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Archs oral Bid

Vol. 30, No. 1,

pp.

71-82,

1985

0003-9969/85

3.00+ 0.00

Printed

in Great

Britain. All rights reserved

Copyright 0 1985Pergamon Press Ltd

EVOLUTIONARY TRENDS OF THE HISTOLOGICAL

PATTERN IN THE TEETH OF EDENTATA XENARTHRA)

J.

FERIGOLO

Department of Palaeontology and Stratigraphy, Federal University of Rio Grande do Sul and Museum

of Natural Sciences, Zoobotanical Foundation, Dr Salvador Franpa, 1427, 90.000-Porto Alegre, RS,

Brazil

Summary-In a comparative study of the dental structure of Edentata, the central tissue was identified

as a modified orthodentine, except in the Glyptodontidae where an osteodentine was found. Some

evolutionary trends of the tissues in these teeth may have been related with the extinction of ground sloths.

Comparative studies of the tissues in mammalian teeth seem to be good tests for systematics.

INTRODUCTION

The structure of the teeth of the Edentata

(Xenarthra) has been studied several times since the

pioneer work of Retzius (1837), but mostly or exclu-

sively in respect of the presence or absence of enamel

(e.g. Tomes, 1874; Pouchet and Chabry, 1884; R&e,

1892; Ballowitz, 1892; Spurgin, 1904; Martin, 1916).

Although some works deal with the different kinds of

dentine with which I am here concerned, no one has

attempted a general comparative study. For edentate

teeth, Owen’s

Odontogruphy

(1840-45) is still the

basic reference. More recent findings in polarized

light are available, for armadillos, in Keil and

Venema (1963) and, for tree sloths, in Schmidt and

Keil (1971).

As concerns enamel proper, I have not detected

it in unabraded teeth of Dasypus novemcinctus,

Euphractus sexcinctus and Tolypeutes matacus, nor

in those of a young Bradypus sp. but, as an enamel

organ exists in the Edentata in general, both the

absence of enamel or its presence as a thin layer

indicate a regressive (Simpson, 1932) or an autapo-

morphic character (McKenna, 1975).

MATERIALS AND METHODS

Teeth of extant and extinct Edentata were studied

in normal and polarized light, as well as in the

scanning electron microscope. For light microscopy,

ground sections were prepared in the usual way. For

the SEM studies, ground sections and fractured

surfaces were used. All the sections, as well as some

of the fractured surfaces, were sometimes treated with

2.5-5.0 per cent HCl for 3O-60min, before being

covered with gold-palladium and examined in a

JEOL (C 35) SEM at 15 kV.

List of species examined (MCN, Museu de Ciin-

cias Naturais):

Order: Edentata (Xenarthra)

Fam.: Dasypodidae

Chaetophractus villosus (MCN-MA 953)

Chaetophractus vellerosus (MCN-MA 952)

Euphractus sexcinctus (MCN-MA 958, 959, 960;

MCN-PV 007*)

Zuedyus pichiy (MCN-MA 963)

Pri odont es giganteus (MCN-MA 961)

Cabassous unicinctus (MCN-MA 951)

Tol ypeutes matacus

(MCN-MA 962)

Dasypus nov emcinctus

(MCN-MA 954,955,956)

Dasypus hybridus (MCN-MA 957)

Fam.: Glyptodontidae

Glyptodon? sp. (MCN-PV OO6*)

Fam.: Megatheriidae

M egatheri um

sp. (MCN-PV 004*)

Fam.: Mylodontidae

Lestodon sp. (MCN-PV 003*)

Scelidodon sp. (MCN-PV 005*)

Fam.: Bradypodidae

Bradypus infi catus

(MCN-MA 964)

Bradypus sp. (MCN-MA 965,966,967,968,969)

Choloepus didactylus (MCN-MA 970)

Choloepus sp. (MCN-MA 971, 972, 973, 974,

975)

Scaeopus torquatus

(MCN-MA 976, 977, 978)

All fossil specimens, marked *, came from Tarija

(Bolivia, Pleistocene); the recent ones came from

South or Central America. Histological nomenclature

follows in general the works by Mrvig (1951), Schmidt

and Keil (1958, 1971), Bradford (1967) and Boyde

(1971) except for the modified orthodentine.

FINDINGS

Dasypodidae (armadill os)

D. novemcinct us, D. hybri dus. In Dasypus, the teeth

consisted of cementum, orthodentine and modified

orthodentine (Plate Fig. 1). The cementum was thick

and cellular, in some teeth composed of concentric

layers with enclosed cementocyte lacunae. These

lacunae were usually more abundant in the layer

adjoining the orthodentine, where they were more

rounded and had fewer canaliculi than elsewhere. In

the outer layers, they were usually more fusiform with

the canaliculi directed mainly towards the external

surface of the tooth. In some teeth, there was also a

thin layer of cementum with few or no lacunae. The

cementum became thinner towards the intra-alveolar

part of the tooth, but a reduction in its thickness

towards the occlusal surface as described by Keil and

Venema (1963) could not be observed. Internal to the

cementum there was a hard tissue similar to other

mammalian orthodentines. The central portion of the

71

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72

J FERIGOLO

tooth was formed by a modified orthodentine with a

different birefringence and fewer dentinal tubules

than the adjacent orthodentine. It showed a larger

number of included vascular canals than that of other

Dasypodinae. The dentinal tubules were directed

axially, at the centre of the crown but were bent

slightly more outwards laterally. The included vascu-

lar canals had a hair-pin shape but no direct commu-

nication with the vessels of the pulp cavity, being

specially numerous near the long axis of teeth (as

described by Arsuffi, 1938, for Bradypus tri dacty lus).

In the specimens studied, the vascular canals were

regularly distributed, their convexity being directed

towards the occlusal surface, or in the lateral part of

the teeth towards the external one. They were always

parallel to the adjacent dentinal tubules.

P. giganteus. In this species, the tissues were similar

to those in other armadillos, though there were some

differences. The cementum was rather thick but

acellular (Plate Fig. 2). The central tissue, a slightly

modified orthodentine, was suggestive of that of

Dasypus, but had only a few vascular canals.

E. sexcinctus, C. unici nctus.

The tissues in the teeth

of these armadillos were similar to those in the others,

but there were also differences. The cementum was

thin and acellular. The slightly modified orthodentine

was like that of the other Dasypodinae, except that

it had no vascular canals. In the teeth of an adult

specimen of

Euphractus

from Tarija, the tissues

were exactly the same as those in the recent adult

specimen.

Z. pi chiy, C. vi ll osus, C. vell erosus, T. matacus. In

the teeth of these species, there were the same tissues

as in other Dasypodinae. The cementum (thin, acel-

lular) and the orthodentine were similar to those of

the armadillos just described. In immature Z. pichiy,

C. vil losus and C. vellerosus, nevertheless, as shown

by the polarizing microscopy, the central tissue was

a poorly-mineralized dentine, in some cases contain-

ing a few vascular canals (Plate Fig. 3). In one

immature specimen of Euphractus, a similar tissue

was found, but not in the adult stage. As evidence of

immaturity, in all these armadillos the skull bones

were still unfused. Only one young specimen of T.

matacus (still having conical teeth) was studied. The

central axis of the tooth had the same slightly-

modified orthodentine without vascular canals as was

observed in adult and young specimens of

Eu-

phractus,

and adult specimens of

Cabassous

as well.

The poorly-mineralized dentine present in immature

Zaedyus, Chaetophractus and Euphractus was not

found in young specimens of armadillos (D.

novemcinctus, Euphractus and Tolypeutes). Because

the specimens of

Zaedyus

and

Chaetophractus

were

immature ones, and that of

Tolypeutes

was young, it

was not possible to be positive about the adult tooth

structure.

Bradypodidae (tree sloths)

B. inj i i scat us, Bradypus sp., S. t orquat us, C. didac-

tylus, Choleopus sp.

In these sloths, the teeth had a

similar structure (with minor irrelevant differences),

but were also peculiar in some respects compared

with other Edentata. They were formed mainly by

tissues homologous with those of the Dasypodinae.

Although thicker than in

Dasypus,

the cementum was

similar. Sometimes a layer of acellular cementum

covered the cellular one. The orthodentine was also

similar to that of other mammals. In the modified

orthodentine, the most striking feature was the pres-

ence of a great number of vascular canals, lying in a

homogeneous mineralized matrix which, closer to the

centre, had few dentinal tubules or none at all. The

vascular canals had no apparent connection with the

pulp cavity vessels, except for those that were close to

the pulp. They were more or less regularly disposed,

parallel with the longitudinal axis of the tooth in the

central part, but more peripherally they diverged

slightly towards the external surface (Plate Fig. 5).

Between the central modified orthodentine and the

external orthodentine, there was another tissue show-

ing both dentinal tubules, continuous with those of

the orthodentine, and vascular canals as in the mod-

ified orthodentine (Plate Fig. 4; orthovasodentine of

Arsuffi, 1938). Although in the teeth of

Choloepus

the

structure was usually similar to that in Bradypus and

Scaeopus, the cementum was sometimes thin, and in

some cases the central dentine was almost amorphous

with only a few vascular canals or none.

Young specimen of Bradypus sp.

In the teeth of a

young Bradypus sp. (skull 48 mm long), some special

features were found. The cementum was thin and

acellular in the cusp tip but, towards the intra-

alveolar part, it gradually became thicker and cellu-

lar. Near the limits of the pulp chamber it again

became thiner but was still cellular. The orthodentine

was similar to that in the teeth of the adult specimens.

In the modified orthodentine, just below the ortho-

dentine of the cusp tip there were irregular dentinal

tubules (Plate Fig. 6) but no vascular canals. In the

direction of the intra-alveolar part, this tissue

presented less dentinal tubules and some few vascular

canals which increased in number in the same direc-

tion. Between the external orthodentine and the

internal modified orthodentine, there was an inter-

mediary tissue, similar to that found in the adult tree

sloths (Arsuffi’s orthovasodentine).

M yl odontidae and M egatheri idae (ground sloths)

Scel i dodon sp., Lestodon sp., Megatherium sp. In

the teeth of these ground sloths, the tissues closely

resembled those in the tree sloths, the modified

orthodentine being, however, highly developed. The

thick cementum was formed as appositional layers in

Scelidodon, but was more strongly developed in Le-

stodon (Plate Fig. 7) and M egatheri um. Particularly

in M egatherium, it was a highly-developed vaso-

cementum presenting a complex pattern of vascular

canals. In all specimens, the orthodentine (Plate Fig.

8) was of similar structure. In Scelidodon, and possi-

bly in Lestodon, this tissue seemed to retain its

thickness. In

Megatheri um

it was reduced to a thin

layer interposed between cementum and modified

orthodentine (cf. Owen, 1840-1845, plate 83). In the

modified orthodentine, the vascular canals (Plate Figs

9-12) were more numerous and longer than in the

homologous tissue of the tree sloths. Between the

external orthodentine and the internal modified or-

thodentine, there was in M egatheri um (Fig. 12) and

Lestodon, an intermediary tissue corresponding again

to the orthovasodentine of Arsuffi (1938). It was not

possible to identify this tissue in Scelidodon (Fig. 9).

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Histological pattern in the teeth of Edentata

13

Glyptodontidae

Glyptodon? sp. Here I found striking differences

from other Edentata. As the available specimen was

not well preserved, the real nature of cementum was

uncertain. The orthodentine showed the usual fea-

tures. The central tissue, however, forming the prom-

inent ridges that have been used for systematic pur-

poses, was not a modified orthodentine but contained

a great number of well developed vascular canals,

surrounded by concentric incremental lines. It was

not possible to find any lacunae for cells (osteocytes)

nor dentinal tubules in these layers (Plate Figs 13

and 14).

DIS USSION

M odi Jed orthodenti ne

In armadillos, the tissue considered by Owen

(184Gl845, p. 342) as a “hard substance, closely

resembling bone” (see also his plate 85) and by

Arsuffi (1938) as a “kanalisiertes Dentin”, was recog-

nized as independent of the surrounding orthodentine

by Keil and Venema (1963) using mainly polarized

light. Arsuffi also described inside these vascular

canals some odontoblasts, connective tissue and what

she called pulpareticulum cells, but could only study

the walls of the vessels near the pulp chamber,

probably due to degeneration of tissues after losing

communication with the pulp vessels. Keil and

Venema (1963) using microhardness tests found that

the modified orthodentine is softer than the sur-

rounding orthodentine, which can be seen by direct

inspection. As far as I can see, the part played by the

tissues in the ridges of the teeth of armadillos is not

clear, because in the same specimen some teeth have

a ridge including all tissues and others have no ridge

at all. In both armadillos and tree sloths, the ridges

seem to depend more on the direction of the masti-

catory movements and on the position of teeth in

occlusion than on the arrangement of tissues.

Concerning Euphractus and Cabassous, the

findings agreed with the observations of Retzius

(1837) and Keil and Venema (1963), but not com-

pletely with those of Owen (184&l 845) dealing with

armadillos in general. Although it is not clear from

his description, Owen probably described the teeth of

Dasypus as if they were of Euphractus, which can be

seen by the presence both of vascular canals in the

modified orthodentine and of cellular cementum (see

Owen plate 85). Contrary to what Owen (p. 324)

supposed, not all armadillos have the same structure

nor a “hard substance, closely resembling bone” in

the central part of the teeth.

The central tissue of the teeth of

Zaedyus, C.

vi ll osus, C. vell erosus

and of the immature specimen

of Euphractus,

is a

poorly-mineralized dentine which

seems to be formed in the growing teeth of immature

specimens, corresponding to the slightly-modified

orthodentine of the adult ones, before full mineral-

ization takes place.

The structure of the teeth of tree sloths in general

agreed with the descriptions by Retzius (1837) Owen

(184&1845), Schmidt (1924) Arsuffi (1938) and

Schmidt and Keil (1958, 1971), except that, contrary

to what was maintained by Retzius and Owen, no

OB3”*1

direct connection was found between the vascular

canals and the dentinal tubules (as also pointed out

by Schmidt and Arsuffi).

The description given by Owen (184&l 845) for a

supposed young

Bradypus

disagrees in several points

with what was found in the specimen here studied.

Contrary to what was said by Owen (p. 329), the teeth

of young Bradypus were not formed “chiefly of the

hard dentine, which is covered by cement, and has its

cavity lined by a layer of unvascular dentine”. As

shown by dentinal-tubules orientation in the superior

portion, and the lack of the occlusal part of the tooth

(absence of cementum and orthodentine), the speci-

men figured on his plate 82, seems to be actually an

oblique section of an already worn tooth (as already

pointed out by Pouchet and Chabry, 1884).

The structure in M egatherium and Scelidodon sub-

stantially agreed with the descriptions by Owen

(1840-1845 pp. 338, 342-344; see also his plates 83

and 84) for M egatheri um and Scelidotherium.

As far as I can see, there are two main reasons for

considering the central tissue of the teeth of the tree

and ground sloths as modified orthodentine, homolo-

gous with that of armadillos: (a) a slightly modified

orthodentine in the central portion of the teeth of a

young Bradypus sp., regarded here as being inter-

mediary between typical orthodentine and the

modified orthodentine of the adult specimens; (b) an

intermediary tissue found between orthodentine and

modified orthodentine in the tree sloths and some

ground sloths (“Ortho-Vasodentin” of Arsuffi, 1938,

p. 758). It is also possible to interpret such tissue as

the most peripheral part of the central modified

orthodentine, but the main point here is not what

name should be applied to this tissue, but to recog-

nize it as intermediary between the typical ortho-

dentine and the modified orthodentine.

In his classification of dentines, Orvig (1951) in-

cluded the “orthovasodentine” of Arsuffi (1938)

among the orthodentines. With regard to the arma-

dillos and sloths (with the possible exception of

Orophodontoidea), this interpretation is more accu-

rate than that of Arsuffi, because the “vasodentines”

and the “orthovasodentines” are only different stages

of a modified orthodentine. As Mrvig (p. 343) said “It

is true that vasodentine differs from ordinary ortho-

dentine in that it is without dentinal tubes and

contains numerous capillaries. The absence of odon-

toblast processes is secondary, however, for. . these

processes are present at the earlier stages of devel-

opment of the vasodentine but disappear more or less

completely at later stages”. In the intermediary tissue

of the teeth of a young

Bradypus

sp., the dentinal

tubules were still present (Fig. 6). In the intermediary

tissue in the tree sloths, and some ground sloths, the

dentinal tubules persisted in adult growing teeth

together with vascular canals, findings usually used to

characterize the vasodentines. Thus, there were in the

sloths all degrees of transition from a typical ortho-

dentine to a vasodentine (i.e. modified orthodentine).

The interpretation in sloths, of different stages of a

modified orthodentine agreed with the opinion of

Schmidt (1924) on the origin of this tissue in B.

tridactylus. According to him, the odontoblasts

should during dentine formation achieve increasing

contact with the tissues of the pulp, and, finally, the

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74

J.

FERIGOLQ

odontoblasts surpass the vascular loops (of the pulp)

that are in this way, included in the dentine. The

absence or scarcity of dentinal tubules he supposed to

be due to reduction. This opinion seems to be corrob-

orated by the facts above.

In armadillos, tree and ground sloths, the name

vasodentine is not appropriate mainly because it has

been used frequently to describe several different

varieties of orthodentine (lilrvig, 1951, 1967). Al-

though Arsuffi (1938) had given a detailed description

of the modified orthodentine (her “vasodentine” or

“calcified pulp”), as far as I can see her interpretation

is not entirely correct, thinking that it is a kind of

mineralized pulp formed to avoid the pulp to be

exposed in the mouth. I do not agree, mainly because

in the young Bradypus sp. discussed here, a well-

developed modified orthodentine was found. The

abrasion process was here in its beginning. The

continuously-growing and abrasion processes should

be considered as normal ones in the teeth of the

Edentata [as already pointed out by Arsuffi (1938) for

B. triductvlus].

The interpretation of the modified

orthodentme as resulting from the fast growing and

abrasion processes is not appropriate mainly because

a portion of a fast growing and typical orthodentine

was still preserved in all teeth examined. Sasso and

Della Serra (1965) were the only authors who inter-

pretated the modified orthodentine (of

Brndypus tri-

dactylus) as a variety of orthodentine (their “vascu-

larized orthodentine”).

Osteodentine

Concerning the histological pattern of the glyp-

todontid, the features agreed with Owen (184&l 845,

p. 325; see also his plate 86) except for certain points.

He described the teeth of

Glyptodon

as having their

central portion formed by “vascular osseous tex-

ture”. He went on to say that “The medullary canals

are surrounded by fine compact concentric strata, but

are wider than in true bone”. Owen observed in these

teeth a tissue similar to, or the same as, in the

specimen discussed here. Forming prominent ridges

in the teeth, this tissue is clearly different from the

modified orthodentine of other Edentata, in the

abrasion process. In my view, the structures in Glyp-

todon

described both by Owen and here

(Glyptodon?)

could be interpreted as bone (osteons) or as dentine

(denteons). Nevertheless, a significant feature is that

in plate

86

of Owen’s

Odontogruphy,

the concentric

layers of hard tissue surrounding the vascular canals

are traversed by thin lines, radially disposed, which

probably correspond to dentinal tubules. Owen did

not show any lacunae for cells (osteocytes) between

these layers. The presence of such supposed dentinal

tubules suggests an interpretation of this tissue as a

typical osteodentine, uncommon in mammalian

teeth, but frequent enough in lower vertebrates (see

e.g. Orvig, 1951, 1967, 1976). Although Owen (p. 325)

gave a full description of dental tissues in

Glyptodon

and other Edentata, he did not realize the funda-

mental difference between osteodentine and modified

orthodentine of the teeth of Glyptodon and arma-

dillos: “In the

Glyptodon

the vascular osseous texture

occupies a larger proportion. than in the small

Armadillos”; ‘*. .

their intimate texture and com-

position are essentially the same”.

Hoffstetter (1958, p. 595) pointed out that the

Orophodontoidea, considered by him as a lateral

branch in the evolution of the ground sloths, have in

the central part of their teeth a “. vascular dentine

(probably osteodentine). This structure recalls that in

the majority of Cingulata especially that of Pam-

patherines” (my translation). If this is correct, one

should deduce that both the Glyptodontidae and

the Orophodontoidea must have osteodentine in

their teeth. One possible representative of the Oro-

phodontoidea,

Palaeopeltis

is supposed to have had

an osseous dermal armour, which could be another

important character shared with the Glyptodontidae.

If Pakzeopeftis actually has an osteodentine in its

teeth, considering this and other characters, it should

be more appropriate to interpret it as belonging to

some Glyptodontidae

incertae sedis

as did Simpson

(1945, p. 75) or as an aberrant glyptodontid as did

Paula Couto (1979, p. 190). The possibility of a

synapomorphy between Glyptodontidae and Oro-

phodontidae should be considered, because, as far as

I know, these would be the only groups of Edentata

(with the possible exception of the Pampatheriinae)

that share this character. On the other hand, the

assumption of Hoffstetter (1958) that the structure of

the teeth of the Orophodontoidea is similar to that of

the Cingulata, is not quite correct, because in the

Dasypodinae here studied the central tissue of the

teeth consisted of a modified orthodentine and not of

an osteodentine. Nevertheless, if his assumption in

what concerns the Pampatheriinae is correct (con-

sidering only this character) this group could be more

closely related to the Glyptodontidae (and Oro-

phodontidae) than we have so far believed. Because

of this, it would be more appropriate to classify the

pampatheres as an independent family, as suggested

by Ameghino (1920) Castellanos (1937) James

(1957) and Paula Couto (1980). This point could be

illuminated by a comparative study of teeth tissues

including the Dasypodinae, Pampatheriinae, Glyp-

todontidae and Orophodontidae.

Cementum

The degree of development of cementum may not

be independent of the formation of the modified

orthodentine but closely related to the development

of orthodentine as a compensatory mechanism for

abrasion. In accord with this interpretation, a greater

apposition of cementum was found in species where

there was a greater development of the modified

orthodentine or a trend towards an increase in the

vascular canals in that tissue. For instance, the

cementum in

Dasypus

(Fig. 1) was thick and cellular

and the modified orthodentine showed the largest

number of vascular canals in the armadillos studied.

Modified orthodentine has a lower degree of re-

sistance to wear than the adjacent orthodentine, as

shown by microhardness tests (Keil and Venema,

1963). Similarly, a still greater development of

modified orthodentine, with a even greater number

of vascular canals, was found in the tree sloths, and

once more a greater apposition of cellular cementum

(Fig. 5). Furthermore in ground sloths there was the

highest degree of development of the modified ortho-

dentine with the greatest number of vascular canals

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Histological pattern in

(Fig. 9) and the

heaviest apposition of cementurn

(Fig. 7). Interpret these extreme degrees of devel-

opment of cementurn as physiological hyper-

cementosis. In the glyptodontids in which there is an

osteodentine which is highly resistant to abrasion,

cementum seemed to be thinner than in the sloths.

Evoluti onary tr ends of t he ti mes

Phylogenetic reconstructions based on the analysis

of a few characters cannot obviously be made, al-

though some speculations are possible. The osteo-

dentine of the Glyptodontidae is different from the

modified orthodentine of other Edentata in its strut,

ture, and has probably evolved in relation to the

Orophodontidae and Pampatheriinae, if Hoffstetter

(1958) is correct. Considering armadillos, tree and

ground sloths, the structure of the teeth suggests two

possibilities namely they may have evolved by one or

by two evolutionary trends. If the teeth of an arma-

dillo like

Dasypus

is the primitive form, all the teeth

of the armadillos and sloths could easily derive from

it, by (Text Fig. 15): (a) a reduction and disap-

pearance of vascular canals in modified orthodentine.

the teeth of Edentata

75

and a reduction in the thickness of cementum (as in

Euphractus

and

Cabassous);

(b) a non-adaptive trend

towards greater development of modified ortho-

dentine (with an increased development of vascular

canals) and of cementum (as in

Bradypus, Scaeopus

and

Choloepus); a still greater development of these

tissues, in ground sloths (as Lestodon, Scelidodon and

mainly M egatheri tun). A stasigenetic stage could be

represented by Dasypus (and in a lesser degree by

Priodontes).

If the teeth of an armadillo like

Euphractus or

Cabassous are regarded as the primitive form, it is

possible to see a unique trend for the derivation of the

dental structure of other armadillos and sloths as well

(Text Fig. 16): (a) an inclusion of a few vascular

canals in the modified orthodentine, and a devel-

opment of a slightly-thicker acellular cementum (as in

Priodonres); (b)

the non-adaptive greater inclusion of

vascular canals in modified orthodentine and a still

greater deposition of cellular cementurn (as in Da-

sypus); (c) an even greater development of modified

orthodentine (and of vascular canals) as in the tree

sloths, the most extreme example being in the

ground

Fig. 15. Diagram of the first hypothesis; (A) represented by Dosypus; (B) by Priodontes; (C) by

Euphractus; (D) by the tree sloths; (E) by M egatherium. Not in scale.

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J. FERIGOLO

Fig. 16. Diagram of the second hypothesis; (A) represented

by

Euphractus;

B) by

Pri odont es; C)

by

Dasypus;

D) by

the tree sloths; (E) by M egatherizun.

Not

in scale.

sloths (like

Lest odon, Scel i dodon ,

and specially

M ega-

therium). A stasigenetic stage could be represented by

Euphractus

and

Cabassous.

As the histological pattern of the teeth of arma-

dillos such as

Euphractus

and

Cabassous

(thin ace-

llular cementum, orthodentine and slightly-modified

orthodentine) is closer to that of most mammals, the

second hypothesis seems the most appropriate one. In

this case, the condition in Euphractus and Cabassous

should be relatively plesiomorphic.

Dental histol ogy and the exti ncti on of some ground

sloths

The development in the Edentata of a modified

orthodentine, which has low resistance to abrasion,

in some ground sloths, is noteworthy as is the thick

cementum in these forms. The vasocementum, for

example, in

Megatherium,

was as easily abraded as

the modified orthodentine. The orthodentine formed

only prominent thin ridges interposed between these

tissues.

If in some ground sloths the relative thickness of

the orthodentine (in comparison with other tissues)

seems to be preserved (e.g.

Srelidodon),

in others

there may not only have been greater development

of modified orthodentine but at the same time a

reduction in the thickness of the orthodentine itself.

As the modified orthodentine seems to have evolved

from a typical orthodentine, it is logical to assume the

development of the modified orthodentine having

taken place at the expense of the orthodentine itself.

The development, in continuously-growing teeth, of

a tissue less resistant to wear could have been a

dangerous trend in the evolution of some ground

sloths and could have contributed to their extinc-

tion, bearing in mind the importance of mastication

and the consequent wear of the teeth in these

huge herbivorous animals. Associated climatic/floral

changes in Pleistocene may also have contributed. A

trend towards the reduction of orthodentine and a

large development of modified orthodentine (an ex-

treme degree of which could be represented by M ega -

therium),

would have been affected by natural selec-

tion. If in this trend a greater wear of the teeth could

be physiologically compensated in some way, for

example, by still greater apposition of the cementum,

a faster rate of growth, such a trend could have

remained unaffected by natural selection for a long

time. Nevertheless, as seen in

M egatherium,

the vaso-

cementum seems no more effective in compensating

wear: apparently it did not increase resistance to wear

of the teeth, except by forming a larger occlusal

surface.

In the latter representatives of animals like

M egatherium, we could have had the deleterious

grade of a non-adaptive trend, i.e. of a failed experi-

ment.

Acknow ledgement s-l

am grateful to the technical staff,

Section of Palaeozoology, Swedish Museum of Natural

History (SMNH), and in-particular to: Mr G. Blom for his

kind heln with the SEM: Mr L. Anderson for the artwork:

Mr B. ‘Bergman for the Plates; Mr U. Samuelson for

photographic copies. 1 should also express my gratitude to

Dr A. G. Johnels and Dr B.-O. Stolt. Section of Vertebrate

Zoology (SMNH), and Dr C. de Paula Couto, Federal

University of Rio Grande do Sul, Brazil, for providing me

material; Dr L. Brundin, Section of Entomology (SMNH),

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Histological pattern in

the teeth of Edentata

for his constructive criticism and advice. I want to express

my great indebtness to Dr Tor 0rvig, Director, Section of

Palaeozoology (SMNH), for the fossil specimens, for the

kind interest he has taken in this research, for stylistic

corrections, and above all for his friendship and kindness

when I was in Stockholm during the winter 1981/82. Finally,

I wish to thank the other authorities of the Swedish Museum

of Natural History (Naturhistoriska riksmuseet), Stock-

holm, where this work was carried out, and to the CNPq,

Brazil, for financial support.

REFEREN ES

Ameghino F. (1920) Cobras(Edited by Torcelli A. J.) Vol. 11.

La Plata Taller impressiones Oficiales, La Plata.

ArsulIi E. (1938) Beitrage zur Kenntnis des Vasodentins. 2.

Anat . EntwGesch. 108, 149-160.

Ballowitz E. (1892) Das Schmelzorgan der Edentaten, seine

Ausbildung im Embryo,

und die Persistenz seines

Keimrandes bei dem erwachsenen Thier.

Arch. mikrosk.

Anat . Entw M ech. 40, 133-156.

Boyde A. (1971) Comparative histology of mammalian

teeth. In: Dental M orphology and Evolut ion (Edited by

Dahlberg A. A.) pp. 81-94. University of Chicago Press,

Chicago.

Bradford E. W.

I

967) Microanatomy and histochemistry of

dentine. In: Structural and Chemical Organizat ion of Teeth

(Edited by Miles A. E. W.) Vol. 2,

pp.

3-34. Academic

Press, New York.

Castellanos A. (1937) Anotaciones sobre la linea filogenetica

de 10s Clamiterios. Publ s I nst. Fisi ogr. Geol. S. Fe 8. l -35.

Hoffstetter R. (1958) Xenarthra. In:

Trait k de Paleontol ogie

(Edited by Piveteau J.) Vol. 6, 2, pp. 535-636. Masson,

Paris.

James G. T. (1957) An edentate from the Pleistocene of

Texas. J. Pal eont . 31, 796808.

Keil A. and Venema B. (1963) Struktur und Mi-

krohlrteuntersuchungen an Zlhnen von Giirteltieren

(Xenarthra).

2001. Bei t r, 9, 173-195.

Martin B. E. (1916) Tooth development in Dasypus nouem-

cinct us. J. M orph . 27, 647-691.

McKenna M. C. 1975) oward a phylogenetic classification

of the Mammalia. In: Phylogeny of the Primates (Edited

bv Luckett W. P. and Szalav F. S.)

DD

2146. Plenum

Press, New York.

I . .

Orvig T. (1951) Histologic studies of placoderms and fossil

77

elasmobranchs. 1: The endoskeleton with remarks on the

hard tissues of lower vertebrates in general Ark. Zool. 2,

321-454.

Orvig T. (1967) Phylogeny of tooth tissues: Evolution of

some calcified tissues in early vertebrates. In:

Structural

and Chemical Organizat ion -of Teeth

(Edited by Miles

A. E. W.) Vol. 1.DP 45-l 10. Academic Press. New York.

Orvig T. (1976) Paiaeohistological notes: 4:’ The inter-

pretation of osteodentine with remarks on the dentition

in the devonian diphoan Griphognathus. Zool. Ser. 5,

79-96.

Owen R. (1840-1845)

Odontography.

Baillibre, London.

Paula Couto C. de (1979) Tratado de Paleomastozoologia.

Academia Brasileira de Citncias, Rio de Janeiro.

Paula Couto C. de (1980) Urn tatu gigante do Pleistocene

de Santa Catarina.

An. Acad. brasil. Cienc., 52, 527-531.

Pouchet G. and Chabry L. (1884) Contribution a

l’odontologie des Matnmiferes. J. Anat. Physiol. 20,

149-192.

Retzius A. (1837) Mikroskopiska undersiikingar iifver Tan-

demes, siideles Tandbenets struktur. KVA Handl.

1836

l-88.

Rose C. (1892) Beitrlge zur Zahnentwickelung der Eden-

taten.

Anat.

Anr. 7, 495-512.

Sasso W. da S. and Della Serra 0. (1965) Observa9bes sobre

as estruturas de dentes de xenartros pertencentes aos

erOS Day pus, Euphractus e Bradypus (Edentata,

Mammalial. Revt a bras. Biol. 25, 157-164.

Schmidt W. ‘J. (1924) Ueber das Dentin von Bra pus

tr iai scty lus. Anat . Am. 58, 97-107.

Schmidt W. J. and Keil A. (1958)

Di e gesunden und die

erk rank ten Zahngew ebe des M enschen und der W ir belt iere

im Polarisat i onmikroskop.

Carl Hanser, Miinchen.

Schmidt W. J. and Keil A. (1971)

Polari zing M icroscopy of

Dental Tissues (Translated by Poole D. F. and Darling

A. I.). Pergamon Press, Braunscheig.

Simpson G. G. (1932) Enamel on the teeth of an Eocene

edentate. Am . Mus. Nov it . 567, 1-4.

Simpson G. G. (1945) The principles of classification and a

classification of mammals.

Bull . Am. M us. nat. Hi st. 85,

l-350.

Spurgin A. M. (1904) Enamel in the teeth of an embryo

edentate (Dasypus novemcinctus Linn.). Am. J. Anat. 3,

75-84.

Tomes C. S. (1874) On the existence of an enamel, organ in

the armadillo. Q. Jl m i crosc. Sci. 1874, 44-48.

Plates 14 overleaf.

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J. FERI KILO

Plate 1.

Fig. 1. Longitudinal thin section of a tooth of

D. nmemcinctus

showing thick cellular cementurn (a),

orthodentine (b) and vascular canals (arrow) in the modified orthodentine (c). MCN-MA 956. x 54

Fig. 2. SEM of longitudinally-fractured tooth of P. gigunfeus showing orthodentine (a) and acellular

cementurn (b). MCN-MA 961. x 1780

Fig. 3. SEM of etched tooth fragment showing modified orthodentine of Z. pi&y with vascular canal

(arrow). MCN-MA 963. x 930

Fig. 4. SEM of etched tooth fragment of Brudypus sp. showing the intermediary tissue (a), orthodentine

(b) and modified orthodentine (c); note dentinal tubules and vascular canals (arrows) in (a). MCN-MA

968. x200

Plate 2.

Fig. 5. Longitudinal thin section of a tooth of Bradypus sp. showing cellular cementum (a), orthodentine

(b) and modified orthodentine (c) with vascular canals (arrow). MCN-MA 966. x 124

Fig. 6. Longitudinal thin section of a tooth of young Bradypus sp. showing irregular dentinal tubules

(arrow) and vascular canals in modified orthodentine (a). MCN-MA 965. x 100

Plate 3.

Fig. 7. SEM of etched transverse section of a tooth of Lestodon sp. showing vascular canals (arrows) in

cementum. MCN-PV 003. x 37

Fig. 8. SEM of etched transverse section of a tooth of Lesfodon sp. showing natural casts of dentinal

tubules. MCN-PV 003. x 2060

Fig. 9. Transverse thin section of a tooth of Scelidodon sp. showing vascular canals (arrow) in modified

orthodentine (a); note absence of an intermediary tissue between (a) and orthodentine (b). MCN-PV 005.

x 158

Fig. 10. SEM of etched transverse section of a tooth of

Scelidodon

sp. showing natural casts of vascular

canals (arrow) in modified orthodentine. MCN-PV 005. x 460

Plate 4.

Fig. 11. SEM of etched transverse section of a tooth of Megatheri um sp. showing natural cast of vascular

canal (arrow) in modified orthodentine. MCN-PV 004. x 460

Fig. 12. Transverse thin section of a tooth of Megurherium sp. showing the intermediary tissue (a) and

orthodentine (b); modified orthodentine not shown; note dentinal tubules and vascular canals (arrow) in

(a) MCN-PV 004. x 390

Fig. 13. Transverse thin section of a tooth of Gfypfodon ? sp. showing orthodentine (a) and osteodentine

(b); note concentrical layers in denteons (arrow). MCN-PV 006. x 160

Fig. 14. SEM of etched transverse section of a tooth of

Glyplodon

?

sp. showing orthodentine (a) and

osteodentine (b). MCN-PV 006. x 110

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Plate 1.

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Plate 2

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81

J

,i

i--F-~

Plate 3.

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Plate 4