PROBOSCIDEA
Suborder Pyrotheria
This suborder was established by Ameghino to receive the peculiar genus
_Pyrotherium_ and related forms. These animals are of large size,
massive build, with narrow elongated skulls, in which the nasal opening
is situated far back, as in animals with a proboscis; with a tiny brain
case surrounded by cellular spaces; with the maxillae, palatines,
pterygoids and alisphenoids developed downward, so that the palatal
plane makes a strong angle with the basicranial plane; and with the
occipital condyles high up on the back of the skull. Then the first and
second upper incisors and the second lower incisors are developed into
enormous tushes with enamel on the anterior sides only. The remaining
incisors, the canines, upper premolar 1, and lower premolars 1 and 2
are wanting; the remaining premolars and the molars being developed
into great quadrilateral grinders, each with two transverse crests.
The neck is short, the limbs massive and short, especially the lower
members of each limb, and the feet were probably five-toed.
The relationship of these forms has been the subject of extended
discussion: Ameghino seeing in this genus the ancestors of the
_Proboscidea_, and comparing them with _Palaeomastodon_, _Dinotherium_
and _Barytherium_, even finding resemblances to _Diprotodon_;
Gaudry concludes that they are not proboscidians; and others have
suggested that they were specialized toxodonts. I have prepared the
following table of comparisons with _Palaeomastodon_, a toxodont, and
_Diprotodon_.
===+======================+====================+===================
| | PYROTHERIUM | PALAEOMASTODON
---+----------------------+--------------------+-------------------
1 | Upper tush | Inc. 1 enlarged |Inc. 1 enlarged
| | | in Moeritherium.
| | Inc. 2 tush | Inc. 2 tush
---+----------------------+--------------------+-------------------
2 | Upper molars | Bilophodont |Bilophodont in
| | | Mastodon and
| | | Dinotherium
---+----------------------+--------------------+-------------------
3 | Lower tush | Inc. 2 (?) | Inc. 2
---+----------------------+--------------------+-------------------
4 | Lower molars | Bilophodont |Bilophodont in
| | | Mastodon and
| | | Dinotherium
---+----------------------+--------------------+-------------------
5 | Nasal opening | Over molar 1 | Over molar 1
---+----------------------+--------------------+-------------------
6 | Basicranial axis |Plane of base of |Plane of base of
| | cranium bent up, | cranium bent up,
| | makes 140° with | makes 155° with
| | plane of palate | plane of palate
---+----------------------+--------------------+-------------------
7 | Pterygoids |Pterygoids plus |Pterygoids plus
| | alisphenoids | alisphenoids
| | make great vertical| make great vertical
| | plates | plates
---+----------------------+--------------------+-------------------
8 | Jugal |Takes small part |Takes small part
| | on glenoid fossa | on glenoid fossa
---+----------------------+--------------------+-------------------
9 | Post-tympanic process|Surrounds meatus, |Surrounds meatus
| of squamosum | and crowds out | and crowds out
| | tympanic | tympanic
---+----------------------+--------------------+-------------------
10 | Tympanic bulla |Small, inflated, |Small, inflated,
| | hollow | hollow
---+----------------------+--------------------+-------------------
11 | Palatine bones |Narrow in front, |Narrow in front,
| | expanding behind | expanding behind
---+----------------------+--------------------+-------------------
12 | Premaxilla |Crowded out from |Crowded out from
| | forming any | forming any
| | portion of palate | portion of palate
---+----------------------+--------------------+-------------------
13 | Antorbital foramen | 2 foramena | 2 foramena
---+----------------------+--------------------+-------------------
14 | Intercellular laminae| Present | Present
---+----------------------+--------------------+-------------------
15 | Atlas |Long, has |Long, has
| | hypophysis | hypophysis
---+----------------------+--------------------+-------------------
16 | Axis |Hemispherical | Rounded odontoid
| | odontoid |
---+----------------------+--------------------+-------------------
17 | Cervicals 3-7 | Very short | Very short
---+----------------------+--------------------+-------------------
18 | Humerus |Flattened deltoid | Flattened deltoid
| | ridge with post. | ridge with post.
| | spur | spur
---+----------------------+--------------------+-------------------
19 | Radius and Ulna |Very short and |
| | massive |
---+----------------------+--------------------+-------------------
20 | Femur |Flattened, |Flattened,
| | Gr. trochanter | Gr. trochanter
| | low, no 3rd | low, trace
| | trochanter | of 3rd trochanter
---+----------------------+--------------------+-------------------
21 | Tibia |Short and massive, |Short and massive,
| | free from fibula | free from fibula
---+----------------------+--------------------+-------------------
===+======================+====================+====================
| | TOXODONT, NESODON | DIPROTODON
---+----------------------+--------------------+--------------------
1 | Upper tush |Inc. 1 reduced | Inc. 1 tush
| |Inc. 2 caniniform |
| | tush | Inc. 2 reduced
---+----------------------+--------------------+--------------------
2 | Upper molars | Rhinoceros-like | Bilophodont
| | |
| | |
---+----------------------+--------------------+--------------------
3 | Lower tush | Inc. 3 | Inc. 1
---+----------------------+--------------------+--------------------
4 | Lower molars | Bicrescentric | Bilophodont
| | |
| | |
---+----------------------+--------------------+--------------------
5 | Nasal opening | Over incisors | Over diastema
---+----------------------+--------------------+--------------------
6 | Basicranial axis |Plane of base of |Plane of base of
| | cranium parallel | cranium parallel
| | with plane of | with plane of
| | palate | palate
---+----------------------+--------------------+--------------------
7 | Pterygoids | Pterygoids normal | Pterygoids normal
| | |
| | |
| | |
| | |
---+----------------------+--------------------+--------------------
8 | Jugal |Takes no part on |Extends to
| | glenoid fossa | glenoid fossa
---+----------------------+--------------------+--------------------
9 | Post-tympanic process|Surrounds meatus |Not surround meatus
| of squamosum | and crowds | nor crowd
| | out tympanic | out tympanic
---+----------------------+--------------------+--------------------
10 | Tympanic bulla |Large, inflated, |
| | hollow |
---+----------------------+--------------------+--------------------
11 | Palatine bones |Wide in front, |
| | narrowing |
| | somewhat |
---+----------------------+--------------------+--------------------
12 | Premaxilla |Makes front of | Fused to maxilla
| | palate |
| | |
---+----------------------+--------------------+--------------------
13 | Antorbital foramen | 1 foramen | 1 foramen
---+----------------------+--------------------+--------------------
14 | Intercellular laminae| None | None
---+----------------------+--------------------+--------------------
15 | Atlas |Long, |Short,
| | no hypophysis | no hypophysis
---+----------------------+--------------------+--------------------
16 | Axis | Peg like odontoid |Odontoid slightly
| | | flattened on top
---+----------------------+--------------------+--------------------
17 | Cervicals 3-7 | Moderately long | Short
---+----------------------+--------------------+--------------------
18 | Humerus |Rounded no spur |Flattened distally,
| | on deltoid ridge | tiny spur on
| | | deltoid ridge
---+----------------------+--------------------+--------------------
19 | Radius and Ulna | Moderate length | Fairly long
| | |
---+----------------------+--------------------+--------------------
20 | Femur |Rounded, |Rounded,
| | Gr. trochanter | Gr. trochanter
| | high, | very low,
| | 3rd trochanter | no 3rd trochanter
---+----------------------+--------------------+--------------------
21 | Tibia |Moderate length, |Moderate length,
| | fused to fibula | free from fibula
| | at upper end |
---+----------------------+--------------------+--------------------
Still other forms like _Amblypoda_ and _Arsinotherium_ have been
suggested as having characters in common with _Pyrotherium_, and it
is clear that, with such a variety of forms, some of the characters
must be parallelisms due to a common adaptation, and only one
of these varied groups can be the one to which _Pyrotherium_ is
related. For myself, I have made comparisons with the _Amblypoda_ and
_Arsinotherium_, and feel that such features as the massive limbs,
shape of individual bones, etc., are due simply to the fact that all
these are massive animals. In the case of _Arsinotherium_, there are
some characters which are also common to hyracoids and elephants, like
the position of various basicranial foramena, the prolongation backward
of the jugal and the shape of the palatines. My conclusion is that
_Pyrotherium_ is related to the proboscideans, and came from the same
stock which gave rise to hyracoids, elephants and _Arsinotherium_. I
think further that _Pyrotherium_ belongs definitely to the proboscidean
line.
Referring back to the foregoing table. The development of tushes may be
an adaptive character; but in the elephants it is inc. 2 of the upper
and inc. 2 of the lower jaw which are so developed. In _Pyrotherium_,
in the upper dentition, it is also inc. 2 which makes the tush, and
inc. 1 is enlarged as in _Moeritherium_, and, so far as we know, has
not been reduced in later forms as it was in the elephant line. In the
lower jaw we have no final evidence which will show whether it is inc.
1 or inc. 2 which makes the tush; but the lower tush bites against
upper inc. 2 and I have considered it to be incisor 2.
The loss of the teeth behind the tushes is a character to be expected
in the development of tushes and gives no data. The bilophodont
character of the back teeth has occurred many times in the animal
kingdom and while it may be the inheritance of the early elephants it
can not be used as an argument.
The position of the nasal opening looks very much like that of
elephants, but again is coincident with the development of a proboscis.
However, this has not occurred a great number of times in the animal
kingdom, and where it has, it takes a variety of forms of modification.
In _Pyrotherium_, the modification is of the type in elephants, and
elephants only.
A very striking feature is the development of the dental region
downward so that the basicranial axis is bent upward, making an angle
of about 140 degrees. There are other cases of the bending of the
basicranial axis; but in the other ungulates it is a bend downward,
the reverse of what we find here and in elephants. To adjust the
posterior part of the nasal chamber to this, the pterygoids and the
alisphenoids are developed into great wing-like plates on either side.
I find this modification of the basicranial axis and of the palatal,
pterygoid and alisphenoid bones in no other group but the elephants. In
_Palaeomastodon_ it has been developed to a degree so that the angle is
about 155 degrees.
The back of the palatine bones is also characteristic, for these begin
as narrow pointed bones and behind the last molar expand into wide
plates, just as in _Palaeomastodon_ (and in no other groups), having
the postpalatine foramen opposite or behind the last molar.
The post-tympanic region of the squamosum is modified so that this
process unites with the anterior squamosal region to crowd out more or
less completely the tympanic bone where it should surround the auditory
meatus. This feature is common to the elephants, the hyracoids, and the
toxodonts, so that I consider it a primitive feature indicative of the
ultimate common ancestry of these groups. The tympanic bulla can be
compared with that of elephants closely, and has much in common with
that of toxodonts, but in this last group the tympanic is much more
highly developed.
The premaxilla bone in _Pyrotherium_ is crowded out, so that it makes
no part of the palate, which is a character of elephants, and in
contrast to toxodonts or other groups which have been mentioned. There
are two antorbital openings as in elephants, and a feature not common,
though not unknown. On either side of the brain case are cellular
spaces with intercellular lamellae, which are so characteristic of
elephants; a confirmatory feature, though in itself not conclusive.
The foramena on the base of the cranium are similar to those on the
base of the cranium of elephants, though there are some variations, as
for instance, the exoccipital foramen, is isolated in _Pyrotherium_,
but fused with the posterior lacerum foramen in elephants, and other
slight variations in position; but, on the whole, the foramena of
_Pyrotherium_ are much closer to those of elephants than of any other
group. There is also much in common with toxodonts and with hyracoids,
as would be expected if they have a common ancestry. There is no
suggestion of a marsupial arrangement as would be necessary if related
to _Diprotodon_.
The atlas of _Pyrotherium_ is peculiar in having a marked hypophysis
which is unusual, but is a feature of the atlas of _Palaeomastodon_ and
_Moeritherium_. The axis is peculiar in that the odontoid is flattened
on the upper side and very short and wide. In this the form is unique.
The continuation of the articular surface on the lower side of the
odontoid with the articular surfaces of the ant. cotyles is a feature
also of elephants. The remaining cervicals are greatly shortened almost
to plates, which is elephantine again, though this short neck is
approximated by _Diprotodon_, some Amblypods and _Arsinotherium_, so
that it must be in general looked upon as an adaptive feature, though
in its detail it shows again an elephant character.
The upper members of the limbs are longer than the lower, which is
common to many massive animals. The humerus is tremendously flattened
from front to back, even more so than in any of the animals used for
comparison, though flattening is a feature of them and of the elephants
the most so. With the flattening, the deltoid ridge is prolonged
enormously making a crest along the outer side of the bone, which at
the lower end rises in a prominent process, as in elephants (also in
_Diprotodon_ but in this case the rest of the bone is very different).
In addition to this, the supinator ridge is prolonged upward until it
almost meets the deltoid, ending in a sharp spur at the top. This spur
is more marked in _Pyrotherium_ than in elephants, although they show
the same development of the supinator ridge.
The femur has the head much higher than the greater trochanter, which
is a feature common to elephants, _Diprotodon_, _Arsinotherium_, etc.,
so that it must be looked upon as an adaptation. The third trochanter
has disappeared, and in elephants, it is lost in the advanced forms,
remaining however as a trace in _Palaeomastodon_.
The tibia is very short and massive and hardly gives any suggestions
of relationship, except that it is not fused with the fibula at the
upper end, in which it is in strong contrast to the toxodonts.
While in the table of comparisons numbers 1, 2, 3, 4, 8, 9, 10,
14, 17, 19, 20, and 21 may be, in part, or wholly, interpreted as
adaptations, and alone would not be at all conclusive of relationship
to elephants, numbers 1, 5, 6, 7, 8, 11, 12, 13, 15, 18, and 21 point
toward the elephants as the close relatives of the _Pyrotheria_. In
the first series of points there are none which mitigate against
associating these two groups, while if the attempt is made to
associate _Pyrotherium_ with any group other than _Proboscidea_ there
are strong points, and a number of them, which would prevent this
association. As a result of the foregoing, together with a feeling
which continued handling of the specimens has given me, I can come to
no other conclusion than that the _Pyrotheria_ should be placed under
_Proboscidea_.
In his Linea Filogenetica de los Proboscideos, Ameghino assigns to this
suborder, or at least puts into the phylogenetic tree, a considerable
number of forms from the Casamayor beds, all of them genera with
bunodont molars, usually known by but one or two teeth, such as
_Asmithwoodwardi_, _Nephracodus_, _Cephanodus_, _Paulogervaisia_, and
the better known genera, _Carloameghinia_, and _Didolodus_, all of
which he makes ancestral to _Pyrotherium_. So far as known, however,
these forms show none of the peculiarities of the _Pyrotherium_ skull
or dentition, so that it is difficult for me to see any reason for
including them even in the suborder. The genus _Carlozittelia_, from
the upper Casamayor, is in a different position, having an enlarged
upper incisor (found isolated) and molars of the bilophodont type. I
should include this in the family Pyrotheridae and none of the others.
=Pyrotheriidae= Ameghino
All the forms assigned to this family are supposed to be closely
related to _Pyrotherium_ and to have much the same structure. Ameghino
has proposed the following genera, _Pyrotherium_, _Parapyrotherium_,
_Richardowenia_, _Archaeolophus_, _Propyrotherium_.
_Parapyrotherium_ is based on a small molar and a tush which Ameghino
first described as _Pyrotherium planum_, later elevating the species
to a genus, designated as _Parapyrotherium_, differentiated by the
transverse crests being low and the valley at either end being blocked
by an intertubercular ridge. Gaudry considered that this genus
represented either the milk teeth of _P. romeri_, or a variation of
that species. I can not see the basis of a new genus in the material.
The genus _Richardoweni_ is based on half of a molar, which has the
transverse crest interrupted in the middle. Too little is known of this
form to base a valid genus or even to associate it with _Pyrotherium_.
_Archaeolophus_ is founded on a small tush and part of an upper molar,
also inadequate material for a genus. It is probably _Pyrotherium_.
_Propyrotherium_ is a smaller form from the Astraponotus beds,
apparently a good genus; the type species being _P. saxeum_, of
considerable smaller size than any of the Deseado species. The
distinctive features of the genus can not be given until more material
is known.
_Carlozitteli_ is based on a small form from the Casamayor with
narrow molars. An incisiform tush is associated with the molar,
which, if correctly associated, would indicate a wide deviation from
_Pyrotherium_, and would probably be an ancestral form. A second
species is reported from the lower Deseado beds, but I am a little
skeptical as to the horizon.
=Pyrotherium= Ameghino
Pyrotherium Amegh., 1889, Actas Acad. Nac. Cienc. Cordoba, t. VI, p.
617.
Pyrotherium Lydekker, 1894, Anal. Mus. La Plata, Palaeontologia
Argentina pt. 3, p. 4.
Pyrotherium Amegh., 1895, Bol. Inst. Geog. Argen., t. 15, p. 609.
Pyrotherium Amegh., 1897, Bol. Inst. Geog. Argen., t. 18, p. 441.
Pyrotherium Amegh., 1902, Anal. Mus. Nac. Buenos Aires, ser. 3, t. 1,
p. 19-43.
Pyrotherium Amegh., 1902, Anal. Mus. Nac. Buenos Aires, ser. 3, t. 1,
p. 223-4.
Pyrotherium Gaudry, 1909, Anal. Palaeontologie, t. 4, p. 1-28.
Parapyrotherium Amegh., 1902, Anal. Mus. Nac. Buenos Aires, ser. 3, t.
1, p. 29.
The type species of the genus is _P. romeri_, which is however a rare
species, most of the material and the best known belonging to _P.
sorondoi_. The Amherst Collection contains a skull, complete except
that the top of the brain case is crushed in and the parietals lost;
a second skull with the full upper dentition but lacking the cranium;
four lower jaws; two isolated tushes; the atlas, axis, and cervicals
3 and 4; the humerus; the proximal end of the femur; and part of the
front foot; all from the Chico del Chubut west of Puerto Visser. Gaudry
had upper and lower dentition and the fore and hind limbs except the
feet. Ameghino described the upper and lower dentitions and a fore
foot, so that with our material we now have a basis for a fairly
complete discussion, the vertebral column being the major part which is
still lacking.
The first striking feature is the dental formula. As formerly given,
it is inaccurate, there being two great tushes on either side of the
upper jaw, instead of one, as described. At first sight, I thought it
might be a meristic variation, but both of my skulls show the same
arrangement on both sides, and these are the first two skulls which
have been found complete to the front end, and neither is by any means
a young individual. The dental formula would then read
2 0 3 3
-------.
1 0 2 3
Upper incisor 1 is a rootless, permanently growing tush about a
fourth smaller than inc. 2, but of the same character, being oval in
cross section and having enamel on the front face only. These first
incisors are directed downward, so that their ends stand between and
very slightly in front of the second incisors. The end of each is worn
bluntly round in contrast to the beveled end of inc. 2. The second
incisor is larger, rootless, and permanently growing, with a hollow
base, enamel on the front face only, and oval in cross section. Both
these teeth have a layer of cement on them, extending some distance
beyond the alveolus. The tips are worn in a long bevel on the posterior
side, very much as is the case on the incisors of rodents.
The third upper incisor, the canine, and premolar 1 are lacking, a long
diastema occupying their place, out of which they have been crowded
by the development of the enormous root of inc. 2, which extends 150
mm. and more back into the jaw. _P. romeri_ is distinguished from the
others by pm. 1 being present.
The teeth of the upper premolar-molar series have their crowns
expanded, and the two series of either side have moved toward each
other; until in front they are in contact while in the rear they
are only 50 mm. apart, narrowing the palate in a unique manner, and
giving the impression that the palate is mostly a grinding surface.
The premolars are completely molariform and the whole series is at an
advanced stage of specialization.
Premolar 2 is three-rooted, with a triangular crown on which are three
mamma-like tubercles, the larger one in front, and two behind. As the
crown is worn, these unite into a flat, grinding surface, surrounding
a central pit which opens behind. Premolars 3 and 4 and all the molars
are large, four-rooted, quadrilateral teeth, each with two transverse
crests running clear across the crown, and with a small cingulum across
the anterior margin. Before they are worn, the top of each crest is
tuberculated, and the cingulum is crenulated. In wearing, the anterior
face of each crest is ground down; so that instead of the crown wearing
to a level surface, it retains throughout life two oblique grinding
surfaces.
The lower dentition is more reduced than the upper. When in position,
the tips of the two lower tushes diverge, so as to come in contact with
the tips of the second upper tushes, from which I conclude that the
lower tush is the second, rather than the first incisor, the latter
having been lost when the second became enlarged as was the case in
elephants. This lower tush has the same oval cross section, enamel
on the front face only, and beveled tip as the corresponding upper
incisor; but, in the same individual, is somewhat longer and slenderer.
When isolated, however, it is difficult to tell whether one is handling
a small upper tush or a larger lower one.
The remaining incisors, the canine, the first and the second premolars
are wanting, and their place is taken by a small diastema. The lower
premolars and the molars are similar to those of the upper jaw, except
the cingulum is on the posterior margin, and the wear is on the
posterior face of each transverse crest.
The skull is very long and narrow, with wide and deep zygomatic arches.
The nasal opening is moved back from the front of the snout to just
opposite the orbit, leaving a long, narrow, but heavy snout, made up
mostly of the premaxillae, on the anterior end of which is an oval
boss, which must have served as an attachment for muscles. With the
tushes developed so as to bite against each other, as in a gnawing
animal, I can not see any possibility for the development of a pendant
proboscis, but think that the snout must have been developed more
like that of a pig, but probably to a greater degree. The premaxillae
are long and heavy, and prolonged backward to contain the roots of
the great tushes; but these bones are not developed on the palatal
side of the snout at all. The maxillae are also massive, carrying
the premolars and molars, and extending forward to the bases of the
tushes. They have developed downward so as to carry the plane of the
palate far below the plane of the basicranium, and causing the upward
bend in the basicranial axis, which is so characteristic of elephants.
This bend leaves the occipital condyles a full foot above the plane of
the teeth. The maxilla extends upward so as to bound the major part of
anterior margin of the nasal opening, and of the orbit, which latter
opening is small and directed forward. The zygomatic process is large
and makes a considerable portion of the arch. The jugal is a broad flat
bone making up most of the zygomatic arch and extending back so as to
take a small part in making the glenoid fossa, as in elephants.
The top of the brain case was crushed in before the burial of the
animal, the anterior part being present, and about 40 mm. below its
normal position, but the parietal region having been loose, exposed
the brain cavity, the ear chamber and some of the cellular vacuities.
The nasal bones are long and light in build, and are pushed back so
that they lie between the postorbital processes of the frontals. The
frontals were united medianly, and prolonged on either side of the
nasals to make the postorbital processes. The back margin of the
frontals is broken away. The parietals are lost, but it is apparent
that there was a short sagittal crest. From the middle, high lambdoidal
crests extend to either side, and become continuous with the upper
margins of the zygomatic arches. The posterior face of the skull slopes
back from the lambdoidal crests for a considerable distance, down to
the moderate sized foramen magnum.
The squamosum is a large bone, with the lambdoidal crest and the
extension of the zygomatic arch on its upper surface. It carries the
major part of the glenoid fossa. Behind the auditory meatus is a
large post-tympanic portion which extends down and unites with the
pre-tympanic portion, completely inclosing the opening of the ear and
crowding the tympanic from being exposed on the side of the skull.
There is a very short paroccipital process, and this posterior portion
of the squamosum is the part which resembles that of elephants,
hyracoids and, to some extent, _Toxodontia_. There is, however, no
cavity in the squamosum as in toxodonts generally. The tympanic bulla
is small, but little swollen, and hollow. It is quite exactly like that
of probocideans. The basioccipital is fused to the exoccipitals. The
occipital condyles are very high above the plane of the teeth, are set
wide apart, and are cylindrical bosses which would not allow a free
movement of the head laterally, but only in the up and down direction.
This last is again a feature of the elephants. The pterygoid bone is
greatly enlarged to compensate for the bend in the basicranial axis,
and the pterygoids, together with the alisphenoids, make broad plates
bounding either side of the posterior nasal chamber, exactly as in
_Palaeomastodon_. The palatal bones are slender in front, and broaden
toward the rear, again, as in elephants.
On the interior of the brain case is the cavity for the brain which
indicates that this organ was of diminutive size, measuring about 150
mm. in length by 50 mm. in width at the widest part. It indicates a
brain with very small cerebral hemispheres, which, however, had a
swollen posterior margin, a larger cerebellum, and a wide medulla
oblongata. The impression which I obtained of this brain is strikingly
like that given for _Palaeomastodon_. On either side of the brain
cavity are a couple of vacuities, apparently for lightening the weight
of the skull. At the inner end of the auditory meatus is a large ear
chamber, divided into a smaller anterior or cochlear portion, and into
a larger posterior ear chamber proper.
[Illustration: Fig. 109. Palatal views of the basicranial region
of A. Pyrotherium, and B. Palaeomastodon, for comparisons; _alc._,
alisphenoidal canal; _als._, alisphenoid bone; _Bsp._, basisphenoid
bone; _eu._, Eustachian canal; _f.l.m._, foramen lacerum medium;
_f.l.p._, foramen lacerum posterior; _f.o._, foramen ovale; _i.c.c._,
foramen for the internal common carotid; _mx._, maxilla; _oc.f._,
occipital foramen; _pal._, palatine bone; _p.p.f._, post-palatal
foramen; _pt._, pterygoid bone; _pt.s._, and _p.ty.sq._, post-tympanic
process of squamosum; _sq._, squamosum; _st.m.f._, stylomastoid
foramen.]
In figure 109, I have placed a diagram of the base of the skull of
_Pyrotherium_, along beside that of _Palaeomastodon_, for comparison
of the basicranial foramena. The skull of _Palaeomastodon_ is somewhat
more elongated, especially in the posterior part. In both, there are
two antorbital foramena; the post-palatal foramena of _Pyrotherium_
are a trifle further back, but this palatal region in both is of
the same type which is peculiar to elephants and _Pyrotherium_. In
_Pyrotherium_ the condylar foramen is separate, while in elephants it
is fused in with the foramen lacerum posterior. This latter foramen in
both cases is situated just back of the tympanic, and in _Pyrotherium_
is of considerably larger size than in _Palaeomastodon_. The foramen
lacerum medium is in front of the tympanic and in _Pyrotherium_ appears
considerably larger, mostly because it is under the margin of the
tympanic in _Palaeomastodon_. The foramen for the internal common
carotid in _Palaeomastodon_ pierces the tympanic bone just to the
inside of the middle line, while in _Pyrotherium_ it is on the outer
margin of the tympanic. The Eustachian canal is on the external border
of the tympanic in both cases, but in _Pyrotherium_ it is further back.
The foramen ovale of _Palaeomastodon_ is in the posterior part of the
alisphenoid bone, but with the shorter alisphenoid of _Pyrotherium_,
this foramen is pushed back to the posterior margin of the bone. In
both cases, the alisphenoidal canal starts under the base of the fused
alisphenoid and pterygoid, and opens into the orbit. The stylomastoid
foramen of _Pyrotherium_ is situated further out than in the case
of _Palaeomastodon_. The fusion of the post-tympanic portion of the
squamosum is, in _Palaeomastodon_, much further advanced than in
_Pyrotherium_, so that the passage to the ear is not apparent in the
basal view of the former, but makes a considerable notch on the under
side of the skull of _Pyrotherium_.
The mandibles are excessively thick and heavy, being united at the
symphysis, which extends back to the front of the second molar. The
ascending rami are prolonged backward, but do not rise above the level
of the articulation.
The atlas is a massive vertebra with the anterior cotyles deeply
excavated, especially on the upper side, so that, as Gaudry suggested,
the head must have been carried low. The flat posterior cotyles face
obliquely downward. The neural arch is light and without a spine or
an opening for the vertebral artery. The basal portion of the bone,
however, is excessively heavy and thick; the socket for the odontoid
process not reaching to the middle of the basal bar. The neural canal
is oval in section, being a good deal wider than high, and of small
size. The transverse processes are short, heavy projections, adapted
to receive heavy muscles. On the ventral surface there projects
from the posterior margin a strong hypophysis, which, as Gaudry has
pointed out, is unusual, but which is a character of the atlas of the
_Palaeomastodon_.
The axis is a short, heavy bone, with the anterior cotyles facing
obliquely upward, a small neural arch, no spine, and with a thick
odontoid process, which has the form of a quarter of a hemisphere set
onto the front of the centrum.
Cervicals 3 and 4 are very short vertebrae with light neural arches
and no spines. The neural canal is fully three times as high as
wide. Thus it is entirely evident that the neck of _Pyrotherium_ was
extremely short, as is the case with elephants, which alone would
not be significant, but coincides with many other elephant features.
Gaudry described a lumbar vertebra which is also a short, heavy bone.
Otherwise the vertebral column of _Pyrotherium_ is unknown.
The distal end of the scapula is described by Gaudry as indicating a
short, heavy bone, with the glenoid cavity compressed so as to be about
twice as long as it is wide. The coracoid is a short, blunt process.
The spine was broken off, but enough remained to indicate a moderately
high spine, prolonged toward the humerus, and bent somewhat forward.
The humerus is a very characteristic bone, short and stout, but greatly
flattened from front to back. It has a large sessile head, which is
strongly convex, and projects internally over the margin of the shaft.
The external tuberosity is large and rugose but does not project above
the level of the head. The deltoid ridge is shifted to the external
side of the bone, and makes a long, muscular ridge, while on the
opposite external margin is a second ridge, and between the first and
second ridges a long furrow or trough is inclosed. These terminate
just below the middle of the bone in roughened bosses, which all but
meet. The epicondyles are large and give the excessive width to the
bone. The external condyle is prolonged upward and ends in a spur. The
trochlea is of moderate width and gently undulated. The supratrochlear
fossa is only slightly depressed, and the anconeal fossa is likewise
shallow. The bone has no exact counterpart, but is similar to that of
_Moeritherium_ and _Palaeomastodon_, but in each case is more flattened
and has the external ridges more developed.
Gaudry describes the radius and ulna. They are ridiculously short,
and very massive. The ulna is stout with a massive olecranon which
is directed well toward the rear. The sigmoid notch is shallow, the
coronoid process short, and the articular area expanded so that the
ulna covers the whole of the posterior of the trochlea of the humerus.
The upper end of the radius is compressed antero-posteriorly, but
distally it expands into a heavy bone. Its upper articulation is
expanded, so that it comes in contact with the full width of the
anterior portion of the trochlea of the humerus.
[Illustration: Fig. 110. Left carpus and metacarpus, outlines after
Tournouer—⅕ natural size.]
The carpus and front foot are of questionable association. Ameghino
described a front foot as _P. romeri_, and later Tournouer assigned
this foot to _Astrapotherium_. However, I have seen no reason to think
it belongs to _Astrapotherium_, being far too small, and so would
for the present consider it as belonging to _Pyrotherium_. We found a
couple of metapodials evidently belonging to the foot as described.
This carpus is of the primitive type, the scaphoid and luna being
large and receiving the radius; while the pyramidal is smaller, low
and broad and received the ulna. The trapezium is larger than usual,
being elongated and standing out from the trapezoid, and supporting
a reduced first metacarpus. The trapezoid is also large and almost
square in outline. The magnum is smaller and considerably flattened.
The unciform is very large. These last three mentioned carpals carry
the three medium metacarpals which are quite normal and seem to have
carried most of the weight of the animal. Metacarpus V articulates on
the outer side of the unciform. It is a massive nodular bone with but a
tiny articulation for the phalanx, which seems on this toe to have been
reduced. Metacarpals IV, III, and II are short, stout bones, flattened
from front to back, and enlarged at either end. On each, the trochlea
extends well onto both the dorsal and palmar surfaces, thus giving
the toes a considerable range of movement, and indicating at least a
semidigitigrade mode of walking.
Of the pelvis, the ilium is known as a broad, heavy bone with the
acetabulum facing down. The hind limb is considerably longer than the
front, and approximately pillar-like. The femur, as compared with the
humerus, is quite a little longer, though, as femora go, it is not a
long bone. The rounded sessile head stands high above the blunt, thick
greater trochanter; the digital fossa is barely indicated; the rotular
trochlea is short; the two condyles are subequal in size and set close
together. The patella is short and nodular. The tibia is short and
very heavy. The fibula is free its entire length and is a rather
heavy bone. The astragulus is a lens-like bone with the trochlea but
slightly convex, and the navicular facet directly below it, indicating
a rectigrade foot.
Ameghino established the following species, _P. romeri_, _P. sorondoi_,
_P. giganteum_, _P. crassidens_, _P. trilophodon_, _P. pluteum_. This
is a very considerable number of species of such a large type to occupy
a limited region. Gaudry has lumped them all under species _P. romeri_.
This, I think, is too drastic and I would find at least two species. It
is true that there is great individual variation in such large animals,
due to age, food supplies and individual vicissitudes; but where there
is a difference of dental formula or a structural divergence I should
consider these as specific in character.
The type species is _P. romeri_ (later spelled _romeroi_) which was
based on a first and second upper premolar and an upper tush, all of
smaller size than _P. sorondoi_ and differing from all the others
described in having pm. 1 present. Gaudry suggests that this may be
the milk dentition but there is no evidence as yet to settle this,
so I have left this species standing. Most of the material found by
Ameghino, by Gaudry and by our party belongs to the type described as
_P. sorondoi_, which is somewhat larger than _P. romeri_, and lacks pm.
1 in the upper jaw. This then is the usual species and to it belongs
most of what is known. It varies some in size but the characters are
very uniform. _P. giganteum_ is based on the root of a large tush, 90
by 70 mm. in cross section, which Lydekker associated with _P. romeri_,
and which Ameghino later took as the type of a new species. I can see
in this only a large individual of _P. sorondoi_. _P. crassidens_ is
based on a last lower molar 90 by 80 mm. in diameter. It seems to me to
be an upper molar and no larger than m. 2 in either of my skulls. _P.
trilophodon_ is based on a lower pm. 3, which, in every way, resembles
the corresponding tooth in lower jaw of _P. sorondoi_. _P. pluteum_
is based on three lower teeth of smaller size than the typical _P.
sorondoi_, but the difference is small and there are no structural
features accompanying it; so I consider it simply a smaller individual
of _P. sorondoi_. In the generic discussion, _Parapyrotherium planum_
was also assigned to _P. sorondoi_.
=Pyrotherium romeri= Ameghino
P. romeri Amegh., 1889, Act. Acad. Nac. Cienc. Cordoba, t. VI, p. 618.
P. romeri Lydekker, in part, 1894, Anal. Mus. La Plata, Palaeontologia
Argen., t. III, supplement, p. 4.
P. romeroi Amegh., 1894, Bol. Inst. Geog. Argen., t. 15, p. 612.
P. romeroi Amegh., 1897, Bol. Inst. Geog. Argen., t. 18, p. 442.
P. romeroi Amegh., 1902, Anal. Mus. Nac. Buenos Aires, ser. 3, t. 1, p.
32.
P. romeri Gaudry, in part, 1909, Anal. Paleontologie, t. 4, p. 21.
This species is characterized by the presence of pm. 1 which is absent
in other species. The tooth is of fair size, two-rooted, narrow in
front and has a narrow rim of enamel around it; and measures 22 mm.
long by 14 mm. wide. The second premolar is 30 mm. long by 33 mm. wide.
A lower tush is also associated with these two teeth and is of smaller
size than in the following species, being at the alveolus border 40 mm.
by 29 mm. in cross section.
=Pyrotherium sorondoi= Ameghino
P. sorondoi Amegh., 1894, Bol. Inst. Geog. Argen., t. 15, p. 613.
P. sorondoi Amegh., 1897, Bol. Inst. Geog. Argen., t. 18, p. 443.
P. sorondoi Amegh., 1902, Anal. Mus. Nac. Buenos Aires, ser. 3, t. 1,
p. 30.
P. sorondoi Amegh., 1906, Anal. Mus. Nac. Buenos Aires, ser. 3, t. 8,
p. 331.
P. romeri Lydekker, in part, 1894, Anal. Mus. La Plata, Paleontologia
Argentina, t. III, supplement, p. 4.
P. romeri Gaudry, in part, 1909, Anal. Paleontologie, t. 4, p. 21.
P. giganteum Amegh., 1897, Bol. Inst. Geog. Argen., t. 18, p. 447.
P. crassidens Amegh., 1902, Anal. Mus. Nac. Buenos Aires, ser. 3, t. 1,
p. 34.
P. planum Amegh., 1897, Bol. Inst. Geog. Argen., t. 18, p. 446.
Parapyrotherium planum Amegh., 1902, Anal. Mus. Nac. B. A., ser. 3, t.
1, p. 29.
P. trilophodon Amegh., 1902, Anal. Mus. Nac. B. A., ser. 3, t. 1, p. 33.
P. pluteum Amegh., 1901, Bol. Acad. Nac. Cienc. Cordoba, t. 16, p. 386.
P. pluteum Amegh., 1902, Anal. Mus. Nac. Buenos Aires, ser. 3, t. 1, p.
29.
[Illustration: Fig. 111. Top of the skull—⅕ natural size; Mate to in 1
on the left side is represented by an alveolus but the tooth had fallen
out before the death of the animal; _a.c._, ear chamber; _B_, brain
case; _V_, vacuities in the bone.]
[Illustration: Fig. 112. Side view of the skull—⅕ natural size, _i.1_,
incisor 1 in outline restored from the right side; _i.2_, incisor
2; _J._, jugale; _M.1_, first molar; _Mx._, maxilla; _pm.2_, second
premolar; _pmx._, premaxilla; _Pt._, pterygoid; the dotted line
indicates position of nasal and frontal which are crushed down in
specimen.]
The species varies in size and in the proportionate development of the
tushes as would be expected in a large and slow-growing animal. Most
all of the material found by any of the collectors falls clearly into
this species. Our specimens all came from the Chico del Chubut, west
of Puerto Visser, which point is about 250 miles north of the locality
where Gaudry’s material was found.
The general features of the skull have been given under the generic
description. The difference between this and the preceding species lies
in the absence of pm. 1, and the somewhat larger size. Both of our
major specimens are mutilated in places; and as the better skull was
found with only the zygomatic arch exposed, we conclude that the parts
missing were lost before burial. On the lower jaw the edges of some of
the teeth were cracked off, and both the ascending rami are lacking,
both things having happened before burial, this specimen being found
well in the bank and never exposed to weathering. It appears as if
the carcasses of the animals lay some time before being buried by the
sediments. The scattered condition of all the finds indicates the same
thing. The head of our femur is still marked by the teeth which cleaned
the meat from the bone. The frequency of isolated tushes indicates that
many jaws originally containing them have been either chewed to pieces
or weathered away before burial. I do not think all the tushes found
originally belonged to the lower jaw (Gaudry reports 18 tushes, all
lower); for the upper and lower tushes when isolated are so much alike
that it is difficult to distinguish them.
The size of the skull is indicated by the following measurements:
SPECIMEN NO. 3207
Length from inc. 1 to occipital condyles 720 mm.
Length from front of premax. to nasal opening 225 mm.
Length of boss on premaxilla 77 mm.
Length of nasal opening at top 80 mm.
Width of nasal opening at top 88 mm.
Length from premax. to lambdoidal crest 540 mm.
Width across zygomatic arches 350 mm.
Width across frontal bones 90 mm.
Transverse diameter of the snout 115 mm.
[Illustration: Fig. 113. Base of the skull—⅕ natural size; _i.1_,
incisor the right side grown over toward the center as its mate is
wanting; _i.2_, incisor 2; _Pal._, palatinum; _Pt._, pterygoid.]
The lower jaws were associated with the above skull, and are complete
to behind the third molars on both sides. They are very short and
heavy, especially in the anterior portion, the symphysis extending back
to opposite the middle of the second molar. The height under molar 3 is
150 mm. See frontispiece.
From the upper dentition, I give the measurements of my two chief
specimens, together with those given by Ameghino for his type of _P.
sorondoi_, and the figures given by Gaudry; from which may be seen the
amount of variation which individuals may show.
UPPER DENTITION SPECIMEN SPECIMEN AMEGHINO’S GAUDRY’S
NO. 3207 NO. 3250 TYPE SPECIMEN
Total length, inc. 1 to m. 3 530 mm.
Inc. 1, length above alveolus 133 mm.
Inc. 1, antero-posterior diam. 49 mm.
Inc. 1, transverse diam. 37 mm. 42 mm.
Inc. 2, length above alveolus 174 mm.
Inc. 2, antero-posterior diam. 59 mm. 77 mm. 65 mm.
Inc. 2, transverse diam. 40 mm. 52 mm. 41 mm.
Premolar 2, length 45 mm. 52 mm. 48 mm. 40 mm.
Premolar 2, width 36 mm. 40 mm. 30 mm. 29 mm.
Premolar 3, length 46 mm. 49 mm. 48 mm. 40 mm.
Premolar 3, width 57 mm. 57 mm. 46 mm. 48 mm.
Premolar 4, length 47 mm. 51 mm. 46 mm. 43 mm.
Premolar 4, width 63 mm. 64 mm. 58 mm. 57 mm.
Molar 1, length 55 mm. 55 mm. 57 mm. 55 mm.
Molar 1, width 68 mm. 69 mm. 61 mm. 61 mm.
Molar 2, length 68 mm. 77 mm. 70 mm. 57 mm.
Molar 2, width 85 mm. 93 mm. 75 mm. 68 mm.
Molar 3, length 75 mm. 68 mm. 83 mm. 64 mm.
Molar 3, width 86 mm. 87 mm. 82 mm. 88 mm.
For the lower dentition, I give the figures which Ameghino records for
his _P. sorondoi_, those given by Gaudry for his _P. romeri_, and the
measurements of specimen No. 3207. The tushes in the lower jaw I would
designate as incisors 2; because when the jaws are closed these diverge
and their tips bite against the tips of the upper incisors 2. The
first incisor seems to have been gradually lost and no space left for
it in the front of the mandible, just as it was reduced and lost in the
development from _Moeritherium_ to _Polymastodon_ or equivalent types.
[Illustration: Fig. 114. Lower dentition—⅕ natural size; edges of teeth
broken off in my specimen are indicated in outline.]
LOWER DENTITION SPECIMEN AMEGHINO’S GAUDRY’S
NO. 3207 TYPE SPECIMEN
Incisor 2 to molar 3, length 510 mm. 540 mm.‡ 415 mm.‡
Premolar 2 to molar 3, length 325 mm. 280 mm. 272 mm.
Inc. 2, length above alveolus 133 mm. 188 mm.‡ 168 mm.‡
Inc. 2, antero-posterior diam. 55 mm. 60 mm. 66 mm.
Inc. 2, transverse diam. 40 mm. 36 mm. 44 mm.
Premolar 3, length 46 mm. 50 mm. 54 mm.
Premolar 3, width 36 mm. 31 mm. 35 mm.
Premolar 4, length 55 mm. 45 mm. 50 mm.
Premolar 4, width 46 mm. 45 mm. 47 mm.
Molar 1, length 65 mm. 50 mm. 51 mm.
Molar 1, width 59 mm. 52 mm. 54 mm.
Molar 2, length 73 mm. 56 mm. 66 mm.
Molar 2, width 73 mm. 63 mm. 66 mm.
Molar 3, length 69 mm. 67 mm. 71 mm.
Molar 3, width 74 mm. 66 mm. 69 mm.
‡ Figures taken from illustrations.
Four cervical vertebrae were preserved with the skull number 3207, of
which only about a third of the atlas is represented, but fortunately
we found a complete atlas isolated and of the same size. The
measurements for the atlas are taken from this separate specimen. While
my skull, especially the teeth, seems to have been larger than the
skull Gaudry described, the cervicals are a little smaller. I give the
measurements of the cervicals which we found, comparing them with the
figures given by Gaudry.
SPECIMEN GAUDRY’S
3344 SPECIMENS
Atlas, antero-posterior length 120 mm. 140 mm.
(without hypophysis)
Atlas, greatest width 304 mm. 365 mm.
Atlas, height 129 mm. 140 mm.
SPECIMEN
3207
Axis, antero-posterior length 116 mm. 124 mm.
Axis, greatest width 223 mm. 248 mm.
Axis, width of odontoid process 96 mm. 88 mm.
Axis, length of odontoid process 48 mm. 44 mm.
Cervical 3, length of centrum antero-posterior 47 mm. 45 mm.
Cervical 3, width of centrum 125 mm. 145 mm.
Cervical 3, height of centrum 105 mm. 100 mm.
Cervical 3, width of neural canal 75 mm.
Cervical 3, height of neural canal 22 mm.
Cervical 4, length of centrum antero-posterior 45 mm.
Cervical 4, width of centrum 132 mm.
Cervical 4, height of centrum 105 mm.
The humerus is flattened from front to back in a striking manner, so
that, seen from the side, it looks most slender; while in reality it is
a very broad bone, nearly straight, and with marked rugosities for the
attachment of the muscles. We found but one specimen of the humerus, an
isolated bone a little smaller than that described by Gaudry.
SPECIMEN GAUDRY’S
NO. 3218 SPECIMEN
Humerus, total length 470 mm. 500 mm.
Humerus, width at proximal end 232 mm. 232 mm.
Humerus, width at middle of shaft 165 mm. 170 mm.
Humerus, antero-posterior diam. of shaft 61 mm.
Humerus, width across epicondyles 230 mm. 240 mm.
We found neither the radius nor the ulna, but Gaudry figures both,
giving the following measurements.
Radius, length 245 mm.
Radius, proximal diam. 127 mm.
Ulna, length (calculated) 280 mm.
Ulna, width of olecranon 140 mm.
[Illustration: Fig. 115. _At._, atlas; _Ax._, axis; _C.3_, third
cervical; _C.4_, fourth cervical—⅕ natural size; apophysis of atlas is
restored after Gaudry and the neural arch of cervical 4 is restored
from the opposite side.]
[Illustration: Fig. 116. Axis—⅕ natural size, front view.]
[Illustration: Fig. 117. Anterior face of the humerus—⅕ natural size.]
For the hind limb I give some of the figures which Gaudry gives
accompanying his illustrations of the hind limb.
Femur, length 630 mm.
Femur, greatest proximal diameter 240 mm.
Femur, distal diameter 170 mm.
Tibia, length 370 mm.
Tibia, greatest proximal diameter 164 mm.
Tibia, greatest distal diameter 114 mm.
Astragulus, antero-posterior diam. 123 mm.
Astragulus, transverse diam. 114 mm.
Astragulus, height 65 mm.