A LARGE SUPERNUMERARY BONE AT THE BREGMA AND METOPISM CO-OCCURRING IN THE SKULL OF AN ANCIENT ROMAN IN SERBIA

8/12/2019 A LARGE SUPERNUMERARY BONE AT THE BREGMA AND METOPISM CO-OCCURRING IN THE SKULL OF AN ANCIENT

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Arch. Biol. Sci., Belgrade, 65 (4), 1637-1643, 2013 DOI:10.2298/ABS1304637R

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A LARGE SUPERNUMERARY BONE AT THE BREGMA AND METOPISM COOCCURRING

IN THE SKULL OF AN ANCIENT ROMAN IN SERBIA

P. RADOVI1*and NAAA MILADINOVI-RADMILOVI2

1 National Museum Kraljevo, 36000 Kraljevo, Serbia2Institute of Archaeology, 11000 Belgrade, Serbia

Abstract - An unusual anatomical variation was observed on a skull excavated at Lanite (Raka district, Serbia), a Romannecropolis dating back to the second hal o the 4thcentury AD. Te skull o an adult male showed a remarkably large su-pernumerary bone at the bregma co-occurring with a continuous persistent metopic suture. Few similar cases have been

reported in scientific literature. We describe the case and discuss possible mechanisms and underlying causes, includingpathological conditions.

Key words: bregmatic bone; metopism; Roman necropolis; 4thcentury AD.

INRODUCION

Wormian bones (ossicles, supernumerary bones)represent one o the most requently reported epi-genetic variants in human skulls (Bergman et al.,1988). Located within the cranial sutures and onta-nelles, these ossicles may be ormed rom a detachedportion o the primary ossification centers o neuro-cranial bones, or they may rise rom a new, abnormalossification center. Teir incidence can be related toa variety o pathological conditions (osteogenesisimperecta, hypothyroidism, cleidocranial dysosto-sis, rickets etc.), but they are also commonly oundin healthy individuals (Murlimanju et al., 2011).Some, such as wormian bones in the vicinity o thelambdoid suture, are requent in human populations(40-50%), but others are very rare (Bergman et al.,1988; Brasili et al., 1999). One o these rare variationsis a supernumerary bone placed at the bregma, themeeting point o the sagittal and coronal sutures; itorms within a large anterior ontanelle, situated be-

tween the anterosuperior angles o parietals and thesuperior angles o the separated halves o the ron-tal bone. Te anterior ontanelle is the largest, kite-shaped, and it closes during the middle o the sec-ond year o postnatal lie; i there are ossicles (one ormore) at the bregma, they ofen reflect the shape othis ontanelle. Te usion o the metopic suture usu-ally takes place during the first year, but completiono this process can last until an individual is 8 yearsold (Scheuer and Black, 2004). However, in some in-dividuals, this suture remains unused, even in adultlie, and in such cases the term used is the persistentmetopic suture (metopism).

Te anterior ontanelle bone can relatively rare-ly be ound in inant clinical cases (Agrawal et al.,2006; Carter and Anslow, 2009; Woods and Johnson,2010). In adults, a number o bregmatic bone casestudies rom the orensic context have been reportedin recent years (Nayak, 2006; Barberini et al., 2008;Hussain et al.,2010). Metopism is not as rare a vari-


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1638 P. RADOVI E AL.

ant, but its co-occurrence with a bone at the bregmais very rare. Here, we report a case o a large breg-

matic bone co-occurring with metopism in an indi-vidual rom a site in southwestern Serbia. We exploredifferent causative mechanisms or this rare variant,including mechanical stress, genetic mutations andpathological conditions.

MAERIALS AND MEHODS

Lanite is located on the fluvial terrace o the riverIbar, near Baljevac (Raka district, Republic o Ser-bia; Fig. 1.). Te archaeological team rom the Na-tional Museum Kraljevo discovered 13 ancient Ro-

man skeletal burials during 2001 and 2002. Coinsand other grave goods date the burials to 4thcenturyAD, most o them to the second hal o the century(Bogosavljevi-Petrovi, 2003; Spasi, 2005). Apartrom the cranium presented in this report (abbre-

viated L12 and showed in Fig. 2), the burial No.12 contained only a damaged right radius, whichcould possibly belong to the same individual. Teincompleteness o the skeletal material may be dueto taphonomic actors, ancient, as well as the recentdevastations, since many illegal excavation pits (made

by unproessional individuals searching or archaeo-logical items made o metal) were recorded on thesite. Considering the stratigraphic position o the re-mains and the act that all inhumated burials on thesite date roughly to 4th century AD, it is highly likelythat the L12 skull also dates rom this period. Teskull was in a relatively good state o preservation,with only minor damage to its base and postmortemloss o teeth (dM1, dM2, sP4, sM1 and sM2were pre-served). We examined morphological characteristicso the skull in order to determine the sex (ollowingFerembach et al., 1980), and dental attrition (ollow-ing Brothwell, 1981 and Lovejoy, 1985) in order todetermine the age o the individual. Te skull wasexamined by naked eye, and measured using sliding/spreading calipers.

RESULS

Our analysis showed that the skull belonged to anadult male individual. Since we had only a small

number o skeletal individuals rom the site or seri-ation procedures, we were not able to determine thespecific dental attrition rate or the Lanite popula-tion. Considering this, the age o 35 to 45 years, basedon the methods o Brothwell (1981) and Lovejoy(1985), do not reflect the exact age o the individual,

but rather indicate only a broad adult age category.Further examination showed rotatio dentis (sP4), M3

hypodontia and marked deviation o the nasal sep-tum (Fig. 2). Te neurocranium exhibited markedrontal and parietal curvatures. A cranial index over85 (see able 1) indicated that this is a hyperbrachy-cranic skull (Bass 1987: 69); some relevant measure-ments and indices are shown in able 1 (ollowingBass, 1987 and Martin und Saller, 1957)

Wormian bones were noted on the lef (20 x 20mm) and right (25 x 17 mm) halves o the lambdoidsuture and at the right asterion (15 x 13 mm) (Fig.2); there were also ew smaller lambdoid ossicles(now missing), but postdepositional distortion anddamage impeded us rom taking measurements. Telarge bregmatic bone was nearly pentagonal in orm,reflecting the shape o the anterior ontanelle; theanterior margins o the bone were regular, straight,compared to the posterior, which showed a less reg-ular outline (Figs. 2, 3). Measurements o the bone

Table 1. Measurements o L12 skull according to Bass (1987) andMartin and Saller (1957) (marked with star).

Measurement/Index L12

Max. cranial length (gl-op) 180

Max. cranial breadth (eu-eu) 157

Horizontal circumerence (gl-op)* 554

Min. rontal breadth (f-f) 105

Interorbital breadth (d-d)* 23

Upper acial breadth (mt-mt)* 108

Upper acial height (n-pr) 68

Bizygomatic breadth (zy-zy) 142

Cranial index 87.22

Fronto-parietal index 66.87

Orbital index (right/lef) 89.61Nasal index 49.52

Maxilloalveolar index 121.65


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A LARGE SUPERNUMERARY BONE A HE BREGMA AND MEOPISM CO-OCCURRING 1639

were taken on the external table. Te sagittal lengtho the bone was 69 mm; transverse breadth was 56mm. Right anterolateral margin was 39 mm long, lefwas 42 mm; right posterolateral was 31 mm, lef was33 mm long, and the length o the posterior marginwas 41 mm. At the endocranial aspect and in the

vicinity o the bone, we observed small arachnoidcalvarial deects (Kauman et al., 1997). A continu-ous metopic suture was present, and the linear chordlength rom nasion to the most anterior point o thebregmatic bone was 96 mm.

DISCUSSION

According to Hauser and DeSteano (1989), the pres-ence o a supernumerary bone at the bregma (ossicu-lum fonticuli anteriorisor the bregmatic bone) is a

very rare occurrence in modern humans. In theirsurvey, most o the examined skeletal populations

(10 o 24) did not show any presence o this trait.For the populations where its presence had been re-corded, requencies were very low (0.22.5%), andthere was no particular sex prevalence. OLoughlins(2004) survey (which included 167 deormed andnormal skulls) also detected no supernumerarybones at the bregma. Tis phenomenon had alsobeen noted in other mammalian species, most no-tably in North American lynx (Lynx rufus), withhigh requencies (37.5-44%). Bregmatic bones werealso ound in smaller mammal species (Erinaceuseuropaeus, Rattus rattus, Sciurus vulgaris, Oryctola-

gus cuniculus, and different species o Microtus), atvery low requencies, comparable to those ound inhumans. Te shapes and dimensions o the breg-matic bones o these animals showed considerableintra- and interspecific variation (Manville, 1959;Pucek, 1962). Persistent metopic suture is not as rareas the occurrence o a bregmatic bone; according toBergman et al. (1988), metopism occurs at requen-cies ranging rom 8.7% to 1% in recent populations.o our knowledge, only one other published case(Nayak, 2006) shows co-occurrence o the bregmatic

bone and persistent metopic suture; compared toL12, Nayaks case showed a relatively small and lessregularly shaped bregmatic bone. Te case presentedby Barberini et al. (2008) was very similar to L12,both in terms o shape (nearly pentagonal) and size(relatively large) o the bregmatic ossicle; however,it showed no metopism, which we observed in theLanite case. Another published case (Hussain et al.,2010) showed a rather differently shaped bregmaticbone (tetragonal), with an asymmetrical relative po-sition (lef lateral margin represented a continuationo the sagittal suture); this was clearly unlike the pat-tern we observed in L12.

A bregmatic bone probably arises rom an ab-normal ossification center in the fibrous membraneat the anterior median ontanelle (Hussain et al.,2010). Direct observations o skull development intransgenic mouse embryos have shown a dual em-bryonic origin o mammalian skull bones (Morriss-Kay, 2001). Te parietals have a mesodermal origin

Fig. 1. Site location map or the Ancient Roman cemetery atLanite, with the position o Serbia in Europe.


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and the rontal bone originates rom the neural crest(Merrill et al., 2006); either o these two embryonictissues could be responsible or the ormation o abregmatic bone, since it is positioned in the area otheir direct interaction.

Sanchez-Lara et al. (2009) showed that mechan-ical actors that spread sutures apart and affect dural

strain within sutures and ontanelles play an impor-tant role in the ormation o wormians within suturesor ontanelles. Teir ormation acts as a kind o adap-tive response o the developing skull to mechanicalstress (Oostra et al., 2005). Tese mechanical orcescould be the result o different pathologies, culturalpractice (purposeul cranial deormation) or o pre-mature ossification o the cranial sutures (cranio-

Fig. 2.Cranial projections o Lanite 12 skull.


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synostosis). Te association o the bone ormationin the anterior ontanelle with craniosynostosis wasconfirmed in clinical studies o children (Woods andJohnson, 2010; Agrawal et al., 2006). Since we see noevidence o craniosynostosis or artificial deorma-tion in the L12 individual, other sources o mechani-cal stress could be involved. It is known that cranio-synostosis causes skull shape deormations due tothe limited growth o the skull bones in the directionperpendicular to the obliterated suture, which is com-pensated by growth in other directions (Auderheideet al., 1998). Similarly, the peculiar shape o the L12skull, exhibiting strong rontal/parietal curvatures(see Fig. 2) and hyperbrachycrany, could be relatedto the ormation o the bregmatic bone. Te growtho a large bone within the anterior ontanelle couldact as a actor that modifies the development o the

surrounding neurocranial bones, rontals and pari-etals become pushed outwards, which is reflected

in their bulging and brachycrany. Recent studieshave ound a positive correlation between brachy-crany and both the ormation o wormian bones(Sanchez-Lara et al., 2009) and metopism (Castilhoet al., 2006).

In the context o pathological syndromes, theanterior ontanelle is a rare site or supernumerarybone ormation. Woods and Johnson (2010) reportassociation with acrocallosal syndrome (ACLS) inone patient; Elson et al. (1991) also report this as-sociation in one patient who, interestingly, also had

a large, unused anterior ontanelle at 3 years o age.Could this possibly account or the eatures we ob-served in L12? ACLS is a rare autosomal recessivedisease, which is characterized by the absence ocorpus callosum and severe mental retardation. Anexpected lie span or individuals with ACLS has notbeen suggested yet, but Hodgson et al. (2009) believethat, with proper medical support, these individualscould survive well into adulthood. Skeletal anoma-lies are present in about 50% o cases, and the mostrequent findings in this regard are pre- and post-ax-

ial polydactyly; among cranioacial anomalies, mostrequent are a prominent orehead, macrocephaly(horizontal circumerence >2 standard deviations)and hypertelorism (urolla et al., 1990). Te ore-head o L12 does not seem to be abnormally promi-nent; we detected no macrocephaly (see able 1 orhorizontal circumerence), nor hypertelorism, sincethe interorbital distance measurement (able 1) isnormal or an adult male (Currarino and Silverman,1960). Since the postcranium was not recovered, wecannot test the eventual presence o axial anomaliesand thereore, we cannot confirm the (unlikely) hy-pothesis o ACLS to account or the eatures we ob-served in the L12 case.

Regarding metopism, some authors proposedthat this trait could be an atavism, a reversion to anevolutionary primitive state (del Sol et al., 1989).However, although the usion o a metopic suturehas been widely accepted as a derived trait or an-thropoids, Rosenberg and Pagano (2008) ound that

Fig. 3. Detail view o the bregmatic bone, also illustrating the

persistent metopic suture (arrow).


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many non-anthropoid ossil and living primates alsoshowed rontal usion. Tis could mean that this

trait is not synapomorphic or anthropoids, and that,consequently, metopism could not be an atavism inhumans. Other potential causes or metopism werealso suggested (mechanical causes, hormonal dys-unction, etc.), but it seems clear that some geneticinfluence is probably involved (del Sol et al., 1989).Tis is in accordance with the studies o orgersen(1951), which showed that there could be a heredi-tary basis or the metopism. Tere are no relevant he-reditary studies concerning bregmatic bone, but thisis mainly because the trait is so rare in humans. AsBarberini et al. (2008) noted, it seems probable that

some non-adaptive, direct genetic influence could beresponsible or the development o a large bregmaticbone. I we accept the genetic basis or metopism andbregmatic bone ormation, the rarity o their co-oc-currence could imply that they involve different setso genes.

CONCLUSION

An adult male skull rom Lanite, showing the co-occurrence o a large bregmatic bone and metopism,

represents an important comparative specimen,which adds to the small number o published cases othis rare neurocranial variant. Different causes havebeen suggested or these phenomena, but their truenature remains poorly understood. Further researchin different scientific fields is needed to decipherthe underlying causes. A detailed genetic and long-term developmental study o patients diagnosedwith bregmatic bone and/or metopism could proveto be particularly useul in this regard. Although alarge bone at the bregma is usually considered a nor-mal anatomical variant, the act that it also occurs insome rare pathological conditions indicates the needto explore urther the relationship o this phenom-ena with disease.

Acknowledgments Tis paper is a result o the projectsRomanization, urbanization and transormation o urbancenters o civil, military and residential character in Romanprovinces on the territory o Serbia (No. 177007) and Urban-ization processes and development o medieval society (No.

177021), unded by the Ministry o Education, Science andechnological Development o the Republic o Serbia. Weexpress our gratitude to our colleague archaeologist atjana

Mihailovi or her expert assistance and useul suggestions,to photographer Sran Vulovi, and also to Jelena Vitezovi,M. A. or prooreading the text.

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A LARGE SUPERNUMERARY BONE AT THE BREGMA AND METOPISM CO-OCCURRING IN THE SKULL OF AN ANCIENT ROMAN IN SERBIA