nov.) resemble exoskeletal elements of some heterostracans
Other vertebrates in the samples comprise Thelodus parvidens Agassiz, Thelodus sculptilis Gross, two to three different cyathaspidid heterostracans
, two anaspids, two osteostracans, and acanthodians Nostolepis striata Pander, Gomphonchus sandelensis (Pander), and Poracanthodes porosus Brotzen.
vertebrates and the Great Eodevonian Biodiversification Event--an essay.
perensae Marss, Nethertonodus laadjalaensis Marss, Trimerolepis tricava (Gross), Longodus acicularis Marss; heterostracan
Archegonaspis sp.; osteostracan Zenaspis?
4E), although it is not as much developed as the rostrum of many basal heterostracans
(e.g., Athenaegis; Soehn & Wilson 1990, fig.
Tiny scales of acanthodians often dominate fish microremains, particularly in drill core samples, and are much more common than macroremains of jawless fishes heterostracans
(psammosteids) and/or placoderms.
Insufficient knowledge has hindered phylogenetic study of the group Heterostraci as a whole, so there has been uncertainty about its relationships with other tessellated heterostracans
Scales and tesserae or fragments of plates of heterostracans
, placoderms, acanthodians, chondrichthyans, and osteichthyans (sarcopterygians and actinopterygians) were found (see Table 1).
From eastern Canada, tolypelepid and corvaspid heterostracans
have been reported from the middle Silurian Eramosa Lagerstatte, Ontario (von Bitter et al.
These fossils were heterostracans
, small, primitive, jawless, armoured fish that occupy a place in the lineage of Man's earliest ancestors.
Remains of psammosteid heterostracans
and acanthodians are very diverse and abundant in the Middle and Upper Devonian (Eifelian, Givetian and Frasnian stages) of the Baltic area, i.e.
Other associated fossils include anaspids, heterostracans
, graptolites, eurypterids, nautiloids, and conodonts.
He included within this taxon heterostracans
in which (1) the orbits are not surrounded by the dorsal shield but form semicircular notches in it, (2) the large oblong branchial plate situated between the dorsal and ventral plates is detached and (3) the dentine ridges forming the surface of the dermal skeleton are smooth and not crenulated as in the pteraspids.
Tiiu Marss pointed out that the lower part of the Pridoli (Kaugatuma and Minija fms, see also Karatajute-Talimaa 1978) is richly dominated by acanthodians, but different heterostracans
become important in the upper half.
are less common in the overlying Razvedochnyj Fm, particularly in its lower, Pragian part.