Max Wisshak, Andreas Kroh, Markus Bertling, Dirk Knaust, Jan K. Nielsen, John W. M. Jagt, Christian Neumann & Kurt S. S. Nielsen

IN DE FENCE OF AN ICONIC ICHNOGENUS –

OICHNUS BROMLEY, 1981

Max WISSHAK

, Andreas KROH

, Markus BERTLING

, Dirk KNAUST

, Jan K. NIEL SEN

,

John W. M. JAGT

, Chris tian NEUMANN

& Kurt S. S. NIEL SEN

1

Ma rine Re search De part ment, Senckenberg am Meer, 26446 Wilhelmshaven, Ger many;

e-mail: max.wisshak@senckenberg.de

2

Nat u ral His tory Mu seum Vi enna, 1010 Vi enna, Aus tria; e-mail: andreas.kroh@nhm-wien.ac.at

3

Geomuseum of the Uni ver sity of Münster, 48149 Münster, Ger many; e-mail: markus.bertling@uni-muenster.de

4

Statoil ASA, 4035 Stavanger, Nor way; e-mail: dkna@statoil.com

5

VNG Norge, 0252 Oslo, Nor way; e-mail: bioerosion@ya hoo.dk

6

Natuurhistorisch Mu seum Maastricht, 6211 KJ Maastricht, the Neth er lands; e-mail: john.jagt@maastricht.nl

7

Mu seum für Naturkunde, Leibniz Institute for Evolution and Biodiversity Science, 10115 Berlin, Ger many;

e-mail: chris tian.neumann@mfn-berlin.de

8

Frederikssund Gym na sium, 3600 Frederikssund, Den mark; e-mail: knieslen@ya hoo.dk

Wisshak, M., Kroh, A., Bertling, M., Knaust, D., Niel sen, J. K., Jagt, J. W. M., Neumann, C. & Niel sen, K. S. S. 2015. In de fence of an iconic ichnogenus – Oichnus Bromley, 1981. Annales Societatis Geologorum Poloniae, 85: 445–451.

Ab stract: By es tab lish ing the bioerosion ichnogenus Oichnus, Rich ard Bromley (1981) ad dressed ‘small round holes in shells’ and catalysed a se ries of still on go ing dis cus sions on ichnotaxonomical prin ci ples. In a re cent re vi sion by Zonneveld and Gingras (2014), Oichnus was re jected, to gether with Tremichnus Brett, 1985 and Fossichnus Niel sen, Niel sen and Bromley, 2003, by means of sub jec tive synonymisation with the pre sumed se nior syn onym Sedilichnus Müller, 1977. How ever, Sedilichnus is nomenclaturally un avail able, be cause it is an atelonym (con di tion ally pro posed). In ad di tion, re in ves ti ga tion of the type ma te rial of ‘Sedilichnus’ shows that it prob a bly de scribes vari ably shaped oscula and thus is a gen u ine mor pho log i cal char ac ter of the host sponge Prokaliapsis ja nus, rather than a bioerosion trace fos sil. The ichnogenera Oichnus and Tremichnus are re vised, lead ing to the synonymisation of Balticapunctum Rozhnov, 1989 with Tremichnus, and of Fossichnus with Oichnus. The re fined ichnogeneric di ag no ses re turn Oichnus to com plete or in com plete bioerosive pen e tra tions in cal car e ous skel e tal sub strates, com monly in ter preted as praedichnia with or with out signs of at tach ment, while Tremichnus (now in clud ing O. excavatus) ex clu sively re fers to shal low pits pass ing into echinoderm skel e tons that are in ter preted as domichnia or fixichnia.

Key words: Ichnology, ichnotaxonomy, Oichnus, Tremichnus, Sedilichnus, bioerosion, pre da tion.

Manu script re ceived 8 July 2015, ac cepted 3 Au gust 2015

IN TRO DUC TION

Few trace fos sils are as iconic as Oichnus, erected with

two ichnospecies in 1981 by Rich ard Bromley for ‘small

round holes in shells’, in con junc tion with a cor ner stone

dis cus sion of con cepts in ichnotaxonomy. Since then, sev

eral ad di tional ichnospecies of Oichnus have been es tab

lished and the orig i nal di ag no sis has been sub jected to mul

-ti ple amend ments and re vi sions (Bromley, 1993; Niel sen

and Niel sen, 2001; Don o van and Jagt, 2002; Niel sen et al.,

2003; Neumann and Wisshak, 2009; Ruggiero and Raia,

2014). Dur ing this ichnotaxonomical prog ress, Oichnus and

its dis puted po ten tial ju nior syn onym Tremichnus Brett,

1985 have con tin ued to fuel ichnological dis cus sions (e.g.,

Pickerill and Don

o

van, 1998; Feldman and Brett, 1998;

Niel sen and Niel sen, 2001; Todd and Palmer, 2002; Niel sen

and Niel sen, 2002; Don o van and Pickerill, 2002; Neumann

and Wisshak, 2006; Wil son et al., 2014). This di a logue has

been kept alive by a re

cent re

vi

sion of Oichnus by

Zonneveld and Gingras (2014). These au thors sug gested

sub jec tive synonymisation of Oichnus (to gether with Trem-

ichnus and Fossichnus Niel

sen, Niel

sen and Bromley,

2003) with the pre

sumed se

nior syn

onym Sedilichnus

Müller, 1977. The aim of the pres ent re view is to dem on

-strate that Sedilichnus is not a nomenclaturally avail able

ichnotaxon and that nei ther Sedilichnus nor Tremichnus are

suit able for synonymisation with Oichnus.

ICHNOTAXONOMIC DIS CUS SION

Sedilichnus is an atelonym (a term for un

avail

able

names sensu Dubois, 2011) be cause it was pro posed on

con di tional terms only, as clearly in di cated by the phrase

“Should it [a tax o nomic char ac ter iza tion] be come nec es

-sary…” (Müller, 1977, p. 890, trans lated from Ger man).

Such con di tion ally pro posed names are ad dressed by ar ti cle

15.1 of the In ter na tional Code of Zoo log i cal No men cla ture

(ICZN, 1999), which ap

plies to names es

tab

lished af

ter

1960. This ren ders the ichnogenus name Sedilichnus, the

ichnospecies name spongiophilus and the two subspecific

nomina mi nus and maximus nomenclaturally un avail able.

Hence, be yond doubt, Oichnus is to be re tained.

Apart from this no men cla tur al cir cum stance, even if

these nomina were avail able, in prac tice Sedilichnus would

be a nomen dubium: It is un clear whether the holes it re fers

to are a na tive mor pho log i cal fea ture of the sponge

Prokaliapsis ja nus (Roemer, 1864), a bioerosion trace, or an ex

-am ple of bioclaustration (as spec i fied by Müller, 1977 in his

di ag no sis). While the ar gu ments for a syn-vivo gen e sis put

for ward by Ulbrich (1974) and Müller (1977) are con vinc

-ing, their lines of rea son ing for commensal bioclaustration

are not (e.g., the pres ence of sur face pores at the bot tom of

the pits). In the opin ion of the pres ent au thors, Sedilichnus

most likely is a quite vari able mor pho log i cal fea ture of the

sponge it self, as al ready in di cated in the orig i nal di ag no sis

by Roemer (1864). Müller’s holotype (Fig. 1A, B) and a se

-lec tion of sec tioned spec i mens from Müller’s and Ulbrich’s

orig i nal ma te rial (Fig. 1C, D) show com plete sili ci fi ca tion

of those sponges. In the best pre served parts, they nev er the

less ex hibit a num ber of fea tures in sup port of the in ter pre ta

tion of the pres ent au thors. The holotype of Sedilichnus dis

-plays astrorhiza, i.e. ca nals (ad dressed by Ulbrich as

apo-physes) ra di at ing from the Sedilichnus pits. Ac cord ing to

Ulbrich (1974), they are a typ i cal fea ture that also sur rounds

the main osculum (paragaster) in Prokaliapsis ja nus. The

sur face struc ture of Sedilichnus is rem i nis cent of that of the

main osculum, be

ing densely cov

ered with small pores

along the en tire cir cum fer ence (ren der ing the bioerosion

hy poth e sis un ten a ble). The in ter nal ar chi tec ture of the

sponge’s spiculate skel e ton is largely over printed by sili ci fi

ca tion. No growth in cre ments are vis i ble, but a cen tral bun

-dle of densely spaced, si lici fied ca nals con nect ing to the

bot tom of the main osculum, as well as sim i lar ca nals ra di at

-ing from the main osculum and the Sedilichnus pits, can be

re cog nised. On most of the spec i mens that were de picted by

Ulbrich (1974) and Müller (1977), in clud ing the spec i men

bear

ing the holotype, the dis

tri

bu

tion of Sedilichnus is

rather reg u lar. Even though Ulbrich ar gued that some

sponges had a more ir reg u lar cover, or were de void of such de

-pres sions, the au thors con sider this ob ser va tion prob a bly to

re flect a con sid er able mor pho log i cal (and per haps partly

also preservational) vari abil ity in Prokaliapsis, as is also ex

pressed by a marked vari abil ity in over all shape. To con

-clude, the pres ent au thors in ter pret most of the Sedilichnus

traces (in clud ing the holotype) as oscula of Prokaliapsis ja

nus. Such a mor pho log i cal fea ture is not un com mon in Cre

-ta ceous and other sponges, e.g. spe cies of Jerea or Becksia

(e.g. Rauff, 1933; Ma³ecki, 1980; Œwierczewska-G³adysz,

2010). In con trast, Müller’s ‘Type II’ traces, which were not

in cluded in his def i ni tion of Sedilichnus (= ‘Type I’), de

-scribe ta per ing pits with an elon gated and al mond- shaped

open ing, and may rep re sent bioerosive struc tures, per haps

pro

duced by endolithic bi

valves. Fur

ther

more, fos

sil

sponges of sim i lar early Campanian age from other sites

close to the type lo cal ity ad di tion ally show straight, deep

(depth:width = 5:1) Trypanites bor ings, which in con trast to

Sedilichnus clearly cut across the sponge’s ca nal sys tem and

might even have been formed post mor tem.

An other as pect of the du bi ous na ture of Sedilichnus is

that Müller (1977) de fined it with out pro vid ing any mor

-pho log i cal cri te ria. In stead, he ex plic itly de noted it as an

embedment struc ture, in a very gen eral sense. He ex cluded

any pos si bil ity of bioerosion in his orig i nal di ag no sis (p.

890): ‘Traces of at tached and ses sile an i mals that were not

pro duced by me chan i cal or chem i cal ac tion of the epibiont,

but be ing a host re ac tion lead ing to in com plete immuration,

trac ing the out line and sur face of the epibiont’ [trans lated

from Ger man]. In con trast, the di ag no sis of the type spe cies

Sedilichnus spongiophilus is based on mor pho log i cal

cri-teria (p. 891): ‘A Sedilichnus with a bowl-shaped,

smooth-walled de pres sion of cir cu lar out line and rounded mar gin’

[trans lated from Ger man]. While this di ag no sis alone may

in di cate a re la tion ship to bioerosional trace fos sils, its clear

ref er ence to an embedment struc ture does not. Bertling et al.

(2006, p. 267) de fined embedment struc tures as ‘… struc

tures in cal car e ous skel e tons that are pro duced by an ac

tively grow ing or gan ism around dis turb ing or ir ri tat ing ob

-jects or liv ing or gan isms …’. Ac cord ing to Goldring et al.

(1997), sub strate ef fects dur ing trace con struc tion should

not be used as ichnotaxobases. In con trast, Tapanila and

Ekdale (2007) re view taxa es tab lished for bioclaustrations

and con sider them valid ichnotaxa. How ever, the con sen sus

put for ward by Bertling et al. (2006) does not sup port this

ap proach by stat ing that embedment struc tures in gen eral

were not com pat i ble with the def i ni tion of a trace fos sil, de

fined therein (p. 266) as ‘a mor pho log i cally re cur rent struc

ture re sult ing from the life ac tiv ity of an in di vid ual or gan

ism (or homotypic or gan isms) mod i fy ing the sub strate‘ (ac

-com pa nied by ta ble 1 ex plic itly ex clud ing em bedment

struc tures). How ever, Bertling et al. (2006) ad mit ted that

oc ca sion ally cases could be com pli cated by the oc cur rence

of a com bi na tion of bioclaustration and bor ing, in which

case those parts that clearly are host re ac tions should not be

ad dressed ichnotaxonomically.

In deed, this case ap plies at least to some ichnospecies

es

tab

lished within the ichnogenus Tremichnus. Its type

ichnospecies T. paraboloides Brett, 1985 does not show a

host re ac tion (Fig. 1G, H), whereas Tremichnus minutus

Brett, 1985 and T. cysticus Brett, 1985 can. The shape of the

cen tral pit in all three ichnospecies is sim i lar. They dif fer in

size, but this – just like host re ac tions – is not con sid ered to

be a suit able ichnotaxobase in it self (Bertling et al., 2006).

Hence, these three ichnospecies can be syn ony mised with

the type ichnospecies T. paraboloides. The last among

Brett’s (1985) suite of Tremichnus ichnospecies, T.

puteo-lus, does not re veal a clear host re ac tion, but bears a strong

mor pho log i cal re sem blance to and thus pos si bly rep re sents

a se nior syn onym of Centrichnus concentricus Bromley and

Martinell, 1991 and the very sim i lar trace Anellusichnus

circularis Santos, May oral and Muñíz, 2005. Re solv ing this

ichnotaxonomical is sue is be yond the scope of the pres ent

pa per, how ever.

Rozhnov (1989) de scribed pits that ex hibit host re ac

-tions by eocrinoids as Balticapunctum inchoatus. Herein,

Balticapunctum is syn ony mised with Tremichnus

parabo-loides Brett, 1985, thus re ject ing it as a valid ichnotaxon. In

any case, host re ac tions such as cysts, swell ings, rims or re

-gen er a tion struc tures, ob served to gether with Tremichnus

or iso

lated (bioclaustrations), may nev

er

the

less be ad

-dressed tax o nom i cally out side the con cept of

ichnotaxo-nomy, sim i lar to other taxa de not ing embedment struc tures

(see Tapanila, 2005, 2008; Tapanila and Ekdale, 2007 for

re views). Ac cord ingly, in a re cent re vi sion of etho log i cal

cat e go ries, Vallon et al. (2015) re ject the term impedichnia

(Tapanila, 2005) and sug gest re place ment by impeditaxa.

In or der to clar ify fur ther the re la tion ship and dis tinc

tion be tween Oichnus and Tremichnus, it is nec es sary to re

-visit the orig i nal di ag no ses (see be low) and name-bear ing

holotypes of the re spec tive type ichnospecies (Fig. 1), and

to re de fine mor pho log i cal lim its (Fig. 2). Orig i nally,

Oichnus was es tab lished ex clu sively for bioerosion traces

and these were in ter preted as re sult ing from drill ing pre da

tion. Suc cess ful pre da tion in ev i ta bly leads to a full pen e tra

-tion of the host skel e ton. This is re flected in ‘small round

holes in shells’ in Bromley’s (1981) ti tle, as well as in the

first sen tence of his orig i nal ichnogeneric di ag no sis. In or

-der to ac com mo date un suc cess ful or in com plete pre da tion

traces as well, Bromley opened the door for in com pletely

pen e tra tive spec i mens in the form of shal low de pres sions or

pits, as re flected in the sec ond sen tence of his di ag no sis (the

term ‘non-pen e tra tive’, as ap plied by Zonneveld and

Gingras, 2014, should be avoided, be cause ‘pen e trate’ is de

-fined as find ing or forc ing a way into or through some thing;

see the Ox ford Dic tio nary (Tulloch, 1995)). A com plete

pen e tra tion and its cor re spond ing in com plete coun ter part

were (and should) be given the same ichnospecies name. In

ichnotaxonomy, this com mon prac tice is in ac cor dance with

other ichnotaxa, for in stance Entobia Bronn, 1837, in which

var i ous ontogenetic stages (growth phases A to E sensu

Bromley and D’Alessandro, 1984) are in cluded within each

ichnospecies. If un fin ished spec i mens can not be iden ti fied

with cer tainty on the ba sis of their out line and shape, they

should be ad dressed as Oichnus isp. in stead. The co her ence

of this con cept was weak ened with the es tab lish ment of

Oichnus excavatus Don o van and Jagt, 2002, which is the

sole ichnospecies of Oichnus that has never been found to

Fig. 1. Re vis it ing holotypes of the type ichnospecies of Sedilichnus Müller, 1977, Oichnus Bromley, 1981, and Tremichnus Brett, 1985. A, B. Over view and close-up of an early Campanian sponge Prokaliapsis ja nus (Roemer, 1864) from Wernigerode, Harz, Ger many, with mul ti ple pits ad dressed by Müller (1977) as embedment struc tures, in clud ing the holotype (ar row) of Sedilichnus spongiophilus (re -jected atelonym), herein re garded as most prob a bly pri mary sponge fea tures; Palaeontological Col lec tion of the TU Bergakademie Freiberg, Ger many, No. FG 210/284. C, D. A sec tioned topotypical and heavily si lici fied Prokaliapsis ja nus (orig i nal to Ulbrich, 1974 and Müller, 1977), il lus trat ing the sur face tex ture of the Sedilichnus walls (right-hand side in close-up) with ra di at ing pores and ca nals, rem i nis cent of the tex ture in the main osculum (up per left in close-up); Palaeontological Col lec tion of the TU Bergakademie Freiberg, Ger many, No. FG 210/285. E. An early Campanian oys ter Arctostrea diluviana from Ivö Klack, south ern Swe den, with the exit of an Oichnus sim plex topotype (holotype cur rently in ac ces si ble, ow ing to col lec tion ren o va tion) on the in ner side of the valve (ar row). F. Close-up of Oichnus sim plex holotype in an other Arctostrea diluviana from Ivö Klack, south ern Swe den; Geo log i cal Mu seum, Uni ver sity of Co pen ha gen, Den mark, No. MGUH 15351 (re pro duced from Bromley, 1981). G, H. The cri noid Ichtyocrinus laevis from the Si lu rian Roch es ter Shale, Lewinston, NY, USA, bear ing nu mer ous Tremichnus paraboloides, in clud ing the lectotype (ar row) shown in close-up; Buf falo Mu seum of Sci ence, Buf falo, NY, USA, No. BMS E23971 (re pro duced from Brett, 1985).

pen e trate through its host skel e ton. Con sid er ing the fair

num ber of spec i mens re corded to date, an in ter pre ta tion as

per

ma

nent drill

ing fail

ure can be ex

cluded and, con

se

-quently, O. excavatus is now thought to be a domichnion

rather than a praedichnion (Don o van and Jagt, 2004). Mor

-pho log i cal and etho log i cal cri te ria alike strongly in di cate

that O. excavatus is better placed in a sep a rate ichnogenus.

Since Tremichnus is never com pletely pen e trat ing through

the host sub strate, it can not be syn ony mised with Oichnus,

but the for mer is a suit able ichnogenus for O. excavatus un

-der the new com bi na tion Tremichnus excavatus (Don o van

and Jagt, 2002). Fur ther more, this match is sup ported by the

fact that Tremichnus is so far only known from echinoderm

host sub strates. The di ag no sis of Tremichnus is con densed

and re vised be low for better ac com mo da tion of T.

excavatus and for ex clu sion of in valid ichnotaxobases. These no

-men cla tur al steps con fine Oichnus once more to com plete

or in com plete pen e tra tions, com monly in ter preted as

praed-ichnia with or with out signs of at tach ment. They fos ter the

dis tinc tion from Tremichnus, now com pris ing ex clu sively

pits in echinoderm skel e tons that do not pass through the

host sub strate and are com monly in ter preted as domichnia

or fixichnia.

The ad vo cated re ten tion of the ichnogenus Oichnus and

re-es tab lish ment of ichnotaxonomic sta bil ity may serve as a

solid base for ad dress ing (ichno-) di ver sity and pro cesses of

drill ing pre da tion and par a sit ism – as ini ti ated more than

two mil len nia ago when Ar is totle for mu lated, ‘The ceryx

and the pur ple murex have this or gan firm and solid; and

just as the myops, or horse-fly, and the oestrus, or gad fly,

can pierce the skin of a quad ru ped, so is that pro bos cis pro

-por

tion

ately stron

ger in these testaceans; for they bore

right through the shells of other shell-fish on which they

prey.’ [from Historia Animalium, writ ten by Ar is totle in

about 350 B.C., trans lated by Thomp son (1910)].

SYS TEM ATIC ICHNOTAXONOMY

Ichnogenus Oichnus Bromley, 1981

Figs 1E, F, 2

non 1977 Sedilichnus – Müller, pp. 890–891, pl. I, figs 1–13, pl. II, figs 1–4 [atelonym; ?part of sponge body fos sil]. *1981 Oichnus – Bromley, pp. 60–62, pls 1–3.

2003 Fossichnus – Niel sen, Niel sen and Bromley, pp. 3–6, figs 1–3 [sub jec tive ju nior syn onym].

Type ichnospecies. Oichnus sim plex Bromley, 1981 from the lower Campanian at Ivö Klack, Swe den, by orig i nal des ig na tion.

Fig. 2. Scheme com pil ing char ac ters of the var i ous ichnospe-cies of Oichnus Bromley, 1981 and Tremichnus Brett, 1985, as seen in plan view and cross-sec tion, ar ranged in or der of ichno-spe cies es tab lish ment. Dot ted lines in cross-sec tions in di cate known or in ferred in com plete stages and dashed line out lines fac -ul ta tive host re ac tions (not part of the trace). Light grey shad ing in plan views in di cates shal low etch ing scars; dark grey in di cates deeper re lief. Al though not of di ag nos tic value, note the con sid er -able range in ap prox i mate size of the re spec tive holotypes.

Other ichnospecies. Oichnus paraboloides Bromley, 1981; O.

ovalis Bromley, 1993; O. coronatus Niel sen and Niel sen, 2001; O. gradatus Niel sen and Niel sen, 2001; O. asperus Niel sen and Niel -sen, 2001; O. so lus (Niel -sen, Niel sen and Bromley, 2003) comb. nov.; O. halo Neumann and Wisshak, 2009; O. taddeii Ruggiero and Raia, 2014.

Orig i nal di ag no sis. Cir cu lar to subcircular holes of biogenic or i -gin bored into hard sub strates. The hole may pass right through the sub strate as a pen e tra tion, where the sub strate is a thin shell; or end within the sub strate as a shal low to deep de pres sion or short, subcylindrical pit.

Emended di ag no sis. Holes with rounded out line, bored into cal car e ous skel e tal sub strates. The sol i tary and com monly per pen dic -u lar traces -us-u ally pass right thro-ugh the s-ub strate, or end as pit (in com plete pen e tra tion), wider than deep.

Dif fer en tial di ag no sis. Dis tin guished from Tremichnus Brett, 1985 by in vari ably com plete pen e tra tion, ex cept in aborted bor ings, and oc cur rence in a wide range of cal car e ous skel e tal sub -strates. Dipatulichnus Niel sen and Niel sen, 2001 is char ac ter ised by holes in pairs. While Oichnus is de fined as com pletely pen e tra -tive or, when in com plete, as pits that are wider than deep, Trypa-nites Mägdefrau, 1932 is dis tinctly deeper than wide and does not pass through the sub strate. Anellusichnus Santos, May oral and MuÔíz, 2005, Centrichnus Bromley and Martinell, 1991, and Ophthalmichnus Wisshak, Alexandrakis and Hoppenrath, 2014 are very shal low at tach ment etch ings of vari able out line, with shal low con cen tric grooves, and they never pass through the sub -strate. Fur ther bioerosion traces with this prop erty that are clearly dis tin guished from in com plete Oichnus are the echinoid bor ing trace Circolites Mikuláš, 1992 and the cyanobacterial microboring Planobola Schmidt, 1992.

Re marks. The di ag no sis was re vised in or der to (1) in clude all ob served out lines, (2) con fine the sub strate type to cal car e ous skel e -tons, (3) dis tin guish sin gle from mul ti ple pen e tra tions, (4) spec ify the ori en ta tion with re spect to the sub strate sur face, and (5) con dense the di ag no sis. Oichnus bavincourti (Vaillant, 1909), in tro -duced as a new com bi na tion by Dunlop and Braddy (2011), is here ex cluded from Oichnus, be cause it is a bur row in siliciclastic sed i -ment, rather than a bor ing in a skel e tal or lithic sub strate. Cteniza bavincourti (Vaillant, 1909) is re garded a nomen dubium on ac count of its in com plete pres er va tion and its orig i nal ten ta tive as -sign ment to a biotaxon (i.e. the spionid polychaete Sabella). There seem to be no fea tures to war rant place ment of Fossichnus so lus in an ichnogenus sep a rate from Oichnus. There fore, the au thors fol -low Zonneveld and Gingras (2014) in syn ony mis ing these two, for mally in tro duc ing O. so lus as a new com bi na tion herein.

Ichnogenus Tremichnus Brett, 1985

Figs 1G, H, 2

non 1977 Sedilichnus – Müller, pp. 890–891, pl. I, figs 1–13, pl. II, figs 1–4 [atelonym; ?part of sponge body fos sil]. *1985 Tremichnus – Brett, pp. 626–631, figs 1–6.

1989 Balticapunctum – Rozhnov, p. 52–54, pl. II, figs 1–11 [sub jec tive ju nior syn onym].

Type ichnospecies. Tremichnus paraboloides Brett, 1985 from the Si lu rian Roch es ter Shale, Lewiston, NY, USA, by orig i nal des -ig na tion.

Other ichnospecies. Tremichnus puteolus Brett, 1985; T.

exca-vatus (Don o van and Jagt, 2002) comb. nov.

Orig i nal di ag no sis. Cir cu lar pits or embedment struc tures of vary ing di am e ter (about 0.1 to 4.0 mm) oc cur ring on the plates of echinoderms, pri mar ily cri noids, with or with out as so ci ated thick en ing or galllike de for ma tion of the plates. Pits reg u larly par a -bolic in cross sec tion, with di am e ter/depth ra tios vari able from about 0.1–1.0; no in ter nal ex pan sion or other ram i fi ca tions. Holes

al ways ori ented per pen dic u larly to ex ter nal plate sur faces, ta per -ing in ward; gen er ally not pen e trat -ing through plates. Ad ja cent pits may over lap one an other.

Emended di ag no sis. Cir cu lar pits, gen er ally wider than deep, per -pen dic u larly bored into os si cles of echinoderms.

Dif fer en tial di ag no sis. Dis tin guished from Oichnus Bromley, 1981 by not pen e trat ing through the sub strate, even in com plete traces, and by re stric tion to echinoderm host sub strates. While Tremichnus is de fined as a pit be ing gen er ally wider than deep, Trypanites Mägdefrau, 1932 is dis tinctly deeper than wide. Dipa-tulichnus Niel sen and Niel sen, 2001 is char ac ter ised by holes in pairs and is com pletely pen e tra tive. Anellusichnus Santos, Mayo-ral and MuÔíz, 2005, Centrichnus Bromley and Martinell, 1991, and Ophthalmichnus Wisshak, Alexandrakis and Hoppenrath, 2014 are very shal low at tach ment etch ings of vari able out line and in part have shal low, con cen tric grooves. The echinoid bor ing trace Circolites Mikuláš, 1992 has a sim i lar mor phol ogy, but of ten has an un du lat ing edge, is far larger (com monly 1 to 4 cm in dia-me ter), and is largely re stricted to non-skel e tal cal car e ous hard-grounds. The cyanobacterial microboring Planobola Schmidt, 1992 in turn is much smaller (com monly less than 30 µm in di am e -ter), has a more clavate mor phol ogy, and is found in non-echino-derm skel e tal car bon ate sub strates.

Re marks. The di ag no sis was re vised in or der to (1) ex clude in valid ichnotaxobases, (2) elim i nate spec i fi ca tions to miss ing fea -tures, (3) better ac com mo date T. excavatus, and (4) to con dense the di ag no sis. Tremichnus minutus Brett, 1985 and T. cysticus Brett, 1985 are syn ony mised with T. paraboloides Brett, 1985 on ac count of their prior dis tinc tion hav ing been based only on in ap -pro pri ate ichnotaxobases (size and host re ac tions). For the lat ter ichnospecies, one trace on cri noid spec i men BMS E23971 is des -ig nated as lectotype (see ar row in F-ig. 1G). Tremichnus puteolus Brett, 1985 is re tained; it is pos si bly a se nior syn onym of Cen-trichnus concentricus Bromley and Martinell, 1991 and Anellus-ichnus circularis Santos, May oral and MuÔíz, 2005. TremAnellus-ichnus cystoidiphilus Frest and Strimple (in Frest, Strimple and Paul), 2011 is a nomen nudum, be cause no holotype was des ig nated (an ICZN re quire ment for ichnotaxa in tro duced in 2000 or later; ICZN, 1999). Balticapunctum inchoatus Rozhnov, 1989 is a sub -jec tive ju nior syn onym of T. paraboloides. Host re ac tions ob -served to gether with Tremichnus, such as cysts, swell ings, or rims formed while the tracemaker was still in place (as ob served for some T. paraboloides on cri noids and T. excavatus in echinoids), and re gen er a tion tex tures formed in aban doned traces (such as echinoid tuberculation ob served in T. excavatus), are not con sid -ered as valid ichnotaxobases (see dis cus sion above) and thus are ex cluded from the di ag no sis. In this con text, it should also be noted that, con trary to the dis cus sion of Don o van and Jagt (2004), there is no ev i dence for in ter pret ing T. excavatus as an embedment struc ture since echinoid tuberculation in aban doned bioerosional traces is a com mon sign of re pair by stereom tis sue in liv ing echinoid host sub strates (e.g., Neumann and Wisshak, 2006; Wisshak and Neumann, 2006). Also, the sole re port of T. excava-tus from a non-echinoid host sub strate (Blissett and Pickerill, 2003) is based on an er ro ne ous in ter pre ta tion: This oc cur rence most likely rep re sents moulds of small spi ral polychaete tubes (e.g. Spirorbidae) at tached to the in te rior of the last whorl of a gas -tro pod, now pre served as pits in the gas -tro pod mould af ter diage-netic dis so lu tion of both gas tro pod and polychaete shells.

Ac knowl edge ments

B. Gaitzsch pro vided a set of im ages of the holotype of Sedil-ichnus spongiophilus and ar ranged a loan of topotypes from the Freiberg col lec tion, and F. Trostheide col lected and pro vided fur -ther fos sil sponge ma te rial. Im ages of Oichnus sim plex topotypes

were pro vided by J. Hagström. We ap pre ci ate the valu able dis cus sion with A. Dubois on no men cla tur al prin ci ples and ICZN mat -ters. We grate fully ac knowl edge C. E. Brett, M. A. Wil son, and L. H. Vallon for dis cus sions con cern ing the va lid ity of Oichnus and Tremichnus, as well as D. Janussen, J. Reitner and N. Hauschke for their ex per tise on sponge mor phol ogy. We thank E. A. JagtYazykova for trans lat ing some Rus sian texts. Valu able re -views were pro vided by P. H. Kelley and A. K. Rindsberg. Last, but not least, we are in debted to R. G. Bromley for es tab lish ing the iconic Oichnus and fore most for his friend ship and mentorship.

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