity. The later, Macroeuphr actus retusus Ameghino, has a fully ossified bulla, to judge from Lydekker's figure. It is probable that an epitympanic sinus is pres- ent in this and other Tertiary euphractines, but sections would be necessary to conclusively dem- onstrate its presence. fProeuphractus Ameghino, 1886 Two specimens of Proeuphractus scalabrinii Moreno and Mercerat, FMNH PI 4360 (fig. 9A- B) and PI 5435, from the Andalgalense of Cata- marca, have been available; both are unfortu- nately incomplete, but nevertheless most of the structure can be determined. Proeuphractus and its close relative Macroeuphractus are similar in general to Euphractus and Zaedius and it will suf- fice here to discuss those points in which they differ. The bulla is less inflated than in the living forms and its anterior border shows an uninterrupted, gently concave sweep when seen in ventral aspect, a feature that is even more pronounced in the giant Macroeuphractus (Lydekker, 1894, pi. 35). The external meatus is as long as in Euphractus and Zaedius but is not closed ventrally by bone. The bony extension of the anterior crus, as in Macro- euphractus, did not turn posteriorly to meet the mastoid process, thus leaving an open V-shaped cleft between the two elements. The bony exten- sion continues ventrally below the porus, forming a groove between the crura. Tympanic and mas- toid are united medially to the point of exit of the facial nerve. The mastoid process is broken in our material; in Macroeuphractus it is very massive. In only one other character is there a major dif- ference between Proeuphractus and the living eu- phractines. As in the Santacruzian Prozaedius (see below), a cleft, reaching almost to the middle of the bulla, separates the entotympanic and tym- panic posteriorly. The position of the cleft is the same as that occupied by the caudal portion of the entotympanic in Cabassous, etc., a fact which sug- gests that this portion of the bone remained unos- sified in Proeuphractus. There is thus no connec- fProzaedius Ameghino, 1 89 1 An excellent skull of Prozaedius exilis Ameghi- no, PU 15579 (fig. 10A-B), from the Santa Cruz Formation of Patagonia, permits the following rather full account of this earliest euphractine. Scott's description of the skull (1903, pp. 70-72), which includes a brief summary of the auditory region, was largely based on this specimen, and van der Klaauw ( 1 93 1 , pp. 3 1 2-3 1 3) has published a brief note upon it. The bulla of this form is, as would be expected, more primitive than in any later euphractine, and resembles the bulla of the Pliocene eutatine Doel- lotatus (see below) in several respects. The tympanic retains some trace of the primi- tive ring form,7 being only moderately expanded medially in the posterior portion. It is considerably prolonged anteromedially, however, in the vicin- ity of the Eustachian tube. The external auditory meatus is barely developed, and above it there is a parallel-sided cleft between the mastoid process and anterior crus, which is U-shaped at the base. The shorter, V-shaped cleft of the Pliocene Paleu- phractus indicates that formation of the tubular meatus in euphractines involved bone growth at the base of the cleft as well as extension of the anterior crus posteriorly. The anterior crus forms a straight, nearly vertical ridge sharply edged lat- erally; there is a steplike indentation at the upper extremity, as in Doellotatus. In contrast to the liv- ing forms, there is no posterior continuation from the anterior portion of the crista tympanica, and 7 It should be noted that what appears at first glance to be a tympanic in Scott's figure (1903, pi. 6, fig. 20) of the closely related but longer skulled Stenotatus pata- gonicus Ameghino is actually the occipital condyle, which, as he states (p. 81), is deeply incised laterally. PATTERSON ET AL.: EAR REGION IN XENARTHRANS. I. CINGULATES 23 \ <3 1 -« r ^ \ d i S i tt. I / o\ o U- 24 FIELDIANA: GEOLOGY PATTERSON ET AL.: EAR REGION IN XENARTHRANS. I. CINGULATES 25 the tympanic consequently does not form a com- plete ring. The posterior cms is, as usual in this group, short in comparison with the anterior and curves upward medial to the mastoid process, which conceals its upper portion when the skull is viewed from the lateral side. As far as its attach- ment is concerned, it is nearly identical with Eu- phractus, the only difference being that the sutural connection to the mastoid process is less extensive. Prozaedius thus shows conclusively that, of the two crura, it is the posterior that earlier attains the definitive form and relationships encountered in the later members of the Euphractus group. This is not surprising since the structure here is merely an exaggeration of that seen in incipient form in the Priodontes and Dasypus groups, whereas the modification of the anterior crus has been much more extensive. The superficies meatus is nearly vertical, as in Doellotatus and juvenile Recent eu- phractines. In contrast to these later forms and due to the fact that the tympanic ring is not com- plete, there is a gap between the arched ventral border of the superficies and the incisura tympan- ica, in which the malleus and incus are visible [but not shown in fig. 10, however]. This is a primitive character and an interesting point of resemblance to armadillos of the Priodontes and Dasypus groups. The projecting tip of the anterior process of the malleus may be seen on both sides of the specimen. The fossa in front of the anterior wall of the meatus and behind the glenoid surface which is so characteristic of the entire Euphractus group is less extensive in Prozaedius than in later euphractines, being narrower transversely, due to the less ex- panded zygoma and anterior crus, and not ex- tending so far posterodorsally. The relations between tympanic and entotym- panic are very clear, the bulla not being "broken up into pieces" as van der Klaauw supposed. The rostral portion of the entotympanic, the only part ossified, is less developed than in later forms. An- teriorly, it completely fills the space between the tympanic and neighboring elements, extending laterally on the anterior face of the bulla to the projecting tip of the processus anterior of the mal- leus, as in Cabassous and Tolypeutes, and forming a curved suture posterior to the Eustachian tube with the anterior half of the medial border of the tympanic. Due to a fracture, it is impossible to be certain whether or not a pterygoid-entotympanic crest was present. This anterior portion of the bone is cancellous. Posteriorly, the entotympanic di- verges from the tympanic, forming a fairly wide medial strip that extends back to the exoccipital. A wide gap is thus formed between the two bones (not within the tympanic, as van der Klaauw thought might be the case), in which no trace of a caudal entotympanic is to be seen. In later forms this gap is closed by progressive ossification of the rostral portion. As already stated, there is no clear evidence that a caudal portion participated at all in the formation of the bulla. The form and po- sition of the opening for the Eustachian tube are as in the living forms. In degree of prominence, the promontorium re- sembles those of Euphractus and Zaedius. The recessus epitympanicus is well developed; the presence of the ossicles makes it impossible to determine whether or not a sinus was present. The pars mastoidea is comparable to that of these Re- cent forms in its degree of exposure, but, due to the much less expanded posterior root of the zygo- ma, the anterior half faces laterally rather than posterolaterally. The mastoid process projects more freely than in later forms, and bears a conspicuous buttress on the lateral edge a short distance below the junction with the occipital crest. Its squamosal component extends far ventrally, reaching to the posterior crus of the tympanic. Prozaedius resembles Paleuphractus in the ab- sence of a "foramen stylomastoideum tertium." The other foramina in the vicinity of the auditory region are precisely as in the living forms. Van der Klaauw's (1931, p. 313) "opening in the rostro- medial part of the bulla" is the usual carotid fo- ramen in the entotympanic. The Chlamyphorines Chlamyphorus Harlan, 1825 Specimens of this and of the related, somewhat larger Burmeisteria are rare in collections, and we are fortunate to have been able to examine a skull of Chlamyphorus truncatus Harlan, PU 538 (fig. 11A-B), an adult individual. The extraordinary little animals, so distinctive in external characters and in the relations of the pelvis and tail to the posterior portion of the carapace, are dwarfed rel- atives of the euphractines, from which group they almost certainly arose. We thus agree with Simp- son's remark (1927, p. 292) that Chlamyphorus is "... a peculiar and highly aberrant derivative of an essentially Dasypus [i.e., Euphractus]-like form." So far as the auditory region is concerned, this is not open to question, and evidence from other parts of the body would appear to be in accord. 26 FIELDIANA: GEOLOGY PATTERSON ET AL.: EAR REGION IN XENARTHRANS. I. CINGULATES 27 The striking features of the skull of Chlamy- phorus, those immediately noticed on comparison with skulls of euphractines— triangular appear- ance, wide, deep, and short cranium, zygomata narrowing anteriorly, frontal protuberances, re- duced orbits, relatively enormous foramen mag- num, and so on— are all consequent upon the size reduction undergone by the chlamyphorines. They are the results of adjustments that have taken place in the head. Compromises have ensued beween overall size reduction and disproportionate re- duction of various parts, some of which (e.g., brain, depth of teeth, sinuses) have undergone relatively less reduction, while others (e.g., eyes) have under- gone more. In the auditory region and vicinity, adjustment to the relatively large size of the brain has resulted in certain differences from the eu- phractines in general appearance. For example, the recess posterior to the glenoid cavity, so conspic- uous in euphractines, is here reduced. The well- inflated bullae are aligned more obliquely, and, as van Kampen has noted, lie in a more ventral plane relative to the basicranium. Posteromedially the bullae have rather extensive contacts with the oc- cipital condyles, which are situated farther forward than in euphractines and greatly expanded in the anteroposterior direction. These distinctions are relatively minor, however, and in no way disguise the fundamental similarity between chlamyphor- ines and euphractines in this area. The bulla closely resembles that of Zaedins in shape, but is smoother and more convex. There is no trace of the prominence extending medially from the meatus, and the groove running ante- rointernally from the vicinity of the mastoid pro- cess is barely discernible; both these features, it will be recalled, were less prominent in the smaller Zaedius than in the larger Euphractus. [It should be noted that Segall has subsequently studied C. truncatus (1 976) and in that work this feature does not appear on the specimen illustrated (Segall, 1976, fig. 1, p. 433; MCZ 3209).] That portion of the tympanic anterointernal to the crista tympan- ica, between this crest and the opening for the Eustachian tube, is relatively more extensive than in Zaedius, in which, in turn, this part is relatively larger than in Euphractus. The attachments of the crura are as in the euphractines, the posterior being partially concealed by the mastoid process and the anterior united suturally with the squamosal. In the structure of the auditory meatus, how- ever, Chlamyphorus is sharply distinct from the Pliocene and later euphractines. The external ca- nal is short, the anterior cms not extending lat- erally and posteriorly to form a long bony meatus. The porus is consequently low on the side of the skull, at a level only slightly above that of the tip of the mastoid process. It is nearly circular in out- line, presents upward and outward, and has a prominent lip. From it a groove, situated mainly in the squamosal, curves upward and forward, ter- minating immediately lateral to the occipital crest. In this groove, and fitting over the lip of the porus, lies the extraordinary tube (van Kampen, 1 905, p. 493), ossified from the cartilaginous meatus,8 which has attracted the attention of all who have studied the chlamyphorine auditory region, from Harlan (1825) and Hyrtl (1854) on [and including Segall (1976, p. 431)]. The tube extends beyond the groove, curves forward over the root of the zygo- ma, and ends above the glenoid articulation. [Se- gall's 1976 dissection (pp. 433, 437) shows this to be a two-part tube, the proximal part occupying the groove, the articulating distal part extending more freely forward nearly to the frontal protu- berance and the eye.] The structure of this area is, of course, decidedly different from that of the Re- cent and Pliocene euphractines, but is derivable from that of the earlier forms. Acquisition of an ossified tube by forms comparable in meatal struc- ture to the Santacruzean Prozaedius would lead to the conditions seen in the chlamyphorines. The position of the glenoid articulation is ex- actly as in the euphractines, but the articular sur- face is rather more convex transversely. As a result of the dwarfing of the animal and the dispropor- tionate [lesser] reduction in brain size, the poste- rior root of the zygoma stands out from the side of the cranium to a greater extent than in euphrac- tines, and, as already noted, the recess behind the articular surface is reduced, although still fully rec- ognizable. No trace of a suture between tympanic and en- totympanic remains, but there can be no doubt that the bulla is compound. The crest formed by the entotympanic and pterygoid is prominent, but, as in Euphractus and Zaedius, it is above the level of the opening for the Eustachian tube, which is here very small. The tympanohyal is completely fused with the surrounding elements and no details of its struc- ture can be seen. A small pit on the occipital sur- face immediately above the bulla and medial to the mastoid process marks the position of the at- tachment of the stylohyal. 8 Van der Klaauw (1931, p. 257) implies that the me- atus in Euphractus and Zaedius is formed in the same way. We do not believe this to be the case. 28 FIELDIANA: GEOLOGY External examination and X-ray photography fail to reveal any trace of an epitympanic sinus. If present in the ancestry of Chlamyphorus, as may have been the case, elimination of this cavity is to be attributed to dwarfing. The pars petrosa of the periotic is not visible in the specimen at our disposal. The sutures between the pars mastoidea and the squamosal and occip- ital elements cannot be seen, but, from the position of the mastoid foramen, it is evident that the pars mastoidea forms the ventrolateral corner of the occipital surface. In comparison with the euphrac- tines, the mastoid process is small and extends laterally to a lesser degree. It conceals the posterior crus of the tympanic in side view and may con- tribute in a minor way to the formation of the groove in which the meatal tube lies. The medial face of the entotympanic is grooved for the reception of the internal carotid but no canal is formed, the artery passing anteriorly to the foramen lacerum medium, which opens at the anterior extremity of the groove. The second ar- tery passes forward in a second, more dorsally situated groove between entotympanic and basi- occipital, runs beneath a bar formed by the en- totympanic and pterygoid, and also enters the cra- nial cavity via the foramen lacerum medium. The postglenoid foramen, as in euphractines, is situ- ated at the posterior extremity of the recess behind the glenoid surface; it is relatively enormous in comparison with the size of the skull. There are no subsquamosal foramina. The mastoid foramen occupies the same position as in euphractines, but there is no groove running ventrally from it. The foramen lacerum posterior resembles those of Eu- phractus and Zaedius. The stylomastoid foramen, again as in these forms, leaves the skull between tympanic and mastoid process. The Eutatines fDoellotatus Bordas, 1932 Three specimens that are apparently referable to Doellotatus prominens (Moreno & Mercerat),9 9 Described as Eutatus prominens. Bordas (1933, p. 584) makes only passing mention of this species in his discussion of the eutatines and leaves the reader in doubt as to the generic assignment. Associated carapacial ma- terial permits at least tentative specific identification of our specimens, and the skulls are very similar to that of Doellotatus inornatus Rovereto, the type species, leaving no doubt as to the generic determination. [Earlier, FMNH PI 4351 (fig. 12D) and PI 4358 (fig. 12C) from the Araucanense and P14526 (fig. 12A-B) from the Corral Quemado, Catamarca, Argentina, have been examined. None of the three is complete and all are either broken or somewhat crushed, but between them most of the structural details can be determined. The tympanic in the later eutatines is an ex- traordinary bone, thick and so dense that it resem- bles the pars petrosa of the periotic in texture. The porus, due to the prominence of the crura, is deep set in the bulla, and has a rather irregular border. The anterior crus is high, reaching to the root of the zygoma, and very robust, expanded in the transverse plane, and with a sharp lateral margin. The upper extremity is indented in steplike fash- ion. There is no indication of a posterior reflection, such as occurs in Recent euphractines, but its pos- terior wall is concave, forming a recess above and slightly anterior to the porus. The posterior crus, as in euphractines, is short and largely covered laterally by the mastoid process, but it also has a prominent lateral margin; the attachments are also almost precisely similar. The margins of both crura continue ventrally beyond the porus, with the re- sult that a conspicuous groove is formed in the lateral face of the bulla, as in Proeuphr actus. The crura meet above the porus, as in Euphractus, ex- cluding the narrow superficies meatus of the squa- mosal from its border. The sutures in this region can be seen clearly in FMNH PI 4526 (fig. 12A- B). As already mentioned above (p. 28), the glenoid area, and in particular the fossa posterior to it, agrees in all essentials of structure with that of the euphractines. The entotympanic, nearly complete on the left side of FMNH PI 4351 (fig. 12D) and on the right of P14526, resembles that of Recent euphractines. It is cancellous in its anterior half, extends laterally above the medial half of the anterior face of the tympanic, where it is concealed externally by the enlargement of the squamosal in this area, and posteriorly to the foramen lacerum posterior. The bulla is thus completely enclosed by bone, in sharp contrast to the Miocene and Pliocene euphractines in which the entotympanic is not completely os- sified posteriorly. The Eustachian tube and styli- form process are comparable to those of Euphrac- tus. Ameghino (1891) had equated E. prominens of Moreno and Mercerat with his species Eutatus distans.] PATTERSON ET AL.: EAR REGION IN XENARTHRANS. I. CINGULATES 29 The ventrolateral face of the pars petrosa of the periotic is rather flat, and has a rounded anterior extremity. [Here I suspect that Patterson has seen some other specimen(s), for only the anterior tip and ventromedial edge are exposed on the pe- trosals of the specimens listed here. The best ex- posure is seen in FMNH PI 43 51.] The promon- torium is low and inconspicuous in comparison with that of the euphractines. The ventral portion of the medial face is deeply grooved, and lower border of the groove forming a sharp edge. [The cranial side of FMNH PI 4526 possibly may have been further prepared subsequent to the Patterson- Segall study of it. That surface is irregular, and the meatus internus acusticus is prominent and deep.] Unfortunately, nothing can be seen of the crista facialis or recessus epitympanicus in any of the specimens. Whether or not an epitympanic sinus was present is uncertain. Doellotatus resembles Prozaedius in the degree of expansion of the posterior root of the zygoma, and the surface exposure of the pars mastoidea is consequently as much lateral as posterior in po- sition, as in that form. The freely projecting mas- toid process is stouter and less flattened antero- posteriorly than in Prozaedius; its base is closer to the condyle than in any euphractine. It bears a buttress on the lateral edge, exactly as in Prozae- dius, and a second eminence, dorsal to this and above and behind the meatus, to which the squa- mosal contributes. There is no groove or opening in the entotym- panic for the carotid, and there would appear to have been a visible foramen lacerum medium an- terointernal to the bulla, as in certain living eu- phractines. The arterial canal between entotym- panic, periotic and basioccipital was present, occupying the groove in the medial face of the pars petrosa. The postglenoid foramen, as in euphrac- tines, opens at the posterior extremity of the deep fossa posterior to the glenoid surface. The sub- squamosal foramina vary in number and size and are situated above the meatus. The mastoid fo- ramen is ventral in position, opening between the base of the mastoid process and the vestigial par- occipital process. In euphractines, the vein runs down the occiput in a groove, which is here com- pletely bridged over by bone. The narrow foramen lacerum posterior resembles that of the euphrac- tines very closely. As in the Tertiary members of this group, the stylomastoid foramen opens lat- erally between the posterior crus of the tympanic and the mastoid process. tEutatus Gervais, 1867 Examination of a specimen of Eutatus seguini Gervais in the American Museum of Natural His- tory (AM 11231, type of Eutatus brevis Ameghino) permits the statement that this latest and largest eutatine is in nearly every respect comparable to the earlier and much smaller Doellotatus. [This also appears reasonable, to judge by the figure giv- en by Ameghino (1906, p. 380, fig. 236).] fProeutatus Ameghino, 1891 Three skulls of Proeutatus oenophorus Ame- ghino, FMNH PI 3 197 (fig. 13A-B), PI 3 199 (fig. 13C-D), and PI 3203, from the Santa Cruz For- mation of Patagonia, have been examined. Scott (1903, p. 44) has stated that "the tympan- ic, which was loosely attached, is a small, incom- plete ring of bone, with large, irregular external meatus." It was not attached in any of the skulls that he figured. An incomplete tympanic is for- tunately preserved in FMNH PI 3 199, permitting us to confirm and to some extent amplify the brief account just quoted. [Unfortunately, it is now lost, or at least is no longer with the specimen. It is good that Patterson and Segall discussed and il- lustrated it, for that is now all we have to go on.] The specimen is incomplete anteriorly, the prox- imal end of the anterior crus being broken off. In contrast to Doellotatus, the tympanic is of prim- itive type, comparable in general to those of Das- ypus and of the Priodontes group. The posterior portion is more expanded than the anterior, and the two parts meet in a very sharp angle, almost precisely as in Priodontes. Again as in this form, there is no groove in the region of the Eustachian tube. No trace is apparent of the thickening that is so striking a feature of Doellotatus. The porus, as Scott states, is irregular; the outline corresponds closely to that of Priodontes. The spina tympanica posterior is conspicuous, the bony meatus short, and the crista, sulcus, and recessus well developed. The posterior crus is attached mainly to the tym- panohyal, with only the spina extending up to the squamosal as in the Priodontes and Dasypus groups; more of it is visible in lateral view than in later eutatines, due to the relatively smaller and shorter mastoid process. The anterior crus is evidently broken off immediately distal to the sulcus mal- leolaris. The small part of the ascending portion that is preserved is very slender, and it would seem 30 FIELDIANA: GEOLOGY 2 cm anterior crus of tympanic meatal porus squamosal mastoid process tympanic stylomastoid foramen mastoid foramen foramen lacerum posterior foramen lacerum medium opening for eustachian tube mastoid process -IL occipital condyle pars mastoidea petrosal entotympanic 2 cm Fig. 1 2. Doellotatus prominens: A-D, three partial skulls shown in right lateral and anterior views (fmnh PI 4526), right lateral view (fmnh P14358), and ventral view (fmnh P14351). likely that the missing portion was similarly con- structed. In all probability the whole resembled the anterior crus in the Priodontes and Dasypus groups, was bound to the squamosal by soft parts only, and did not extend dorsally much above the level of the posterior crus. The structure of the malleus confirms this inference. The adjacent sur- face of the squamosal, anterointernal to the su- perficies meatus, forms a conspicuous, thick ridge, second in prominence only to Priodontes among the forms studied. The recess in the squamosal posterior to the glenoid area, characteristic of all members of the Euphractus group, is present in Proeutatus also. PATTERSON ET AL.: EAR REGION IN XENARTHRANS. I. CINGULATES 31 B basisphenoid pit basioccipital glenoid postglenoid process 3 cm occipital condyle mastoid foramen occipital crest pars petrosa foramen magnum foramen rotundum foramen ovale alisphenoid anterior crus of tympanic crista tympanica sulcus tympanicus< recessus meatus glenoid fossa posterior crus of tympanic 1 cm paroccipital process groove below mastoid foramen occipital condyle pars petrd^a fenestra oval is : fen. vestibuli) external auditory meatus tympanohyal 1 cm Fig. 13. Proeutatus: A-C, two partial crania shown in right lateral and ventral views (P. cf. oenophorus, fmnh PI 3 197) and ventral view (P. oenophorus, fmnh PI 3 199); D, right tympanum shown in internal (left) and external views (fmnh PI 3 199). In this form, however, the distance between the base of the mastoid process and the rim of the recess is much less than in other members of the group, the arched superficies meatus actually being anterior to the rim rather than posterior to it as in Prozaedius. Proeutatus thus indicates that ac- quisition of the postglenoid recess preceded, and may have been the structural prerequisite for, en- largement of the anterior crus in members of the Euphractus group, but at the same time shows that enlargement of the crus was accompanied by fur- ther enlargement of that portion of the squamosal forming the rim of the process. No trace of an entotympanic is present in our material nor in that figured by Scott. The tympanohyal is very well preserved in FMNH PI 3 1 99. At the base it is indistinguishably fused with the crista facialis and curves laterally, 32 FIELDIANA: GEOLOGY providing a base of attachment for the posterior cms of the tympanic. The posterior surface is grooved for the passage of the facial nerve. The pars petrosa of the periotic runs to a blunt point anterointernally, and has a sharp ventro- medial border that is only slightly above the level of the basicranium. Above this border, as in Doel- lotatus, there is a groove in the medial face of the bone. The promontorium agrees with that ofDoel- lotatus in being notably less prominent than in euphractines. The crista facialis is very sharply defined and bears the usual xenarthran process, which is unfortunately broken away anteriorly in the available specimens. The recessus epitympan- icus is rather shallow toward the lateral side but is sharply bounded medially due to the promi- nence of the crista facialis. There is no epitympanic sinus. The pars mastoidea is less extensive than in Doellotatus, and is more widely exposed on the occipital than on the lateral surface of the skull. The mastoid process is very notably smaller and shorter than in any other member of the Euphrac- tus group, and is further distinguished by being widened in the anteroposterior rather than in the transverse direction. Due to the absence (or lack of ossification of the entotympanic) nothing can be said concerning the carotid foramen. To judge from the space between the anterior extremity of the pars petrosa and the alisphenoid, a foramen lacerum medium was present. The groove in the medial surface of the pars petrosa, which is converted into a canal by the basioccipital, extends toward a foramen that pierces the alisphenoid anterior to the tip of the petrosal. This in turn leads to a canal that opens in the posterior part of the sella. The postglenoid foramen, as in other members of the Euphractus group, is situated in the posterior portion of the postglenoid recess. There are several small venous foramina above the recess. The mastoid foramen is in the usual position; the groove running ven- trally from it does not appear to have been roofed over by bone. The foramen lacerum posterius has the usual slitlike form. The stylomastoid foramen is situated between the tympanic and mastoid pro- cess, and is lower in position than in other mem- bers of the group. It will be evident from the figure that the fora- men ovale and the opening of the transverse canal are more lateral in position than is usual in eden- tates, the transverse canal opening occupying the usual position of the foramen ovale. Although out- side of the auditory region, a note on the transverse canal may be interpolated here; among armadillos, the canal is present in the Dasypus and Euphractus groups and absent in the others. Glyptodonts, ant- eaters, and sloths do not have it, and there has been no record of its occurrence in palaeanodonts. The Peltephilus Group fPeltephilus Ameghino, 1887 Two skulls of Peltephilus pumilus (= Peltephilus ferox) Ameghino (PU 1 539 1 , fig. 1 4A-B; AM 9524) from the Santa Cruz Formation of Patagonia have been examined. The peculiarities of structure ex- hibited by these remarkable armadillos extend also to the auditory region, the group being highly dis- tinctive in the structure of this area. The bulla is complete and well inflated. The tympanic forms a long tubular meatus as in Recent euphractines, but the resemblance between the two ends here. In Peltephilus the meatus extends not only dorsally but anteroexternally to a marked de- gree as well, a unique feature. Both crura, and not the anterior alone, contribute to the formation of the ventral half of the tube. How much of the dorsal half may be supplied by them and how much by the superficies meatus of the squamosal cannot be determined. Scott (1903, p. 90) states that the dorsal surface is formed by the zygomatic process of the squamosal and the anterior by the postglenoid process. This is quite uncertain and at least partly erroneous. There is no postglenoid pro- cess, and it is virtually certain that a strip from the anterior cms of the tympanic lines the anterior part of the meatus, and [it is] possible that it may extend to the dorsal surface as well. Whatever its composition, the dorsal half is less arched than in other armidillos. In consequence, the poms is oval with the long axis in the anteroposterior direction. The anteroexternal inclination of the meatus is so pronounced that its anterior portion actually lies above the external portion of the wide glenoid cavity; the tympanic and squamosal are indistin- guishably fused in this area. Again as a result of the direction of the meatus, the posterior cms is well separated from the mastoid process. The ven- tral surface of the meatus bears a rounded, irreg- ular ridge that curves posteriorly to the vicinity of the tympanohyal, and joins the bulla proper in an irregular manner. Anteriorly, the bulla extends al- most to the glenoid cavity, the two being separated only by a rather shallow but well defined fissura Glaseri. The posterior end of the bulla is in very close contact with and in places fused with the PATTERSON ET AL.: EAR REGION IN XENARTHRANS. I. CINGULATES 33 C 2 t r«-> O m CO "" «, t 34 FIELDIANA: GEOLOGY adjoining portion of the pars mastoidea of the peri- otic. The glenoid cavity, it should be noted, is lower on the skull than in any other armadillo. The boundary between entotympanic and tym- panic cannot be determined. There is no reason to doubt, however, that the relations of the two bones were essentially as in Euphractus and allies. The opening for the Eustachian tube is in the same position as in these forms, but is larger. As Scott has noted, Peltephilus is the only Santa Cruz armadillo that has a completely ossified bul- la. Members of this group are in fact the first xe- narthrans known to have acquired this condition. The Myrmecophagidae are a close second, but there is some doubt (see below) as to whether the tym- panic is completely fused with the surrounding elements in the Santa Cruz Promyrmephagus. The tympanohyal cannot be distinguished; it is, however, almost surely fused with surrounding elements in the shallow depression medial to the mastoid process. Nothing can be seen of the pars petrosa in our material, except for a narrow strip anterior to the foramen lacerum posterius that is not covered by the bulla. The pars mastoidea is very well devel- oped, and is broadly exposed both on the occiput and on the lateral side of the skull. The mastoid process is massive and rather short, situated lat- erally on the skull and sharply set off from the posterior cms of the tympanic by a wide and deep groove. The extent to which the squamosal par- ticipates in the process cannot be seen in the spec- imens. The lateral extension of the exoccipital be- yond the condyle is well separated from the mastoid process. The carotid foramen and canal occupy the same position as in the Euphractus group. The presence of the second arterial canal is uncertain; if present it was small and ran forward between the dorsal surface of the entotympanic and the ventral sur- face of the periotic. There is a small foramen lac- erum medium at the anterointernal corner of the bulla. In other edentates the foramen ovale is sit- uated well in advance of the bulla, and is hence outside the region under consideration. In Pelteph- ilus, however, as Scott noted, it adjoins the bulla, being above and slightly in front of the opening for the Eustachian tube. There is no postglenoid foramen, but a number of vascular foramina occur in the dorsal surface of the squamosal. The mas- toid foramen is in the usual position, and a very well defined groove runs ventrally from it. Some minor foramina, presumably vascular, are present around the posterior margin of the bulla. The fo- ramen lacerum posterior is larger than in members of the Euphractus group. The stylomastoid fora- men is slitlike and opens externally at the ventro- medial extremity of the cleft between the meatus and the mastoid process. The Chlamytherium Group tPlaina Castellanos, 1937'° A magnificent skull of this form, referred ten- tatively to Plaina subintermedia Rovereto, has been available and is currently under study by A. G. Edmund. The specimen, FMNH PI 4424 (fig. 1 5A- B), comes from the Corral Quemado horizon, Ca- tamarca, Argentina. The tympanic and entotympanic (if this element was ossified) are missing in this specimen and in other skulls of chlamytheres thus far described (Castellanos, 1937; Bordas, 1939b; the bulla in- dicated in fig. 1 of this paper is the ventral surface of the periotic"). There can be no doubt that the tympanic was of the primitive, horseshoe-shaped type seen in such forms as Priodontes and Dasypus, and was, likewise, loosely attached by soft parts to the squamosal anteriorly and resting almost en- tirely on the tympanohyal posteriorly. The meatus faced laterally and was farther posterior to the glenoid cavity than in other armadillos, a point of resemblance to the glyptodonts. The glenoid surface differs from that of other armadillos and strongly resembles that of the glyp- todonts. The articular surface is at right angles to the long axis of the skull, narrow anteroposteriorly, wide transversely and gently convex in both these directions. A very large, U-shaped notch separates the glenoid articulation from the mastoid process; this is labeled as the glenoid cavity in Bordas's Figure 1 . Between the glenoid surface and the au- ditory region proper there is a conspicuous, ven- trally facing fossa within which the postglenoid foramen is situated. The fossa is separated from the auditory region by the thick ridge formed by 10 [A. G. Edmund, who is reviewing the Pampatheres, tells me that Plaina will have to be abandoned, since its genus type is a synonym. Vassallia is the appropriate replacement generic name, the species being V. maxima Castellanos, 1946.] " Bordas appears to have been influenced in his ac- count of the auditory region of Chlamytherium by the works of Huxley (1865) and Burmeister (1870-1874) on glyptodonts. Van Kam pen's correction of the errors made by these authors was apparently not available to him. PATTERSON ET AL.: EAR REGION IN XENARTHRANS. I. CINGULATES 35 OQ CO CO E o in c CO 00 , ■ CD CD o 00 "O o CD O jo c o E CO o O c 0 E o CO 00 CO CD O 2 n CO CO o "55 Q. CO CD 'o W CO GO o a E CD CD O O Q. B Q. C z> O O en "•£ 05 c '2 CO oo CO a E CO O ro c CD E CO "o o o "i§ CO "oo o CL a5 CD E CO a CO CL •"- tf'f £>^>. o 36 FIELDIANA: GEOLOGY the squamosal, which is so characteristic a feature of the Xenarthra. In the somewhat earlier, late Miocene Kraglievichia, this ridge would appear to have been more prominent than in Plaina, to judge from Castellanos's figure (1937, fig. 2). The tympanohyal is present, although incom- plete ventrally, on the right side of the skull. Here it projects medially, as a continuation of the crista facialis, as in other armadillos. The promontorium is well rounded, and slopes evenly upward and forward to the rather sharp anterointernal tip [of the petrosal], which is, how- ever, less pointed than in glyptodonts. There is a wide gap anteriorly between periotic [petrosal] and neighboring elements. Behind this promontorium and set off from it by a groove, the ventral surface of the pars petrosa forms a rather flat shelf. The fenestra rotundum ("fosa para el atrohial" in Bor- das's figure) is situated in the posterior part of the promontorium just beneath the junction of pro- montorium and shelf. The recessus epitympanicus is comparable in degree of definition to those of other armadillos. There is no indication of an epi- tympanic sinus. The crista facialis has evidently been damaged somewhat, especially in its poste- rior portion, during the preparation of the skull from the very hard matrix that enveloped it. On the left side, part at least of the processus cristae facialis remains; the extremity is thick and blunt, much as in the glyptodonts. The pars mastoidea has a large occipital exposure and forms the ven- trolateral corner of the occiput. The mastoid pro- cess (referred to as the postglenoid process by Bor- das), nearly all of which is formed by the pars mastoidea, is a massive structure directed antero- ventrally and terminating in a blunt tip. On the lateral side, near the junction of process and oc- cipital crest, there is a prominent protuberance. As in Priodontes, and [as in that form] presumably correlated with large size, the paroccipital process is well developed— for an armadillo.12 Situated immediately lateral to the condyle, it consists of a ventrally projecting knob of bone, which, again as in Priodontes, descends slightly lower on the side of the skull than the mastoid process. The two processes are separated by a deep and rather nar- row cleft, considerably narrower than the corre- sponding one in Priodontes. The internal carotid evidently entered the cra- 12 Large euphractines show no such development, but in these forms formation of a paroccipital process would appear to have been prevented by union of bulla and pars mastoidea immediately lateral to the occipital con- dyle. nial cavity via the gap anterior to the periotic. Bordas identifies the lateral portion of this gap as the foramen ovale, but this is not the case; the foramen ovale opens farther forward, well within the alisphenoid, as in all edentates. The second arterial canal appears to have run forward, as usu- al, between the periotic and the basicranial ele- ments. The postglenoid foramen is small and is situated within the fossa posterior to the glenoid articulation, as noted above; in glyptodonts the same foramen is similarly situated. The small subsquamosal foramen opens in a groove between the root of the mastoid process and the ridge that forms the upper border of the zygomatic process of the squamosal, a position precisely similar to that occupied by this foramen in glyptodonts. In Chlamytherium the subsquamosal is evidently larger than in Plaina. Bordas identified this as the porus, which is certainly not correct (the parts la- beled as external auditory meatus and crista meati in his fig. 1 are evidently portions of the mastoid process). The mastoid foramen is in the usual po- sition. The foramen lacerum posterior, as noted by Bordas, is relatively small. The facial nerve, after leaving the foramen stylomastoideum prim- itivum, ran ventrally in a groove in the medial surface of the mastoid process. The general appearance of the auditory region and of the surrounding parts of the chlamythere skull, taken as a whole, is highly distinctive. The very broad, ventrally convex, tuberculate basis cranii with the periotics set well above it; the bluntly terminating processus cristae facialis; the close ap- proximation of the mastoid process and exoccip- ital; the wide, transversely aligned glenoid surface and the zygomata that are so notably wider than the cranium; the fossa posterior to the glenoid sur- face, into which the postglenoid foramen opens; the relatively short basicranial region; the stout pterygoid processes— all these combine, as ob- served by Bordas, to form a whole that is decidedly glyptodont-like. Glyptodontoids Glyptodontidae Available material of this group is limited in extent.13 Fortunately, this lack is not particularly 13 This was true when Patterson and Segall did the study; while still somewhat limited today, such materials are more abundant now than when that statement was PATTERSON ET AL.: EAR REGION IN XENARTHRANS. I. CINGULATES 37 serious, since the glyptodont auditory region is stereotyped in comparison with the diversity en- countered among armadillos and sloths. In this section, therefore, individual descriptions are not given and a general account only is presented, based on the following skulls (those in Field Museum's collections bear "P" prefix): Propalaeohoplopho- rus australis Ameghino, PI 3205, from the early Miocene Santa Cruz Formation of Patagonia; Stromaphorus compressideus14 Castellanos (fide Hoffstetter, 1958) from the Andalgala Formation, Catamarca, Argentina; Hoplophractus proximus Moreno and Mercerat, PI 4501 (fig. 16A-B); and Eleutherocercus solidus14 Rovereto, P14475 (fig. 17), both from the Corral Quemado formation, Catamarca, Argentina. [These last two skulls are nearly complete, and are deserving of additional study. For example, that of Hoplophractus pre- serves the right premaxillary, which is small and endentulous but has a pair of anteriorly directed pits, one dorsal to its tip, the other ventral and adjacent the midline. To me these suggest attach- ment surfaces for tendons of a proboscis. Gillette and Ray (1981) did not find a preserved premax- illary in any of their Glyptotherium material, but they conclusively inferred its presence on the basis of thickness and form of the adjacent bones.] No trace of a tympanic or an entotympanic has yet been found in any glyptodont. Description of parts of the tympanic by earlier authors, Huxley (1865) and Burmeister (1870-1874), are now known to be erroneous and to have been based on misidentifications of other parts of the auditory region (see below). The tympanic very evidently was of the primitive horseshoe-shaped type, loose- ly attached to the tympanohyal posteriorly and to the squamosal ridge anteriorly; this ridge is more rounded and much more massive than in arma- dillos. Ridge and tympanohyal are well separated, and the incisura tympanica must therefore have been relatively wide. It is clear that the meatus written. There is as yet undescribed new material from South America, and two significant published works con- siderably improve the situation for glyptodont cranial study: that of Vinacci Thul (1945) [which Patterson and Segall were unaware of], whose description of the skull appears to be the first serious attempt in that direction since Burmeister (1 870-1 874) and Owen ( 1 845), and the more recent thorough and detailed monograph of the North American glyptodonts by Gillette and Ray (1981). 14 [The species compressideus is a Moreno and Mer- cerat species that Ameghino (1891) denied belonged to the genus Neuryurus, where M. & M. had placed it. The species solidas was named by Ameghino (1891) and questionably assigned to the genus Protoglyptodon.] was situated far behind the glenoid articulation, notably farther posteriorly than in all armadillos except the chlamytheres. The glenoid articulation is highly characteristic of the group. It is very wide transversely and nar- row anteroposteriorly, and stands out at a right angle to the skull. Posterior to and above the me- dial portion there is a large fossa [mandibular fos- sa] in which the postglenoid foramen (or foramina) is situated. ' 5 [Gillette & Ray (1981) show the man- dibular fossa in their illustrations of Glyptothe- rium taxonicum and Glyptotherium arizonae (their figs. 7-8, lOb-c), but they make no mention of a postglenoid foramen. In both Field Museum spec- imens here described, that foramen opens into the fossa.] Glyptodonts differ from all armadillos, again with the exception of the chlamytheres, in the structure of this area. The tympanohyal is best shown in our material on the left side of the skull of//, proximus, and even in this specimen the bone may not be com- plete ventrally. [Since this was written there has been further damage, so it is fortunate that the illustration, fig. 16B, was made at an earlier date.] As preserved, it is a relatively stout bar extending posterointernally from the crista facialis and pars mastoidea to the posterior portion of the ventral surface of the pars petrosa, where it comes in con- tact with a small spur from this surface. The ventral surface of the periotic [petrosal] is extensive. The promontorium is not at all sharply defined, no more so than in the eutatines, which are outstanding among armadillos in this respect. Anterior to it is a laterally compressed antero- ventromedially extending portion that terminates more sharply than in any armadillo. Medial and dorsal to this compressed portion is a shelf, vary- ing in width in the different forms, that slopes down to a large quadrangular, somewhat irregu- larly surfaced area behind the promontorium. This area, which is much larger than in any armadillo, continues posterolaterally into the pars mastoidea. On the left side of//, proximus, above the medial extremity of the tympanohyal, the quadrangular area sends down a small, posteriorly curving pro- cess, with which the tip of the tympanohyal comes into contact. [This can now only be seen on the right side due to subsequent damage.] No such process is to be seen on any of the other specimens available to us, but a small structure of this sort 15 Several of Lydekker's plates (1894, pis. 8, 16, 22, 31-32) show the condyle of the jaw resting in this fossa and not in articulation with the glenoid surface. 38 FIELDIANA: GEOLOGY PATTERSON ET AL.: EAR REGION IN XENARTHRANS. I. CINGULATES 39 ■g "o c _CD Ui CD CO b CO o CO CO o CO CD o CD CO CD CD a O T3 c O £ CO CO CO Q. CO Cl E E CO Cl CD CO Q. c CD E CO o p o H — • CO CO E CO C 3 CO O Q) C) l o