The statement by YSO that Kangaroos were known by both the Torah and by Chazal confused me at first, because it seemed to pose a difficulty to the mishna. But Baruch Hashem, using scientific methodology we have been able to clearly resolve all difficulties and show that Hashem is the Boreh Olam!
The mishna in Bikurim (2:7) states that:
דם מהלכי שתיים--שווה לדם בהמה, להכשיר את הזרעים; ודם השרץ, אין חייבין עליו.
The blood of those who go on 2 [legs] is equivalent to the blood of those who go on four [legs] to prepare plants [to enable them to beoome ritually impure]. And the blood of a sheretz [creepy crawly] - one is not liable for.
The strange phrase of 'go on two' is usually understood as referring to humans. However, kangaroos (and wallabies) also hop on two legs, thereby creating what at first seems an insurmountable difficulty.
We see from this video that kangaroos certainly 'go on two' [legs]. So one may have been misled to think that their blood is the same as human blood.
However, Baruch Hashem, a study of the meforshim (who all question why the mishna didn't simply use the word "man" rather than the less specific term "go on two") shows that they, know through their ruach hakodesh, of kangaroos.
Rishon le-Tziyon points out that from this wording one may have been confused and thought that it also included ofot. The word ofot is not clearly defined in Hebrew. It may refer to chicken (or turkey if you are American) or to birds in general.
However, I consulted with my Hebrew expert, who confirmed my suspicions, that the word עוף can also be read as "UP". This then, is clearly a reference to kangaroos who jump "up" when they move (unlike birds, for example, who simply fly). Therefore the mishna is precise in its terminology of saying 'go on two' to exclude kangaroos (and wallabies) who go 'up'.
R. Slifkin (R. stands for Natan) challenged that kangaroos were unknown to the audience of the Torah and the mishna. Which is not only irrelevant, but also false. Since the Torah and mishna were written with Divine Inspiration it makes no difference where they lived. Furthermore, only a small fraction of the land of Eretz Yisroel has been excavated for fossils, so it is entirely reasonable to assume that they will eventually discover kangaroo (and wallaby) fossils in Israel. Furthermore, I wrote a letter to the author of the book on kangaroos of the biblical era, and questioned his/her methodology. Since I heard no further response I assume that they agree with me that one cannot disprove the existence of kangaroos in the ancient Middle East.
In addition, anyone who goes to the Jerusalem zoo will see that there are both wallabies and kangaroos there. So it is false to say that there are no kangaroos in Israel!
Perhaps you will ask "What about gorillas? - They also walk on 2 legs". To which I answer that there is not a shred of evidence that gorillas walk on two legs.
Just two further points about Dr Betech:
1. He admits that he was involved in the ban on (Rabbi) Slifkins books.
The Chofetz Chaim (Hilchot Lashon HaRa 5:3) writes that one who says about a Rav that he does not know Torah and thereby causes his status to be diminished (and potentially causes him loss of livelihood) denigrates Torah and causes laxity in observance of mitzvot.
2. In his book, Betech fails to mention Rabbi Slifkin's book on the subject at all, even though he has certainly read it and is very familiar with it (and seems to have taken some of his sources from it). Furthermore, when a Rabbi says something that Betech does not agree with he either excludes it completely (like the opinon of Rabbi Tendler) or instead attributes Rabbi Lubin's opinionto a random parsha sheet (North Hendon Adath) to avoid presenting a difficulty to his theory.
Nodeh Be'Yehuda (Tanina: Orech Chaim 20) writes that one who fails to attribute a source (b'shem omro) is considered a thief and transgresses a Biblical command.
(disclosure: I found this reference in she'arim metzuyanim be'halacha siman 27, along with many other sources who state the same thing).
So in summary, one who denigrates a Rabbi and claims that he is not intelligent denigrates the Torah and causes people to be lax in their mitzva observance. Furthermore one who does not attribute their source transgresses a Biblical prohibition.
I'll end with a quote from Rebecca Driver:
Kangaroos are ingenious examples of God’s craftsmanship, designed by a Creator who knew perfectly what He was doing. To Him all praise, glory, and honour is forever due.