1. Bony shell
Caretta caretta (L. 1758), Cheloniidae
Ab - an abdominal scute, An - an anal scute, Ax –
an axillary scute, cphf - a costoperipheral fontanelle, EEHH –
epientohyoplastral hinge, EHH - epihyoplastral hinge, ent -
entoplastron; epi - epiplastron; F - a femoral scute, G - a
gular scute, H - a humeral scute, hhf – a hyohypoplastral
fontanelle, hhxf - a hyohypoxiphiplastral fontanelle, hxf -
hypoxiphiplastral fontanelle, hyo - hyoplastron; hyp –
hypoplastron, HXH - hypoxiphiplastral hinge, Ia – an interanal
scute, Ig - an intergular scute, Im - an inframarginal scute, M
– a marginal scute, msp - mesoplastron, n - a peripheral
contacting with a nuchal, Nu - a nuchal scute, nuch - a nuchal,
Nui - a nuchaloid scute, p - a pygal; pepi - preepiplastron, prn
- a prenuchal, SC – supracaudal scute, sp - a suprapygal, ppf
– plastroperipheral fontanelle, xiph - xiphiplastron, xf - a
· Prenuchal – a small oval bone at the front of the carapace in some trionychoids - cyclanorbids (Lissemys spp., Cyclanorbis senegalensis) and trionychids (Dogania subplana, plastomenusines, etc.). It occurs sporadically in old specimens of the trionychine Platypeltis ferox.
· Nuchal - a large, wide bone at the front of the carapace. This name is nearly universal although Carr (1952) called it the “proneural”.
– the series of bones behind the nuchal outgrowths of the neural
arches of the thoracic vertebrae (see discussion in Kordikova
term is universally accepted in spite of some authors also using
“vertebral plates”. Besides, many researchers use the term
„preneural“ for the most anterior neural if it is highly
differentiated in form or “extra”. However, this term just
demonstrates the specific status and position of the plate. It is not so
informative because it does not facilitate homologization of thoracic
vertebrae of turtles with those of other tetrapods. A number of authors
(Hasan 1941, Carpenter (1981, Meylan 1984, Kordikova
1993b, 2000) call the most anterior neural („preneural“)
„the first neural“. Two neurals between a first pair of costals
occur as a norm in some trionychoids (Lissemys spp., cyclanorbines,
aspideretines, Late Cretaceous paraplastomenusines, Late Cretaceous and
Eocene ulutrionychines), baenids, etc. This bone in above-mentioned
turtles is not sutured to the neural arch of the thoracic vertebra I but
appears to be formed as an expansion of perichondral ossifications of
the neural arch of the thoracic vertebra I (Kordikova
1993b, 2000; compare with Cherepanov
1995). The neural I is reduced in most chelonians but it is not fused
with next to it neural as Webb
(1962), Gaffney (1979) and Meylan
(1987) suggested. I also prefer to call „first neural“ the
most anterior neural, taking into account its formation as a modified
element of the neural arch of the thoracic vertebra I (Kordikova
1991, 1993b, 2000). The
following neurals after the neural I have corresponding numeration: the
neural of the thoracic vertebra II is the neural II, the neural of the
vertebra III is the neural III, etc.
are often reduced or missing in some chelids,
– the series of bones on
each side of the neurals. Many authorities use this term,
although some authors use "pleurals" (Meylan 1987, Gaffney 1990, Pritchard & Trebbau 1984, etc.).
Pritchard & Trebbau (1984) take into consideration the position of bones,
which are more superficial structures, external to the lungs or pleura
and argue that it is preferable to use an exclusively Greek
nomenclature for the carapace bones and Latin nomenclature for the
scutes. However, I prefer to use „costals“ because this term comes
from the ribs or costae and points to the origin of the plates, which
form from outgrowths of corresponding ribs. Moreover, costals are
modified ribs of the corresponding vertebrae and, consequently, the rib
of the thoracic vertebra I forms its own costal I, the rib of the
vertebra II forms the costal II, etc. (Kordikova
2000). Usage of either Greek or
Latin term is inessential if it does not reflect homology of bony
elements and confuses a number of researchers. Some authors (Siebenrock
1902, Meylan 1984, 1987) use a term „callosities“ for the
carapace and plastral ossifications that refers to the dermal origin of
- bones forming the edge of the carapace, a nearly universal
term. However, they are sometimes termed "marginals."
Peripherals are formed by respective myosepta, which also take part in
the formation of corresponding ribs and vertebrae (Cherepanov
1989). Thus, the numbering of peripherals corresponds to that of the
myosepta and, consequently, the ribs and vertebrae: the myoseptum number
I is that from which the thoracic rib (I) and peripheral (I) originates,
the myoseptum II is that from which the thoracic rib (II) and peripheral
(II) originates, etc. The nuchal and the nuchal peripherals also
originate in the same myoseptum (Kordikova
is the most posterior bone of the carapace forming together with
peripherals the edge of the
carapace; a term universally used.
- the bones between the neurals and the pygal, of which
suprapygals may be one or more. In comparison with neurals suprapygals
are formed in the dermis independently but not as outgrowths of the
neural arches of the thoracic vertebrae. They have a sutured contact
with vertebrae secondarily (Cherepanov
1989). Boulenger (1889)
called these bone the “pygals”, but otherwise “suprapygal” is
The paired bones of the plastron are, from anterior to posterior, the epiplastra,
hyoplastra, hypoplastra, and xiphiplastra.
A single bone encircled by the epiplastra and hyoplastra is the entoplastron (Smith
& Smith 1980, preferred the spelling
"endoplastron"). The additional bones between the hyoplastra
and hypoplastra in proganochelyids, platypeltids, baenids, desmostylids,
pelomedusids, etc. are the mesoplastra.
Sometimes they are called interplastra (Sukhanov 1964). An additional pair of epiplastral
bones – preepiplastra can form in the cyclanorbid Cyclanorbis
There are many authors (Siebenrock
1902, Romer 1956, Zangerl 1969,
who distinguish two kinds of plastral bones in the chelonian shell and
use a term „callosities“ for plastral ossifications. However, such
viewpoint is not confirmed by morphogenesis - there are no independent
superficial ossicles over the plastral bony primordial (see wide
discussion on this question in Cherepanov
1997 as well as in Kordikova
2000). Here, I prefer to use plastral bones or plastral ossifications
for the epi-, hyo-, hypo-, xiphiplastra and entoplastron.
2. Horny shell
use terms “scale” and “scute” for shell integumentary
structures: “scales” for tiny horny formations distributed on the
whole body, including shell, and “scutes” for the wide horny plates
forming the surface of the shell. Scales are present in all turtles
(they are ossified in dermochelyids) while scutes are present in most
chelonians except trionychoids and dermochelyids (scutes are usually
reduced in chelonioids and carettochelyids). Carr (1952) proposed that scutes be termed
"laminae" instead, but Zangerl
(1969) observed correctly that this term is ambiguous, having an
established usage in osteology, and should not be used.
The old term “corneoscutes” is accurate but laborious and is
little used today (Pritchard
& Trebbau 1984).
Nuchal scute -
a median scute that lies over the nuchal bone anterior to the vertebral
scutes in many turtles (e.g., Pritchard & Trebbau 1984). Carr (1952) called it the “precentral” but this has not
been accepted by others authors. Zangerl
(1969) proposed the term "cervical scute" but no
previous authors and only a few subsequent ones (e.g., Ernst
& Barbour 1989) have used this term. Nuchal scute is usually
small or absent in pleurodires (it is wide in Hydromedusa).
Nuchaloid scute –
the small anterior most marginal scute that lies over the lateral part
of the nuchal bone and anterolateral part of the nuchal peripheral bone
between the nuchal scute and the marginal I. This term was proposed by Chkhikvadze
(1973) but has not
been used by others, who
consider this scute to be the marginal I. However, the nuchaloid scutes
distinguish from other marginal scutes by size and
anteromedial expansion in many pleurodires.
Vertebral scutes are
the (usually five) large scutes along the midline of the carapace. This
term is nearly unanimous although Carr (1952) used “centrals”.
Pleural scutes or
pleurals are the large scutes forming a longitudinal series on each
side of the vertebrals. This term was proposed by Zangerl
(1969) and a number of authors have subsequently adopted Zangerl's
usage. Carr (1952) used
“lateral”. These scutes are termed “costals” by Pritchard
(1984). This has also been accepted by other authors. However, this term
is more often used for the underlying bones than for the scutes (see the
discussion under costals justifying use of this term). I prefer to avoid
usage “costals” for scutes because they have different origin and it
is necessary to distinguish between the underlying bone of the axial
skeleton and the superficial horny scute. In comparison with the costal
bones and pleural scutes both the nuchal scute and nuchal bone have
the numerous small scutes around the edge of the shell, except those on
the anterior (the nuchal and nuchaloid scutes) and posterior (a
supracaudal scute) midline.
are represented the two rearmost scutes of the carapace (following Pritchard
& Trebbau 1984). In some turtles they are fused
into a single scute. Carr (1952)
proposed the alternative term “postcentrals”. Some authors,
including Hay (1908) and Zangerl
(1969), have simply considered these scutes to be the
posteriormost (normally the twelfth) pair of marginals, and this is
indeed how they appear when they are paired. However, the single large
scute in this position (typical of most tortoises, for example) has a
different appearance and according to Pritchard
& Trebbau (1984) justifies a different name.
Kinosternon cruentatum (DumÉril & bibron 1851), Kinosternidae
Abbreviations: Ab - an abdominal scute, An - an anal scute, cphf - a costoperipheral fontanelle, EHH - epihyoplastral hinge, ent - entoplastron; epi - epiplastron; F - a femoral scute, G - a gular scute, H - a humeral scute, hhf – a hyohypoplastral fontanelle, hhxf - a hyohypoxiphiplastral fontanelle, hxf - hypoxiphiplastral fontanelle, hyo - hyoplastron; hyp – hypoplastron, HXH - hypoxiphiplastral hinge, Ig - an intergular scute, Im - an inframarginal scute, M – a marginal scute, n - a peripheral contacting with a nuchal, Nu - a nuchal scute, nuch - a nuchal, Nui - a nuchaloid scute, p - a pygal; SC – supracaudal scute, sp - a suprapygal, xiph - xiphiplastron.
plastron (not the intergular, single gular, interanal, undivided anal,
etc.) are divided into pairs by a median longitudinal seam. Anteriorly
there is a pair of gular scutes. In some families (notably
plesiochelyids, cheloniids, most kinosternids, dermatemydids,
pleurodires) an intergular scute or pair of intergular scutes is
also present. In kinosternids Hutchison
& Bramble (1981)
homologizate the intergular scute(s) with the gulars, and the
posterior humerals with the abdominals
of other turtles (see
discussion in Kordikova
2000, 2002). Paired humerals, pectorals, abdominals,
femorals, and anals follow, respectively, and in the
Cheloniidae an interanal is sometimes present. Some tortoises
have two additional pairs of plastral scutes – pregulars and preintergulars
anterior to the gulars and intergulars.
· Inframarginals - scutes between the main plastral scutes and the ventral edge of the marginal scutes. They are mainly present in Cheloniidae, Chelydridae, Dermatemydidae, Kinosternidae and Platysternidae. Inframarginals are often reduced to just the anteriormost and posteriormost members, known as the axillaries and inguinals, respectively. Some authors (Chkhikvadze 1973) use the term latiplastral.
are not named by all authors even though fontanelles are present at
least in early stages of morphogeny in almost all Testudinata. I
distinguish the following
· Postnuchal fontanelle - fontanelle between the nuchal and anterior pair of costals.
It can be
unpaired or paired. Some authors (Meylan 1987, Pritchard 1993)
call it suprascapular one.
- fontanelles between costals and neurals.
· Intercostal fontanelles - fontanelles between neighboring thoracic ribs or costals.
· Costoperipheral fontanelles – lateral fontanelles between costals and peripherals.
fontanelle – central
fontanelle between epi-, hyo-, hypo- and xiphiplastra. It is present in Dermochelys
fontanelle(s) - unpaired or
paired ventral fontanelles between entoplastron and hyoplastra.
fontanelle(s) - unpaired
fontanelle between entoplastron, hyo- and hypoplastra.
or central fontanelle - fontanelle between hyo- and hypoplastra.
It is as a rule unpaired.
fontanelle or hyohypoxiphiplastral
fontanelles - central fontanelle between hypo- and xiphiplastra or
between hyo-, hypo- and xiphiplastra. It is unpaired. This fontanelle is
very often present in some pelomedusids (e.g. Pelomedusa subrufa)
or adult cheloniids and trionychoids.
- unpaired fontanelle between xiphiplastra.
fontanelles - paired lateral
fontanelles between hyo-hypoplastra and peripherals.
Many turtles have
carapacial or plastral hinges (Borkin 1973, Bramble 1974, Bramble & Hutchison 1981, Brumble et al. 1984, Pritchard & Trebbau 1984, Ernst & Barbour 1989, Broadley 1993, Pritchard 1993, etc.).
These hinges allow the carapace or plastron to be closed to protect head
and limbs if they are large and mobile enough. Hinges in chelonians can
be classified as:
- a transverse carapacial hinge that always lies between the 5th
and 6th costals and peripherals or, sometimes, between the 6th
and 7th costals and peripherals. Most species of the
testudinid genus Kinixys only has such a hinge.
hinge - a transverse
carapacial hinge between the 5th and 6th
peripherals in Kinixys natalensis.
· Carapacial and plastral pankinesis (Pritchard 1993) – kinesis between all elements of the carapace and plastron – is characteristic for chelonians having paedomorphic features. Among living species carapacial and plastral pankinesis is present in most trionychoids as well as in the cheloniid Eretmochelys imbricata. Plastral pankinesis is characteristic for cheloniids and some other chelonioids. In sea turtles the plastron has lines of flexibility at the bridge and the midline. Carettochelys insculpta has costoperipheral and plastroperipheral kinesis as well as the kinesis between the epi- and entoplastra, on the one hand, and hypoplastra, on the other hand. There is also a movable link between the hyo-, hypo- and xiphiplastra of the left and right sides. In most trionychoids the bony carapace is completely rigid, as is the hyohypoplastral suture line.
The carapacial and plastral pankinesis is associated with changes in shell depth and is the result of adaptive evolution within different groups.
- a movable plastral hinge, which lies between the epiplastra and
hyoplastra - between the humeral and pectoral scutes, either, crossing
the posterior portion of the entoplastron or behind it. It is present in
Pyxis (Testudinidae). In kinosternids this hinge lies across the
humeral scute (following Bramle
et al. 1984) or between the humeral and abdominal scutes because of
reduction of the pectoral scute.
– a transverse plastral hinge placed between hyo- and mesoplastra. It
is present in Pelusios (Pelomedusidae) but it is rather rigid in P.
broadleyi and P. adansoni.
– a transverse plastral hinge placed between the hyo- and hypoplastra
- between pectoral and abdominal scutes. It occurs in many genera of
emydids such as Emys, Emydoidea, Terrapene, Cuora, Cyclemys, Pyxidea,
Notochelys and Rhinoclemmys.
interhypoplastral hinge – a
longitudinal plastral hinge along the hyo- and hypoplastral sutures (in Sternotherus
– a transverse plastral hinge between hypo- and xiphiplastra - between
the abdominal and femoral scutes. Hypoxiphiplastral hinge is well
developed in kinosternids. The plastron of kinosternids may contain
either an inconspicuous single epihyoplastral hinge (e.g. Claudius,
Staurotypus) or two transverse movable hinges - epihyoplastral and
hypoxiphiplastral hinges (in most species of Kinosternon). Most
species of Testudo and Gopherus (Testudinidae) have a weak
- a longitudinal plastral
hinge between the xiphiplastra (in Kinosternon scorpioides).
Plastroperipheral hinge -
a longitudinal hinge between the hyohypoplastra and peripherals of the
carapace (in Claudius angustatus and in emydids - Emys
orbicularis, Emydoidea spp. and Terrapene spp., etc.)
Though this shell nomenclature
proposed here and earlier (Kordikova
2000) represents a relatively recent innovation it seems to be
logical and it has an embryological and comparative morphological
(homological) basis for evolutionary applications.
- a term for the line of connection between two scutes.
Suture - a
term for the connection between two bones.
Sulcus - a
term for the impression that a seam leaves on the underlying bone, are
of universal usage.