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N.Jb.Geol. Palàont.Abh. 224(1) 31-48 Stuttgart, April 2002
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Skin remains in a juvenile /Wacrocnemus
bassani/ NoPcsA(Reptilia, Prolacertiformes)
from the Middle Triassic of Northern Italy u'l; ' '''
Silvio Renesto, Milano and Marco Avanzini, Trento Ì [ - 4 3{ #..
With 6 figures and l table
RTNKsro. S. & AvANziNi. M. (2002): Skin remains in a juvenile J4acrocnemtfs
bassa/zfl NopcsA (Rcptilia. Prolacertiformes) fì'om the Middle Triassic of Northern
Italy. N. Jb. Geol. Palàont. Abh.. 224: 31 48: Stuttgart.
Abstract: A .luveniÌc IVacrocnemz/s bassam// from Besano shows remains of scale
covering in the sacra] and proxima] cauda] region. The scalcs are preserved as
fossilized elements and not as impressions. By comparison with another specimen
of i\4acroc/remus. a taphonomic model is proposed to explain the partem of pre-
servation; suggesting that rapid burial in marine scdimcnt occurred just after death,
and that the we]] deve]oped muscu]aturc of the sacra] and proximal caudal regions
contributed to the process of phosphatization of the scalea, aÌiowing their fossili-
za.ti on
Zusammenfassung: Bei einem juvenilc IMacroc/zenit/s bassa/z/i aus der Fund-
steiÌe Besano sind Reste der Beschuppung in der Becker- und vorderen Schwanz-
region ùberliefer{. Die Erhalt:ung ist ràumlich, nicht nur im Abdruck. Nach einem
Vergieich mit einem andcrcn Exemplar dcr gleichen Art wird ein taphonomisches
Models entwickelt. In diesem wird cine rasche postmortale Einbett:ung angenommen:
wobei dic stark cntwickelte Muskulatur gerade dieser Kórperregion bei ihrem Zerfàlt
zur Phosphatisierung dcr Schuppen beigetragen hat.
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0077- 7749/02/0224-0031$ 4.50
© 2002 E. Schweizerbart'sche Verlagsbuchhandlung, D-70t 76 Stuttgart
32 S. Renesto and M. Avanzini
Introduction
The Prolacertiformes Coup: 1945: is an assemblage of diapsid reptiles
mainly restricted to the Triassic (see EVANS, 19881 BENTON &, ALLEN. 1997
and Jxut. 1997 for a survey), which is usually considered a clade (BENTON.
1985. EVANS. 1988. BENTON &, ALLEN 1997. .1.AUL 1997) belonging to the
Archosauromopha (OLSEN. 1979. BENTON 1985. EVANS. 1980, 1984. 1988,
BENTON &. ALLEN. ]997 and JAI.ii.. 1997. but WILD, 1973. 1980 supports
lepidosaur affinitìes. and DILKES. 1998 gives a more restrictive diagnosis for
the group).
Among the Prolacertiformes: the better known genera are undoubtedly
.Vac/r9c/7e//zzn- and Za/z,vó//op/zetfs. described since last century (BAssANI,
]886. NOPCSA 1930. 1931. PETER 1931. 1937. WILD. 1973. 1980. 1987)
from several well preserved specirnens found mainly in the Middle Triassic
beds ofthe Besano Formation(Grenzbitumenzone. RiEBEK. 1 973) that crops
out in many localities on Monte San Giorgio(Switzerland) and near the small
town of Besano (Italy). Recently, the staff of the Museo Civico di Storia
Naturale (Natural History Museum) of Milano collected at the Besano site
a nearly complete and artìculated specimen belonging to .Vacroc/zerlzl/.'.
in which the scale covering is partially preserved. Its study allowed to
recognize the specimen as a juvenile and to leconstruct the pattern of
the squamation in the sacral and proximal caudal regions. along with a
discussion ofthe taphonomy.
Systematic Palaeontology
Class
Subclass
Supcrdivision
Di\ psion
Order
Genus
Reptilia
Diapsida OSBORN 1903
Neodiapslda BEn }oN 1985
Arcbosauromorpha x/ou llUENE 1946
Proìaccrtiformes CAMP. 1 945
,Wac/-oc'nemzzJS Nopcs.\ 1 930
.Vac'rocnemt s óczssa/z// Nopcsx 1 930
] 93 1 .Wac/-oc/ze/ 2 s bassa/z//
\ 9'bl Macìocnelìltls bassa ì ì
\ 962. Maci'oclte} tt s bassalìii
Nopcsa: pp. 655-656.
PETER. PP. t-!40
KLUX. SCHNYOER. PP. I I0-133
Material: A nearly complete specimen (Fig. 1) exposed in dorval view.
labelled as BES SC 1 1 1 of the catalogue of the Museo Civico di Storia
Naturale di Milano (Italy). Most of the skeleton is preserved on the main
stab. only part ofthe left foot is preserved on the counterslab.
Skin remains in a juvenile /Wacrocnemus Z)assam/i, from the Middle Trlassic 33
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Fig. 1. Wcìcfocnc/in/i bassa/?// NopcsA, specimen BES SC 1 1 1 as preserved
bar equals 2 cm. Scale
34 S. Renesto and M. Avanzini
Description
,Varroe/zena/s is l(nown from several specimens and has already been
thoroughly described (PETER 1937; KUHN-ScnnvDEK. 1962. RtEppEL.
1989). Specimen BES SC Il l completely fils the original descriptions given
for .Vac/oc/zenit/.s bassam// according to Nop(SA (1 93 1 ) and PETER ( 1 937).
Since the aìm ofthe paper is to discuss the soft part preservation, a detaìled
description of the specimen is not given apart for those feature that were
previously unknown or controversial or that are related to juvenìle condition.
The skeleton
BES SC 1 1 1 is the first .Vac/'ocfzenzl/s specimen known with a complete and
articulated presacral vertebral column. Only the distal portion of the tail is
hacking (after the 1 7th caudal vertebra), along with some phalanges of both
feet: their impressìons are detectable however. As it is frequent in long
necked animals. the neck is beni dorsally, owing to post mortem contraction
ot ligaments. The skeleton ìs very much compressed and several bones are
crushed. rendering their reconstruction and the recognition of bone sutures
difficult.
The skull (Fils. 1 -2A) is triangular. with rather elongate snout and wide
orbits. The left and right halves ofthe skull are shifted with respect to each
other. The premaxilla bears nine conical sharply pointed teeth. they are
slightly curved and larger than those on the maxilla. It bears the posterior
process typical for the Archosauromorpha (BENTON. 1985; EvxNS 1988).
The maxilla is subtriangular with a long taperlng posterlor portion. It beats
approximately 34-35 triangular. sharp teeth which decrease gradually in size
toward the posterior margin of the bone. The prefrontal has a crescent shape
and forms the anterior margin ofthe orbit. lts interior margin is convex. The
nasals are obscured by other bones. but it seems that the nasal openings were
placed rather posterior with respect to the tip of the snout. The lacrimal is
small and narrow. it contacts the maxilla. the prefrontal and the jugal. The
frontal is a narrow elongate bone. somewhat thickened in the orbital rim. The
parietal is also barrow; but its posterlor portion cannot be reconstructed
owing to the splitting of the bones. The postorbital is small and triradiate.
with a posterior process. The postfrontal is a small triangular bone formine
the posterodorsal margin of the orbit. The squamosal seems tetraradiate.
its shape correspondlng to the description of' Kuhn-ScilNvoEK ( 1 962). The
quadrate has shared anterìorly with respect to the squamosal. lts shape
cannot be completely observed. but the proximal and distal articular areas are
stout and convex suggesting that it could have been mobile with respect
to other skull bones. The jugal is narrow and spender, with an anteriorly
Skin remains in a luvenile /Wacrocnemus l)assad//, from the Middle Trlassic 35
l
H
Fig. 2. A) tdac/'oc'ne/nt/ó- basca/?// NopcsA. specimen BES SC 1 1 1 : reconstruction ol'
the skull as preserved. Abbreviations: a: angular: ar: articular: c: ceratobranchial:
d: dental: f: trontal: j: jugal: mx: maxilla; op: opisthotìc: pa: parletal: pf: post-
fì'ontal: po: postorbital: pmx: premaxilla; pra: prearticular: prf: prefrontale q:
quadratel sa: surangular; sp: splenìal: sq: squamosal: Scale bar equals l cm.
B) Carpus and manus as preserved. C) The left tarsus, dorval view. Abbreviations in
B are: dc: distaJ carpal 4: in: ìntermedium. i-v: metacarpals. abbrevìations in C
a: astraga]us: c: centrale; ca: ca]caneum; dt: dista] tarsa] 4; i-v: metatarsals. Scale
bars for B and C equal 0. 5 cm.
36 S. Renesto and M. Avanzini
tapering process that contacts the maxìlla and the lacrimal: its posterior
portion is partially obscured by other bones: ìt seems however that the lower
temporal bar was incomplete. No quadratojugal was found. The dentary
(Fig. 2A) is elongate and narrow. tapering posteriorly. It bears 30 conical
teeth. the first five to six teeth being somewhat langer than the following
ones. The surangular bears a tiny coronoid process. The angular forms
part of the posteroventral margin of the lower jaw. The splenial is elongate
with a well-developed ventral process. Two elongate. rodlìke bones lyingjust
ventral to the leR half of the mandibles are interpreted as ceratobranchials.
The dentition is sub-thecodont.
The vertebral colunm consists of 8 cervical. 1 7 dorval. 2 sacral and up to
1 7 caudal vertebrae. The number of cervical vertebrae of .Vac/oc/lenzi/x has
been debated: PEVEK ( 1 937) counted seven cervicale. WILD(1973) nine and
TscnANZ ( 1988) eight. RnppEL (1989) counted eight cervical vertebrae in
specimen T 4355 of the Palaeontologisches Institut und Museum in Zurich
(the only one previously known with the entire neck preserved), specimen
BES SC 1 1 1 thus confimìs the RiEppEL and TscuANZ courts. On the other
han(L the number ofdorsal vertebrae ofspecimen BES SC 111 is higher than
reported in any other /\4ac/'ocnernt/.s: 1 7 instead of 1 6. As in specimen T 4355
(RiEppEL. 1989), only the neural spine and arch ofthe atlas can be observed.
partially overlapping the neural spine of the axis: this batter is short. it shows
a rather deep centrum and horizontal postzygapophyses. The other cervical
vertebrae and associated ribs do not show any diHerence with respect to pre-
vious descriptions (PETER. 1937: RiEppEL. 1989). No intercentra are present
in the neck (as suggested by RiEppPL: 1989: contra PETER, 1937). Dorsal
vertebrae are notably shorter than cervical ones as in other prolacertiforms.
Again. nothing significant can be added to previous descriptìons (PETER.
1 937. RiEppEL. 1989). As in other prolacertiforms. the rios ofthe last four to
five dorval vertebrae are short and straight. allow,ing the distinction of a
'lumbar" region. The sacral vertebrae are similar in size and shape to the
more posterior dorval ones. but bear larger transverse processes associated
u,ith stout. wide sacral rios. The more proximal caudal vertebrae bear very
long caudal rios gradually decreasìng in size posteriorly. These structures can
be detected up Lmtil the 1 3th caudal vertebra.
Only the central margin ofthe coracoids and the glenoid portion ofthe left
scapula are clearly detectable, showing that the scapula and coracoid are not
fused. The bones of the pelvic girdle are disarticulated and the detectable
portions reveal nothing different from previous descriptions. Nothing signi-
ficant can be added also to the descriptions of the long bones of the limbs
given by PEVEK (1937) and RiEppEL (1989). ]t can be noted. however. that
humeri and remora are flattened and crushed in a way suggesting that
they may have been hollow. and matrix seems to have filled in some part the
Skin remains in a juvenile /Wacrocnemus bassani/, from the Middle Iriasslc 37
cavities ofthese bones. Only two carpal bones are ossified (Fig. 2B), they
are Interpreted as the intermedium and distal carpal 4 according to the
pattern ofdevelopment ofcarpal bones in reptiles (following RiEppEL 1 992 a.
b. 19931. The metacarpals increase their length until the fourth. which
reaches three times the length of the first, the fifth metacarpal is very short.
The phalangeal formula is primitive: 2, 3. 4. 5. 3.
The proximal head ofthe femur is expanded but not angled with the shaft
of the bone. suggesting a fully sprawling posture. The distal head is flexed
ventrally and bears hemispherical articular surfaces for tibia and fabula
allowing good possibilities of flexion. The tarsus (Fig. 2C) consists of four
ossified elements closely fitted together. On both topographical and onto-
genetic bases (RIEppEL, 1 992a. b. 1993) the first three can be interpreted as
the astragalus. the calcaneum. and the fourth distal tarsal. The fourth element
is identified as the centrale according to both Gow (1975) and RieppEL
( 1 989). The astragalus is L-shaped. the calcaneum is large and rounded the
foramen for the perforating artery being poorly developed. Metatarsals and
phalanges are broken and in the left foot they are partially preserved on the
counterslab. However, the structure ofthe foot can be reconstructed. The first
four metatarsals are very long and closely associated while the fifth is short
and hooked. In general. the fifth toe is short. in contrast to tanystropheids
(WILD. 1973; OLSEN 1979, BENTON: 1985: EVANS 1988, RENESTO 1994). The
phalangeal formula for the pes is 2, 3: 4. 5, 4.
Juvenile features
BES SC 1 1 1 is the smallest /Vac/'acne/nl/s specimen so far known; thus a
.iuvenile stage may be hypothesised. However, absolute size (Tab. 1) is not
enough to establish the immaturity of a specimen (DEEMING et al. 1993;
JonxsoN. 1 997; SANDER, 1 988), other size independent criteria are required
like the degree of osslfication in the skeleton and some size independent
In the skeleton ofBES SC 1 1 1 some elements are not yet ossified and this
is surely due to the early growth stage. Some of the transverse processes of
the caudal vertebrae are only sutured with the neural arches. while in langer
specimens they appear to be fused. In the campus. only two elements are
present. while RiEppEL (1989) reports five ossified carpal bones for larger
specimen T2474 (all specimens here identified with T fbllowed by catalogue
number are housed in the Palaeontologisches Institut und Museum in
Zurich), and PETER ( 1 937), counted six elements for the same specimen. The
ossification ofthe tarsus ofspecimen BES SC 1 1 1 is far more advanced (in
many reptiles the carpus starTS to ossify after hatching, and this explains
the lag in the ossification between tarsal and carpal elements): four ossified
ratlos
38 S, Renesto and M. Avanzini
Table [. Measuremcnts (in mm) taken fì'om BES SC ] ] ]
Length of the skull
Orbit length
Length of the lou'er .law
Length ofcerv. vert. 3-8
Length ofmid dorsa] vertebra
length of the left humems
length of the leR uma
length ofmetacarpals 1-5
!ength of the left f'emur
}cngth of thc }cft tibia
[ength ofmetatarsa] 1-4
Standard length (length of last four dorval vertebrae)
38
] o
37
8. 9. 9. 8.5. 7.5
4
27
24
3.5. 4.5. 5.5. 6.
34.5
38
8.5, 13. 15.5. 1
]6
(6)
2
9
elements are present and the perforating foramen between astragalus and
calcaneum is indeed present but poorly developed: while in larger specimens
(T 4355) six ossified tarsal bones are reported (RìEppn-[989) and at ]east in
some specimen the foramen is well visible.
According to PEVEK ( 1937) the size range of /Vac/.or/zc'//lz/s may have
\aned from 35 to 86 cm. but the author suggested that langer specimens may
have existed. RiEppEL (1989), using a conservative estimate of about 40
caudal vertebrae (PEVEK: 1 937. suggested that the tail might have conslsted
of40 to 50 vertebrae) gave an estimated total length ofabout 1 1 3 to 1 1 8 cm
for one of the better preserved and mole complete specìmens (T 4355). with
a snout-vent length ofapproximately 38 cm and a femur length of something
more than 70 mm. It has to be noted that an incomplete specimen (T 2470:
RiEppEL, 1989) shows a femur length of 95 mm. suggesting an even larger
maximum size for the species. In specimen BES SC 1 Il the snout-vent
Fig. 3. /Vac'roc/zeman bassam/f. specimen BES SC 1 1 } . Close-up photos ofthc main
areas of skin preservation. A) pelvic region and base ot' the Edili B) mid-caudal
region. Scale bar equals l cm.
Skin remains in a juvenile /14acrocrìemc/s hassan/i, from the Middle 7rlassic 39
&
:)È!.: -;'
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Fig. 3 (Legend see p. 38)
40 S. Renesto and M. Avanzini
length ìs of about 1 7 cm. with a femur length of 34.5 mm. Given the same
proportions and keeping same number of caudal vertebrae hypothesised by
RìEppEL (1989), the whole length ofspecimen BES SC Il l should have been
approximately 50 cm. about 45 % ofT 4355. but this is tentativo. however.
Among size independent criteria that may be evaluated there are the
relative size of the skull to the standard length. the ratio of the orbit to the
skull length or the ratio ofthe skull length to the snout-vent length. Specimen
BES SC 1 1 1 shows a skull length/ standard length ratio of 2.37. a pro-
portionally very large skull compared to those of larger specimens. espe-
cially ofthe langer one (T 4355), a supposed adult specimen. which shows a
sku[[ [ength/standard [ength ratio of ] ,94. BES SC ] ] ] shows a]so an orbit
length/skull length ratio of26.3. which is significantly above the mean ratio
for supposedly adults .Vac/'oclzemlzs specimens. Also the skull length/
snout-vent length ratio suggests a juvenile condition. with a remarkable diff
terence between BES SC 1 1 1 and the other supposed adults specimens.
These data should confirm thejuvenile stage of BES SC 111: the large skull
relative to the body length and the large eyes in relation to the skull are in
fact considered indicative ofan early growth stage (SANDER. 1 9891.
Squamation
Specimen BES SC 1 1 1 retains portions ofthe skin in the sacral region and
along the tail (Figa. 3. 4. 5). Skin remains are visible posteriorly to the 1 7th
dorsal vertebra. covering part of the billy, of the pelvic girdle and the
proximal part ofthe 6emur. then continues along the tail till the 14th caudal
vertebra. The scalea are particularly evident in the pelvic region. on the right
side of the tail between the fourth and eighth and near the 12th and 14th
caudal vertebrae.
The morphology and outline of the scale changes from the sacral to the
caudal regions (Fig. 4-5 ):
Starting from the second sacral vertebra till the second caudal vertebra the
scalea are significantly overlapping each other. with semicircular margine
and raised distal edges (0.9 mm x 0.9 mm). In some cases arched "carinae
(0.2-0.3 mm height) can be observed.
Between the second and the fifth caudal vertebra the scales are still over-
]apping with semicircular borders but the edges are less raised (0. 8 x 0. 8
mm). In correspondence to the fifth and sixth caudal vertebrae the scalea
become more squared in shape. but they still overlap each other and their
edges are rounded. Near the sixth caudal vertebra scales become noticeably
square and are arranged in parallel rows. positioned obliquely with respect to
the spinal column. The pattern remains similar till the 1 2th caudal vertebra.
Skin remains in a luvenile Macrocnemus hassan//, from the Middle Triassic 41
Fig. 4. 1) Drawing of the area in which the skin covering preserved (in grey:): A,
B and C represent areas with diHerent scale morphology of which close-ups are
shawn in Fig. 5 Sca]e bar equa]s ] cm.
42 S. Renesto and M. Avanzini
Between the ]2th and the 14th caudal vertebra scales gradually change
their shape from square to recTangular, slightly carinate. as can be observed
near the 14th caudal vertebra. The last preserved scales are elongate (0.85 x
1 .2 mm), overlapping each other and with rounded distal edges. A small
nonch marks the beginning of a carina which runs on the long axis of the
There is no clear evidence for the presence of tubercles or ornamentation
apart fiom [wo sina]] spiny protuberances on the right side ofthe tail near the
first caudal vertebra. Their morphology is not completely clear and their
Interpretation as possible cutaneous spines must be evaluated with caution.
The arched carinas which can be observed near the proximal head of the
right femur; in our opinion. could be also interpieted as scale edges rotated
almost vertically, due to the processes oF contraction of the epidermal tissue
which preceded the fossilisation ofthe specimen.
Remains of skin are preserved also in another /Wac/oc/zé'/nt/ó specimen.
catalogue numberT 4822 ofthe Palaeontologisches Institut und Museum der
Universität. Zurich (Switzerland). This specimen was described by PETER
(1937), who reported that fragments of skin are visible along the spinal
column in front of the right ilium. corresponding to the ventral region and
along the leR fèmur. A very accurate cast of this specimen is housed in
the Museo Tridentino di Scienze Naturali (Trento. N. Italy) with the scale
covering perf'ectly reproduced allowing a comparison between the two
specimens. The pattern of squamation and the areas in which preservation
occurred are approxìmately the same in both specimens T4822 and BES
SC lll (Fig. 6). Along the right side ofthe tail between the first and the fifth
caudal vertebra. small crescent-shaped raised elements (around 0.2-0.3 mm
wide) can be seen. oriented transversally with respect to the axis ofthe tail.
These structures. according to PE\'EK ( 1 937), could represent elongate tuber-
cles situated at the centre ofthe scales. However. these latter may simply be
the raised edges of the scalea like in the region of the femur on specimen
BES SC lll. Ifthis were the case also on T 4822, we would see a pattern of
overlapping scalea with semicircular raised edges. As those of the tail, the
scales on the femur overlap each other and show a semicircular outline.
overall morphology of the scalea and the gradual change of their
shape described above is a common feature of many exTant squamates and
the reconstruction of the pattern of squamation of the tail ofBES SC l l l
shows a very high resemblance with the skin of some common wizards like
the green lizard tace/'/a vz/-/dfs.
It is .Interesting that one specimen of Za/7,p//-ac/ze/os (another prolacerti-
form. (OLSEN. 1979) is preserved with its body outline (OLSEN. 1979: OLSEN
& JoHANssoN 1994). The organic film residue ofthe soR tissue lacks how-
ever a distinct texture. According to OLSEN & JouxKssoK ( 1 994) the pattern
scale
Skin remains in a juvenile /Wacrocnemus bassarì//, from the Middle Trlassic 43
'w: -;l 8
H
Fig. 5. Variation of the morphology of thc scalcs in different areas of the tail as
illustrated in Fig. 4. AI base. B) mid section: C) distal portìon. Scale bars equal
l mm
44 S. Renesto and M. Avanzini
of the texture should be due to the presence of' a smooth skin surface in
Zanyr/uc/ze/os rather than diH'erent conditions of fossilisation. This may be
due to an adaptation to different environments: 7à/zv//uc/ze/os has been con-
sidered as mainly aquatic (OLSEN. 1979), while terrestrial habits have been
proposed for /Vac/'acme zlrs (RiEppEL. 1 989 ).
Taphonomy
The areas still covered with skin in BES SC 1 1 1 are nearly the same as in T
4822. apart from the edges ofthe skin preserved along the 6emur of the left
]eg. It may be hypothesised that the taphonomic conditions that caused the
preservation ofthe skin in the two speciinens were similar. The post-mortem
position ofthe two specimens is nearly identical. but gives little indications
of the taphonomic history, despite the assessment of WncELÌ ( 1 927) desic-
cation of the carcass on dry land that lead to "unnatural. contorted positions
not usually found in living animals". Jndeed, post mortem contraction of
muscles and ligaments may occur also in water. The difference between
specimens showing ligament contraction rather than a more loose "passive"
position like many nothosaurs from the same sites yielding Mac/,oc/zé'/zzt/s.
may be more due to the morphology of the animal. or to the different con-
ditions of the microenvironment around the carcass rather than occurrence
or absence of preliminary desiccation on land. Both the prolacertiform
7Zrn);s//'op/lez/s and neusticosaurs are long necked aquatic animals which are
frequently found in the Besano Formation; the morphology of their cervical
vertebrae is completely different (Wll,D: 1 973. SANDER. 1 989) however. and
this may explain why Zany17rop/ze&fs specimens show strong post-mortem
contraction phenomena. especially in the long neck (WILD, 1973), while
neusticosaurs usually are preserved in a loose position with the neck straight
(SANDER, 1989').
The preservation of the skin is even more strictly related to the environ-
mental conditions in which the animal died and was buried. It is not required
that the carcass spent some time in a subaerial environment. sufi'ering a
partial mummifìcation. to allow the partial preservation ofthe skin. and the
scales may have fossilised directly in water. All evidences support a rapid
burial in aquatic environment just after death: All postcranial elements
appear to be articulated (the slight distortion and disarticulation of loosely
sutured elements of the skull is probably due TO a collapse during burlal or
sediment compaction ). SATA DER ( 1 989) mentioned a /Vez/sf/cosalzrz/ from the
same site with scales preserved around the throat region. Like in the two
.Vacroc/zemin specimens, the scales were fossilìsed and are preserved in
apatlte. This indicates that phosphatization occurred during fossilization. It
might be assumed that the local occurrence of particular environmental
Skin remains in a juveniie /Wacrocnemus hassan//, from the Middle Triasslc 45
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46 S. Renesto and M. Avanzini
conditions that tended TO cavour natural preservation of soft tissue in some
specimens. for example acidic and anaerobic conditions. may allow soft
tissue preservation by inhibition of bacterial activity(ALysoN: 1 990).
The areas of preservation of scales in the two .Wac/ocnem /s specimens
may have been the same owing to the presence of well developed muscles in
those regions (RiEppEL. 1 989) that may have acted as a center of reaction for
the deposition of phosphates (MAlsEY. 1991 ) allowing the preservation of
scalea. while in other body sections the absence of muscle masses prevented
the process to occur.
Conclusions
Despite the depositional environment in which all .Wac-/'nc/ze/nl/ó specimens
were found this genus has been considered as fully [errestrial (RiEppEL.
1989) on anatomical grounds. The pattern of preservation of BES SC l l l
and T 4822 does not contradict this hypothesis. but may rather indicate a dìF-
fèrent pattern of preservation between these small specimen and larger ones.
Most of the large specimens of .Mac-/oc/lenze/s and of Za/zys//'0/2/2ezf.v: as well
as many ashes, are preserved disarticulaTed (PETER, 1937), suggesting
currents and bottom conditions that where not fully anoxic. BES SC 111 and
T4822 skeletons are nearly undisturbed. perhaps because they were quickly
buried at the bottom of the basan, just after death. Local acidity may have
developed locally favourable conditions in the pore water in the sediments
even ifthe environment was not completely anoxic (in the Besano Formation
framboidal pyrite. one of the strongest indicators of anoxla. is absent: A.
TINTORI pers. comm.). These condition allowed the fossìlìzation ofthe scalea
u,ithout prior mummification.
Acknowledgements
Thanks are duc to the entire staff ofthc Museo Civico di Scienze Naturali di Milano.
and particularly to Dr. CRISI-IANO DAI, SASSO and Dr. GioKcro TEKuzzi. for the per-
mission to examine specimen BES SC 1 1 1. CRISTINA LOMBARDO (Milano) helpcd
with the ana]ysis of the morpho]ogica] variation in Adacrocnemlzs during growth
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Addresses of the authors
Dr. Stl.x.io REKESTo: Dipartimento di Scienze della Terra. Università degli Studi di
Milano: via Mangiagalli 34. 1-20133 Milano:Italy:
e-mail : renesto(@mailserver.animi.it r
Dr. MxKco AvANziwt. Museo Tridentino di Scienze Naturali: Via Calepina 14.
1-38100 Trento. Italy;
c-Inail : avanzini@,mtsn .tn.it t
